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OTH 93 398

COMPUTER SIMULATIONOF THE PERFORMANCE OF

LIFEJACKETS - A Feasibililty Study

Prepared by

Frazer-Nash Consultancy LimitedShelsley House, Randalls Way

LeatherheadSurrey KT22 7TX

London: HMSO

Health and Safety Executive - Offshore Technology Report

© Crown copyright 1993Applications for reproduction should be made to HMSO:

First published 1993ISBN 0-11-882176-8

This report is published by the Health and Safety Executiveas part of a series of reports of work which has beensupported by funds formerly provided by the Department ofEnergy and lately by the Executive. Neither the Executive,the Deparment nor the contractors concerned assume anyliability for the reports nor do they necessarily reflect theviews or policy of the Executive or the Department.

Results, including detailed evaluation and, where relevant,recommendations stemming from their reearch projects arepublished in the OTH series of reports.

Background information and data arising from theseresearch projects are published in the OTI series of reports.

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CONTENTS

12Simulation of Trials5.2

12Lifejacket models5.1

12INITIAL SIMULATIONS BASED ON TRIALS5.

10Results4.4

9Test Procedure4.3

9Lifejackets4.2

9Test Facility4.1

9SELF-RIGHTING TRIALS4.

7Results3.3

7Description3.2

7Introduction3.1

7DYNAMAN DEMONSTRATION SIMULATION3.

5Summary of Simulation Features2.7

4Test Case2.6

4Sea Conditions2.5

3Drag2.4

3Buoyancy2.3

2The Forces on Bodies in Water2.2

2The DYNAMAN Technique2.1

2THE SIMULATION CONCEPT2.

1INTRODUCTION1.

iiiSUMMARY

PAGE

1

21Results of Revised Simulations9.2

21Model Changes9.1

21REVISED SIMULATIONS9.

19BUOYANCY AND DENSITY MEASUREMENT8.

17Simulation Improvements7.4

17Inherently Buoyant Lifejacket7.3

16Inflatable Lifejacket7.2

16Righting Mode7.1

16DISCUSSION7.

15Inherently Buoyant Lifejacket6.2

15Inflatable Lifejacket6.1

15COMPARISON BETWEEN TRIALS AND INITIALSIMULATIONS

6.

13Results5.3

2

SUMMARY

This report describes work carried out by Frazer-Nash Consultancy Limited (FNC)on behalf of the Offshore Safety Division of the Health and Safety Executive (HSE)under agreement number E/5B/CON/8387/2804.

The objective of the work has been to demonstrate the feasibility of using theDYNAMAN computer simulation technique, developed by FNC, to study theperformance of lifejackets.

The effects of buoyancy and drag have been implemented in DYNAMAN to allowlifejacket behaviour to be modelled. In addition, the ability to model simulated waveconditions has been included. These features have been quantitatively validated withsimple test cases.

A series of in-water trials has been carried out at the Institute of Naval Medicine(INM) with a marine manikin to obtain data on the self-righting characteristics of themanikin wearing two types of lifejacket. Computer simulations of the trials havebeen generated to validate the modelling technique. These initial simulationshighlighted the need for accurate buoyancy and density data. Further, detailedmeasurements of the buoyancy and density properties for the marine manikin andlifejackets were therefore made at INM. These data were used in revisedsimulations aimed at achieving a closer match between the trials and simulations.

The simulations have shown that the DYNAMAN technique can be used to modelthe self-righting behaviour of lifejackets. Very good correlation can be achievedbetween trials and computer simulations provided that the weight and buoyancydistribution in DYNAMAN himself and in his lifejacket are correctly modelled.

Applications of the technique have been identified as:

w gaining an understanding of the principles of buoyancy aidbehaviour, in particular in the case of complex systems such aslifejacket/survival suit combinations;

w use as a design tool for screening designs at an early stage, reducingthe need for expensive prototyping;

w use as a means of assessing the suitability of a particular aid to meetspecific performance requirements;

w use as part of an approval process, either to help define physicaltests or to assess designs in conditions where physical testing isinappropriate.

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1. INTRODUCTION

This report describes work carried out by Frazer-Nash Consultancy Ltd (FNC) onbehalf of the Offshore Safety Division of the Health and Safety Executive (HSE)under agreement number E/5B/CON/8387/2804.

The purpose of the work has been to demonstrate the feasibility of using theDYNAMAN computer simulation technique, developed by FNC, to study theperformance of lifejackets. Computer simulation could have a number attractions:

w For many applications the cost of computer simulations is lower thanthat of corresponding physical tests.

w The timescales for simulations are often shorter which can be veryimportant in bringing new products rapidly to the market place oridentifying possible problems during the design process.

w Sometimes a simulation can actually give more understanding ofunderlying mechanisms than a physical test since a correctrepresentation of the fundamental physics of a problem is an integralpart of any simulation.

w For studying lifejacket performance, computer simulation wouldavoid the ethical and safety issues associated with the use of humansubjects in physical testing.

The work has been carried out in a number of stages as follows:

w The effects of buoyancy and drag forces were implemented inDYNA3D. The implementation was validated with a simple testcase.

w A demonstration simulation was carried out in which DYNAMANwas used to simulate the behaviour of a man wearing a typicallifejacket in simulated wave conditions. The purpose of this stagewas to demonstrate the feasibility of using the DYNAMANtechnique to model behaviour in a moving sea.

w A series of self-righting trials was carried out at the Institute ofNaval Medicine (INM) using a marine manikin and two types oflifejacket; a typical inherently buoyant jacket and a typical inflatablejacket. These trials provided self-righting data against which theDYNAMAN technique could be validated.

w DYNAMAN simulations of the self-righting trials were carried out.One simulation was run for each lifejacket. The results of thesimulations were compared with the trials. Assessment of theresults highlighted the need for more accurate buoyancy data for themanikin and lifejackets.

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w As a result of the previous stage, detailed measurements weremade at INM of the density and volume of each part of the marinemanikin and the two lifejackets. This allowed the buoyancy of themanikin and lifejackets to be determined.

w The computer simulations were re-run with revised input data basedon the measurements made at INM. The results of the revisedsimulations were compared with the self-righting trial data.

Section 2 describes the theoretical basis of the simulation technique and theimplementation of buoyancy and drag forces to allow lifejacket behaviour to bemodelled. A validation test case is also presented in this section. Section 3 describesthe demonstration simulation. In Section 4, the self-righting trials carried out at INMare described. In Section 5 the initial computer simulations based on the trials aredescribed and the results presented. Comparisons between the trials and simulationsare drawn in Section 6 and discussed further in Section 7. The measurements madeto determine the buoyancy of manikin and lifejackets are described in Section 8. InSection 9 the revised computer simulations are described. The results are comparedwith the self-righting trials in Section 10.

Conclusions from the work, recommendations for further work and applications ofthe technique are summarised in Section 11.

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2. THE SIMULATION CONCEPT

2.1 THE DYNAMAN TECHNIQUE

The DYNAMAN technique was developed by FNC for modelling the dynamicbehaviour of human, or surrogate dummies, under a range of different loadings.DYNAMAN is based on the finite element analysis code DYNA3D (Reference 1).DYNA3D has been written specifically for modelling transient events where thereare large material or geometric non-linearities. FNC has already successfully usedDYNAMAN in work carried out for the HSE Railway Inspectorate (Reference 2).In particular, the model helped to explain injury patterns in the Cannon Street railcrash.

Figure 1 shows a typical DYNAMAN model of the type used to assess rail crashinjuries. The dimensions of any part of the body can be adjusted to suit therequirements of the particular simulation and mass and inertia properties of each partcan be individually assigned. The limbs are joined together so that each joint is freeto bend (as would be the case with a human) but rotations are limited to a realisticextent.

In a typical DYNAMAN analysis, the model is adjusted to the required position anda dynamic loading is then applied. The load may be applied either direct toDYNAMAN (such as in a blast loading scenario) or to the structure modelledaround him (such as in a rail crash). DYNAMAN predicts the resulting motion ofthe person including any impact between the person and his surrounding. From theresults of a simulation it is possible to make an assessment of likely injuries, examinethe effect of adding padding or restraints, etc.

In this project, DYNAMAN has been used to model the dynamic behaviour ofunconscious people or surrogate dummies wearing buoyancy aids in water. Theresults that are of particular interest in this application include the general motion ofDYNAMAN, the relative position of the airways to the water surface, and the timetaken for the body to right from a face down position. These are important indicatorsof the relative performance of different buoyancy aid designs.

2.2 THE FORCES ON BODIES IN WATER

In order to model the behaviour of bodies in water, the forces acting on them mustbe correctly applied. The form include:

w buoyancy

w drag

w gravity

w surface tension

w wind loading

Figure 2 illustrates these forces.

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The first three of these forces are believed to be the most significant ones for theanalysis of lifejacket self-righting performance. It was agreed with the HSE thatonly these effects would be considered in this work programme.

The ability to apply gravitational forces is a standard feature of DYNAMAN.However, it has been necessary to include the effects of buoyancy and drag to allowlifejacket performance to be modelled. The theory used and its implementation inDYNAMAN is described in the next two sections.

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2.3 BUOYANCY

When a body is fully or partially immersed in a fluid the fluid exerts a pressure on itas shown in Figure 3. If the pressure were uniform over the entire surface therewould be no resultant force on the object. However, where pressure varies (forexample, with depth) there will be a net resultant force on the object. This force isknown as the buoyancy force.

On any small area, A, on the surface of an object, the buoyancy force, which actsnormal to the surface of the object, is given by;

Eqn 1

Fbuoy = ρwater g ∆hA

Where ρwater = density of waterg = gravitational acceleration∆h = depth of the centre of the area, A, below the water surface.

In DYNAMAN this buoyancy force is implemented by applying a pressure Pbuoy toeach small segment of the man or lifejacket which is below the surface of the water.Pbuoy is given by;

Eqn 2

Pbuoy = ρwater g ∆h

2.4 DRAG

The conventional theory of hydrodynamics assumes that the total drag force actingon an object moving relative to surrounding water is given by;

Eqn 3

Fdrag = ½ ρwater u2 CDA

a reference area of the object (often the presented area of the object).=Adrag coefficient=CD

velocity of the object relative to the water=udensity of water=ρ

Where

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CD is an empirically determined factor dependent (among other things) on the shapeof the object. Typical values of CD for some simple shapes are given below:

1Long cylinder

1.2Sphere

2Flat plate

CDShape

In DYNAMAN it is assumed that the total drag force is due to high pressure onparts of the object's surface which are moving into the fluid and low pressure onparts of the object's surface moving away from the fluid as shown in Figure 4.Surfaces moving into the flow are given an increased pressure given by

Eqn 4

Pdrag = ½ ρwater U2

and surfaces moving away from the fluid are given a reduced pressure given by

Eqn 5

Pdrag = ½ ρwater U2 (1 - Cp)

The total drag force on the whole object is then given by Equation 3.

For objects partly immersed in the water, drag forces act only on the wettedsurface. Although wind loading is not being considered here, the form acting due tothe wind could be calculated in a similar way and applied to those surfaces not in thewater.

2.5 SEA CONDITIONS

To investigate the behaviour of buoyancy aids in rough sea conditions an idealisedsinusoidal motion of the sea surface has been included in the DYNAMAN model.The height of the water surface is given by

Eqn 6

h = ho + hav sin w (vx t + x)

time=tx position =xwave velocity =vx

wave frequency =wwave amplitude =hav

mean depth of sea =h0

Where,

9

In addition to the plane wave travelling on the sea surface, currents in the plane ofthe sea can also be included in the model. Other, possibly more realistic, sea surfaceshapes could be incorporated into the model at a later date.

For visualisation purposes a sheet of shell elements has been used to represent thesea surface.

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2.6 TEST CASE

2.6.1 Description

A simple test case has been used to demonstrate and validate the features whichhave been added to DYNAMAN. The test model consists of a low density ball(relative density 0.5) which is released a distance below the surface of the water.The water surface has a sinusoidal shape. The model is shown in Figure 5.

2.6.2 Expected Behaviour

The expected behaviour of the ball in this model is that it should initially accelerateupwards towards the water surface due to buoyancy. At some stage the drag forceplus the gravitational force will balance the buoyancy force and the ball should reacha terminal velocity. The ball should then rise at the terminal velocity until it reachesthe water surface. When it reaches the surface the ball should oscillate slightly andthen take up a periodic motion with the same frequency as the surface wave. Sinceits relative density is 0.5, approximately half of the ball should be visible on thesurface of the water as it oscillates.

The expected terminal velocity, u, occurs when:

Drag force + Gravitational force = Buoyancy force

ie

Eqn 7

½ ρwater ut2 CDA + ρbody g v = ρwater g v

gravitational acceleration=gradius of ball=rdensity=ρvolume of the ball = 4/3 Π r3=Vplan area of the ball = Π r2=Aterminal velocity=ut

where

Equation 7 can be rearranged to give;

Eqn 8

= u t

43 (qw ater−qbody) r g

12 qw ater CD

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In the test case

1.2=CD

5 mm=r500 kg/m3=ρbody

1000 kg/m3=Ρwater

In this case, from Equation 8, the predicted terminal velocity is 233 mm/s.

The equations of motion of the ball can be solved numerically to give the expectedvariation of vertical velocity with time.

2.6.3 Results

Figure 6 compares the velocity history of the ball obtained from the simulation withthe expected behaviour. It can be seen that the correct temporal variation is obtainedand the terminal velocity is 233 mm/s as expected.

The vertical motion history of the ball is shown in Figure 7. It can be sew that, aftera small oscillation in the first cycle, the ball settles down to a smooth, roughlysinusoidal motion as expected. The position the ball takes on the surface of thewater is shown in Figure 8. As expected half the volume is out of the water.

This test case validates the implementation of the buoyancy and drag laws and thesinusoidal sea surface described in Sections 2.3, 2.4 and 2.5.

2.7 SUMMARY OF SIMULATION FEATURES

With the features described above successfully implemented in DYNAMAN, thesimulation technique now has the ability to model the following features:

w Properties of each segment of the person

dimensions

inertial properties

effective drag coefficient

w Properties of the lifejacket

shape

weight

method of attachment

effective drag coefficient

w Properties of the water

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surface motion (Sinusoidal motion. Amplitude, speed andfrequency are specified by the user)

current (constant in the horizontal plane)

Post-processing allows both the person and the water surface to be displayedpictorially. In addition, the displacement, velocity and acceleration of any point onDYNAMAN or the lifejacket may be plotted as a function of time.

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3. DYNAMAN DEMONSTRATION SIMULATION

3.1 INTRODUCTION

As a demonstration simulation, the behaviour of a 'person' wearing a typicallifejacket in simulated waves has been modelled using DYNAMAN. For thedemonstration DYNAMAN is configured to behave in a similar manner to a marinemanikin representing an unconscious person. The lifejacket used in the simulations isnot representative of any particular design but has a representative volume.

3.2 DESCRIPTION

Figure 9 shows the initial configuration of the demonstration model. Note that twoviews of the model are shown, one from above and one from below the watersurface. The model consists of three main parts:

w The “man”,

w The lifejacket

w The water

The standard DYNAMAN torso consists of three sections; the thorax, the abdomenand the pelvis which can all move relative to each other. However, to representmore closely the stiffness a marine manikin these sections of DYNAMAN havebeen joined together so that they move as one part.

The density data used for DYNAMAN was taken from Reference 3 which givesdensities of the parts of an actual human body. Using these figures the overallrelative density of the body is very close to 1.0. The relative density of the lifejacketis very much lower (about 0.02). The overall relative density of the body andlifejacket combined is about 0.8.

For the purpose of this simulation a simple representation of a lifejacket wasgenerated to demonstrate qualitatively the body behaviour when supported by abuoyancy aid. Thus the model has a rather square appearance compared with a reallifejacket.

Some lifejackets hold the head quite snugly when fitted to prevent the head movingrelative to the lifejacket. In the simulation, the head and neck are not allowed tomove at all relative to the lifejacket. The removed degrees of freedom can easily bereintroduced for other lifejacket designs. The lifejacket is attached to DYNAMANby springs which represent the tapes which would be used to tie a jacket on.

The wave conditions chosen for the test represent a swell of 600 mm peak to trough,and a period of 4 seconds.

In the simulation DYNAMAN is initially lying on his back. The initial position chosenfor DYNAMAN is such that the mass of water displaced by DYNAMAN and thejacket is close to the mass of DYNAMAN to minimise the time taken for the modelto reach a realistic floating position.

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3.3 RESULTS

Figures 9 to 13 show the motion of DYNAMAN and the water surface at intervalsof 1.0 second for a total of 9 seconds. Figure 14 shows the motion history ofDYNAMAN's nose during the analysis. The following features of the motionshould be noted from Figures 9 to 14:

w From the initial position DYNAMAN rises out of the water. Thisindicates that in the initial position the buoyancy forces exceed thegravitational forces.

w As the first wave passes over DYNAMAN the legs and pelvis droprelative to the torso. This happens for two reasons: firstly becausethe large buoyancy force lifts the lifejacket and thorax causingrotation at the hips, and secondly because the legs and pelvis areslightly denser than water and so tend to drop anyway. The armsdrop for similar reasons.

w From the initial straight position the joints of the model bend andDYNAMAN takes a very realistic relaxed position in the water.

w As the waves pass DYNAMAN rises and falls in the water. Thepostures assumed by DYNAMAN are the same at each point insuccessive waves.

w As the water surface rises so the sea covers more of the lifejacket.Similarly, as the water falls so the jacket rides higher in the water.

w Figure 14 gives an indication of DYNAMAN's motion during theanalysis. The X-displacement history shows that DYNAMANmoves backwards and forwards as he slides down the wavesurfaces. Overall he moves in the direction of travel of the wave.The Y-displacement history shows very little lateral movement. TheZ-displacement history shows that, after the first half cycle,DYNAMAN assumes a cyclic vertical motion in phase with thewave.

Discussions with experts at INM confirmed that the motion of DYNAMAN in thissimulation is representative of the types of motion which would be expected ofunconscious subjects in wave conditions.

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4. SELF-RIGHTING TRIALS

A series of in-water trials were carried out at INM using a marine manikin to obtaindata on the self righting characteristics of a manikin wearing two types of lifejacket.The self-righting trials were conducted by INM staff. The trials were observed byFNC.

The trials and the results of the trials are discussed in this section. InitialDYNAMAN simulations of the trials are presented in Section 5.

4.1 TEST FACILITY

The INM testing facility consists of a large water tank with lifting equipment to aidhandling of the manikin. Underwater video cameras were positioned in the tank sothat video recordings could be made of the trials from both the head of the manikinand side on to the manikin.

The manikin was manually positioned in the water for the tests by an INM memberof staff from inside the water tank.

4.2 LIFEJACKETS

Two lifejackets were used for the trials. The first was a typical inflatable jacket andthe second a typical inherently buoyant jacket.

4.2.1 Inflatable Lifejacket

This is a single piece jacket which is put on in the uninflated state and inflated whenneeded by means of a gas discharge or the wearer blowing it up. The majority of thebuoyancy aid is worn at the front although a collar around the back of the neck fitssnugly and can support the head when in the water. The jacket is secured to thebody with a single waist strap.

4.2.2 Inherently Buoyant Jacket

The inherently buoyant jacket consisted of a series of nylon bags filled with buoyantmaterial. A large section forms the front, a slightly smaller on the back, and two verysmall sections act as epaulettes holding the front and back together.

The jacket is secured by long tapes which pass through loops on the front and backsections of the jacket. The tapes are finally tied across the front of the jacket.

It was found that the jacket could be fastened in a number of ways so that thepositioning on the body is variable. The jacket does not make contact with the headand therefore offers no support to the head.

4.3 TEST PROCEDURE

The manikin was unclothed for the trials and a 4 litre lung was fitted into the chestrepresenting the full lung capacity of a man.

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A series of trials was carried out with each of the lifejackets. The lifejackets werefitted to the manikin out of the water and tied on as tightly as possible at thebeginning of each series of trials.

The conventional test procedure for determining lifejacket righting times involvesholding the jacketed manikin or person face down in the water with legs and armsstraight and in line with the torso and then letting go once settled. It was founddifficult for only one person holding the manikin to achieve this starting position in thewater so a different initial position was adopted for the purpose of these trials. Themanikin was held face downward with the arms and legs dropped down so that itwas lying on top of the lifejacket. It is felt that this may be a more severe test of thejacket's self righting ability.

The manikin was held still in the initial position described above. Once the water hadsettled, the manikin was let go.

Several trials were carried out with each of the lifejackets and videoed for lateranalysis.

4.4 RESULTS

4.4.1 The General Behaviour of the Marine Manikin

The manikin used in the trials is intended to represent an unconscious person. Theneck is very flexible allowing the head to move in all directions but other joints arefairly stiff. In particular, it was found that in certain positions the joints (particularlythe shoulder) could lock-up. When wearing a lifejacket in the water the manikin tookup a relaxed position on its back. The torso lay at an angle of about 30° to the watersurface with the arms lying close to the torso in the same attitude. The legs bent atthe knees and hips with the thighs adopting almost a sitting position.

4.4.2 Righting Modes

Throughout the trials two different modes of self righting could be identified. In one,the hips drop, the jacket rises and the man manikin tries to sit up (the “sit-up” mode).In the other, the shoulders rotate about a head-hip axis as the lifejacket rises out ofthe water to one side of the body and the manikin rolls over (the “roll-over” mode).Figure 15 illustrates the two modes. In reality any particular righting motion includesa combination of both modes. However, one is usually dominant.

A typical response of the manikin in the trials was as follows:

w When released the hips were seen to drop (sit up mode).

w One shoulder rose up out of the water as the body rotated about thehead to hip axis (roll over mode).

w The body turned through 90° about the hip to hip axis and 90° aboutthe head to hip axis.

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w Once righted the manikin took up the position described in Section4.4.1.

4.4.3 Self Righting Time

The determination of a self righting time is somewhat subjective since it is difficult todefine precisely a starting and finishing point. This was made particularly difficultbecause each trial produced slightly different body motions.

The most workable definition of the self righting time was found to be from the timewhen the hips began to drop until the time when the lifejacket was furthest out of thewater with the head fully visible.

From this definition, typical righting times from the trials are summarised in Table 1.Note that, there was considerable scatter in the results for each jacket even thoughthe initial conditions were nominally the same in each case.

Table 1Trial Self Righting Times

3.63.52.4Inherently Buoyant Life Jacket

221.9Inflatable lifejacket

Trial 3Trial 2Trial 1

Righting Time (sec)Jacket

4.4.4 Lifejacket Position

During each of the trials the lifejackets were seen to move around on the manikin.To some extent this movement would be restricted in a real situation by clothingsince friction form would be generated between the fabric straps and clothing. Theinflatable lifejacket remained in position somewhat better than the inherently buoyantlifejacket and also held the head more firmly.

4.4.5 Position of Airways

With the equipment available it was not possible to measure the relative position ofthe water surface and the airways on the manikin accurately enough to determine anairway motion history.

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5. INITIAL SIMULATIONS BASED ON TRIALS

5.1 LIFEJACKET MODELS

In order to simulate the self righting trials, DYNAMAN models of the manikinwearing the two life jackets were required. These models were generated asdiscussed below.

It should be noted that in this stage of the work the two simulations were set up withprior knowledge of the manikin's initial position and with access to the jacketsthemselves. However, the results presented in this section are from the first iterationof each simulation. That is, no tuning or modification of the models was carried outat this stage to make the simulation fit the trials better.


The inflatable lifejacket consists of two layers of material which are sealed at theedges and blown up with gas. The inflated shape of the jacket is difficult to measureand is difficult to generate as a finite element mesh. For this reason the jacketgeometry for the simulation was generated by mimicking the inflation process.

The jacket material was modelled with shell elements connected around theperiphery and a pressure was applied to their inside surfaces. The resultant shape ofthe jacket is shown on DYNAMAN in Figure 16. It was found that this methodproduced a realistic jacket shape.

The positioning of the jacket on the body was determined by examining its fit on areal person. The jacket fits snugly around the neck such that an attachment here isnot necessary. The lower part of the jacket is pulled into the body by two strapsfixed to a belt. These have been modelled in DYNAMAN by stiff spring elementsbetween the jacket and abdomen. Very little movement is therefore allowedbetween the jacket and DYNAMAN. The density of the elements forming thejacket has been chosen such that the overall mass of the jacket in the model is thesame as the real jacket.

The real lifejacket holds the head reasonably securely. In the simulation the head isassumed to be held completely by the jacket.

5.1.2 Inherently Buoyant Lifejacket

The inherently buoyant lifejacket consists of a series of nylon bags filled withbuoyant material. It comprises two large rectangular sections, one of which formsthe front of the jacket, the other sits behind the head. These pieces are joined by twobuoyant epaulettes.

A model of this jacket has been generated as shown in Figure 17. Its positioning onDYNAMAN was determined by examining a person wearing the jacket. In practicethe jacket could be tied to the body in a number of ways and the relative motionbetween the wearer and jacket will be dependent on the ability of the wearer tofasten it tightly. In the simulation, motion has been prevented between the jacket andthorax to simulate the case where the jacket is attached very securely. In contrast to

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the inflatable lifejacket, the inherently buoyant jacket does not hold the head at all. Inthe simulation the head is therefore allowed to move freely.

The density of the jacket was chosen so that the model mass is equal to the actualmass of the jacket.

5.2 SIMULATION OF TRIALS

A DYNAMAN simulation was generated and run for each of the life jacketsrepresenting as closely as possible the trial conditions.

From the video of the trials a typical starting position was determined forDYNAMAN, as shown in Figure 18. DYNAMAN is face down in the water witharms and legs hanging down. The relative positions of parts of the body and thewater surface were taken from sketches made from the video.

In the simulation, some simplifying assumptions were made as follows:

w The water was assumed to be stationary although in practice somedisturbance was unavoidable,

w The relative motion of the lifejacket and DYNAMAN wasrestricted as discussed in Section 5.1,

w A drag coefficient of 1.0 was assumed for all parts of the model.

DYNAMAN was allowed to move freely from the initial position from time zero.The total simulation time was 8 seconds in each case.

5.3 RESULTS

The results of the simulations which were used to make a comparison between thetrials and the computer simulations are the general motion of the body and therighting time as defined in Section 4.4.3. These are presented for each lifejacket inthe following sections.


The motion of DYNAMAN in this simulation is shown in Figures 19 and 20. To aidwith determining the self righting time, the vertical position of a point on the centre ofthe life jacket is plotted in Figure 21. To show airway motion, the vertical position ofDYNAMAN's nose is plotted in Figure 22.

The following points should be noted:

w Self righting occurs in one smooth movement. Initially the modelstarts to turn in a “roll-over” mode (Section 4.4.2). However, thehips quickly drop and righting continues in a “sit-up” mode.

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w From examination of Figures 19 - 22, it is estimated that rightingbegins at about 0.5 seconds and is complete by about 3.5 secondsgiving a self righting time of about 3 seconds.

w At the end of the simulation (8 seconds) the model has reached anequilibrium position. The body lies at about 45° to the horizontal withthe arms dropped vertically and the legs in line with the torso. Thebody has turned through just over 90° about a vertical axis. Theairway ends up about 100 mm above the water surface.


The motion of DYNAMAN wearing this jacket is shown in Figure 23 and 24. To aiddetermination of the self righting time the vertical motion of the centre of thelifejacket is shown in Figure 25. The height of the nose above water is shown inFigure 26.

The following points should be noted:

w The model takes some time to begin to right. Righting occurs mainlyin the “roll-over” mode although towards the end the hips do dropinto a “sit-up” mode. The head moves around considerably duringthe simulation.

w It is estimated that righting begins at about 2.25 seconds and iscompleted at about 7.5 seconds giving a righting time of about 5.25seconds. There is a noticeable pause from about 4.5 seconds to 5.5seconds where the manikin has rolled to about 90° and remains atthat angle.

w At the end of the simulation (8 seconds) the model has not yetreached equilibrium. It is believed that, given a longer simulationtime, the model would end face up in a similar position to the finalstate in the inflatable lifejacket simulation but with the head to oneside. The airway reaches a maximum height of 175 mm above thewater surface but is clearly moving down again at the end of thesimulation.

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6. COMPARISON BETWEEN TRIALS AND INITIALSIMULATIONS

Comparison between the trials results described in Section 4 and the initialsimulations described in Section 5 shows that the simulation of the inflatablelifejacket agrees quite well with the trial. However, the simulation of the inherentlybuoyant lifejacket agrees less well.

The following sections compare the trials and simulations for each jacket in turn.

6.1 INFLATABLE LIFEJACKET

The following comparisons can be made:

w In both the trial and the simulation, the jacket succeeded in selfrighting.

w Righting occurred in a single, smooth movement dominated by thesit-up mode in both the trial and the simulation. However, there wasalso some roll-over mode apparent. This was more noticeable in thesimulation than in the trial.

w In the trial, self righting was estimated to take about 2 seconds. Inthe simulation, self righting took longer, about 3 seconds.

w The final positions were very similar. However, in the simulation thearms hung more vertically and the legs were spread apart.

w In the trial, some movement of the jacket relative to the manikinoccurred. In particular, the belt holding the jacket slid up themanikin's torso. In the simulation this could not occur.

6.2 INHERENTLY BUOYANT LIFEJACKET


w In both the trial and the simulation, the jacket succeeded in selfrighting.

w In the trial, the manikin righted in a smooth movement dominated bythe sit-up mode with a small roll-over component. However, in thesimulation the reverse was true. The greater part of the motion wasin the roll-over mode and was by no way continuous (see Section5.3.2). Only at the end of the simulation, where righting was almostcomplete, did the model begin to sit-up.

w The trial and simulation give significantly different righting times (2.4-3.6 seconds in the trial and 5.25 seconds in the simulation).

w In the simulation the model did not reach an equilibrium positionwithin the 8 seconds of the analysis. However, it is believed that the

22

final position would be similar to that seen in the trial with the headrolled to one side and the torso tilted with one shoulder lower in thewater than the other. As with the inflatable lifejacket the inherentlybuoyant lifejacket simulation would probably give the arms morevertical than in the trial and the legs spread further apart.

w In the trial the inherently buoyant jacket moved around a great dealon the manikin. In particular, the jacket had a noticeable tendency toslip sideways on the manikin and also to ride up towards the head.In the simulation the position of the jacket relative to the torso wasfixed and no relative movement occurred.

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7. DISCUSSION

It would appear that the inflatable lifejacket simulation agreed much more closelywith the trials than did the inherently buoyant lifejacket simulation in that the overallmotion of the model and the righting time were closer to those observed in the trial.In the inherently buoyant lifejacket simulation righting was much slower than wasobserved in the trials.

As noted in Section 5.1, the results presented here represent the first iteration ofboth models. The following sections discuss the factors which influence righting andthen consider in detail changes which could be made to the simulations to improvethe results.

7.1 RIGHTING MODE

The “sit-up” and “roll-over” righting modes can be explained in terms of the principalforces acting on the lifejacket and the body as it rights.

The forces acting are the downward force due to the weight of the body acting atthe centre of gravity (typically somewhere in the abdomen), and the upwardbuoyancy force acting at the centre of buoyancy (typically near the centre of thelifejacket). These forces are shown pictorially in Figure 27.

The side-on view in Figure 27 shows how the forces act to cause the sit-up mode.The lines of action of the gravitational and buoyancy forces are separated by adistance ‘x’ which gives rise to a turning moment about a lateral axis.

The head on view in Figure 27 shows how the forces act to cause the roll-overmode. The fines of action of the gravitational and buoyancy forces are separated bya distance ‘y’ which gives rise to a turning moment about a head-to-hip axis.

Clearly both of those moments will be dependent on the magnitude of thegravitational and buoyancy forces. An increase in either will increase the turningmoment and speed up self-righting.

Which of the two modes is dominant will depend on the relative magnitude of thedistances ‘x’ and ‘y’ and the rotational inertia of the body about the two axes. Ingeneral, as ‘x’ increases (ie the centre of buoyancy moves away from the centre ofgravity) the sit up component of the righting mode will become more significant, andas ‘y’ increases the more significant will be the rolling component of the rightingmode.

In a self-righting trial the righting motion will be a complex combination of roll-overand sit up modes. Although the size of the gravitational force will be constant, the Cof G will move as the body bends. In addition, the centre of buoyancy and the size ofthe buoyancy force will change constantly as the volume of water displaced changesas parts of the body and lifejacket move in and out of the water. Thus x and y andthe magnitude of the buoyancy force will change throughout the righting process.

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The overall righting motion for the inflatable lifejacket simulation was close to thatseen in the trials. However, righting was a bit slow to start. In the trials the firstobserved movement of the manikin was the hips dropping (see Section 4.4.2). Therewas a noticeable delay in the hips dropping in the simulation which suggests that thecentre of gravity of the body may have been too close to the head of DYNAMANor the centre of buoyancy may have been too close to the hips of DYNAMAN.

In addition the righting time in the simulation was 1½ times longer than observed inthe trials. This implies that the turning moment was too small or the resistance tomotion eg inertia, drag too high.

The discrepancy in the positions of the centre of gravity or the centre of buoyancyand the size of the forces could be due to some combination of the following:

w The mass of DYNAMAN may have been different to the manikinsuch that the gravitational force was incorrect.

w The density distribution of DYNAMAN may have been different tothat in the marine manikin so that DYNAMAN's centre of gravitywas nearer the head than in the manikin which would reduce theturning moment.

w The model of the lifejacket may have been smaller than in reality.This would mean that the buoyancy force and turning momentprovided by the jacket was too small.

w The lifejacket may have been incorrectly positioned onDYNAMAN. If it were too low down the chest the centre ofbuoyancy would be brought closer to the centre of gravity thusreducing the sit-up moment. Although the jacket was free to moveaway from DYNAMAN on springs representing tapes holding thejacket, it was not free to slide up the chest. In the trials this wasseen to happen on the manikin as the chest strap slid over thesmooth surface of the manikin.

w The drag forces acting on the body could have been larger than inreality. However, results of the simulation showed that these forcesare small in comparison to the buoyancy forces and probably have aless significant effect on righting time and mode.

The other difference between the inflatable lifejacket simulation and the trials wasthe final position of the bodies. In the simulation, DYNAMAN's arms droppedvertically in the water and the legs were splayed and relaxed. The arms and legs ofthe manikin however, remained in line and close to the body. The difference in theposition arises because the joints of DYNAMAN have less resistance to rotationand do not “lock up” as the manikin's tended to in some positions. This increasedfreedom allows hips to rotate, legs to spread, shoulders to relax and arms to drop.

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The righting time of DYNAMAN in the inherently buoyant lifejacket simulation wasclearly greater than measured in the trials with the marine manikin.

The possible reasons for the differences between the trials and simulation are as forthe inflatable jacket, ie different density distribution, undersize jacket (possibly of aslightly different shape) and jacket attachment.

However, with this jacket when the body has rolled through 90° it appears to pausein the rolling mode (Figures 28 and 29). This pause occurs when the back of thejacket enters the water so that buoyancy forces act each side of the centre ofgravity giving a stable system which is reluctant to continue to roll. This featurecould have arisen because of an incorrect distribution of buoyancy between the frontand back of the jacket in the simulation.

At the end of the 8 second simulation DYNAMAN had not reached a stableposition. However, the final position would be much the same as that achieved in theinflatable lifejacket simulation with one exception. Because the head rolls to one sidein the inherently buoyant lifejacket simulation the body floats with one shoulderfurther in the water than the other. This occurred in the trials also. A likelydifference between the final positions in the simulation and trial would be the positionof the arms and legs due to the greater flexibility of DYNAMAN as discussed in7.2.

7.4 SIMULATION IMPROVEMENTS

From the preceding discussion it is evident that the prediction of correct rightingmotion and times will require some improvement in the initial simulations.

Aspects of the simulation which could be varied include:

w Provision of more accurate density data for the marine manikin andlifejackets. This would enable the correct magnitude of thegravitational force to be calculated.

w Provision of more accurate volume data for the marine manikin andlifejacket. This would provide the correct buoyancy forces.

w Revision of lifejacket position on the body.

w Introduction of some movement in the water which may provideadditional turning moments.

w Modification of the drag coefficient used to determine the fluidresistance to body motion.

Of these possible modifications, the first three were considered likely to have thegreatest effect on the behaviour of DYNAMAN. As a result, it was agreed withHSE that further measurements would be made on the real manikin and lifejacketsto allow more accurate simulations to be generated. Section 8 describes the

26

measurements which were made while Section 9 describes revised simulationswhich incorporate the new data.

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8. BUOYANCY AND DENSITY MEASUREMENT

As discussed in Section 7.4, a series of measurements were made at INM after theinitial simulations had been carried out to determine the volume and density of eachmajor component of the marine manikin and lifejackets used in the self-righting trialsreported in Section 4.

The volume and density were determined by weighing each component in air andthen in water. In the case of buoyant components (ie density less than water) sinkweights were used in the measurements. The volume and density were calculated asfollows:

Eqn 9

Weight in air (WA) - ρc g Vc + WsA

Eqn 10

Weight in water (Ww) =

ρc g Vc - ρw g Vc W +Wsw

weight of sink weight in water.=Wsw

weight of sink weight in air=Ws

volume of component=Vc

gravity=gdensity of water=ρw

density of component=ρc

Where

From (9) and (10)

qc =qw

1 −Ww − Wsw

1 − WA − WsA

and

Vc =

WA − WsAq cg

The marine manikin was disassembled into the following components formeasurement;

w 4 litre lung

w thigh

w shin and foot

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w upper arm

w lower arm and hand

w head and torso (without lung)

w pelvis and abdomen.

The measured values for these component parts and the two lifejackets arecompared in Table 2 with the values used in the initial simulations. Note that theinherently buoyant jacket is composed of three sections, the front, the back and theshoulder epaulettes as shown in Figure 17.

It can be seen from Table 2 that the densities of the individual parts and overalldensity of DYNAMAN used in the initial simulations were slightly lower than thevalues measured or the marine manikin. The table also shows that the volume of thebody parts used in the initial simulation were larger than measured.

In addition, the lifejacket densities were larger and volumes significantly smaller inthe initial simulations compared with the measured values.

In summary, the table shows that DYNAMAN was more buoyant and the jacketsless buoyant in the initial simulation compared with the values for the marine manikinand lifejackets measured at INM.

Table 2Density and Buoyancy Measurements

68.61.0578.50.99Total with 4 litre lung

24.40.0919.70.1Inherently Buoyant lifejacket

17.90.0414.10.07Inflatable lifejacket

40.41.0347.90.95Head and torso

2.61.091.91.07Lower arm and hard

1.91.112.21.07Upper arm

4.51.085.11.04Shin and foot

5.71.066.11.04Thigh

4.50.0540.054 litre lung

Volume(litres)

RelativeDensity

Volume(litres)

RelativeDensity

Measured ValuesInitial SimulationsComponent

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9. REVISED SIMULATIONS

The two simulations presented in Section 5 were refined using the measured datapresented in Section 8.

Modifications were made to the volume and density of DYNAMAN to more closelyrepresent the marine manikin. The volume of the lifejackets was also revised. Thespecific changes and the results of the revised simulations are presented in thissection.

9.1 MODEL CHANGES

9.1.1 DYNAMAN

The value of density and volume given in Table 2 were used to adjust the size anddensity of the individual components of DYNAMAN. The changes resulted in a7.8% decrease in total mass of DYNAMAN. The centre of gravity of the revisedDYNAMAN moved away from the head towards the feet by 36 mm.

The volume changes gave a 12.8% reduction in DYNAMAN volume and hence anequivalent decrease in the buoyancy force. The change in volume is greater than thechange in mass since the marine manikin was found to be slightly denser overall thanthe DYNAMAN used in the initial simulations.

9.1.2 Lifejackets

As shown in Section 8, the volume measurements made of the lifejackets showedthat the models used in the initial simulations were both about 25% too small. Thisdifference will have a significant effect on the turning moment generated by thejackets.

The revised shape of the inflatable jacket is shown in Figure 28. The shape wasgenerated by inflating the jacket within the simulation as described in Section 5, usinga higher inflation pressure than in the initial simulation to achieve the requiredincrease in volume.

The revised shape and position of the inherently buoyant lifejacket is shown in Figure34. This jacket is modelled as a solid as described in Section 5. The dimensions ofthe front, back and epaulettes were adjusted to achieve the required volume.

In the initial simulations the position of the jackets was determined from theobserved position taken when the manikin was out of the water as described inSection 5. In the revised simulation, the jackets have been repositioned to representthe position taken when the manikin is in the water. The revised inflatable lifejacketsimulation has the jacket further away from the chest as can be seen by comparingFigure 28 with Figure 16. In the revised inherently buoyant jacket simulation thejacket is positioned higher up DYNAMAN's chest as can be seen by comparingFigures 29 and 17.

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9.2 RESULTS OF REVISED SIMULATIONS

The results of the simulations which were used to make a comparison between thetrials and computer simulations are the general motion of the body and the rightingtime as defined in Section 4.4.3. These are presented for each lifejacket in thefollowing sections.


The motion of DYNAMAN in this simulation is shown in Figures 30 and 31. To aidwith determining the self-righting time, the vertical position of a point on the centreof the lifejacket is plotted in Figure 32. To show airway motion, the vertical positionof DYNAMAN's nose is plotted in Figure 33.

The following points should be noted and compared with the behaviour described inSection 5.3.1 for the initial simulation:

Self-righting occurs in one smooth movement. The hips drop quickly andDYNAMAN rights in predominantly the 'sit-up' mode.

From the figures it is estimated that righting begins as soon as the simulation startsand is completed in about 1.6 seconds.

Within 4 seconds DYNAMAN has reached an equilibrium position. The body lies atabout 60° to the horizontal with the arms dropped vertically and legs in line with thetorso. The body has turned through about 60° about a vertical axis. The airway endsup about 180 mm above the water surface.


The motion of DYNAMAN in this simulation is shown in Figures 34 and 35. To aidwith determining the self-righting time the vertical position of a point on the centre ofthe lifejacket is plotted in Figure 36. To show airway motion, the vertical position ofDYNAMAN's nose is plotted in Figure 37.

The following points should be noted and compared with the behaviour described inSection 5.3.2 for the initial simulation:

w Self-righting occurs in one smooth movement. Righting occursmainly in the ‘roll’-over mode although the hips drop more quicklythan in the initial simulation. The head moves around considerablyduring the simulation.

w It is estimated from Figure 41 that righting begins at about 0.5seconds and is complete by about 3 seconds giving a righting time ofabout 2.5 seconds. There is a short pause in the righting at about 1.5- 2.0 seconds.

w Within about 6 seconds, DYNAMAN has reached equilibrium. Thebody lies at about 45° to the horizontal with the arm and legsdropped vertically. The body has turned through just over 90° about

31

a vertical axis. The airway ends up about 250 mm above the watersurface.

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10. COMPARISON OF TRIALS WITH INITIAL AND REVISEDSIMULATIONS

A comparison between the trials and initial simulations is made in Section 6. It wasfound that the initial simulations were slow to right (the inherently buoyant simulationbeing particularly slow). The simulations were revised to improve buoyancy anddensity properties as described in Section 8.

The following sections compare the trials with the revised simulations and highlightimprovements over the initial simulations.



w In both the trials and revised simulation the jacket succeeded inself-righting.

w In the trial, self-righting was estimated to take 2 seconds. In theinitial simulation self-righting took longer, about 3 seconds.However, in the revised simulation the self-righting time was only1.6 seconds. This significant decrease in righting time was due tothe increase in turning moment resulting from the increase inbuoyancy force and the increased separation between the centresof gravity and buoyancy due to changes in DYNAMAN's massdistribution and repositioning of the larger lifejacket.

w Righting occurred in a single, smooth movement in both simulations.In the initial simulation this was dominated by the roll-over mode.However, in the revised simulation it was dominated by the sit-upmode. The reason for this is that in the revised simulation the jacketis positioned significantly further away from DYNAMAN's chest.As explained in Section 6, this increases the turning moment aboutthe shoulder to shoulder axis compared to that about a head to hipaxis and hence increases the ‘Sit-up’ mode in the righting action.

w In the trials, the equilibrium position of the manikin in the water wasto lie at about 45° to the horizontal with the arms in line with andbeside the torso. The legs were bent with the knees at about 90° tothe thighs which were slightly raised relative to the fine of the torso.The knees stayed together.In the initial simulation the torso was seen to take up a similarequilibrium position, however the limbs were spread and relaxed dueto differing joint constraints between DYNAMAN and the manikin.In the revised simulation, DYNAMAN lay at about 60° to thehorizontal with limbs in the same relaxed position. The increase inthe angle of the body to the horizontal occurred due to the increasedangle between the jacket and DYNAMAN in the revisedsimulation.

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w In the trial some movement of the jacket relative to the manikinoccurred. In both simulations such movement could not occur.



w In both the trial and the simulations, the jacket succeeded inself-righting.

w The righting time in the trial was 2.4 - 3.6 seconds and in the initialsimulation was 5.25 seconds. However, the righting time wasreduced to 2.5 seconds in the revised simulation. As with theinflatable lifejacket, this reduction in righting time was due to theincreased turning moment brought about by the revisions made tothe DYNAMAN

w In the trial, the manikin righted in an apparently smooth movement.However, in the initial simulation righting was by no meanscontinuous. The body was seen to stay on its side for severalseconds before righting was completed.In the revised simulation the right motion was much improved in thatit occurred in a smoother movement although a small delay stilloccurred when the body was on its side.

w The equilibrium position of the manikin in the trials wearing theinherently buoyant jacket was similar to its position when wearingthe inflatable jacket described in Section 10.1.In the initial simulation, DYNAMAN did not reach equilibrium after8 seconds. In the revised simulation, equilibrium was reached about6 seconds into the simulation. As for the inflatable jacket simulationthe body lay at about 45° to the horizontal with relaxed limbs layingalmost vertically. The relaxed final position of the limbs indicate theincreased joint flexibility in DYNAMAN compared to a manikin.

w In the trial the jacket moved around a great deal on the manikin. Inparticular, the jacket had a noticeable tendency to slip sideways andmove up towards the head. In both the initial and revised simulationthis motion was prevented.

10.3 SUMMARY

The revised simulations have given much better righting times then the initialsimulations. The results are summarised in Table 3. The inflatable jacket rights alittle faster than measured (1.6 seconds as opposed to 2 seconds) and the inherentlybuoyant jacket rights within the range of observed time (2.5 seconds in the revisedsimulation as opposed to 2.4 to 3.6 seconds measured).

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Table 3Self-Righting Times

2.5 sees1.6 secsRevised Simulation

5.25 secs3.00 secsInitial Simulation

2.4 - 3.6 secs1.9 - 2.00 secsTrial

Inherently BuoyantInflatable

Jacket

The reduction in righting time is a direct consequence of the increase in buoyancy ofthe jackets and the adjustment in density and volume of DYNAMAN.

The predicted righting modes differ between the initial and revised simulations but itwas apparent from the trials that a range of modes can occur and the one whichoccurs is very much dependent on the initial position of the lifejacket. This point isdemonstrated most clearly by the change from roll-over to sit-up mode observedwith the inflatable jacket in the initial and revised simulation.

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11. CONCLUSIONS, RECOMMENDATIONS ANDAPPLICATIONS OF THE TECHNIQUE

11.1 CONCLUSIONS

The work carried out in this project has demonstrated that the DYNAMANtechnique can be used to investigate the behaviour of humans and manikins wearingbuoyancy aide.

The effects of buoyancy and drag have been implemented in DYNAMAN for thisparticular modelling application. The validation test cases give quantitatively correctbehaviour when compared with analytical results. Good results have also beenobtained in a demonstration simulation of a lifejacket wearer in simulated waves.

A series of trials were carried out at INM with a marine manikin to obtain data onthe self righting characteristics of two lifejackets. Initial DYNAMAN simulationswere then carried out based on these trials and the results compared with the trialdata. The simulations were not specially tuned to obtain better agreement after thefirst iteration.

The initial simulations produced slower righting times than measured in the trials.Several reasons for this were identified. The most significant cause of the differentwas felt to be inaccurate volume and mass distributions in the simulation.Measurements were made at INM to obtain data for the manikin and lifejacket. Thecomputer simulations were revised to incorporate this data. Righting times in therevised simulations were then much closer to those measured.

The computer simulations showed that self righting in still water can be modelledwith the DYNAMAN technique. The results demonstrated that good correlation canbe achieved between trials and simulation provided that the distributions of weightand buoyancy are correct. A major contributor to the buoyancy is (of course) thelifejacket.

11.2 RECOMMENDATIONS

The current work programme has contributed, significantly to the understanding oflifejacket behaviour. Further benefit would be gained from extra work. In particular,further work is recommended in the following areas:

w Investigate further the mechanisms of self righting, including:

simulate people, not manikins

simulate clothed subjects

investigate behaviour in real sea conditions

simulate survival suits and suit-jacket combinations

simulate buoyancy aids which inflate in the water.

36

Some of this investigation could use DYNAMAN as it stands.Other aspects may require development of the simulation technique.

w Investigate the sensitivity of the righting behaviour to,

lifejacket attachments

person size and shape

lifejacket size and shape

other factors.

This investigation should be carried out by generating and analysingfurther DYNAMAN models.

11.3 APPLICATIONS OF THE TECHNIQUE

Ultimately the technique could have four main arm of application:

w As a research tool to understand more about the principles oflifejacket behaviour and the way that different types of designwould work. This could be particularly valuable in the case oflifejackets for very specialist applications or for looking at morecomplex systems such as lifejacket/survival suit combinations;

w The technique could help the lifejacket manufacturer to developnew products quicker and more cheaply. It could, for example,allow him to try out new designs on the computer without having togo to the expense of prototyping and physical testing until he hassome confidence in the design;

w DYNAMAN could help the lifejacket user - especially those userswith very specific performance requirements - to ensure that theychose a product which will do exactly what they want it to do;

w The technique could be used as part of an approval process either tohelp define appropriate physical tests or to allow a new design to beassessed for conditions which would not be practical to test.

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12. REFERENCES

1. “DYNA3D User's Manual (Non-Linear Dynamic Analysis of Structures inThree Dimensions)” J.O. Hallquist, D J Benson, Lawrence LivermoreNational Laboratory.

2. “Dynamic Modelling of Occupant Motion - Final Report”. FNC 731/2475RFrazer-Nash Consultancy report to HSE Railway Inspectorate.

3. “Properties of Body Segments based on Size and Weigh” American Journalof Anatomy, 1967.

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