os 01 optimisation of effective-tatatechnologies

8/9/2019 OS 01 Optimisation of Effective-TATATechnologies

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Simulate to Innovate 1

Optimization An Effective Tool In Bonnet Design Cycle

Kiran KausadikarTeam Leader, CAE

TATA Technologies ltdBlue Ridge, SEZ Building IT-

3, 6th FloorHinjewadi, Pune-411057

Pankaj BhirudProject Manager, CAETATA Technologies ltd

Blue Ridge, SEZ Building IT-3,6th Floor

Hinjewadi, Pune-411057

Ajay Virmalwar,Project Manager, CAETATA Technologies ltd

Blue Ridge, SEZ Building IT-3,

6th FloorHinjewadi, Pune-411057

Chetan KhadsareTeam Leader, CAE

TATA Technologies ltdBlue Ridge, SEZ Building IT-3,

6th FloorHinjewadi, Pune-411057

Keywords: Topology optimization, Pedestrian safety, Anti-flutter Adhesive, HIC.

AbstractIn a global automotive world product development is an important phase which provides competitive edge over others. Todayoptimization methods are extensively used in product development as a tool for optimizing design solutions throughout theproduct development phase. Bonnet in passenger vehicles provides access to engine compartment. Bonnet design is nowheavily influenced by pedestrian safety requirements. At the same time durability must be maintained. Pedestrian safetystiffness needs differ from durability needs. Meeting both of these requirements from conceptual design to final design duringdevelopment phases is challenging task. Optimization can be used as effective method to find out feasible design solutions insuch cases. This paper demonstrates importance of optimization during initial and final design phase for bonnet design. Thispaper highlights optimization work done on bonnet to meet severe load case targets as part of durability requirement at initial

and final design phase considering pedestrian design needs. Topology optimization of bonnet inner panel at initial conceptualphase and topology optimization of anti-flutter adhesive at final design phase to meet bonnet durability requirements usingOptiStruct is presented.

Introduction:

Bonnet of a passenger car provides access to engine compartment. The major components of

bonnet sub system include outer panel, inner panel, hinge assembly, hinge reinforcements, latch

assembly, latch reinforcements etc. Design of bonnet sub system is carried for satisfying pedestrian

safety and durability performance tests. These two requirements tests are performed simultaneously

during bonnet design cycle.


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Simulate to Innovate

Bonnet system design:

In passenger cars Bonnet subDepending upon its mounting frontrespectively. Design of bonnet ouoverall stiffness depending upon isuch as hinges, latches and bumpneumatic or hydraulic lift cylinderopen or close the bonnet. Positiotorsional and bending strength ofBonnet outer panel is attached to iadhesive and also anti-flutter glue iof bonnet can be designed in matype, grid type etc. Multicone stru

structure has week and hard pointwhich gives necessary global and l

Fig.1 Out

Pedestrian Safety requiremen

Pedestrian safety norms in manyfatalities due to pedestrian impactdesigns which concentrate on ped

system provides access to engine compartside or rear side (near wind screen) it can opeer panel is influenced by vehicle front stylings designs such as Wraparound or Inlaid type.p stops are used to mount bonnet to the vehiattached to bonnet on one side and vehicle boof bump stops, lift cylinder attachment points

onnet. Generally there will be reinforcements anner panel at the periphery by hemming operatis placed between inner and outer at different locny such as beam type, cutout type, multiconeture type design provides uniform stiffness wh

s. Optimization may be used to design such bea ocal stiffness with reduced mass.

r panel designs (Inlaid / wraparound type)

Fig.2 various inner panel designs

ts:

countries are gaining importance because of hobserved in many studies. Hence safety is impostrian and occupant safety.

2

ment underneath.from rear or front

nd also it adds tother components

icle. There will bey on other side toalso influence thehinges and latch.

on using structuralations. Inner paneltructure, skeletonreas beam-cutout

m-cutout structure

igh percentage ofrtant criteria in car


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Fig.3 Crash Fatalities

The overall vehicle star rating includes adult protection, child protection, pedestrian protection andsafety assists. Pedestrian protection weigh to overall star rating has been increased recently inEuroNCAP 2012.

Mostly vehicle has to meet set targets for below major pedestrian safety tests and based on the levelof compliment to these targets score points are awarded.-Lower Legform test on bumper area (max 6 score points)-Upper Legform test on bumper area (max 6 score points)-Child/ Small adult Head form test (max 12 score points)-Adult Head form test (max 12 score points)Percentage pedestrian score is calculated based on overall points scored in these tests. Pedestriansafety considers mainly two types of injuries. One is head injuries and other leg injuries. Abovementioned test covers these types of injuries.Out of total pedestrian fatalities 60 % are contributed to death due to head injury. Hence it is importantto design bonnet sub-system to meet Head injury criteria (HIC). Head injury criteria is calculated asbelow,

Time duration considered for calculating HIC is 15 ms. this criterion corresponds to maximum value offloating average of head impactor center deceleration. Major factors influencing the HIC are activemass, stiffness, clearance to components under bonnet, interaction between contacting parts, impactlocation (center, edge). One of the main reasons behind high HIC value in the event of collision is highstiffness of bonnet sub system. Stiffness of bonnet sub system depends on design of inner panel,outer panel, reinforcements and gluing. Stiffness of inner and outer panel can be optimized to meetHIC criteria by controlling fallowing factors.


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Durability performance requirements:

Some year ago, when pedestrian safety norms were not necessary in vehicle development, thebonnet is designed has just to meet only Standard durability performance tests. The target for each ofthe below load cases is specified by manufacturer based upon vehicle program requirements.- Bonnet Torsion load case- Bonnet Bending load case- Bonnet corner stiffness load case- Bonnet oil canning load caseEach of above requirement ensures the response of bonnet subsystem within specified targets tovarious kinds of loads experienced during its usage. Out of above loads torsion and bending loadsmajorly determines overall structural stiffness of bonnet sub system. Here we have illustrated some ofthe simulations which are used further in optimization work.

Bonnet Torsion load case: This simulation determines torsional rigidity of bonnet subsystem. Such

kind of simulation is carried generally in two ways on vehicle (onbody) in fully open condition and onbench condition wherein bonnet is mounted in horizontal position and is held fixed at pivot hinges.One of bump stop location is constrained in z direction and at other bump stop point verticallydownward load is applied.

Bonnet Bending load case: This simulation determines bending rigidity of bonnet subsystem. Itensures robustness of bonnet under its own weight. It prevents bonnet from sagging or bending whenin the open position& when customer pulls/ pushes bonnet edge down to close. Bonnet is mounted inhorizontal position and is held fixed hinges. Lift cylinder attachment points on both the side RH andLH are constrained in Z direction. One of bump stop location is constrained in z direction and at otherend point load is applied.

Bonnet Corner stiffness load case:This requirement evaluates bonnet front corner stiffness when it issupported rigidly at hinges, latch & bumpstops for flutter avoidance. Uniformly distributed load isapplied at one of the corner on inner panel in vertically upward direction.

Bonnet Design cycle:The conceptual geometry release is used asa starting point for bonnet design. Pedestrian anddurability tests are performed on this geometry at initial phase. An optimization work (topology) isperformed on inner panel considering major durability requirements. Output from this work (innerpanel cut-out pattern) is used while designing bonnet inner from pedestrian point of view. Later indevelopment phase pedestrian test iterations are performed first and same design changes areverified for durability tests. In the final phase there is limited scope to modify the inner panel (material,geometry, and gauge) as the matured design has already passed the pedestrian requirements.Topology optimization is performed on anti-flutter to meet the durability test without affecting thepedestrian results.


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Topology Optimization of Inn

At initial design phase it was obdurability target with current innerwas performed to get optimized cfull bonnet assembly is considereconsidering under bonnet space. Ilatches as per required loadcasemajor durability load cases as belo

Fig.5 Conceptual Inner panel struc

Fig.4 Bonnet design cycle

r Panel:

served that the conceptual bonnet design wapanel cut-out pattern. Hence topology optimizat-out pattern. Only Inner panel as an individualfor analysis. Conceptual cut-out pattern is fill-i

Inner panel is restrained at hinge bolt mountingequirement as shown in fig.6.Optimization probl

.

ure Fig.6 Topology optimiz

Desi n

Fixed

Bum sto

5

not meeting theion of inner panelcomponent out ofn with material by, bump stops andlems are setup for

tion model set up

Torsion load

Fixed


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Fig.7Topolog

Fig.8 Con

Optimisation problem definitions

Objective Mi

Constraints

Design Va riable Inner

Torsion Loadcase

optimization thickness contour plots

ceptual to Final design Inner panel pattern

Torsion Loadcase Bending Loadcase

n. of static displacement Min. of Total static compliance


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Inner Panel Topology optimization results and discussion:

From Topology optimization results, it is observed that to improve inner panel stiffness for all majordurability load cases the cut-outs can be made in more or less same regions and also it is showingthe areas where material is needed. These results provided important information about the criticalareas from durability point of view and considered during development phase wherein an iterativeapproach between pedestrian and durability resulted in to a design as shown in fig.8which meets allpedestrian targets and is close to meet durability targets as well.

Topology optimization of Anti-flutters:The function of an anti-flutter adhesive, as the name implies, is to reduce or eliminate any flutteringor vibration of the outer, inner panels and reinforcements relative to each other. The anti-flutteradhesive used has a low modulus and lower strength but its placement provide important support totransfer compressive loads from outer panel to inner panel or reinforcements. We have seen fromprevious section that results from topology optimization of inner panel was used to create a final

design model which was complying with pedestrian requirements but still some work has to be doneon bonnet design to meet close durability targets. In the final design phase, there was very limitedscope for the modification bonnet design for durability load cases since the pedestrian criteria arealready complied. Any major changes are not allowed in the design once it is made safe forpedestrian targets.In such scenario, the anti-flutter topology optimization provided effective way for complying durabilitytargets without changing material, gauge or any kind profile modification.

Fig.9Anti-flutters Topology optimization model set up and results

The process starts with modeling of continues lines of anti-flutter solid elements as a topology designvariable. The modeling of anti-flutter in the area is avoided where they cannot be poured due tomanufacturing constraints. This will make sure the topology results are shown at desired location.The optimization is carried out for given different load cases together. The optimal deign constraints(e.g. displacement, Stresses etc.) are set to obtain the feasible solution. The topology response canbe either displacement or total mass minimization.This method is quite effective for most of durability load cases but quite sensitive for bonnet torsionload case without deteriorating the pedestrian results. As shown in fig.9 the topology results highlightsthe critical locations of anti-flutter which plays important role in set of durability load cases. Referringthe maximum material locations the anti-flutter lengths are re arranged for further analysis.


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Conclusions:

From this bonnet development project it is evident that optimization can be used in aneffective way at initial as well as final design phase for meeting conflicting pedestrian and durabilityrequirement in effective way.

Future Scope:

The major learning from the project is developing an efficient and robust product developmentapproach, which enables savings in time and effort. In future MDO (Multidisciplinary optimization)methodology can be used to combine the pedestrian test and durability test requirements for creatingfinal design eliminating the iterations needed during development phase.

ACKNOWLEDGEMENTS

The author would like to thank the following for their valuable inputs

1. Chris Paul, Closures Team Leader, JLR, UK2. Lee Warriner, Closures Team Leader, JLR, UK3. Peter Wakelin, Group Manager Body CAE, JLR UK4. David Coleman, Senior Manager Body CAE & Integration CORE, JLR, UK.

The authors are extremely grateful to the Closures Durability group at Tata Technologies Ltd. Andentire HyperWorks team for their support.

REFERENCES

[1] Altair Engineering Inc., "Introduction To Topology &Topography.

[2] Altair Engineering Inc., "Help for HWSolvers ".

[3] Ramesh C. K, Dr. Srikari S., Suman M. L. J, Design of Hood Stiffener of a Sedan Car for Pedestrian Safety, SASTECHJournal,Volume 11, Issue 2, Sep 2012.

[4] ChristophKerkeling, Joachim Schfer, Dr. Grace-Mary Thompson, Structural HoodandHinge concepts for pedestrianprotection.

[5] F. MERCIER, M. GUILLON, S MAILLOT, Deployment of optimization studies using Alternova: design of a hood innerpanel for pedestrian safety performance.

[6] RevathiKrishnamoorthy, A thesis on Optimisation of Hood Panels of a Passenger Car for Pedestrian Protection.

[7] http://www.a2mac1.com

[8] http://www.adhesives.org/

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