analysis of the cover latch mechanism using msc...

MSC.Software VPD Conference | July 17-19, 2006 | Huntington Beach, California

Analysis of the Cover Latch Mechanism Using MSC Adams®

Devinder S. Sachdeva & Jerry Browne

General Dynamics Armament and Technical Products

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AbstractAnalysis of the Cover Latch Mechanism Using MSC AdamsPresentation Number 2006-59

Devinder S. Sachdeva & Jerry BrowneGeneral Dynamics Armament and Technical Products128 Lakeside Avenue, Burlington, Vermont, 05401-4985Phone: 802-657-6916, Fax: 802-657-6799, email: [email protected]

This paper describes the process and results of the modeling and analysis of an equipment cover latching system using Adams along with lessons learnt. The cover involved is over thirty feet long and consists of two panels, each about 5-6 ft high and wide. At the top, the cover halves are hinged to large frame like structure using ten hinges each. When closed, they latch to each other at the bottom using 21 latches. Due to their large size and weight, the covers have varying amounts of deformation at the bottom where they are latched. Further, the hinges are not exactly collinear due to support structure deformations. As a result, this was not a simple mechanism analysis problem and required several creative ideas to tackle various modeling and simulation issues.

The cover halves had to be modeled as flexible bodies to capture both, the deflections due to their weight as well as those due to the hinge-line deformations. The analysis task involved (1) assessing the effect of the deformed hinge-line on the ability of the cover halves to open/close through 100 degrees of rotation and (2) assessing the ability of the misaligned latches to successfully proceed through the latching process. These latches had to be modeled using contacts so their ability to align themselves as well as the forces involved could be calculated and assessed.

The model was created from CAD geometry data in I-DEAS and exported to Adams as a rigid body model and to FEA for the creation of modal neutral files (MNF) of the cover panels which were then imported into Adams for flex-body incorporation. The flex-body swap as well as coarsening worked quite smoothly in Adams v2005. The very large model size due to 673 moving parts, 22 cylindrical joints, 195 revolute joints, 563 fixed joints, 4 translational joints, 4 motions, 42 pair of contacts and two large flexible bodies each consisting of over 15k elements, made the analyses quite challenging and took several innovative and creative techniques to overcome. Tools, process, results, problems faced and lessons learnt are presented.

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Agenda

• Introduction - Objective• Methodology• Modeling details• Results/Conclusions• Lessons Learned – MSC Adams User ROI

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Introduction

• Objective• Determine the effect of door flexibility & hinge deformations on

door operability, latching/unlatching and attachment loads in the door panels

• Background• Large (>20’ long) flexible doors are hinged to a support

structure which has some load induced deflections resulting in misaligned hinges

• Doors have latches that need to be opened/closed for servicing equipment

• Use analytical approach to avoid need for physical prototype to assess viability of design as well as loads at attachments points (hinges, latches, etc)

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Methodology

IDEAS Model•Setup configuration

•Dummy parts

•Assembly

MSC AdamsFlex-Body Model•Hinge deformations

•Run simulations

•Post-process

MSC AdamsRigid-body Model

•Connections

•Contacts, constraints

•Debugging

FEA•Door FEM

•MNF files

IDEAS Mechanism

•Rigid bodies

•Markers

•Export to Adams

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Modeling Details – MSC Adams Rigid-body Model

MSC AdamsModel:• 600+ parts• Mass• Moment of Inertia

Joints:• Fixed• Revolute• Cylindrical• Translational

Motions:• Actuators• Latch Hooks

Right Door Left Door

Right Fwd Actuator Left Fwd Actuator

Right Aft Actuator Left Aft Actuator

Right Fwd Bulkhead Left Fwd Bulkhead

Right Aft Bulkhead Left Aft Bulkhead

Latches (21)

Support

Right Hinges (10) Left Hinges (10)

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Modeling Details – MSC Adams Rigid-body Model

Key modeling tasks:• Ensuring proper connectivity between parts

• Set up connections between doors and other components using dummy bodies for flex-body swap

• Set up actuator motions with proper timing in relation to latch opening & closing

• Developing and debugging simulations• Door opening/closing simulation• Latch sequential opening/closing simulations• Set up simulations & run rigid-body analyses to ensure intent• Modify latch model to improve efficiency of simulations

• Hook Motion generated and applied to full model• Deleted unneeded parts & latch handle forces

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Modeling Details - Hinge-Line Deformations

• Three rigid plates fixed together can’t turn about three non-collinear hinges

• Simulation fails when rotation is applied

• When plates are connected to each other using springs instead of the fixed joints, the plates can rotate

• Experimentation with this simple model helped get confidence in the concept

• Hinge-line deformations are possible with flex-body door panels because they behave like several little bodies connected together with compliance between them, so each little body can turn about its own axis

(Click to animate)

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Door flex-body mesh coarsened to improve analysis efficiency

Modeling Details – MSC Adams Flex-Body Model

Implementing Hinge-Line Deformations

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Results - Animations

•Hinge-Line Deformation

•Open/Close

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Results - Animation - Sequential Latching

Close up of the middle three latches during the closing simulation

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Results – Load Plots

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• Doors will open and close even in the presence of the hinge-line deformations

• Sequential latching and unlatching works in the model as intended• Loads in the door nodes seem to be reasonable except for the fore

aft loads due to the hinge-line deformation and the fact that the bulkheads and actuators are rigid in the model while in real life they will have some flexibility

Results: Conclusions

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Lessons Learned – MSC Adams User ROI

• Crawl, walk, run approach can help successfully model complex systems

• Initially model was too large to simulate due to memory and time needed; so latch-hook motions replaced latch components in the door assembly simulations to reduce the time and memory requirements

• Rigid door to flex-body swap went quite smoothly in A/Flex v2005 – proper planning is key when you have a large # of connections (45/door)

• Flex-body coarsening was essential – also went smoothly –MNF size reduced by 70%

analysis of the cover latch mechanism using msc...

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