ATC2013 Supacat JThe HMT MK2 – A CAE Led Vehicle Development Programme

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Altair Engineering 2013 1

The HMT MK2 A CAE Led Vehicle DevelopmentProgramme

Dr Jonathan FarleyPrincipal Systems Engineer, Supacat LtdThe Airfield, Dunkeswell, Honiton, Devon, EX14 [email protected]

Abstract

The High Mobility Transporter (HMT) has been developed by Supacat since 1990 and isused extensively by the UK armed forces around the world. Over 600 vehicles are currently

in operation in a wide variety of roles. The requirements for modern conflict have put anincreasing priority on troop protection from high explosives, the result of which is significantbase vehicle weight increase. In an effort to continue to provide the user with the mobilitythey require, the HMT has undergone a significant development from the chassis up. Thispaper provides an overview of some of these activities and how CAE techniques have beenapplied throughout systems development to minimise design & test, reduce weight andreduce program costs.

Keywords: Defence, HMT, MotionSolve, Optimisation, LS-DYNA

1.0 Introduction

The HMT vehicle has been developed by Supacat since 1990 to meet a specific need for alightweight, highly mobile and versatile vehicle platform which has found favour in themilitary market. The HMT was developed with automotive technology in mind, utilising anefficient space-frame chassis, balanced axle loading (mid-engine), responsive steering andvariable ride height pneumatic suspension. The HMT has become a favoured vehicle foruse by military personnel due to its unmatched mobility and jump in anddrive feel.

Used previously by Special Forces in a range of countries around the globe, the HMT wasintroduced into the British Army in 2007 to offer support for the Afghan conflict. Commonlytermed the Jackal (4x4 config) and Coyote (6x6 config) there are over 600 HMT vehicles inuse by the UK MoD (Figure 1). The vehicle has undergone a number of modifications since

its inception to meet specific requirements in the field and continues to be used in a varietyof roles. The vehicles modular chassis and load-bay gives the users a range of equipmentfit options and the ability to rapidly reconfigure the vehicle on the frontline.

The current state of warfare has created a heavy mass burden on military vehicles. IEDsremain a significant threat to vehicles in theatre, leading Supacat to develop a ballistic andblast protection system that integrates efficiently with a platform not originally designed tocounter this threat. The addition of electronic countermeasures and high poweredcommunications equipment also generate a heavy electrical and mass burden on thevehicles. The combined effect of increased mass and electrical power draw have adetrimental effect on vehicle mobility, increasing fuel consumption and reducing payloadcapacity, vehicle range and in some cases mobility. To address these challenges, Supacathave undergone an extensive vehicle development program uprating various systems


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Altair Engineering 2013 The HMT MK2 A CAE Led Vehicle Development Programme 2

through the vehicle whilst aiming to maintain the core feel of the vehicle desired by theusers.

Figure1: The Jackal and Coyote Vehicles in use by UK MoD

2.0 Applications of CAE

2.1 Suspension Upgrade

Increases in vehicle protection equipment inevitably increase the base vehicle mass whichhas the effect of eroding available payload. In an effort to provide the user with moreversatility in vehicle configuration, Supacat has developed the suspension arrangement toincrease the axle load rating by 500kg. To improve the suspension capacity, the mechanicaladvantage has been improved. This allows an increase in axle loads whilst avoidingoverload of the suspension airbag.

MotionSolve was used to develop a kinematic model of the HMT suspension corner (Figure2a). By modelling the positions of the suspension points, the kinematic model allowed theeffect of changes to the suspension geometry to be quickly assessed, calculating the loadson each component and ensure the appropriate motion ratio was achieved (Figure 2b).

Figure2 a) Kinematic mod el of HMT suspension in Motion Solve, b) Calculated

mot ion ratio for tw o suspension geometr ies


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To minimise component mass, topology optimisation was conducted on a number of parts,including the upper ball joint mount. Load vectors obtained from the kinematic model wereused to drive the topology optimisation. A maximum package space for the component wasdefined to ensure adequate clearance was maintained from any adjacent parts. Clearanceholes were included for tool access. Areas of non-design space or fixed topology weredefined to provide adequate land for bolting positions and interfacing with the suspensionassembly. A breakdown of the topology optimisation settings are outlined in Table 1.

Requirement / Setting Value

Objective Minimise weighted compliance

Constraint 5% design space volume

Symmetry Single plane, side to side

Draw Single direction, front to back

Min member thickness 20mm

Table 1 Upper Bal l Joint Moun t Topology Optim isat ion Sett ings

The final topology iteration for the upper ball joint mount is presented in Figure 3a. This

optimised shape was used as a design guide and the final component remodelled to meetthe requirements for manufacture and assembly. Finite Element Analysis was thenconducted on the final design to confirm adequate strength and durability (Figure 3b).

Figure 4 shows the final manufactured upper ball joint mount fitted for the upgraded 4.5tonsuspension arrangement. Manufactured in Austempered Ductile Iron (ADI), this componenthas a load capacity increase of +15% whilst giving a mass reduction of 50%.

Figure3 a) Topolog y optim isat ion of up per taper block, b) Linear FEA on final taper

block design


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Figure4 a) Final ised Upper Taper Bloc k in CAD, b) Taper bloc k on fi t ted to uprig ht

2.2 Chassis Upgrades

In addition to the suspension system, the vehicle chassis has undergone a significantredesign to provide improved load carrying capability and through life durability. Thisincludes developments to improve vehicle recovery, transportation and tie-down. Self-recovery has also been improved with a higher capacity winch. Detailed finite elementanalysis has been completed on the entire chassis assembly to accurately simulate theresponse of the chassis to the complex range of loadings.

Linear FEA was conducted using OptiStruct to investigate how the chassis structureresponds to the loads applied during vehicle recovery and tie-down. The chassis must bedesigned to be compliant to a number of military standards to ensure the vehicle logisticsburden remains as low as possible. STANAG 23-06 [1] & STANAG 00-03 [2] define designlimit loads required for vehicle recovery and tie-down points to ensure adequate strength.This typically equates to 1.5 x Gross Vehicle Weight (GVW) applied to each recovery point.

For external transportation by helicopter, termed underslung, a 4.3 x GVW load case mustbe applied based on an approved lifting configuration [3].

Figure 5 shows a Von-Mises stress plot of a fully laden HMT platform in level underslungconfiguration. A simple kinematic model was used to determine the load share across thefour lifting points to maintain equilibrium based on the vehicle laden centre of gravityposition. Inertia relief analysis was used to react the point loads applied to the respectivelifting points. This gives a representative spread of the reaction forces around the chassiscaused by accelerating the various lump masses to the required 4.3G load case.


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Figure 5 HMT ful l chassis s ubjected to un derslung lo ads using inert ia rel ief

The finalised chassis provides a 50% improvement in recovery and tie-down capacity,achieving full compliance to the aforementioned standards. Torsional stiffness has alsobeen increased by 20%. Due to some significant changes to the rear chassis module, thevehicle towing fatigue life has been doubled. Through the use of CAE tools, theseimprovements to the chassis were achieved with a minimal mass increase of less than 13%.

2.3 Non-linear analysis of ROPS system

One further area of development has been in the vehicle Roll-Over Protection System

(ROPS). The HMT vehicle has been designed to the requirements specified in ISO8082 [3].The standard defines the impact energy required to be dissipated by the ROPS structure.The energy must be dissipated without any portion of the vehicle structure impinging on apredetermined Displacement Limiting Volume (DLV), which represents the survivabilityspace of a vehicle occupant.

The impact energy and loading direction are based on the vehicle geometry and GVW. Fora side roll off the HMT, this equates to impact of a rigid ground plan at approximately10degs to vertical with energy of 75kJ. The ROPS simulation was conducted in LS-Dynausing a fill chassis model with trimmed masses. Non-linear material curves were appliedbased on minimum material grades.

Figure 6 shows the effective plastic strain plots at three time steps during the side impactevent. The rigid ground plane can be seen to contact the upper ROPS, permanentlydeforming the upper tubes whilst maintaining clearance from the DLVs of the rear seatedcrew members.


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Figu re 6: Effective Plastic Strain in HMT Rear ROPS at a) 0ms, b)30ms & c ) 70ms

Figure 7 shows plots of the indenter displacement and velocity against simulation time.The indenter initial velocity has been derived from the kinetic energy requirement for a givenindenter mass (2.2ton). The plot of impact velocity indicates the full energy requirement hasbeen absorbed at approximately 70ms, this corresponds to the displacement of 358mm ofthe ROPS structure. The deformation fringe plots (Figure 6) confirm no impingement of thechassis structure into the DLVs demonstrating the ROPS structure meets the design

requirements. The use of simulation techniques such as this significantly reduce designtime allowing a range of different design solutions to be assessed rapidly without therequirement for significant and costly testing.

Figure7: Plots of a) indenter displacement and b ) indenter veloci ty versus time

3.0 Conclusions

This paper provides a brief overview of some areas of development that have beenundertaken by Supacat in the development of the MKII HMT vehicle. Supacat employ arange of simulation techniques from structural optimisation to non-linear impact analysisthroughout the design process. Advanced simulation techniques have enabled rapid designassessment prior to physical test programs, reducing the overall program developmenttimes and subsequently cost.

4.0 References

[1] DEFSTAN 00-23, Iss4, Technical Guidance for Military Logistic Vehicles, MoD, Nov2005

[2] DEFSTAN 00-03, Iss3, Design Guide for Transportability of Equipment, MoD, May1985

[3] Airportability Information and Design Guide, Iss6, JADTEU, Aug 2011[4] ISO8082-1, Libratory Tests and Performance Requirements for ROPS, BSI, 2009

Documents

ATC2013 Supacat JThe HMT MK2 – A CAE Led Vehicle Development Programme