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Multi-Objective Optimization of Vehicle Handling & Comfort Performances with modeFRONTIER and MSC.ADAMS Car

In questo articolo si mostra come la versione customizzata per FIAT di MSC.ADAMS Car, denominata MB-SHARC, è stata utilizzata per ottenere i principali parametri che sintetizzano il confort ed il comportamento su strada di una vettura, mentre modeFRONTIER, un ambiente software per l’ottimizzazione multi-obiettivo nei processi progettuali, ha permesso di ottimizzare detti parametri.Grazie all’utilizzo integrato di MB-SHARC e modeFRONTIER, è stato possibile definire la correlazione tra i parametri in ingresso, che descrivono le caratteristiche delle sospensioni dell’automobile, e le performance della stessa. Il processo di ottimizzazione ha portato a definire le soluzioni di trade-off, ovvero quelle configurazioni che garantiscono di ottenere un ottimo comportamento su strada della vettura, senza sacrificare il confort che la stessa può offrire agli occupanti. L’utilizzo di modeFRONTIER, ha permesso inoltre di verificare la robustezza delle soluzioni ottenute. La metodologia progettuale messa a punto in questo lavoro, potrà essere riutilizzata nella progettazione di qualsiasi altro veicolo, riducendo il tempo ed i costi tradizionalmente necessari per la loro messa a punto.

This article illustrates an application example in the field of Vehicle Dynamics. The study focuses on the simulation of the Handling and Comfort performance of the vehicle with the objective to optimize both aspects. The simulations are performed in the Multibody environment MSC.ADAMS/Car or more precisely, the customized version Fiat MB-SHARC. Automatic post-processing in MB-SHARC enables designers and engineers to monitor key parameters representing Handling and Ride-Comfort performances, taking into account both the stability as well as more subjective-related parameters to define a set of optimum solutions. The application presented here deals with the optimization of suspension mount characteristics. The process involved an initial DOE (Design of Experiments method) that allowed to select influent input variables and representative objectives and constraints. The consequent MOGA Optimization lead to a Pareto FRONTIER containing optimum solutions from various and conflicting aspects. Improvements in the overall Handling and Comfort performances, and most importantly, an understanding of the correlation between all input variables and vehicle’s performances could be achieved.

Multi-objective Optimization Handling & Comfort
The trade-off between Ride-Comfort and Handling targets represents a challenging task in a vehicle development project. Depending on brand and vehicle type (commercial-, passenger- or sports car), priorities between conflicting objectives vary, hence the weighting of single performances has to be evaluated differently for every single project.

modefrontier and msc adams

Multibody Models: Rear Suspension and Full-Vehicle Handling Model - assembling Front Suspension, Steering system, Anti-roll-bar, Driveline, Engine, Rear Suspension, Body and Front & Rear Tires


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Application
The aim of this work was to optimize conflicting aspects with regard to Ride&Comfort performances and Handling performances of a light commercial vehicle. Besides performances, the robustness of the solution was an important factor when choosing the optimized set-up.

modefrontier and msc adams

Input variables: Rear suspension longitudinal arm attachment orientation and characteristics


Simulation Models and Calculation Environments
To simulate the Comfort and Handling performance, two Full-Vehicle models were used, for Comfort and Handling respectively. Prior to this and to verify constraints related to, for example vehicle height from ground, two suspension models were used – a Front and Rear Suspension model.

All models were assembled in the Multibody environment of MSC.ADAMS/Car, and the customized version Fiat MB-SHARC which enable the designer to perform special maneuvers as well as a complete post-processing and calculation of synthesis parameters of interest.

The extremely short calculation time in the Multibody environment allows to include an important number of designs covering several input variables and their full range of interest.

Input Variables, Study Constraints and Objectives
The chosen input variables must provide significant parameters for both, the Handling and Comfort performances. Typically, they can be synthesized in the front and rear suspension spring, bump stop and damper characteristics. In the application presented here though, an especially influent suspension mount was monitored.

Input variables:

  • Rear suspension bushing pt1 – stiffnesses and orientations

Constraints concerned mount feasible characteristics and working points during maneuvers.
The objectives included significant Comfort and Handling synthesis parameters, such as yaw velocity, sideslip angle gain, peak accelerations and time dissipation in seat rail during comfort missions.

modefrontier and msc adams

Objective Scatter Charts: The left illustrates the tendency of a Handling objective modifying the ratio between the radial and axial stiffness of the bushing. On the right, an example of two conflicting objectives.


modefrontier and msc adams

Influence Scatter Charts: The left illustrates the influence of the orientation of the bushing in the X-Y plane. The right, an elasto-cinematic parameter monitored as a function of the same input variable.


Objectives:

  • 2 Handling
  • 2 Comfort

Besides these objectives, a long list of other K&C, Handling and Comfort parameters of interest was monitored.

Application Results
An initial DOE allowed to validate the important influence of each input variable and to check the significance of the constraints thus ensuring objectives are met.
A Sobol DOE Study was executed and, on the basis of approximately 1000 designs, a MOGA-II optimization was performed.

Given the conflicting objectives, the optimization obviously did not lead to an optimum set-up, but to a pareto FRONTIER containing several set-ups. The reverse tendency of some parameters was confirmed. However, compared to the initial, already manually optimized set-up, some significant improvements could be achieved.

The optimization provided clear indications for the optimum values of the input variables, especially with respect to the orientation of the bushing and the ratio between its axial and radial stiffness.

After the most promising configurations were selected to weight the four objectives, and besides analyzing the synthesis parameters, the improvements were evaluated thus launching all maneuvers of interest and analyzing the time-histories and graphs of every single maneuver. Usually, this verifying stage includes more maneuvers to guarantee the solutions on a broader prospective.
The real graphs confirmed significant improvements of most of the parameters.

Robust Design Study
The study concerning the robustness of the solution was performed accordingly with the optimization. The study consisted in analyzing a set of representative pareto FRONTIER configurations to focus on the STDEV of the main parameters of interest.

Taking into consideration the production tolerances of the rear suspension, the robust design study showed that some of the optimum solutions not only improved the performance but also the robustness of the solution.
Adding the robust design of the solution to the primary objectives, allowed to choose a set-up which not only improved performances but also provided a more robust suspension set-up.

modefrontier and msc adams

Optimum set-ups: On the far left, the parallel coordinates graph illustrating some of the pareto FRONTIER solutions, in the middle and on the right, two examples of improvements obtained in a Comfort and Handling maneuver


Conclusions
The activity involved 3 different models in MSC.ADAMS Car for a unique optimization.
The customized version of ADAMS Car MB-SHARC was used to obtain principal Handling and Comfort synthesis parameters.
The study allowed to gain a deep understanding of the influences from input variables and the correlation between all input data and performances. The optimization allowed to improve both aspects, Handling and Comfort, and enabled to choose a “best compromise” solution. The application presented here involved only a few input variables. However, and for a complete study, the optimization could be performed including also other parameters of interest.

The use of modeFRONTIER, a multi-objective optimization and design environment software, allowed to save time and hence to focus on and to analyze the results thus reducing the efforts spent normally on daily continuous modifications of the models and multiple analysis. The short calculation time in the Multibody environment allowed to perform the optimization in only a few days time.

The study involving the robustness of the set-up solution, enabled designers and engineers to improve the dispersion of vehicle performance in production due to production tolerances of the suspension.

The procedure created can be applied to any other vehicle, reducing vehicle testing and experimental tuning - time and costs, and will help to approach an optimum solution, already from the start.


 

Articolo pubblicato sulla Newsletter EnginSoft Anno 5 n°4

 

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