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Seating and ride comfort for a driver during a test drive are the vital factors when making the decision for a new vehicle. Typically, big test series with test drivers are carried out for static and dynamic seat comfort in the lab and for riding comfort on specified road profiles considering all relevant scenarios. The amount of subjectivity involved in the evaluation of the comfort reduces the reliability of such studies to serve as a basis for design. Numerical simulations represent a cost-effective, yet highly reliable method to evaluate the seating and the ride comfort. There exist several approaches using FEA (finite element analysis) for seating comfort and MBS (multi body system) analysis for riding comfort. Although both parts influence each other there exist no real interfaces between the different types of analysis. This paper presents a numerical approach to the analysis of the impact of vibrations on the human body arising from real excitations of the whole vehicle.

Predicting the vibration comfort is a difficult challenge in seat design. There is a broad range of requirements as the load cases strongly vary, representing different excitation levels, e.g. cobblestones or California roads. Another demand is the driver expectation, which is different for a pickup and a sports car. There are several approaches for assessing the vibrations of occupants while driving. One approach is the evaluation of comfort by integral quantities like the SEAT value, taking into account a weighting based on the human body sensitivity. Another approach is the dimension of perception developed by BMW, which is similar to psychoacoustics as the frequency range is separated with respect to occurring vibration phenomena. The seat transmissibility is in the focus of all activities. In the frequency range it defines the relation between the input at the seat slides and the output at the interface of human body and trim.

The objective evaluation of occupant comfort is a complex task where numerous aspects such as posture, pressure distribution, internal tissue loads, handling of steering wheel or gear shift have to be taken into consideration. Currently the standard evaluation procedures are hardware tests with human subjects, who are sensitive to all these aspects. However, the reproducibility of subjective tests for the comparison of design variants is a questionable issue and the costs for each test cycle with new prototypes are very high. As an alternative, numerical approaches using human body models such as AnyBody [1], CASIMIR [2] or RAMSIS [3] are applied. Here the issue of reproducibility does not exist and only little effort is required to investigate new setups. However, the disadvantage is that each approach focuses only on one specific aspect of occupant comfort, while in reality the emotions of the occupant are always a combination of all impressions.

The software CASIMIR/Automotive represents a virtual process chain for the development of seats. Integrated in standard software tools it enables the user to investigate a great variety of possible seat optimisations with marginal effort. Within this paper the steps starting with the setup of the finite-element-model of the metallic seat structure through to the complete occupant-seat model are shown. Finally exemplary results of a typical application are presented to demonstrate the software's capabilities.

For the evaluation of seats under comfort and health aspects by means of a Finite-Element (FE) simulation a detailed static and dynamic occupant model is required. The occupant model CASIMIR, which is presented here, in combination with seat model was used in different comfort simulation projects where a good correlation to measurements - seat pressure distribution and transfer function - was found. In order to increase the accuracy of results for internal quantities e.g. the load on the intervertebral disks, CASIMIR was enhanced to improve the force transmission from the seat to the human body. Due to the consideration of the different tissues by corresponding material parameters and the modelling of the filamentary force transmission via springs and dampers for muscles, the human anatomy is modelled more realistically.

To perform virtual development phase simulations in the field of seating comfort, an occupant model is needed which reflects the static and dynamic properties of humans. In this paper, the application of the dynamic finite-element-occupant-model CASIMIR to the development of an automotive seat is described. For static seating comfort simulations, CASIMIR is used with a finite-element representation of the seat. Results of such simulations are the static pressure distributions and measures like “meat-to-metal”, or the real position of the occupant inside the vehicle considering compliances of seat, seat cushion, and human body. Dynamic seating comfort is closely related to the seat transfer function, which can be simulated with CASIMIR. Knowledge about seat transfer functions enable the developers of cars and/or seats to adopt dynamic characteristics of the seat to the special NVH-requirements of a specific vehicle and to avoid matching of resonances of seat and vehicle body.