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With the amount of adjustability present in today's automotive seat, it is a given that some form of looseness and free-play will exist in the structure. The automotive seat community is commonly faced with free-play issues; this is a significant issue where modal analysis is concerned. Free-play creates a non-linear situation, causing a violation of the linear mathematics that modal analysis is based on. Obviously, this situation is not the ideal circumstances under which to perform modal testing and analysis, but 99.9% of the time, the receipt of better samples (reduced free-play) is not a likely option, and the test must still go on. Ideally, you would want to test this structure using random excitation with a shaker to minimize the nonlinearities and provide a repeatable input force.

This paper contributes to the Committee on Commonized Aerodynamics Automotive Testing Standards (CAATS) initiative, established by the late Gary Elfstrom. It is collaboratively compiled by automotive wind tunnel users and operators within the Subsonic Aerodynamic Testing Association (SATA). Its specific focus lies in automotive wind tunnel test techniques, encompassing both those relevant to passenger car and race car development. It is part of the comprehensive CAATS series, which addresses not only test techniques but also wind tunnel calibration, uncertainty analysis, and wind tunnel correction methods. The core objective of this paper is to furnish comprehensive guidelines for wind tunnel testing and associated techniques. It begins by elucidating the initial wind tunnel setup and vehicle arrangement within it.

Many structures of practical interest exhibit a significant degree of nonlinearity. In such cases, the modal frequencies, damping, and amplitudes will change depending upon the excitation force level, response level and spectrum shape. When reporting the measured modal parameters from an artificial excitation test, the excitation conditions and response levels should be specified, and different modal models may be needed to represent the structural dynamics at different response amplitude levels. If the frequency responses are measured by moving accelerometers in multiple test runs, then it is important to maintain a consistent response level for all test runs. This paper describes a method to eliminate the variability of the response level between data sets by means of closed-loop control of the RMS level. The amplitude control program uses a nonlinear gain estimation technique to set the gain on a “proportional-integral” controller.

As a result of the severity of occupant injuries during a side impact collision, there has been an escalating demand for accurate component level side impact simulation. Three major components for accurate simulation are accurate door velocity, door to seat relative velocity, and door deformation. This paper shows data demonstrating accurate door velocity reproduction, presents test methods to passively and actively control relative seat to door velocity in a non destructive manner, and presents test methods to simulate real time door deformation in a destructive manner. All side impact waveforms include a negative acceleration, high positive accelerations, high jerk, and high frequency content that add to the complexity of this simulation. The simulated door velocity is produced by means of a MTS deceleration brake that only applies a braking force during the deceleration portion of the waveform to maximize acceleration capacity.

The automotive vehicle design process has relied for many years on both analytical studies and physical testing. Testing remains to be required due to the inherent complexities of structures and systems and the simplifications made in analytical studies. Simulation test methods, i.e. tests that load components with forces derived from actual operating conditions, have become the accepted standard. Advanced simulation tools like iterative deconvolution methods have been developed to address this need. Analytical techniques, such as multi body simulation have advanced to the degree that it is practical to investigate the dynamic behavior of components and even full vehicles under the influence of operational loads. However, the approach of testing and analysis are quite unique and no seamless bridge between the two exists. This paper demonstrates an integrated approach to combine testing and analysis together in the form of virtual testing.