Modern vehicles are increasingly becoming mobile retreats. With the progress of automation, usage scenarios are shifting: reading, watching films, or sleeping during driving are becoming realistic everyday situations. Especially in Asian markets, concepts such as “Zero Gravity Seating” are becoming established. This development poses new challenges for vehicle design, since conventional tests in an upright position are no longer sufficient to realistically assess comfort and physical load.
Objective: Realistic Model Validation for Dynamic Seating Comfort
A recent measurement campaign conducted by Wölfel Engineering in cooperation with NHK Spring Company investigates how relaxed postures influence the vibrational behaviour of the human body. The aim is to use the measurement data to validate anatomical human models under realistic conditions – as a basis for reliable analyses of comfort and load in the vehicles of the future.
Key Parameters: Seat Transfer Function and Apparent Mass
Seat Transfer Function
This parameter describes how strongly vibrations are transmitted from the seat structure to the seating surface. Ideally, resonance amplifications remain low while high frequencies are effectively isolated. However, the evaluation requires complex trade-offs between material selection and vibration behaviour.
Apparent Mass
The apparent mass describes the force-acceleration relationship at the interface between the human body and the seat. Due to the compliant properties of human tissue, the response is frequency-dependent – unlike that of rigid test bodies. This measurement quantity is particularly suitable for validating simulation models such as CASIMIR/Automotive.
Three Realistic Seating Postures Under Test
To obtain practice-oriented results, three typical seating postures in a passenger car were examined:
- UP (Upright): Conventional upright driving position
- RX1 (Relax-1): Slightly reclined, e.g. during media consumption
- RX2 (Relax-2): Strongly reclined, comparable to a sleeping posture
The focus was on the 50th percentile of body height distribution, supplemented by individual measurements of additional percentiles.
Results: What Happens to the Vibrational Behaviour?
The measurements clearly show that the vibrational behaviour changes significantly with increasing backrest inclination. Especially between 4 and 8 Hz, double peaks occur – an indication of several vibration modes being excited simultaneously. These effects had already been predicted by the human model CASIMIR/Automotive and have now been confirmed experimentally.
Observed reactions such as hip rotations correspond well with the model predictions and underline the suitability of the models for realistic forecasts.
Technical Particularity: Choice of the Coordinate System
In strongly reclined seating positions, the choice between a global and a local coordinate system significantly influences the interpretation of the results. In certain directions (X/Z), a local evaluation can be more meaningful, even though global systems offer better comparability.
Conclusion: Models for the Mobility of Tomorrow
The study demonstrates that conventional measurement data are no longer sufficient to assess new seating concepts. The combination of realistic postures, robust measurement data and validated models provides a forward-looking approach to evaluating comfort and health in vehicles.
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With CASIMIR/Automotive, you simulate the dynamic vibrational behaviour of the human body and assess seating comfort already during virtual development.
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