Nonlinear Dynamics of Seat-Occupant Systems with Nonlinear Viscoelastic Models of Flexible Polyurethane Foam

座椅乘员的静态和动态（乘坐）舒适性至关重要。 大多数座椅设计仍然是根据经验和试验和错误的原型。 基于简化的振动运动模型，结合一系列的线性弹簧，质量和阻尼器的实验测量的响应为人类受试者或人体模型进行解释。 这些模型与系统的几何形状、刚体部件特性以及座椅悬架和支撑性柔性聚氨酯泡沫的结构系统的实际物理特性无关。 因此，它们不能用于了解设计变化对乘员舒适度的影响或用于区分座椅的其他措施。 最近的一些努力已经显示出有限的成功，已经引入了二维模型，其中乘员被认为是由有限数量的线性弹簧和阻尼器支撑。 这种模型，当开发充分，有可能最终是有用的乘员的各种道路条件的响应的现实模拟。 这种能力将大大减少对试错原型的依赖，并降低未来汽车座椅开发的相关成本。 这一发展的关键是柔性聚氨酯泡沫塑料（FPU）的精确模型。 整个系统动力学还取决于座椅泡沫和乘客身体之间的界面，这是复杂的，可能会打滑，以及在高振动水平下失去接触和冲击。 最后，泡沫模型也将是有用的，因为这种材料已成为缓冲和支撑应用的首选材料，包括汽车和飞机座椅，轮椅和医院床上用品，以及运动器材，如鞋和护胫。 这项工作的目标是开发全面的基于物理的二维模型的座椅人体模型系统，并调查这些动态模型的性能，在预测人体模型的各种动态输入的响应。 这种动态座椅-人体模型系统模型的基本物理组件包括人体模型的刚体模型、足够逼真的柔性聚氨酯泡沫模型以及座椅靠背和座椅底部处的座椅-乘员界面模型。 1.软质聚氨酯泡沫塑料（FPU）是一种高度非线性和粘弹性材料，其行为也取决于其微观结构特性。 这项工作将构建聚氨酯泡沫的2D和3D非线性粘超弹性材料模型，用于精确建模泡沫行为和座椅-乘员界面处出现的复杂剪切相互作用。 利用互连的非线性粘弹性梁的泡沫微观结构的有限元模型将被用来模拟微观结构的行为。 实验和系统识别技术将被用来提取宏观模型的参数，以适应实验结果以及基于微观结构的模型的预测。 2.泡沫的非线性粘弹性模型将被纳入多体座椅乘员模型，特别注意在界面处的相互作用模型。 由此产生的座椅人体模型将在非线性积分微分代数方程的形式。 这些模型预计能够预测系统响应下的现实激励，包括瞬态和稳定的振动周期性输入。 这种数学模型的解决方案技术没有得到很好的发展，除了直接的数值模拟。 基于多频谐波平衡法的半解析技术将被开发用于预测周期激励的响应。 将频率-振幅响应预测与直接时间积分结果和不同水平垂直激励下的实验测量响应进行比较，从而验证模型以及模型开发方法。 因此，所进行的研究，预计将推进建模的非线性粘弹性材料的微观结构，以及准确地模拟座椅乘员系统的动力学的能力。

The static and dynamic (ride) comfort of seat occupants are of paramount importance. Most seat design is still done from experience, and trial and error prototyping. The experimentally measured responses for human subjects or mannequins are explained based on simplified vibratory motion models incorporating a series of linear springs, masses and dashpots. These models have no relationship to the actual physics of the system in terms of its geometry, rigid-body component properties, and the structural system of seat suspension and supportive flexible polyurethane foam. So, they cannot be used for understanding effects of design changes on occupant comfort or other measures used to distinguish between seats. Some recent efforts that have shown limited success have introduced two-dimensional models wherein the occupant is considered supported by a finite number of linear springs and dashpots. Such models, when developed sufficiently, have the potential to ultimately be useful for realistic simulations of the occupant's response to various road conditions. This capability will lead the way to significantly reduced dependence on trial-and-error prototyping and the associated costs in the development of future automotive seats. The key to this development is accurate models of flexible polyurethane foam (FPU). The overall system dynamics also depends on the interface between the seat foam and the occupant body, which is complex with possible slipping, as well as loss of contact and impacts at high vibration levels. Finally, the foam models will also be useful as this material has become the material of choice in cushioning and support applications, including automotive and airplane seats, wheelchairs and hospital bedding, and sports equipment like shoes and shin guards. The goal of this work is to develop comprehensive physics-based two-dimensional models of seat-mannequin systems and to investigate the performance of these dynamic models in predicting the response of mannequins to various dynamic inputs. The essential physical components of such a dynamic seat-mannequin system model include rigid-body model of the mannequin, a sufficiently realistic model of flexible polyurethane foam, and models for seat-occupant interfaces at the seatback and the seat bottom. 1. Flexible Polyurethane Foam (FPU) is a highly nonlinear and viscoelastic material whose behavior is also dependent on its microstructural properties. This work will construct 2D- and 3D-nonlinear visco-hyperelastic material models of polyurethane foam for accurate modeling of foam behavior and the complex shear interactions that arise at the seat-occupant interface. Finite element models of microstructure of foam utilizing interconnected nonlinear viscoelastic beams will be used to model the microstructural behavior. Experiments and system identification techniques will be utilized to extract parameters for macroscopic models to fit experimental results as well as predictions from microstructure-based models. 2. The nonlinear viscoelastic models of foam will be incorporated into multi-body seat-occupant models, with special attention paid to models of interactions at the interfaces. The resulting seat-mannequin models will be in the form of nonlinear integro-differential-algebraic equations. These models are expected to be capable of predicting system responses under realistic excitations including transients and steady vibrations to periodic inputs. Solution techniques for such mathematical models are not well developed other than direct numerical simulation. Semi-analytical techniques based on multi-frequency harmonic balance method will be developed to predict responses for periodic excitations. The frequency-amplitude response predictions will be compared to results of direct time-integration and experimentally measured responses at different levels of vertical excitations, thus verifying the model as well as the model development methodology. Thus, the research undertaken is expected to advance the modeling of nonlinear viscoelastic materials with microstructure as well as the ability to accurately simulate the dynamics of seat-occupant systems.