Use of scale models to determine the structural dynamic characteristics of space vehicles

Scale model designs for determining structural dynamic characteristics of future spacecraf

Structure-thermal coupling in viscoelastic material in rubber bushing of vehicle system

The objective of this research is to utilize the frequency-dependent viscoelastic material model and characterize the dynamic response of rubber bushing under external excitation. Furthermore, with appropriate modeling, two heat generation mechanisms of rubber bushing are explored and their thermal fields are investigated. Due to the nonlinear force-deflection relationship of the viscoelastic material, finding satisfactory mechanical properties of rubber components still poses a great challenge. However, industry nowadays is in urgent demand for precise finite element analysis (FEA) modeling of rubber components. For example, a proper constitutive relationship of rubber components is critical to providing a reliable and trustable simulation of vehicle suspension systems. As for current FEA commercial software, the frequency-dependent modulus of viscoelastic material hasn\u27t been presented well and they have failed to provide satisfactory results. Therefore, two approaches, FEA and the multi-body dynamic analysis have been selected together to give a more comprehensive and credible prediction of suspension system\u27s performance in different working conditions. The FEA approach evaluated the stability of rubber bushing in view of the dynamic response and temperature distribution under high frequency excitation. With these results, the life prediction of rubber bushing becomes more feasible. The multi-body dynamic analysis explores the structure instability of rubber bushing when exposed to extremely high frequency and estimates the energy dissipation in the rubber core.^ The key innovations of this paper can be classified into four aspects. The first one is the application of multi-body dynamics in the dynamic analysis of rubber bushing. Based on experimental modal analysis, the sandwich cylindrical rubber bushing is treated as multi-body. With the multi-body model, the transfer function of the rubber bushing is calculated in order to estimate the dynamic response. The second innovation comes from the development of the FORTRAN program to solve the system transfer function of the structure made of viscoelastic material. Since the geometry and boundary conditions are amenable in FEA compared with the experimental modal testing, this approach is not just applicable in rubber bushing dynamic analysis, but also useful in dynamic analysis of different rubber components. The third innovative contribution of this research is connecting the multi-body analysis with continuum mechanics to evaluate the mechanical properties of rubber bushing. The last innovation is the structure-thermal coupling of rubber bushing to predict its temperature distribution based on the heat source calculated from the FEA simulation. The finite volume method (FVM) is applied using MATLAB in the simulation of temperature distribution. In this research, the classical standard linear model is applied in the FEA program to characterize the variation of viscoelastic material in the frequency domain. The three parameters of this model have been identified with the batch data measurement using dynamic mechanical analysis equipment (DMA). Specially, two heat generation mechanisms are explored to emphasize the friction-induced hysteresis damping except for the commonly discussed viscous damping. As complementation of FORTRAN program simulation in the frequency domain, the multi-physics commercial software COMSOL is employed to estimate the dynamic response of rubber bushing and temperature distribution in the time domain. To verify the results of FEA and multi-body dynamic approach in the dynamic and thermal analysis of rubber bushing, dynamic tests have been carried out using torsion and tensile testing machines. The experimental temperature distribution is in good agreement with the simulation results, which indicated the feasibility of the FEA method.^ However, due to the limited experience and complicated constitutive relationship of the viscoelastic material, the standard linear viscoelastic model is chosen to simulate the heat dissipation mechanism of rubber core. The high-frequency or high-temperature dynamic testing are almost impossible because of the experiment equipments\u27 range of service. As the first step of predicting the dissipation energy density and temperature distribution of rubber components, the initial explorations are significant and provide a proper guidance for further predictions about life expectation

Effects of variable resistance on smart structures of cubic reconnaissance satellites in various thermal and frequency shocking conditions

Piezoelectric materials are widely used as smart structures in cubic reconnaissance satellites because of their sensing, actuating, and energy-harvesting abilities. In this study, an analytical model is developed in specific mechanical thermal shocking conditions. A special circuit and apparatus is designed for experimentation on the basis of the inverse piezoelectric effect. An equivalent circuit method is used to establish the relationship between the resistance and peak-to-peak voltage of lead zirconate titanate used as smart materials for cubic reconnaissance satellites. Various frequencies and resistance were applied in different mechanical thermal shocking conditions. Moreover, numerical simulations are conducted in various mechanical loading conditions to determine the accumulative effect. The model provides a novel mechanism to characterize the smart structures in cubic reconnaissance satellites. A rise in temperature increases peak-to-peak voltage; a rise in frequency decreases peak-to-peak voltage; and intensified resistance decreases peak-to-peak voltage. Based on experimentation and simulation, the optimum resistance is predicted for the various frequencies and temperatures. The various conditions may correspond to the different applications of smart structures for cubic reconnaissance satellites. The analytical calculations are in good agreement with experimental and numerical calculations. © 2017, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany

Modeling of tire vertical behavior using a test bench

Tire models are of great importance for precise investigations of vertical vehicle dynamics, including vehicular safety and riding comfort. An adequate modeling of the tire is crucial to properly reproduce vehicle vertical behavior in simulations and to evaluate the influence of the tire in the overall performance of the suspension system. This paper introduced vehicle single-point tire models and, thereafter, investigated the influence of the excitation frequency and inflation pressure on the damping and stiffness coefficients of the proposed tires experimentally. In this manner, a test-bench was used to obtain the model parameters of a light vehicle tire and a motorcycle tire. Given the obtained results, it has been observed that both factors have a significant effect on the parameters of the proposed tire models. Moreover, a quarter car suspension model was investigated using the modelled tires to illustrate the influence of the correct characterization of the tire on the vertical suspension performance

Optimisation of racing car suspensions featuring inerters

Racing car suspensions are a critical system in the overall performance of the vehicle. They must be able to accurately control ride dynamics as well as influencing the handling characteristics of the vehicle and providing stability under the action of external forces. This work is a research study on the design and optimisation of high performance vehicle suspensions using inerters. The starting point is a theoretical investigation of the dynamics of a system fitted with an ideal inerter. This sets the foundation for developing a more complex and novel vehicle suspension model incorporating real inerters. The accuracy and predictability of this model has been assessed and validated against experimental data from 4- post rig testing. In order to maximise overall vehicle performance, a race car suspension must meet a large number of conflicting objectives. Hence, suspension design and optimisation is a complex task where a compromised solution among a set of objectives needs to be adopted. The first task in this process is to define a set of performance based objective functions. The approach taken was to relate the ride dynamic behaviour of the suspension to the overall performance of the race car. The second task of the optimisation process is to develop an efficient and robust optimisation methodology. To address this, a multi-stage optimisation algorithm has been developed. The algorithm is based on two stages, a hybrid surrogate model based multiobjective evolutionary algorithm to obtain a set of non-dominated optimal suspension solutions and a transient lap-time simulation tool to incorporate external factors to the decision process and provide a final optimal solution. A transient lap-time simulation tool has been developed. The minimum time manoeuvring problem has been defined as an Optimal Control problem. A novel solution method based on a multi-level algorithm and a closed-loop driver steering control has been proposed to find the optimal lap time. The results obtained suggest that performance gains can be obtained by incorporating inerters into the suspension system. The work suggests that the use of inerters provides the car with an optimised aerodynamic platform and the overall stability of the vehicle is improved

A Government/Industry Summary of the Design Analysis Methods for Vibrations (DAMVIBS) Program

The NASA Langley Research Center in 1984 initiated a rotorcraft structural dynamics program, designated DAMVIBS (Design Analysis Methods for VIBrationS), with the objective of establishing the technology base needed by the rotorcraft industry for developing an advanced finite-element-based dynamics design analysis capability for vibrations. An assessment of the program showed that the DAMVIBS Program has resulted in notable technical achievements and major changes in industrial design practice, all of which have significantly advanced the industry's capability to use and rely on finite-element-based dynamics analyses during the design process

Advanced suspension system using magnetorheological technology for vehicle vibration control

In the past forty years, the concept of controllable vehicle suspension has attracted extensive attention. Since high price of an active suspension system and deficiencies on a passive suspension, researchers pay a lot attention to semi-active suspension. Magneto-rheological fluid (MRF) is always an ideal material of semi-active structure. Thanks to its outstanding features like large yield stress, fast response time, low energy consumption and significant rheological effect. MR damper gradually becomes a preferred component of semi-active suspension for improving the riding performance of vehicle. However, because of the inherent nonlinear nature of MR damper, one of the challenging aspects of utilizing MR dampers to achieve high levels of performance is the development of an appropriate control strategy that can take advantage of the unique characteristics of MR dampers. This is why this project has studied semi-active MR control technology of vehicle suspensions to improve their performance. Focusing on MR semi-active suspension, the aim of this thesis sought to develop system structure and semi-active control strategy to give a vehicle opportunity to have a better performance on riding comfort. The issues of vibration control of the vehicle suspension were systematically analysed in this project. As a part of this research, a quarter-car test rig was built; the models of suspension and MR damper were established; the optimization work of mechanical structure and controller parameters was conducted to further improve the system performance; an optimized MR damper (OMRD) for a vehicle suspension was designed, fabricated, and tested. To utilize OMRD to achieve higher level of performance, an appropriate semi-active control algorithm, state observer-based Takagi-Sugeno fuzzy controller (SOTSFC), was designed for the semi-active suspension system, and its feasibility was verified through an experiment. Several tests were conducted on the quarter-car suspension to investigate the real effect of this semiactive control by changing suspension damping. In order to further enhance the vibration reduction performance of the vehicle, a fullsize variable stiffness and variable damping (VSVD) suspension was further designed, fabricated, and tested in this project. The suspension can be easily installed into a vehicle suspension system without any change to the original configuration. A new 3- degree of freedom (DOF) phenomenological model to further accurately describe the dynamic characteristic of the VSVD suspension was also presented. Based on a simple on-off controller, the performance of the variable stiffness and damping suspension was verified numerically. In addition, an innovative TS fuzzy modelling based VSVD controller was designed. The TS fuzzy modelling controller includes a skyhook damping control module and a state observer based stiffness control module which considering road dominant frequency in real-time. The performance evaluation of the VSVD control algorithm was based on the quarter-car test rig which equipping the VSVD suspension. The experiment results showed that this strategy increases riding comfort effectively, especially under off-road working condition. The semi-active control system developed in this thesis can be adapted and used on a vehicle suspension in order to better control vibration

Efficient simulation of non-linear kerb impact events in ground vehicle suspensions

In the increasing competition which pervades the automobile sector, it is necessary to develop simple methods to enable prediction of suspension loading level envelope in an early development stage. For this purpose, the FORD specified standard driving manoeuvres, based on kerb strike and pothole braking, inducing worst case loading scenarios are employed. The damaging nature of these tests and the relatively expensive physical prototypes make simple simulation models essential. These models should cope with an initial rudimentary assessment, but must suffice to predict the maximum wheel centre loads with a reasonable degree of accuracy. Enhanced model features are required to represent edge-type tyre deformation and impulsive bumper deflection. State of the art approaches are physical tyre models extended to rim clash modelling and rheological bumper models embedded in an multibody system (MBS) environment. These enhancements lead to increased complexity. The thesis proposes a minimal parameter vehicle model, tailored to predict vertical suspension loads caused by the FORD kerb strike manoeuvre. Since the focus is put on model simplicity, an in-plane bicycle model is extended to 7 degrees of freedom. Nonlinear and hysteretic characteristics of the bump-stop elements are included through use of a spatial map concept, based on displacement and velocity dependent hysteresis. Furthermore, a static tyre model is described to predict the radial stiffness against penetration of an edge and flat-type rigid body geometry. The full mathematical model is derived on the basis of the shell theory and represented in terms of few geometrical input parameters. A distinct tyre model, representing the tyre belt as a multi-link chain is also derived to confirm the assumptions made in the simple mathematical model. Model validation is supported through experiments at both component and system levels. It is shown that the bumper map concept provides an accurate, yet simple alternative to a rheological model, if applied to polyurethane foam type bumpers. This approach is also confirmed for the tyre model, substituting a comprehensive physical model approach