Zhaoye Qin

Analytical model of bolted disk–drum joints and its application to dynamic analysis of jointed rotor

Bolted joints are widely used in aero-engines. One of the common applications is to connect the rotor disks and drums. An analytical model for the bending stiffness of the bolted disk–drum joints is developed. The joint stiffness calculated using the analytical model shows sound agreement with the calculation obtained based on finite element analyses. The joint stiffness model is then implemented into the dynamic model of a simple rotor connected through the bolted disk–drum joint. Finally, the whirling characteristics and steady-state response of the jointed rotor are investigated to evaluate the influence of the joint on the rotor dynamics, where the harmonic balance method is employed to calculate the steady-state response to unbalance force. The simulation results show that the joint influence on the whirling characteristics of the rotor system can be neglected; whereas, the presence of the bolted disk–drum joint may lead to a decrease in the rotor critical speeds due to the softening of the joint stiffness. The proposed analytical model for the bolted disk–drum joints can be adopted conveniently for different types of rotor systems connected by bolted disk–drum joints.

Vibration and damping characteristics of sandwich plates with viscoelastic core

As an effective approach to suppress vibrations and noise, passive constrained layer damping (PCLD) treatments are widely used in engineering practice. However most of the studies concentrate on the one-dimensional beams with active/passive constrained damping layer, the analysis on the two-dimensional plates are relatively small. This research proposes an efficient sandwich modeling technique to deal with the vibration and damping characteristics of the PLCD plate structure. A type of three-layer four-node rectangular element with seven degrees of freedom on every node is used to simulate the PLCD plate structure. The displacement relationships of each layer are obtained based on the first-order shear deformation theory. The finite element equations of motions are derived by the Hamilton principle in variation form. The natural frequency and loss factor are discussed based on the eigenvalue problems. Numerical examples are provided to verify the accuracy and efficiency of the present finite element method. Finally, the influences of the layer thickness, the loss factors of the viscoelastic cores on the natural frequencies and loss factors of the PLCD plate structure are discussed as well.

Influence of clamp band joint on dynamic behavior of launching system in ascent flight

A dynamic model for the launching system incorporating the influence of the clamp band joint is developed using the finite element method, where both of the launch vehicle and the spacecraft are modeled as Timoshenko beams. The clamp band joint is represented by a massless beam element, of which the element stiffness matrix is developed based on the expressions for the axial and bending stiffnesses of the joint deduced by the authors in the previous works. Dynamic analyses are performed to evaluate the joint influence on the launching system, where the variations of the mass and length of the launching system due to the fuel combustion and stage jettisons during the ascent flight are considered. The dynamic model presented here can be applied to investigate dynamics of launching systems involving the influence of clamp band joints conveniently.

A comparative study of finite element modeling techniques for dynamic analysis of elastic-viscoelastic-elastic sandwich structures

Two finite element formulations using different laminate plate theories are developed for the elastic-viscoelastic-elastic sandwich plates. A critical comparison and assessment between them are provided. The dynamic characteristics, namely, the natural frequencies and associated loss factors of the elastic-viscoelastic-elastic sandwich plates are calculated using the two finite element models. The two models are validated through the numerical example and experiment results. Comparisons of the accuracy and computational efficiency of the two finite element models are given. The results show that both of the two finite element models have good accuracy in predicting the natural frequencies and the loss factors with different efficiency. The works in this article have instructive significance in the calculation and application of the elastic-viscoelastic-elastic sandwich structures.

Application of 2D finite element model for nonlinear dynamic analysis of clamp band joint

Due to frictional slippage between the joint components, clamp band joints may generate nonlinear stiffness and friction damping, which will affect the dynamics of the joint structures. Accurate modeling of the frictional behavior in clamp band joints is crucial for reliable estimation of the joint structure dynamics. While the finite element (FE) method is a powerful tool to analyze structures assembled with joints, it is computationally expensive and inefficient to perform transient analyses with three-dimensional (3D) FE models involving contact nonlinearity. In this paper, a two-dimensional (2D) FE model of much more efficiency is applied to investigate the dynamics of a clamp band jointed structure subjected to longitudinal base excitations. Prior to dynamic analyses, the sources of the model inaccuracy are determined, upon which a two-step model updating technique is proposed to improve the accuracy of the 2D model in accordance with the quasi-static test data. Then, based on the updated 2D model, the nonlinear influence of the clamp band joint on the dynamic response of the joint structure is investigated. Sine-sweep tests are carried out to validate the updated 2D FE model. The FE modeling and updating techniques proposed here can be applied to other types of structures of cyclic symmetry to develop accurate model with high computational efficiency.

Dynamic analysis of satellite separation considering the flexibility of interface rings

Dynamic characteristics of satellite separation are synthetical results of various influencing factors. The improvement of research methods for designing and analyzing the separation system is of great importance for optimizing the dynamic performance of satellite separation. However, there is lack of an integrated approach for studying the satellite separation dynamics with full consideration of the attitude dynamics of satellites, the dynamic envelope of clamp band and the separation shock responses. This paper proposes a modeling and simulation method for comprehensively predicting the dynamic characteristics of satellite separation with the consideration of the flexibility of interface rings. A contrastive analysis of separation dynamics is carried out to determine the effects of the flexible interface rings on satellite separation dynamic characteristics. Subsequently, parametric studies on dynamics of satellite separation are performed, and research emphasis is placed on investigating the effects of position relative to the separation plane, the preload of clamp band, the friction coefficient and the pyroshock of explosive bolts on separation shock responses. The research method proposed in this paper provides a reference for the initial engineering design of the clamp band joint of satellite separation system.

A compression shear mixed finite element model for vibration and damping analysis of viscoelastic sandwich structures

A finite element model is developed to investigate the vibration and damping of elastic–viscoelastic–elastic sandwich beams. Two energy dissipation mechanisms, namely the shear and compression damping, are combined in the finite element model. Numerical examples are provided to verify the finite element model. The vibration and damping characteristics of the viscoelastic sandwich beams are investigated in detail. The numerical results show that the present finite element model has a good accuracy in predicting the natural frequencies and loss factors of viscoelastic sandwich beam structures. Moreover, it shows good applicability for both the thin and relatively thick sandwich beams. Its comprehensive performance is much better than the traditional shear and compression damping models. The effect of the viscoelastic material and geometrical parameters on the natural frequencies and loss factors of elastic–viscoelastic–elastic sandwich beam is studied as well. The results obtained have some significance in engineering application.

A Finite Element Model for Elastic-Viscoelastic-Elastic Composite Structures

A finite element model is developed to investigate the vibration and energy dissipation characteristics of elastic-viscoelastic-elastic composite (EVEC) beams. The theoretical energy dissipation characteristics of the EVEC beams are quantized by the loss factors. Two energy dissipation mechanisms, namely the shear and compression damping are combined in the finite element model. Numerical examples are provided to verify the finite element model. The instructive conclusions are important to make the EVEC beam more suitable for controlling structural vibrations and noise.

Improved Formulation for Predicting the Load Capacity of Marman Clamps

Marman clamps are the most commonly used attachments for spacecraft to expendable launch vehicles. Accurate prediction of the load capacity of the marman clamps is required for spacecraft programs....

Dynamic analysis of slender launching system connected by clamp band joint using harmonic balance method

Clamp band joints are widely used to fasten spacecrafts onto launching systems. Due to the unilateral constraints and the frictional slippage at the joint interface, clamp band joints may bring nonlinearity into launching systems during launching process. In this paper, the dynamics of a slender launching system with clamp band joint is investigated using harmonic balance method. Firstly, the formulas for the joint stiffness of the clamp band joint are proposed. Then, the finite element model for the launch vehicle and the spacecraft connected by the clamp band joint is developed, where the clamp band joint is represented by a massless beam element. Finally, harmonic balance method is applied to calculate the steady state response of the launching system.