Papers by Keyword: Variable Stiffness

Abstract: The problem of bending of a beam of variable stiffness resting on a continuous homogeneous elastic Winkler-type foundation is considered. The exact solution of the corresponding bending differential equation is found for the case when the beam stiffness is an arbitrary continuous function. Based on the exact solution, an analytical method for beam calculation is developed. This method produces accurate results and is computationally efficient. It is implemented in a computer program and demonstrated by the calculation of a truncated wedge-shaped beam. The calculation results are provided in numerical and graphical formats.

Abstract: The variable stiffness and damping (VSVD) suspension system offers an interesting option to improve driver comfort in an energy efficient way. The aim of this study is to analyze the influence of the spring ratio on the VSVD. The realization of the VSVD is obtained by the application of variable damping with magnetorheological (MR) damper. In this study, the nonlinear damping force characteristic of the MR damper is modeled with the Bouc-Wen model and the road disturbance is modeled by a stationary random process with road displacement power spectral density. It is shown from simulation that VSVD has a potential benefit in improving performance of vehicle suspension.

Abstract: Variable angle tow (VAT) describes fibres in a composite lamina that have been steered curvilinearly. In so doing, substantially enlarged freedom for stiffness tailoring of composite laminates is enabled. VAT composite structures have been shown to have improved buckling and postbuckling load carrying capability when compared to straight fibre composites. However, their structural analysis and optimal design is more computationally expensive due to the exponential increase in number of variables associated with spatially varying planar fibre orientations in addition to stacking sequence considerations. In this work, an efficient two-level optim isation framework using lamination parameters as design variables has been enhanced and general ised to the design of VAT plates. Explicit stiffness matrices are found in terms of component material invariants and lamination parameters. The convex hull property of B-splines is exploited to ensure point-wise feasibility of lamination parameters. In addition, a small set of explicit closed-form expressions is used to define the feasible region of two in-plane and two out-of-plane lamination parameters, which are used for the design of orthotropic laminates. Finally, numerical examples of plates under compression loading with different boundary conditions and aspect ratios are investigated. Reliable optimal solutions demonstrate the robustness and computational efficiency of the proposed optimisation methodology.

Abstract: The variable stiffness micro-springs’ load and deformation have nonlinear relationship, thus they can be used in special occasions. MEMS processing technology can manufacture any complex structures in a plane, using this feature, a variable stiffness design idea for the planar micro-spring is proposed. That is, using one type of structure named contact pairs to achieve stiffness change during the micro-spring’s stretching process. Using contact pairs, two types of variable stiffness springs are designed: stiffness increase spring and stiffness convexity spring. Because of the influence of processing precision, the contact pairs’ sizes of the first type of variable stiffness spring are different each other, the machining error makes the test results and simulation results various. In order to avoid the above problem of above spring, this paper designs another two variable stiffness micro-springs, test results indicate that the improved variable stiffness springs can realize the variable stiffness’ tendency.

Abstract: A novel tunable stiffness and damping vibration isolator based on magnetorheological nanocomposites filled with carbon nanotubes (CNMRE) was proposed. The stiffness and damping is controlled by the current applied to the magnetic excitation coil. Under the combined ON–OFF control law, the proposed vibration isolator shows satisfying isolation effect. The simulation results indicate that, in comparison to MRE isolator with ON–OFF stiffness and damping control, CNMRE isolator with ON–OFF control not only has high stiffness and damping capacity, corrosion resistance, and high failure strength which are demanded in industries, but also significantly suppresses vibration under sinusoid excitation, random excitation, and pulse excitation. The proposed vibration isolator is very simple and easy to be applied in practical system.

Abstract: The combined variable stiffness and damping on-off control strategy is investigated using a magnetorheological elastomer (MRE) isolator. A one-degree-of-freedom system has been adopted to assess the efficiency of different control strategies under sinusoidal and random and pulse excitations. The obtained results illustrate that a single tunable stiffness control with maximal damping values under both excitations can simultaneously performs better control of displacement than using minimal damping if the relative displacement and relative velocity of load are in contrary directions . Moreover, on-off variable stiffness control plays a more important role than damping control, therefore it is feasible to only control magnetic field to change MRE elastic and damping property for simplicity.

Abstract: In the paper, a set of analysis formulas of pile-group of variable stiffness composite foundations was derived.The reasonability and reliability of the proposed method were showed by the results of a large scale model experiment.It is valuable to the analysis of the pile-group of composite settlement, the design optimization and the study of mechanism of pile-to-pile interaction.

Abstract: An experimental investigation on the dynamic characteristics of unbounded prestressed concrete simply support beams is presented. A total of 5 unbounded prestressed concrete simply support beams were constructed and tested. The influence of prestressing on natural vibration frequency of concrete beams is studied by applying prestress gradually. A model of variable stiffness is proposed to calculate the natural vibration frequency of unbounded prestressed concrete beams. The finite element program Sap2000 is used to calculate the frequency of unbounded prestressed concrete beams. The results show that the calculating results agree well with experimental ones.

Abstract: This papers deals with the study of the influence of prestress force on the natural frequencies for unbonded prestressed concrete beams. A total of 5 unbounded prestressed concrete simply support beams were constructed and tested. The test results show that the prestress force has little effect on the nature frequencies of unbonded prestressed concrete beams. A model of variable stiffness is proposed to calculate the natural frequencies of prestressed concrete beams with unbonded tendons, which assumed that the flexural rigidity of the beam is changing when beams vibrating. The calculate results show that the calculation results by the proposed model agree well with experimental ones.

Abstract: Based on the semi-active suspension system with variable stiffness and damping, the full vehicle model was established in Adams/Car software, which included front suspension and rear suspension with variable stiffness and damping, steering system, car body and tires model. The variable universe fuzzy controller of semi-active suspension was designed according to variable universe fuzzy theory, which was compared with the traditional fuzzy controller. The co-simulation model was built by Matlab/Simulink and Adams/Car software. Then the model was simulated and analyzed in the inputs of random road and roof road. The results of the co-simulation show that, compared with the full vehicle model with passive suspension, the full vehicle model with variable stiffness and damping semi-active suspension effectively reduced the vibration of car body and improved the vehicle ride quality, and the variable universe fuzzy controller is better than the traditional fuzzy controller in decreasing vibration.