Papers by Keyword: Nonlinearity

Abstract: The model that describes the friction between contact surfaces of motion pair of the feed system has been established use of Stribeck friction theory, it fully reflected the various lubrication conditions. The bifurcation and stability analysis of the model has been done. The experimental methods were used to research the nonlinear dynamics characteristics of the feed system under the external excitation. The influences that friction force to the nonlinear characteristics of the system at the certain parameters condition were analyzed. Utilize the research findings of the dynamical characteristics that caused by friction in the feed system can effectively provide a theoretical basis for designing optimization of complex systems in engineering, fault diagnosis and vibration control.

Abstract: Active control and passive base isolation strategies are exerted on one continuous isolated prestressed concrete bridge. The goal of this study is to check the applicability of the LQR control law on the isolated continuous or rigid-connection type bridge, to find a more effective control strategy when nonlinearity is introduced. A spaced frame finite-element model is developed by a MATLAB program coded by the author, its validity is checked through comparisons with a sap2000 model. In this program, the nonlinearities of 3 different columns and 5 isolators are considered with their bilinear force-deformation relationship. the factors such as the control devices, sensors, and the corresponding noises and time delay are all considered in the model. Model reduction technique was applied to set up the controllers. The seismic response measurements and regulated outputs are adjusted to optimize control effects.

Abstract: A three dimensional numerical model for a typical earth dam and its valley site was established and the nonlinear seismic response of this model was performed. Experimental data of cyclic triaxial tests were adopted to determine the curves of modulus ratio and damping ratio that vary with dynamic strain amplitude. Free-field artificial boundary and viscous artificial boundary were employed and the input waves were the revised ground motions obtained from the station near the dam. Distributions of the PGA, displacement, residual deformation, shear strain increment and element failure state were presented. Results demonstrate that the 3D local valley site effect has a significant influence on the seismic response of earth dam.

Abstract: Vortex-induced dynamic response is the most important issue influencing marine riser. This paper presents an investigation on the vortex-induced nonlinear dynamic response of marine riser subjected to combined waves,currents and platform movement. The in-line force was solved by Morison equation under combined waves,currents and platform movement while cross-flow force was solved by wake oscillator model. Updated Lagrangianmethod was used to solve the nonlinear problem.The governing equations were discretized by finite element method and solved by Newmark-β method in time domain. Influence of nonlinearity, comparisons of vortex-induced dynamic responses under different boundary conditions and different flow profiles were discussed.

Abstract: A detailed analysis about the nonlinearity of a mode-matching MEMS vibratory gyroscope is presented in this paper, then closed loop control for the sense mode is adopted to improved the performances. Experimental results figure out that the mode-matching gyroscope with closed loop controlled sense mode achieves a scale factor of 65mV/deg/s with nonlinearity of 0.05% and asymmetry of 0.1%, and a bias instability of 0.77deg/h, while they are 60mV/deg/s, 1%, 4.6% and 9.8deg/h in the open loop controlled sense mode system, respectively. These performances can be improved by more than one order of magnitude in the closed loop control system.

Abstract: A high-order interface circuit based on sigma-delta (ΣΔ) modulation is advantageous to enhance the resolution and reduce the quantization noise of micro-accelerometer, while the performance is restricted by the effect of nonlinearity of op-amp, electrostatic force feedback and quantizer. A fifth-order closed-loop ΣΔ capacitive accelerometer is proposed in this paper and a theoretic nonlinearity of the accelerometer was investigated. The nonlinear behavioral models based on SIMULINK are given in the paper. The simulation and test result are presented through optimization based on the nonlinearity analysis at last.

Abstract: In this paper a novel RF receiver modeling approach is presented. The novelty consists in the usage of the object oriented programming instead of the usual imperative programming. Classes were defined for entities as signal, non-ideality and RF/analog block, in order to achieve a basic RF receiver model. The main circuit non-idealities were identified, non-ideality parameters and their analytical models were encapsulated into classes. The effectiveness of the proposed modeling approach was demonstrated by developing in MATLAB a fairly complete model of a direct conversion receiver.

Abstract: The characteristics of the transient heating control process of aerodynamic simulation experiments are complicated, transient, highly nonlinear, and strongly coupled, which make it difficult or impossible to develop a mathematical model. By using the fuzzy control method, many good qualities (such as robustness, high adaptability to changing parameters, and a short transition process time) can be obtained. Based on the fuzzy control method, a transient aerodynamic heating simulation control system for missiles was established. It was demonstrated that quick dynamic control of the aerodynamic simulation heating process according to the transient and continual change in heat flow on the surface of high-speed aircrafts can be completed by using this control system.

Abstract: A broadband supercontinuum source is demonstrated with phosphosilicate-doped Raman fiber laser. By lunching 1495nm continuous-wave pump into a short length of microstructure fiber with high nonlinearity and flat dispersion, high efficiency continuum spanning from 1450nm to 1650nm is generated, covering the whole communication windows. The average output power is as high as 2W when the pump is set as 4.14W, corresponding to a spectral density of 10mW/nm. This all -fiber light source can be applied in fiber sensing system.

Abstract: In this paper, the nonlinear relationship between the bending moment and curvature of non-bonded flexible pipes was studied. It was found that the relation was a function of internal and external pressure, axial force, and bending moment load. The model used in this paper took into consideration of the flexural, tensile and torsional strength of layers as well as the frictions between them. Symmetrical axial load was first applied, and then the bending load. Due to friction, the response of the unbonded flexible pipes is hysteretic to the loads. In conclusion, the response of unbonded flexible pipes are both related to its own structural properties and external loads.Coupling factors of different conditions should also be considered.