Papers by Keyword: Nonlinearity

Abstract: This paper presents an application of the probabilistic analysis of structural resistance of the bubble tower structure of a VVER 440/213. The evaluation is based on an extension of the smeared crack model developed on base of Kupfer's bidimensional failure criterion, rotated crack, CEB-FIP model of failure energy and implemented into the ANSYS system. The non-linear analysis was considered for the median values of the input data and the probabilistic analysis models the uncertainties of loads, material resistance and other modeling issues.

Abstract: Maximum Length Sequence has great potential as testing signal in non-destructive testing. Because its autocorrelation is almost a delta function, the sequence can be used for speed of sound assessment. Resulting Impulse response contains very similar data as Impact-echo. Unlike Impact-echo, where strike energy is limited by nonlinear effects, Maximum Length Sequence can deliver virtually unlimited energy over time. Length of the sequence and also signal generation rate is a curtail choice in order to achieve the best results.

Abstract: The paper presents simulation studies, performed using Simulink, the impact of nonlinear flexural stiffness of shafts for critical speed range and amplitude of vibration. The tests were performed on the selected model of a rotating machine, consisting of a drive, two torsional vibration dampers, shaft with mounted on it two rigid rotors (discs), supported on a three self-aligning roller bearings and mechanical power receiver (brake). The machine startup and braking with crossing the critical states was simulated using specialized Simulink library, which was developed by authors for analysis of transient states in rotating machines and flexural-torsional couplings. In accordance with the concept of modeling adopted by the authors, rotating system is divided into inertial rigid elements (rotors, bearings, clutches, etc..) and compliance elements (parts of the shaft). The main component of the currently developed library is block modeling rigid rotor with 6 degrees of freedom and with the static and dynamic unbalance. By assumption the library is a modular, expandable and allows modeling the systems of any configuration. The goal of the simulation was to verify how nonlinear flexural stiffness of shaft influences the values of critical speeds and the level of flexural and torsional vibrations.

Abstract: In this article the micro flow self-sensing actuator has carried on the theoretical analysis and experimental research. Using output micro-displacement generated by the first inverse piezoelectric effect to realize cell micro flow injection, using output voltage generated by secondary direct piezoelectric effect of piezoelectric ceramic to self-sensing the output displacement in the process of the micro flow injection. The experimental results show that the micro-displacement of micro-flow self-sensing actuator has nonlinear error, error is 5.03%. The error between measured micro-displacement and self-sensing micro-displacement is 63.13%. In this paper, the error causes analysis of micro-flow self-sensing actuator is from non-linearity and hysteresis, external factors, it lay the foundation for the further study of micro-flow self-sensing actuator.

Abstract: The paper studies the efficiency of seismic isolation system in the form of rubber-metal bearings with different height buildings at multicomponent seismic impact. As an example, seismically insulated monolithic reinforced concrete 5-, 9-and 16-storey buildings are considered. The solution of the problem is obtained by a direct integration of the motion equations for an explicit scheme in the software package LS-DYNA. The calculation is performed considering nonlinear nature of rubber bearings. The analysis of the effectiveness of buildings with seismic insulation and without it is performed.

Abstract: Practical engineering structures commonly display nonlinear dynamic response when damage is present in the system. Hence, the studies on nonlinear system identification have increased within these past few years. Current study is aimed on the structural identification of nonlinear systems based on the extraction of underlying linear frequency response function (FRF). The methods chosen to obtain the FRF are the Conditioned Reverse Path (CRP) and the Orthogonalised Reverse Path (ORP) method. The well-known frequency-domain CRP method has been recognised for its ability in solving nonlinear problems; detecting and quantifying nonlinearities in structures. In contrary, the ORP is a new algorithm developed in time-domain which gives simpler formulation for describing the underlying linear dynamics of nonlinear systems. Results show that the performance of the new ORP algorithm in handling nonlinearities is as good as the CRP method. The ability of ORP method has become the aim of the current study to assess the robustness of both algorithms towards nonlinear system identification of structures with multi-degree-of-freedom (MDOF) system.

Abstract: In this paper, we examine the nonlinear nanoelectromechanical effect on a doubly clamped suspended single-walled carbon nanotube which could be used for pressure sensor. Coulomb-blockade effects will be explored and investigated. We adopt the full expression of curvature term in the elastic energy and use a modified Euler’s method to determine the nanotube’s maximum displacement in all bending regimes. We find that while the approximate solution given by Sapmaz et al. [1] underestimates the maximum displacement of the buckled nanotube in the weak bending regime, the approximate solution fails to obtain the correct maximum displacement as given by our numerical solution. Accordingly, the effect of curvature must be properly addressed for this nanoelectromechanical system to be used as an accurate sensor.

Abstract: Basing on the finite element analysis software, the emergence of crack under the effect of gradual changed temperature load and the change of stress which are in the condition of super reinforced concrete frame structure are analyzed from the linear and nonlinear numeral simulation. The simulation shows that the structure component under the normal condition is cracked and turn into the nonlinear condition and the steel bars still works under the elastic stage. Meanwhile the actual stage which is reflected by the elastic-plastic analysis of the internal force and deformation is compared by the results which are obtained by the actual project observed results and the calculation of the simplified model. So the distribution of the stress which is caused by the structure temperature reduction is greatly evaluated by the usage of the cracking model which is nonlinear finite element and also plays an important role in the engineering project and practice.

Abstract: In order to improve the nonlinear problems of power amplifier, this paper discussed about the nonlinear characteristic of power amplifier without memory and put forward a kind of new pre-distortion model. The MATLAB simulation process was being used to obtain the input and output amplitude curves, and calculated the normalized mean square error NMES and error vector magnitude EVM, the results show that the power amplifier linearization improved after pre-distortion processing.

Abstract: This paper presents numerical solutions of straight plane beam structures rested on an elastic (Winkler's) foundation. It is a continuation of our previous work (see Part 1 of this article) focused on practical applications and solutions including nonlinearities in the foundation (i.e. bilateral linear, bilateral linear + cubic, bilateral linear + cubic + quintic approximations and unilateral approximation for dependencies of reaction forces on deflection in the foundation). For solutions of nonlinear problems of mechanics (i.e. differential 4^th-order equations), the Finite Difference Method (i.e. the Central Difference Method) is applied in combination with the Newton (Newton–Raphson) Method. Finally, in one example, linear and nonlinear approaches are solved, evaluated and compared. In some cases, there are evident major differences between the linear and nonlinear solutions.