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131.
S.G. Kryzhevich 《Journal of Applied Mathematics and Mechanics》2008,72(4):383-390
The bifurcations of dynamical systems, described by a second-order differential equation with periodic coefficients and an impact condition, are investigated. It is shown that a continuous change in the coefficients of the system, during which the number of impacts of the periodic solution increases, leads to the occurrence of a chaotic invariant set. 相似文献
132.
Enhanced targeted energy transfer for adaptive vibration suppression of pipes conveying fluid 总被引:1,自引:0,他引:1
Nonlinear Dynamics - In this paper, a nonlinear energy sink and a negative stiffness element are integrated for achieving enhanced, passive, and adaptive vibration suppression for a pipe conveying... 相似文献
133.
This paper presents two‐dimensional and unsteady RANS computations of time dependent, periodic, turbulent flow around a square block. Two turbulence models are used: the Launder–Sharma low‐Reynolds number k–ε model and a non‐linear extension sensitive to the anisotropy of turbulence. The Reynolds number based on the free stream velocity and obstacle side is Re=2.2×104. The present numerical results have been obtained using a finite volume code that solves the governing equations in a vertical plane, located at the lateral mid‐point of the channel. The pressure field is obtained with the SIMPLE algorithm. A bounded version of the third‐order QUICK scheme is used for the convective terms. Comparisons of the numerical results with the experimental data indicate that a preliminary steady solution of the governing equations using the linear k–ε does not lead to correct flow field predictions in the wake region downstream of the square cylinder. Consequently, the time derivatives of dependent variables are included in the transport equations and are discretized using the second‐order Crank–Nicolson scheme. The unsteady computations using the linear and non‐linear k–ε models significantly improve the velocity field predictions. However, the linear k–ε shows a number of predictive deficiencies, even in unsteady flow computations, especially in the prediction of the turbulence field. The introduction of a non‐linear k–ε model brings the two‐dimensional unsteady predictions of the time‐averaged velocity and turbulence fields and also the predicted values of the global parameters such as the Strouhal number and the drag coefficient to close agreement with the data. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
134.
Simon E. Gant 《Flow, Turbulence and Combustion》2010,84(2):325-335
Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES) and Scale-Adaptive Simulation (SAS) are increasingly being used
as engineering tools to predict the behaviour of complex industrial flows. Often the flows studied have not been examined
previously and the required grid resolution is unknown. Industrial users studying these flows tend to be using commercial
CFD codes and do not usually have access to high-performance computing facilities. Due to the significant computing times
required, it is difficult to undertake systematic grid-dependence studies. There is therefore a risk that LES, DES and SAS
will be performed using overly coarse grids which may lead to unreliable predictions. The present work surveys a number of
practical techniques that provide a means of assessing the quality of the grid resolution in large-eddy simulations and related
approaches. To examine the usefulness of these techniques, a gas release in a ventilated room is examined using DES and SAS.
The grid resolution measures indicate that overall the grids used are relatively coarse. Both DES and SAS model predictions
are found to be in poor agreement with experimental data compared to steady and unsteady Reynolds-averaged Navier–Stokes (RANS)
results using the SST model. The SAS model also shows the greatest grid sensitivity of the four models tested. The work highlights
the need for grid-dependence studies and the potential problems of using coarse grids. 相似文献
135.
《Finite Elements in Analysis and Design》2009,45(1):25-36
This paper overviews a systematic approach for minimizing the time required for finite element analysis (FEA) while achieving a desired level of accuracy in the simulations. The framework uses the design of experiments (DOE) method in the process as a guide in determining the level of detail needed in the modelling effort to achieve the desired level of accuracy. From the reuse of previously validated analysis components, the automated method supports the selection of the physical model and an adapted mesh to be simulated in order to control the cost (time) and the quality of the whole FEA. 相似文献
136.
A solution of the problem of the diffraction of unsteady elastic waves by a thin strip-like delaminated rigid inclusion in an unbounded elastic medium under conditions of planer strain is proposed. We have in mind an inclusion, one side of which is completely bonded with the medium while, the other side is delaminated and conditions of smooth contact are satisfied on it. The method of solution is based on the use of discontinuous solutions of the Lamé equations of motion under conditions of planer strain, which have been constructed earlier in the space of Laplace transforms. As a result, the problem reduces to solving a system of three singular integral equations for the transforms of the unknown discontinuities. The inverse transforms are found by a numerical method, based on the replacement of a Mellin integral by a Fourier series. 相似文献
137.
138.
Chandra Sekhar Pedamallu Linet Özdamar Tibor Csendes Tamás Vinkó 《Journal of Global Optimization》2008,42(3):369-384
A new efficient interval partitioning approach to solve constrained global optimization problems is proposed. This involves
a new parallel subdivision direction selection method as well as an adaptive tree search. The latter explores nodes (intervals
in variable domains) using a restricted hybrid depth-first and best-first branching strategy. This hybrid approach is also
used for activating local search to identify feasible stationary points. The new tree search management technique results
in improved performance across standard solution and computational indicators when compared to previously proposed techniques.
On the other hand, the new parallel subdivision direction selection rule detects infeasible and suboptimal boxes earlier than
existing rules, and this contributes to performance by enabling earlier reliable deletion of such subintervals from the search
space. 相似文献
139.
140.
In this paper, an experiment has been used to study the effect of pyrolysis stage (from injection to combustion) to dioxin exhaust from diesel engine. The characteristics of diesel fuel pyrolysis have been applied in order to calculate the mean molecular weight in varied temperatures and measure the concentration of inorganic chlorine (HCl). On the other hand, measuring the chlorine content of these particles after diesel pyrolysis enables researchers to find out the pyrolysis temperature that has the lowest possibility to produce dioxin. Additionally, the post-pyrolysis carbon particle diameter has been observed through electronic microscope so as to evaluate the combustion condition of the combustion stage. Result from this study would be helpful for researchers to understand the probability of dioxin formation. 相似文献