汽车液压阻尼器的四段线性化模型

通过对现有某车用液压阻尼器的实验研究和车辆悬架系统动力学仿真研究，发现这种阻尼器的动力学特性存在复杂的非线性行为。为准确描述这类阻尼器的动力学特性和进行汽车悬架系统的动力学仿真研究，本文根据阻尼器的实验数据，提出一种新型四段线性化阻尼器模型，并建立其相应的数学模型。通过汽车悬架系统的动力学仿真研究表明，采用四段线性化阻尼器模型，汽车悬架系统簧载质量在不同路面不平度函数作用下的加速度响应和均方根加速度响应随频率变化不会出现大的波动。与等效线性化阻尼器模型相比，四段线性化阻尼器模型，能较好降低汽车悬架系统簧载质量的加速度响应和均方根加速度响应，有利于提高汽车乘坐舒适性和行驶稳定性，并为新型阻尼器设计提供一个新的思路。     

CFD modeling using heterogeneous reaction kinetics for catalytic dehydrogenation syngas reactions in a fixed-bed reactor

A comprehensive 2D computational fluid dynamics （CFD） model was developed to simulate the flow behavior and catalytic dehydrogenation reaction of syngas in a heterogenous fixed-bed reactor （FBR）. The model combined the porous medium CFD model with a reaction kinetics model. To acquire an accu- rate reaction kinetics model, a comprehensive reaction mechanism was studied for the heterogeneous catalytic dehydrogenation reaction ofsyngas over a supported metal catalyst. Based on the reaction mech- anism and a statistical test, a reliable kinetics model was proposed. The CFD model combined with the above kinetics model was validated with one set of experimental data. The CFD model was also used to predict key reaction variable distributions such as the temperature and the component concentrations in the reactor.     

A mixed-timescale SGS model for thermal field at various Prandtl numbers

A new subgrid-scale (SGS) model for the thermal field is proposed. The model is an extended version of the mixed-timescale (MTS) SGS model for velocity field by Inagaki et al. (2005), which has been confirmed to be a refined SGS model for velocity field suited to engineering-relevant practical large eddy simulation (LES). In the proposed model for the thermal field, a hybrid timescale between the timescales of the velocity and thermal fields is introduced in a manner similar to velocity-field modeling. Thus, the present model dispenses with an ambiguous SGS turbulent Prandtl number, like the dynamic SGS model. In addition, the wall-limiting behavior of turbulence is satisfied, which is not in the original MTS model, by incorporating the wall-damping function for LES based on the Kolmogorov velocity scale proposed by Inagaki et al. (2010). The model performance is tested in plane channel flows at various Prandtl numbers, and the results show that this model gives the ratio of the timescales between the velocity and thermal fields similar to that obtained using the dynamic Smagorinsky model with locally calculated model parameters. It is also shown that the proposed model predicts better mean and fluctuating temperature profiles in cooperation with the revised MTS model for the velocity field, than the Smagorinsky model and the dynamic Smagorinsky model. The present model is constructed with fixed model parameters, so that it does not suffer from computational instability with the dynamic model. Thus, it is expected to be a refined and versatile SGS model suited for practical LES of the thermal field.     

Principles of Integrated Flow Modeling

Integrated flow modeling is the combination of a traditional flow simulator with a petrophysical model. By combining a petrophysical model with a traditional flow model, it is possible to perform calculations that improve our ability to monitor fluid movement in porous media. This paper outlines the formulation of an integrated flow model IFLO and its multi-variable, Newton–Raphson IMPES solution procedure. The benefits of integrated flow modeling and the underlying principles involved in the integration of a flow model with a petrophysical model are presented. Results from the IFLO model are used to illustrate the principles.     

Grid-averaged Lagrangian LES model for multiphase turbulent flow

A grid-averaged Lagrangian (GAL) model for dispersed particle motion in multiphase turbulent flow is presented to provide a large eddy simulation (LES) model for multiphase turbulent flow in which a quite large number of particles are involved. The GAL model is based on an averaging operation for a Lagrangian-type equation of motion of a particle over a computational grid volume and a procedure of reallocation of a dispersed particle cloud with its centroid movement to each grid. The model is therefore a mixed Eulerian–Lagrangian model which can effectively reduce computational time compared with existing Lagrangian-type models, without losing the advantage of Lagrangian-type models that they can properly describe the dynamical evolution of particles. Since the GAL model adopts the grid-volume averaging operation it can easily provide an effective SGS model for LES modeling of multiphase turbulent flow. The validity of the multiphase LES model developed, which is named the GAL-LES model, is confirmed through its application to a particle plume, in which the present model is found to simulate large-eddy motion usually observed in a jet and plume, and to give good agreements with experimental data.     

Numerical simulation of pollutant transport acted by wave for a shallow water sea bay

A numerical model of pollutant transport acted by water waves on a shallow‐water mild‐slope beach is established in this study. The numerical model is combined with a wave propagation model, a multiple wave‐breaking model, a wave‐induced current model and a pollutant convection–dispersion model. The wave propagation model is based on the higher‐order approximation of parabolic mild‐slope equation which can be used to simulate the wave refraction, diffraction and breaking in a large area of near‐shore zone combined with the wave‐breaking model. The wave‐induced current model is established using the concept of the radiation stress and considering the effect of bottom resistance caused by waves. The numerical model is verified by laboratory experiment results of regular and irregular waves over two mild beaches with different slopes. The numerical results agree well with experimental results. The numerical model has been applied in the near‐shore zone of Bohai bay in China. It is concluded that pollutant transport parallel to the shoreline due to the action of waves, which will induce serious pollution on the beach. Copyright © 2005 John Wiley & Sons, Ltd.     

Gravitational forces in dual-porosity systems: II. Computational validation of the homogenized model

Three models are considered for single component, single phase flow in naturally fractured porous media. The microscopic model holds on the Darcy scale, and it is considered to govern the system. The macroscopic, dual-porosity model was derived in Part I of this work from the microscopic model by two-scale mathematical homogenization. In this paper, we show that the dual-porosity model predicts well the behavior of the microscopic model by comparing their computed solutions in certain reasonable test cases. Homogenization gives a complex formula for a key parameter in the dual-porosity model; herein a simple approximation to this formula is presented. The third model considered is a single-porosity model with averaged parameters. It is shown that this type of model cannot predict the behavior of the microscopic flow.This work was supported in part by the National Science Foundation and by the State of Texas Governor's Energy Office.     

基于最小概率DWO的激光陀螺温度误差模型辨识

鉴于激光陀螺温度误差模型的非线性和时变性,从提高模型辨识质量的需要出发,运用基于最小概率DWO（直接加权优化）的非线性系统辨识方法进行激光陀螺温度误差模型辨识研究,提出了一种精度更高的激光陀螺温度误差模型。该模型以带宽作为唯一需要确定的模型参数,避免了以往温度误差模型研究中的结构与参数辨识等复杂问题,从而在保证模型辨识质量的基础上,也相应提高了模型的适应能力,并通过两种温度误差特性有显著区别的激光陀螺（四频差动激光陀螺和二频机抖激光陀螺）的温度实验数据验证了该模型的正确性和适应性。     

回采工作面周期来压步距的灰色预测

利用灰色系统理论, 将回采工作面周期来压视为灾变, 仿线性GM(1, 1)预测模型建模机理, 本文建立了包括线性模型在内的统一非线性GM(1, 1)预报模型。利用非线性模型特例Verhulst模型和线性模型分别对两个不同矿山条件老顶周期来压步距进行预测, 结果表明, 不同的地质条件将适合不同的预测模型, 不能简单一概用线性模型进行预测。对于地质条件发生灾变的情形可建立激励预测模型对周期来压步距进行预测。     

Photoelastic model measurement with rotated principal axes by scattered-light photoelasticity

The method of measurement of a three-dimensional photoelastic model with rotated principal axes has not yet been fully experimentally established. It is known that a three-dimensional photoelastic model can be reduced to an optically equivalent model. In this paper, the optically equivalent model is realized from a stratified model consisting of two layers of the frozen stress model. The secondary principal stress direction and the relative phase retardation of the frozen disk model in the stratified frozen stress model are determined for the entire field from Stokes parameters obtained by scattered-light photoelasticity using unpolarized light. The accuracy of these values is confirmed by a comparison with results only from the frozen stress disk model.     

Aeroelastic prediction of the limit cycle oscillations of a cropped delta wing

The flutter and limit cycle oscillation (LCO) behavior of a cropped delta wing are investigated using a newly developed computational aeroelastic solver. This computational model includes a well-validated Euler finite difference solver coupled to a high-fidelity finite element structural solver. The nonlinear structural model includes geometric nonlinearities which are modelled using a co-rotational formulation. The LCOs of the cropped delta wing are computed and the results are compared to previous computations and to experiment. Over the range of dynamic pressures for which experimental results are reported, the LCO magnitudes computed using the current model are comparable to those from a previous computation which used a lower-order von Karman structural model. However, for larger dynamic pressures, the current computational model and the model which used the von Karman theory start to differ significantly, with the current model predicting larger deflections for a given dynamic pressure. This results in a LCO curve which is in better qualitative agreement with experiment. Flow features which were present in the previous computational model such as a leading edge vortex and a shock wave are enhanced in the current model due to the prediction of larger deflections and rotations at the higher dynamic pressures.     

Different effects of economic and structural performance indexes on model construction of structural topology optimization

The objective and constraint functions related to structural optimization designs are classified into economic and performance indexes in this paper.The influences of their different roles in model construction of structural topology optimization are also discussed.Furthermore,two structural topology optimization models,optimizing a performance index under the limitation of an economic index,represented by the minimum compliance with a volume constraint(MCVC)model,and optimizing an economic index under the limitation of a performance index,represented by the minimum weight with a displacement constraint(MWDC)model,are presented.Based on a comparison of numerical example results,the conclusions can be summarized as follows:(1)under the same external loading and displacement performance conditions,the results of the MWDC model are almost equal to those of the MCVC model;(2)the MWDC model overcomes the difficulties and shortcomings of the MCVC model;this makes the MWDC model more feasible in model construction;(3)constructing a model of minimizing an economic index under the limitations of performance indexes is better at meeting the needs of practical engineering problems and completely satisfies safety and economic requirements in mechanical engineering,which have remained unchanged since the early days of mechanical engineering.     

多孔格栅均匀化模型平压仿真分析

为了研究均匀化方法在一种多孔格栅结构中的应用,从格栅单胞尺度入手,建立了一种适用于有限元仿真分析的三维周期性边界条件.以ABAQUS作为分析平台,对周期性边界条件下的格栅单胞模型进行了平压仿真分析,并将仿真结果与文献实验结果对比,验证了该边界条件的可靠性.利用均匀化理论建立了格栅单胞力学平衡方程,得到了格栅均匀化模型....     

结构动力学有限元模型修正的发展——————模型确认

结构动力学有限元建模精度问题是力学分支中受到广泛关注的研究课题之一. 以提高建模精度为目标的有限元模型修正技术的发展日臻完善, 并已逐步在工业界得到应用. 然而模型修正技术未能全面解决建模精度中存在的问题. 近几年以美国三大国家实验室为代表的科技人员提出了模型确认技术, 以希望全面解决结构动力学建模精度问题. 本文以模型修正为基础, 讨论模型确认的相关问题以及与模型修正的关系.      

Solving parametric complex fluids models in rheometric flows

Inverse identification of complex fluid behaviors is a tricky task because sometimes there are several rheological parameters and the identification procedure itself is quite expensive from the computational time viewpoint. Standard inverse identification procedures solve the model for a choice of the model parameters, and then parameters are updated trying to minimize the gap between the model predictions and some available experimental measures. Thus, the model has to be evaluated for each trial set of the model parameters. When models involve a great number of degrees of freedom the identification procedure becomes a computationally expensive task. In this paper we propose a new procedure able to solve once the model for any value of the model parameters. For this purpose, all the model parameters are considered as extra-coordinates of the model. Thus, the model results finally defined in a multidimensional space including the physical space x, the time t and a number of extra-coordinates related to the model parameters. The solution of such model needs for circumventing the curse of dimensionality illness that suffer multidimensional models.     

T-Y tube model of human ascending aortic input impedance

Arterialimpedancehasitsparticularsignificancebecauseitdescribesthephysicalandgeometricalcharactersofthewholearterialsystem.Moreover.itisagoodmeasureoftheleftventricleafterload.Numerousexperimentalandtheoreticalresearchesha\'ebeendoneinthisarea.Itisshownth…     

Coupling methods between finite element–based Boussinesq‐type wave and particle‐based free‐surface flow models

We develop one‐way coupling methods between a Boussinesq‐type wave model based on the discontinuous Galerkin finite element method and a free‐surface flow model based on a mesh‐free particle method to strike a balance between accuracy and computational cost. In our proposed model, computation of the wave model in the global domain is conducted first, and the nonconstant velocity profiles in the vertical direction are reproduced by using its results. Computation of the free‐surface flow is performed in a local domain included within the global domain with interface boundaries that move along the reproduced velocity field in a Lagrangian fashion. To represent the moving interfaces, we used a polygon wall boundary model for mesh‐free particle methods. Verification and validation tests of our proposed model are performed, and results obtained by the model are compared with theoretical values and experimental results to show its accuracy and applicability.     

On the model formulations for the interaction of nonlinear waves and current

We study the model formulations of wave–current interactions in the framework of Euler equations. This work is intrigued by a recent paper from Wang et al. (2018) (hereafter WMY), which proposes such a model for the evolution of nonlinear broadband surface waves under the influence of a prescribed steady and irrotational current without vertical shear. We show that WMY’s model can be derived from a more general model accounting for an arbitrary steady and irrotational current. Under further assumption of scale separation between waves and current (i.e. horizontally slowly-varying current), WMY’s model is equivalent to an earlier model, in contrast to WMY’s claim that their model includes additional higher-order effects in wave steepness. We demonstrate the usefulness of such models in a numerical study on wave blocking by opposing current, where the nonlinear effect on the caustic location and wave amplitude amplification is elucidated. We further show that the model formulation in the framework of Euler equations form a Hamiltonian system conserving the total energy of waves and current, justifying the theoretical significance of the model equations. Finally, we generalize the formulation to nonlinear wave evolution in the presence of a rotational current with constant vorticity, which overcomes a limitation of such models that has been overlooked in previous work.