考虑内力分项贡献度的框架构件重要性评价

提出了一种水平和竖向荷载共同作用下的框架结构构件重要性评价方法。首先,基于线弹性材料假设,利用应变能方程和节点-外荷载关系计算梁柱构件的轴力、剪力和弯矩;然后,定义构件内力分项计算值与抗力分项值之比为构件分项重要性系数,用于体现构件抗力利用水平;再组合各内力分项系数,针对不同外荷载形式定义构件综合重要性系数,用于体现构件对框架体系整体承载力的贡献;最后,通过两榀框架算例验证了方法的可行性,可为框架的结构优化设计和连续性倒塌分析提供定量依据。     

A Model of Contact Forces in Pneumatic Motor Vanes

The paper presents an investigation on the dynamic equilibrium of a pneumatic motor vane. The investigation was based on an analysis of the vane's free body diagram. In particular, a model was formulated for determining the contact forces between vane, rotor and stator and the contact configuration from the known motor geometry, friction coefficients and chamber pressures. In addition, the paper presents experimental measurements of friction coefficients in vane-rotor and vane-stator contact together with a validation of the model through comparison with a FEM model.     

钴基合金刷丝与碳化铬涂层高线速度磨损行为研究

在超高速磨损试验器上开展刷式密封磨损试验,摩擦副为GH5605钴基高温合金刷丝束和喷涂碳化铬耐磨涂层的跑道试样,最高摩擦线速度达到400 m/s.利用扫描电镜和能谱分析研究了摩擦表面的磨损形貌及材料成分,发现试验后的碳化铬涂层存在材料剥落和刷丝材料附着,刷丝尖端出现以犁沟和涂抹为主要特征的磨损,且摩擦线速度达到400 m/s时出现刷丝尖端粘连和严重氧化现象.通过分析刷丝尖端磨损形貌的形成机制及摩擦表面的材料转移机理,认为刷丝尖端的主要磨损机制为二体磨粒磨损,而涂层的材料剥落现象会加剧其对刷丝的磨粒磨损作用.使用共聚焦显微镜测量了磨痕深度,并与转子离心涨大变形量进行对比分析,分析结果表明超高线速度条件下转子的离心涨大增加了刷丝束和跑道涂层间的干涉,显著加剧了摩擦副的磨损.     

Development of a one-way coupled diffraction/trapped air model for predicting wave loading on bridges under water wave attack

In recent years, a number of researchers have applied various computational methods to study the wave and tsunami forcing on bridge superstructure problems. Usually, these computational analyses have relied upon application of computational fluid dynamic (CFD) codes. While CFD models provide accurate results, their disadvantage is that they tend to be computationally expensive. Thus, it may be difficult to apply these techniques during risk assessment analyses. During this study, an alternative computational method was explored in which a previously-developed diffraction model was combined with a previously-developed trapped air model under worst-case wave loading conditions (i.e., when the water surface was at the same elevation as the bottom bridge chord elevation). The governing equations were solved using a finite difference algorithm for the case where the bridge was attacked by a single wave in two dimensions. Resultant water forces were computed using results from the diffraction/trapped air computations, and water force values were compared with data from three datasets. In general, excellent agreement between the diffraction/trapped air model and data was observed. The computational time associated with the model was only approximately one hour per bridge configuration, which would appear to be an improvement when compared with other computational techniques.     

A numerical and experimental hybrid approach for the investigation of aerodynamic forces on stay cables suffering from rain-wind induced vibration

The aerodynamic forces on a stay cable under a rain-wind induced vibration (RWIV) are difficult to measure directly in a wind tunnel test. This paper presents a hybrid approach that combines an experiment with computational fluid dynamics (CFD) for the investigation on aerodynamic forces of a stay cable under a RWIV. The stay cable and flow field were considered as two substructures of the system. The oscillation of the stay cable was first measured by using a wind tunnel test of a RWIV under an artificial rainfall condition. The oscillation of the cable was treated as a previously known moving boundary condition and applied to the flow field. Only the flow field with the known moving cable boundary was then numerically simulated by using a CFD method (such as Fluent 6.3). The transient aerodynamic forces of the stay cable with a predetermined cable oscillation were obtained from numerical calculations. The characteristics of the aerodynamic forces in the time domain and frequency domain were then analysed for various cases. To verify the feasibility and accuracy of the proposed hybrid approach, the transient aerodynamic forces were applied to a single-degree-of-freedom model (SDOF) of the stay cable to calculate the RWIV of the cable. A comparison was performed between the oscillation responses of the stay cable obtained from the calculated (SDOF model) and experimental results, and the results indicate that the hybrid approach accurately simulates the transient aerodynamic forces of the stay cable. The equivalent damping ratios induced by the aerodynamic forces were obtained for various wind speeds. Furthermore, a nonlinear model of the aerodynamic force is proposed based on the calculation results, and the coefficients in the model were identified by a nonlinear least-squares technique.     

深基坑无锚撑护壁桩变形状态及圈梁约束分析

根据成都地区某高层建筑深基坑护壁桩的实测资料,采用数值方法分析了护壁桩在基坑开挖过程中的变形规律,计算结果表明护壁桩具有柔性支护构件特征,由于圈梁对桩顶的有效约束使护壁桩的变形状态不同于悬臂构件,文中对桩顶圈梁的约束作用也进行了讨论。     

Validation of the Rayleigh–Ritz method for the postbuckling analysis of rectangular plates with application to delamination growth

Postbuckling solutions of laminated rectangular plates are obtained by the Rayleigh–Ritz method using von Karman’s nonlinear strain displacement relations and high-order polynomial expansions of the displacements. The potential energy function and the nonlinear algebraic equations governing the undetermined coefficients are obtained by Mathematica. Reasonably accurate solutions for the membrane forces, the bending and twisting moments and the pointwise energy-release rates generally require more undeterminated coefficients. Such refined postbuckling solutions show significant non-uniformity of the in-plane forces and strains and certain boundary effects characterized by concentration of the curvatures and the bending moment.     

On the propagation of one-dimensional acoustic waves in liquids

Within the framework of one-dimensional unsteady compressible flow in deformable pipes, the present work proposes expressions able to represent the stress state of a “fluid-pipe” continuous system. The coefficients needed to define the friction forces are calibrated against experimental results. The proposed expressions highlight the crucial role played by the fluid compressibility on the wave resistance.     

微纳米空间弯曲诱导的反常驱动力 —— 从泡利的魔鬼谈起

介绍了高度卷曲的微纳米物质空间诱发的反常驱动力,指出构成反常驱动力的基本要素有两个：一个是空间的弯曲程度,即曲率, 另一个是空间弯曲的不均匀程度,即曲率的梯度.     

Pressure weighted upwinding for flow induced force predictions: application to iced surfaces

This paper addresses two main topics, namely the development of a pressure‐weighted upwinding method and its application to flow induced forces on iced cylinders. Although the near‐wall convective upwinding exhibits special applicability to iced surfaces, its capabilities extend more generally to other applications. By fully linking pressure and velocity at a sub‐element level near the wall, a higher order accuracy can be obtained. Also, a non‐physical de‐coupling between pressure and velocity can be prevented. The method is developed under the context of a control‐volume‐based finite element method for 2‐D, incompressible flows. Drag and lift coefficients are predicted, based on the pressure weighted upwinding near the wall. The numerical predictions are successfully compared against experimental data, including flow induced forces on iced cables. Copyright © 2004 John Wiley & Sons, Ltd.     

Fluttering flags: An experimental study of fluid forces

Unsteady fluid forces are measured at the onset of flutter and during the post-critical flutter of flags placed in a wind tunnel, focusing on the drag force and the moment around the flagpole. The evolution of these forces during flutter mode switches, induced by varying either the mass ratio or the wind velocity, is discussed by using additional high-speed imaging. For the highest wind velocities, losses of periodicity and snapping events are reported. Time-averaged and unsteady drag coefficients are reported and compared to previous works.     

Dynamics of fibres in a turbulent flow field – A particle-level simulation technique

A particle-level simulation technique has been developed for modelling the flow of fibres in a turbulent flow field. A single fibre is conceived here as a chain of segments, thus enabling the model fibre to have all the degrees of freedom (translation, rotation, bending and twisting) needed to realistically reproduce the dynamics of real fibres. Equations of motion are solved for each segment, accounting for the interaction forces with the fluid, the contact forces with other fibres and the forces that maintain integrity of the fibre.The motion of the fluid is resolved as a combination of 3D mean flow velocities obtained from a CFD code and fluctuating turbulent velocities derived from the Langevin equation. A case of homogeneous turbulence is treated in this paper.The results obtained show that fibre flocs in air-fibre flows can be created even when attractive forces are not present. In such a case, contacts between fibres, properties of an individual fibre (such as flexibility and equilibrium shapes) and properties of the flow of the carrying fluid are shown to govern the physics behind formation and breaking up of fibre flocs. Highly irregular fibre shapes and stiff fibres lead to strong flocculation.The modelling framework applied in this work aims at making possible a numerical model applicable for designing processes involving transport of fibres by air at industrial scale.     

直立码头前船波浪力耦合计算模型

建立了外域用Boussinesq方程、内域用刚体运动方程的直立码头前二维船剖面波浪力的时 域计算耦合模型，内域与外域在交界面的匹配条件是流量连续和压力相等. 进行了相关模型 实验，并把计算结果与实验结果进行了对比. 推导了船体与水底和直立码头之间间隙内流体 运动的自振频率，研究了间隙内流体运动的共振现象.     

The computational fluid dynamics modelling of the autorotation of square,flat plates

This paper examines the use of a coupled Computational Fluid Dynamics (CFD) – Rigid Body Dynamics (RBD) model to study the fixed-axis autorotation of a square flat plate. The calibration of the model against existing wind tunnel data is described. During the calibration, the CFD models were able to identify complex period autoration rates, which were attributable to a mass eccentricity in the experimental plate. The predicted flow fields around the autorotating plates are found to be consistent with existing observations. In addition, the pressure coefficients from the wind tunnel and computational work were found to be in good agreement. By comparing these pressure distributions and the vortex shedding patterns at various stages through an autorotation cycle, it was possible to gain important insights into the flow structures that evolve around the plate. The CFD model is also compared against existing correlation functions that relate the mean tip speed ratio of the plate to the aspect ratio, thickness ratio and mass moment of inertia of the plate. Agreement is found to be good for aspect ratios of 1, but poor away from this value. However, other aspects of the numerical modelling are consistent with the correlations.     

Investigations on the porous resistance coefficients for fishing net structures

The porous media model has been successfully applied to numerical simulation of current and wave interaction with traditional permeable coastal structures such as breakwaters. Recently this model was employed to simulate flow through and around fishing net structures, where the unknown porous resistance coefficients were adjusted by fitting the available experimental data. In the present paper, a new approach was proposed to calculate the porous resistance coefficients based on the transformation of Morison type load model. The transformation follows the principle that the total forces acting on a net panel from Morison type load model should be equal to the forces obtained from the porous media model. In order to account for the interaction effects in-between the twines, two coefficients were introduced, and they were calibrated by minimizing the least square error function. Extensive validation cases were carried out to examine the performance of the numerical model. This includes steady current flow through plane net panels and circular fish cages, and wave interaction with plane net panels. A variety of fishing nets with different solidity ratios were used in the validation cases, from which it was seen that the overall agreement between the numerical and experimental results is fair.     

Stress concentration near a thin elastic inclusion under interaction with harmonic waves in the case of smooth contact

We solve the problem on the interaction of plane harmonic waves with a thin elastic plate-shaped inclusion. The ambient medium is assumed to be in plane strain. The smooth contact conditions are satisfied on both sides of the inclusion. The bending displacements of the inclusion are determined from the corresponding differential equation. In the statement of boundary conditions for this equation, one should take into account the transverse forces and bending moments applied to the lateral edges of the inclusion, while the boundary conditions are posed on the midplane of the inclusion. Using the discontinuous solution method, we reduce the problem to a system of two singular integral equations, which are solved numerically by the mechanical quadrature method. We obtain approximate formulas for the stress intensity coefficients near the ends of the inclusion and for the transverse forces and moments applied to the inclusion.     

A new model for nucleate boiling heat transfer

A new model to calculate heat transfer coefficients in nucleate boiling is presented. Heat transfer and fluid flow around a single bubble are investigated taking into account the influence of meniscus curvature, adhesion forces and interfacial thermal resistance on the thermodynamic equilibrium at the gas-liquid interface. The model requires only bubble site densities and departure diameters. Further quantities except the thermophysical properties are not needed. From the results bubble growth rates can be derived. As an example nucleate boiling heat transfer coefficients of R-114 were calculated. They agree with experimental values within the experimental accuracy.     

可渗透圆柱壳流固耦合问题的流场与内力分析

在弹性薄壳的非线性理论和流体力学基本方程的基础上,研究了可渗透圆柱壳的流固耦合问题.假定壳体具有均布孔隙且孔的面积很小,不考虑其阻力,忽略对弯曲刚度和壳体腔内流体微小运动影响,应用相容欧拉--拉格朗日法建立了带孔的圆柱壳在流体中相互作用的基本方程.通过具体算例求解,给出了流场速度与压力的变化、圆柱壳的变形及内力分布,并对相关参数进行了讨论.     

非定常短轴承油膜力公式的变分修正

本文采用了变分方法对非定常短轴承的油膜压力分布公式进行了修正，既保留了短轴承公式的简洁形式，又使其适用于大长径比轴承。得出了具有足够精度、适合轴颈大扰动情况下的有限长圆柱轴承非定常油膜力的解析公式。与差分充零算法相比，短轴承公式的结果在轴承长径比为0．6时，误差已经超过百分之二百，而本方法计算结果的误差小于百分之五。因此采用本方法既提高了短轴承油膜力公式的计算精度，又保持了油膜力公式的简洁形式，不失为进行转子-轴承系统非线性动力分析的一种有效方法。     

Linear and Nonlinear Aerodynamic Theory of Interaction between Flexible Long Structure and Wind

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