Optimum dynamic design for beam shapes subjected to a moving concentrated load

We are concerned with an optimum dynamic design of beams subjected to a moving concentrated load with constant speed. The influence of the dynamic behaviour of the beams is considered in a proposed optimum design problem. The optimum shapes of beams are determined by the minimization of two kinds of performance indices. The optimization procedure is performed by non-linear programming on the basis of the exterior penalty function and BFGS methods. Optimization is calculated by the modal coordinates transformation and the numerical integration method     

A new approach to the calculations of the limit load of steel structure supports of electric overhead lines of the highest tensions

Starting from the Lagrange equations the generalized algebraic eigenproblem has been obtained. The notions of the statical compression measure density matrix as well as the coefficient α of the statical compression measure density (α-N) of the bar finite element have been introduced. On the basis of the above formulae the limit load P of the two steel structure supports of 110 kV electric lines has been calculated using the author's own CAD system named SLEN. After solving the generalized algebraic eigenproblem, the lowest eigenvalue α₁ < 1 for all cases has been calculated. The average value of the α₁, was about 0.7. Then the calculated limit load P was about 30% lower than the real limit load P_o. For the technical conformity of the limit loads, calculated (P) and measured at the trial station (P_o), the following has been proposed:

• 1.(1) assumption of the statical compression measure density coefficient α ≠ 1,
• 2.(2) assumption of the relation α = α₁,
• 3.(3) calculation of the coefficient α₁ by the statistical identification process.

     

基于PCL的三维流体载荷向结构载荷转换方法

为在MSC Patran中实现三维流体载荷向结构载荷的转换,分别基于反距离加权（InverseDistance Weighted,IDW）插值法和薄板样条（Thin Plate Spline,TPS）法,用PCL编写载荷转换程序.在MSC Patran中通过创建空间场来调用该程序,再通过创建压力载荷来调用所创建的空间场,从而实现转换.用该程序对内部受流体压力的管道进行结构分析,结果表明IDW插值法和TPS法都能很好地实现载荷转换,运算耗时相当;使用IDW插值法时,若插值点过多则会降低插值精度.     

Optimum design of Beck's column with a constraint on the static buckling load

The paper is concerned with optimization of a damped column subjected to a follower load. The aim is to determine the colum of least volume which has the same critical load as a uniform reference column. The stability analysis is based on the finite element method. The optimization problem is solved by sequential linear programming. By only including a constraint on the flutter load in the volume minimization, a very large volume reduction is possible but the static buckling load (by a pure conservative loading) becomes very small.In applications, it may be important that the optimal column also is capable of supporting a conservative load. Consequently, the volume is minimized with constraints on both the flutter load and the static buckling load. The constraint on the buckling loadp _b has the formp _b ^opt cp _b ⁰ , 0c1, where the upper index opt refers to the optimal design while the upper index 0 refers to the uniform initial design. It is found that, as the constantc approaches 1, the optimal column approaches the optimal Euler column of Tadjbakhsh and Keller (1962).Notation c slack parameter on the constraint on the static buckling load; defined by (9) - c _int,c _ext dimensionless internal and external damping parameters defined by (3) - d _j eigenvalue margin defined by (9) - d vector of time-independent nodal displacements and rotations - _e length of thee-th finite element - L total length of the column - vector of element lengths defined by (11) - m, m(x) mass distribution function - m _i design variables; the mass distribution function evaluated at the nodal points - upper and lower bounds on the design parameters - m design vector with elementsm _i - M mass matrix - N _e the number of finite elements used - p load parameter - Q load matrix - S stiffness matrix - t time - x distance along the column, measured from the clamped end - y lateral deflection of the column - y vector of nodal displacements and rotations - complex eigenvalue - b refers to buckling (static instability by conservative loading) - d refers to divergence (static instability by nonconservative loading) - f refers to flutter (dynamic instability by nonconservative loading)     

Using cognitive load theory to structure computer‐based learning including MOOCs

A massive, open, online course (MOOC) is a form of computer‐based learning that offers open access, internet‐based education for unlimited numbers of participants. However, the general quality and utility of MOOCs has been criticized. Most MOOCs have been structured with minimal consideration of relevant aspects of human cognitive architecture and instructional design principles. This paper suggests cognitive load theory, with its roots embedded in our knowledge of human cognitive architecture and evolutionary educational psychology, is ideally placed to provide instructional design principles for all forms of computer‐based learning, including MOOCs. The paper outlines the theory and indicates instructional design principles that could be used to structure online learning and to provide an appropriate base for instructional design when using computer‐based learning.     

Optimum target stiffness allocation for design of a reinforcing member on an existing structure

Structural and Multidisciplinary Optimization - The reinforcing members are often added on an existing structure to improve stiffness of the structure up to required level. In general, the design...     

采用十进制最佳个体置换遗传算法求解高校排课问题

本文分析了高校排课问题,建立了其数学优化模型,构建了它的基本求解框架。针对高校排课问题的特点,引入遗传算法,设计了多种改进方案,包括十进制编码方案、初始种群生成方案、适应度函数设计方案、最佳个体置换策略、自适应交叉概率和自适应变异概率设计方案。仿真结果表明,该算法能够满足高校排课问题的多重约束条件,能更有效地解决高校排课问题。     

Extension of a uniform canopy reflectance model to include row effects

The reflectance model for a uniform crop canopy is extended to include the effects of crops planted in rows. The effect of row structure is assumed to be caused by the variation in density of vegetation across rows rather than to a profile in canopy height. The calculation of crop reflectance using vegetation density modulation across rows follows a parallel procedure to that for a uniform canopy. Predictions using the row model for wheat show that the effect of changes in sun to row azimuth are greatest in Landsat Band 5 (red band) and can result in underestimation of crop biomass.     

The nonlinear behaviour of a slender flexible cylinder pinned or clamped at both ends and subjected to axial flow

The nonlinear dynamics of a slender flexible cylinder subjected to axial flow is studied when both its ends are either pinned or clamped, particularly focusing on the post-critical behaviour. In both cases, the system is stable at low flow velocities until the critical flow for divergence, at which point the initial equilibrium position of the cylinder becomes unstable and a new stable buckled solution arises (together with its symmetric counterpart). The amplitude of the buckled solution increases with the flow velocity. At higher flow, the buckled stationary cylinder loses stability by a Hopf bifurcation, after which a periodic solution arises. The frequency of oscillation after this Hopf bifurcation, in the case of a pinned–pinned cylinder, is almost twice as high as that in the clamped–clamped case, due to the dynamic loss of stability in a higher mode in the former case. The periodic solution is followed by a period-doubling bifurcation, giving rise to period-2 oscillations. The system undergoes a torus bifurcation afterward, followed by quasiperiodic and chaotic oscillations at higher flow velocities. All the critical flow velocities for the pinned–pinned cylinder are smaller than those for the clamped–clamped one. In the case of a pinned–pinned cylinder, at still higher flow velocities, there exists a range of flow velocities in which chaotic and static solutions co-exist; this has not been observed in the clamped–clamped case.     

Postural load during VDU work: a comparison between various work postures

The aim of this study was to compare the postural load during VDU work in the following work postures: (1) Supporting and not supporting the forearms on the table top, (2) Sitting and standing positons, and (3) Sightline to the centre of the screen at an angle of 15 and 30 below the horizontal. The muscle load from the upper part of musculus trapezius and from the lumbar part of musculus erector spinae (L3 level) was measured by electromyography (EMG). Postural angles of head, upper arm and back were measured by inclinometers. The load on m. trapezius when using the keyboard was significantly less in sitting with supported forearms compared to sitting and standing without forearm support. Further, the time and number of periods when the trapezius load was below 1% MVC was significantly greater with support versus no support. The load on the right erector spinae lumbalis was also significantly less and the time when the load was below 1% MVC was significantly longer in a sitting work position with support versus standing without support. In addition, when using a mouse supporting the forearms reduced the static trapezius load in sitting. The results from this study document clearly the importance of giving the operator the possibility of supporting the forearms on the table top.     

Lumbar motion response to a constant load velocity lift

An experiment was performed to evaluate the motions of the lumbar spine during a constant load velocity lift. For the purposes of this study, a constant load velocity refers to the linear vertical velocity of the load. This vertical load velocity was controlled using a modified angular isokinetic dynamometer, which produced linear isokinetic motion during a lift. A lumbar monitor was used to observe the position, velocity, and acceleration changes that occurred in the lumbar spine during the lifting task. The results indicate that under constant load velocity conditions, significant angular accelerations occur at the lumbar level. The nature of these accelerations was found to depend on several variables associated with a lifting task, such as the load velocity and the asymmetry of the lift. The physical significance of these results would be increased spinal loading above that which would be predicted using a static model.     

基于自适应多核潜结构映射选择性集成模型的磨机负荷参数预测

磨机负荷参数是影响选矿流程产品质量和产量的难以检测关键过程变量.磨机研磨产生的多源机械信号频谱与磨机负荷参数间存在复杂的非线性映射关系.核潜结构映射(KPLS)算法适合构建基于频谱数据的磨机负荷参数预测(MLPF)模型.针对上述难点,本文提出一种面向MLPF的自适应多核潜结构映射选择性集成(SEN)模型.首先,基于经验模态分解(EEMD)和时频变换技术处理多源机械信号,得到基于不同时间尺度候选子信号的频谱数据;接着,采用KPLS和分支定界选择性集成(BBSEN)算法,构建基于多尺度频谱的候选子子模型和SEN子模型;最后,从候选子子模型和SEN子模型中优选获得不同时间尺度的候选子信号模型,并再次采用BBSEN算法优选集成子信号模型并加权组合,构建最终的MLPF模型.基于实验球磨机的实际运行数据仿真验证了所提方法的有效性.     

Optimum design of a controlled cable stayed bridge subject to earthquakes

This paper describes a formulation to optimize the dynamic behavior of an integrated cable-stayed bridge and control strategy system during seismic events. The dynamic analysis uses an analytical solution and accounts for spatial variability, sensor placement and actuator delay. The optimization algorithm deals with model geometry, deck sections and control algorithm as design variables. Control devices were used to improve the dynamic properties and energy dissipation.     

变速移动弹簧阻尼质量系统作用下梁的动态响应

为了分析移动载荷作用下梁的动态响应问题,建立了移动振动质量系统作用下梁的动力学模型,推导出带有附加矩阵和附加向量的时变动力学耦合方程,并整理成便于数值求解的二阶微分方程组,通过与移动力模型和移动质量模型的比较,验证了这一方法的可行性,在算例中比较了移动载荷不同运动情况下梁的挠度、弯矩和剪力动载系数.