A method for system identification using the optimality criteria optimization approach

An algorithm similar to the optimality criteria approach used in structural optimization is presented for identifying stiffnesses of structural members by using vibration test data. A set of equivalent static inertia forces are obtained from the vibration analysis using d'Alembert's principle and are used to solve the multiple displacement constraint problem. The displacement constraint values are specified based on the measured experimental modal displacement data at critical locations. The algorithm is used to find the changes needed in the stiffnesses of the elements and the distribution of nonstructural mass of the nominal analytical model to correlate the analytical and experimental data. The algorithm alternates between the vibration analysis and static analysis to find the equivalent load vector and modify the stiffnesses. The identified stiffness properties of the structural elements can be used to control and study the dynamic response of the structure.     

Dissipative particle dynamics simulation of shear flow in a microchannel with a deformable membrane

Thin deformable membranes are encountered in a number of microfluidics-based applications. These are often employed for enhancing sorting, mixing, cross-diffusion transport, etc. Microfluidic systems with deformable membranes can be better understood by employing simple models and efficient computational procedures. In this paper, we present a dissipative particle dynamics model to simulate the interaction between a deformable membrane and fluid flow in a two-dimensional microchannel. The membrane is modeled as a bead-spring system with both extensional and torsional springs to simulate extensional stiffness and bending rigidity, respectively. By performing detailed simulations on a membrane pinned at both ends and oriented parallel to the flow, we observe different steady state conformations. These membrane deflections are found to be relatively large for low bending stiffnesses and small for high stiffnesses. The membrane was found to exhibit a simple bowing out mode for high stiffness values and more complex conformations at lower stiffnesses.     

An equivalent layer sandwich panel model

An equivalent layer method for modeling sandwich panels with thin laminated composite facings and honeycomb cores is presented. It avoids the need for separate face sheet and core representations. The equivalent layer is given Mindlin plate behavior and it reproduces the face sheet midsurface strains and displacements, while matching the strain energy and work of external loads. The equivalent layer also matches the eight resultants of stress in the sandwich panel. This article starts with a derivation of the sandwich panel strain energy and the inherent bending, stretching, and transverse shearing stiffnesses. It is then shown that the available equivalent layer stiffness parameters can be used for exact matching if the sandwich has a special neutral surface. Therefore, the equivalent layer can be used for linear or geometrically nonlinear analyses for in-plane and out-of-plane loads. Examples are given illustrating two general types of sandwich panels for which exact equivalence is possible. Included are equivalent layer linear response calculations using finite element computer code ADINA.     

大范围运动矩形板动力刚化分析

针对大范围运动下弹性矩形板，采用有限元技术和Lagrange方程建立了系统刚柔耦合一次近似动力学方程组．不同于传统动力学建模方法，本文采用两个弧长变量和一个笛卡尔坐标变量来描述板的变形，利用有限元方法离散，在动力学方程中得到了动力刚度项．数值仿真表明，在大范围运动下，传统的动力学模型不能正确的预示系统动力学行为；而本文动力学模型能够较好的预测系统的动力学行为，且比采用假设模态离散板变形的方法更为精确．     

Sensitivity of structural joint stiffnesses with respect to beam properties: A hybrid approach

In the optimization of frame structures the sizes of the beam members change, as do the stiffnesses of the joints where such members meet. In this paper a method for calculating the design sensitivities of structural joints to changes in the size of the members, using a finite element formulation, is presented. The method uses the initial joint stiffness, predicted from a more detailed shell finite element model or experimental data, to calculate the design sensitivies for any number of joint members. The method is developed into a computer program that does not require a finite element model of the joint. The formulation of the method and a test case are presented.     

Robot link and contact surface dynamic interaction: An experimental study of contact task instability

In this article we explore, both theoretically and experimentally, the effect of multiple structural compliance sources on robot stability during contact task execution. Here we examine the effect of link compliance and compliance of the contact surface on overall system stability. Using the theory associated with singularly perturbed dynamic systems, the stability of the robotic system is examined for three distinct cases: (1) link stiffness much greater than contact surface stiffness; (2) contact surface stiffness much greater than link stiffness; and (3) link stiffness comparable to surface stiffness. Theoretical results lead to a conclusion of stability only for case (1). Experiments indicate stable behavior for all these cases. Through the use of singular perturbation modeling and analysis, we are able to write dynamic models of the robot during contact with a complaint surface such that the complaint behavior of the robot links and contact surface are parameterized with just two variables. In doing so, theoretical examination and experimental study of stability, or the lack thereof, is greatly simplified. Instead of exhaustive tests in which experiments or stability analyses are conducted over a wide range of values of link and contact surface compliance, a select number of cases are examined. Under the assumptions that validate the use of singular perturbation modeling techniques, the resultant stability analysis and experimental results are hence conducted in an efficient manner. © 1997 John Wiley & Sons, Inc.     

Finite element free vibration analysis of damped stiffened panels

Free vibration characleristics of a damped stiffened panel with applied viscoelastic damping on the flanges of the stiffeners are studied using finite element method. The complex nature of the rotational and transverse stiffnesses of the stringers is taken into consideration while deriving the stiffness and mass matrices of the damped stiffener element. The finite element method consists of representing the panel by rectangular plate elements of 12 d.o.f. and the stiffeners by beam elements of 8 d.o.f. which allow for bending, torsional and warping effects. Numerical results showing the effect of the geometric and material properties of the damping layer treatment on the resonant frequencies and loss factors of the composite panel are presented.     

民用飞机结构强度设计中的全机精细有限元 分析技术及其应用

借助大型计算机云计算资源,最大程度地保留结构细节特征进行全机精细有限元建模,并应用于大型民用飞机全机静力试验数值模拟仿真计算。全机精细有限元模型仿真数据与试验数据的对比结果表明：与传统的内力求解等效刚度有限元模型相比,精细模型在结构应力、稳定性和连接强度的计算精度方面具有独特优势。对全机精细有限元模型的建模特点、精度优势和技术难点进行剖析,探讨其在民用飞机结构强度设计中的应用前景。     

Study on visual machine-learning on the omnidirectional transporting robot

We present a computer vision solution integrated to an omnidirectional transporting robot to perform the position tracking of multiple trays moving on its planar acrylic plate surface. The trays were designed to carry lightweight materials on top of their surface so that the mechanism could be implemented as an automated transporting system for applications that require the displacement of products and/or materials in any given space. One hurdle faced by the visual system for suitable detection was the partial occlusion of the image of a tray when placing arbitrary objects on its surface. Our strategy to overcome this challenge consisted on the implementation of machine learning algorithms, such as Support Vector Machines (SVM), using datasets of images containing trays with different occlusion patterns for fast object detection through rigorous training. The results of experimental tests validate the implementation of our proposal as a reliable approach for the object tracking of multiple trays on the robotic device, even under partial occlusion. We also studied the accuracy of the position measurements performed by our visual system with respect to the position measurements taken by the OPTITRACK motion capture system and evaluated the processing time per frame required by the software implementation.     

板式气体吸收塔干板开车动态模拟方法

提出板式气体吸收塔干板开车动态模拟法,编写了用于求解板式气体吸收塔干板开车常微分方程组的MATLAB程序,并举例说明。本数学模型作了理论板、等温操作、恒摩尔持液假定,忽略持气量和塔板上的流体流动动态行为;针对开车实际过程,塔板一面从上到下逐板充液,一面逐一扩展常微分方程数,并巧妙地赋以各板常微分方程的积分初值,使动态解亦得以随时更新,直至塔底最后一板充液完成并顺利得出稳态解。本模型对于化学工程师了解板式气体吸收塔开车过程中塔板上持液量、液相组成和气相组成动态变化的细节具有重要意义。     

Evaluation of criteria for selecting temperature control trays in distillation columns

The use of tray temperatures to infer compositions is widespread in distillation control. A number of criteria have been proposed for selecting which trays to hold at constant temperature. The most commonly used are (1) choosing a tray where there are large changes in temperature from tray to tray (“slope” of the temperature profile), (2) finding the tray where there is the largest change in temperature for a change in the manipulated variable (“sensitivity”), (3) using singular value decomposition (SVD) analysis, (4) selecting the tray where the temperature does not change as feed composition changes while producing the desired distillate and bottoms purities and (5) choosing the tray that produces the smallest changes in product purities when it is held constant in the face of feed composition disturbances.This paper provides a quantitative comparison of the effectiveness of these five alternative criteria. Several systems are considered, ranging from ideal binary to azeotropic multi-component. Results show that SVD analysis provides a simple and effective method for selecting temperature control tray location.     

Scheduling shipments in closed-loop sortation conveyors

At the very core of most automated sorting systems— for example, at airports for baggage handling and in parcel distribution centers for sorting mail—we find closed-loop tilt tray sortation conveyors. In such a system, trays are loaded with cargo as they pass through loading stations, and are later tilted upon reaching the outbound container dedicated to a shipment’s destination. This paper addresses the question of whether the simple decision rules typically applied in the real world when deciding which parcel should be loaded onto what tray are, indeed, a good choice. We formulate a short-term deterministic scheduling problem where a finite set of shipments must be loaded onto trays such that the makespan is minimized. We consider different levels of flexibility in how to arrange shipments on the feeding conveyors, and distinguish between unidirectional and bidirectional systems. In a comprehensive computational study, we compare these sophisticated optimization procedures with widespread rules of thumb, and find that the latter perform surprisingly well. For almost all problem settings, some priority rule can be identified which leads to a low-single-digit optimality gap. In addition, we systematically evaluate the performance gains promised by different sorter layouts.     

飞行器空气舵系统的高效刚度分配优化方法研究

空气舵系统是飞行器典型操纵部件,其伺服作动器、连杆、摇臂、舵轴和舵面等子结构对空气舵系统的整体刚度有着不同程度的贡献,合理分配各子结构的刚度,可使空气舵系统的整体刚度得到进一步优化.本文提出了一种基于多体系统传递矩阵法和遗传算法相结合的空气舵系统高效刚度分配优化方法.首先,基于多体系统传递矩阵法建立了以结构尺寸和材料属性为参数的高效结构动力学计算模型,仿真结果表明,基于该计算模型所预测的空气舵第一阶俯仰模态固有频率与商业软件计算结果的误差仅为1.06%.其次,基于本文建立的高效结构动力学计算模型对各子结构刚度对空气舵系统动力学特性的贡献进行了灵敏度分析,给出了各部件对系统固有频率贡献的规律.最后,采取将遗传算法和多体系统传递矩阵法相结合的思路,以所建立的空气舵高效结构动力学模型为适应度函数,各子部件尺寸作为待优化变量,空气舵系统整体质量为约束条件,对空气舵系统各个子结构的刚度分配进行了优化.优化结果表明,在保持空气舵系统整体重量不变的条件下,可将空气舵系统第一阶俯仰模态固有频率提高约15.8%.     

Qualitative models of seat discomfort including static and dynamic factors

Judgements of overall seating comfort in dynamic conditions sometimes correlate better with the static characteristics of a seat than with measures of the dynamic environment. This study developed qualitative models of overall seat discomfort to include both static and dynamic seat characteristics. A dynamic factor that reflected how vibration discomfort increased as vibration magnitude increased was combined with a static seat factor which reflected seating comfort without vibration. The ability of the model to predict the relative and overall importance of dynamic and static seat characteristics on comfort was tested in two experiments. A paired comparison experiment, using four polyurethane foam cushions (50, 70, 100, 120 mm thick), provided different static and dynamic comfort when 12 subjects were exposed to one-third octave band random vertical vibration with centre frequencies of 2.5 and 5.5 Hz, at magnitudes of 0.00, 0.25 and 0.50 m x s(-2) rms measured beneath the foam samples. Subject judgements of the relative discomfort of the different conditions depended on both static and dynamic characteristics in a manner consistent with the model. The effect of static and dynamic seat factors on overall seat discomfort was investigated by magnitude estimation using three foam cushions (of different hardness) and a rigid wooden seat at six vibration magnitudes with 20 subjects. Static seat factors (i.e. cushion stiffness) affected the manner in which vibration influenced the overall discomfort: cushions with lower stiffness were more comfortable and more sensitive to changes in vibration magnitude than those with higher stiffness. The experiments confirm that judgements of overall seat discomfort can be affected by both the static and dynamic characteristics of a seat, with the effect depending on vibration magnitude: when vibration magnitude was low, discomfort was dominated by static seat factors; as the vibration magnitude increased, discomfort became dominated by dynamic factors.     

Dynamic analysis and control of sieve tray gas absorption column using MATALB and SIMULINK

The present work highlights the powerful combination of SIMULINK/MATLAB software as an effective flowsheeting tool which was used to simulate steady state, open and closed loop dynamics of a sieve tray gas absorption column. A complete mathematical model, which consists of a system of differential and algebraic equations was developed. The S-Functions were used to build user defined blocks for steady state and dynamic column models which were programmed using MATLAB and SIMULINK flowsheeting environment. As a case study, the dynamic behaviour and control of a sieve tray column to absorb ethanol from CO₂ stream in a fermentation process were analysed. The linear difference equation relating the actual and equilibrium gas phase compositions was solved analytically to relate the actual gas phase composition to the liquid phase with Murphree tray efficiency as a parameter. The steady state mathematical model was found to be nonlinear (w.r.t. number of stages) due to the introduction of the Murphree tray efficiency. To avoid the solution of large linear algebraic system, a sequential steady state solution algorithm was developed and tested through the idea of tearing the recycle stream in the closed loop configuration. The number of iterations needed to achieve a given tolerance was found to be function of the Murphree tray efficiency. The open-loop dynamic analysis showed that the gas phase composition response was nonlinear with respect to the inlet gas flow rate, while it was linear with respect to inlet gas composition. The nonlinearity increased along the column height and was maximum at the top tray. On the other hand, the Murphree tray efficiency had little effect on the dynamic behaviour of the column. The controlled variable was found to exhibit fairly large overshoots due to step change in the inlet gas flow rate, while the PID controller performance was satisfactory for step change in the inlet gas composition. The closed-loop dynamic analysis showed that the controlled variable (outlet gas phase composition) had a fairly linear dynamics due to step changes in the set point.     

Microgimbal torsion beam design using open, thin-walled crosssections

A thin-film micromolding process enabled the construction of microtorsional springs with unique cross-sectional designs by combining high-aspect-ratio beams with horizontal surface features. Cross sections such as T-bars, pi sections, and channels were utilized in creating torsional springs with low torsional stiffnesses and high in- and out-of-plane bending stiffnesses. Experimental modal analysis was used to determine torsional stiffnesses as low as 0.13 μN·m/deg with T-bar springs 45 μm tall, 50 μm wide, and 100 μm long. Springs of the same outer dimensions but with solid rectangular cross sections were calculated to have torsional stiffnesses of at least two orders of magnitude greater. Several microgimbals were constructed using the thin-film micromolding process with various torsional spring designs. Modal analysis was used to experimentally determine pitch and roll natural frequencies. Torsional stiffness models for open, thin-walled sections that included warping effects were developed and used to analytically predict the torsional natural frequencies of tested spring designs to within 20%     

Qualitative models of seat discomfort including static and dynamic factors

Judgements of overall seating comfort in dynamic conditions sometimes correlate better with the static characteristics of a seat than with measures of the dynamic environment. This study developed qualitative models of overall seat discomfort to include both static and dynamic seat characteristics. A dynamic factor that reflected how vibration discomfort increased as vibration magnitude increased was combined with a static seat factor which reflected seating comfort without vibration. The ability of the model to predict the relative and overall importance of dynamic and static seat characteristics on comfort was tested in two experiments. A paired comparison experiment, using four polyurethane foam cushions (50, 70, 100, 120 mm thick), provided different static and dynamic comfort when 12 subjects were exposed to one-third octave band random vertical vibration with centre frequencies of 2.5 and 5.5 Hz, at magnitudes of 0.00, 0.25 and 0.50 m.s^-2 rms measured beneath the foam samples. Subject judgements of the relative discomfort of the different conditions depended on both static and dynamic characteristics in a manner consistent with the model. The effect of static and dynamic seat factors on overall seat discomfort was investigated by magnitude estimation using three foam cushions (of different hardness) and a rigid wooden seat at six vibration magnitudes with 20 subjects. Static seat factors (i.e. cushion stiffness) affected the manner in which vibration influenced the overall discomfort: cushions with lower stiffness were more comfortable and more sensitive to changes in vibration magnitude than those with higher stiffness. The experiments confirm that judgements of overall seat discomfort can be affected by both the static and dynamic characteristics of a seat, with the effect depending on vibration magnitude: when vibration magnitude was low, discomfort was dominated by static seat factors; as the vibration magnitude increased, discomfort became dominated by dynamic factors.     

Transmission of vibration through glove materials: effects of contact force

This study investigated effects of applied force on the apparent mass of the hand, the dynamic stiffness of glove materials and the transmission of vibration through gloves to the hand. For 10 subjects, 3 glove materials and 3 contact forces, apparent masses and glove transmissibilities were measured at the palm and at a finger at frequencies in the range 5–300 Hz. The dynamic stiffnesses of the materials were also measured. With increasing force, the dynamic stiffnesses of the materials increased, the apparent mass at the palm increased at frequencies greater than the resonance and the apparent mass at the finger increased at low frequencies. The effects of force on transmissibilities therefore differed between materials and depended on vibration frequency, but changes in apparent mass and dynamic stiffness had predictable effects on material transmissibility. Depending on the glove material, the transmission of vibration through a glove can be increased or decreased when increasing the applied force.

Practitioner summary: Increasing the contact force (i.e. push force or grip force) can increase or decrease the transmission of vibration through a glove. The vibration transmissibilities of gloves should be assessed with a range of contact forces to understand their likely influence on the exposure of the hand and fingers to vibration.     

Bandgap analysis of a tunable elastic-metamaterial-based vibration absorber with electromagnetic stiffness

Vibration is a mechanical phenomenon and exists throughout society. The vibrations in daily life would cause emotional discomfort as well as physical fatigue. Vibration even can give a life threat depending on its magnitude. Vibration is one of the significantly important factors to consider for the safety of the overall society, and therefore study of vibration reduction is indispensable. This paper presents a novel tunable electromagnetic vibration absorber based on an elastic metamaterial. The electromagnetic vibration absorber is a lattice structure dynamic model comprising elastic metamaterial unit cells having negative refractive index property and interconnected by springs. To verify the tunability of the elastic-metamaterial-based vibration absorber, the electromagnetic stiffness change in a finite element (FE) model of the electromagnet was analyzed through a parametric study of the air gap size, internal composition of the electromagnet, and amount of current. The conditions under which the electromagnet generates the highest electromagnetic stiffness were also explored. Each different value of electromagnetic stiffness obtained from the parametric studies was used for FE analysis of the dynamic model to investigate the influence on bandgap variations. The results reveal that the variation of electromagnetic stiffness has an effect on the location and bandwidth of bandgap. Moreover, vibration reduction was achieved due to the structural aspects of the dynamic model and the negative refractive index property of the elastic metamaterial. It is demonstrated that the elastic metamaterial vibration absorber is tunable in real time with the change of electromagnetic stiffness and has vibration reduction effect in various frequency ranges.