Numerical analysis and computations of a high accuracy time relaxation fluid flow model

We present a numerical study based on continuous finite element analysis for a time relaxation regularization of Navier–Stokes equations. This regularization is based on filtering and deconvolution. We study the convergence of the regularized equations using a fully discretized filter and deconvolution algorithm. Velocity and pressure error estimates and the L ₂ Aubin–Nitsche lift technique are proved for the equilibrium problem, and this analysis is accompanied by the velocity error estimate for the time-dependent problem, too. Thus, optimal error estimates in L ₂ and H ¹ norms are derived and followed by their computational verification. Also, computational results of the vortex street are presented for the two-dimensional cylinder benchmark flow problem. Maximum drag and lift coefficients and difference in pressure between the front and back of the cylinder at the final time were investigated as well, showing that the time relaxation regularization can attain the benchmark values.     

Weighted archetypal analysis of the multi-element graph for query-focused multi-document summarization

Most existing research on applying the matrix factorization approaches to query-focused multi-document summarization (Q-MDS) explores either soft/hard clustering or low rank approximation methods. We employ a different kind of matrix factorization method, namely weighted archetypal analysis (wAA) to Q-MDS. In query-focused summarization, given a graph representation of a set of sentences weighted by similarity to the given query, positively and/or negatively salient sentences are values on the weighted data set boundary. We choose to use wAA to compute these extreme values, archetypes, and hence to estimate the importance of sentences in target documents set. We investigate the impact of using the multi-element graph model for query focused summarization via wAA. We conducted experiments on the data of document understanding conference (DUC) 2005 and 2006. Experimental results evidence the improvement of the proposed approach over other closely related methods and many of state-of-the-art systems.     

A lift simulation prototype

We present a simple simulation of lift (or elevator) operation that has been developed as a prototype to address the need for the development of such systems. We first define the type of simulation that has been developed as a discrete-event, dynamic, stochastic simulation. To do this, we present an overview of pertinent research in computer simulation, and identify some ambiguity in the use of terminology. We then describe the system that we have developed. Next we discuss the decisions taken in its realization, which are related to our research overview, and end by identifying some areas that we feel warrant further development. We believe that such a simulation can provide an important tool for the designers of lift systems. This prototype demonstrates its feasibility.     

Prediction of the maximum acceptable weight of lift from the frequency of lift

It is known that maximum acceptable weight of lift (MAWL) decreases as the frequency of lifting increases. The purpose of this study was to quantify the relationship between lifting frequency and the MAWL, and to generate models for predicting the mean MAWLs for males and females from frequency of lifting. Published experimental studies that have reported the MAWL at different lifting frequencies were identified and regression methods were used to evaluate the relationship between the frequency of lifting and the MAWL. The best fitting models were logarithmic but they accounted for less than 50% of the variance. This reflects the heterogeneity of the experiments included. Normalising the MAWL to the MAWL at one lift per minute improved the predictive power of the models, accounting for more than 80% of the variance. Linear and power models for predicting work rate in kg/min showed even higher levels of accuracy.     

Precision markedly attenuates repetitive lift capacity

This study investigated the effect of precision on time to task failure in a repetitive whole-body manual handling task. Twelve participants were required to repetitively lift a box weighing 65% of their single repetition maximum to shoulder height using either precise or unconstrained box placement. Muscle activity, forces exerted at the ground, 2D body kinematics, box acceleration and psychophysical measures of performance were recorded until task failure was reached. With precision, time to task failure for repetitive lifting was reduced by 72%, whereas the duration taken to complete a single lift and anterior deltoid muscle activation increased by 39% and 25%, respectively. Yet, no significant difference was observed in ratings of perceived exertion or heart rate at task failure. In conclusion, our results suggest that when accuracy is a characteristic of a repetitive manual handling task, physical work capacity will decline markedly.

Practitioner Summary: The capacity to lift repetitively to shoulder height was reduced by 72% when increased accuracy was required to place a box upon a shelf. Lifting strategy and muscle activity were also modified, confirming practitioners should take into consideration movement precision when evaluating the demands of repetitive manual handling tasks.     

Automation and optimization in crane lift planning: A critical review

Safe and efficient crane operations play a significant role in successful delivery of construction projects, and thus meticulous planning of crane lifts becomes increasingly critical. Crane lift planning involves a series of complex decisions to be made, while satisfying a wide range of criteria and constraints. Conventionally, making these decisions is time-consuming and to a large extent relies on the planner’s experience. To make more informed and optimized planning decisions, past research works investigated various automated planning techniques and optimization algorithms. However, most studies focus on an individual planning decision or a particular lifting scenario, which makes the findings hard to be generalized. Thus, the knowledge in lift planning is rather fragmented and the state-of-the-art in lift planning is not explicitly presented. This study, therefore, aims to conduct a critical review and assessment on the literature on crane lift planning automation and optimization and to establish a solid foundation to inform future research. It first presents an overview of the literature in crane lift planning with respect to the planning decision and the type of cranes the studies focus on. Secondly, for each lift planning decision, the assumptions, objectives, decision variables, and constraints are formulated based on the literature and analyzed from the perspectives of problem formulation coherence. Furthermore, each problem-solving method is evaluated with regard to a tri-axial evaluation diagram to allow an in-depth discussion on the efficacy and practicality of planning results. Finally, based on the discussion and existing literature, a BIM-based lift planning framework is presented and future research directions are recommended to further improve the effectiveness and efficiency of lift planning practice.     

无线收发芯片nRF401在施工升降机控制系统中的应用

nRF401为单片无线收发芯片，施工升降机是高层建筑施工必备的运输设备之一，施工升降机自动控制系统包括楼层呼叫信号系统和吊笼主控系统。利用nRF401芯片很好地解决了施工升降机楼层呼叫信号系统与吊笼主控系统之间的信号传输及两吊笼主控系统之间运输协调．提高了施工升降机的运输效率。     

适于硬件实现的二维小波提升结构的优化设计

在提升算法的基础上,设计了一种有效利用存储器资源的二维小波提升结构,此结构是根据奇数长度对称滤波器的特点简化得到的,使用它一次只需缓存六行数据就可以做完垂直提升生成一个垂直低通行和一个垂直高通行,再做水平方向的提升就生成了LL,HL,LH和HH四个子带行。这种结构可以大大减少存储器的消耗。另外本文又采用一种避免内存碎片产生的存储器申请算法,即先集中登记需要使用的内存总量,再统一分配一块连续地址的空间。     

压差测量仪在水泵扬程测试中的应用

介绍了用压差测量仪测试水泵扬程的方法。给水泵站中的水泵经过长时间的运行 ,由于叶轮受到磨损 ,水泵实际扬程已达不到其理论扬程 ,所以在管网水力计算以及现状分析时要测试水泵的实际扬程。压差测量仪具有很高的测量精度 ,通过所测压差可以准确地计算出水泵的实际扬程。     

压力传感器在升降式运输车称重系统中的应用

介绍了采用压力传感器来检测货物质量的方法,在阐述了压力传感器检测原理和框架车称重原理之后,根据现场测试数据进行了曲线拟合,并建立了称重的数学模型,提出了称重系统硬件和软件的具体实现方法。试验表明:在测量范围内,检测误差为0.6~0.8 t,符合设计要求。     

Obesity does not reduce maximum acceptable weights of lift

The maximum acceptable weights of lift (MAWL) of obese and non-obese participants were empirically investigated. Three obesity levels were considered: non-obese (18.5 kg/m(2)< or= body mass index (BMI)or= 40 kg/m(2)). Ten male and 10 female participants were recruited for each obesity level. The participants determined their MAWL for 18 different lifting task conditions (six lifting frequencies x three lifting heights). An analysis of variance (ANOVA) was conducted to determine the effects of obesity level, gender, lifting height, lifting frequency and their interactions on MAWL. Overall, the ANOVA results indicated that obesity does not reduce MAWL, and thus, suggested that the existing MAWL data can be used to accommodate both general and obese workers. However, further studies based on the biomechanical and physiological approaches are required to provide more complete understanding of obesity effects on lifting tolerance limits.     

基于自适应GOP的三维提升小波视频编码技术

在三维提升视频编码框架中,视频运动场景切换时相邻视频帧之间的时间相关性将显著减弱,使得解码视频图像在场景切换处质量急剧下降.针对这一问题,提出了一种新的基于视频亮度分量的场景切换检测方法,并根据场景切换自适应分配图像组(groupof picture GOP)大小.实验结果表明,该自适应分配GOP策略有效提高了三维提升小波视频图像的编解码质量,降低了场景切换对视频编码的影响.     

Three-dimensional MHD high-resolution computations with CWENO employing adaptive mesh refinement

Until recently, numerical simulations of discontinuities in highly super-Alfvénic plasmas have been severely limited by comparatively crude resolution and accuracy. Significant progress in the numerical simulation of such plasmas was achieved with the recently implemented Central Weighted Essentially Non-Oscillatory (CWENO) scheme. Combining this technique with that of adaptive mesh refinement (AMR), we have developed a third-order numerical scheme, which is able to efficiently capture strong gradients on spatial scales being small compared to the overall scale of the plasma system considered. Here, we first describe important algorithmic aspects of the scheme as well as the physics included in it. Second, we present the results of various performance tests. And, third, we illustrate its application to ‘real world problems’ using the example of the dynamics of a Sedov-type explosion.     

Scissor lift with real-time self-adjustment ability based on variable gravity compensation mechanism

Most robots involved in vertical movement against gravitation require actuators large enough to support their own weight. To improve the inherent safety of such robots against the large actuators and reduce their energy consumption, numerous gravity compensation mechanisms (GCMs) have been proposed. Our previous study proposed a variable GCM (VGCM) that uses two types of springs and can adjust the compensation force. In this paper, a VGCM-based scissor lift (pantograph lift) that uses three springs and a smaller actuator is proposed. A prototype is designed and fabricated, and the performance of the prototype is evaluated experimentally. The results demonstrate that the developed scissor lift meets the design specifications. In addition, a load estimator is established based on the dynamic model of the scissor lift. A real-time self-adjustment method that automatically changes the compensation force is proposed, and its effectiveness is verified.     

Multiple‐model sliding mode observer for an artificial gas lift system

Artificial gas lift is widely used in the oil industry to enhance oil recovery. Active feedback control of this process would lead to its stabilization, that in some operating modes may otherwise be unstable, and to the increase of oil production. However, the control strategies are normally constrained to the use of the surface‐measured process variables. The use of down‐hole measurements would improve the performance of the control system but is technically hardly feasible due to the necessity of placing instruments in harsh conditions. The use of state observation might be a feasible alternative to the down‐hole measurements. Recent development of a new accurate model of the artificial gas lift process enables us to increase accuracy of observation due to the account of pressure and density distribution along the well depth. Besides, a new approach to a nonlinear model treatment proposed in the present paper leads to a high computational efficiency of the observer for the gas lift. The paper presents an approach to the design of a novel sliding mode observer for the gas lift process. The observer uses multiple linearized models representing deviations from a set of equilibrium points. These models are then incorporated to produce estimates for the gas lift process variables. The approach is supported by simulations.     

Three-dimensional lattice Boltzmann simulations of high density ratio two-phase flows in porous media

A three-dimensional multiphase lattice Boltzmann model is implemented to study the spontaneous phase transport in complex porous media. The model is validated against the analytical solution of Young’s and Laplace’s laws. Afterward, three-dimensional porous layers are randomly generated to investigate droplet penetration into a substrate, liquid transport in a porous channel as well as extraction of a droplet from a porous medium. Effects of several geometrical and flow parameters such as porosity, density ratio, Reynolds number, Weber number, Froude number and contact angle are considered. A parametric study of the influence of main non-dimensional parameters upon the impact of liquid drops on permeable surface is performed. Results show that while increasing Froude number causes spreading of the droplet on the surface, increasing Reynolds number, Weber number, porosity and liquid-air density ratio will enhance the penetration rate into the surface. Furthermore, increasing the contact angle decreases both the spreading and the penetration rate at the same time. In the same way, for the liquid transport in a porous channel, it is found that increasing the porosity and Reynolds number will result in increasing penetration rate in the channel. For the extraction of a droplet from a porous medium, it is shown that by increasing the gravitational force and/or porosity the droplet extracts faster from the substrate.     

基于PAC的零航速减摇鳍升力测量系统研究

零航速减摇鳍是一种新型减摇装置,其升力产生机理、控制策略都与传统减摇鳍不同。通过对现有实验设备数据采集和控制系统的改进,建立一套适合零航速减摇鳍控制系统特点和实验要求的实验室升力检测系统。升力检测系统包括基于压阻式升力传感器的检测元件和基于PAC的数据采集及记录的控制系统。可用于分析和验证零航速减摇鳍的升力理论模型,为工程实验提供有价值的信息。     

Three-dimensional non-Newtonian computations of extrudate swell with the finite element method

Numerical simulations have been carried out for the extrudate swell problem in three-dimensional domains. The finite element method is used with streamline elements, which render the calculations fast and efficient for flows through long extrusion dies (no reservoir present). The method is first tested against purely viscous (Newtonian), viscoplastic (Bingham), and slightly viscoelastic (CEF model) results for the determination of extrudate swell from circular dies, which have a two-dimensional counterpart. Full three-dimensional die designs are also studied, such as extrusion from a square and a cross-shaped die.     

Evaluation of a bounded high order upwind scheme for 3D incompressible free surface flow computations

In the context of normalized variable formulation (NVF) of Leonard and total variation diminishing (TVD) constraints of Harten, this paper presents an extension of a previous work by the authors for solving unsteady incompressible flow problems. The main contributions of the paper are threefold. First, it presents the results of the development and implementation of a bounded high order upwind adaptative QUICKEST scheme in the 3D robust code (Freeflow), for the numerical solution of the full incompressible Navier–Stokes equations. Second, it reports numerical simulation results for 1D shock tube problem, 2D impinging jet and 2D/3D broken dam flows. Furthermore, these results are compared with existing analytical and experimental data. And third, it presents the application of the numerical method for solving 3D free surface flow problems.     

船舶零航速减摇鳍升力测量研究

船舶零航速减摇鳍是指在来流速度为零的流场中依靠鳍的主动摆动产生升力,以对抗海浪的作用力,从而减小船舶摇摆的减摇技术。在升力测量中,将升力控制引入零航速减摇技术中,根据实船安装环境几个耦合因素的影响,针对零航速减摇鳍,设计了零航速减摇鳍升力传感器;通过反馈信号合成算法,合成的升力信号有足够的精度,证明所设计系统能够满足船舶零航速减摇的要求。