A study on equivalence of nonlinear energy dissipation between first-order computational homogenization(FOCH)and re duce d-order homogenization(ROH)methods

Nowadays,studies on the mechanism of macro-scopic nonlinear behavior of materials by accumulation of micro-scopic degradation are attracting more attention from researchers.Among numerous approaches,multiscale methods have been proved as powerful and practical approaches in predicting macro-scopic material status by averaging and homogenizing physical information from associated micro-scopic mate-rial behavior.Usually in mechanical problem,the stress,consistent material modulus,and possible mate-rial state variables are quantities in interest through the upscaling process.However,the energy-related quantities are not studied much.Some initiative work has been done in the early year including but not limited to the Hill-Mandel condition in multiscale framework,which gives that the macro-scopic elastic strain energy density can be computed by volumetric averaging of that in the micro-scale.However,in the nonlinear analysis,the energy dissipation is an important quantity to measure the degradation status.In this manuscript,two typical multiscale methods,the first-order computational homogenization(FOCH)and reduced-order homogenization(ROH),are adopted to numerically analyze a fiber-reinforced compos-ite material with capability in material nonlinearity.With numerical experiments,it can be shown that energy dissipation is the same for both approaches.

Vortex Dissipation Due to Airfoil-Vortex Interaction

The influences due to several AVIs （airfoil-vortex interactions） are studied by using a two-dimensional CFD （computational fluid dynamics） method. The primary goal of this effort is to assess the variation of vortex center location and vortex circulation associated with sequential AVI toward an improvement of the hybrid method of CFD and prescribed wake model, which closely relates to predicting the BVI （blade-vortex interaction） noise radiated from a helicopter rotor. The representative of sequential AVI is performed by single vortex and two airfoils. Investigations with respect to vortex center location and vortex circulation after AVIs have been made by varying the miss-distance, which is the vertical distance between the airfoil leading edge and the vortex center. Correlations between miss-distance and vorticity field show that there exists complicated vortex wake flow with several vortices newly induced in 1st AVI. The pressure fluctuation amplitude clarifies that the intensity in 2nd AV1 is significantly low compared to the intensity in 1st AVI due to the influence of vortex dissipation. Simulations turned out to modify the vortex center location represented by the hybrid method using an offset value for a streamwise direction and to dissipate the vortex circulation for improving the accuracy of BVI noise prediction.

Unit stream power,minimum energy dissipation rate,and river engineering

Unit stream power is the most important and dominant parameter for the determination of transport rate of sand,gravel,and hyper-concentrated sediment with wash load.Minimum energy dissipation rate theory,or its simplified minimum unit stream power and minimum stream power theories,can provide engineers the needed theoretical basis for river morphology and river engineering studies.The Generalized Sediment Transport model for Alluvial River Simulation computer mode series have been developed based on the above theories.The computer model series have been successfully applied in many countries.Examples will be used to illustrate the applications of the computer models to solving a wide range of river morphology and river engineering problems.

A High Resolution Low Dissipation Hybrid Scheme for Compressible Flows

In this paper, an efficient hybrid shock capturing scheme is proposed to obtain accurate results both in the smooth region and around discontinuities for compressible flows. The hybrid algorithm is based on a fifth-order weighted essentially non-oscillatory （WENO） scheme in the finite volume form to solve the smooth part of the flow field, which is coupled with a characteristic-based monotone upstream-centered scheme for conservation laws （MUSCL） to capture discontinuities. The hybrid scheme is intended to combine high resolution of MUSCL scheme and low dissipation of WENO scheme. The two ingredients in this hybrid scheme are switched with an indicator. Three typical indicators are chosen and compared. MUSCL and WENO are both shock capturing schemes making the choice of the indicator parameter less crucial. Several test cases are carried out to investigate hybrid scheme with different indicators in terms of accuracy and efficiency. Numerical results demonstrate that the hybrid scheme in the present work performs well in a broad range of problems.

Application of computational fluid dynamics in design of viscous dampers-CFD modeling and full-scale dynamic testing

Computational fluid dynamics(CFD)provides a powerful tool for investigating complicated fluid flows.This paper aims to study the applicability of CFD in the preliminary design of linear and nonlinear fluid viscous dampers.Two fluid viscous dampers were designed based on CFD models.The first device was a linear viscous damper with straight orifices.The second was a nonlinear viscous damper containing a one-way pressure-responsive valve inside its orifices.Both dampers were detailed based on CFD simulations,and their internal fluid flows were investigated.Full-scale specimens of both dampers were manufactured and tested under dynamic loads.According to the tests results,both dampers demonstrate stable cyclic behaviors,and as expected,the nonlinear damper generally tends to dissipate more energy compared to its linear counterpart.Good compatibility was achieved between the experimentally measured damper force-velocity curves and those estimated from CFD analyses.Using a thermography camera,a rise in temperature of the dampers was measured during the tests.It was found that output force of the manufactured devices was virtually independent of temperature even during long duration loadings.Accordingly,temperature dependence can be ignored in CFD models,because a reliable temperature compensator mechanism was used(or intended to be used)by the damper manufacturer.

Computational Stability of the Explicit Difference Schemes of the Forced Dissipative Nonlinear Evolution Equations

The computational stability of the explicit difference schemes of the forced dissipative nonlinear evolution equations is analyzed and the computational quasi-stability criterion of explicit difference schemes of the forced dissipative nonlinear atmospheric equations is obtained on account of the concept of computational quasi-stability, Therefore, it provides the new train of thought and theoretical basis for designing computational stable difference scheme of the forced dissipative nonlinear atmospheric equations. Key words Computational quasi-stability - Computational stability - Forced dissipative nonlinear evolution equation - Explicit difference scheme This work was supported by the National Outstanding Youth Scientist Foundation of China (Grant No. 49825109), the Key Innovation Project of Chinese Academy of Sciences (KZCX1-10-07), the National Natural Science Foundation of China (Grant Nos, 49905007 and 49975020) and the Outstanding State Key Laboratory Project (Grant No. 40023001).

Computational investigation of hydraulic performance variation with geometry in gabion stepped spillways

Over recent years, there has been a clear increase in the frequency of reported flooding events around the world. Gabion structures offer one means of flood mitigation in dam spillways. These types of structures provide an additional challenge to the computational modeller in that flow through the porous gabions must be simulated. We have used a computational model to investigate the flow over gabion stepped spillways. The model was first validated against published experimental results. Then, gabion stepped spillways with four different step geometries were tested under the same conditions in order to facilitate inter-comparisons and to choose the best option in terms of energy dissipation. The results show that normal gabion steps can dissipate more energy than overlap, inclined, and pooled steps. An intensive set of tests with varying slope, stone size, and porosity were undertaken. The location of the inception point and the water depth at this point obtained from this study were compared with those from existing formulae. Two new empirical equations have been derived, on the basis of a regression analysis, to provide improved results for gabion stepped spillways.

Stark-Chirped Rapid Adiabatic Passage in Presence of Dissipation for Quantum Computation

Stark-chirped rapid adiabatic passage(SCRAP) is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with noises.

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Multi-orifice cross-flow jet mixers(MOCJMs)are used in various industrial applications due to their excellent mixing efficiency,but few studies have focused on the micromixing performance of MOCJMs.Herein,the flow characteristics and micromixing performance inside the MOCJM were investigated using experiments and computational fluid dynamics(CFD)simulations based on the Villermaux/Dushman system and the finite-rate/modified eddy-dissipation model.The optimal A value was correlated with the characteristic parameters of MOCJMs to develop a CFD calculation method applicable to the study of the micromixing performance of the MOCJMs.Then the micromixing efficiency was evaluated using the segregation index XS,and the effects of operational and geometric parameters such as mixing flow Reynolds number(ReM),flow ratio(RF),total jet area(ST),the number of jet orifices(n),and outlet configuration on the micromixing efficiency were investigated.It was found that the intensive turbulent region generated by interactions between jets,as well as between jets and crossflows,facilitated rapid reactions.XS decreased with increasing ReM and decreasing RF.Furthermore,MOCJMs with lower ST,four jet orifices,and the narrower outlet configuration demonstrated a better micromixing efficiency.This study contributes to a deeper understanding of the micromixing performance of MOCJMs and provides valuable guidance for their design,optimization,and industrial application.

基于GA-BPNN代理模型的混合式黏滞阻尼器构造优化

采取CFD(computational fluid dynamics)数值模拟和基于代理模型的优化方法,研究混合式黏滞阻尼器在多参数设计空间内的构造参数优化问题。首先,分析黏滞阻尼器参数对力学性能的影响规律,基于正交试验理论选取间隙宽度、缸体内径、活塞厚度、阻尼孔直径为关键参数,利用优化拉丁超立方设计和CFD数值模拟获得初始样本点耗能性能指标;然后,使用遗传算法(genetic algorithm,GA)和反向传播神经网络(backpropagation neural network,BPNN)的方法构建代理模型,其能够准确反映构造参数耗能性能指标和构造参数之间的繁复关系。进一步地,循环更新GA-BPNN代理模型并结合非支配排序遗传算法(non-dominated sorting genetic algorithm-II,NSGA-II),以最佳耗能能力为目标,实现在全设计空间内的寻优,确定在典型阻尼介质黏度下双出杆混合式黏滞阻尼器的最优构造参数。最后,探讨了构造参数对黏滞阻尼器流动性能的影响机理。研究结果表明,优化双出杆混合式黏滞阻尼器构造参数在选用基于GA-BPNN代理模型的优化方法时,可有效提高计算效率且具有较高预测精度。从性能指标提升角度,全黏度下最优构造参数阻尼孔直径、活塞厚度、缸体内径和间隙宽度分别为1.31 mm、120.78 mm、199.87 mm、0.5 mm,相较于基准构造,最大阻尼力和能量耗材比分别提升33.8%和64.8%。该方法可为黏滞阻尼器构造参数优化及相关研究提供参考。

新型三段式粗颗粒浮选柱内流场数值模拟

本文对一种新型三段式粗颗粒浮选柱内流场特性进行了研究,结果表明,稳流板的加入可增强粗颗粒浮选柱内流体的湍动能和湍流耗散率,促进气泡和粗颗粒的相互作用以及湍动能、湍流耗散率和液相速度的均匀分布,从而利于矿化气泡的输送。射流管个数的增加使粗颗粒浮选柱内湍动能和湍流耗散率分布趋向于均匀。对称的4个射流管可显著改善流场分布,形成的漩涡促进了气泡与颗粒的相互作用,稳流板使气泡速度分布均匀。浮选柱内湍动能随着上升水量和充气量的增加而增大,稳流板作用明显。上升水量对稳流板上下方区域湍流耗散率的影响呈梯级分布,可实现底部紊流矿化、中部紊流−稳流转变、上部静态流态化浮选的三段式流体环境,利于粗颗粒矿物浮选的回收。

基于耗散粒子动力学模拟辅助的纳米结构脂质载体优化制备

基于分子模拟能够探究纳米结构脂质载体(nanostructure lipid carriers,NLC)各物质间的结合能、溶解度参数等,预测混合物的相容性,从而用于指导实验前原料种类以及用量选择。该文以姜黄素(curcumin,Cur)为模型营养物,以固体脂质(单硬脂酸甘油酯)和液体脂质(中链甘油三酯、葵花籽油、甜橙油)及表面活性剂(泊洛沙姆188、卵磷脂、吐温-80)作为筛选对象,采用耗散粒子动力学(dissipative particle dynamics,DPD)方法进行模拟筛选,再通过正交试验制备NLC以对模拟结果进行验证,最后对NLC的粒径和微观形态等进行表征。模拟与实验结果均表明,单硬脂酸甘油酯-中链甘油三酯(medium chain triglycerides,MCT)-卵磷脂能形成较好的载体体系,固液脂质比为1∶3(质量比),卵磷脂含量为5%(质量分数),姜黄素含量占总脂质的3%(质量分数)时形成的球壳结构最好。优化后制备的姜黄素NLC平均粒径为(233.8±2.4)nm,电位为(-38.2±0.6)mV,包封率为85.06%,微观形态均匀分散、没有明显聚集现象。

多样化算力对服务器的散热挑战分析

多样化算力对于服务器散热设计提出严峻挑战,在对服务器散热问题进行解析之后,给出了通用算力和智算算力服务器散热受限的主要原因,并从工质是否相变的角度对常用的散热技术重新进行梳理与分类;对冷板式和浸没式液冷技术规模商用受限的核心限制因素进行分析与介绍;对常用的无源两相散热技术的问题和使用前景进行概述。最后,提出推动跨层级的合作会更有效的应对服务器散热挑战。

一种计算机CPU被动式散热器的设计、仿真与实验研究

针对当前高功率CPU静音散热需求,提出了一种新型被动式散热器.应用数值仿真与实验验证的方式对该散热器在不同加热功率下的温度、启动性能、热阻进行了研究.仿真结果表明:在120 W加热条件下,该散热器温度分布均匀,波动较小,最高温度仅为64.00℃,启动时间在900 s左右,平均接触热阻处在0.01~0.2℃/W之间.实验结果表明:在120 W加热条件下,该散热器最高温度仅为68.28℃,启动时间在900 s左右,平均接触热阻仅为0.11℃/W,满足计算机CPU在该功率下正常运行需求.

Efficient Energy Optimized Faithful Adder with Parallel Carry Generation

Abstract:Approximate computing has received significant attention in the design of portable CMOS hardware for error-tolerant applications.This work proposes an approximate adder that to optimize area delay and achieve energy efficiency using Parallel Carry(PC)generation logic.For‘n’bits in input,the proposed algorithm use approximate addition for least n/2 significant bits and exact addition for most n/2 significant bits.A simple OR logic with no carry propagation is used to implement the approximate part.In the exact part,addition is performed using 4-bit adder blocks that implement PC at block level to reduce node capacitance in the critical path.Evaluations reveal that the maximum error of the proposed adder confines not more than 2n/2.As an enhancement of the proposed algorithm,we use the Error Recovery(ER)module to reduce the average error.Synthesis results of Proposed-PC(P-PC)and Proposed-PCER(P-PCER)adders with n-16 in 180nm Application Specific Integrated Circuit(ASIC)PDK technology revealed 44.2%&41.7%PDP reductions and 43.4%&40.7%ADP reductions,respectively compared to the latest best approximate design compared.The functional and driving effectiveness of proposed adders are examined through digital image processing applications.

微通道中液滴的耗散粒子动力学模拟

利用耗散粒子动力学(DPD)对三维微通道中的液滴动力学进行了研究.通过提高两种流体之间的保守力系数获得不互溶的两种流体,并分析了相应的F lory-Hugg ins模型中的χ参数.DPD计算所获得的表面张力与G root等给出的理论公式相符合.计算采用消息传递并行计算技术(M P I),计算过程模拟了高分子液滴穿过突扩突缩通道时的形态变化.计算结果表明,不同尺寸的高分子液滴穿过微通道所需要的时间不同,随着液滴直径与通道高度比值的增加,所需时间单调上升,但上升的趋势逐渐减缓.

计算电容型设备介质损耗因数的相关函数法的改进

由于不能在整周期区间内准确积分, 当采样频率与电网信号频率不同步时,采用有限时间离散相关函数法计算电容型设备的介质损耗因数(介损)会产生较大的误差。采用插值法修正了相关函数法的积分区间,用梯形积分代替矩形积分,采用优化的采样频率和采样点数来提高计算精度仿真实验表明经过修正的相关函数法对电网频率波动有较强的抑制能力,可明显减少介损的计算误差,从而不必使用同步采集卡。此外,该方法的采样频率不高、采样点数不多,易于通过基于微控制器单元(MCU)或数字信号处理器(DSP)的测量系统实现。

计算控制论的理论与应用

针对目前控制论研究分支越来越多、对模型的依赖越来越强、分析算法和控制器设计算法越来越复杂的问题 ,为了有效地提高控制系统设计精度和鲁棒性 ,改善系统分析和设计的环境 ,提出了计算控制论的概念 ,指出了稳定性和耗散性质是系统的基本特征 ,在此基础上导出了系统鲁棒性分析和鲁棒控制器设计所需要的基本定理和公式 .研究结果表明 ,基于系统能量的耗散性概念可以建立系统分析的统一框架 ,基于LMI可以建立系统解算的统一框架 .最后还就计算控制论的研究内容和问题及其有关研究方法。

红树林多孔介质阻力模型与消波效果仿真分析

滩涂植被的防风消浪对堤岸保护具有重要作用,该研究根据动量守恒方程和多孔介质源项为速度的冪率方程,建立红树林多孔介质水流阻力数学模型,并利用计算流体动力学软件Fluent分析不同影响因子对红树林水流的阻力效果,结果显示:林带疏透度、宽度及水深与消波效应具有密切关系,其中,林带宽度的消波效应更明显;波速随疏透度的增加起初呈现急剧增加的趋势,当疏透度大于0.4时,波速变化较平缓;随着林带宽度增加,波速呈不同程度下降趋势,4参数Logistic方程拟合结果显示,波速随林带宽度增加呈反S型曲线下降。该研究可为红树林抗浪效果与性能评价提供参考。

交通信息云计算及其应用研究

云计算借助高速网络将各种计算能力联接起来,为交通信息提供了几乎无上限的可伸缩的计算能力.本文分析了交通信息云计算的优势、特征、方法和部署,认为交通信息云计算也是一种信息高效采集和服务的概念,是实现交通行为控制的基础.以车辆GPS定位信息的获取、传送、计算和应用为例,对比了浮动车信息现有处理模式与云计算信息处理模式,提出了以云计算模式产生高效用度、闭环可验证的个性化路径导航信息作用于海量驾驶员个体,实现控制性路径诱导的方法.