Iterative optimization for joint design of source and channel codes using genetic algorithms

Abstract

This paper presents a novel algorithm for the joint design of source and channel codes. In the algorithm, channel‐optimized vector quantization (COVQ) and rate‐punctured convolutional coding (RCPC) are used for design of the source code and the channel code, respectively. We employ the genetic algorithm (GA) to prevent the design of COVQ from falling into a poor local optimum. We also adopt the GA to reduce the computational time needed for realizing the unequal error protection scheme best matched to the COVQ. Both the GA‐based source coding and channel coding scheme are then iteratively combined to achieve a near global optimal solution for the joint design. Numerical results show that the algorithm can be an effective alternative for applications where high rate‐distortion performance and low computational complexity are desired.     

A frequency converter with controllable characteristics

The area of practical application of measuring instruments with frequency conversion, in which the economic costs of their operating cycle are related to the control of the accuracy of the converters, is considered. Methods of constructing stroboscopic frequency converters, adapted to a specific class of measurement problems with respect to the “accuracy” parameter, are described. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 47–51, January, 2008.     

并联机床的动力学特性对加工精度影响的分析

为了提高并联机床的加工精度,分析了并联机床的动力学特性对加工精度的影响。根据牛顿—欧拉方程,得到并联机床的动力学方程,解得连杆的驱动力;根据杆件轴向伸长量与受力之间的关系,得到连杆的长度误差;以无长度误差的连杆长度为优化目标,用优化的方法,得到动平台的位姿,并与连杆有长度误差时动平台的位姿比较,得动平台的位姿误差;根据刀具在动平台坐标系中位置,得刀具加工位置误差及对被加工零件精度的影响。结果表明：并联机床连杆的长度误差,引起刀具加工位置误差,使被加工零件产生形位误差和尺寸误差;并联机床电主轴偏心引起连杆的长度误差的扰动,产生刀具加工位置的扰动误差,影响被加工零件的表面粗糙度。     

A method of calculating the dynamic error of a nonlinear detector

A method is considered for determining the dynamic error of a detector in the presence of various forms of nonlinear characteristic. The use of the method is demonstrated on simple examples. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 15–19, February, 2006.     

The least‐squares meshfree method

A new efficient meshfree method is presented in which the first‐order least‐squares method is employed instead of the Galerkin's method. In the meshfree methods based on the Galerkin formulation, the source of many difficulties is in the numerical integration. The current method, in this respect, has different characteristics and is expected to remove some of the integration‐related problems. It is demonstrated through numerical examples that the present formulation is highly robust to integration errors. Therefore, numerical integration can be performed with great ease and effectiveness using very simple algorithms. Copyright © 2001 John Wiley & Sons, Ltd.     

New bounding techniques for goal‐oriented error estimation applied to linear problems

The paper deals with the accuracy of guaranteed error bounds on outputs of interest computed from approximate methods such as the finite element method. A considerable improvement is introduced for linear problems, thanks to new bounding techniques based on Saint‐Venant's principle. The main breakthrough of these optimized bounding techniques is the use of properties of homothetic domains that enables to cleverly derive guaranteed and accurate bounding of contributions to the global error estimate over a local region of the domain. Performances of these techniques are illustrated through several numerical experiments. Copyright © 2012 John Wiley & Sons, Ltd.     

The dynamic error of a multichannel measurement system

It is shown that the dynamic error of a multichannel measurement system containing a single analog-to-digital converter with signal source switching is not dependent on the signal waveform and is governed by the rate of change. Translated from Izmeritel’naya Tekhnika, No. 1, pp. 3–6, January, 2009.     

基于 Sound Blaster 声卡的数据采集系统

目的在对SoundBlaster声卡性能特点分析的基础上,利用SoundBlaster声卡建立了数据采集系统的硬件电路和软件结构.方法对采集过程中所遇到的隔直问题,提出切实可行的解决办法.结果与结论具有一定的实践参考意义.     

A dynamic algorithm for integration in the boundary element method

The discretization of the boundary in boundary element method generates integrals over elements that can be evaluated using numerical quadrature that approximate the integrands or semi-analytical schemes that approximate the integration path. In semi-analytical integration schemes, the integration path is usually created using straight-line segments. Corners formed by the straight-line segments do not affect the accuracy in the interior significantly, but as the field point approaches these corners large errors may be introduced in the integration. In this paper, the boundary is described by a cubic spline on which an integration path of straight-line segments is dynamically created when the field point approaches the boundary. The algorithm described improves the accuracy in semi-analytical integration schemes by orders of magnitude at insignificant increase in the total solution time by the boundary element method. Results from two indirect BEM and a direct BEM formulation in which the unknowns are approximated by linear and quadratic Lagrange polynomial and a cubic Hermite polynomial demonstrate the versatility of the described algorithm. © 1998 John Wiley & Sons, Ltd.     

主轴系统结合面对主轴系统动力学特性的影响分析

数控机床主轴系统存在着主轴-轴承、主轴-刀柄、刀柄-刀具结合面,这些结合面的特性对主轴系统动力学有着显著的影响,而获得该影响规律对于主轴系统动态设计及动力学修改有着重要意义。本文以某立式加工中心主轴系统为对象,采用有限元法对其进行了动力学建模,在此基础上,对比分析了结合面特性对该主轴系统固有特性和刀尖点频响函数的影响规律。具体可以描述为：主轴-轴承结合面特性影响主轴系统的刚体模态和刀尖点低频段的频响函数;而主轴-刀柄结合面、刀柄-刀具结合面特性直接影响主轴系统的弹性模态和刀尖点高频段频响函数。此外,本文研究也可为主轴系统动力学特性及稳定性预估提供参考。     

内凹-反手性蜂窝结构的面内动态压溃性能研究

通过内凹六边形蜂窝与反手性蜂窝的结合得到一种内凹-反手性蜂窝(re-entrant anti-trichiral honeycomb,RATH)结构。利用显式动力有限元软件LS-DYNA对不同冲击速度和不同相对密度下内凹-反手性蜂窝的变形模式、抗冲击性能及拉胀性能进行了研究。结果表明,引入内凹结构可以显著增强中低速冲击时反手性蜂窝的局部“颈缩”现象,且在靠近内凹-反手性蜂窝的冲击端呈现出明显的“V形”变形带。与三边反手性蜂窝及传统蜂窝相比,内凹-反手性蜂窝的能量吸收性能更强,负泊松比效应更明显。基于一维冲击波理论,推导了内凹-反手性蜂窝的临界冲击速度和平台应力的经验公式。此外,讨论了冲击速度和胞壁厚度对平台应力及平台应变的影响。该研究将为混合变形机制拉胀蜂窝结构的设计提供新的思路。     

负载动态特性对伺服电机跟随性能影响研究

伺服系统工程应用越来越广泛,但负载动态特性对伺服电机跟随性能的影响关系目前仍不完全明确．为明确其影响关系,提出负载动态特性对伺服电机跟随性能影响的分析方法,根据伺服驱动理论,建立伺服驱动数学模型,分析伺服电机跟随误差的形成原理,建立伺服电机跟随误差与负载的函数关系．设计不同动态特性负载实验,验证了负载动态特性对伺服电机跟随性能的影响与理论分析相符．根据伺服电机跟随误差与负载的函数关系优化负载动态特性、电机惯量和伺服周期三个变量,进行对比实验,结果表明伺服电机的跟随性能得到了提升．     

A time domain FEM approach based on implicit Green's functions for non‐linear dynamic analysis

The present paper describes an unconditionally stable algorithm to integrate the equations of motion in time. The standard FEM displacement model is employed to perform space discretization, and the time‐marching process is carried out through an algorithm based on the Green's function of the mechanical system in nodal co‐ordinates. In the present ‘implicit Green's function approach’ (ImGA), mechanical system Green's functions are not explicitly computed; rather they are implicitly considered through an iterative pseudo‐forces process. Under certain simplifying hypothesis, iterations are not necessary and the ImGA becomes cheaper than standard Newmark/Newton–Raphson algorithm. At the end of the paper numerical examples are presented in order to illustrate the accuracy of the present approach. Copyright © 2004 John Wiley & Sons, Ltd.     

An efficient global optimization algorithm for multifactor dynamic systems

Abstract

In this study we present an efficient global optimization method, DIviding RECTangle (DIRECT) algorithm, for parametric analysis of dynamic systems. In a bounded constrained problem the DIRECT algorithm explores multiple potentially optimal subspaces in one search. The algorithm also eliminates the need for derivative calculations which are required in some efficient gradient‐based methods. In this study the first optimization example is to find the dynamic parameters of a tennis racket. The second example is a biomechanical parametric study of a heel‐toe running model governed by six factors. The effectiveness of the DIRECT algorithm is compared with a genetic algorithm in an analysis of heel‐toe running. The result shows that the DIRECT algorithm obtains an improved result in 83% less execution time. It is demonstrated that the straightforward DIRECT algorithm provides a general procedure for solving global optimization problems efficiently and confidently.     

Buoyancy potential conserving technique for dynamic analysis of offshore pipes and risers

The paper describes the midpoint algorithm for the solution of dynamic equilibrium equations in the marine environment for the non‐linear dynamic analysis of flexible pipes and riser systems in 3D configuration. It has been shown that proposed method has an advantage over traditional time marching method by means of long‐term stability and larger time steps. The mid‐point algorithm used for the time integration is considered ‘approximate buoyancy‐energy conserving algorithm’. Emphasis is placed on elements that use the Reissner–Simo beam theory or a related co‐rotational approach. Copyright © 2005 John Wiley & Sons, Ltd.     

空频域量化误差最小的光学小波滤波器设计

通过理论分析和仿真计算,研究利用不同小波基构造的光学小波滤波器的量化误差,分析交换分解和重构滤波器对光学小波滤波器量化误差的影响.实验结果表明不同小波基的量化误差通常是不同的,具有最小空、频域量化误差的小波基是交换分解和重构滤波器后的5/3 小波.根据光学小波滤波器的空、频域量化误差最小原则,基于提升算法,构造出空、频域量化误差最小的最优小波.     

The dynamic response characteristics of traumatic brain injury

Traumatic brain injury (TBI) continues to be a leading cause of morbidity and mortality throughout the world. Research has been undertaken in order to better understand the characteristics of the injury event and measure the risk of injury to develop more effective environmental, technological, and clinical management strategies. This research used methods that have limited applications to predicting human responses. This limits the current understanding of the mechanisms of TBI in humans. As a result, the purpose of this research was to examine the characteristics of impact and dynamic response that leads to a high risk of sustaining a TBI in a human population. Twenty TBI events collected from hospital reports and eyewitness accounts were reconstructed in the laboratory using a combination of computational mechanics models and Hybrid III anthropometric dummy systems. All cases were falls, with an average impact velocity of approximately 4.0 m/s onto hard impact surfaces. The results of the methodology were consistent with current TBI research, describing TBI to occur in the range of 335–445 g linear accelerations and 23.7–51.2 krad/s² angular accelerations. More significantly, this research demonstrated that lower responses in the antero-posterior direction can cause TBI, with lateral impact responses requiring larger magnitudes for the same types of brain lesions. This suggests an increased likelihood of sustaining TBI for impacts to the front or back of the head, a result that has implications affecting current understanding of the mechanisms of TBI and associated threshold parameters.     

数控机床整机动态特性评价方法

动态特性是衡量机床性能的一项重要指标,但目前并没有较好的数控机床整机动态特性评价方法。利用真实的动态切削力对数控机床进行激励,能够快速获取机床在切削力作用下的动态特性。鉴于切削参数会影响各频率成分对应的切削力幅值,基于不同工件材料和切削参数下的动态切削力,建立动态激振力模型,通过分频段激励来检验数控机床在不同频段下的动态特性。通过有限元仿真分析,判断数控机床在各个频段下的动态特性;对振动信号进行快速傅里叶变换,得到机床振动时的主要频率成分,为优化机床动态特性提供指导;对比各种动态切削力激振下不同机床的动刚度,评价不同机床动态特性的优劣。最后,通过激振试验验证了仿真结果的准确性。结果表明上述方法简单实用,能快速评价数控机床的动态特性,具有一定的实用价值。