灌溉技术的新进展——微灌

微灌技术的出现与应用,是灌溉技术的一个进步。它是现代各种灌溉方法中,水的利用率最高的一种灌溉技术。本文综合了微灌技术的发展和特点,微灌系统的组成,设备功能与结构,以及微灌的水力学问题,指出我国微灌技术的应用前景及有待解决的问题。      

Recent developments in enhanced heat transfer

Enhanced heat transfer has evolved into an important component of heat transfer experimentation and theory. The accumulated literature includes thousands of references. To give an overview of the current state of this important technology—for the past ten years, representative developments in each category of enhancement techniques are cited and commented on. The discussion is divided into the literature, passive enhancement techniques, active enhancement techniques, and compound enhancement techniques.     

公路隧道防排水技术进展

综述了公路隧道近几十年防排水技术的进展。其内容包括 :公路隧道防排水技术标准 ,复合式衬砌防排水技术 ,断层、破碎带地层中的防排水技术 ,隧道导排水结构。并结合某些工程问题进行了讨论。     

云纹干涉制栅新技术

本文介绍了两种新的光栅复制技术,它们具有快速、高质量、低成本、操作简单、使用方便、不需特殊仪器等特点.该技术从我国一般力学实验室条件出发,解决了试件栅制作困难,其中漆栅方法可极大地缩短云纹干涉方法的实验周期,该技术也为光栅测试技术的广泛应用提供了方便.     

Recent developments and further aspects of experimental stress analysis in the Federal Republic of Germany and Western Europe

With respect to the fast developments in computer techniques, new fields of application of experimental stress analysis are opened. As only a combination of theoretical and experimental stress analysis in all statical, dynamical and stability problems guarantees reliable and most accurate results, hybrid techniques based on advanced theories are to be introduced. This is possible under the presupposition of modern measuring devices and higher precision in data acquisition and evaluation by means of automatic devices. The recent developments in semiconductor techniques and the availability of computers with high-storage capacity render possible on-line procedures in experimental techniques on the basis of the already known methods.     

先进微制造力学

元器件小型化带来了功耗低、响应快、比容量大等显著优点,但同时也带来了新的技术挑战和科学问题,需要对微纳尺度下材料的机械物理性能及制造工艺进行深入研究。论文围绕先进微纳米制造技术与微纳米力学的密切关系,首先综述了聚焦离子束、纳米压印、3D打印等微纳米材料与结构的先进制造技术,并着重阐述了先进微纳米制造技术在力学前沿课题研究中的重要作用;另一方面,从方法与原理的角度阐述了力学思想和方法对先进微纳米制造技术的指导与促进作用。最后,还对目前一些先进微纳米制造技术及相关前沿力学问题进行了展望。     

Détection de fissures dans les poutres d'acier : une nouvelle approche par balayage de mesures de vibrations

In the last few years, the techniques of detection and identification of damage in structures benefited from important research efforts. Several methods of non-destructive damage detection, such as techniques based on modal analysis, were developed in addition to the traditional methods. The difficulties encountered by these techniques are their low performance, considering the industrial requirements to detect cracks as early as possible.     

粒子图像测速技术研究进展

粒子图像测速技术(PIV)作为一种全新的无扰、瞬态、全场速度测量方法,在流体力学及空气动力学研究领域具有极高的学术意义和实用价值.本文对PIV技术的原理、分类作了简要地介绍,详细归纳和评述了现有的各种速度信息的提取方法,并对拓扑图论、神经网络、遗传算法、模糊聚类等新技术在PIV中的应用以及三维PIV技术、两相流PIV测试技术进行了介绍.指出当前PIV技术除了向三维和多相流方向发展外,如何提高PIV的测量精度以及缩短计算时间仍然是目前研究的主要目标.PIV技术随着计算机技术、激光技术和CCD性能的发展,必将取得更大的发展与突破      

A BRIEF REVIEW AND PROSPECT OF EXPERIMENTAL SOLID MECHANICS IN CHINA

In this review, acritical look at the research progress ofexperimentalsolid mechanics in China for the past years is presented. Issues are discussed of the discovery and development of new fundamental methods and techniques versus performance benchmarking for many of their applications. Included herein are photoelasticity and various forms of modern photomechanics, acoustical techniques, image processing and videometrics, radial and spectrum techniques, and experimental mechanics on micro/nano scale. It is also noticed that both the ever developed instrumentation and specialized synthetical techniques have played important roles in advancing experimental mechanics in scientific researches and industrial applications. Finally, an attempt is made to look into the future of experimental solid mechanics with personal opinions offered on what the future trends will be for the researches in the field.     

Multi-parameter accelerated modified Newton-Raphson methods for rigid-plastic FE analysis

Applications of certain multi-parameter acceleration techniques used with the modified Newton-Raphson (mN-R) methods to solve the nonlinear equations arising from rigid-plastic finite element analysis are investigated. New modified multi-parameter techniques, developed from Crisfield's multi-parameter methods, are utilized to solve these nonlinear equations. The numerical performance of these techniques is compared with the standard Newton-Raphson method (sN-R), Crisfield's single parameter method (C1), Crisfield's two parameter method (C2) and Crisfield's three parameter method (C3). The new techniques do not involve additional residual force calculation and require little extra computational effort. In addition, they are more robust and efficient than other existing acceleration techniques.     

表面工程摩擦学研究进展

综述了第二代表面工程技术和表面工程摩擦学的研究进展 ,展望了 2 1世纪表面工程摩擦学研究的发展动向 .     

Two techniques for PIV-based aeroacoustic prediction and their application to a rod-airfoil experiment

In this paper, we discuss techniques by which the aeroacoustic properties of the turbulent flow in a rod-airfoil benchmark experiment can be inferred from time-resolved PIV measurement. While acoustic measurements can be made directly using microphones, the proposed techniques provide a means to directly link acoustic waves with specific flow events, which is invaluable in devising noise mitigation strategies. The approaches are possible thanks to recent improvements in digital and camera technology that can provide time-resolved measurements in air flows, necessary for the determination of unsteady flow quantities related to aeroacoustic production. Both techniques are based on Curle’s acoustic analogy, where one is based on Lagrangian determination of the required quantities, while the other requires all flow quantities to be converted into Fourier modes. Application of both techniques yields results that are in reasonable agreement with microphone noise measurements for the rod-airfoil experiment.     

Structural-test applications utilizing large continuous photoelastic coatings

This paper presents the techniques employed by the author in full-scale structural-test applications utilizing large continuous photoelastic coatings. Emphasis is placed on the procedures employed in making a contoured sheet up to 24×36 in. in size and subsequent machining, bonding and testing techniques. The general preparation and testing techniques employed for a typical missile-structural assembly are presented. Calibration and measurement techniques are presented to illustrate efficient procedures for obtaining birefringence readings on a point-by-point basis with reflection polariscopes or whole-field measurements of shear-stress distribution using remote-controlled cameras when safety considerations dictate their use. Techniques are presented for simplified preparation of isoclinic maps and stress trajectories. The procedures employed for coating removal upon completion of testing are presented, and the photoelastic-coating technique is compared, for a particular structural-test application, with a straingage analysis.     

Simulation of Fluid Flow on Fractures and Implications for Reactive Transport Simulations

The diverse numerical simulation techniques employed to predict fluid flow properties of fractures yield differing results which limits their applicability for reactive transport simulations. Basically the fluid flow simulation techniques can be divided in two groups: (i) techniques that yield average fluid flow characteristics and (ii) techniques that produce space-resolved properties. These differences may have substantial impact on the reactive transport simulations but may also depend on the fracture characteristics. For this reason, a sensitivity analysis of the geometrical properties of fractures on the fluid flow properties is conducted and evaluated with respect to their impact on reactive transport modeling. Although employing space-resolved simulation techniques, the results of the tests show average values for permeability and fluid velocity that are comparable to previous studies that used other simulation techniques. Observed fluid flow channeling appears to be related to fracture surfaces matching and anisotropy. However, average flow velocities at potential sites for reactive transport differ up to a factor of five from the average ones for the entire fracture. Furthermore, extreme values at reactive transport sites may differ even more and the flow may be directed against the applied pressure gradient. For studies concerned with simulation of reactive transport, these deviations are crucial and should be explicitly considered in the calculations. Hence space-resolved fluid flow simulations should be employed for the simulation of reactive transport.     

Generation and visualization of volumetric PIV data fields

This review paper addresses the integration of advanced visualization techniques into the analysis of volumetric vector fields obtained by experimental measurement techniques such as holographic PIV, tomographic PIV, 3D PTV or defocusing PIV. The paper follows the idea of the pipeline process for flow visualization focusing on experimental data generation and advanced visualization techniques. The paper tries to help the experimentalist navigating the landscape of recently developed volumetric measurement techniques and advanced visualization techniques. The processing steps and related difficulties are illustrated with the transitional backward facing step flow experiment at Re _h = 4,440. The paper shows the usage of flow visualization for quantitative volumetric PIV data analysis.     

Whole-field density measurements by ‘synthetic schlieren’

 This paper outlines novel techniques for producing qualitative visualisations of density fluctuations and for obtaining quantitative whole-field density measurements in two-dimensional density-stratified flows. These techniques, which utilise image processing technology, are much simpler to set up than the classical schlieren and interferometry methods, and provide useful information in situations where shadowgraph is of little or no value. Moreover, they may be set-up to analyse much larger domains than is feasible with the classical approaches, and do not require high quality optical windows in the experimental apparatus. Ultimately the greatest strength of these techniques is the ability to extract accurate, quantitative measurements of the density field. Application of these techniques is illustrated by an internal wave field produced by an oscillating cylinder. Recent theoretical advances for this classical problem make it the ideal test bed. Results are presented for both a circular and a square cylinder oscillating vertically in a linear stratification. Further aspects of the techniques are illustrated by considering thermal convection from a hand and flow over an obstacle towed through a density stratified fluid. Received: 27 October 1998 /Accepted: 24 May 1999     

Rapid stabilization of thawing soils: field experience and application

Thawing soils can severely restrict vehicle travel on unpaved surfaces. However, a variety of materials and construction techniques can be used to stabilize thawing soils to reduce immobilization problems. The US Engineer Research and Development Center's Army Cold Regions Research and Engineering Laboratory (CRREL) and the Wisconsin National Guard evaluated several stabilization techniques in a field demonstration project during spring thaw at Fort McCoy, Wisconsin, in 1995. Additional tests on chemical stabilizing techniques were conducted at CRREL's Frost Effects Research Facility. The results of these test programs were reduced to a decision matrix for stabilizing thawing ground, and used during the deployment of US troops in Bosnia during January and February of 1996. The soil frost and moisture conditions expected during this time frame were predicted using MIDFROCAL (MIDwest FROst CALculator). This paper is an overview of the stabilization techniques evaluated and their recommended application based on the expected soil frost conditions and traffic requirements. Although the experiments were performed with military vehicles in mind, the techniques are suitable for many civilian applications such as forestry, construction, mining, and oil exploration.     

Hybrid experimental-numerical stress analysis

The hybrid experimental-numerical stress-analysis technique, which saw limited applications during the 1950's, has been resurrected with the vastly improved numerical techniques of the 1970's. By inputing the experimental results as initial and boundary conditions, modern computer codes are executed in its generation and application modes to yield results which are unobtainable when only one of the two techniques is used. The hybrid technique thus exemplifies the complementary role of the experimental and numerical techniques.     

A review of measurements of heat flux density applicable to the field of combustion

The techniques that have been developed for the measurement of heat flux density are reviewed briefly. These techniques may be divided into two broad categories: (1) indirect methods based on the fundamental theories of heat transfer and (2) direct methods using a heat flux density sensor. Various methods are compared in order to stimulate further research and the development of sophisticated techniques for the measurement of heat flux density in the field of combustion.     

On the uniqueness and sensitivity of indentation testing of isotropic materials

Instrumented indentation is a popular technique to extract the material properties of small scale structures. The uniqueness and sensitivity to experimental errors determine the practical usefulness of such experiments. Here, a method to identify test techniques that minimizes sensitivity to experimental erros is in indentation experiments developed. The methods are based on considering “shape functions,” which are sets of functions that describe the force–displacement relationship obtained during the indentation test. The concept of condition number is used to investigate the relative reliability of various possible dual indentation techniques. Interestingly, it was found that many dual indentation techniques can be as unreliable as single indentation techniques. Sensitivity analyses were employed for further understanding of the uniqueness and sensitivity to experimental errors of indentation techniques. The advantage of the Monte Carlo approach over other procedures is established. Practical guidelines regarding the selection of shape functions of force–displacement relationship and geometric parameters, while carrying out indentation analysis are provided. The results suggest that indentation experiments need to be very accurate to extract reliable material properties.