Showing papers by "Tsinghua University published in 1984"
111 citations
TL;DR: In this paper, the boundary layer approximation of Mei and Foda is studied for a cylindrical cavity in a porous solid and the effect of fluid compressibility due to possible entrainment of air is discussed.
44 citations
TL;DR: If a nonrigid robotic arm is viewed as a composite rod with some degrees of freedom, the planning of collision-free paths of a robotic arm can be solved in a similar way to a rod.
Abstract: A theory for planning collision-free paths of a moving object among obstacles is described. Using the concepts of state space and rotation mapping, the relationship between the positions and the corresponding collision-free orientations of a moving object among obstacles is represented as some set of a state space. This set is called the rotation mapping graph (RMG) of that object. The problem of finding collision-free paths for an object translating and rotating among obstacles is thus transformed to that of considering the connectivity of the RMG. Since the connectivity of the graph can be solved by topological methods, the problem of planning collision-free paths is easily solved in theory. Using this theory, a topological method for planning collision-free paths of a rod-object translating and rotating among obstacles is presented. If a nonrigid robotic arm is viewed as a composite rod with some degrees of freedom, the planning of collision-free paths of a robotic arm can be solved in a similar way to a rod.
43 citations
TL;DR: In this article, the authors used the differential quadrature method to solve partial differential equations arising in chemical reactor design and compared it with the finite difference approach, which was used to solve the same problem.
30 citations
TL;DR: In this paper, the relationship between fracture mechanics parameters (J integral and crack tip opening displacement) determined by mechanics tests and geometrical parameters of deformed crack tip (stretched zone width, SZW and stretched zone depth,SZD) derived from microfractography is described.
Abstract: An experimental investigation into the relationship between fracture mechanics parameters (J integral and crack tip opening displacement) determined by mechanics tests and geometrical parameters of deformed crack tip (stretched zone width,SZW and stretched zone depth,SZD) derived from microfractography is described. On the basis of these correlations and results of stereoscopic analysis ofSZ, it is proved thatSZD instead ofSZW is equivalent toCTOD and theSZW = 1/2CTOD is not true.SZ can be divided into two part: the horizontal part (HSZ) nearly parallel to the fatigue precracked surface and the tilt part (TSZ) which intersects the fatigue precracked surface at a blunting angle θ′. The occurence ofHSZ is related to the deformation at crack flank behind crack tip and leads to the inconsistence betweenSZW andCTOD. The connection between the stage 11 fatigue crack growth by the ductile striation andSZ formation process is discussed. The rate ofFCG should be directly related to the width ofSZ formed during fatigue loading, and not be dominated byCTOD.
24 citations
TL;DR: In this article, an illustration of the application of the Estimation-Identification Approach (EIA) presented in ref. [1] for a special metering system is presented.
Abstract: This paper gives an illustration of the application of The Estimation-Identification Approach (EIA) presented in ref. [1] for a special metering system--The Only-line Metering System (AEP).
14 citations
TL;DR: In this paper, a simple method for determining the parameter stability regions of linear control systems with some variable elements in system matrix A is presented, these variable elements may lie in the same row or in different rows.
Abstract: This technical note presents a simple method for determining the parameter stability regions of linear control systems with some variable elements in system matrix A . These variable elements may lie in the same row or in different rows. An example is then given for illustration.
12 citations
TL;DR: In this paper, an inverse problem technique has been developed for detecting irregular cavities in circular cylinders, where the cavity is considered a part of the unknown geometry of the investigated system, and the evaluated temperature is used to locate this geometry.
Abstract: An inverse problem technique has been developed for detecting irregular cavities in circular cylinders. In this method, the cavity is considered a part of the unknown geometry of the investigated system, and the evaluated temperature is used to locate this geometry. An auxiliary problem is introduced in the solution of this problem; and in the solution, the cavity wall is located by forcing the temperature to satisfy the condition imposed at the cavity. The new methodology is validated by an experiment presented in this paper, and the test results indicate that this method is highly successful in locating cavities. The accuracy of the method is closely related to the accuracy of the temperature that can be measured at the surface. A small error in the surface temperature results in a slight cavity error for deep cavities, while a shallow cavity is not severely affected by a surface temperature error. This method is particularly attractive in detecting shallow cavities in nondestructive evaluation.
11 citations
TL;DR: In this paper, the boundary value problems for one-dimensional filtration in partially saturated porous media were considered and the existence, uniqueness and regularity of weak solutions were obtained.
Abstract: In this paper we considered the first and the second boundary value problems for one-dimensional filtration in partially saturated porous media. The existence, uniqueness and regularity of weak solutions were obtained. We also studied the interface problems and discussed the asymptotic behavior of weak solutions.
9 citations
TL;DR: In this article, the eigenvalue method was used to determine three-dimensional deformation of geological bodies from two-dimensional data on three or more nonparallel sections, and a least-squares method was employed to fit an overdetermined system for uniquely determining an ellipsoid.
Abstract: The eigenvalue method (Gendzwill and Stauffer, 1981) is adopted to determine three-dimensional deformation of geological bodies from two-dimensional data on three or more nonparallel sections. A least-squares method is employed to fit an overdetermined system for uniquely determining an ellipsoid. The inverse problem is treated more directly. Calculated examples show that the errors are caused mainly from inaccuracy of the procedures used to obtain two-dimensional data.
9 citations
TL;DR: In this article, the authors studied the infiltration problem with constant rate in partially saturated porous media and found that there exists an unique weak solution to the infiltrate problem with two degenerate situations, and when the infiltration rate is not large enough, the partially saturated state will fall down to completely unsaturated state with the increase of time.
Abstract: In the present paper we study the infiltration problem with constant rate in partially saturated porous media. The main results are: (i) There exists an unique weak solution to the infiltration problem with two degenerate situations. (ii) When the infiltration rate is not large enough, the partially saturated state will fall down to completely unsaturated state with the increase of time.
TL;DR: In this paper, the problem of determining decentralized control for linear, time-invariant interconnected systems with quadratic performance measures is treated as one of constrained optimization under structural control restrictions.
Abstract: The problem of determining decentralized control for linear, time-invariant interconnected systems with quadratic performance measures is considered. The problem is treated as one of constrained optimization under structural control restrictions. An iterative block-diagonalization procedure is developed whereby a local minimum is attained ; the overall system stability is guaranteed at each iteration and the computational burden is greatly reduced in comparison with that required by existing methods.
18 Jun 1984
TL;DR: In this paper, four-wave and six-wave optical processes using the potassium ns2S1/2 states (7 ≤ n ≤ 20) were investigated with input beam provided by a pulsed dye laser pumped by a frequency-doubled Nd:YAG laser.
Abstract: Four-wave and six-wave optical processes using the potassium ns2S1/2 states (7 ≤ n ≤ 20) are investigated with input beam provided by a pulsed dye laser pumped by a frequency-doubled Nd:YAG laser. The beam is focused into a heat-pipe oven containing potassium vapor (nk ≈ 1016 cm−3). More than 120 coherent UV or near-UV lines between 288 and 422 nm are generated through the processes ωUV ± ωIR = 2ωl and ωUV + ωIR′ + ωIR" ± ωIR'" = 2ωL.
TL;DR: In this article, the microstructure and fracture characteristics of a high strength cast steel and a forged steel with the same chemical composition and strength and both subjected to the same heat treatment were studied.
01 Jan 1984
TL;DR: In this paper, the authors studied the effect of conic wall die on the plastic stress and flow field of hydrostatic extrusion and found that the conic and elliptic curve is the best contour for extruding brittle metals.
Abstract: The contour of die wall influences on the plastic stress and flow field of hydrostatic extrusion. At present, conic wall die is mostly used. However when it is used to extrude brittle metals, defects are often found on the products. In order to investigate the cause, the stress field and flow pattern of hydrostatic extrusion with dies of equal strain rate, sine curve, Richmond curve, conic and elliptic curve have been computed and studied by elasto-plastic finite element method. Results show that extrusion with die of equal strain rate has the most uniform stress and strain field as well as the less extrusion pressure and tensile stress. It seems that die curve of this kind is the best contour for extruding brittle metals.
TL;DR: In this article, a mathematical model is presented to cover the effect of a pressure gradient caused by the increasing vapor film thickness along the flow direction, and approximate heat transfer solutions are obtained analytically for laminar film boiling of a liquid deviating greatly from critical state.
01 Jan 1984
TL;DR: In this paper, the cleavage fracture of smooth, notched and cracked specimens of simulated HAZ structure for 15MnVN steel was investigated and the measured cleavage strength, defined by the maximum principal stress at fracture varies with the volume involved in the fracture process.
Abstract: Tests on cleavage fracture of smooth, notched and cracked specimens of simulated HAZ structure for 15MnVN steel show that the measured cleavage strength, σ†*, defined by the maximum principal stress at fracture varies with the volume involved in fracture process Metallographic and SEM examination of fracture specimens lead to the conclusion that the cleavage fracture of the welded structure initiates at the crack nuclei formed in granular islands of M-A constituents and propagates into the ferrite matrix In order to clarify the volume effect on cleavage stress for different specimen geometries, Weibull type statistical formulae are derived based on the ‘weakest link theory’ and the measured size distribution of M-A constituents The volume effect on measured cleavage stresses of smooth, notched and cracked specimens are then explained
TL;DR: In this article, the perturbation method about two parameters is applied to the problem of large deflection of a cricular plate with exponentially varying thickness under uniform pressure, and an asymptotic solution up to the third-order is derived.
Abstract: In this paper the perturbation method about two parameters is applied to the problem of large deflection of a cricular plate with exponentially varying thickness under uniform pressure. An asymptotic solution up to the third-order is derived. In comparison with the exact solutions in special cases, the asymptotic solution shows a precise accuracy.
TL;DR: In this article, a theoretical and experimental study of the mass flow field inside the free burning arc induced by a transverse magnetic field is presented, where the authors show that the induced mass flow through the arc can cool the arc and flatten its temperature field effectively.
TL;DR: Based on the experience of the operators in tuning the parameters of the widely used PI controller, a PI model reference fuzzy adaptive control system (MRFAC) is studied and the fuzzy control can be represented explicitly.
TL;DR: In this paper, the problem of bending a rectangular plate on the elastic foundation is solved by the method of superposition, which satisfies the differential equation, the boundary conditions of the edges and the free corners.
Abstract: In the theory of elastic thin plates, the bending of a rectangular plate on the elastic foundation is also a difficult problem. This paper provides a rigorous solution by the method of superposition. It satisfies the differential equation, the boundary conditions of the edges and the free corners. Thus we are led to a system of infinite simultaneous equations. The problem solved is for a plate with a concentrated load at its center. The reactive forces from the foundation should be made to be in equilibrium with the concentrated force to see whether our calculation is correct or not.
01 May 1984
TL;DR: In this article, the value of using narrowly spaced frequencies within a microwave band to measure wind speeds and rain rates over tropical storms with radiometers is reviewed, focusing on results obtained in the overflights of Hurricane Allen during 5 and 8 of August, 1980.
Abstract: The value of using narrowly spaced frequencies within a microwave band to measure wind speeds and rain rates over tropical storms with radiometers is reviewed. The technique focuses on results obtained in the overflights of Hurricane Allen during 5 and 8 of August, 1980.
TL;DR: In this paper, two remarkable effects influencing the four-wave mixing efficiency are found: (1)transient energy transfer between writing beams, and (2) the time matching between reading beam and the molecular relaxation time of medium.
Abstract: Infrared to visible frequency up-conversion with efficiency as large as 377 percent and real-time storage of nanosecond pulses for a few tenths of a millisecond have been simultaneously achieved in a BDN organic dye solution in toluene. Two remarkable effects influencing the four-wave mixing (FWM) efficiency are found: (1)transient energy transfer between writing beams, and (2) the time matching between reading beam and the molecular relaxation time of medium. The full frequency-domain absorption characteristic and full time-domain storage characteristic of BDN have been studied in detail. The experimental results are identical to preliminary theoretical analysis.
TL;DR: In this paper, a filtration problem with second initial-boundary value in partially saturated porous media is considered, in which the existence and uniqueness of weak solution of the problem are discussed.
Abstract: A filtration problem with second initial-boundary value in partially saturated porous media is considered, In addition to discussion of the existence and uniqueness of weak solution of the problem, it is demonstrated that the interface between the saturated and unsaturated regions exists and continues under certain conditions and the solution possesses some properties, e.g., the balance of water content, the time-limit existence of weak solution ect. which differ from those of the solutions of the first initial-boundary value problem.
19 Jun 1984
TL;DR: The monolithic-isolated single-mode end pumped-ring (MISER) laser as mentioned in this paper was proposed for coherent Doppler radar operating at 1.06 µm.
Abstract: Globes and Brienza1 showed that it is possible to achieve single-mode operation of Nd:YAG without etalons if the laser resonator is constructed as a unidirectional ring. Zhou et al.2 showed that excellent open loop frequency stability is possible if a Nd:YAG laser is constructed with the mirrors applied directly to the laser medium (monolithic construction). We describe a new laser design which combines these two advantages. We call this design the monolithic-isolated single-mode end pumped-ring (MISER) laser. We hope to use a laser of this design as the local oscillator for coherent Doppler radar operating at 1.06 µm. Other possible applications are in coherent communications or ring laser inertial guidance.
01 Jan 1984
TL;DR: A simpler system consisting of a single solute, hexane, dissolved in a single-component, dioleyl lecithin, bilayer is studied, to define a physicochemical framework within which interactions in biological membranes can be better described.
Abstract: The generally accepted architectural scheme for biological membranes is the fluid mosaic model (1), in which integral proteins are dispersed singly or as aggregates in a quasi-two-dimensional lipid bilayer matrix. Such molecules, which are strongly partitioned into the bilayer interior, must form mixtures of some type with the alkyl chains. It thus seems reasonable to view the membrane as a quasi-two-dimensional solution of lipids and proteins (2,3). If the bilayer can be understood as a solvent system, it should be possible to define a physicochemical framework within which interactions in biological membranes can be better described. The characterization of natural biological membranes in terms of the interactions of their component parts is a complex problem because of the multiplicity of different kinds of lipids and proteins involved. Thus, as a first step toward the attainment of this goal, we have chosen to study a simpler system consisting of a single solute, hexane, dissolved in a single-component, dioleyl lecithin, bilayer. In addition, we chose to observe the effects of varying water activity on the bilayer structure. Three things we wish to determine from our neutron diffraction studies of this system are (a) the distribution with respect to thickness of hexane and water in the bilayer, (b) the structural modifications of the bilayer induced by the varying hexane and water activities, and (c) the spatial constraints of packing the alkane and water into the bilayer system.
TL;DR: In this article, a method for evaluating effective potential for local composite fields based on loop expansion was developed, which can be applied to a wider class of models than can the auxiliary field method.
Abstract: We have developed, in this paper, a method for evaluating effective potential for local composite fields based on loop expansion by first renormalizing the generating functional of connected Green's functions and then making the Legendre transformation. A consistency condition reflecting the fact that no condensate effect occurs at tree level is proposed, which plays an important role in this method. The method is illustrated through the Gross-Neveu model. This method can be applied to a wider class of models than can the auxiliary field method.
TL;DR: In this paper, the authors deal with the application of invariant imbedding to solve a particularly important design problem, namely, the duration of the process, and use only the usual design data.
TL;DR: A quantitative framework to the problem of regional economic planning is developed using a dynamical input-output model with multiple-year time-delays using the decomposition and coordination Clethod in control theory.
TL;DR: In this article, experimental results for large V-VxOy-Pb Josephson junctions with overlap-type geometry have been obtained in the framework of the linearized current-phase model.
Abstract: Experiments concerning large V-VxOy-Pb Josephson junctions have been performed. Structures having an overlap-type geometry have been considered. Preliminary experimental results are justified in the framework of the linearized current-phase model.