波形测量技术的发展趋势--兼谈YOKOGAWADE的示波器发展

本文着重论述了波形测量技术的最新发展趋势。     

An expert system that performs a satellite stationkeeping maneuver

The development and capabilities of a prototype expert system that provides real-time spacecraft system analysis and command generation are described. At present, ESSOC (Expert System for Satellite Orbit Control) is capable of performing the stationkeeping maneuver for a geostationary satellite. ESSOC guides the operator through the stationkeeping operation by recommending appropriate commands that reflect both the changing spacecraft condition and previous procedural action. Information regarding satellite status is stored in a knowledge base internal to the expert system. This knowledge base is continuously updated with processed spacecraft telemetry. Information on the procedural structure is encoded in production rules. The independence of the procedural rules from each other, and from the knowledge base, makes the system easy to maintain and expand. Particular attention is directed to distinctive features of the ESSOC system and its development, namely, the structured methods of knowledge acquisition, and the design and performance-enhancing techniques that enable ESSOC to operate in a real-time environment.     

Alternative approach to shakedown as a solution of a min-max problem

Summary Melan's classical shakedown theorem for continuous media considered as a problem of methematical programming with constraints is reformulated and reduced to a solution of a certain min-max problem. A similar approach is presented for the structural theory described in terms of generalized variables. A distinction is made between alternating plasticity and incremental collapse modes in the analysis of structures with nonsandwich cross-sections.     

A parametric algorithm for semigroup computation on mesh with buses

In this paper, we present a new parametric parallel algorithm for semigroup computation on mesh with reconfigurable buses (MRB). Givenn operands, our parallel algorithm can be performed in $O(2^{(2c^2 + 3c)/(4c + 1)} n^{1/(8c + 2)} )$ , time on a $2^{(c^2 - c)/(8c + 2)} n^{(5c + 1)/(8c + 2)} \times 2^{(c - c^2 )/(8c + 2)} n^{(3c + 1)/(8c + 2)} $ MRB ofn processors, where $0 \leqslant c \leqslant O(\sqrt {\log _2 n} )$ . Specifically, whenc=0, it takes $O(\sqrt n )$ time on the $\sqrt n \times \sqrt n $ MRB and is equal to the result on the mesh-connected computers; whenc=1, it takesO(n ^1/10) time on then ^3/5×n ^2/5 MRB and is equal to the previous result on the mesh-connected computers with segmented multiple buses; whenc=2, it takesO(n ^1/18) time on the 2^1/9 n ^11/18×2^(?1/9) n ^7/18 MRB; when $O(\sqrt {\log _2 n} )$ , it takesO(log₂ n) time and is equal to the previous result on the MRB. Consequently, our results can be viewed as a unification of some best known results on different parallel computational models.     

On shape sensitivity approaches in the numerical analysis of structures

The semi-analytical, analytical and direct methods for numerical structural shape sensitivity analysis are discussed for a beam model and the general three-dimensional case. While the two first methods are applied directly to the finite element model of a structure, the direct approach follows from a continuous formulation and only the final results can be discretized.     

A viscoplastic material model and its application to cyclic loading

Summary A kinematic hardening model is generalized by introducing plastic and viscous residual back stresses , that govern the translation of the yield surface. The evolution equations for and are proposed and the material functions are identified for a construction steel by carrying out tension-compression tests at different strain rates. The cyclic tests with changing strain amplitudes and frequencies are next carried out and model predictions are compared with experimental results.

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Ein viskoplastisches Stoffmodell und seine Anwendungen bei zyklischer Belastung

Zusammenfassung Ein Modell mit kinetmatischer Verfestigung wird durch die Einführung plastischer und viskoser bleibender Hintergrundspannungen , verallgemeinert, die die Bewegungen der Fließfläche steuern. Die Wachstumsgleichungen für und werden aufgestellt und die Materialfunktionen für einen Baustahl aus Zug-Druckversuchen mit verschiedener Dehnungsrate bestimmt. Die zyklischen Versuche mit sich ändernden Dehnungsamplituden und Fequenzen werden als nächstes durchgeführt und die Modellaussagen mit den experimentellen Ergebnissen verglichen.

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With 14 Figures     

On a lower bound theorem for the buckling load of elastic beams subjected to nonconservative,compressive follower loads

Summary For beams loaded withuniformly distributed follower forces, there exists a lower bound theorem, which allows to evaluate the actual buckling load approximately by means of the buckling load of the same beam loaded correspondingly with conservative unidirectional forces of the same magnitude. In this paper it is shown that the theorem remains valid for monotonically decreasing or at least not increasing follower forces. Moreover, a modified lower bound theorem can be formulated for follower loads which monotonically increase over a part or even over the whole length of the beam. In that case, a lower bound curve has to be constructed using the eigenvalue curve of the conservatively loaded beam. The intersection of the lower bound curve with the vertical axis yields a lower bound for the buckling load of the nonconservatively loaded beam.

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Zu einem Satz über die untere Schranke der Knicklast elastischer, durch Folgekräfte belasteter Stäbe

Zusammenfassung Ein für Stäbe untergleichförmig verteilten Folgekräften gültiger Satz für die untere Schranke der Knicklast gestattet die näherungsweise Ermittlung der tatsächlichen Knicklast aus der desselben Stabes unter richtungstreuer Belastung derselben Größe. In dieser Arbeit wird gezeigt, daß dieser Satz auch für monoton abnehmende oder zumindest nicht zunehmende Folgekräfte gilt. Weiters kann ein modifizierter Satz für über einen Teil des Stabes oder die ganze Stablänge monoton zunehemende Folgekräfte formuliert werden. In diesem Fall muß unter Verwendung der Eigenwertkurve des konservativ belasteten Stabes eine untere Grenzkurve ermittelt werden. Der Schnittpunkt dieser Kurve mit der vertikalen Achse ergibt eine untere Schranke der Knicklast des nichtkonservativ belasteten Stabes.

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With 8 Fugures     

Optimal joint positions and stiffness distribution for minimum mass frames with damping constraints

Optimal design of frames including cross-sectional dimensions (size parameters) and rigid joint positions between beams (configuration parameters) is treated in the paper. The optimal design corresponds to a minimal mass structure with constraints set on damping capacity of free vibration modes. The sensitivity analysis of distinct as well as multiple frequencies is performed analytically using a complex variable sensitivity method. The linking process of size and configuration variables is applied to generate different classes of optimal designs. The numerical algorithm is based on quadratic approximation of the objective function and linear approximation of active constraints. The examples are provided for 2, 12, and 124 beam frames.Presented at WCSMO-2, Zakopane, Poland, May 26–30, 1997     

A design perspective of mechanical function and its object-oriented representation scheme

The purpose of this paper is to present a functional schema which can be used to develop computer tools to assist designers during the early stages of the mechanical product design process. The schema is based on an analysis of the meaning of function. five main types of mechanical function are described: performance, assembly, manufacturing, marketing and maintenance. The paper focuses on the specification and representation of performance functions. These are defined using a natural language, which is an extension of the verb-noun pair technique. Three levels of performance functions are identified: overall, embodiment and geometric. The relationship between these levels of functions and the physical structures required to implement them is discussed in detail. An architecture to implement the schema using object-oriented technology is described. A research prototype based on this architecture has been developed in the programming language Incr Tcl/Tk.