Actual System Behavior Research Articles

Software congestion, mobile servers, and the hyperbolic model

The phenomenon of software congestion is examined. The term refers to situations in which the performance bottleneck of a system is an element of software, rather than a hardware device. Software congestion can occur in any system which contains one or more elements of software whose services may be simultaneously desired by multiple clients, but which can service only one client at a time. It is shown that the use of models which ignore software congestion can produce results that are completely irrelevant to actual system behavior. Furthermore, software congestion is frequently invisible to conventional performance measurement tools. A notational scheme, called mobile servers representation, is introduced for describing those systems in which software congestion may be important. An approximate analytical model, called the hyperbolic model, is developed for analyzing systems with software congestion. >

A Method of Transient Stability Control of Generator in Power System by Using Nonlinear Optimal Regulator

The linear optimal regulators in linear mathematical models of physical systems have proved useful in numerous technical applications, although most differential equations describing the actual system behavior are generally nonlinear. However, a nonlinear optimal regulator is necessary in the inherent nonlinear system which shows remarkable nonlinearity.In this paper we propose a new method, using a Liapunov function, which both asymptotically stabilize the nonlinear system and minimizes a certain cost function. This method is considered to be an extension of the optimal regulator which uses a quadratic cost function.We confirm the validity of this method by applying it to the transient stability control of a generator in a power system.

Deep-reasoning fault diagnosis: an aid and a model

The design and evaluation are presented for the knowledge-based assistance of a human operator who must diagnose a novel fault in a dynamic, physical system. A computer aid based on a qualitative model of the system was built to help the operators overcome some of their cognitive limitations. This aid differs from most expert systems in that it operates at several levels of interaction that are believed to be more suitable for deep reasoning. Four aiding approaches, each of which provided unique information to the operator, were evaluated. The aiding features were designed to help the human's casual reasoning about the system in predicting normal system behavior (N aiding), integrating observations into actual system behavior (O aiding), finding discrepancies between the two (O-N aiding), or finding discrepancies between observed behavior and hypothetical behavior (O-HN aiding). Human diagnostic performance was found to improve by almost a factor of two with O aiding and O-N aiding.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GEOTRACK Model for Railroad Truck Performance

In order to provide a basis for predicting track performance, an analytical model is necessary that will realistically represent the actual behavior of the track system subjected to vehicle loading conditions. The model should adequately characterize the three-dimensional nature of this problem; the various soil and ballast layers can be distinguished and be given proper material properties. In this paper a model is presented that incorporates both of these requirements with a feature which permits loss of contact between tie and ballast when the rail springs up. This model, named GEOTRACK, was developed primarily to characterize the geotechnical aspects of the track behavior. The predictions of this model are in good agreement with measured stresses, strains, and displacements from field experiments at the government test track in Pueblo, Colo.

Stochastic Simulation of Wood Load-Sharing Systems

A generalized procedure was developed to predict the effect of material variability on the variability of system performance when the material properties of the system component members are correlated. This procedure utilized Monte Carlo simulations to predict the load-carrying capacity (strength behavior) of parallel-member wood load-sharing systems from a linear-elastic mathematical model also developed in this study. The simulated strength behavior obtained using this procedure was compared to the strength behavior of actual wood load-sharing systems tested to failure. This simulation technique was shown to be an extremely good predictor of system variability. Although this procedure was developed for specific application to the prediction of wood-joist floor behavior, it can easily be applied to any area of structures research in which the members exhibit correlated properties.

MODEL FORMULATION FOR FLEET SIZE ANALYSIS OF A UNIVERSITY MOTOR POOL

ABSTRACTA GPSS/360 model was developed to investigate the behavior of a university's motor pool dispatch fleet. Time‐series data were collected and frequency distributions were constructed for vehicle request patterns and trip‐duration times. Regression analysis was performed to formulate trip mileage generators as functions of service time. Appropriate statistical goodness‐of‐fit tests were conducted to ascertain the extent of congruence between actual system behavior and expectations based on a number of theoretical distributions. Analysis of simulated response variables indicates that the model's internal structure reproduces reality to a high degree. Fifteen years of simulated experience were generated for six alternative fleet size configurations; results suggest that reductions in existing fleet capacity could be realized without effecting undue impairment in service levels.

Stability of the Solar System

This paper reviews the present status of research on the problem of stability of satellite and planetary systems in general. In addition new results concerning the stability of the solar system are described. Hill's method is generalized and related to bifurcation (or catastrophe) theory. The general and the restricted problems of three bodies are used as dynamical models. A quantitative measure of stability is introduced by establishing the differences between the actual behavior of the dynamical system as given today and its critical state. The marginal stability of the lunar orbit is discussed as well as the behavior of the Sun-Jupiter-Saturn system. Numerical values representing the measure of stability of several components of the solar system are given, indicating in the majority of cases bounded behavior.

Conformational dynamics and the rotational isomeric state model

Abstract The dynamics of diffusion of a system described by a one-dimensional periodic potential is examined as a function of the parameters of the potential. The same system is analyzed employing the rotational isomeric site model. It is found that the site model does not describe the actual system behavior at short times. If the barriers are of the order kT or less, the site model is inadequate for times up to the order of the system relaxation time. Good agreement is found for long times providing the infinite time asymptotes are made to agree by employing only the site model orientations in the computation of the mean dipole moment. This systematic error in the calculation of a static property increases as the barriers decrease.

Constitutive modeling and numerical solution of field problems

Abstract In formulating phenomenological models and developing solution algorithms for problems in continuum and structural mechanics, experience with the behavior of actual systems has always played an important guidance role for the engineer concerned with predicting performance of feasible alternatives. By exercising control over various system parameters the engineer attempts to minimize the difference between a desired objective and a predicted approximation thereof. Constitutive modeling of mechanical behavior of materials is an example typical of this activity. In this paper constitutive modeling of an isolated material element is discussed as an identification problem. The mathematical structure of the problem is discussed and limitations arising from experimental sources, measurement errors, and material nonlinearity are noted. As a consequence of the structure of the problem it is shown that an inverse initial-boundary value problem must be considered, in which material identification and numerical analysis of this problem must proceed simultaneously. This paper discusses a discretized form of the inverse problem and illustrates the methodology by citing a number of examples in the literature which appear as special cases of the present treatment.

Analytical modeling of respiratory protective devices.

An analytical description of a generalized respiratory protective device is developed by representing the physical system as an equivalent electrical circuit. As a first step, a system of nomenclature is presented which divides the generalized respiratory protective device into several subsystems, and identifies the possible individual components in each subsystem. Each component is then modeled by its electrical analog, and by combining the appropriate components an electrical analog to a particular respirator system is generated. To evaluate the validity of this generalized analytical model, the U.S. Army M-17 protective mask is modeled, using data obtained through an experimental testing program. The model is analyzed mathematically, with a digital computer employed as necessary, and its accuracy is evaluated by comparing the behavior of the M-17 respirator system, as predicted by the model, to actual system behavior obtained experimentally.

Friction-Induced Vibration

Friction-induced vibration has been studied in a system consisting of an elastically suspended, damped slider which is loaded against a surface moving at a constant velocity. Exact analysis reveals a critical velocity which limits the incidence of vibration. The critical velocity depends on damping, load, stiffness, and friction characteristics which vary with time and velocity. Approximations in the theory yield an amplitude-velocity equation and another critical velocity relationship. Reasonable agreement is found to exist between the exact and approximate theories for critical velocity. Experimental results for several systems illustrate amplitude-velocity relationships and the existence of critical velocities. The correlation between the experimental results and the approximate theory indicates that the analytical method could be used to predict the vibration behavior of actual systems.

Enzymatic polymerization. II. Branching by rearrangement and its application to the dextran system

AbstractIt is shown that increases in molecular weight and branching during the formation of dextran can be qualitatively accounted for by a random rearrangement of initially linear chains. Very large increases of molecular weight can result from the formation of branches at less than 1% of the glucose units of the original chains. The expressions presented do not account rigorously for the actual behavior of the dextran system, probably chiefly because the rearrangement process is no longer random when the molecules have become very large and highly branched.