Simulation Practice and Theory最新文献

The paper deals with the dynamic analysis of double acting actuators, both linear and rotary ones. Two different formulations to model a pneumatic circuit, composed of an actuator and a digital valve, are presented. In the first one an air thermodynamic transformation is assumed and the simulation is carried out in the MATLAB-Simulink environment, while in the second one also the energy equation is introduced, so that the thermic exchange between the chambers and the external ambient is considered. Furthermore models of actuators, both linear and rotary, using the bondgraph method are presented; the energy and continuity equations are implement by using two C-fields. Finally simulations results, obtained in the two different environments, are compared and discussed.

Along with an ever increasing model complexity, a so-called object oriented approach to physical systems modeling has become more and more popular throughout the last few years. Frequently used keywords are multi-domain modeling, model reuse, and non-causal equations. On the other hand the physical systems modeling methodology based on bond graphs has been in use worldwide since Paynter devised bond graphs more than 35 years ago. It seems that due to different roots and a different terminology, aspects of one of the two approaches are not fully appreciated by those who adhere to the other modeling paradigm. By relating features of object-oriented modeling (OOM) to corresponding ones of the older bond graph methodology, it is pointed out what both modeling approaches have in common and what is different. As a working modeling language, Modelica is used since it seems that this object oriented modeling language is going to receive an increasing attention as a neutral exchange format between proprietary modeling tools. As an application example that combines the electrical, the hydraulic and the mechanical energy domain in a single system, a hydraulic drive with a controlled displacement pump is considered.

The Bondgraph represents mechanical, hydraulic and electric components with their power flow in an unified manner and is used here for a three port regulator valve for pressure. It consists of a valve spool and a valve body or casing, and an electric solenoid. The valve assembly has three ports and two variable metering orifices, represented by modulated R-elements. They are the combination of a proportional and a quadratic characteristic, each by separate R-elements. One of them is in conductance causality, the other one in resistance causality and they are on a 1-junction. This gives an algebraic loop that can be broken by a first order element. Even with a closed port, there is some passage, or leakage in the valve due to clearance. The solenoid is non-linear. The whole is represented by a Bondgraph and simulated by the TUTSIM program, where real parameters are used. This leads the valve dynamics much quicker than solving differential equations

We discuss the modeling and simulation package 20-sim, a tool for modeling and simulation of dynamic behavior of engineering systems. Engineering systems as application domain means that we focus on systems that span multiple physical domains and the information domain. The 20-sim software is an interactive tool, where model entry and model processing are fully integrated. This means that already during model entry and editing, models can be checked on their consistency. 20-sim has its own simulator, using sophisticated numerical integration methods, taken from. internationally accepted numerical libraries. The use of 20-sim is demonstrated by an example, in which a 3-dof scara robot with controller is modeled and simulated.

In this paper it will be shown that a common modeling approach based on extrapolation from standard (textbook) models may lead to the unnecessary use of the state-event construct. Although this may be hand-waved as the result of bad modeling practice, the running example discussed herein has been used for quite some time as a benchmark problem for event handling in the literature [F. Breitenecker, ‘Comparison 7: Constrained pendulum’, Simulation News Europe, No. 7, p. 29, March 1993, ARGESIM, Vienna University of Technology, Vienna, Austria (the benchmark proposed herein was used in several later issues of this journal)]. Unnecessary use of the state-event construct may be prevented by using a model representation that increases insight in the physical meaning of the state variables used in the model and in the way they are handled. Herein the mentioned benchmark problem is analyzed in order to demonstrate the problem and some guidelines are given which may increase this insight.

In this article a short route to arrive at bondgraph model of induction motor is discussed. Creating a model of an induction motor with electrical, magnetic and mechanical ports is a considerably puzzling issue. The usual approach is to view induction motor as an extended transformer with a resistor varying as a function of slip. Such models are inadequate when motors are driving a general class of loads and when electrical input is not a pure harmonic. Though there are several models with intertance fields derived in classical manner they obscure the physics of the system and are often intractable. In this article a general principle of modelling induction motors is presented by viewing the fluctuation of magnetic field from two coordinates, one fixed to stator and other to the rotor. The mechanical port emerges out naturally and the model is computationally efficient and compact. An interesting phenomenon of such a motor driving a rotor with material damping beyond its threshold speed of instability is simulated and discussed. Rotors with internal damping tend to become unstable when driven beyond a speed which is entirely determined by a ratio of external and internal dampings and the critical speed. When such rotors are driven by an induction motor with supply frequency beyond the threshold speed of instability very interesting phenomena are observed in the coupled system like entrainment of rotor speed, existence of limiting oribit of the rotor, small fluctuation of angular speed caused by unbalance and seemingly chaotic behaviour. This example shows the power of bondgraph modelling of induction motor with a mechanical port which can be coupled to a general class of loads.

We present a new lumped model of the pump behaviour of the mammalian left ventricle based on simple but physiologically plausible sub-models of chemo-mechanical energy transduction in muscle, mechano-hydraulic energy transduction in the ventricular wall and hemodynamical coupling of the ventricle and its arterial load. The model builds upon the foundation of classical analog ventricular models (dynamic compliance and visco-elastic models). However, we show that these classical models are not coherent from an energy viewpoint. To insure this coherency, we introduce explicit cross-bridge mechanisms linked to the mechano-hydraulical part of the model by a two-port capacitive (2PC) transducer representing chemo-mechanical coupling. We show that this 2PC is thermodynamically plausible and, when coupled to dissipative models of chemical energy generation and transfer, provides a novel and consistent characterisation of cardiac energetics at the global pump level. Finally, we briefly discuss some generalisations using nonlinear elements described by functional equations to represent muscle memory and sur-activation.

It is a well-known fact that languages shape perception. Of all the lumped modelling languages, the bond graph (BG) method is the only one to use the notion of a 2PC as a primitive modelling concept. Our hypothesis (mental model) is thus directly inspired by the fact that we use the BG language. Our claim is thus that our work demonstrates very clearly the heuristic and descriptive power of BGs in shaping new ideas about multi-energy and nonlinear physiological applications.

Several aspects can be defined for modelling languages. This paper establishes three important concepts:

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  Discipline: specifies which domain(s) of science can be represented.

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  Paradigm: states the main mathematical characteristics of the language.

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  Modelling level: qualifies the semantic basement of the representation.

Modelling languages can thus be positioned in a three-axis view, yielding a clear and unambiguous expression of their application scope. There is no absolute “best” choice among the modelling languages. Any simulation specialist must be aware of the characteristics of the different formalisms to be able to select the one that fits any particular problem.

System inversion techniques and bond graph representations are used here to present a methodology for the dimensioning of actuating components for the proper operation of the overall system based on dynamic and energy criteria associated to some prescribed specifications. The proposed methodology to deal with the so-called sizing problem is then illustrated by the validation of the actuators of a two-link manipulator for a specified end-effector trajectory. The study shows that the components imposing limitations to the system performance and the causes of their inappropriateness can conveniently be identified and analysed.