Glossary

Bond-Graph

A bond graph is a graphical representation of a physical dynamic system. It is similar to the better known block diagram and signal-flow graph, with the major difference that the arcs in bond grap hs represent bi-directional exchange of physical energy, while those in block di agrams and signal-flow graphs represent uni-directional flow of information. Also, bond graphs are multi domain and domain neutral. This means a bond graph can incorporate multiple domains seamlessly. Bond graph is an explicit graphical tool for capturing the common energy structure of systems. It increases one's insight into systems behavior. In the vector form, they give concise description of complex systems. Moreover, the notations of causality provides a tool not only for formulation of system equations, but also for intuition based discussion of system behavior, controllability, observability, fault diagnosis, etc. In 1959, Prof. H.M.Paynter gave the revolutionary idea of portraying systems in terms of power bonds, connecting the elements of the physical system to the so called junction structures which were manifestations of the constraints. This power exchange po rtray of a system is called "Bond Graph"(some refer it as "Bondgraph"), which can be both power and information oriented. Later on, Bond Graph theory has been further developed by many researchers like Karnopp, Rosenberg, Thoma, Breedveld, etc. who have worked on extending this modeling technique to power hydraulics, mechatronics, general thermodynamic systems and recently to electronics and non-energetic systems like economics and queuing theory

C-Elements

Consider a 1-port device in which a static constitutive relation exists between an effort and a displacement. Such a device stores and gives up energy without loss. In bond graph terminology, an element that relates effort to the generalized displacement (or time integral of flow) is called a one port capacitor. In the physical terms, a capacitor is an idealization of devices like springs, torsion bars, electrical capacitors, gravity tanks, and accumulators, etc.

Dissipation

Dissipation embodies the concept of a dynamic system where important mechanical modes, such as waves or oscillations, loose en ergy over time, typically due to the action of friction or tu rbulence. The lost energy is converted into 64/68 Activity Index November 2013 heat, raising the temperature of the system. Such systems are called dissipative systems.

Distributed Parameter Model

The distributed element model or transmission line model of networks assumes that the attributes of the circuit (resistance, capacitance, inductance) are distributed across the whole geometry. In this model, each circuit element is infinitesimally small, and the wires connecting elements are not assumed to be perfect conductors; that is, they have impedance. Unlike the lumped element model, it assumes non-uniform flows along each branch and non-uniform effort along each node. The model is used at high frequencies where the wavelength approaches the physical dimensio ns of the circuit, so the lumped element model used at lower frequencies becomes inaccurate.

Energy

Energy is a quantity that is often understood as the ability to perform work. This quantity can be assigned to any particle, object, or system of objects as a consequence of its physical state. The energy is the integral of the power.

Fidelity

Fidelity refers to the degree to which a model or simulation reproduces the state and behavior of a real world object, feature or condition. Fidelity is therefore a measure of the realism of a model or simulation.

I-Elements

An inertial energy storing 1-port arises if the momentum, P, is related by a static constitutive law to the flow, f. Such an element is called an inertial element in bond graph terminology. The inertial element is used to model inductance effects in electrical systems and mass or inertia effects in mechanical or fluid systems

Lumped Parameter Model

The lumped element model (also called lumped parameter model, or lumped component model) simplifies the description of the behavior of spatially distributed physical systems into a topology consisting of discrete entities that approximate the behavior of the distributed system under certain assumptions. Mathematically speaking, the simplification reduces the state space of the system to a finite number, and the partial differential equations (PDEs) of the continuous (infinite-dimensional) time and space model of the physical system into ordinary differential equations (ODEs) with a finite number of parameters.

Model Reduction

Model reduction or model order reduction is a mathematical theory to find a low-dimensional approximation for a system of ordinary differential equations (ODEs).

Power

Power is the rate at which work is performed or energy is converted. The factors of power i.e., Effort and Flow, have different interpretations in different physical domains. Yet, power can always be used as a generalized coordinate to model coupled systems residing in several energy domains.

R-Elements

The 1-port resistor is an element in which the effort and flow variables at the single port are related by a static function. Usually, resistors dissipate energy. This must be true for simple electrical resistors, mechanical dampers or dashpots, porous plugs in fluid lines, and other analogous passive elements.

State Variable

A state variable is one of the set of variables that describe the "state" of a dynamic system. Intuitively, the state of a system describes enough about the system to determine its future behavior.