In the field of

simulation A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of models; the model represents the key characteristics or behaviors of the selected system or process, whereas the ...

, a

discrete Discrete may refer to: *Discrete particle or quantum in physics, for example in quantum theory *Discrete device, an electronic component with just one circuit element, either passive or active, other than an integrated circuit *Discrete group, a ...

rate simulation models the behavior of mixed discrete and continuous systems. This methodology is used to simulate linear continuous systems, hybrid continuous and discrete-event systems, and any other system that involves the rate-based movement or flow of material from one location to another.

Areas of application

Industrial areas where discrete rate simulation is used include: *

Bulk material handling Bulk material handling is an engineering field that is centered on the design of equipment used for the handling of dry materials. Bulk materials are those dry materials which are powdery, granular or lumpy in nature, and are stored in heaps.http ...

(e.g. minerals and ores, powders, particles, mixed wastes, wood chips) * Liquids and gases * Pulp and paper processing * Oil and gas pipelines * Traffic * High speed/volume

production lines A production line is a set of sequential operations established in a factory where components are assembled to make a finished article or where materials are put through a refining process to produce an end-product that is suitable for onward co ...

in the food & beverage, consumer products, and pharmaceutical industries.

Compared to discrete-event and continuous simulation

Discrete rate simulation combines the event-based timing of

discrete event simulation A discrete-event simulation (DES) models the operation of a system as a ( discrete) sequence of events in time. Each event occurs at a particular instant in time and marks a change of state in the system. Between consecutive events, no change in ...

and the continuous variables calculations found in

continuous simulation Continuous Simulation refers to simulation approaches where a system is modeled with the help of variables that change continuously according to a set of differential equations. History It is notable as one of the first uses ever put to computers, ...

. It predicts and schedules events when the system needs to calculate a new set of rates and determines the appropriate rate of flow for each branch or stream. Discrete rate simulation is similar to discrete event simulation in that both methodologies model the operation of the system as a discrete

sequence of events Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to co ...

in time. However, while discrete event simulation assumes there is no change in the system between consecutive events, in a discrete rate simulation model the flow continues to move at a constant rate such that, for example, the level in a tank could change. Another difference is that discrete event simulation models are overwhelmingly concerned with the status of system entities (discrete objects moving through the system) while discrete rate simulation models are concerned with the status (quantity and location) of homogeneous flow. For rate-based systems, discrete rate simulation has faster computational times and is more accurate in calculating mass balance compared to discrete event simulation. Discrete rate simulation is also similar to continuous simulation in that it simulates homogeneous flow. In addition, both methods recalculate flow rates, which are continuous variables, whenever a state change occurs. However, discrete rate simulation S differs from continuous simulation in that it is event-based and does not simulate every time slice. Modeling linear flow systems using continuous simulation has limitations because it usually is unable to detect important events, such as a tank becoming full or empty, until after the event has occurred plus requires many more system recalculations during the course of the simulation.

Example

An exercise in learning how to build discrete-rate simulations is to model a tank filling and emptying over time. The tank fills at a constant rate and empties at two different rates, one rate until it is full and a faster rate until it is empty. There are 4 types of events in the simulation: start simulation, storage full, storage empty, and end simulation. At each event the model determines which emptying rate to use; between events the emptying rate remains constant.

References

{{reflist

External links

Comparison of Discrete Rate Modeling and Discrete Event Simulation

Discrete Rate Simulation Using Linear Programming

A Global Approach for Discrete Rate Simulation
Simulation Events (computing) Simulation software