Simulacion GPSS

SOCIETY OF

MINING ENGINEERS

.K. Fytas

Lava1 University

Quebec, Canada

E. B. Wilson

Queen's University

Ontario, Canada

R. K. Singhal

CANMET, Energy Mines and Resources

Edmonton, Canada

COMPARISON OF FORTRAN AND GPSS LANGUAGES

IN THE SIMULATION OF A SHOVEL - TRUCK OPEN PIT OPERATION

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Abstract. The General Purpose Simulation

System (GPSS) is a computer simulation language

that has been used for simulations of open pit

haulage operations since the 60's. It is easy

to learn, simple to use, and has a block-diagram

structure that is amenable to load-haul systems.

However, due to its lack of flexibility, there are situations where another language should be

chosen. This paper reviews the characteristics

and capabilities of both GPSS and FORTFAN with

regard to open pit shovel and truck simulation.

The relative advantages and disadvantages are

highlighted and a case study presented along with

comparative results frqu two computer models

(one written in GPSS and the other written in

FORTRAN). .

Introduction

The General Purpose Simulation System. GPSS,

has been used for the simulations of open pit

and underground haulage operations'since the

60's (2,5,7). The choice of this computer language was made because it is easy to learn, simple to use and has a block diagram structure that

is amenable to load-haul systems.

It is claimed that no simulation language can be learned as quickly nor can be made so compact.

Certainly, with respect to haulage cycles, novice

programmers have found that GPSS is a relatively

simple language to learn and apply. No doubt,

the simplicity can be attributed to the direct

relationship between the transactions and blocks

of GPSS and the equipment and cyclical steps of

the actual operation under study. The ease of

application is achieved because whole subroutines can be initiated, in many cases, with one or two

compact statements.

Although load and haul operations can be ex- pressed in GPSS terms with relative ease, there

are simulations where another language should be

chosen. If a sufficient part of a model must be

described in a statement oriented (FORTRAN) rather than a block oriented language (GPSS), it is

better to choose another simulation language.

However, with the GPSS-V version of GPSS, now

being widely used, it is possible to communicate

with statement oriented programs written in FORTRAN or PL11.

The objective of this paper is to review the

characteristics and capabilities of both GPSS and

FORTRAN with regard to open pit shovel and truck

simulation. Two computer simulation models are

compared: the PITSIM-I1 which is a generalized

shovel and truck simulator written in FORTRAN-IV

and the GPMODEL which is a shovel and truck simulator written in GPSS, specifically for the

shovel-truck operation illustrated in Figure 1

(that includes 3 waste shovels, 2 ore shovels,

3 waste dumps and 1 crusher).

Characteristics of PITSIM-I1

The PITSIM-I1 is a computer simulation model

. of shovel and truck systems that was developed at

Queen's University (3,4). It is an interactive,

fixed time incrementing simulation program written

in FORTPAN-IV. The main Eeatures of the model

are :

- It is a generalized and flexible simulator

that can simulate any shovel and truck system independent of the number of shovels, trucks, waste

dumps and crushers involved. - It does not require any advanced programming

knowledge in order to analyze a specific system,

since it is completely interactive and user

friendly as far as the running and modification

procedures are concerned.

- It can take into account both standard or empirical probability distributions as far as the

shovel cycle times are concerned. - In calculating the haul and return cycle

times it can take into account both empirical cycle time data or the performance charts of the

trucks (speed-rimpull and brake performance

curves).

- In simulating truck dispatching systems it

offers the following options: a. Manual dispatching, when the.user based on information for each shovel prompted

by the computer, dispatches the trucks

interactively according to his judgement.

b. Automatic dispatching, when the program

itself, based on built in dispatching

criteria, dispatches trucks automatically

to the various shovels. c. Non dispatching, when the system operates

with the original shovel-truck assignments (closed or static system).

d. Linear programming dispatching, when

using linear programming the model establishes the optimal truck flows for each

section of the haul-return road and subsequently truck dispatching is carried

out based on these optimal flows in order

to meet certain productivity and blending

targets.

Relative Advantages and Disadvantages

The major advantages of GPSS are that is easy

to learn and simple to use. Its readability is

an additional advantage, since the names of the

available statements, which are components of the

language, correspond closely with the ideas used

in simulation. This is of great value whenever

several people must work on the same computer

model

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