## ABSTRACT

PSD Calculation ........................................................................... 175 3.5 Comparison Between Recently Study Works About

Simulation and Modeling Methods for PSD Calculating in Carbons Materials ........................................................................ 184

Keywords .............................................................................................. 191

3.1 INTRODUCTION

Simulation is the imitation of the operation of a real world or system over time to develop a set of assumptions of mathematical, logical and symbolic relationship between the entities of interest of the system, to estimate the measures of performance of the system with the simulation generated data. Simulation can be used to verify analytic solutions. By simulating different capabilities for a machine requirements can be determined. Simulation is not appropriate in some cases include:

• when the problem can be solved using common sense and the problem can be solved analytically;

• when it is easier to perform direct experiments and the simulation costs exceed the savings;

• when the resources or time are not available and system behavior is too complex or can’t be defined;

• when there isn’t the ability to verify and validate the model. Simulation is the appropriate tool in some cases include: • simulation can be used to experiment with new designs or policies

prior to implementation, so as to prepare for what may happen; • simulation can be used to verify analytic solutions and by simulating

different capabilities for a machine, requirements can be determined. Advantages of simulation include: • new polices, operating procedures, decision rules, information

flows, organizational procedures, and soon can be explored without disrupting ongoing operations of the real system;

• new hardware designs, physical layouts, transportation systems, and soon, can be tested without committing resources for their acquisition;

• hypotheses about how or why certain phenomena occur can be tested for feasibility;

• insight can be obtained about the interaction of variables; • insight can be obtained about the importance of variables to the per-

formance of the system; • a simulation study can help in understanding how the system oper-

ates rather than how individuals think the system operates; • “what-if “questions can be answered. This is particularly useful in

the design of new system;

• the two main families of simulation technique are molecular dynamics (MD) and Monte Carlo (MC); additionally, there is a whole range of hybrid techniques which combine features from both [161-165].