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发表于 2010-2-3 13:59:39
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7.PHOENICS入门简介（英文版）-1
INTRODUCTION TO PHOENICS
Contents
•What PHOENICS does
•The Structure of PHOENICS
•How the problem is defined
•How PHOENICS makes the predictions
•How the results are displayed
•Hardware •Customization of PHOENICS
•Learning to use PHOENICS
•The Virtual-Reality Interface
•EARTH
•GROUND
•Built-in Features of EARTH
•Display via VR
• HOTON
•AUTOPLOT
•Other Input and Output Facilities
•rogrammability
•LANT What PHOENICS does
PHOENICS, operated by its users, performs three main functions: 1.problem definition, in which the user prescribes the situation to be simulated and the questions to which he wants the answers; 2.simulation, by means of computation, of what the laws of science indicate will PROBABLY take place in the prescribed circumstances; 3.presentation of the results of the computation, by way of graphical displays, tables of numbers, and other means. PHOENICS, like many but not all CFD codes, has a distinct software module for each function. This sub-division allows functions (1) and (3), say, to be performed on the user's home computer, while the power-hungry function (2) can be carried out remotely.
The Structure of PHOENICS
•PHOENICS has a ‘planetary’ arrangement, with a central core of subroutines called EARTH, and a SATELLITE program, which accepts inputs through the Virtual Reality (VR) interface or otherwise, which correspond to a particular flow simulation.
•EARTH and SATELLITE are distinct programs.
•SATELLITE is a data-preparation program; it writes a data file which EARTH reads.
•PHOENICS users work mainly with SATELLITE, but they can access EARTH also in controlled ways.
•GROUND is the EARTH subroutine which users access when incorporating special features of their own. The diagram below is a schematic of the three main functions of PHOENICS, i.e., 1.Pre-processor - problem definition 2.Solver - simulation 3.Post-processor - presentation of results
8.PHOENICS入门简介（英文版）-2
How the problem is defined
Problem definition normally involves making statements about:
•geometry, ie shapes, sizes and positions of objects and intervening spaces;
•materials, ie thermodynamic, transport and other properties of the fluids and solids involved;
•processes, for example:- whether the materials are inert or reactive; whether turbulence is to be simulated and if so by what model; whether temperatures are to be computed in both fluids and solids; and whether stresses in solids are to be computed;
•grid, ie the manner and fineness of the sub-division of space and time, ie what is called the "discretization"; and
•other numerical (ie non-physical) parameters affecting the speed, accuracy and economy of the simulation. SPECIAL FEATURES of problem definition which distinguish PHOENICS are:- •problem definition can be carried out in a VARIETY of ways, selected by the user according to his experience or preference;
•thus, engineers who use CAD packages can export the corresponding files directly to PHOENICS-VR (ie Virtual Reality);
•VR, and other interactive input procedures of PHOENICS, create as a record a "command file", called Q1, which experienced users of PHOENICS can modify by editing, thus sparing themselves the tedium (as they sometimes see it) of further interactive sessions;
•the "PLANT" feature of PHOENICS allows the property laws of new materials to be supplied by the writing of formulae into the command file; and
•hundreds of quality-assured command files are supplied with the standard PHOENICS sofware in a set of easily accessible LIBRARIES, so that the user rarely has to start from scratch. PHOENICS has indeed its own high-level input language, called PIL, in which the Q1 files are written.
PIL is a directly-interpreted language, requiring no compilation; and its capabilities include:
- direct assignment, as in:NX=10; CARTES=F (ie false); PI=3.1416
- interrogation, as in:NX?; CARTES? which print their values
- arithmetic commands, as in: NX=2*NY
- conditional settings, as in: IF(NX.EQ.10) THEN; CARTES=F; ENDIF
- DO loops, as in: DO II=1,3
MESG(Three cheers! HURRAH! ENDDO
- INCLUDE commands, as in: INCL(file name
- LOAD commands, as in (library case number
- numerous other facilities for setting grids, boundary and initial conditions, material properties, output needs and other data.
So far as is known, PIL is the most powerful and flexible input language ever devised for the setting up of CFD problems.
How PHOENICS makes the predictions
PHOENICS simulates the prescribed physical phenomena by
•expressing the relevant laws of physics and chemistry, and the "models" which supplement them, in the form of equations linking the values of pressure, temperature, concentration, etc which prevail at clusters of points distributed through space and time;
•locating these point-clusters (which constitute the computational grid) sufficiently close to each other to represent adequately the continuity of actual objects and fluids;
•solving the equations by systematic, iterative, error-reduction methods, the progress of which is made visible on the VDU screen;
•enabling the computations to be interrupted, and the controlling settings to be modified, as the user desires;
•terminating when the errors have been sufficently reduced. SPECIAL FEATURES relating to how PHOENICS makes the predictions are:
•PHOENICS can handle a WIDER RANGE OF PHYSICAL PROCESSES, and is equipped with a MORE EXTENSIVE VARIETY OF PHYSICAL MODELS, than any of its competitors. •The ways in which these physical processes are represented in the computer language, Fortran, are visible and accessible to users, and NOT hidden as in most other codes. The relevant coding, called GROUND, constitutes more than fifty percent of the EARTH module.
•This open-source coding is written in a well-annotated easy-to-follow manner, in order that users can, if they wish: ounderstand, odecide whether CHAM's provision meets their needs, and oeither modify it or add coding of their own.
•For users who are not confident of their ability to do this, CHAM has provided the PLANT option, which reduces the user's duties to entering the required formulae into the command file.
•Unlike those other CFD codes which cope with geometrical complexity by the use of "unstructured grids", PHOENICS retains the computational economy of the more-orderly "STRUCTURED GRIDS", while utilising "MULTI-BLOCK", "FINE-GRID-EMBEDDING" and PARSOL, ie "cut-cell" techniques for handling geometric complexity.
•A related and unique feature is the MOVSOL, feature, which makes it easy, economical and accurate to allow curvilinear solids to move relative to each other across curvilinear grids.
•PHOENICS possesses a unique EXPERT feature, which automatically optimises the numerical parameters as the computation proceeds.
•PHOENICS also employs an economical and unique-to-it "PARABOLIC" grid when flow is of the very common "boundary-layer" character.
•The PHOENICS grid has lent itself particularly well to "DOMAIN-DECOMPOSITION", which is what is needed for parallel computers. How the results are displayed
PHOENICS can display the results of its flow simulations in a wide variety of forms.
It has its own stand-alone graphics package called PHOTON; and it can also export results to such third-party packages as TECPLOT, AVS, and FEMVIEW.
Unique to PHOENICS is its ability to take the results of its flow predictions back into the same VIRTUAL-REALITY environment as is used for setting up the problem at the start.
This facilitates understanding by the user; and it also affords a means of conveying the significance of the flow-simulation operation to interested but non-technical persons, eg. high-level managers.
Of course, numerical results are also provided, in the RESULT file.This, when the appropriate commands in the Q1 file, can provide either sparse or voluminous information. |
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