Thread View: comp.simulation
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Started by Moderator: Paul Fishwick
Wed, 26 Aug 1992 19:01
SIMULATION DIGEST V28 N10
Author: Moderator: Paul Fishwick
Date: Wed, 26 Aug 1992 19:01
Date: Wed, 26 Aug 1992 19:01
898 lines
38158 bytes
38158 bytes
Volume: 28, Issue: 10, Wed Aug 26 15:00:49 EDT 1992
+----------------+
| TODAY'S TOPICS |
+----------------+
[NEW QUESTIONS]
DYNAMO Packages for MAC and UNIX
Implementing the Pspice LAPLACE Option
Dewdney's Planiverse
Fluid Dynamics Simulation
Generating Qualitative Descriptions
[REGARDING PAST QUESTIONS]
Simulating Group Behavior
N Body Simulation
[CALL FOR PAPERS/PARTICIPATION]
Computer Aided Design
[DEPARTMENTS]
Simulation in the Service of Society
* Moderator: Paul Fishwick, Univ. of Florida
* Send topical mail to: simulation@bikini.cis.ufl.edu OR
post to comp.simulation via USENET
* Archives available via FTP to bikini.cis.ufl.edu (128.227.224.1).
Login as 'anonymous', use your e-mail address as the password, change
directory to pub/simdigest. Do 'binary' before any file transfers.
* Simulation Tools available by doing above and changing the
directory to pub/simdigest/tools.
-----------------------------------------------------------------------------
Subject: [NEW QUESTIONS]
------------------------------
From pvye@u.washington.edu Wed Aug 19 01:21:35 1992
(5.65/UW-NDC Revision: 2.22 ) id AA09388; Tue, 18 Aug 92 22:21:34 -0700
Date: Tue, 18 Aug 92 22:21:34 -0700
From: Patrick Vye <pvye@u.washington.edu>
Sender: pvye@milton.u.washington.edu
To: simulation@bikini.cis.ufl.edu
Subject: System Dynamic Simulation package?
Hello,
I am trying to get some help finding a simulation package.
I am trying to find a continuous simulation package that is similar
to DYNAMO but works on the MAC or under UNIX.
I don't need a graphical capability, but would like the syntax
to be similar to DYNAMO so that I can set up an an input file that
specifies rate, level and auxiliary equations. It can solve the
equations using Euler's method or Runge-Kutta. Again, there is
no need for a graphical capability for either input or output.
I plan to use the simulation in batch with another application.
Any pointers to a package would be greatly appreciated.
Pat
------------------------------
To: comp-simulation@inria.inria.fr
Path: corton!geocub!gonzales!bardo
From: bardo@ief-paris-sud.fr (Bardo Muller)
Newsgroups: comp.lsi.cad,comp.lsi,comp.simulation,alt.cad,sci.comp-aided,sci.math.num-analysis
Subject: PSPICE, option LAPLACE - algorithm ?
Keywords: spice,laplace transform,transient analysis,convolution
Date: 19 Aug 92 14:00:00 GMT
Sender: usenet@greco-prog.fr (le facteur fnet)
Reply-To: bardo@ief-paris-sud.fr
Followup-To: comp.lsi.cad
Organization: Universite de Paris
Hi there!
Does anyone have any pointers, code, literature or other comments on how to
implement something similar to the PSPICE LAPLACE option ?
[ you describe an (arbitrary ?) function F(s) in the frequency domain which is then used in a (nonlinear, variable timestep) transient analysis ]
Convolution with the inverse transform of the impulse response should be
one viable method. Is there any more analytical (even approximative) approach known ?
At the moment I experiment with a backward-euler for rational functions N(s)/D(s).
Ideas ? Please e-mail. I will post a summary of the proposals.
Thank you !
Bardo
___________________________________________________________________________
| Bardo MULLER | phone : [33] [1] 69 41 78 50 |
| Institut d'Electronique Fondamentale | fax : [33] [1] 60 19 25 93 |
| Bat. 220 Universite Paris Sud | e-mail : bardo@ief-paris-sud.fr |
| 91405 ORSAY CEDEX FRANCE | THE NET WORKS ! |
|_______________________________________|__________________________________|
------------------------------
Posted-Date: Mon, 24 Aug 1992 16:37:27 GMT
Newsgroups: comp.simulation
Path: wlh04953
From: wlh04953@aero.org (William L. Hayden)
Subject: planiverse
Relay-Version: version Trumpet 1.03; site elp.aero.org
Summary: Is there any life on this group ?
Sender: news@aero.org
Organization: The Aerospace Corporation
Posting-Version: version Trumpet 1.03; site elp.aero.org
Date: Mon, 24 Aug 1992 16:37:27 GMT
Apparently-To: comp-simulation@ucsd.edu
Just read DEWDNEY's Planiverse.
Does the class project program 2DWORLD or equivalent exist ?
If so is it available for download somewhere (FTP) ?
Thanks in advance for any response.
------------------------------
Newsgroups: sci.areonautics,comp.simulation
Path: johng
From: infmx!johng@uunet.UU.NET (John Galloway)
Subject: Fluid dynaics sim (50mph air) on a Quadra 700, is it possible?
Originator: johng@godzilla
Sender: infmx!news@uunet.UU.NET (Usenet News)
Organization: Galloway Research
Distribution: ca
Date: Tue, 25 Aug 92 09:30:14 GMT
Apparently-To: uunet!comp-simulation
I have been tinkering around with various edge treatments for the
windshield on my motorcycle in an attempt to reduce/move/affect
the turblance layer that comes off the trailing/top edge (right into
my helmeted head (helmet skirts and/or ear plugs are the existing
answer).
I would like to get more scientific about this and am wondering if
my mostly idle but up all day Quadra 700 A/UX system could be useful
doing fluid dynamics simulations of proposed configurations.
I would appreciate some guesses as to the complexity of such calculations
(navier-stokes or something like that?) needed to carry out such simulations
(even assuming the sw is available and not toooo expensive).
Just wild guessing I get:
3.00 width (ft.)
3.00 length
3.00 height
46,656.00 cubic inches
8.00 points/inch
23,887,872.00 points/data set
3.00 floats per point in dataset (3D pressure vector?)
4.00 bytes per float
15.00 flops/point/itteration (vector to components and back and?)
1,025.16 MFlops/itteration
50 itterations (gives ?? 1/4 second at 50 mph?)
500.00 MFLOPS of sys
30 % of run MFLOPing
341.72 hours for run
14.24 days for run
0.01 MB/sec (reading/writing compressed data for run)
273.38 MB/raw data set
2.73 compression ratio to achive:
100.00 MB/compress data
Which says that even on a 500MFLOP machine I would need 1/2 month, with 1/8
inch grid spacing, on a 5(?)MFLOP Quadra => no way. Is this problem really
not this bad, or have I guessed close enough to be clear that its totally not
feasable to get any meaningfull results (for design assistance) within a few
days on a Quadra. The data set size is actually viable, I could make good
use of a new 1.5GB disk, and 68MB of memory, but its the crunchyness, or
lack of it, that kills the idea. right? thanks.
-jrg
internet jrg@galloway.sj.ca.us John R. Galloway, Jr 795 Beaver Creek Way
applelink D3413 CEO...receptionist San Jose, CA 95133
Galloway Research (408) 259-2490
--
internet jrg@galloway.sj.ca.us John R. Galloway, Jr 795 Beaver Creek Way
applelink D3413 CEO...receptionist San Jose, CA 95133
Galloway Research (408) 259-2490
------------------------------
Newsgroups: comp.ai,comp.simulation
Path: cbl6rjw
From: cbl6rjw@gps1.leeds.ac.uk (R.J. Williams)
Subject: qualitative description of the output of a quantitative simulation
Sender: usenet@sbcs.sunysb.edu (Usenet poster)
Nntp-Posting-Host: gps1.leeds.ac.uk
Organization: University of Leeds, England
Date: Wed, 26 Aug 1992 16:35:20 GMT
Apparently-To: simulation@uflorida.cis.ufl.edu
Hello,
I am trying to find information on any systems that can generate
qualitative descriptions of output from a quantitative simulation. We
are utilising a quantitative modelling system which uses a flow metaphor;
instrumentation can be placed anywhere on the model. Each piece of
instrumentation produces a value every dt.
[[ED: You might consider using qualitative analysis for systems of
differential equations. Consider "Practical Numerical Algorithms for
Chaotic Systems" by Parker and Chua for algorithms yielding qualitative
insights (Lyapunov exponents, fixed points, etc.). Also, there is work
in AI that has focused on this area -- see the past few AAAI/IJCAI
proceedings -PAF]]
We have a knowledge based version of the quantitative model with
dependencies represented (but not the actual formulas). We would
like to produce a qualitative description using this together with the
quantitative output. Recognising maxima, minima, decreasing and
increasing values is ok, but we would also like to be able to notice
periodicity, possible relationships between features in different
output streams and trend analysis.
Thanks for any pointers,
rod
----
Roderick Williams rodw@cbl.leeds.ac.uk
------------------------------
Subject: [REGARDING PAST QUESTIONS]
------------------------------
Newsgroups: comp.simulation
Path: news
From: jones@pyrite.cs.uiowa.edu (Douglas W. Jones,201H MLH,3193350740,3193382879)
Subject: Re: Application to the Softer Sciences
Sender: news@nexus.uiowa.edu (News)
Date: Fri, 21 Aug 1992 16:25:15 GMT
References: <1992Aug21.072608.22299@uwm.edu>
Nntp-Posting-Host: pyrite.cs.uiowa.edu
Organization: University of Iowa, Iowa City, IA, USA
Apparently-To: comp-simulation@uunet.uu.net
>From article <1992Aug21.072608.22299@uwm.edu> in sci.cognitive,
by spice@convex.csd.uwm.edu (James G Spice):
> I am a graduate student in Political Science, a field not well known
> for its mathamatical or modeling sophistication (though exceptions
> certainly exist). Does anyone know of any applications of cognitive
> science methods in the softer social sciences?
I can't help in the area of political science, but I'm involved in
developing a system for simulating the behavior of small groups of
people confonting crisis situations, known as Icarus because it is
a bit of a high-risk venture. Icarus uses a discrete-event simulation
framework (as commonly used in operations research) with small expert
systems used to model each human participant in the group.
One aim of Icarus is to allow simulation models to express the contents
of the "rule books" for such contexts as nuclear reactor control rooms
in order to ask the question "if people played by these particular
rules through this scenario, what is the likelyhood of a successful
outcome." The cost of such experiments using human subjects can be
outrageous, but cased like Three Mile Island and the Stark incident
make such experiments quite valuable.
A second aim is to allow the formulation of more nearly formal theories
about small group behavior in the form of simulation models. The use
of simulation methodology can give such a theory a predictive value
comparable to the predictive value of traditional theories in the hard
sciences, and this can significantly reduce the number of experiments
needed to explore the behavior of such a group.
The Icarus simulator is extremely limited in what it can accomplish!
It cannot model learning, metaknowledge (that is, my knowledge about
what I or others know), complex concepts, or convoluted reasoning, and
we cannot handle more than a handfull of people in one of our models.
Without learning, Icarus can be used to model crisis situations where
the feedback on which learning could be based happens too late to
influence the outcome. We can deal with simple quantitative knowledge,
including, eventually, fuzzy quantities, and this should be quite
adequate for many purposes, for example, the reactor control example
where things like water pressure, temperature, and level are the key
bits of knowledge exchanged by the participants.
Currently, our work on Icarus is bogged down in some interesting
technical problems that arise when you try to combine expert systems
with discrete-event simulation. We now know two or three ways to fix
these problems, but we don't know which is right way to go. When we've
solved these problems, we'll start to try to attract a user community
from among small-group sociologists and the management science
community.
Doug Jones
jones@cs.uiowa.edu
------------------------------
Newsgroups: comp.simulation
Path: uad1184
From: uad1184@dircon.co.uk (Dino Dini)
Subject: Re: Gravitational motion errors
Date: Tue, 25 Aug 1992 22:53:47 GMT
References: <36817@uflorida.cis.ufl.edu>
simulation@uflorida.cis.ufl.edu writes:
>I am going to be writing a little routine to do N-body gravitational
>motion simulations in 2 dimensions.
>
>The first time I tried this I had some sort of error (perhaps a rounding
>error) that caused free objects to continuously gain momentum down
>the screen. When I modified it to allow objects that drop off the
>bottom of the grid/screen to reappear at the top, they quickly gained
>significant momentum and zipped around in an interesting, if not
>useful, way.
>
>Does it sound like I just need to be more careful about rounding
>off numerical values?
>
>Sorry if this is lame... I haven't much simulation experience.
>
>Michael McGinnis Internet: mcginnis@kuhub.cc.ukans.edu
>Computer Center Bitnet: mcginnis@ukanvax
>University of Kansas Voice: (913)864-0413
>Lawrence, KS 66045 FAX: (913)864-0485
>
>Rust never sleeps.
It is difficult to say without seeing your listing. I have done
an N-body simulation crudely in X using floating point. Rounding
errors create inaccuaracies, but the general behavior is consistent
with what you expect. From the sound of it you had a fairly
major bug in there.
------------------------------
Subject: [CALL FOR PAPERS/PARTICIPATION]
------------------------------
To: comp-simulation@ux1.cso.uiuc.edu
Subject: ICCAD-92 Registration (CAD Conference)
Path: roundup.crhc.uiuc.edu!news
From: fuchs@crhc.uiuc.edu (W. Kent Fuchs)
Newsgroups: comp.lsi.cad,comp.lsi,comp.simulation,comp.lang.vhdl,news.announce.conferences,comp.lsi.testing,comp.cad.cadence,alt.cad,comp.sys.mentor,comp.lang.verilog
Subject: ICCAD-92 Registration (CAD Conference)
Date: 24 Aug 1992 22:08:32 -0500
Organization: Center for Reliable and High-Performance Computing, University of Illinois at Urbana-Champaign
Nntp-Posting-Host: roundup.crhc.uiuc.edu
Summary: Registration Information for ICCAD-92
Keywords: CAD Conference Registration Tutorials
ACM/IEEE International Conference on Computer-Aided Design
November 8-12, 1992, Santa Clara, CA USA
ICCAD-92
Preregistration deadline: October 12, 1992
Contents of This Post:
1) Conference Overview
2) Schedule of Conference Sessions
3) Registration Forms (print, clip and mail)
---------------------------------------------------------------------------
CONFERENCE OVERVIEW CONFERENCE OVERVIEW CONFERENCE OVERVIEW
---------------------------------------------------------------------------
The Tenth International Conference on Computer-Aided Design,
ICCAD-92, offers an exceptionally strong schedule of papers, tu-
torials, and vendor suites. The program promises to challenge ex-
perienced CAD developers, hardware designers, and academic
researchers who want to learn from the latest in CAD research and
development.
ICCAD-92 will be held November 8-12, 1992 in the Santa Clara
Convention Center, Santa Clara, California. The conference con-
centrates on CAD for electronic design and features three days of
technical sessions, one day of four different tutorials, and a
lively evening panel discussion. To complement the technical
program, numerous CAD vendors will have suites at ICCAD-92.
This offers the conference attendees a unique opportunity to hold
in-depth technical discussions with vendors on their latest pro-
ducts.
An advance program is available and can be requested from the
conference managers, MP associates, by phone, fax or mail:
MP Associates
7490 Clubhouse Road, Suite 102
Boulder, CO 80301
Telephone: (303) 530-4562
FAX: (303) 530-4334
--------------------------------------------------------------------------
ICCAD-92 AT A GLANCE ICCAD-92 AT A GLANCE ICCAD-92 AT A GLANCE
--------------------------------------------------------------------------
Monday, Nov. 9
8:30 PLENARY SESSION
10:00
10:30 2A: Design for 2B: Technology and 2C: FPGA Synthesis
12:30 Test Layout
2:00 3A: Waveform 3B: Topics in 3C: Asynchronous
3:30 Evaluation Simulation Circuit Synthesis
4:00 4A: Clocking and 4B: High Density 4C: Formal
6:00 Level Sensitive Module Hardware
Latches Assembly Verification
6:30 PANEL "University Faculty: Visionaries or Mercenaries?"
8:00
Tuesday, Nov. 10
8:30 5A: CMOS Power 5B: Sequential 5C: High-Level
10:00 and Timing Circuit Design
Estimation Test Generation
10:30 6A: Classical 6B: Testing & 6C: Synthesis for
12:30 Simulation Diagnosis DSP Applications
2:00 7A: Analog 7B: Multi-View 7C: Timing in High-
3:30 CAD Design Level Synthesis
Representations
4:00 8A: High 8B: Detailed 8C: Topics in
6:00 Performance Routing Logic
Simulation Synthesis
7:00 Banquet
10:00
Wednesday, Nov. 11
8:30 9A: Partitioning 9B: Interconnect 9C: Engineering and
10:00 & Clustering Analysis Education:
Trends and Needs
10:30 10A: High 10B: Hardware/ 10C: Retiming and
12:30 Performance Software Sensitization
Routing Co-Design Conditions
2:00 11A: Design 11B: Delay 11C: Asynchronous
3:30 Management Testing Synthesis
Styles
4:00 12A: Placement & 12B: High-Level 12C: Hazards in
6:00 Floorplan Testing Combinational
Design Synthesis
Thursday, Nov. 12
Tutorials:
- Multi-Level Logic Synthesis
- Interconnect and Packaging Analysis
- Introduction to Embedded System Design
- Architectures for Software Systems
-----------------------------------------------------------------------------
Please notice that registration and hotel reservation are two different forms
that go to two different places, and that only the hotel reservations can use
a credit card.
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
REGISTRATION REGISTRATION REGISTRATION REGISTRATION REGISTRATION REGISTRATION
-----------------------------------------------------------------------------
Advance Registration Form
ICCAD-92
November 8-12, 1992, Santa Clara, CA USA
Advance Registration Deadline: October 12, 1992
Send completed registration form and check payable to ICCAD-92 to:
MP Associates
Registration Desk
7490 Clubhouse Rd. #102
Boulder, CO 80301
Information Only: (303) 530-4562
All advance registrations must be postmarked by October 12,
1992. On-site conference payments must be made by check or cash.
NO CREDIT CARDS! No refunds unless cancellation is received be-
fore October 12, 1992. All refunds are subject to a $15 fee.
Name _______________________________________________________________
Company ____________________________________________________________
Mailing Address ____________________________________________________
Mail Stop __________________________________________________________
City ________________________________ State __________ Zip _________
Country _____________________________ Telephone (_____)_____________
Member No. ACM/IEEE ________________________________________________
Conference Registration Fees:
Before After
Oct. 12 Oct. 12 Amount
IEEE/ACM Members $200 $260 ___________
Non-Members $260 $325 ___________
Students $100 $100 ___________
One Day Only $120 $140 ___________
select day: ____ Mon ____ Tues ____ Wed
Tutorial Fees:
Before After
Oct. 12 Oct. 12 Amount
IEE/ACM Member Full Day $280 $325 ___________
Non-Member Full Day $350 $435 ___________
Students $100 $100 ___________
Total Amount (Conference and Tutorial) ___________
TUTORIAL REGISTRATION: To participate in the tutorials there must
be at least a one-day conference registration. If you have paid
the proper amount to include a tutorial, please indicate first
(1) and second (2) choices. Tutorials are limited to a first-
come, first-served basis.
_______ Multi-Level Logic Synthesis
_______ Interconnect and Packaging Analysis
_______ Introduction to Embedded System Design
_______ Architectures for Software Systems
-----------------------------------------------------------------------------
Please notice that registration and hotel reservation are two different forms
that go to two different places, and that only the hotel reservations can use
a credit card.
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL HOTEL
-----------------------------------------------------------------------------
Hotel Reservations for ICCAD: 10th Intl. Conference on Computer Aided Design
November 8-12, 1992, Santa Clara, CA USA
Hotel Reservation Deadline: October 12, 1992
Hotel reservations will be handled on a first-come, first-served
basis by the Santa Clara Housing Bureau. Reservations must be
postmarked by OCTOBER 12, 1992 to guarantee availability of rooms
and rates at the conference hotels. The following hotels are
available:
Please indicate first (1) and second (2) choices.
HOTEL Single Double
____ Westin Hotel $ 95.00 $105.00
____ Holiday Inn $ 53.00 $ 53.00
____ Days Inn $ 53.00 $ 53.00
The Days Inn and the Holiday Inn will provide shuttle service to
the Santa Clara Convention Center. The Westin Hotel is attached
to the Conference Center.
Indicate hotel preference above and send completed hotel form to:
Santa Clara Housing Bureau I
C/O Santa Clara Convention and Visitors Bureau
PO Box 387
Santa Clara, CA 95052 Caution: Hotel Reservations
sent to MPA office will be
Information Only: (408) 296-7111 discarded! No telephone
Fax Reservations: (415) 227-2602 reservations!
Name _____________________________________________________________
Company ___________________________________ Mail Stop ____________
Mailing Address __________________________________________________
City __________________________________ State ______ Zip _________
Country __________________________ Phone (_____) _________________
FAX (____) ______________________________
Arrival Date _____________________________ Time __________ AM / PM
Departure Date ___________________________ Time __________ AM / PM
A deposit of $85.00, regardless of hotel room rate, is required
by check or credit card. Make check payable to Santa Clara Hous-
ing Bureau. Your reservation will be confirmed by both the Santa
Clara Housing Bureau and the hotel at which you have a reserva-
tion. The $85.00 deposit will be applied to your room bill at
check-in.
____ VISA ____ MasterCard ____ American Express
Number_________________________________ Expiration Date __________
Signature_________________________________________________________
-----------------------------------------------------------------------------
Please notice that registration and hotel reservation are two different forms
that go to two different places, and that only the hotel reservations can use
a credit card.
-----------------------------------------------------------------------------
------------------------------
Subject: [DEPARTMENTS]
------------------------------
From mcleod@Sdsc.Edu Fri Aug 21 17:39:01 1992
Date: Fri, 21 Aug 92 21:20:51 GMT
From: mcleod@Sdsc.Edu
Subject: e-s3-8-1
The following sample issue of our electronic magazine, "E-S3",
covering selected topics about computer modeling and simulation,
is sent to you with the compliments of the publisher of the
technical journal SIMULATION, the Society for Computer
Simulation, and John and Suzette McLeod, the Editors of
Simulation in the Service of Society (S3), a special section of
that journal. If you do not care to receive future issues please
type REPLY -- cancel. Let's not clutter up our E-mail with "Junk
Mail"!
-----------------------------------------------------------------
E-S3 Vol. 1, No. 8, Part One
based on the August 1992 issue of
"Simulation in the Service of Society"
John McLeod, Technical Editor Suzette McLeod, Managing Editor
8484 La Jolla Shores Dr., La Jolla, CA 92037.
E-mail: mcleod@sdsc.bitnet
*
S3 is a special section of
SIMULATION
the monthly journal of the
SOCIETY for COMPUTER SIMULATION
P.O.Box 17900, San Diego, CA 92177-7900
Phone: (619) 277-3888 FAX: (619) 277-3930
*
[Copyright Notice: E-S3 is the electronically delivered version
of "Simulation in the Service of Society" which is a special
section of SIMULATION, a monthly technical journal of the
Society for Computer Simulation International. It may be
reproduced only for personal use or for the use of students. In
any case full credit must be given to the original source of
publication: SIMULATION 59:2, August 1992.
All rights reserved, (c) 1992, Simulation Councils, Inc.]
-----------------------------------------------------------------
Oil on Troubled Waters
Herewith we present edited excerpts from an article originally
published in Water Resources Research, v. 26, No. 9, September
1990.
Multidimensional Simulation Applied to Water Resources
Management
A.S. Camara, F.C. Ferreira, M.J.Seixas
Environmental Systems Analysis Group
New University of Lisbon, Portugal
D.P. Loucks
School of Civil and Environmental Engineering
Cornell University
Ithaca, New York
Introduction
Mathematical modeling has been traditionally dominated by
quantitative formulations which can be easily manipulated. Thus
reality, which is usually described qualitatively by pictures and
words, has been mapped into numerical representations. In this
paper we explore how spatially related objects can be represented
and manipulated visually and how abstract concepts can be
represented using natural language.
Today models using linguistic and pictorial entities and
operators, in addition to the traditional numerical formulations,
are clearly lacking. Modelers tend to limit the use of pictures
or graphics to the input-output stages of the modeling process
and use natural language as a medium of interaction between
humans and machines. Theoretical concepts underlying an
integrated decision aiding simulator (IDEAS), which considers
numerical, linguistic, and pictorial entities and operations, are
applied to the impact assessment of an oil spill in the sea.
This example illustrates the potential applications of IDEAS for
environmental and water resources management.
Application
The Valdez accident in Alaska contributed to the increasing
worldwide interest in the environmental, social, and economic
impacts of oil spills. Although many methods have been developed
over the years to assess those impacts, IDEAS may provide a rapid
modeling alternative using more intuitive representations for
simulation model variables and operations. A generic oil spill
model implemented on a microcomputer, following the IDEAS
methodology, is described in the following paragraphs.
Problem Description
The assessment of the fate of an oil spill and its effects is a
complex process. Typically the oil spilled is dispersed
immediately after discharge because of advection and spreading.
The area and thickness of the oil is then affected by
evaporation, sedimentation, and decay phenomena. Advection is
influenced by dominant winds and currents. Spreading results
from a dynamic equilibrium between the forces of gravity,
inertia, friction, viscosity, and surface tension.
Evaporation accounts for the loss of one third to two thirds of
the oil mass in a period of a few hours after the spillage.
Calculation of evaporation rate is difficult because it depends
on a number of factors, all of which may change with time.
However, one may say that the rate of evaporation from a thick,
cold slick under calm conditions will be orders of magnitude
slower than from a thin, warm slick under stormy conditions.
Oil may be transported to the bottom sediments through
hydrodynamic processes. Oil consumed by the zooplankton also
reaches the sediments in the form of fecal pellets.
Photochemical oxidation and microbial action are the two most
important decay processes, depending on the amount of light and
temperature in the area, respectively. Cold water with reduced
light, as in the Valdez case, can slow decay. Warm water with
plenty of light can accelerate it.
Figure 1 shows the causal diagram extracted from this problem
description, while Table 1 lists the entities included in the
model. The dictionaries for the pictorial and linguistic
entities are shown in Figure 2 and Table 2 respectively. Note
that current and wind direction are treated as linguistic
entities with north, south, west, and east directions.
Model Results
The oil spill model was applied to a generic case, and a sample
of the model outputs using a monochromatic monitor is presented
in Figure 3. This figure illustrates the wealth and
complementarity of information provided by models using
numerical, linguistic, and pictorial entities. The latter
include plant and profile views of the oil spill and iconic
representations of the sea (fish) and shoreline (salt marshes)
wildlife. In this example the oil spread is starting to reach
the shoreline, damaging the wildlife. After 18 days, two thirds
of the total amount of oil spilled still remains. Note that the
oil spread contour seems to have been randomly drawn because of
the wind direction and speed changes.
Future Developments
Further development of IDEAS will be directed toward the
improvement of pictorial entities representations and the
numerical, linguistic, and pictorial modeling methods. For
example, other pictorial variables such as orientation, texture,
and value will be considered. Efforts will be made to handle
additions or deletions of entities and relationships during the
modeling process. Modeling of a contaminated estuary changing
from aerobic to anaerobic conditions and back to aerobic is an
example of the need to develop such rules.
IDEAS may be useful in combination with a geographic information
system (GIS). Pictorial and linguistic methods included in the
proposed approach may be applied to solve problems requiring
geographical information. The environmental impact analysis of
water resource infrastructures is a potential application of an
IDEAS-GIS system.
More substantial modeling developments are tied to the adoption
of parallel processing. The application of cellular automata
formulations, which are ideally implemented on parallel
computers, instead of differential equations, is one of the
topics to be studied in this context.
In brief, a cellular automaton considers a discrete lattice of
sites, evolution in discrete time steps, each site taking a
finite set of possible values, the value of each site evolving
according to deterministic or nondeterministic rules, and the
rules for the evolution of a site depending only on a local
neighborhood of sites around it. This alternative numerical
modeling approach may consider millions of cells. Cellular
automata applied to water quality modeling thus may enable
particle tracking (each cell with a nonzero value could represent
a particle.) This feature may be relevant if there is a need to
obtain spatial patterns of the pollutants.
Parallel processing will certainly benefit the use of linguistic
and pictorial models. These models divide the continuum into a
number of discrete categories (i.e., high, medium, and low for a
linguistic variable; black, grey, and white for the color of a
pictorial object) and the operations are also scaled on a discrete
basis (i.e., absorption may be none, half, or total).
It is obvious that an aggregate discretization of a continuum,
which is the feasible option for standard computers, could lead
to significant error. However, disaggregate discretization,
which is feasible with parallel processing, can certainly
minimize the errors of the discrete linguistic and pictorial
models, making them comparable to approximate numerical models,
with the advantage of being more intuitive.
Another significant development relates to the creation of
pictorial explanation tools which allow one to determine
pictorially the control options required to obtain a frame B from
a frame A. The tuning of a television image is a quite similar
problem. In this case there are few control variables (color,
sound, brightness, contrast) and they are independent. The search
for the perfect image is thus relatively simple. Similarly,
if one represents control variables as pictures with color, size,
shape, and position, to solve a simple problem one just changes
those properties until one goes from frame A to frame B.
Backtracking those changes allows one to define the required
strategy for turning A into B. However, if there are many
control variables and their pictorial properties are not
independent, the problem may involve combinatorial optimization.
[The original article contained 36 references, 11 figures, and 5
tables, and notes that the work resulted in part from a Visiting
Fulbright Scholarship and a NATO Fellowship granted to the first
author for research on this topic at Cornell University.
Note that this e-mail version of S3 cannot duplicate figures
and tables as they appear in the version published in the
journal SIMULATION. JM]
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END OF SIMULATION DIGEST
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