SIMULATION: Transactions of The Society for Modeling and Simulation International

Groner, Gabriel F.

doi: 10.1177/003754977201800402pmid: N/A

Armstrong, J.S.

doi: 10.1177/003754977201800403pmid: N/A

This paper reviews the software and hardware requirements for on-line computing. It shows these facilities can be used to conduct on-line simulation experiments of models of agricultural systems. The general problems associated with modelling are indicated and the advantages of the on-line approach are discussed.Key words and phrases: on-line computing, modelling agricultural systems, systems analysis in agricul ture.

Stanbery, S.R.; Hoberock, L.L.; Thompson, J.G.

doi: 10.1177/003754977201800404pmid: N/A

Hybrid computation can be extremely efficient, not only in solving certain dynamics and control-system problems, but also in the graphical presentation and analysis of results. Analysis routines, simu lation, and animation can be interactively graphed in a time-shared mode using analog generated dis play with storage-type terminal screens. Many types of control problems amenable to graphical analysis and solution display may not require the large memory and sophistication of all-digital graphics. Hybrid-analog graphics provide an effi cient alternative, as demonstrated with two examples using root-locus and Nyquist diagram analyses. By employing the digital computer on an intermittent basis for calculation of root-locus and Nyquist data, efficient use is made of the analog in solving differential equations describing the system and in generating displays. Parallel effort between the two computers minimizes the total computational time required. Programming of analog logic allows a number of users of terminals to simultaneously select analysis, simulation, or animation options; to set parameter values, initial conditions, and display options; and to change problem configurations. This allows each user interactive graphics for system analysis on a fast, time-shared basis.

Shoup, Jerry F.; Adams, William S.

doi: 10.1177/003754977201800405pmid: N/A

This paper describes a digitally controlled MOSFET switching array capable of programming a module of 37 analog computer components for a hybrid compu ter system. Using the patching scheme to program the analog portion of a hybrid computer has allowed full time-sharing of the system. A time- sharing monitor has been developed allowing remote access to the system.

Capehart, Barney L.; Schneider, Donald P.

doi: 10.1177/003754977201800406pmid: N/A

Benham, R.D.

doi: 10.1177/003754977201800407pmid: N/A

PHYSBE is an acroynm for PHYsiological Simulation Benchmark Experiment, and was introduced1as a suggested standard for evaluating tools and tech niques available for physiological simulation. The mathematical model relates pressure, volume, flow, and resistance in a simplified cardiovascular system.PHYSBE is an excellent benchmark problem because it is not easy to obtain accurate results with an all-analog or all-digital simulation. The large differences in time-dependent constants (1.63 to 90.0) allow a good check of digital integration routines. Roundoff accumulation errors can be devastating to digital solutions. On the other hand the compliance generators (the driving func tions) are difficult to program with general- purpose diode function generators found on analog computers.Previous PHYSBE articles2,3,4have discussed the amount of time it has taken to program with FORTRAN (on a CDC 3600 computer), MIMIC and DSL/90 (on an IBM 7090 computer), CSMP (on an IBM 1130 computer), and DARE I (on a PDP-9 computer). Very little attention has been focused on solution accuracy.Examination of published results for the all digital simulations of PHYSBE show serious accuracy problems. There appears to be a 5% to 10% difference in pressure and volume values that are published. There is good reason for the FORTRAN, MIMIC, and DSL/90 results to agree, but they do not. Also one would expect the CSMP and DARE I results to agree, but they do not.This ISL-8 simulation shows that good agreement was obtained with an IBM 1130 CSMP solution after an error was corrected in the CSMP program. Detailed accuracy comparisons with the other solu tions are complicated because not all of the same variables are reported in the same manner. There fore the documentation format suggested by McLeod2 is used here so that ISL-8 and CSMP solutions can be compared with future work with PHYSBE.

Ledger, John

doi: 10.1177/003754977201800408pmid: N/A