Reference / Paper · 1964

The Simulation of Transport Delay with the HYDAC Computing System

This two-page EAI bulletin (No. ALHC 64019, 1964) describes a hybrid computing technique for simulating transport delay on the HYDAC Computing System using analog-to-digital conversion, digital function storage, and logic components. The program supports up to ten independent delay channels with storage capacities of 16, 64, or 256 words per channel and variable delay times, overcoming the phase-error and multiplier-count limitations of classical Pade-polynomial analog approaches. Sample results for two-channel transport delay with a velocity step change are presented.

Manufacturer: EAI
System: HYDAC
Year: 1964
Type: Reference / Paper
Language: English
Learning track: specific applications
Pages: 2
Credit: Copyright Electronic Associates, Inc., 1964. Bulletin No. ALHC 64019.

HYDAC
EAI
transport delay simulation
hybrid analog-digital computation
HYDAC system
partial differential equations

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THE SIMULATION OF TRANSPORT DELAY WITH THE HYDAC* COMPUTING SYSTEM INTRODUCTION These notes describe the simulation of transport delay with the EAI HYDAC Computing System, utilizing a combination of analog and digital components to provide a high speed, multichannel, variable delay capability. g e, t F- Ir I( b t F t-TD t- X ro t- w T TD TI ME o: Temperoture Functi onoi P i pe Inl et The need to simulate a transport delay arises frequently in analog computation, occurring as the solution of flow and wave partial differential equations. That is, the realistic simulation of systems involving the flow of liquids and gases in pipes or the propagation of electric or acoustic waves requires the representation of the transport delay phenomena. The standard analog computer approach -- alinear computer eircuit with delay transfer frurctions approximated by Pade polynomials -- suffers from two basic limitations: 1) the large phase errors at high frequencies prevent realistic representation of rapidly changing and discontinuous functions, and 2) the large number of multipliers required for variable time delay make this approach uneconomical. An alternative approach employs sampling of the analog signal, storage of the discrete samples in memory cells, and reconstruction of a stair-step approximation to the fiurction by reading out each stored value after a delay of rp seconds. The HYDAC program used in the study described employs this method for simulating transport delay. conversion, digital It utilizes analog-to-digital fwrction storage, and appropriate logic components to provide a pure delay of sampled functions from the analog computer. The analogy shown in Figure 1 will help to clarify this discrete simulation approach. b: F l ui d F l ow os R epr es enr ed by W el l M i x ed Sec ti o n s Fl o w ing fron Lefr b Righr li ''''l,,iiiiiii x+ c: Discrelized Leng* FIGU R El . Temperoiure Prc{ile os o Function of Pipe P i ctori olR epresentotiof on D i scr et eSom pling Method of Simuloting Fluid FlowTronsport Deloy BENEFITS Several benefits are provided through this simulation technique. hr particular, in terms of capacity and versatility, the program o provides up to ten independent channelsof delay o makes available storage capacities of 16, 64 or 256 words per channel o permits a wide range of delay times since each channel can accept adifferent velocity variable, can use memo ry unit s of different capacity, and o has the capability to simulate very long delays through the use of digitat storage. @ Efec tr oni c As s oc i o i e s , lnc. , 1964 t T ro d e Mq rk Al l R i ghr s R es er v ed P ri n re d i n U .S .A.464 Bul l er i n N o. ALH C 6 4 0 1 9 COMPUTER PROGRAM The basic operations performed by the HYDAC Transport Delay Program are shown in the block diagram of Figure 2. FIGURE 2, Block Diogromof TronsporrDcloy Progrom RESULTSAND CONCLUSIONS A pnot of typical results obtained on the HYDAC System using the Tran sport Del ay P rogram i s shown in Figure 3. To illustrate the effect of variable delay, the velocity of both channels was reduced by a factor of two at the point indicated in the figure. This stepchange caused an immediate reduction in the frequency at the output of the pipe, which is sustained until the input appears at the ou@ut with the new velocity. As shown, channel one had not yet reached the new steady state at the end of the recording shown. Although such a pure step change may not be realizable in physical systems, this simulated condition can be considered a worst case test. This hybrid transport delay stmulation program is but one of a series of standald general pur?ose programs whtch are availableas..softwarett forthe HYDAC system. For complete details on tlre program described, please write for Hybrtd Computing Techniques: 1.3.7h, Bullettn No. ALHC 63011. FIGURE3' SompleResults for Two ChonnelTronsportDeloy IncludingEffectof Vilocity Chonge EAI' ELECTRONIC ASSOCIATES, INC.long Branch,Nezolersey ADVANCED SYSTEMSANATYSIS AND COMPUTATION SERVICES/ANAIOG COMPUTERS/HYBRID ANATOG-DIGITAT COMPUTATION EQUIPMENT/SIMUTATIONSYSTEMS/ SCIENTIFICAND LABORATORY INSTRUMENTS/INDUSTRIAT PROCESS CONTROT SYSTEMS/PHOTOGRAMMETRIC EQUIPMENT/RANGE INSTRUMENTATIONSYSTEMS/TEST AND CHECK-OUTSYSTEMS/MILITARY AND INDUSTRTAL RESEARCHAND DEVETOPMENT ENGINEERINGAND EQUIPMENTMAINTENANCESERVICES. SERVICES/FIELD )