H.N. Abramson - The dynamic behavior of liquids in moving containers. With applications to space vehicle technology (798543), страница 41
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This contract effortwas admini~t~eredby Aerospace Corp., and theLt~ngley Research Center provided t'echnicalsupport and facilit,ies for the initial model tests.Further and more detailed experimental studiesare currently being pursued by NASA a tLangley.Figure 5.41 shows the model of the Titan 111installed in the test tower. Some of the detailsof the bottom of the central core may be seeni11 figure 5.42 where the model is suspendedabove a 9 10-kg electromagnetic shaker forinvestigation of the longitudinal vibrationlr~odesand response.During the tests, the masses of the hypergolicpropellnnts were sirnulnted by Freon, and u.mixture of alcohol tlnd water.
The mttsses ofthe strup-on solid propellctnts were simulateduith lead weights as shown in figure 5.43.SIMULATION AND EXPERIMENTAL TECRNIQUES189FIGURE5.42.-Bottom section of Titan I11 core andvibration exciter.FIGURE5.41.-1/5ecaledynamic model of Titan I11installed in test tower at Langley.The model test philosophy for the Titan I11was somewhat different than for the SaturnSA-1. In t.bia r.e.sej t'he primary purpose ofthe model tests was to check the adequacy ofthe theory for prediction of the full-scale TitanI11 response. Then if the theory, with slightmodifications to treat discrepancies betweenthe model and full-scale structures, proved adequate for analyzing the dynamic model, i tcould be applied with confidence to predictfull-scale responses, and the need for structuraldynamics testing of the full-scale vehicle wouldbe obviated.At the time of writing, comparison betweenthe theory and initial test results from themodel indicates that modifications of the theoryand future iterations with experiments arenecessary and are now in progress.
Initialresults of the test program and comparisonwith theory are given in reference 5.47.VThe )&-scale dynamic model of the SaturnV launch vehicle, the umbilical ton-er, and thecran-1er platform are shown in figure 5.44.The components of the model are shown infigure 5.45. This large-scale model is part ofthe overall Saturn V dynamic model programto advance the technology of dynamic modelingof launch vehicles and to generate data per1140-Scale Dynamic M o d e l of Saturn190THE DYNAMIC BEHAVIOR OF LIQUIDSFIGURE5.43.-Top view of model of Titan I11 solidsshowing simulated masses.tinent to the Saturn V vehicle. Specificobjectives of this model were to determinethe degree to which the full-scale and KO-scalereplica model responses could be predictedwith an inexpensive and comparatively simpledynamically similar model, to ascertain theeffects of fluid propellant coupling with thestructure.
and to investigate- the coupledresponse of theand launchtower.The model myas designed so that the ratiosof the fundamental fuel-sloshing frequency(as simulated) to the natural friquenEies ofthe structural bending vibrations of the vehiclecould be varied over a range of values whichinclude the full-scale frequency ratios. Thismas done to facilitate investigation of the,effect of coupling of these modes which, asnoted previously, is not possible in a replicamodel. The scaling of the structural aspectscan be summarized as follows:FIGURE5.4.-1/40.8cale dFamic model of Saturn V,umbilical tower and crawler platform.For a replica modelFIGURE5.45.-Components of 1140-scalemodel of Saturn V.191SIMIJLATION AND EXPERIMENTAL TECHNIQUESand for the %,-scale Saturn V modelwherew=structural frequencyE= modulus of elasticityI=area moment of inertiam'=mass per unit lengthl=length of the structureM=subscript to denote modelF=subscript to denote full scaleA=characteristic length ratioThe model stiffness was reduced by constructing it of magnesium rather t,han aluminum, and it was increased by increasing thethickness of the skin relat,ive to that of afro-scale replica model.
The model mass distribution was then increased by a factor of(411.5) relative to replica values so that theresulting model/prototype frequency ratios ofthe basic structure would be identical to thoseof a replica model.With respect to the simulated propellantfrequency ratioFor a replica model(WW F 2y=(1)(A)and for %o-scaleSaturn V model(+(A)WF(A)where a is the acceleration field, and the othersymbols and subscripts are as previously defined. The acceleration ratio is effectivelyincreased by a factor X re!ati:re tc? n replicamodel by simulating the propellants by meansof a spring-mass system. The masses includean alloy which has a low melting temperatureplaced in containers equipped with electricalheaters so that the alloy can be liquefied to varythe effective inertia of the propellant simulants.The %o-scalemodel of the launch umbilicaltower (LUT) is also a dynamically similarmodel where the stiffness, mass, center of gravity, and inertia properties are scaled from fullscale values.
This LUT model is used to studycoupling between the vehicle and the tower.Test data from lateral tests obtained a t thetime of writing indicate good correlation withresults from the larger KO-scalemodel and withresults from analytical studies of the full-scalevehicle. Both the experimental and the analytical studies are being continued.1110-Scale Dynamic M o d e l of SaturnVThe 50-scale dynamic model of the Saturn V,supported in the high-bay harness suspensionsystem to simulate fight conditions, is shown infigure 5.46. Replica scaling, which necessitatedan extension of the state-of-the-art in fabrication, was employed with a resulting 11-metertall model that has excellent duplicate representation of full-scale structure from thefirst-stage-engine gimbals through the LunarExcursion Module adapter of the payload.Some of the construction details of the firststage thrust structure are shown in figure 5.47,where the thrust and holddown posts, the reinforced cross-beams, the ring frames, the lowerfuel bulkhead, and the actuator supportstructure are evident.
Further indication ofthe details built into the model are shown onfigure 5.48, where the interior of the first-stagefuel tank, prior to completion, can be seen.The complicated bulkhead, LOX suction ducts,slosh baffles, and integrally milled tank skinsare visible. As an indication of structuraldetail, the skin thickness of the skin-stringerforward skirt of the third stage is 0.076 millimeter, while the cover sheets of the honeycombin the LEM adapter are 0.043 millimeter thick.Extreme full-scale design details, such as hatsection stringers spike welded to skins, corrugated intertank sections, and scaled tensionstrap joint reproduction, have been included inthe fabrication of the jio-scaie model.Other Xu-scale model components availablefor the test program include a multicell firststage, other interstage sections constructed ofhoneycomb or modified monocoque, and simulated holddown spring restraints.The LOX and RP-1 propellants are simulated in the Xo-scale model with deionized-192THE DYNAMIC BEHAVIOR OF LIQUIDSFIGURE5.47.-First-stage thrust structure details ofl/lO-scale model of Saturn V.FIGURE5.46.-1/10-scale dynamic model of Saturn V.water.
The mass distribution of the hydrogenfuel in the second and third stages is simulatedwith plastic balls possessing the proper specificgravity. A discussion of the early model testresults, including comparison with theory, isgiven in reference 5.48.VIBRATION TESTS OF FULL-SCALE THORAGENAFIGURE5.48.-Interior view of firstetage fuel tank of1110-scale model of Saturn V.The Langley Research Center is also conducting vibration analyses and tests of a full-scaleThor-Agena vehicle to define the structuraldynamic characteristics of typical launch ve-5.11SIMTLATION AND EXPE,Platform "I("-25 MetersPlatform "J",7 - 7,IBIC~IIS imu lated payloadIStation 745.5- AgenaStation 794 1Platform"HIStation 876.7Station 888.5-M MetersL-JStation 977.6Stations 989.6 ( Agena)and 107.0 (Thor)Station 151.0Platform "G"rPlatform "PIIPlatform ITE"c,I II IStation 336.0Station M9.0Platform-10 MetersPlatform "C"rrI Ili IPlatform "5"FIGURE5.50.-Erection of Thor in the Dynamics ResearchLaboratory.Station 6025Station 636.7Platform "A"13.700 kg.
exciter13.700 kg1 exciterFIGURE5.49.-Structuralcomponents of the Thor-Agenaprogram.hicle structures. Figure 5.49 shows the components of the various sections of the test setup.Figure 5.50 shows the Thor while being erectedin the Langley Research Center's DynamicsZesearch Laboratory.A unique air-bellows suspension system wasdeveloped io vertically support the vehicleduring longitudinal testing.
Figure 5.51 is asketch of the vehicle on the air suspensionsystem with a 13700-kilogram shaker attachedthrough the gimbal thrust pad. Lateral restraining cables prevent lateral, pitching, orrolling motions of the vehicle while providingminimum restraint to vert,ical or longit,udinalmotions.
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