Random Vibration Analysis of the Electronic Equipment Cabinet

Random Vibration Analysis of the Electronic Equipment CabinetLIU Yanping' LIU Dongqing2( 1. Key Laboratory of Condition Monitoring and Control for Power Plant Equipment of Ministry of Education ,North China Elctric Power University , Bejjing 102206 China ,E-mail :1yp@ ncepu. edu. cn ;2. Beijing University of Science and Technology ,Beijing 100083 , China )Abstract : In order to understand the vibrat ion characteristic of system structure of electronic equipment cabinet within theparticular vibration frequency , the finite element analysis softuare一ANSYS is used to simulate the tests of random vibrations ofthe cabinet system and obtain the isopleths graph of deformation and stress of the cabinet. It can confirm maximum of deformationand stress of the cabinet and position happened . Through more analysis of the frequency response curve，rwhich can confirm harm-ful consequences random vibrations caused and reak link of the cabinet structure. The numerical simulation results are in good a-greement wvith the experimental results. It shorus that this research provides an efficient method for the anti - seismic cdesign and thedynamic optimization design .Key words : random vibrations test ; vibration characteristic ; mumerical simulation ; finite element analysis ; elec-tronic equipment cabinet ; ANSYS software1 IntroductionAt present ,in our country to meet the requirements of mechanical structures for electronic equipment ran-dom vibration-tests , no uniform standard is issued. Since our country having joined WTO , electronic productshave entered into the international market , where if anyone wants to keep a firm status and possess strong com-petitiveness , the critical and reliable international standards of tests must be followed. However , with the rapiddevelopment of economy in the modern society , customers pay more and more attention to the capability of bear-ing vibration of electronic equipment.Mechanical force that the electronic equipment cabinet receives in the real working environment has variouskinds of forms such as vibration , impact , centrifugal force and frictional etc. force produced by mechanism mo-tion , among which vibration and impact are the most harmful to the electronic equipment 11. Non- stationary vi-bration of the electronic equipment may take place under any of the following :1 ) during transportation of prod-ucts ;2 ) existing blasting earthquakes around the factory building probably ;3 ) earthquakes ;4 ) the running ma-chines in the workrooms. In the paper , through the numerical simulation , various kinds of response values ofthe cabinet in the environment of random vibration tests were analyzed and discussed.2 Requires and Course of the Random Vibrations Test of the Cabinet2.1 Random Vibration Test Requirements( 1 )The cabinet configuration and loading condition for test set-up , shown in fig. 1.( 2) The test responsespectrum( TRS ) shall match or exceed the required TRS. ( 3 )During the test ,it is necessary to measure thedisplacement of the upper side of the enclosure. The maximum deflection shall not allow over 50 mnt2.2 Test ConditionsA cabinet or rack shall be mounted direct to the shaker table in accordance with the intended bolt -down po-sitions and requirements and the test shall be performed under the conditions and Fig. 1.2.3 Test Procedure( 1 ) The test wave for the seismic test shall be a synthesized waveform as described in Fig.2. Its zero periodacceleration shall conform to the values of the severity levels ir中国煤化工- irement level.: began from test in ad-(2 ) Testing axis : each axis once- -X Y Z. Changing orvance.:TYHCNM HG(3 ) Loading way : exerting the acceleration load on the single axis direction , the concrete values shown inFig.2.(4 ) Duration : indicated in Fig. 2.一709一，600' 「600schemeN3 x510°F2000Simulate load10*14-、300400101oUnt.nmFrequeney HzFig.1 Cabinet configuration and loeding condition for test sel-upFig2 Require response spectra3 Numerical Simulation Procedure for the Random Vibrations TestNumerical simulation of using the finite element software to perform the random vibrations test is a spec-trum analysis in substance. Spectrum analysis , an analysis technology that associates modal analysis results witha known spectrum ,is mainly used for specifying the dynamic response of random or changing over time load，such as earthquake , wind , marine wave , engine vibration of the rocket etc. Three types of spectra are availablefor a spectrum analysis of ANSYS- Response Spectrum , Dynamic Design Analysis Method( DDAM ) and PowerSpectral Density( PSD ). However response spectrum and DDAM analyses are deterministic ( quantitative ) anal-yses because both the input data and output data are actual maximum values. Random vibration analysis is prob-abilistic( qualitative ) , because both input data and output data represent only the probability that they take oncertain values. This paper utilizes the finite element software ANSYS to numerically simulate and analyze ran-dom vibration test , namely a PSD analysis , which consists of six main steps 35 J.1 ) Build the model ,( including defining job name , analysis title , element type ,element real constants ,ma-terial properties , model geometry and so on ) , meshing units and applying loads ;2 ) Obtaining the modal solu-tion ;3 ) Expanding the modes ;4 )Obtaining the spectrum solution ;5 )Combining the modes万) Reviewing theresults.4 Numerical Simulation Instance of the Random Vibrations Test4.1 Build the Finite Element ModelThe finite element model for PSD may be set up by three- dimensional drawing application software PRC )/E ,UG ,etC 6]. Then the geometry model is channeled into numerical analysis software ANSYS applying IGESfile layout- ra standard form which exchanges and shares model between different CAD and CAE system- -orPARASOLID text form. And the model is repaired and simplified by topologically or geometrically. The entityis established , entity' s type is added and the net is divided. The advantage in modeling of the three dimensionaldrawing software as PRO/E is easy and swift to the complicated model and has such characteristics as parame-ter , relativity ,series , and so on. While establishing models ,it will bring you the facility while revising in thefuture ,so as to change relevant size and it will become another part that you need. However , the cabinet struc-ture roof beam in the article is mainly cold curved and rolled by the sheet metal. Its structure is more special ,forthe model is set up adopting PRC )/E while channeled into ANSYS would produce a large number of form distor-tion. A large amount of topological repair were needed , and it is very simple to utilize ANSYS to build directlymodel , so the finite element model that using ANSYS to set up directly like Fig. 3( a).4.2 Applying Loads and Obtaining the SolutionAccording to the standard of test and the cabinet material selected for use in design ,in the paper ,the mate-rial trade mark of the cabinet is Q235A , Modulus of elasticity of the material 2.0X1 011 Pa , Major Poisson' sratios 0. 3261. In the modal analysis , four nodes( 324 325 3.中国煤化工the screw bearing thatthe corresponding cabinet of finite element model reserves andMYHCNMH GGown in Fig. 3( b). Ac-cording to the frequency relation with acceleration illustrated in 1 ig. c, uullng uie wuise of calculating responsespectrum solution , the acceleration load is exerted at four screw bearings( nodes )along X , Y ,Z axis separate-ly , thus exerting of load is finished. The procedure of solving concretely is as follows 71.4.2.1 Solving the mode shapes- 71ANSYS85(间) The finite element model(b) Applying constraintsFig.3 The finite element model and constraints of the cabinetModal solution of the structure is a premise of spectrum solution , whose purpose is for the natural frequen-cies and mode shapes of a structure. When solving , these points is remembered :1 ) the mode extraction may beadopted by Subspace method , Block Lanczos method , Reduced ( Householder ) method. Block Lanczos methodwas adopted in this paper. The solver performs well when the model consists of shells or a combination of shellsand solids. The velocity rapidly but requires about 50% more memory than subspace ;2 ) the number of modesextracted should be enough to characterize the structure' s response in the frequency range of interest. The modenumber 20 is chosen in terms of experiences ; 3 ) material-dependent damping must be specified in the modalanalysis. This paper selected 0. 05 as the standard of test requires ;4 )it is sure to constrain those Degree ofFreedom( DOF ) where you want to apply a base excitation spectrum.4.2.2 Expanding the modesThe expanded modes are preceding step of the mode combination. The mode expansion can be performed asa separate step ,or can be included in the modal analysis phase by combining the modal solution and mode expan-sion steps by including the MXPAND command. Expanding the modes applies not just to reduced mode shapesfor the Reduced mode extraction method , but to full mode shapes from the other mode extraction methods( in-cluding Block Lanczos method ) as well. Its purpose is to review mode of structure of the cabinet in the postpro-cessor. This paper took mode expansion as a separate step and expanded all the modes. Before or after the ex-pansion pass , leave SOLUTION with the FINISH command explicitly.4.2.3 Obtaining the spectrum solutionFirst enter SOLUTION , define the analysis type and options and specify load step options. Later apply thePSD excitation at the desired nodes and the excitation direction is implied by the UX ,UY , UZ labels. Lastlybegin participation factor calculations for the above PSD excitation ,specify the output controls and start solutioncalculations. During the course it showed input PSD , which according to Fig. 2.Furthermore similar response spectrum analysis , a random vibration analysis may be single-point or multi-point. The test adopted single- point base excitation , it can only exert restraint which is exerted in modal analy-sis , namely at the 4 nodes on the screw bearing. In a single- point random vibration analysis ,one PSD spectrumis specified at a set of points in the model , while in a multi- point random vibration analysis , different PSD spec-tra at different points 8].4.2.4 Combining the modesMode combination mainly has two items , defining analysis type or choosing analysis type spectrum. Onlythe PSD mode combination method is used. This method will calculate 1σ results of displacements and stresses ofthe cabinet structure. 1σ results are typically used for : first failure calculations , that is probability that the dis-placement at a DOF restricted will exceed a displacement limit in a given time period ifatigue calculations , basedon the premise that the stress level is at or below 1σ 68. 3% of the time , between 1σ and 2σ 27.2% of the time( 95.4-68.3 ) , and between 2σ and 3σ 4. 33% of the time( 99. 73-95. 4 ) , and above 3σ only 0.27% of the time( 100-99.73 94. The mode combination determines how the structure' s modal responses are to be combined. Ifseleet displacement as the response type , displacements and stre中国煤化工bined ;for velocity，ve-locities and stress velocities are combined ; for acceleration , accfHCNMHGrationtoo5 Analysis and Post-processingAfter finishing the above-mentioned solution , 1σ results of the finite element mode can be observed throughthe general postprocessor( POST1 ). Isopleths graph of stress and deformation of the cabinet is shown in Fig. 4一711-and Fig. 5( a),( b)( c). The nodes that the maximum deformation( 595 ) and maximum stress( 324 ) produce are found clearly from iso-pleths graphs. It educes the conclusion obviously from graphics that de-formation and stress of the electronic equipment cabinet locate within theparticular vibration frequency and makes for more analysis of the adverseconsequences of random vibration and specifies the weak points of thecabinet structure. The time history preprocessor , POST26 , can reviewthe frequency response curve for displacement , velocity or acceleration ofthe finite element model. The paper takes the displacement responsecurves of node 735( anyone at the middle of the cabinet ),Fig.6 for ex-Fig.4 Stress isopleths grapb( Z)ample.小山世a地(间) Deformation Isopleths Graph (xX) () Deformation isopleths graph (I)() Deformation isopleths graph (2)Fig. 5 Distributing of deformation at loading condition1; g:最大响应8.75(d) X direction (735)(e) Y direction (735)(f) Z direction (735)Fig. 6 Displacement- frequency response curves6 Conclusions( 1 ) From deformation isopleths graph , when loading at X，Y or Z direction , 1σ displacement results arecorrespondingly 13. 859 mm ,24. 835 mm and 38.312 mm，whose happening probability is 68.3%. The maxi-mum deflection wasn' t over 50 mm required in the test. The deformation between 1σ and 2σ , namely 76. 624mm , is more than that of requires of test standard only loading at Z direction , and its probability is 27. 1%.The deformation over 3σ is 41.577 mm、74.505 mm、114. 936 mm at three directions , that is. Deformation atY or Z direction is beyond that of requires of test standard , but its probability only 0.27%. And from abovegraphs the weak link may be visually found , which is in the junction of the soleplate and the crossbeam of bot-tom , where should be strengthened in the design.(2 ) From stress isopleths graph , the stress that locates in four screws where test jig connects with cabinetbase is most dangerous.' Therefore , the firmer connection way should be chosen while testing.( 3 )From displacement-frequency response curve of three-中国煤化工the displacement is thebiggest in the middle part of the panel vertical to the loading dYHCNMHGparallel to the directionof the panel is far smaller than that perpendicular to its directorl. IMoreover ，ine encouragement panel or itsjunction with beams is most serious , which should be paid much attention to in the design.( 4 ) The numerical simulation of this paper can not only be simply identical with random vibration test , butobtain the dangerous situation produced by random vibration qualitatively.-.71In conclusion , the random vibration simulation and analysis plays a very important role in improving the an-ti-seismic characteristic of products or the optimal design of structure. It can not merely contribute to the mostoptimal solution to seek at the stage of research and development of products , but obviously shorten product de-velopment cycle , reduce the production cost , guarantee product quality and increase economic efficiency .References[1 ] QIU Chengti. Design Principle of the Electronic Equipment Structure[ M ]. 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