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1、Thermal AnalysisChapter SixANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisChapter OverviewIn this chapter, performing steady-state thermal analyses in Design Simulation will be covered:Geometry and ElementsContact and Types of Supported Assemblies
2、Environment, including Loads and SupportsSolving ModelsResults and PostprocessingThe capabilities described in this section are generally applicable to ANSYS DesignSpace Entra licenses and above, except for an ANSYS Structural license.Some options discussed in this chapter may require more advanced
3、licenses, but these are noted accordingly.It is assumed that the user has reviewed Chapters 1-3 prior to this chapter. (Chapters 4-5 are optional)February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisBasics of Steady-St
4、ate Heat TransferA steady-state thermal analysis is performed to determine the thermal response under applied steady-state loadsTemperatures and heat flow rate are usually the items of interest, although heat fluxes can be reported as well.The general thermal equation is as follows:where t is time a
5、nd T is temperature, C is the specific heat (thermal capacitance) matrix, K is the conductivity matrix, and Q is the heat flow rate load vector.In a steady-state analysis, all time-dependent terms are removed. However, nonlinearities are still present:February 2, 2004Inventory #0020106-ANSYS Workben
6、ch - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisBasics of Steady-State Heat TransferFor a steady-state thermal analysis in Design Simulation, the temperatures T are solved for in the matrix below:This results in the following assumptions:No transient effects ar
7、e considered in a steady-state analysisK can be constant or a function of temperatureTemperature-dependent thermal conductivity can be input for each material propertyQ can be constant or a function of temperatureTemperature-dependent film coefficients can be input for convective boundary conditions
8、February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisBasics of Steady-State Heat TransferFouriers Law provides the basis of the previous equation:This means that the thermal analysis Design Simulation solves for is a c
9、onduction-based equation.Heat flow within a solid (Fouriers Law) is the basis of KHeat flux, heat flow rate, and convection are treated as boundary conditions on the system QNo radiation is currently consideredNo time-dependent effects are currently consideredHeat transfer analysis is different from
10、 CFD (Computational Fluid Dynamics)Convection is treated as a simple boundary condition, although temperature-dependent film coefficients are possible.If conjugate heat transfer/fluid problem needs to be analyzed, one must use ANSYS CFD tools instead.It is important to remember these assumptions rel
11、ated to performing thermal analyses in Design Simulation.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisA. GeometryIn thermal analyses, most types of bodies supported by Design Simulation may be used.Solid and su
12、rface bodies are supported by all products which support thermal analyses.For surface bodies, thickness must be input in the Details view of the Geometry branchLine bodies are only supported under ANSYS Professional licenses and above.The cross-section and orientation of line bodies is defined withi
13、n DesignModeler and is imported into Design Simulation automatically. Although the cross-section and orientation is defined, this information is meant for structural analyses, and the actual thermal link element will have an effective cross-section based on the input properties.No heat flux or vecto
14、r heat flux output is available with line bodies. Only temperature results are available for line bodies.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis GeometryIt is important to understand assumptions related t
15、o using shell and line bodies:For shell bodies, through-thickness temperature gradients are not considered. A shell body should be used for thin structures when it can be safe to assume temperatures on top and bottom of surface are the same.Temperature variation will still be considered across the s
16、urface, just not through the thickness, which is not explicitly modeled.For line bodies, thickness variation in the cross-section is not considered. A line body should be used for beam- or truss-like structures, where the temperature can be assumed to be constant across the cross-section.Temperature
17、 variation will still be considered along the line body, just not through the cross-section, which is not explicitly modeled.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Elements UsedIn Design Simulation, the
18、following elements are used:Solid bodies are meshed with 10-node tetrahedral or 20-node hexahedral elementsSOLID87 and SOLID90Surface bodies are meshed with 4-node quad shell elementsSHELL57 using real constants(SHELL131 or SHELL132 are currently not used.)Line bodies are meshed with 2-node line ele
19、mentsLINK33 using real constantsAn equivalent cross-sectional area, as defined in DesignModeler, is used for LINK33For thermal-stress analyses, a coupled-field element is not used. The thermal-stress analysis is performed sequentially, so the above thermal elements are used, then the temperature fie
20、ld is read into corresponding structural elements.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Material PropertiesThe only required material property is thermal conductivity.Material input is under the “Engine
21、ering Data” branch, and material assignment is per part under the “Geometry” branchThermal Conductivity is input as a sub-branch of the material property. Temperature-dependent thermal conductivity can be input as a table.Specific heat can be input as well, but it iscurrently not used.Other material
22、 inputis not used in thermal.If any temperature-dependent material properties exist, this will result in a nonlinear solution. This is because the temperatures are solved for, but the materials are dependent on the temperatures, so it is not linear.February 2, 2004Inventory #0020106-ANSYS Workbench
23、- SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Material PropertiesThermal conductivity is input into ANSYS as MP commands.For temperature-dependent thermal conductivity, the appropriate MPTEMP and MPDATA commands are issuedAlthough specific heat may be defined i
24、n the “Engineering Data” branch, it is currently unused and not passed to ANSYSNo MP,C command is written for specific heatFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisB. Assemblies Solid Body ContactWhen impor
25、ting assemblies of solid parts, contact regions are automatically created between the solid bodies.Surface-to-surface contact allows non-matching meshes at boundaries between solid partsContact enables heat transfer between parts in an assemblyModel shown is from a sample Inventor assembly.February
26、2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Contact RegionIn Design Simulation, the concept of contact and target surfaces are used for each contact region.One side of the contact region is comprised of “co
27、ntact” face(s), the other side of the region is made of “target” face(s).Heat flow is allowed between contact and target faces (based on the contact normal direction)When one side is the contact and the other side is the target, this is called asymmetric contact. On the other hand, if both sides are
28、 made to be contact & target, this is called symmetric contact. However, the designation of which side is contact or target is unimportant in thermal analysis.By default, Design Simulation uses symmetric contact for solid assemblies.For ANSYS Professional licenses and above, the user may change to a
29、symmetriccontact, as desired.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Contact RegionAs noted in the previous slide, heat flows within a contact region in the contact normal directionNo heat spre
30、ading is considered in the contact/target interfaceHeat spreading is considered within shell or solid elements at the contact or target surfaces because of Fouriers LawHeat flow within the contact region is in the contact normal direction onlyThis means that, regardless of the definition of the cont
31、act region, heat flows only if a target element is present in the normal directionIn the figure on the left, the solid green double-arrows indicate heat flow within the contact region. Heat flow only occurs if a target surface is normal to a contact surface.The light, dotted green arrows indicate th
32、at no heat transfer will occur between parts.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Contact RegionIn Design Simulation, various contact behaviors existIn general, the contact type is meant for
33、 structural applicationsIf the parts are initially in contact, heat transfer will occur between the parts. If the parts are initially out of contact, the parts will not transfer heat between each other.Based on the contact type, whether heat will be transferred between contact and target surfaces is
34、 outlined below:The pinball region is automatically defined and set to a relatively small value to accommodate small gaps which may present in the model. The pinball region will be discussed next.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining Manu
35、alSteady-State Thermal Analysis Assemblies Contact RegionThe pinball region may be input and visualized in ANSYS Professional licenses and above.If the target nodes lie within the pinball region and the contact is bonded or no separation, then heat transfer will occur (solid green lines)Otherwise, n
36、o heat transfer will occur between nodes (dotted green lines)In this figure on the right, the gap between the two parts is bigger than the pinball region, so no heat transfer will occur between the partsPinball RadiusFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - Si
37、mulationTraining ManualSteady-State Thermal Analysis Assemblies Thermal ConductanceBy default, a high thermal contact conductance (TCC) is defined between parts of an assemblyThe amount of heat flow between two parts is defined by the contact heat flux q:where Tcontact is the temperature of a contac
38、t “node” and Ttarget is the temperature of the corresponding target “node” located in the contact normal direction.By default, TCC is set to a relatively high value, based on the largest material conductivity defined in the model KXX and the diagonal of the overall geometry bounding box ASMDIAG.This
39、 essentially provides perfect conductance between parts.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Thermal ConductancePerfect thermal contact conductance between parts means that no temperature dr
40、op is assumed at the interface.One may want to include finite thermal conductance insteadTwo surfaces (at different temperatures) in contact experience a temperature drop across the interface. The drop is due to imperfect contact between the two surfaces. The imperfect contact, and hence the finite
41、contact conductance, can be influenced by many factors such as:surface flatnesssurface finishoxidesentrapped fluidscontact pressuresurface temperatureuse of conductive greaseD DTTxFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State T
42、hermal Analysis Assemblies Thermal ConductanceIn ANSYS Professional licenses and above, the user may define a finite thermal contact conductance (TCC)The thermal contact conductance per unit area is input for each contact region in the Details view, as shown below.If thermal contact resistance is kn
43、own, invert this value and divide by the contacting area to obtain TCC value.When this is done, there will now be a temperature drop between the contact and target surfaces for a contact region.If “Thermal Conductance” is left at “Program Chosen,” near-perfect thermal contact conductance will be def
44、ined.The user can change this to “Manual” to input finite thermal contact conductance instead, which is the same as including thermal contact resistance at a contact interface.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Therm
45、al Analysis Assemblies Thermal ConductanceIf using symmetric contact, the user does not need to account for a double thermal contact resistance.Input values as normalMPC bonded contact allows for perfect thermal contact conductance.In this case, because constraint equations are used, no thermal cont
46、act conductance is used nor defined.The contact “node” and corresponding target “node” will have the same temperature because of perfect contact conductance.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assembl
47、ies Solid Body ContactInternally, thermal contact for solid faces is defined with CONTA174 and TARGE170 elements.KEYOPT(1)=2 set for thermal DOF onlyKEYOPT(12) is based on contact type usedFor example, bonded type is KEYOPT(12)=5. KEYOPT(2), KEYOPT(5), KEYOPT(9), and FKN are also set. These contact
48、settings are most critical for structural contact, so the various default settings are outlined in Chapter 4.Default thermal contact conductance (TCC) is based on highest value of thermal conductivity of materials and overall geometry sizeTCC=KXX*10,000/ASMDIAGKXX is of highest thermal conductivity
49、value of used materialsASMDIAG is diagonal of overall bounding box of assembly February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Surface Body ContactFor ANSYS Professional1 licenses and above, mixed asse
50、mblies of shells and solids are supportedAllows for more complex modeling of assemblies, taking advantage of the benefits of shells, when applicable1 For ANSYS Professional, surface contact supported with ANSYS 8.0 Service Pack 1 and aboveFebruary 2, 2004Inventory #0020106-ANSYS Workbench - Simulati
51、onANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Surface Body ContactEdge contact is a subset of general contactFor contact including shell faces or solid edges, only bonded or no separation behavior is allowed.For contact involving shell edges, only bonded behav
52、ior using MPC formulation is allowed.For MPC-based bonded contact, user can set the search direction (the way in which the multi-point constraints are written) as eitherthe target normal or pinball region.If a gap exists (as is often the case with shell assemblies), the pinball region can beused for
53、 the search direction to detect contact beyond a gap.MPC results in perfect contact conductanceFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Surface Body ContactInternally, any contact including an e
54、dge (solid body edge or surface edge) results in asymmetric contact with CONTA175 for the edge and TARGE170 for the edge/faceUndocumented KEYOPT(1)=2 is set for thermal contactContact involving solid edges default to pure penalty methodContact involving surface edges use MPC formulation. Instead of
55、“target normal,” if search direction is “pinball region,” KEYOPT(5)=4 set on companion TARGE170 element.For bonded contact (default), both use KEYOPT(12)=5 and KEYOPT(9)=1.For surface faces in contact with other faces, standard surface-to-surface contact is used, namely CONTA174 and TARGE170CONTA175
56、 elementsTARGE170 elementsFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Spot WeldSpot welds provide a means of connecting shell assemblies at discrete points for heat transferAlthough the ANSYS Desig
57、nSpace licenses support structural spot welds, these do not support thermal spot welds.Spotweld definition is done in the CAD software. Currently, only DesignModeler and Unigraphics define spotwelds in a manner that Design Simulation supports.Spotwelds can also be created in Design Simulation manual
58、ly, but only at discrete vertices.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Assemblies Spot WeldInternally, spot welds are defined as a set of LINK33 elements. The spot weld is defined with one link element
59、, and the top and bottom of the spot weld is connected to the shell or solid elements with a spider web of multiple links.The LINK33 elements usesame thermal conductivityas underlying materials butwith a circular cross-sectionwith radius=5*thickness ofunderlying shellsFigure on right shows twospot w
60、elds between two sets of shell elements, which aremade translucent for clarity.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisC. LoadsThere are three types of loads in thermal analyses:Heat Loads:These loads pump
61、 heat into the system.Heat loads can be input as a known heat flow rate or heat flow rate per unit area or unit volume.Adiabatic Condition:This is the naturally-occurring boundary condition, where there is not heat flow through the surface.Thermal Boundary Conditions:These boundary conditions act as
62、 heat sources or heat sinks with a known temperature condition.These can be either a prescribed temperature or a convection boundary condition with a known bulk temperature.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal
63、Analysis Heat LoadsHeat Flow:A heat flow rate can be applied to a vertex, edge, or surface. The load gets distributed for multiple selections.Heat flow has units of energy/time (i.e., power).Heat Flux:A heat flux can be applied to surfaces only.Heat flux has units of energy/time/area (i.e., power/ar
64、ea)Internal Heat Generation:An internal heat generation rate can be applied to bodies only.Heat generation has units of energy/time/volumeA positive value for heat load will add energy to the system. Also, if multiple loads are present, the effect is cumulative.February 2, 2004Inventory #0020106-ANS
65、YS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Adiabatic ConditionsPerfectly Insulated:Perfectly insulated condition is applied to surfacesCan be thought of as a zero heat flow rate loadingThis is actually the naturally-occurring condition in therma
66、l analyses, when no load is applied.Usually, one does not need to apply a perfectly insulated condition on surfaces since that is the natural behavior for a regular surface.Hence, this loading is meant to be used as a way to remove loading on specified surfaces. For example, it may be easier for a u
67、ser to apply heat flux or convection on all surfaces, then use the perfectly insulated condition to selectively remove the loading on some surfaces (such as those in contact with other parts).February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSt
68、eady-State Thermal Analysis Thermal Boundary ConditionsThermal boundary conditions present a known local or remote temperature condition.At least one type of thermal boundary condition must be present. Otherwise, the steady-state temperature will be infinite if only heat is pumped into a system!Also
69、, Given Temperature or Convection load should not be applied on surfaces that already have another heat load or thermal boundary condition applied to it.If applied on an entity which also has a heat load, the temperature boundary condition will override.Perfect insulation will override thermal bound
70、ary conditions.Given Temperature:This imposes a temperature on vertices, edges, or surfaces.Temperature is the degree of freedom solved for, but this fixes the temperature on selected entities to a given value.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - Simulatio
71、nTraining ManualSteady-State Thermal Analysis Thermal Boundary ConditionsConvection:Applied to surfaces only.Convection relates a ambient temperature with the surface temperature:where the convective heat flux q is related to a film coefficient h, the surface area A, and the difference in the surfac
72、e temperature Tsurface & ambient temperature Tbulk.Meant to provide a simplified way of accounting for heat transport from a fluid. “h” and “Tbulk” are user-input values.The film coefficient h can be constant or input from a file (next)February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationA
73、NSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Thermal Boundary ConditionsTemperature-Dependent Convection (continued):If film coefficent h is input from a file, this can be a constant or temperature-dependent value h(T).Select the Engineering branch and use the “Convection”
74、 toolbar to add or create a new convection file.Determine what temperature is used for h(T) first, for temperature-dependent film coefficients. Temperature can be:Average film temperatureT=(Tsurface+Tbulk)/2Surface temperatureT= TsurfaceBulk temperatureT= TbulkDifference of surface and bulk temperat
75、uresT=(Tsurface-Tbulk)Select the temperature-dependency from the pull-down menuFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Thermal Boundary ConditionsTemperature-Dependent Convection (continued):After the typ
76、e of temperature-dependency is selected, the user may select the “Film Coefficient vs. Temperature” branch on the Outline Tree to input the film coefficients and temperatures in a table. The values are plotted on a graph, as shown below.If any temperature-dependent convection load is applied, this w
77、ill result in a nonlinear solution since the surface temperature is solved for, but the film coefficient h is based on a function of the surface temperature.The only exception is if the film coefficient h is based on a function of the bulk temperature only. In Design Simulation, the bulk temperature
78、 is constant and input by the user, so this load will not be nonlinear.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Thermal Loads in ANSYSThe internal representation of loads in ANSYS:Heat flow for an edge or
79、vertex is a heat flow rate (F,HEAT)Heat flux or heat flow for a surface is surface load (SF,HFLUX)Internal heat generation is applied as a body load (BFE,HGEN)Given temperature is applied as a constraint (D,TEMP)Perfectly insulated condition internally removes any loads applied in Design Simulation
80、on those surface(s).Convection is defined by surface effect SURF152 elementsBulk temperature and film coefficient is applied on the surface effect elements (SF,CONV,film,bulk)If temperature-dependent film coefficients exist, these are defined with a temperature-dependent HF material property (MPDATA
81、,HF). The film coefficient value applied will be “HF_number,” and ANSYS knows to use the referenced HF material property number.KEYOPT(8) is set to be consistent with temperature evaluation of h(T), such as evaluate h(T) based on surface temperature.February 2, 2004Inventory #0020106-ANSYS Workbench
82、 - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Thermal Loads SummaryFor some structural users, it may be useful to provide an analogy of structural and thermal analyses:There are some types of loads that do not have any analogyThere is no thermal equivalent for
83、 inertial loads such as rotational velocity or accelerationThe analogy of convective boundary condition is a foundation stiffness support in structural terms, similar to a grounded springFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-
84、State Thermal AnalysisD. Solution OptionsSolution options can be set under the “Solutions” branch:The ANSYS database can be saved if “SaveANSYS db” is setUseful if you want to open a database in ANSYSTwo solvers are available in Design SimulationThe default solver is automatically chosen. Inthermal
85、analyses, the user usually does not needto change the solver type.The “Iterative” solver can be efficient for solvinglarge models whereas the “Direct” solver is a robust solver and handles any situation.The ability to change the default solver is under “Tools Control Panel Solution Solver Type”The “
86、Weak Springs” and “Large Deflection”options are meant for structural analyses only,so they can be ignored for a thermal analysis.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Solution OptionsInformative setting
87、s show the user the status of the analysis:For a regular thermal analysis, the “Analysis Type”will be set to “Static Thermal.” If structuralsupports and results are present, then theanalysis type will be “Thermal Stress.”A nonlinear solution will be required if temperature-dependent (a) material pro
88、perties or(b) convection film coefficients are present. This means that several internal iterations will be run to achieve heat equilibrium.The solver working directory is where scratch filesare saved during the solution of the equations.By default, the TEMP directory of your Windowssystem environme
89、nt variable is used, although thiscan be changed in “Tools Control Panel Solution Solver Working Directory”.Any solver messages which appear after solution can be checked afterwards under“Solver Messages”February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTrain
90、ing ManualSteady-State Thermal Analysis Solving the ModelTo solve the model, request results first (covered next) and click on the “Solve” button on the Standard ToolbarBy default, two processors (if present) will be used for parallel processing. To set the number of processors, use “Tools Control P
91、anel Solution Number of Processors to Use”Recall that under “Worksheet” tab of the “Solution” branch, the details of the solution output can be examined.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Solving the
92、 ModelTo perform a thermal-stress solution, simply add structural support(s) and request structural results, then solve the model.Structural loads are optional but can also be added.Design Simulation will know that a thermal-stress analysis is to be performed (under Details view of the Solution bran
93、ch). The following will be performed automatically:A steady-state thermal analysis will be performedThe temperature field will be mapped back onto the structural modelA structural analysis will be performedSee Chapter 4 for details on Structural AnalysesDesign Simulation automates this type of coupl
94、ed-field solution, so the user does not have to worry about the above details.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Solution Options in ANSYSThe solver selection for direct vs. iterative:The solvers use
95、d are either the direct sparse solver (EQSLV,SPARSE) or the PCG solver (EQSLV,PCG)The JCG solver is not used in thermal analysesA simplified discussion between the two solvers:If given the linear static case of Kx = F, Direct solvers factorize K to solve for K-1. Then, x = K-1F. This factorization i
96、s computationally expensive but is done once.Iterative solvers use a preconditioner Q to solve the equation QKx = QF. Assume that Q = K-1. In this trivial case, Ix = K-1F. However, the preconditioner is not usually K-1. The closer Q is to K-1, the better the preconditioning is, and this process is r
97、epeated - hence the name, iterative solver.For iterative solvers, matrix multiplication (not factorization) is performed. This is much faster than matrix inversion if done entirely in RAM, so, as long as the number of iterations is not very high (which happens for well-conditioned matrices), iterati
98、ve solvers can be more efficient than sparse solvers.The main difference between the iterative solvers in ANSYS PCG, JCG, ICCG is the type of pre-conditioner used.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis S
99、olution Options in ANSYSSolver working directory:The ANSYS input file is written as “ds.dat” in the solver directory. The output file is “solve.out” and can be viewed in the “Worksheet” tab of the “Solution” branch.ANSYS is executed in batch mode (-b) as a separate process. During solution, the resu
100、lts file .rst is written. The results are also read in and XML results files are generated in batch mode. The XML files are then read into Design Simulation.All associated ANSYS files have default jobname of “file” and are deleted after solution, unless changed in “Tools Control Panel Solution Save
101、Ansys Files”.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Solution Options in ANSYSSome solution options are also defined:Solution control is usedThis is different from structural analyses in Design Simulation
102、 where Solution Control is turned offANSYS shape checking is turned off (SHPP,OFF)If nonlinear, the number of substeps (NSUBST,1,10,1) and number of equilibrium iterations (NEQIT,20) are definedCNVTOL also set, where minimum reference heat flow rate is defined as 1e-6 WOnly Design Simulation-support
103、ed results is output with OUTRES, not everything by defaultResults are later written to XML files in /POST1, which are then read back into Design Simulation. Hence, Design Simulation does not directly read the results from the .rth fileFebruary 2, 2004Inventory #0020106-ANSYS Workbench - SimulationA
104、NSYS Workbench - SimulationTraining ManualSteady-State Thermal AnalysisE. Results and PostprocessingVarious results are available for postprocessing:TemperatureHeat Flux“Reaction” Heat Flow RateIn Design Simulation, results are usually requested before solving, but they can be requested afterwards,
105、too.If you solve a model then request results afterwards, click on the “Solve” button , and the results will be retrieved. A new solution is not required for retrieving output of a solved model.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining Manual
106、Steady-State Thermal Analysis TemperatureTemperature contour plots can be requested:Temperature is the degree of freedom solved for,and it is the most basic output request.Temperature is a scalar quantity and, therefore,has no direction associated with it.February 2, 2004Inventory #0020106-ANSYS Wor
107、kbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Heat FluxHeat flux contour or vector plots are available:Heat flux q is defined asand is related to the thermal gradient T. The heat flux output has three components and can aid the user in seeing how the hea
108、t is flowing.The magnitude plotted as contours: “Total Heat Flux”The magnitude & direction as vectors: “Vector Heat Flux”Recall that wireframe is best for viewing vectorsComponents of heat flux can be requested with “Directional Heat Flux” and can be mapped on any coordinate system.February 2, 2004I
109、nventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Reaction Heat Flow RateReaction heat flow rates is available for any Given Temperature or Convection boundary conditionRecall that both given temperature and convection supply a kno
110、wn temperature, either directly or indirectly. Hence, this acts as a heat source/sink, and the amount of heat flowing in (positive) or out (negative) of the support can be output.For each individual Given Temperature orConvection load, the Reaction heat flow rateis printed in the Details view after
111、a solution.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis Reaction Heat Flow RateThe “Worksheet” tab for “Environment” branch has a tabular summary of reaction heat flow rates.If a thermal support shares a verte
112、x, edge, or surface with another thermal support or load, the reported reaction heat flow rate may be incorrect. This is due to the fact that the underlying mesh will have multiple supports applied to the same nodes. The solution will still be valid, but the reported values may not be accurate becau
113、se of this.February 2, 2004Inventory #0020106-ANSYS Workbench - SimulationANSYS Workbench - SimulationTraining ManualSteady-State Thermal Analysis F. Workshop 6Workshop 6 Thermal AnalysisGoal:Analyze the pump housing shown below for its heat transfer characteristics.February 2, 2004Inventory #0020106-February 2, 2004Inventory #0020106-
