What is intertwined in ANSYS
Department of Electrical Engineering / Information Technology. ANSYS tutorial. For the Steady State Thermal analysis system and the Icepak component system.
1 Department of Electrical Engineering / Information Technology ANSYS Tutorial For the Steady State Thermal analysis system and the Icepak component system Content: Simulation of internal heat generation, caused by electrical power loss and its propagation, as well as a flow simulation of air flowing by Prof. Dr. Detlef Redlich 2011
2 ANSYS Thermal Analysis I List of Figures List of Figures Figure 1: Possible solution methods for computer-aided simulations Figure 2: Difference between FEM, FDM and BEM Figure 3: Start interface / project view of ANSYS 12.1 Workbench Figure 4: Starting the CAD Configuration Manager Figure 5: ANSYS-CAD -Configuration Manager Figure 6: Status message if the configuration is correct Figure 7: All CAD formats that can be imported Figure 8: Set up CAD interface to ANSYS Figure 9: Setting the contacts / connections Figure 10: View of the mechanical interface of ANSYS Workbench Figure 11: Details and missing information Figure 12: The different possibilities of mesh generation Figure 13: Influence of relevance on the network structure Figure 14: Element size applied to bodies, surfaces, edges and points Figure 15: Networking methods Figure 16: Possibilities for influencing the network in the contact area I Figure 17: Heat transfer mechanisms [physics for engineers, 8.
3 ANSYS Thermal Analysis II List of Figures Figure 41: Project view with an Icepak analysis Figure 42: ANSYS Icepak start screen Figure 43: Menu item for selecting the CAD geometries to be used Figure 44: Selection menu of the CAD elements Figure 45: Appearance of Icepak after the successful creation of the Geometry elements Figure 46: Pull-down menu to edit an object Figure 47: Setting options for the substance-specific properties Figure 48: Window for editing the properties of an opening object Figure 49: Menu item for generating a mesh Figure 50: Creating a hex-domain mesh Figure 51: Radiation remove from the calculation
4 ANSYS Thermal Analysis III List of Tables List of Tables Table 1: Explanation of symbols in the project view Table 2: Explanation of symbols for the mechanical surface Table 3: Material data for inverters ... Error! Bookmark not defined. Table 4: Power losses of the active components ... Error! Bookmark not defined. Table 5: Guide values for heat transfer coefficients (1)
5 ANSYS Thermal Analysis IV Contents Contents List of Figures ... I List of Tables ... III Contents ... IV 1 Introduction The ANSYS Workbench program The user interface in the project view Setting up the CAD interface Import options for CAD geometries The user interface of Mechanical [Multi Physics ] - View The network as the basis of the calculation Basics of thermal simulation Thermal equivalent circuit Procedure for a steady state thermal analysis Managing material data for the current project Importing CAD geometries Model descriptions and defining the setup Results of the FEM analysis Project task 1 ... Error! Bookmark not defined Sub-task Sub-task 3 ... Error! Bookmark not defined. 4.2 Project task 2 ... error! Bookmark not defined Sub-task 2 ... Error! Bookmark not defined Sub-task 3 ... Error! Bookmark not defined. 4.3 Project task 3 ... Error! Bookmark not defined Sub-task 2 ... Error! Bookmark not defined Sub-task 3 ... Error! Bookmark not defined. 4.4 Project task 4 ... Error! Bookmark not defined Sub-task 2 ... Error! Bookmark not defined. 5 Bibliography
6 ANSYS Thermal Analysis Introduction 1 Introduction This tutorial was created with the ANSYS 12.1 Workbench simulation program and is intended to provide a comprehensive introduction to stationary heat simulation. The solver Stady-State Thermal in conjunction with Static Structural are used for the analyzes under consideration. There are a variety of simulation tools with different specializations. The most frequently used programs are ESATAN, NASTRAN and ANSYS, the reason for this is a wide range of simulation options. All programs are based on a numerical calculation method. Figure 1: Possible solution methods for computer-aided simulations The analytical method is to be understood as the solution of the differential equation that describes the problem under consideration. The computer-aided numerical method is also based on the relevant differential equation for the analysis. The following figure shows the differences between the methods used. ANSYS uses the FE method for the calculation.
7 ANSYS Thermal Analysis Introduction Figure 2: Difference between FEM, FDM and BEM
8 ANSYS Thermal Analysis The ANSYS Workbench program 2 The ANSYS Workbench program 2.1 The user interface in the project view The user interface is divided into different levels. At the beginning of a new simulation, the project view opens. The analysis options acquired for the ANSYS package are listed on the left in window 1. The current project is shown in the middle window 2, starting with the geometry and the analyzes to be examined. Output 3 messages in window. all errors and warnings are displayed during the project. Properties of the selected object are displayed in window 4 on the right-hand side of the screen. Figure 3: Start interface / project view of ANSYS 12.1 Workbench
9 ANSYS Thermal Analysis The ANSYS Workbench program shown. Table 1: Symbol Explanation of symbols in the project view Explanation Condition not fulfilled: required data is missing Please note: it may be that a correction is necessary or data is missing Refresh required: data has changed in the meantime. Updating the cell also causes the interlocking results to be regenerated. Update necessary: the data has been changed, the cell must be updated. The data is up to date. Input data change is imminent: the cell is locally up-to-date, it will be changed during the next update. The solution can be resumed by retriggering the solution or with Check Results. in progress: a process group is currently being calculated 2.2 Setting up the CAD interface There are various options for importing the geometry to be analyzed into the ANSYS Workbench. ANSYS offers a configuration manager for the most common CAD programs. The configuration manager can be found under Start ANSYS 12.1 Utilities CAD Configuration Manager. Frequently used CAD programs are: Catia V5, Co Create One Space Modeling, Inventor, Mechanical Desktop, Unigraphics NX, Pro / Engineer, Solid Edge and SolidWorks. Already during the installation of ANSYS Workbench you will be asked for the existing CAD software. It turns out to be very practical to install the CAD program first and then the ANSYS Workbench. You shouldn't have any influence on Figure 4: Starting the CAD Configuration Manager
10 ANSYS Thermal Analysis The program ANSYS-Workbench Installation has the possibility to create the interface between CAD software and the simulation software via the CAD Configuration Manager. The CAD Configuration Manager can be seen in Figure 5. Only the listed CAD products are supported as geometry interfaces. In order to be able to select a CAD product, the interface (left) must be selected, usually Advertising and ANSYS geometry interfaces. (In this tutorial, all geometries are generated with Pro / Engineer.) Then the installation position of the CAD program used is required as well as the start command. To complete the CAD configuration, the button Configure selected CAD interface must be pressed, the result can be seen in Figure 6. Figure 5: ANSYS-CAD configuration manager 12.1 Figure 6: Status message for correct configuration
11 ANSYS Thermal Analysis The ANSYS Workbench program 2.3 Import options for CAD geometries ANSYS Workbench can import the following files (Figure 7) as geometry. Users of other CAD products have the option of loading the geometry to be examined into ANSYS Workbench via a STEP file 1, IGES file 2 or other file formats. Figure 7: All CAD formats that can be imported The configuration of the CAD interface considerably simplifies the cooperation between the CAD product and the simulation program. The properly set up interface for the CAD program Pro / Engineer looks like this: Figure 8: Set up CAD interface to ANSYS 2.4 The user interface of the Mechanical [Multi Physics] - view STEP file: Standard for the Exchange of Product model data , STEP is an interface standard initiated by ISO (ISO 10303) that goes beyond the pure exchange of geometry data. Possible file extensions: * .stp, * .step IGES file - English: Initial Graphics Exchange Specification, IGES is a platform-independent data format that enables the digital exchange of 2D and 3D models for simulations and production
12 ANSYS Thermal Analysis The ANSYS Workbench program The mechanical user interface represents the actual simulation tool, with the physical properties of the analysis as well as the networking, calculation and presentation of results. In Figure 10, on the left edge of the screen (window 1), the project is clearly laid out Structure tree can be seen. In the structure tree, all geometries created as individual parts are listed as well as imported coordinate systems or coordinate systems created in ANSYS. Under the menu item Contacts / Connections, all contacts from the CAD geometry are recognized and set to composite by default. There are also other ways to define contacts: No Separation, Friction Free, Rough, and Frictional. Figure 9: Setting the contacts / connections To change the properties of the contact area, look for the desired connection in the structure tree under Contacts / Connections. In the detail window (window 3) under definition type, the change can be made, as shown in Figure 9. The selected contact area is shown in color in the graphics window, all surfaces that are not involved become transparent. The network and its creation is explained in Chapter 2.5 The network as the basis of the calculation.
13 ANSYS Thermal Analysis The ANSYS Workbench program Figure 10: View of the mechanical surface of ANSYS Workbench In the selection / results window (window 2), points, edges, surfaces or solids can be selected with the mouse. In the detail window (window 3) all details / settings for the selected point in the structure tree are displayed, as shown in Figure 11. In the case of question marks in front of elements in the structure tree, missing entries must be added. These are highlighted in yellow in the detailed view. Figure 11: Details and missing information
14 ANSYS Thermal Analysis The ANSYS Workbench program The results are also selected using the structure tree. Selected solutions are displayed in window 2 (Figure 10). Detailed solution information can be seen under the screen excerpt (window 2). ANSYS Workbench offers the possibility to visualize the results in the form of an animation (window 5) (Figure 10). Special starting and boundary conditions must be specified for each analysis. ANSYS Workbench provides the possible conditions and desired results for the respective analysis and solution in window 4 (Figure 10). The material data are also adapted to the analyzes, so there is no need to enter unnecessary data. Further buttons for program control are explained in the following table: Table 2: Symbol Explanations of symbols for the mechanical surface Explanations starts the mechanical wizard - provides helpful and easily understandable assistance for the current analysis, starts the calculation of the analysis - provided there are no more question marks in the structure tree the solution is calculated.Create a new section plane - this tool enables you to cut the component by drawing a straight line; the section can be deleted in the newly created section planes window.Graphic labels - enables user-defined descriptions to be created New diagram / table - creates a new sub-item diagram in the report , in which a separate tabular overview is created for the object selected from the structure tree for the desired output quantities. The output quantities can be selected under Details. New comment - adds a comment as text to the displayed and calculated solution in the structure tree. New image - creates images for exporting the solution in the following formats: * .jpg, * .bmp, * .tif, * .eps, and * .png format . Under Windows 7, the aero surface must be switched off in order to generate an image.
15 ANSYS Thermal Analysis The ANSYS Workbench program Table 3: The symbols in the structure tree have the following meanings Green tick: Everything is ok Blue question mark: Waiting for input to be able to solve Gray X: Element is suppressed in the structure tree Red exclamation mark: Warning, yellow flash: All Entries available, ready for a solution Green lightning: Calculation is taking place at the moment Red lightning: Calculation was canceled, either by the user or by the program Red arrow down: the outsourced calculation was canceled and is ready for loading
16 ANSYS Thermal Analysis The program ANSYS-Workbench 2.5 The network as the basis of the calculation Finite Element Method, on which the ANSYS-Workench is based, states that the component under consideration is broken down into finite parts, the finite elements. The elements are connected to one another at the corner nodes and, if available, at the middle nodes, thus forming the network. Automatic or conservative manual networking can be used, which relieves the user of a detailed quality check of individual elements. For this reason, the FE method can also be used by sporadic users if the physical fundamentals are available. The following options are available for generating a mesh: Figure 12: The various options for generating a mesh For a rough and rough calculation, it is often sufficient to carry out an automatic meshing. A network is created by right-clicking on the Mesh element in the structure tree and on Create Mesh in the pull-down menu. For coarse structures and large areas, fewer nodes and thus a more extensive network are created. Filigree structures are recognized and correspondingly more finely networked. In many cases, however, such a network is inadequate; Figure 12 shows the options for intervening in the network. In the simplest case, relevance can be used to influence the global network fineness. For the setting, the network must be marked in the structure tree and the relevance can be changed from -100 (coarse) to 100 (fine) using the slider in the detail window under standard settings. The setting and the result can be seen in Figure 13.
17 ANSYS Thermal Analysis The ANSYS Workbench Program Relevance Relevance +100 Figure 13: Influence of relevance on the network structure If the relevance setting is negative, the computational effort and thus the calculation time is reduced, but the result is less precise. If the slider is in the positive section, the quality of the result increases due to the longer calculation time. In addition to changing the relevance in the detail window, the element size of the network can also be controlled under element size physics-based relevance via the settings fine, medium and coarse. In the element size sub-item, an absolute value can be specified for each FEM element. Changes to global network settings are only useful for global results such as deformation, natural frequencies or temperature. Changes to the global grid control are not effective for local results such as stresses or heat flows. It is also possible to provide individual geometries with a network structure of different densities. By right-clicking on Insert Mesh Element Size, a new sub-item appears under Mesh in the structure tree. Different geometries, surfaces, edges or points can now be assigned to this new sub-item element size. In the detail window of element size, any element size can be entered under Definition. A clear change in the original network can be seen in Figure 14.
18 ANSYS Thermal Analysis The ANSYS Workbench program Figure 14: Element size applied to bodies, surfaces, edges and points Figure 12 shows further methods of network control, the most common of them are explained in the following section. The method enables the user to directly influence the shape of the element; individual geometries can have different meshes. The methods available for selection are shown in Figure 15. Figure 15: Meshing methods The contact element size refers exclusively to the meshing in the contact area of geometries. When inserting this network control, the following options are available:
19 ANSYS Thermal Analysis The ANSYS Workbench program Figure 16: Options for influencing the networking in the contact area The type of the network can be changed via the relevance or by entering element sizes.By inserting a refinement, the existing network can be refined in three stages in the detail window.
20 ANSYS Thermal Analysis Basics of Thermosimulation 3 Basics of Thermosimulation As can be seen in Figure 17, the heat transfer can be divided into three transfer mechanisms: heat conduction, heat radiation and convection. Only heat conduction occurs in solids. The energy is transmitted to neighboring molecules by vibration and the kinetic energy of the conduction electrons in collision processes. In liquids, free convection takes place between heated subsets even without an externally imposed forced flow. If a flow is caused by external forces, it is called forced convection. In gases, convection and thermal radiation dominate between the walls of the gas volume. In a vacuum, heat radiation and heat conduction in the material are the only possibilities of the heat transfer mechanism. Figure 17: Heat transfer mechanisms [physics for engineers, 8th edition, Springer]
21 Temperature in the component Temperature of the base plate Temperature of the circuit board Temperature of the base plate Ambient temperature Internal thermal resistance of the component Contact surface resistance between component housing, circuit board and potting compound Contact surface resistance between circuit board and base plate Thermal resistance of the base plate and potting compound ANSYS thermal analysis Basics of thermal simulation 3.1 Thermal equivalent circuit diagram Figure 18 shows the complete Static-thermal equivalent circuit diagram for an inverter is shown. R th G-VG R th VG-U PVR th G-Pl R th IG R th Pl-GP R th GP-U ϑ I ϑ G ϑ Pl ϑ G ϑ U Figure 18: Complete thermal equivalent circuit diagram of the inverter Figure 19: Inverter without potting compound
22 ANSYS thermal analysis Basics of thermal simulation The equivalent circuit diagram from Figure 18 can only be calculated with great effort. For this reason, the following simplifications can be made: the release of thermal energy through the potting compound to the environment is neglected in this consideration. This creates a pure series connection of resistors that can be combined to form a thermal equivalent resistance. Values relevant for the calculation can be seen in Figure 20: the power loss, the temperature inside the inverter and the ambient temperature. PVR th substitute Figure 20: ϑ I ϑ U Simplified thermal equivalent circuit diagram The following analogies exist between Ohm's law and the thermal equivalent circuit diagram: URR th IQ 1 PV 3.2 Procedure for a steady state thermal analysis After the ANSYS Workbench has been successfully started, the project view is as follows See Figure 3. A list of the possible analyzes is located on the left-hand side of the screen. In order to get the first analysis into the project window, it is irrelevant whether the selection is made by double-clicking or dragging and dropping it into the project window. The drag and drop method is recommended for further and combined simulations. While dragging, ANSYS shows which results from previous analyzes can be used.
23 ANSYS thermal analysis Basics of thermal simulation Figure 21: Display (red frame) which elements can be used for a new analysis Figure 22: Linked analyzes Linking analyzes reduces the storage requirements of the project and enables a clear presentation. Changes can only be made to the original elements (e.g. Figure 22 left part A). After a modification, the Refresh project button must be pressed so that the change takes effect in the entire project. When working on projects, we recommend vertical processing starting with the first element, Engineering Data.
24 ANSYS thermal analysis Basics of thermal simulation Manage material data for the current project To edit the individual elements of an analysis in the project view, they are called up with a double click or in the pulldown menu via Edit, which opens with a right click. The editing window for the material data has the following appearance: Figure 23: Management of the material data for the current project In window 1 of Figure 21, all available material libraries are listed. The last line is available to integrate your own material libraries: The material libraries must be in * .xml format. Window 2 enables the selected material database to be viewed. All materials are listed and can be added to the current project using the yellow plus to the right of the material name. Figure 24: Material list of a material library As soon as the book symbol appears in column C, the material is added to the engineering data, which represents the database of the current project.
25 ANSYS thermal analysis Basics of thermal simulation In window 3 all material properties of the material marked in window 2 are displayed. Changes to certain material properties can only be made to the materials in the project-specific engineering data database, not in the material library. An entry is made possible by double-clicking on the value to be changed. The units of the individual values can be changed by clicking (LMB 3) via the pull-down menu that appears, as can be seen in Figure 25. Figure 25: Changing the unit of a material value Window 4 shows all material properties for the pending analysis. Due to the multitude of possibilities for the results to be calculated, not all material properties are required for every case. The following physical properties are required for a thermal analysis (steady-state thermal): Density, isotropic elasticity, isotropic thermal conductivity. The following properties are required for a static structural analysis (Static Structural): Density and isotropic elasticity. In window 5, changing material properties, caused by varying temperatures in the analysis, can be taken into account in the form of a table. Window 6 is a graphic implementation of the table from window 5. 3 LMB - Left mouse button
26 ANSYS thermal analysis Basics of thermal simulation Importing CAD geometries If the CAD interface is not configured, there are the following options for loading geometries: Figure 26: Options for importing a geometry Right-clicking on Geometry opens the pull-down menu shown in Figure 26, there are 2 Options available. The ANSYS Workbench's DesignModeler opens under the New Geometry selection. In the DesignModeler, the user has the option of creating geometries or importing external geometry files (Figure 28). After selecting the geometry, click the Create button (Figure 27) to confirm the import. Figure 28: Importing external geometry in the DesignModeler Figure 27: With "Create" the geometry is generated and displayed in the DesignModeler. The other option according to Figure 26 is to import the file without the DesignModeler. The geometry can be selected by selecting the menu item Import Geometry in an Explorer window.
27 ANSYS Thermal analysis Basics of thermal simulation Model descriptions and definition of the setup By double-clicking on Model, the mechanical interface opens in the project view. Figure 29: Double click on model to open the mechanical surface. The mechanical surface is already described in detail in chapter 2.4 The user interface of the Mechanical [Multi Physics] view. In the structure tree, we also recommend a top-down processing sequence. At the beginning it makes sense to assign the corresponding material to all geometries. It is not necessary to make changes to the contacts / connections for the model of the inverter. The standard contact position is left on composite. When creating the mesh, automatic mesh generation can usually be used for a first simulation run. Provided that the dimensions of the individual geometries do not differ too much from one another. After the first calculation, points of particular interest, such as stresses etc., can be meshed more finely.
28 ANSYS thermal analysis Basics of thermal simulation Figure 30: Representation of the automatic networking The setup of the thermal analysis is stored under this point. If this element is marked in the structure tree, a new toolbox with thermal boundary conditions appears above the graphics window: Every thermal problem can be described using these boundary conditions Step: Assigning the internal heat generation From the boundary conditions, call the pull-down menu Heat and select the internal heat generation there. A sub-item internal heat generation appears in the structure tree under thermal-stationary analysis. The above question mark means that there is still no information about the calculation. The missing entries are highlighted in yellow in the detail window of the internal heat generation. Figure 31: Sequence for assigning internal heat generation
29 ANSYS Thermal analysis Basics of thermal simulation The electronic component of the DIP 4 design has a simplified interior, which can be seen in Figure 32, but is sufficiently precise for a thermal simulation. Figure 32: greatly simplified inner workings of a DIP component In the detail window for internal heat generation, click on the yellow field to start the geometry selection (see Figure 31). Then the inside of the chip is marked in the graphics window (to enable the selection, it is recommended to hide the remaining elements in the structure tree under the item Geometry, Figure 33), by clicking again in the Geometry field, an Apply button appears to confirm the Selection. Figure 33: Hide all unneeded elements in the sub-item Geometry 4 DIP - Dual in-line package or Dual In-Line (DIL) for short is the designation for an elongated housing shape of an electronic component with two-row connection options
30 ANSYS thermal analysis Basics of thermal simulation The definition of internal heat generation includes not only the geometry selection but also the dissipative power loss. For the calculation, the power loss is assumed to be evenly distributed over the entire geometry. Thus, in the detail window of the internal heat generation under Size (Figure 31), the actual power loss must be calculated over the respective volume of the body. A real component should be used for a better understanding. A dual operational amplifier from SGS-Thomson, model L272, is used. internal dissipative power Chip 1.2W heat generation 0, 025 W 3 48mm mm volume inner workings 3 The following picture should then be visible: Figure 34: Representation for successful allocation of an "internal heat generation"
31 ANSYS Thermal analysis Basics of thermal simulation Step: Assigning convection and radiation So that the operational amplifier can interact with its environment in the simulation, the surfaces must be given radiation properties and the possibility of convection. Radiation and convection can be selected directly under the boundary conditions of the thermal analysis. The thermal radiation will also play a role in this consideration. When inserting a convection, ANSYS Workbench expects a geometry selection and a heat transfer coefficient, as can be seen in Figure 35. Figure 35: Settings for convection The underside of the component is not used for convection, the distance to the circuit board is too small to allow effective convection. However, the radiation from the component on the underside should not be neglected. Heat transfer coefficient (occurring power loss) Convection area * Temperature difference Q A *
32 ANSYS Thermal analysis Basics of thermal simulation Guide values for heat transfer coefficients in stagnant air can be found in Table 4 below. Table 4: Guide values for heat transfer coefficients (1) Fluid Type of flow Heat transfer coefficient α (W / (m²K)) Gases and vapors Free flow 4 25 Gases and vapors Forced flow Gases, air at rest 2 10 The radiant power of a body over its surfaces can be reduced in the Thermal simulation can also be taken into account. The emissivity is assigned in the same way as convection. Guide values for the emissivity of surfaces can be found in Table 5 below. The values are mean values for the expected temperature range of 22 C 150 C. Table 5: Averaged emissivity of various substances in the temperature range of C Substance Emissivity Epoxy resin 0.79 Polished copper 0.3 Gold 0.26 PVC (with carbon black pigments) 0.97 Solder resist (glossy) 0.8 The following figure shows the thermal loads on the DIP component.
33 ANSYS thermal analysis Basics of thermal simulation Figure 36: List of thermal loads
34 ANSYS Thermal analysis Results of the FEM analysis 4 Results of the FEM analysis The result after a successful simulation looks like this: Figure 37: Sectional representation of the temperature distribution of a dual OPV with 1.2 W power loss The temperature balance of the component is mainly caused by the convection over the housing as well as influenced by the thermal conduction of the pins. The circuit board is represented here by a 70 µm thick copper layer, which has the emission properties of clear, glossy solder mask. The following figure shows the temperatures at the pins. Figure 38: Temperature distribution on the pins
35 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak 5 Computational Fluid Dynamics with ANSYS Icepak In many cases a static analysis with solids without flowing fluids is insufficient. ANSYS offers the following options to calculate a dynamic fluid simulation: In-house: Fluid Flow BlowMolding Fluid Flow Extrusion Fluid Flow (CFX) Mergers with other companies: CFX FLUENT Icapak Polyflow The following simulation is carried out on a 2-fold operational amplifier, the associated The data sheet can be found in the appendix. 5.1 Importing CAD geometries via the ANSYS Design Modeler In the Icepak itself there is no possibility to import geometries. It is therefore advisable to drag and drop a geometry module from the Component System in the ANSYS Workbench view into the project window. Figure 39: creating an independent geometry
36 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak The ANSYS DesignModeler opens by double-clicking on geometry, which is currently still marked with a question mark. Figure 40: Importing external geometry files All common geometry files can be selected in the selection menu, as described in Section 2.3. Following the selection, the actual import must be confirmed using the Create button. If the desired geometry can be seen in the graphics window, the import was successful. The DesignModeler can be closed. 5.2 The user interface of Icepak The Icapak analysis can also be dragged and dropped into the project window. Icepak starts with a double click on Setup in cell B. Figure 41: Project view with an Icepak analysis
37 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak Material data is managed in the Icepak program itself, so the sub-item Engineering Data in cell B is omitted Figure 42: ANSYS Icepak start screen In window 1, a structure tree is similar to the mechanical interface of ANSYS Workbench can be seen in which all elements present in the simulation, such as geometries, simulation results and analysis settings are listed. In area 2 there are symbols for the simplified control of the Icepak analysis tool. Area 3 framed in blue represents the cabinet (cuboid room). The cabinet is the area in which the simulation takes place; outside of this area, no calculations are made. Window 4 represents the communication interface to the user. All input requests and errors for operating the program are displayed here.
38 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak Area 5 represents the toolbox for the different views of the model. In the toolbox, which is marked as area 6, the orientation of the model in the graphics window can be changed. The toolbox in area 7 is responsible for networking, boundary conditions and starting the simulation. The post-processing, such as displaying the results and much more, is carried out by the toolbox in the selection of geometries to be generated area. In a short time after starting the program, the geometry to be examined can be seen in the graphics window. In order to make the CAD data usable for the simulation, you have to be selected in the Model menu under CAD data. After successful selection, all elements of the model can be seen in the structure tree on the left side of the screen under the item Cabinet. Figure 43: Menu item for selecting the CAD geometries to be used The following Figure 44 shows the selection menu for the CAD elements. At the beginning of the selection, all elements are selected, in the window at the top right. The names of the individual elements are not adopted. Each individual CAD geometry must be selected and defined as a block. Each assigned geometry now appears in the structure tree under the cabinet.If only a few and very simple bodies are used for simulation, the geometry to be expected for Icepak can be specified in the CAD data window (bottom left). If a body cannot be restricted to the basic geometries, it is highly recommended to check the box for
39 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak Use CAD Surfaces directly. This means that any shape can be adopted in the cabinet. However, this selection limits the creation of possible mesh types. Figure 44: Selection menu of the CAD elements In order to achieve a better assignment of the geometries, it is advisable to name each element in the structure tree individually. The following appearance should then result: Figure 45: Appearance after successful creation of the geometry elements The material data are now assigned to each element in the structure tree, multiple selection is possible with the Ctrl key. By right-clicking on a desired
40 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak Element opens a pull-down menu in which all settings can be made via Edit Object. Figure 46: Pull-down menu to edit an object In the following window, the created block can be given specific properties. Its physical state, its surface and its specific thermal properties can be changed under the Properties tab. Figure 47: Setting options for the substance-specific properties In contrast to the ANSYS Mechanical surface, a dissipative power loss can be specified directly under Thermal specification. The following materials were chosen for the individual elements:
41 ANSYS Thermal Analysis Table 6: Computational Fluid Dynamics with ANSYS Icepak Materials for Icepak Thermal Simulation Element Housing Internal Soldered Connections Bonding Wire Foot (Pin) Board Material Epoxy-Resin-Typical Si-Typical Solder Pb39,2 Sn60,8 Au-Typical Ag-Typical FR- 4 Since Icepak is ideally suited for a flow simulation in connection with a thermal analysis, the flowing fluid still has to be defined. The program offers a simple variant via the openings elements. Openings are attached to the cabinet and represent a kind of opening / window to the otherwise closed simulation environment. The properties of these elements can also be edited. Figure 48: Window for editing the properties of an opening object In order to generate a continuous flow, one opening must represent the inlet of the fluid and another opening the outlet. By assigning a negative velocity (velocity), the direction of flow can be influenced. There is air in the cabinet as standard. The opening, which represents the exit, does not require any additional information on flow velocities. If other fluids are required, these must be generated and assigned as a separate geometry.
42 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak 5.4 Networking in the Icepak Due to the complex geometries, the possible network selection is reduced to a hexdominat Mesh Mesher-HD. The mesh is generated via the menu -> Model -> Generate Mesh. Figure 49: Menu item for mesh generation In the following window, settings for element size, mesh type, maximum number of nodes and much more can be made. Be made. The Generate mesh button must be clicked to generate the desired mesh. If the distance between the nodes is too large, a message will be displayed and you can have the program refine it. The generated network can be displayed under the Display tab. Due to the small dimensions of some geometric elements, such as the bonding wires and the soldered connections, the network is quite fine and takes a long time to create. Figure 50: Creating a hex domain mesh
43 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak 5.5 Solving the simulation In the structure tree under the first point, problem setup options are available to define general settings for the analysis. In this flow simulation, radiation takes a back seat, as only a very small percentage of the dissipative power loss comes into play in it. For this reason, the radiation is removed from the calculation under the basic parameters. Figure 51: Remove radiation from the calculation In order to start the calculation after successful networking, select the menu item Solve -> Run Solution. No settings need to be made to the calculation option. The results can be presented in various ways. It is possible to generate a result for each element in the structure tree. This means that unimportant geometric elements that are important for the calculation but are undesirable for the display of the results can be hidden. The following representations can be implemented in Icepak: Symbol Table 7: Postprocessing settings Explanation of temperature distribution of the object Representation of the temperature profile on a cutting plane Display of surfaces with the same temperature Set a test point, size of the surface area Selectable Set surface sample
44 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak When displaying different results, it should be noted that all of them are always displayed in the graphics window; unwanted results can be deactivated by right-clicking. The following temperature distribution should result: Loads: 1.2 W dissipative power loss (geometry element: internal) 20 C of the inflowing air Flow velocity is 2 m / s Radiation from the calculation except for Figure 52: Temperature distribution on the chip and on the circuit board
45 ANSYS Thermal Analysis Computational Fluid Dynamics with ANSYS Icepak Figure 53: Representation of the flowing air and its temperature behavior
46 ANSYS Thermal Analysis Bibliography 6 Bibliography 1. Gebhardt, Christof. Design-accompanying calculation with ANSYS DesignSpace, ISBN: Munich: Carl Hanser Verlag, Lawrence, Kent L. Ansys Workbench Tutorial Release 11: Structural & Thermal Analysis Using the Ansys Workbench Release 11.0 Environment, ISBN: s.l. : Schroff Development Corp, Swiss, Anton. Project planning aid for generator sets Formula collection - calculation programs. [Online] March Inc., ANSYS. ANSYS training
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