This is the script for the TEMP/W tutorial movie. Please follow along with the movie, TEMP/W Getting Started.

Transcription

1 TEMP/W Tutorial This is the script for the TEMP/W tutorial movie. Please follow along with the movie, TEMP/W Getting Started. Introduction Here is a schematic diagram of the problem to be solved. An ice skating rink is being installed and the objective is to compute the depth of the frozen zone that will develop beneath the ice surface if the temperature of the ice is maintained at -5 C for a period of 8 months. Outside the ice surface, the floor in the building is assumed to be insulated so that no heat can cross over this area. Prior to placing the ice, the ground temperatures are steady at 3 C at the ground surface and 3.1 C at a depth of 4m. The material model used for this simulation will be a simplified thermal model using the thermal conductivity and heat capacity values shown here. Define We start by creating a new TEMP/W project from the Start Page of GeoStudio. When the KEYIN: Analysis dialogue box appears, select what type of analysis you are going to do and give it a name and description. The TEMP/W tutorial will actually consist of two separate analyses; a steady-state one and a transient one. Let s first create and solve the steady-state analysis, which will create the initial temperature profile that the transient analysis will use. The first time you start working with GeoStudio it is helpful to learn what different toolbars exist. Many of the dropdown commands are also available as individual icons on the many different toolbars. You can familiarize yourself with the toolbars by toggling them on and off. When developing a numerical model, the first step is usually to set the working area, which defines the size of the space available. The working area may be smaller, equal to or greater than the printer page The next step is to set the units and scale. The units for this particular simulation need to be set for length units of meters, time units of days, temperature units of degrees Celsius and heat energy units as kilojoules. The scale should be set such that the minimum and maximum extents in TEMP/W match those required for the analysis. Define the x and y minimum and maximum extents to get an idea of an approximate scale and then fine tune it so that you are working with a 1:1 aspect ratio.

2 A background grid of points will help you to draw the problem. It s always a good idea to save your file frequently. It is often helpful to sketch an axis. Before you start, click the zoom page icon so you can view the entire working area. Then choose Axis from the SKETCH menu. The axis is drawn by moving the cursor from the bottom left corner and stretching it outward. The number of increments can be adjusted using the SET: Axis drop down menu. Before defining the geometry in TEMP/W, it is convenient to first sketch the problem. Select Polylines from the SKETCH menu or use the sketch polyline icon. Use the cursor like a pencil, clicking the left mouse button to create a series of lines to outline the problem features. The lines are objects, which can be adjusted or deleted by using the MODIFY: Objects command. The approach to use when developing a numerical model is to draw the geometry; create and assign materials, create and assign boundary conditions and then finally, to review and fine-tune the finite element mesh. Let s start by drawing the geometry. Individual soil regions are created using the DRAW: Regions command. Click the left mouse button to create region points. Once the polygon region has been closed, you can either continue to draw additional regions, or exit draw regions mode. Materials are first created and then assigned to geometry objects. Choose Materials from the DRAW dropdown menu. Click on KEYIN to create a material. Add a new material, name it and select the material model from the dropdown list. We are going to be using a simplified thermal analysis soil model which only requires constant values as input. The material can now be assigned to the geometry regions. Boundary conditions are created and assigned in the same way materials are. Create your own boundary condition by clicking on the add button. For this steady-state example, we need two thermal boundary conditions that will be used to establish the thermal profile through the soil. The temperatures will be 3.1 C, and 3 C. Once the boundary conditions have been created, you can then apply them to the region geometry. The temperature at the bottom of the soil is 3.1 C while the temperature at the top is initially 3 C. Boundary conditions can be applied to region edges, region points, region faces, free lines or free points. Let s think ahead a little bit. We know that the transient analysis is only going to require boundary conditions along a portion of the top region edge due to the presence of the insulated floor. To break up a region edge so that the boundary conditions can be assigned to only a portion of it, you can add a region point.

3 Now that the geometry has been drawn, the material properties have been created and assigned and the boundary conditions applied, it s time to review the finite element mesh and make any necessary adjustments. You can view the finite element mesh using DRAW: Mesh Properties. The meshing algorithm in TEMP/W is defaulted to use a global element size. To change the global element size, type in a different value and then either use the ENTER key to update the field or click the cursor somewhere on the profile. While you can apply meshing constraints to individual geometry objects, it is often best to start with the default mesh and then constrain the mesh only if necessary. We are also going to use secondary nodes for each element which can help in obtaining a good solution for a thermal analysis. The finite element mesh will disappear after you leave the DRAW: Mesh Properties view. If you wish to leave it on, you can click the view mesh icon on the view preferences toolbar. Now it s time to verify the problem and TEMP/W will run a number of checks to see if there are any errors in the problem definition. Solve The solver for TEMP/W can be launched by clicking on the SOLVE icon. Click the start button to activate the solver. You can view the results directly by clicking on the CONTOUR icon in the analysis toolbar. By default, the CONTOUR results will include heat flow vectors and temperature contours. Since the bottom of the profile was slightly warmer, the flow is upward. To make sure that the initial temperature profile is correct, let s draw a graph of temperature versus y coordinate. Choose Graph from the DRAW menu. Add Additional Analysis Now we want to model the transient analysis which will help identify how far the frozen zone will be in the soil when the ice surface is maintained at a constant temperature of -5 C for 8 months. One of the new features of GeoStudio 2007 is the ability to solve multiple analyses in a single project file. Let s go back into DEFINE by clicking on the pencil icon and add the transient analysis using KEYIN: Analyses. Since the materials assigned to the regions are going to remain the same, I m going to create a clone analysis instead of starting a new one.

4 The conditions computed at the end of the steady-state analysis are going to be used as the starting point for the transient analysis. This means that the initial analysis is the parent of the transient analysis. Since a transient analysis means that there is a time dependency we also need to define time steps. The freezing period is 8 months long which is approximately 240 days. Let s define 10 time steps which increase exponentially from a starting increment size of 0.2 days, saving every 2nd time step. Since the material properties are the same, we just need to change the boundary conditions on the profile. First we need to create the boundary condition for the -5 C ice surface. We already inserted the point to break up the region edge; so just apply the new boundary condition to the ice surface edge, and remove the initial temperature boundary condition from under the insulated floor. Verify the problem once again and solve the transient simulation. You ll notice at the end of the solve process that a message appears that the maximum number of iterations was reached and the solution may not have converged. Convergence details can be adjusted using KEYIN Analyses. Let s try giving it a few more iterations, a slightly lower tolerance and increase the phase change number of iterations since a frozen zone is developing. This time the solution reaches the defined tolerance before the maximum number of iterations is exceeded. When you go into CONTOUR, you will see the results for the last time step, along with the zero temperature isoline. By using your arrow keys and the dropdown time list, you can scroll through the results for the various time steps. To update the temperature contours for any time step, use the update range button under DRAW: CONTOUR. Let s create a graph of the temperature profile through the soil for all the various time steps. You can also create a movie of the temperature profile and the advancement of the zero temperature line during the freeze process by using the VIEW: Movie command. You can spot check results at specific nodes using the VIEW: Result Information command. By holding down the CTRL key, you can select several points at the same time. New to GeoStudio 2007 is a reporting feature. If you need to generate a report of your input for a particular analysis; select Report from the VIEW menu. Once you save the report file, your default word processing program will open with a generated report. You can now insert pictures, apply style templates or add and delete data.

5 If at any time you need help with understanding a dialogue box, you can click on the question mark in the top left corner to access the on-line help or use F1 on your keyboard. You can also switch to the Analysis Start Page which has PDF copies of all the engineering books for GeoStudio under the documentation section. These books are very helpful in describing the features in the software and the theory behind them. You can also search through the examples database using specific keywords. When you are done, you can return to your analysis by clicking on the analysis list. We have reached the end of this introductory lesson. Not all of the powerful features of TEMP/W have been used or discussed during this lesson. Specific details about each command are given in the on-line help and in the supporting documentation for TEMP/W. Thanks for watching.