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CORNELL BEE 4530 - Tutorial - Drug Delivery

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Tutorial: Drug Delivery Problem Specification Step 1: Run the software GAMBIT to create the geometry and to mesh it Step 2: Create Geometry and Mesh in GAMBIT Create the vertices Create the edges Create the face Mesh Mesh the remaining edges Mesh face Define boundary zones and entities Define the boundary zones Specify the continuum Save Step 3: Start the interface PreSTO for solving the problem Step 4: Specify Model Step 5: Specify Material Properties Step 6: Specify Boundary Conditions and Initial Condition Specify BC on the Boundary PATCHSpecify BC on the Boundary L_SKINSpecify BC on the Boundary R_SKINSpecify Initial Condition Step 7: Specify Solver Controls Specify the Time Integration Method for the transient problem Step 8: Processing (Create and Run) Create Input File Create FIDAP Database Run the problem Step9: Post-Processing Open FIDAP from PreSTO Input the File Display the mesh with node numbers Plot Drug Concentration vs. Time at a particular node Obtain the contour plot of drug concentration at time, t = 1.33 Specify Time Step Specify the type of contour (lines/ solid) Specify the variable Step10: Save and Exit Exit FIDAPBEE453 Professor Ashim Datta Tutorial: Drug Delivery 2005 Cornell University BEE453, Professor Ashim Datta Authored by Vineet Rakesh Software: GAMBIT 2.1.6/ FIDAP 8.7.2 /Presto 1.2 Tutorial: Drug Delivery ..................................................................................................................................1 Problem Specification................................................................................................................................1 Step 1: Run the software GAMBIT to create the geometry and to mesh it...............................................1 Step 2:Create Geometry and Mesh in GAMBIT........................................................................................4 Step 3: Start the interface PreSTO for solving the problem....................................................................19 Step 4: Specify Model..............................................................................................................................20 Step 5: Specify Material Properties.........................................................................................................22 Step 6: Specify Boundary Conditions and Initial Condition.....................................................................22 Step 7: Specify Solver Controls...............................................................................................................24 Step 8: Processing (Create and Run) .....................................................................................................26 Step9: Post-Processing...........................................................................................................................29 Step10: Save and Exit.............................................................................................................................36 Problem Specification Here is an example to demonstrate how to setup up a problem in FIDAP and to solve it. The example deals with the analysis of a birth control patch. The contraceptive patch is a very effective method for birth control. The patch can be placed on multiple parts of the skin and the drugs are then transferred through the tissue by diffusion to the blood stream. The blood stream in turn transports these drugs to various parts of the body. Norelgestromin and ethinyl estradiol are the two drugs used in the patch. In this example, we model the movement of Norelgestromin through the tissue. The patch is considered to be circular with a radius of 2.4 cm. We model 0.6 cm of the skin around it to see how the drug spreads out from the edge of the patch. The thickness of the tissue is assumed to be 1.2 cm and the drugs diffuse into the blood stream after that. The schematic is shown in Fig. 1. It is assumed that the entire drug is taken away by the blood stream. The diffusivity of Norelgestromin is 1.11 x 10-11 m2/s and the patch provides a constant flux of 8.849 x 10-7 g/m2s. 2005 Cornell University 1BEE453 Professor Ashim Datta (a) (b) Figure 1. (a) Three dimensional view of the skin-patch system, (b) Axisymmetric geometry The geometry is modeled as shown in Fig. 1(b) in FIDAP. The transport of the drug is symmetric about the axis and so we can use the axisymmetric geometry to simplify the problem. The problem is non-dimensionalized since we are dealing with a very low value of diffusivity. The non-dimensional values of the parameters are given below: 1. Diffusivity: 1 2. Thickness of the tissue: 1 3. Radius of the patch: 20 4. Length of the skin surrounding the patch: 5 5. Flux = 95.665 6. 1 week is equivalent to 4.662 time units in the non-dimensional form. We now go ahead and solve the problem in FIDAP. 2005 Cornell University 2BEE453 Professor Ashim Datta Step 1: Run the software GAMBIT to create the geometry and to mesh it In the Command Prompt, type: gambit –id drugddrugd is the filename Remember: The filename should be at the most 7 characters long. Now Gambit is launched. Click on Solver menu at the top of the Gambit window and choose FIDAP. 2005 Cornell University 3BEE453 Professor Ashim Datta Step 2: Create Geometry and Mesh in GAMBIT The geometry in this case is a cylinder. However, since this is an axi-symmetric problem we will solve it with the help of a 2D geometry. We will first create the vertices and then connect these vertices in pairs to form edges and then create the faces by selecting the appropriate edges. Create the vertices This step specifies the coordinates of the vertices to be created. The coordinates of the vertices of the rectangle for our problem are (0, 0, 0), (1,0,0), (0,20,0), (0, 25, 0) and (1, 25,0) 1) Under the Operations panel, click on the Geometry command button 2) Under the Geometry panel, click on the Vertex command button 3) Under the Vertex panel, click on Create Vertex. Create Real Vertex Window pops up. 4) In the Create Real Vertex Window under Global, type in the coordinates of the vertex (0, 0, 0) in the text boxes 5) Click on Apply 6) Repeat for the other vertices: (1, 0, 0), (0, 20, 0), (0, 25, 0) and (1, 25, 0) 2005 Cornell University 4BEE453 Professor Ashim Datta 1) Click on Fit to Window to see the zoomed view 2005 Cornell University


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