1 ME-430 INTRODUCTION TO COMPUTER AIDED DESIGN Crankshaft Optimization Using Behavior Modeling Pro/ENGINEER Wildfire 2.0 Dr. Herli Surjanhata The engine designer has a requirement to keep the crank in balance and an objective of reducing the crank mass to enable quicker engine startup. Four basic studies will be performed on the crankshaft model: • Analysis Features • Sensitivity Study • Feasibility Study • Optimization Study Sensitivity Analysis Sensitivity analysis allows you to analyze how various measured quantities (parameters) vary when a model dimension or an independent model parameter is varied within a specified range. The result is a graph for each selected parameter showing the value of the parameter as a function of the dimension. This provides for understanding exactly how geometric changes to your model will affect your engineering goals or specifications. Feasibility and Optimization Studies Feasibility and optimization studies allow you to have the system compute dimension values that cause the model to satisfy certain user-specified constraints. In a feasibility study, you define the following: • A set of model dimensions to vary. • A range within which each dimension can vary. • A set of constraints that you want the design to satisfy. The analysis constraints are defined as equalities or inequalities that use parameters (which are the result of an analysis feature) and constant values. A sample constraint may appear as follows: length < 6.3 or distance = 11. To perform a feasibility study, the system does the following: 2 • The system attempts to find a set of dimension values within the specified ranges that satisfies all of the constraints. • If a solution is found, the model display changes to show these dimensions modified to the new values. You can either accept these new dimensions or undo the changes. The model can be reverted to its state before the feasibility study. There can be many solutions in a feasibility study that satisfy all constraint. The system converges to one of the solutions. With an optimization study, you can specify the goal function in addition to the parameters for a feasibility study. In an optimization study, you define the following: • A set of dimensions to vary • A range within which each dimension can vary • A set of constraints that you want the design to satisfy • A goal function to be optimized (maximized or minimized)–a goal function is created as the result of an analysis feature To perform an optimization study, the system does the following: • The system looks for feasible solutions. • Out of feasible solutions, the system selects the solution that optimizes the goal function The crankshaft has the following dimensions: 3 Step 1: Create a 1.25 in diameter cylinder using FRONT datum plane as sketching plane. The extrusion depth is 0.5 in. Note that the center of the cylinder is 1.75 in. above TOP datum plane. Step 2: Create an extrusion for the balancing body of the crankshaft. The dimensions of the section to be extruded are shown below. The extrusion depth is 0.5 in. 4 Step 3: Create another cylindrical extrusion with 1.5 in diameter and 2.0 in. length. Step 4: Mirror the geometry. MATERIAL DENSITY Under Edit pull down menu, select Setup -> Mass Props Enter density of steel as material of crankshaft. OK Done. 5 ANALYSIS FEATURES Click the Insert an analysis feature icon . The ANALYSIS dialog box appears. Change the Name to be CG, and hit Enter. Choose Model Analysis. Hit Next button to continue. 6 Click the Compute button. Then choose Close. 7 Parameters can be created for all the results of the analysis. The can be used later in relations, in notes in drawing, or to drive optimizations. In this case, create a parameter for volume (by default). Then click the Next button. 8 Features can be created at the center of gravity (COG). In this case create a point at the center of gravity. Select PNT_COG_ (e.g. PNT_COG_282) Choose YES under Create. Click the Check button to finish. The analysis feature CG is now in the model tree. 9 A view of the model from the FRONT shows that Point located at CG is not located at the axis of revolution. These must be brought together to meet the design goal. Analyze the distance between the axis and point of CG. AXIS OF REVOLUTION Datum point at CG 10 Click the Insert an analysis feature icon . The ANALYSIS dialog box appears. Change the Name to be OFFSET, and hit Enter. Make sure the Type of analysis is Measure. Hit Next button to continue. [...]... set of dimensional changes coupled with a design goal In this case, we will seek to satisfy two design constraints: 1 The crankshaft is balanced 2 The shoulder distance maintains a value of 0.25 in or greater Select Analysis pull-down menu Then choose Feasibility /Optimization The Optimization/ Feasibility dialog box appears 17 Under Study Type/Name choose Feasibility Add design constraints by selecting... Choose Run tab Click OK button Choose Compute from Optimization/ Feasibility dialog box HEIGHT RADIUS Graphs will be displayed showing that the goal is reached WIDHT 20 The model changes to match the new, balanced configuration Change the view to FRONT view, and notice that point of CG is now align to the axis of rotation 21 OPTIMIZATION STUDIES The optimization study is setup very much like the feasibility... appears 15 Click the Dimension button , select the balancing body feature to show dimensions, and choose the 3.000 dimension This is the height of the axis of revolution to the bottom of balancing body of crankshaft Change the range that the dimension will be iterated through Choose the parameters to plot by clicking the under Parameters To Plot Choose the number of iterations desired Click the Compute... under Results Click the Close button 11 Select Yes (under Create) to create a parameter for the distance This is the offset from balance condition Click the Check button to finish Before we balance the crankshaft, we have one more condition must be satisfied It is required that the balancing body be at least 0.25 in larger than the shaft The desired clearance is measured here 12 Click the Insert an analysis... finish SENSITIVITY STUDIES Sensitivity studies allow us to see how changing a model will affect our design goals We select a given dimension to modify and describe the range through which it will move Pro/ENGINEER evaluates the model at intervals throughout the range of the variable and graphs one or more design parameters (e.g the offset distance vs the dimension) 14 Select Analysis pull-down menu... can specify a goal This means that we not only arrive at a solution that works: we arrive at the best solution possible In this case, we will set a goal of minimizing volume (and weight) Fill out the Optimization/ Feasibility dialog box as shown below, and click Compute 22 The resulting graphs: 23 24 25 The model has been balance and optimized! Also the dimensions have changed as shown below Select . distance 3 .00 0; the overall WIDTH 4 .00 0 and bottom RADIUS 8 .00 0 of balancing body. The three dimensions are highlighted in red. Click OK. 20 Select Options. 1 ME-4 30 INTRODUCTION TO COMPUTER AIDED DESIGN Crankshaft Optimization Using Behavior Modeling Pro/ENGINEER Wildfire 2. 0 Dr. Herli Surjanhata