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Unformatted text preview: MAE 486
Design of Mechanical Systems
Lecture 17
Fall 2011 Today s topics: Midterm Review;
Modeling (Chapter 10); MidTerm Review MidTerm Review Models in Engineering Design • What is model? Why model is needed in product/system design? • What are the diﬀerent models? Types of Models • How to categorize? • (1) staEc or dynamic; (2) determinisEc or probabilisEc, and (3) iconic, analog, or symbolic. MathemaEcal Model
Building Process • Problem statement: decide what it is your need to learn. • What are the steps? • Analysis: • Validate the model: Modeling Examples • CharacterisEcs of design model • Overall model for a steam power plant • Block diagram of major components of power plant Modeling Examples (cont’d) • Detailed systems for a coal
ﬁred power plant One Modeling Example • Problem Statement: What size motor should be selected to drive a conveyor belt to deliver sand at a ﬂow rate of 100 tons/hr using the following design. One Modeling Example (cont’d) • Design decision space: What are the quesEons we need to answer? • Boundaries of the model: • Data to support the model: It is required to liZ the sand to a height h=55 ft, and the angle of the conveyor is H=20o. The density of sand is 100 lb/ft3. The area of a cross secEon of the sand on the belt is A=0.5 ft2. One Modeling Example (cont’d) • Physical principles: • Assump:ons: One Modeling Example (cont’d) • Construct the model: What are the design variables? How they are related to each other? • Analysis: What does the above equaEon tell us? Se\ng Q=50 lb/s: Q: What is the minimal horsepower? One Modeling Example (cont’d) • V is an variable: How V is related to Q? • How the above equaEon is used in motor selecEon? Dimensional Analysis • What is it? • Why use it? What are the advantages? • What does it based on? – The Buckingham π theorem. Dimensional Analysis (cont’d) • What is the main idea? • What is the procedure to determine the pi terms using the method of repeaEng variable? Example of Dimensional Analysis • Goal: Analysis how the fricEon in the bearing varies with operaEon condiEons of a lubricated journal bearing. Example of Dimensional Analysis • List all the variables in the problem (k=?): • Express each of the variables in terms of their basic dimensions: • Determine the required number of pi terms • Select the repeaEng variables. • Select the variable to be the dependent variable. • Form a pi term by mulEplying one of the nonrepeaEng variables by the product of the repeaEng variables Example of Dimensional Analysis • Form a pi term by mulEplying one of the nonrepeaEng variables by the product of the repeaEng variables. For example Similarly, we obtain Example of Dimensional Analysis • When these three dimensionless groups are plofed, a clear picture of bearing performance is given. ...
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This note was uploaded on 02/26/2012 for the course 650 486 taught by Professor Zou during the Fall '11 term at Rutgers.
 Fall '11
 Zou

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