MAE486_Fall11_L17_S

MAE486_Fall11_L17_S - MAE 486 Design of Mechanical Systems...

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Unformatted text preview: MAE 486 Design of Mechanical Systems Lecture 17 Fall 2011 Today s topics: Mid-term 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.

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