Lecture_01-30-08 - 1 MECH 668 Vehicle Noise, Vibration and...

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Unformatted text preview: 1 MECH 668 Vehicle Noise, Vibration and Harshness (NVH) Practical Applications of Dynamic Finite Element Analysis Winter 2008 2 Finite Element Analysis ¡ Static analysis – Conservative assumptions – Over design is common ¡ Dynamic analysis – Conservative assumptions not applicable ¡ Example – Representing auto body with spot welds 3 Finite Element Analysis ¡ Static analysis – Easier to understand ¡ Dynamic analysis – Comprehension of results more complex – Typical engineer with BS has only introductory vibrations background 4 Design Changes ¡ Statics – Most loads not dependent on structure ¡ Dynamics – Structural changes impact stiffness and mass 5 Finite Element Modeling ¡ Solid modeling/FE modeling evolution – Easier to create increasingly large models – More for analyst to consider – Good graphics – Software marketing – Everything is EZ! – Analyst may develop unwarranted confidence 6 Finite Element Analysis ¡ Recent dynamic analysis example – Engine block/cylinder models – One million DOF – Desired frequency results accurate to within 3% of test data up to 6,000 Hz. 7 Finite Element Model Checks ¡ Perform model checks – Weight – Free edge – Coincident nodes/elements – Element distortion – Others… – Perform on entire model and repeat on logical subcomponents 8 Finite Elements ¡ Element types – Beam has 6 DOF – Thin shell may have 5 or 6 DOF • Different FE codes vary – Solid has 3 DOF – Degree of freedom mismatches by connecting different element types are potential problems if not handled correctly! 9 DOF Mismatch ¡ Example – Shell to solid creates hinge – Static analysis yields singularity – Dynamic run has zero energy mode of shells rotating about line of connection to solids 10 Driveline Model Example ¡ Beams – Add axes for viewing torsion modes 11 Beam Model ¡ Torsion and bending modes – Not always obvious, single mode may have both bending and torsion component – Can model two coincident elements, one with bending characteristics and the other with torsion characteristics – Look at strain energy in different elements to determine contributing behavior 12...
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This note was uploaded on 10/13/2010 for the course MECH 668 taught by Professor Lim during the Winter '08 term at University of Cincinnati.

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Lecture_01-30-08 - 1 MECH 668 Vehicle Noise, Vibration and...

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