MAE M269A Course Overview

Jiann-Wen Ju, instructor of MAE M269A

MAE M269A Course Overview

Dynamics of Structures

Description of the Course
Lecture, four hours; outside study, eight hours. Principles of dynamics. Determination of normal modes and frequencies by differential and integral equation solutions. Transient and steady state response. Emphasis on derivation and solution of governing equations using
matrix formulation. Letter grading.

Background students will need
Although prerequisites are not enforced for graduate students, it is strongly recommended that each student has taken courses equivalent to “Introduction to Mechanical Vibrations.”

About the Instructor
Jiann-Wen Ju: My current research interests concern mechanics of materials and constitutive modelings of advanced engineering materials. In particular, I am interested in micromechanical damage mechanics of brittle composites, micromechanics of random heterogeneous elastic and inelastic fibrous and particulate composites, continuum elastoplastic damage mechanics, plasticity and viscoplasticity theories and computational algorithms, advanced constitutive modeling of materials, nonlinear computational solid mechanics and nondestructive testing. Applications can be made to high-strength plain concretes and fiber reinforced concretes, geological materials, advanced ceramics and ceramic composites, metals and metal matrix composites, and so on.

Syllabus

Free vibration analysis of SDOF equation of motion (Lecture 1)
- Components of the basic SDOF dynamic system
- Equation of motion (linear system)
- Influence of gravity
- Influence of support excitation
- Undamped free vibrations; Damped free vibrations
- Logarithmic decrement (for underdamped system)
- Numerical examples
Dynamic response to harmonic loading (Lecture 2)
- Response to harmonic loading of a SDOF system
- Undamped system, Damped system
- Steady-state vibration response
- Resonant response
- Accelerometers and displacement meters
- Vibration isolation
- Numerical examples
Dynamic response to periodic loading and impulsive loads (Lecture 3)
- Fourier series expression of the loading
- Response to Fourier series loading: undamped and damped
- Response to impulsive loads: Rectangular impulse, triangular impulse, sine-wave impulse
- Numerical examples
Dynamic response to general dynamic loading (Lecture 4)
- Time domain: Duhamel integral for an undamped system
- Numerical integration of Duhamel integral
- Response of damped system
- Numerical examples
Formulation of MDOF EOM (Lecture 5)
- Formulation of the MDOF equation of motion. Matrix formulation
- Evaluation of elastic properties
- Evaluation of mass properties
- Evaluation of damping properties
- External loading
MDOF Undamped free vibrations (Lecture 6)
- Vibration frequencies and corresponding mode shapes
- Orthogonality conditions
- Modal superposition method
- Numerical examples
MDOF Analysis of damped system: modal superposition (Lecture 7)
- Damped uncoupled equations of motion
- Conditions for damping orthogonality; Rayleigh and Caughey damping
- Numerical examples
Vibrations of undamped continuous systems (strings) (Lecture 8)
- Problem overview and summary of general solution procedure
  - Free vibration analysis
  - Orthogonality of mode shapes
  - Modal expansion theorem
  - Forced vibration – normal mode method
  - Initial conditions
- Vibrating strings
Examples on strings, and longitudinal vibrations of rods (Lecture 9)
- Examples – vibrating strings
  - Free vibrations of a string supported on both ends
  - Free vibrations of a string with a spring/mass system on one end
  - Forced vibrations of a string fixed at both ends
- Longitudinal vibrations of rods
Examples on rods, and transverse vibrations of beams (Lecture 10)
- Examples – longitudinal vibration of rods
  - Free vibrations with one end fixed and other end free
  - Free vibrations with both ends fixed
  - Free vibrations of two bars with fixed and free ends3
  - Free vibrations of bar with a concentrated mass Mc at free End
- Transverse vibrations of beams
Examples on transverse vibrations of beams (Lecture 11)
- Examples – transverse vibrations of beams
  - Free vibrations of a simply supported beam on both ends
  - Free vibrations of a beam fixed on both ends
  - Free vibrations of a free-free beam
  - Two beams hinged together with ends simply–supported
Vibrations of structural systems (Lecture 12)
- Vibrations of structural systems
- Examples – vibrations of structural systems
  - Two beams with an additional massless spring
  - Two beams with an axial force member
  - Two beams interconnected by springs with an attached mass
Hamilton’s principle on dynamic structural systems I (Lecture 13)
- Hamilton’s principle
- Kinetic energy
- Strain energy
Hamilton’s principle on dynamic structural systems II (Lecture 14)
- Potential energy of external forces
- Potential energy due to axial shortening
- Equation of motion via Hamilton’s principle
  - Axial force members
  - Examples on axial force members
Hamilton’s principle on dynamic structural systems III (Lecture 15)
- Equation of motion via Hamilton’s principle
  - Circular cylinders – torsion members
  - Example on torsional shaft system
  - Bernoulli-Euler beams
  - Example on Bernoulli-Euler beam with spring and lumped mass at one end
  - Bernoulli-Euler beam under an axial force
Hamilton’s principle on dynamic structural systems IV (Lecture 16)
- Equation of motion via Hamilton’s principle
  - Examples on Bernoulli-Euler beams
    - Forced vibration of a beam – column supporting a mass
    - L shape frame
    - L shape frame/re-derivation considering axial motions
    - Beam with a rigid appendage supporting a lumped mass4
Global approximation methods (Lecture 17)
- Preliminary remarks
- Rayleigh’s Quotient
  - Numerical examples
  - Upper boundedness of Rayleigh’s Quotient
  - An additional comment
The Ritz method I (Lecture 18)
- The Ritz method
- Numerical examples:
  - Clamped bar attached to massless linear spring
  - Vibration of a simply-supported beam with an additional spring
The Ritz method II (Lecture 19)
- Numerical examples:
  - Use of more coordinate functions in example 1
  - Free vibration of a frame
  - Structural system with a member under compression.

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