Page 58 - ASME DSCC 2015 Program

Technical Program

Continuous Structures With Viscoelastic Supports: Tuning of Material finite Element Modelling of a Generic Rotor Bearing System and
Parameters and Support location Experimental Validation
Contributed regular paper. DSCC2015-9846 Contributed regular paper. DSCC2015-9901
kumar Singh, danielle oliver, xiaoxuan Ling, Miami University, Oxford, S.M. ahmad, gIk-Institute, Swabi, pakistan, a. rehman, ghulam Ishaq
OH, United States Khan Institute of Engineering Sciences and Technology, Swabi, Pakistan,
K.S. Ahmed, farjad umrani, B. Munir, A. Mehboob, Ghulam Ishaq Khan
Polymeric smart materials exhibit viscoelastic behavior and their dynamic
Institute of Engineering Sciences and Technology, Topi, Pakistan, Z. Kazmi,
characteristics are dependent on both frequency and temperature. This al-
IST-Islamabad, Islamabad, Pakistan
lows the tuning of material properties (stiffness and loss factor) to manipulate
the vibration behavior for a wide range of engineering applications. In this The design and development of rotating machinery require precise identifi-
research, the effects of viscoelastic supports on the vibration of continuous cation of its dynamic response for efficient operation and failure prevention.
structures such as axially vibrating rods and transversely vibrating beams Determination of critical speeds and mode shapes is crucial in this regard. In
are investigated. The governing equations of motion for harmonically excit- this paper, a finite element model (FEM) based on Euler beam theory is de-
ed rods with end supports, and the free vibration of beams with intermediate veloped for investigating dynamic behavior of flexible rotors. In-house code
viscoelastic support are developed. The analytical response equation for in Scilab environment, an open source platform, is developed to solve the
a harmonically excited rod with viscoelastic ends is obtained. The resulting matrix equation of motion of the rotor-bearing system. Finite element model
frequency response equations are then used to design the modification of is validated by impact hammer test and dynamic testing performed on rotors
the stiffness and loss factor of the viscoelastic materials in order to achieve supported on purpose-built experimental setup. Bearing stiffness is approx-
the desired vibration response of the rod. By solving the resulting transcen- imated by using Hertzian contact theory. Obtaining the critical speeds and
dental eigenvalue problems, the natural frequencies and damping ratios as mode shapes further improves the understanding of dynamic response of
a function of viscoelastic support parameters are computed for beams. The rotors. This study paves way towards advanced research in rotordynamics in
performance of structures with viscoelastic support is demonstrated with Faculty of Mechanical Engineering, GIK Institute.
various numerical examples. The formulation and results can be utilized Analysis of Stability and Bifurcation of an Asymmetrical Rotor
for estimating the optimal material tuning parameters as well as support Contributed regular paper. DSCC2015-9728
locations for controlling and manipulating the vibration response of the
Majid Shahgholi, Shahid Rajaee Teacher Training University, Tehran, Iran,
structures. S.E. Khadem, Tarbiat Modares University, Tehran, Iran, Mahsa Asgari
A Control Theoretic framework for optimally locating Passive Sabet, Michigan Technological University, Houghton, MI, United States
Vibration Isolators to Minimize Residual Vibration The effect of shaft and disk asymmetry on the harmonic resonances of an
Contributed regular paper. DSCC2015-9871 imbalanced rotor system with the in-extensional nonlinearity and large ampli-
Amirhossein Ghasemi, Jihyun lee, Chinedum okwudire, University of tude are investigated. Two rotor systems, one of which has been comprised
Michigan, Ann Arbor, MI, United States of a symmetrical shaft and an asymmetrical disk (SA), and the other one has
been comprised of an asymmetrical shaft and an asymmetrical disk (AA) are
This paper investigates the problem of optimally locating passive vibration
investigated. The shaft in the AA rotor has unequal mass moments of inertia and
isolators to minimize residual vibration caused by exogenous disturbance
bending stiffness in the direction of principal axes. Also, in the AA system the
forces. The stiffness and damping properties of the isolators are assumed
rigid disk is asymmetric with unequal mass moments of inertia. The equations
to be known and the task is to determine the isolator locations, which are
of motion are derived by the Hamiltonian principle. The stability and bifurcations
nonlinearly related to system states. This paper proposes an approach for
are obtained using the multiple scales method. The influences of asymmetry of
reformulating the nonlinear isolator placement problem as a LTI control
shaft, asymmetry of disk, inequality between two eccentricities corresponding to
problem by linking the exogenous disturbance forces to controlled outputs
the principal axes, disk position and external damping on the stability and bifur-
using a feedforward term. Accordingly, the isolator locations show up as a
cations of SA and AA rotors are investigated. The results achieved from multiple
static output feedback gain matrix which is optimized for residual vibration
scales method in accordance with those of numerical simulations.
reduction using standard H optimal control methods. Simulations and exper-
iments on SISO and MIMO case studies are used to demonstrate the merits efficient Spatial dynamics for continuum arms
of the proposed approach. Even though presented in the specific context of Contributed regular paper. DSCC2015-9932
ultra-precision manufacturing machines, the proposed method is applicable
Isuru Godage, Raul Wirz, Robert J Webster III, Vanderbilt University,
to the optimal design of other passive systems with nonlinear relationships Nashville, TN, United States, Ian D Walker, Clemson University, Clemson,
between design variables and system states. SC, United States
Continuum robot dynamic models have previously involved a choice
between high accuracy, numerically intensive models, and low accuracy,
computationally efficient models. The objective of this paper is to provide an
accurate dynamic model with low computational overhead. Our approach is
to place point masses at the center of gravity of the continuum section, rath-
er than along the robot’s backbone or centerline. This enables the model to
match the robot’s energetic characteristics with many fewer point masses.
We experimentally validate the model using a pneumatic muscle actuated
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continuum arm. We find that the proposed model successfully captures both
the transient and steady state dynamics of the arm.