bluuebunny/crossref_metadata_2025_split huggingface dataset:
Closed Form Modeling of Continuous Parameter Robotic Systems-Contact/Impact and Wave Propagation
Authors: Barhorst Alan A. 
Published: March 2021

Abstract
The high fidelity modeling of robotic systems is addressed. The operation of a robot usually consists of a free-flight regime, a contact/impact regime, and a constrained motion regime. Presented in this paper is a demonstration of a systematic method for modeling the complete motion of a manipulator. The model is complete in the sense that all motion regimes are seamlessly handled and the inherently distributed nature of elasticity and mass are rigorously modeled. Since the model properly integrates the distributed parameters with the discrete parameters (boundary conditions too), the effects of disturbance waves propagating in the robotic chain of bodies can be studied.
The methodology demonstrated in this work is a recent development. The methodology is based in variational principles but its operational aspects hide the variational calculus. The method seamlessly handles holonomic and nonholonomic motion constraints. The method also allows the determination of post impact velocities and pointwise velocity fields for hybrid parameter multiple body (HPMB) systems. Exact relationships used to determine when the separation of colliding bodies has occurred are also readily generated. For analysts familiar with Kane’s form of the Gibbs-Appell equations, the method will be affable.
The system modeled in this paper will allow all the curious HPMB system dynamics to be studied. That is: a two flexible link planar manipulator undergoing all three motion regimes mentioned above. The flexible beams are taken as Euler-Bernoulli beams with large deflections. The modeling technique will be demonstrated by deriving the complete model of this system.
Some of the advantages of the technique demonstrated herein include: a) closed form hybrid parameter models, b) automatic boundary conditions, c) holonomic and nonholonomic motion, d) wave propagation, and e) rapid regeneration of system models.
Simulated Behavior of a System With Base Excitation Using an Electrorheological Fluid Damper
Authors: Rieder Paul N. , Tichy John A. 
Published: March 2021

Abstract
The flow properties of electrorheological (ER) fluids change with the application of an electric field. Presently, these materials are a novelty with few direct applications, but they have drawn considerable interest. Proposed applications include lubricants, dampers, clutches, brakes, etc.
Existing ER fluids are best described by the Bingham fluid model. The Bingham material is described by two parameters, a yield shear stress and a viscosity. When the shear stress magnitude exceeds the yield shear stress, quasi-Newtonian flow results; otherwise the material is rigid. For many ER fluids, the yield shear stress is proportional to the square of the applied electric field. In the present study, the Bingham model is applied to a rectangular flow channel. A rigid core forms midway across the film, the core thickness being proportional to the yield shear stress. The damper force is predicted as a function of a dimensionless parameter which depends on the yield shear stress, the flow rate, and channel geometry.
Calculations are performed for a simple vibration isolation system. Such a system may represent a smart shock absorber to minimize vibration response to oscillation input from a bumpy road. The ER damper is shown to be effective in isolating vibration within a band of linear behavior.
Active Optimum Control of Orthotropic Plates Using Piezoelectric Stiffeners
Authors: Birman Victor , Adali Sarp 
Published: March 2021

Abstract
Active control of orthotropic plates subjected to an impulse loading is considered. The dynamic response is minimized using in-plane forces or bending moments induced by piezoelectric stiffeners bonded to the opposite surfaces of the plate and placed symmetrically with respect to the middle plane. The control forces and moments are activated by a piece-wise constant alternating voltage with varying switch-over time intervals. The magnitude of voltage is bounded while the switch-over time intervals are constantly adjusted to achieve an optimum control. Numerical examples presented in the paper demonstrate the effectiveness of the method and the possibility of reducing the vibrations to very small amplitudes within a short time interval which is in the order of a second.
Free and Forced Localization in a Nonlinear Periodic Lattice
Authors: Vakakis Alexander F. , King Melvin E. , Pearlstein Arne J. 
Published: March 2021

Abstract
Free and forced localized periodic motions in an infinite nonlinear periodic lattice are analytically investigated. The lattice consists of weakly coupled identical masses, each connected to the ground by a nonlinear stiffness. In order to study the localized motions of the discrete system a continuoum approximation is assumed, and the ordinary differential equations of motion are replaced by a single nonlinear partial differential equation. The time-periodic solutions of this equation are then obtained by an averaging method, and their stability is examined using an analytic linearized method. It is shown that localized periodic motions of the lattice correspond to standing solitary solutions of the partial differential equation of the continuous approximation. For the free lattice, localized free motions occur when the coupling stiffnesses forces are much smaller than the nonlinear effects of the grounding stiffnesses. Moreover, these free localized motions are detected in the perfectly periodic nonlinear lattice, i.e., even in the absence of structural disorder (a feature which is an essential prerequisite for linear mode localization). When harmonic forcing is applied to the chain, localized, non-localized, and chaotic motions occur, depending on the spatial distribution and the magnitude of the applied loads. A variety of spatially distributed harmonic loads and analytic expressions for the resulting localized motions of the chain are derived.
On Eigenmode Statistics and Power Variances in Randomly Shaped Membranes
Authors: Weaver Richard L. 
Published: March 2021

Abstract
The eigenmodes and eigenfrequencies of finite differenced membranes with rough boundaries are obtained numerically. Such systems are approximations to reverberation rooms. The statistics of the eigenfrequencies are found to be identical to those of the Gaussian Orthogonal Ensemble (GOE) of random matrices. The Wigner conjecture that the modes may be understood to be uncorrelated random superpositions of plane waves with no significant inter-modal correlations is also corroborated. The consequences of these eigen-statistics upon the statistics of responses are discussed.
Localization of Vibration in Disordered Multi-Span Beams With Damping
Authors: Bouzit Djamel , Pierre Christophe 
Published: March 2021

Abstract
The combined effects of disorder and structural damping on the dynamics of a multi-span beam with slight randomness in the spacing between supports are investigated. A wave transfer matrix approach is chosen to calculate the free and forced harmonic responses of this nearly periodic structure. It is shown that both harmonic waves and normal modes of vibration that extend throughout the ordered, undamped beam become spatially attenuated if either small damping or small disorder is present in the system. The physical mechanism which causes this attenuation, however, is one of energy dissipation in the case of damping but one of energy confinement in the case of disorder. The corresponding rates of spatial exponential decay are estimated by applying statistical perturbation methods. It is found that the effects of damping and disorder simply superpose for a multi-span beam with strong interspan coupling, but interact less trivially in the weak coupling case. Furthermore, the effect of disorder is found to be small relative to that of damping in the case of strong interspan coupling, but of comparable magnitude for weak coupling between spans. The adequacy of the statistical analysis to predict accurately localization in finite disordered beams with boundary conditions is also examined.
Vibration Localization in Dual-Span, Axially Moving Beams: Formulation and Results
Authors: Al-jawi A. A. N. , Pierre Christophe , Ulsoy A. G. 
Published: March 2021

Abstract
An investigation of the vibration localization phenomenon in dual-span, axially moving beams is presented. The effects of a tension difference among the spans, also referred to as disorder, on the natural modes of free vibration are studied in terms of interspan coupling and transport speed. The equations governing the transverse vibration of the two-span, axially moving beam are derived through Hamilton’s principle and solution methods are developed. Results demonstrate that normal mode localization indeed occurs for both stationary and translating disordered two-span beams, especially for small interspan coupling. The occurrence of localization is characterized by a peak deflection much greater in one span than in the other. In the stationary disordered case, localization becomes more pronounced as interspan coupling decreases, i.e., as the span axial tension increases. In the axially moving disordered case, the transport speed has a significant influence on localization, and generally speaking localization becomes stronger with increasing speed. For a moving beam with identical spans, the two loci of each pair of natural frequencies may exhibit one or more crossing(s) (depending on the value of tension) when plotted against the axial transport speed. These crossings become veerings when the beam is disordered, and localization is strongest at those speeds where the eigenvalue veerings occur.
An Experimental Study of the Influence of Disk Flexibility and Rubbing on Rotordynamics
Authors: Wu Fangsheng , Flowers George T. 
Published: March 2021

Abstract
This study is an experimental investigation of the influence of disk flexibility and rubbing on rotordynamics. The rotor rigs used in the experiments were designed to have included disk flexibility and a rubbing mechanism. The governing equations of motion are similar to those studied in analytical investigations. The system responses to imbalance were recorded and orbit trajectories were plotted at a set of different rotating speeds. The results show the rubbing response development from light forward bouncing, mixed forward bouncing, to high amplitude backward whirling heavy rubbing. The results also show that the flexible-disk rotor has the tendency of having a high frequency component at the upper rotor speed range of mixed bouncing. These agree very well with the results from an earlier analytical study.
Whirling of Composite-Material Driveshafts Including Bending-Twisting Coupling and Transverse Shear Deformation
Authors: Bert Charles W. , Kim Chun-Do 
Published: March 2021

Abstract
A simplified theory for predicting the first-order critical speed of a shear deformable, composite-material driveshaft is presented. The shaft is modeled as a Bresse-Timoshenko beam generalized to include bending-twisting coupling. Numerical results are compared with those for both thin and thick walled shell theories and generalized Bernoulli-Euler theory.
A New Damper Seal for Turbomachinery
Authors: Vance John M. , Schultz Richard R. 
Published: March 2021

Abstract
A new type of labyrinth seal for damping vibration and whirl in turbomachinery has been invented and tested at Texas A&M University (TAMU). Test results of the prototype, along with a conventional labyrinth seal, show that the new design has fifteen times more direct damping than the conventional bladed seal. The design also has a feature that blocks swirl of the working fluid, which is known to be destabilizing in machines with conventional seals. This paper shows how the new design is different from conventional bladed seals and honeycomb seals, describes the test apparatus and results, describes a theory which explains the test results, and explains how the seal can be much more effective than a bearing damper for reducing vibration in turbomachines with a compressible working fluid.
Theory Versus Experiment for Short (L/D = 1/6) Honeycomb and Smooth Annular Pressure Seals
Authors: Childs Dara W. , Kleynhans George F. 
Published: March 2021

Abstract
A study which compares theoretical predictions of experimental rotordynamic and leakage results is presented for short (L/D = 1/6) honeycomb and smooth annular pressure seals. A computer code used in this comparison has been developed from a theory that employs a perturbation analysis of the governing equations flow and uses Moody’s pipe friction relationship for the surface friction of the rotor and stator. This study was undertaken to investigate how well an existing code could predict these characteristics with input provided from recorded test data and independent flat-plate tests. The results examine the effect that the following independent test parameters have on the experimental measurements and theoretical predictions: inlet preswirl, rotor speed, inlet pressure, pressure ratio across seal, seal clearance, and honeycomb cell width. Experimental results show that leakage is reduced by decreasing the honeycomb cell width. Rotordynamically, the short seals are stabilizing over all test parameter ranges. However, the short seals did not perform as favorably as longer (L/D = 1/3) seals. In general, the theory overpredicts rotordynamic coefficients and leakage.
A Theoretical Approach to Determine Angular Stiffness and Damping Coefficients of an Axial Spline Coupling in High-Speed Rotating Machinery
Authors: Ku C.-P. Roger , Walton James F. , Lund Jorgen W. 
Published: March 2021

Abstract
This paper provided the first opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in high-speed turbomachinery. A unique test methodology and data reduction procedures were developed. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a non-rotating shaft was excited by an external shaker. A rotordynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. In addition, sensitivity analyses were performed to demonstrate that the accuracy of the dynamic coefficients do not rely on the accuracy of the data reduction procedures.
Crack Detection in Turbo Rotors Vibrational Analysis and Fault Detection
Authors: Söffker Dirk , Bajkowski Jozef , Müller Peter C. 
Published: March 2021

Abstract
Applying the theory of Lyapunov exponents for nonsmooth dynamical systems, chaotic motions and strange attractors are found in the case of a cracked rotor. To detect the crack and establish a clear relation between shaft cracks in turbo rotors and induced phenomena in vibrations measured in bearings, a model-based method is applied. Based on a fictitious model of the time behaviour of the nonlinearities, a state observer of an extended dynamical system is designed resulting in estimates of the nonlinear effects.
Explicit Solution of LQG Compensator Design Problem for Flexible Structures With Collocated Rate Sensors
Authors: Balakrishnan A. V. 
Published: March 2021

Abstract
We present an explicit solution to a stochastic control problem generally referred to as the LQG (Linear Quadratic Gaussian) or Stochastic Regulator problem for continuum models of flexible structures with collocated rate sensors, which holds a fortiori for FEM or truncated modal models. Robustness properties accruing from the positive realness of the optimal compensator transfer function are described, and convergence of modal approximations is proved. Preliminary experimental results on the NASA LaRC SCOLE testbed are included.
An Application of Active Dynamic Absorber to the Milling Process and its Experimental Verification
Authors: Liu K. J. , Rouch Keith E. 
Published: March 2021

Abstract
In order to reach the inside surfaces of some workpieces, a prototype for milling extension is developed. The milling extension has a low static stiffness and is prone to machine tool chatter, therefore vibration control in this type of machining is of importance. The paper proposes the application of an active dynamic absorber to the milling process. A finite element model for the milling extension with consideration of the cutting dynamics is developed. An annular ring serving as the dynamic absorber mass is connected to the main system through active force generating systems which are piezoelectric translators functioning as actuators. The annular ring and the actuators are functioning as an active dynamic absorber in the theory to suppress the vibration of the milling system. Optimal control algorithms are used to calculate the Kalman feedback control for the equivalent lumped-mass milling structure model. Transient responses of the system are obtained. Oscillation of the milling extension equipped with the active dynamic absorber is attenuated appreciably, therefore the surface finish of a workpiece is improved. Harmonic responses are also obtained with and without the feedback control to show the superiority of the active control technique. A proof-of-concept experiment is designed and conducted to verify the theoretical prediction. Comparisons between the simulation and experimental results are made.
A Brief Study of Passive Viscous Damping for the SPICE Bulkhead Structure
Authors: Thompson Thomas J. , Baumgarten Joseph R. 
Published: March 2021

Abstract
The SPICE Testbed at Phillips Laboratory is being used to evaluate the effects of structural vibration on line-of-sight error for this strut built structure. A design incorporating active control and passive damping techniques is suggested to reduce the optical path distortion created in the vibrating structure. The passive viscous damping applied to the structure serves to aid the active control system stability in the cross-over and spill-over frequency range by producing a specified magnitude of damping in specified critical modes. This magnitude of damping is to be achieved by replacing the standard filament wound undamped struts with optimally placed D-struts which contain series and parallel combinations of springs and viscous dampers and produce damped vibration response from in-line strut deflection. This D-strut must replace standard struts in a tear-down of the bulkhead. The present study proposes to provide the requisite damping by adding on viscous damping at diagonal nodal locations in the bulkhead, circumventing the need to disassemble the SPICE bulkhead. The study shows specific increase in loss factor and improved damping ratio provided by the diagonal dampers when compared to in-line D-struts for specific modes and frequencies.
Combined Piezoelectric-Hydraulic Actuator Based Active Vibration Control for Rotordynamic System
Authors: Tang Punan , Palazzolo Alan , Kascak Albert , Montague Gerald , Li Wenduan 
Published: March 2021

Abstract
Previous research by the authors concentrated on using piezoelectric actuators for active vibration control (AVC) of rotating machinery. The current work extends this by positioning the piezoactuator remotely from the controlled structure and transmitting the control force via a hydraulic line and two pistons. Liquid plastic is employed as a transmission “fluid” to obtain a high bulk modulus and low leakage. The paper presents results for bulk moduli measurement, and bench and rig tests for the entire actuator system. These results show the high effectiveness of the hybrid actuator for controlling vibrations on a laboratory rotor test rig.
Analysis of Modal Parameters of Adhesively Bonded Double-Strap Joints by the Modal Strain Energy Method
Authors: Rao Mohan D. , Gorrepati Krishna M. 
Published: March 2021

Abstract
This paper presents the analysis of modal parameters (natural frequencies, damping ratios and mode shapes) of a simply supported beam with adhesively bonded double-strap joint by the finite-element based Modal Strain Energy (MSE) method using ANSYS 4.4A software. The results obtained by the MSE method are compared with closed form analytical solutions previously obtained by the first author for flexural vibration of the same system. Good agreement has been obtained between the two methods for both the natural frequencies and system loss factors. The effects of structural parameters and material properties of the adhesive on the modal properties of the joint system are also studied which are useful in the design of the joint system for passive vibration and noise control. In order to evaluate the MSE and analytical results, some experiments were conducted using aluminum double-strap joint with 3M ISD112 damping material. The experimental results agreed well with both analytical and MSE results indicating the validity of both analytical and MSE methods. Finally, a comparative study has been conducted using various commercially available damping materials to evaluate their relative merits for use in the design of these joints.
A Forced Response Analysis and Application of Impact Dampers to Rotordynamic Vibration Suppression in a Cryogenic Environment
Authors: Moore J. J. , Palazzolo A. , Gadangi R. , Nale T. A. , Klusman S. A. , Brown G. V. , Kascak A. F. 
Published: March 2021

Abstract
A high speed damper test rig has been assembled at Texas A&M University to develop rotordynamic dampers for rocket engine turbopumps that operate at cryogenic temperatures, such as those used in the Space Shuttle Main Engines (SSMEs). Damping is difficult to obtain in this class of turbomachinery due to the low temperature and viscosity of the operating fluid. An impact damper has been designed and tested as a means to obtain effective damping in a rotorbearing system. The performance and behavior of the impact damper is verified experimentally in a cryogenic test rig at Texas A&M. Analytical investigations indicate a strong amplitude dependence on the performance of the impact damper. An optimum operating amplitude exists and is determined both analytically and experimentally. In addition, the damper performance is characterized by an equivalent viscous damping coefficient. The test results prove the impact damper to be a viable means to suppress vibration in a cryogenic rotorbearing system.
A Variational Method for Solving Vibration Problems
Authors: Shirahatti Uday S. , Raju Pollapragada K. 
Published: March 2021

Abstract
Rayleigh-Ritz and Galerkin methods are frequently used in engineering to solve boundary value and eigenvalue problems. The success in applying these methods depends entirely on the construction of a variational entity called the functional, and the choice of a system of elements known as the basis functions. This in some cases greatly narrows down the class of problems to which the above methods may be applied. Here, we present a specific but sufficiently general method known as the Methods of Moments for constructing the elements going into the expansion of the approximate solution. The Method of Moments has been shown to posses the capability of generating the basis functions successfully. The Method of Moments in its various forms has been widely used in electromagnetism. Due to generality involved in the construction of these basis functions, the Method of Moments may be readily used to solve a large variety of problems arising in discrete as well as continuous vibrating systems. This idea forms the central theme of this article.