bluuebunny/crossref_metadata_2025 huggingface dataset:
Piezothermoelastic Characteristics and Control of Active Piezoelectric Structures
Authors: Tzou H. S. , Ye R.
Published: March 2021

Piezothermoelastic characteristics of distributed piezoelectric structural systems are investigated. A new piezothermoelastic finite element formulation for modeling static and dynamic responses of piezoelectric laminated continua subjected to combined thermal, electric, and mechanical excitations is proposed. A “thin” eight-node solid element with three internal degrees of freedom is formulated. Thermal influence to the distributed sensor/actuator systems is investigated. Vibration suppression of a piezoelectric laminated structure subjected to thermal excitations is studied and a correction method demonstrated.
Decoupling Methods in Flexible Multibody Dynamics
Authors: Hwang Yunn-Lin
Published: March 2021

The inertia projection schemes used in the existing recursive methods for the dynamic analysis of flexible multibody systems lead to dense coefficient matrices in the acceleration equations. Consequently, there is a strong dynamic coupling between the joint and modal coordinates. When the number of modal degrees of freedom increases, the size of the coefficient matrix in the acceleration equations becomes large and consequently the use of these recursive methods for solving the joint and modal accelerations becomes less efficient. This investigation discusses the problems associated with the inertia projection schemes used in the existing recursive methods, and it is shown that decoupling the joint and modal accelerations using these methods requires the factorization of nonlinear matrices whose dimensions depend on the number of modal degrees of freedom of the system. An amalgamated formulation that can be used to decouple the modal and joint accelerations is proposed. In this amalgamated formulation, the relationships between the Cartesian, modal and joint variables and the generalized Newton-Euler equations are utilized to develop systems of loosely coupled equations that have sparse matrix structure. Using the structure of the inertia matrix of the deformable body and the fact that joint reaction forces associated with modal coordinates do not represent independent variables, a reduced system of equations whoSe dimension is independent of the number of modal degrees of freedom is obtained. This system can be solved for the joint accelerations as well as the joint reaction forces. The use of the procedure developed in this paper can be used for open-loop and closed-loop mechanical systems.
Trajectory Planning for a Mobile Robot in an Unknown Environment by Fuzzy Based Method
Authors: Beaufrere Bertrand , Zeghloul Said
Published: March 2021

The objective of this paper is to present a simple local navigation method for a mobile robot in an unknown environment. A part of the simulation aspect is presented. It concerns the model environment technic and the motion control system. The local free environment of the robot is perceived by 12 ultrasonic sensors. We present a method which uses the sensor’s data to determine free channel. Then, we describe our free path planning method which is based on these sensor’s information in order to reach a target point. The described method uses a Fuzzy reasoning Some simulation results are included in the last section.
A Generic Framework for Diagnosis
Authors: Amyot J. R.
Published: March 2021

A generic diagnostic framework, called GENDIAG, is described. It facilitates the development of diagnostic expert systems by providing a standard user interface and an application-independent diagnostic inference engine. It reduces the application development time by letting the knowledge engineer concentrate on domain knowledge acquisition and entry into the system.
An Efficient Algorithm for CSG Rendering
Authors: Chao Ming , Zhao Wei
Published: March 2021

CAD modelling encompasses many problems, from realistic rendering to process planning. This paper presents a new surface scanning algorithm for five typical primitives (block, sphere, cylinder, cone and torus). The algorithm is efficient and robust. The speed of scanning mainly depends on the 2D screen area on which the primitive surface casts, while back-face is eliminated before scanning. Since primitive surfaces are scanned from their algebraic definition, a compact database can be maintained. A new approach of utilising space-coherence to minimise the process time for point-membership classification is described.
A Mechanical Design Framework Based on Object-Oriented Approach
Authors: Jeong Taesik , Kicher Thomas P. , Zab Ronald J.
Published: March 2021

An object-oriented programming (OOP) technique is investigated in order to develop the framework for mechanical design automation systems. A task-oriented decomposition approach is applied to conceptualize the task-object (or task-performing-object) in which common behavior and communication protocols are encapsulated [1]. Each task in the entire design process, either controlling design strategies or performing design methods, is made into an object. The design method objects are implemented using Artificial Intelligence (AI) paradigms, such as artificial neural networks and expert systems.

This report explains how OOP is integrated to develop a mechanical design framework (MDF). A single reduction gear box design process was used to identify some of the general tasks involved in mechanical design process. From this process the guidelines for developing task-objects for future systems are formed. Full details of these guidelines and an implementation example in Smalltalk on a PC are available in [7].
The Effect of Transducer Response Rate on Thermal Radiation Data
Authors: Loucks Richard B.
Published: March 2021

The Thermal Radiation Source (TRS) at ARL is used as a research tool to develop a reliable TRS unit for integration with the 2.44 m probative tube. Part of this study includes measuring the rise and fall times as well as the extent of flux variation of the TRS events. The Garden type gage is the primary transducer used to measure the flux output. This gage consists of a constantan diaphragm welded to a copper wire and body. This creates two thermocouple junctions. The electrical output of the gage is linearly related to the incident thermal radiation on the face of the diaphragm.

A concern is about the response rate of these gages. The typical gage used in TRS work has a response rate of one time constant within 50 ms. In the past, the transient output of the TRS was considered slow. A faster acting gage was not necessary. To test this theory, a mathematical correction formula was applied to existing TRS data. The correction formulation was to demonstrate the actual incident radiation on the gage face by assuming a response rate. The data was processed using the correction formula. The results of the correction processing yielded a higher rise and fall time, as expected, but demonstrated a much higher flux variation during a TRS event. The overall fluence remained the same.

To verify the correction formula is accurate, a special gage was constructed. It has a response rate of 6 ms to the first time constant. An experiment was conducted by placing the special gage next to a regular gage. The results show the faster acting gage produces a signal that matches the corrected signal of the slower gage, with one exception. The overall fluence increased.

The most profound effect of this gage is realized when attempting to improve the performance of a TRS system. By realizing the capabilities of the gages, a more accurate determination of the thermal output of future TRS systems can be assessed. This will have direct impact on future Nuclear Survivability criterion by realizing the true capabilities of TRS systems.
An Integrated Modeling and Analysis Methodology for Configuration Design of Disk Drive Actuators
Authors: Strzepa M. C. , Grosse Ian R.
Published: March 2021

In this research we have developed a methodology for integrating design and finite element analysis, with special emphasis on design. System performance goals are translated into local performance goals based on generic physical principles. A complete search of the design domain may not be possible due to its size and not realistic due to time-to-market pressures. Furthermore, the complexity and non-linearity of the design domain prohibit a qualitative comparison of design configurations without design instantiation and evaluation. The use of a “pruning” process of the configuration design space is highly desirable since it provides the means of selecting a single candidate configuration having the greatest potential for success. Therefore, an approach is used in which design configurations are parameterized from a product knowledge base through the use of a library of design templates. The design process involves an enumeration of candidate design templates and domain-specific automated procedures for finite element mesh generation. Through exploitation of domain-dependent knowledge, FEA solution accuracy requirements are defined. Quantitative behavior is then inferred from numerical results. Examples involving the design of a computer disk drive actuator are presented which convey these concepts.
An Investigation Into Mathematical Models of Optimal Tolerancing Supporting Concurrent Engineering
Authors: Zhang Genbao , Porchet Michel
Published: March 2021

This paper presents a new tolerance design theory — simultaneous tolerancing which works in the concurrent engineering context. After the necessity to develop a simultaneous tolerancing theory is stated, by showing the shortcomings of conventional tolerancing technique, the concept of simultaneous tolerancing is given, and its elements are briefly presented. Then we focus our attention on the development of a general mathematical model of optimal tolerancing supporting concurrent engineering. Two commonly used models, worst-case and statistical, are discussed in detail. Next, a method of “interim tolerances”, which help to determine an appropriate machining process without using functional tolerances, is proposed.

The simultaneous tolerancing theory presented in this paper permits of determining directly optimal machining tolerances in product design, reducing the manufacturing cost and improving the quality of products.
Monitoring Systems Using PVM
Authors: Li Qiang , Yip T. Gary
Published: March 2021

This paper presents a cost-effective implementation of a sensor monitoring system based on a network of workstations and microprocessor building blocks. The PVM (Parallel Virtual Machine) system is used as the software platform running the workstations. Owing to PVM, the burden of network programming is eliminated. The control software running on multiple workstations can be implemented in a way similar to that of a single workstation. The interfaces to users and to databases can be easily implemented.
Simulation and Shape Synthesis of Kinematic Pairs via Small-Scale Interference Detection: Advanced Examples Demonstrating Shape Optimization and Non-Fixed Axis Members
Authors: Gupta Rakesh , Jakiela Mark J.
Published: March 2021

A method to simulate the interactions between kinematic pairs (meshing gears, cams and followers, Geneva mechanisms, etc.) has been described in an earlier paper (Gupta and Jakiela, 1992a). This second paper, through several examples, demonstrates how our representations and algorithms for kinematic simulation and shape synthesis facilitate subsequent reasoning for design tasks. Included are examples of a complex industrially relevant simulation, shape optimization motivated by kinematic behavior, and extensions of the approach for non-fixed-axis members.
The Importance of Free-Hand Sketching in Conceptual Design: Automatic Sketch Input
Authors: Jenkins D. L. , Martin R. R.
Published: March 2021

Free-hand drawing (sketching) is important in the conceptual design stage. Current CAD tools are not well suited to sketching. This statement is supported by an examination of free-hand drawing, a brief overview of some commercially available drawing packages and a discussion of other authors’ work in this area. Finally we present objectives for automatic sketch input and their partial realisation in our drawing system called Easel.
Extraction and Reuse of Design Information
Authors: Jamalabad Vikram R. , Langrana Noshir A.
Published: March 2021

An iterative design procedure constitutes a significant part in many design process with no closed form solutions. Of importance to this procedure is the acceleration of this cycle to reduce turnaround time. The analysis packages concerned have a large execution time and defined sets of input and output parameters. The number of these parameters is large and information about the design space is incomplete. The aim is to minimize the number of analysis calls during the design procedure. We have developed a system (Learning Shell for Iterative Design, or, L’SID) to enable a current iterative design system to extract and use information from an analysis package during the iterative design process. L’SID is a domain independent system written in lisp that has been demonstrated to operate on the said class of analysis modules. The system compiles domain information in a domain independent data structure. The modularity of the system enables us to change analysis packages, search methods, iterative processes and comparison functions. Results encourage us to believe that such systems will be helpful in maintaining, averring or refuting domain specific information for routine design systems.
Recursive Annealing: A Computational Model for Machine Design
Authors: Schmidt Linda C. , Cagan Jonathan
Published: March 2021

A recursive model of conceptual design occurring along an abstraction continuum is introduced. An algorithm based upon recursive simulated annealing is proposed for a computational implementation of the model. The mapping from function to form is accomplished using an abstraction grammar, a set of compatible string grammars for representing the function and form nature of machine components at various levels of abstraction. The promise of a recursive approach to machine design is demonstrated.
On the Axiomatic Foundation of Design
Authors: Dimarogonas Andrew D.
Published: March 2021

Mechanical design methodology has its origins in the writings of ancient Greek and Alexandrine authors between 300 BC and 100 AD when also the first aesthetic theory was proposed. German authors of the middle of 19th Century have introduced the foundation for Mechanical Design on basic Design Principles, modernized the machine element methodology and introduced the parallel development of the function with the form. F. Redtenbacher introduced a set of design principles. Reuleaux (1852) introduced two fundamental Design Principles (Ground Rules), re-introduced recently in axiomatic form by Suh et al. The paper discusses the merits of establishing Design Principles or Design Axioms as the fundamental Rules of design and the implications of these Rules on the design and manufacturing methodology. The relation of the Design Rules with the principles of the total quality engineering in the Taguchi sense is also investigated.
Non-Linear Normal Modes, Invariance, and Modal Dynamics Approximations of Non-Linear Systems
Authors: Boivin Nicolas , Pierre Christophe , Shaw Steven W.
Published: March 2021

Non-linear systems are here tackled in a manner directly inherited from linear ones, i.e., by denning proper normal modes of motion. These are defined in terms of invariant manifolds in the system’s phase space, on which the uncoupled system dynamics can be studied. Two different methodologies which were previously developed to derive the non-linear normal modes of continuous systems — one based on a purely continuous approach, and one based on a discretized approach where the theory developed for discrete systems can be applied — are simultaneously applied to the same study case — an Euler-Bernoulli beam constrained by a non-linear spring —, and compared as regards accuracy and reliability, resulting in the abandonment of the continuous approach for lack of reliability. Numerical simulations of purely non-linear modal motions are performed using these approaches, and compared to simulations of equations obtained by a classical projection onto the linear modes. The invariance properties of the nonlinear normal modes are demonstrated, and it is also found that, for a purely non-linear modal motion, the invariant manifold approach achieves the same accuracy as that obtained using several linear normal modes, but with significantly reduced computational cost. This is mainly due to the possibility of obtaining high-order accuracy in the dynamics by solving only one non-linear ordinary differentia] equation.
Steady State Solutions to a Forced Nonlinear Oscillator: A Comparison of Results Using a Generalized Harmonic Balance Method and by Numerical Integrations
Authors: Noble Ben , Wu Julian J.
Published: March 2021

Steady state solutions for nonlinear dynamic problems are interesting because (1) the long time behaviors of many problems are of practical concern, and, (2) these behaviors are often difficult to predict. This paper first presents a brief description of a generalized harmonic balance method (GHB) for steady state solutions to nonlinear problems via a nonlinear oscillator problem with a quadratic nonlinearity. Using this approach, steady state solutions are obtained for problems with several parameters: damping, nonlinearity and frequency (subharmonic, superharmonic and primary resonance). These results, plotted in time evolution curves and phase diagrams are compared with those obtained by numerically integrating the original differential equations. The effect of initial conditions on long time solutions is discussed. This investigation indicates that (1) the GHB steady state is an excellent approximate solution to that of the original equation if such a solution is numerically stable, and (2) the GHB steady state simply indicates a region of instability when the numerical solution to the original equation, using a point in that region as the initial point, is unstable.
A Preliminary Study of Self-Loosening in Bolted Connections
Authors: Zadoks Rick I. , Yu Xiong
Published: March 2021

Bolted connections are the most common method used to fasten together two or more structural elements. After fatigue, self-loosening is the most frequent cause of failure of dynamically loaded bolted connections. Bolted connections experience self-loosening due to relative motion between the thread flanks and between other contact surfaces of the clamped or clamping elements. If the relative motions are eliminated, then no dynamic self-loosening can occur. It is found that the relative transverse motion d at a bolted connection is directly related to the preload Q and the transverse force F applied to the bolt. As a basis for the study of bolt self-loosening, a model of thread slipping is established, and relationships between Q, F and d are theoretically derived. It is found that the stiffness of the bolt threads is approximately parabolic. Due to this nonlinear relationship between Q and d, it is found that the relationship between F and d is also nonlinear. For a given set of geometrical and material parameters, the critical transverse force Fcr (i.e., the minimum force needed to make the threads slip) can be predicted. Experiments are run and though the results are obscured by the presence of other effects including sliding friction between the clamped parts and bending of the bolt body, it seems that qualitative agreement exists between the theoretical model and a physical system. The results presented in this work serve as the preliminaries to the development of a model of the dynamic self-loosening of bolted connections and, as such, offer an insight into the mechanisms that lead to self-loosening. Additionally, these results offer clues regarding methods that could be used to prevent bolted connection failures.
A Successive Merging and Condensation (SMAC) Method Applied to Transient Analysis of Multi-Shaft Rotor System
Authors: Ratan Santosh , Rodriguez Jorge
Published: March 2021

A method for performing transient dynamic analysis of multi-shaft rotor system is proposed. The proposed methodology uses the reported Successive Merge and Condensation (SMAC) method [12] and a decoupling technique to decouple the shafts. Multi-shaft rotor systems are treated as systems of many independent single shaft rotor systems with external unknown coupling forces acting at the points of couplings. For each time step, first, the SMAC method is used to get the transient response in terms of the unknown coupling forces. This is followed by the application of the coupling constraints to calculate the coupling forces and, in turn, the response at the end of that time step. The proposed method preserves the efficiency advantages of the SMAC algorithm for single-shaft rotor system. Numerical examples to validate and illustrate the applicability of the method are given. The method is shown to be applicable to linear and non-linear coupling problems.
Resonant Vibrations in Weakly Coupled Nonlinear Structures With Cyclic Symmetry
Authors: Samaranayake S. , Bajaj Anil K. , Nwokah O. D. I.
Published: March 2021

Periodic structures with cyclic symmetry are often used as idealized models of physical systems including bladed-disk assemblies, large space antennas, circular saws and disks, and flexible magnetic storage media. The present work considers a simplified model of such structures and investigates the nonlinear vibratory response to periodic excitations. The model consists of n identical particles, arranged in a circular ring, interconnected by extensional springs with linear and nonlinear stiffness characteristics, and hinged to the ground individually by nonlinear torsional springs. When the linear couping stiffness is O(ε), the cyclic system consists of n weakly coupled identical nonlinear oscillators so that all the oscillators are in internal resonance. The dynamic response of this system to resonant periodic excitation is studied using the method of averaging. The amplitude equations consist of a 2n system of first order ordinary differential equations that depend on the forcing amplitude and frequency, the modal damping, and the nature of the excitation. These equations are analyzed using local bifurcation theory, and the effects of coupling strength to nonlinearity parameter on the steady-state responses are determined. It is found that when only one particle is excited, the response for very weak coupling essentially remains localized. For larger coupling strength, both localized and extended responses are found over different excitation frequency intervals.
The Use of a Simplified Model for the Nonlinear Dynamic Analysis of Fixed Offshore Structures
Authors: Souza Marco A. , Pinto Osvaldo C.
Published: March 2021

A simplified model is used in the nonlinear dynamic analysis of fixed offshore platforms. The characteristics of the model are presented and its adequacy for the study is discussed. The action of ocean waves on the model is obtained using typical waves of the Brazilian coast. The nonlinear equation of motion is obtained in its exact form and is expanded up to the cubic term. A comparison between the nonlinear analysis and the linear dynamic analysis is presented. A comparison between experimental results and those obtained with the model is also presented.
Resonant Oscillations and Stability of Asymmetric Rotors
Authors: Ganesan R. , Sankar T. S.
Published: March 2021

Non-stationary oscillations of an asymmetric rotor while passing through primary resonance and the associated stability behaviour are analyzed. Solutions are developed based on a Jeffcott rotor model and the equations of motion are rewritten in a form suitable for applying the method of multiple scales. The many-variable version using “slow” and “fast” lime scales is applied to obtain the uniform expansions of amplitudes of motion. Similar general expressions for amplitude and frequency modulation functions are explicitly obtained and are specialized to yield steady-state solutions. Frequency-amplitude relationships resulting from combined parametric and mass unbalance excitations, for the nonlinear vibration are derived. Stability regions in the parameter space are obtained for a stable solution in terms of the perturbed steady-state solutions of the governing equations of motion. Also, trivial solutions are examined for stability. The sensitivity of vibration amplitudes to various rotor-dynamic system parameters is illustrated through a numerical study.
Transient Dynamic Response of a Whip Antenna to a Simulated Nuclear Event
Authors: Corder Paul R.
Published: March 2021

The objective of this study was to perform analyses for the static and dynamic mechanical response of a 36 ft fiberglass whip antenna for the purpose of determining survivability under nuclear weapons effects. The static analysis was to obtain the stiffness/deflection characteristics of the antenna using material, wall-thickness, and mechanical loading history provided by the Naval Surface Warfare Center. The results of the static analysis were then to be used in a NASTRAN transient dynamic analysis. The effect of the thermal pulse associated with the blast was not directly considered in these studies.

An analytical model of the whip antenna deflected by transverse loading was developed using Castigliano’s Theorem. The resulting integrals were evaluated using Mathematica™. The diameters, wall thicknesses, and mass density resulting from the static response study were then used in the linear, transient dynamic analysis.

These studies concluded that the suggested modeling approach is suitable for the static and linear transient dynamic response analysis of a standard 36 foot fiberglass whip antenna to a 4 KT, 7 psi air blast (without thermal effects). The “Basic” model suggests a linear finite element model maximum deformation to be within 10% of the deflection of about 16 feet observed in the test video. Low-to-midrange stresses are expected at this deformation. A 1 MT, 7 psi air blast would probably, but not necessarily, fail the antenna. These studies support the conclusion that the dynamic response of a standard 36 ft whip antenna is “duration-dependent” within the range of overpressures considered.
On the Stability of Forced Radial Oscillations of an Experimental Spring Pendulum
Authors: Bayly Philip V. , Virgin Lawrence N.
Published: March 2021

The elastic pendulum is a 2-degree-of-freedom, nonlinear device in which the pendulum bob may slide up and down the pendulum arm subject to the restoring force of a linear spring. In this study, radial motion (motion along the arm) is excited directly. Responses to this excitation include purely radial oscillations as well as swinging motion due to a 2:1 internal resonance. Changes in the behavior of the nonlinear spring pendulum occur when, under the control of a parameter, radial oscillations become unstable and are replaced by radial plus swinging motion. This bifurcation is explored analytically, numerically and experimentally, using the basic ideas of Floquet theory. Poincaré sampling is used to reduce the problem of describing the stability of a limit cycle to the easier task of defining the stability of the fixed point of a Poincaré map.
Effect of Gravity on the Static and Dynamic Characteristics of a Single Link Component of Flexible Multibody Systems
Authors: Smart David W. , Wiens Gloria J.
Published: March 2021

As large space structures and the component links of robotic manipulators become increasingly more flexible, axial loadings are playing an increasingly more important role in the elastic characteristics of the systems. The research presented in this paper provides a relatively simple theoretical model based on the quasi-dynamics of a component link for flexible multibody systems. The theoretical model has shown that the axial component of gravity can play a major role in predicting accurate first and second natural frequencies and the static deflections of component links typical of flexible multibody systems. By definition, the axial loading contribution is a function of rigid body orientation, with the more significant influence occurring in the vertical positions. Furthermore, the degree of this effect is directional, depending on whether the axial loading is compressive or tensile. The results elude to a possible simple, approximation approach for modeling complex multilink systems subject to gravitational loading. In addition, the presented analysis approach has been experimentally validated where the theoretical results have been shown to agree very well with the experimental findings.
Vibration Suppression by Modulation of Elastic Modulus Using Shape Memory Alloy
Authors: Segalman Daniel J. , Parker Gordon G. , Inman Daniel J.
Published: March 2021

A method is proposed for suppressing the resonances that occur as an item of rotating machinery is spun-up from rest to its operating speed. This proposed method invokes “stiffness scheduling” so that the resonant frequency of the system is shifted during spin-up so as to be distant from the excitation frequency. A strategy for modulating the stiffness through the use of shape memory alloy is also presented.
Piezothermoelasticity and Control of Piezoelectric Laminates Exposed to a Steady-State Temperature Field
Authors: Tzou H. S. , Ye R.
Published: March 2021

Piezothermoelastic effects of distributed piezoelectric sensors and actuators are investigated. Vibration control of piezoelectric laminates subjected to a steady-state temperature field is studied. A new 3-D piezothermoelastic finite element with three internal degrees of freedom is formulated using a variational formulation. A system equation for the piezoelectric continuum exposed to combined elastic, electric, and thermal fields is formulated. Distributed sensing and control equations are derived. All these effects are studied in a case study.
Modelling Fluid Inertia Forces of Short Journal Bearings for Rotordynamic Applications
Authors: El-Shafei A.
Published: March 2021

It has been recently suggested that fluid inertia may play an important role in the dynamic behavior of rotors supported on journal bearings. This paper presents a model for fluid inertia forces in short cylindrical journal bearings based on an energy approximation. The inertialess velocity profiles predicted by the solution of Reynolds’ equation are inserted in the axial momentum equation multiplied by the axial velocity profile and integrated across the film thickness, to obtain the pressure in short journal bearings including the fluid inertia effect. The pressure is then integrated to obtain the fluid inertia forces. It is shown that the inertia forces thus obtained are proportional to the usual radial, centripetal, tangential and coriolis accelerations of the journal, in addition to a nonlinear radial acceleration. Moreover, it is shown that the inertia forces contribute to the stiffness and damping characteristics of the journal bearings. The inertia coefficients of the bearings are obtained in cartezian and cylindrical coordinates, for both uncavitated and cavitated bearings, and are plotted versus the eccentricity ratio. The model thus obtained is an analytical closed form model for fluid inertia forces in short journal bearings. Such a model is the most suitable for rotordynamic applications, particularly for time transient rotordynamic simulations.
An Experimental Investigation of the Dynamic Characteristics of an Axial Spline Coupling in High-Speed Rotating Machinery
Authors: Walton James F. , Ku C.-P. Roger , Lund Jorgen W.
Published: March 2021

This paper presents the results of the second part of an investigation of the dynamic characteristics of an axial spline coupling in high-speed rotating machinery. In the experimental method described herein, the bending moments and angular deflections transmitted across the axial spline coupling were measured while the nonrotating shaft was excited by an external shaker. The effects of external force and frequency on the angular stiffness and damping coefficients were investigated. The angular stiffness and damping coefficients were used to perform a linear steady-state rotordynamics stability analysis, and the unstable natural frequency was calculated and compared to experimental measurements. In addition, the mechanism and source of internal rotor friction instability caused by the axial spline couplings was studied.
Active Control of Machine Tool Chatter for a Boring Bar: Experimental Results
Authors: Tewani Sanjiv G. , Switzer Thad C. , Walcott Bruce L. , Rouch Keith E. , Massa Ted R.
Published: March 2021

A typical boring bar is a metal cutting tool with large overhang ratio, due to which it is characterized by low dynamic stiffness. Therefore, during cutting process, it is susceptible to cutting instability, known as machine tool chatter. In this paper, the use of an active dynamic absorber to actively control machine tool chatter in a boring bar is studied.

An active dynamic absorber is designed such that it can be easily assembled with a commercially available steel boring bar. A piezoelectric pusher is used as the actuator for the active dynamic absorber. The dynamic equations of the boring bar with active dynamic absorber are calculated from experimentally obtained frequency response functions of the system. Optimal control theory is applied to the dynamic equations to calculate state variable feedback parameters. The state variable feedback is implemented using a Digital Signal Processing (DSP) chip. Cutting tests were performed with this setup for different cutting conditions, and for different overhangs of the boring bar. Stable cutting operations were performed using the boring bar with active dynamic absorber, for length to diameter (L/D) ratio upto 9.
Pneumatic Vibration Isolation of a Table Traversed by a Moving Load
Authors: Vu Hung V. , Torby Bruce J.
Published: March 2021

The modeling and analysis of a vibration isolated table system is investigated as a preliminary study for the design of an active feedback control system. The system consists of a table, a moving load traversing on the top surface of the table, and four identical pneumatic isolators supporting the table at four corners. For each isolator, there is a spool valve and a needle valve. A mathematical model of the system is developed, which includes the governing differential equations of the rigid table and pneumatic isolators, the nonlinear saturating characteristics of the spool valve, and the flow restriction of the needle valve. The isolation table is commercially available. Using MATRIXX/SystemBuild, the time response of the table is simulated for a few representative cases. The results indicate that the table will descend and not return to the original position, for any speed of the moving load, until the load stops. The higher the speed of the load, the quicker and farther down the table will descend. The larger the opening of the needle valve is, the table oscillates more because of less damping. The table response is relatively well damped even when the needle valve is fully open. The speed of the response, which is measured by the settling time, is fastest when the needle valve is open at about 25%.
Multi-Mass Absorbers Effective in Wide Frequency Band
Authors: Einstein George , Wernerowski Krzysztof
Published: March 2021

One of the most efficient method of vibration control is the method of dynamic damping. Most existing theory enables a design of a dynamics damper for a one degree-of-freedom system. Here the theory is extended to allow for a design of dynamic mass dampers with viscous friction suitable for a systems with multiple degrees-of-freedom. Effective method of multi-mass absorbers in a wide angular frequency band was designed and developed.

Finally, by inspection of the frequencies for the amplitudes of vibrations of the essential masses within the vibratory system are reduced or decreased to zero. One may optimize the various designs of dynamic systems containing mass-damping elements. Detailed numerical analysis and specific calculations are performed in this publication.
Forced Vibration of Thick Viscoelastic Cylinders
Authors: Hamidzadeh H. R. , Minor G. R.
Published: March 2021

Harmonic forced vibration of thick viscoelastic hollow cylinders of infinite extent is considered. The cylinder is excited by stresses applied at the inner and outer boundaries. The governing equation of motion is developed by utilizing three dimensional theory of elastodynamics. The material damping is allowed using complex elastic moduli for the viscoelastic medium. Modal displacements and stresses at any point in the medium are formulated in terms of boundary stresses. Frequency responses for radial, tangential and axial displacements are computed for different circumferential and axial wave numbers. The effect of different material loss factors on the frequency responses is examined for axial and nonaxisymmetric modes. The dimensionless resonant frequencies for zero loss factor are compared with dimensionless natural frequencies available for elastic material. Comparison indicates excellent agreement between the results.
Static and Dynamic Characteristics of Spot Welded Sheet Metal Beams
Authors: Pal Kaushik , Cronin Donald L.
Published: March 2021

Although widely used as structural components in the auto industry, spot welded sheet metal beams manifest static and dynamic behavior that is not well characterized.

For the present study, sample beams of three representative cross-sections — hat, box and box with partition — were fabricated of sheet steel. The spacing between the spot welds that hold these sections together was varied from 25.4 mm (1 inch) to 203.2 mm (8 inch) using a 25.4 mm (1 inch) increment. The beams were subjected to static bending and static torsion tests, and bending and torsional stiffnesses were determined as functions of spot weld spacing. The beams were then vibrated, and significant lower natural frequencies were determined as functions of spot weld spacing. Mode shapes were also observed for these frequencies.

Pains were taken throughout the testing to ensure that the results obtained were of good statistical quality. Work was also done to distinguish the effect on results of beam length and end conditions from that of spot weld spacing.

As part of the study, finite element models of the beams were constructed. The results of finite element analysis (FEA) and experiment are compared and insights are offered concerning the appropriate modeling of such structures.
Dynamic Behavior of Vehicles Travelling on Bridges
Authors: Esmailzadeh Ebrahim , Ghorashi Mehrdaad
Published: March 2021

An investigation into the dynamic behavior of a bridge with simply supported boundary conditions, carrying a moving vehicle, is performed. The vehicle has been modelled as a two degree of freedom lumped-parameter system travelling at a uniform speed. Furthermore, the bridge is assumed to obey the Euler-Bernoulli beam theory of vibration. This analysis may well be applied to a beam with different boundary conditions, but the computer simulation results given in this paper are set for only the case of freely hinged ends. Numerical solutions for the derived differential equations of motion are obtained and their close agreement, in some extreme cases, with those reported earlier by the authors are observed. Finally, the effect of speed on the maximum dynamic deflection of bridge is shown to be of much importance and hence an estimation for the critical speed of the vehicle is presented.
A Dynamic System Model for Estimating Surface-Induced Frame Loads During Off-Road Cycling
Authors: Wilczynski Herve , Hull Maury L.
Published: March 2021

To facilitate the rational design analysis of off-road bicycle frames, this paper reports a dynamic model of the bicycle/rider system which estimates frame loads for bicycles traveling over rough surfaces. To develop this model, the frame loads at rider contact points were first measured experimentally as a rider coasted over a test track with randomly spaced surface irregularities in both seated and standing positions. Following this measurement, a dynamic system model was developed with the aid of the commercial software package, Dynamic Analysis and Design Software (DADS). The development process consisted of two stages. The first stage involved developing component models (e.g., seat) which could reproduce the essentials of the measured data. The second stage involved identification of parameter values for those parameters shown to most profoundly affect simulated load results. These parameters were all associated with the dynamics of the body thus emphasizing the importance of reflecting the dynamic system nature of the body in the model. Following parameter identification, simulated loads were statistically tested and were not significantly different from experimental loads. Also, maximum magnitude dynamic loads were compared to corresponding static load magnitudes and were larger for eight of the ten load components measured. With the importance of dynamic loads demonstrated and the model verified, it can now be used advantageously to generate a loading database for design analysis purposes.
On First-Order Decoupling of Equations of Motion for Constrained Dynamical Systems
Authors: Loduha Timothy A. , Ravani Bahram
Published: March 2021

In this paper we present a method for obtaining first-order decoupled equations of motion for multi-rigid body systems. The inherent flexibility in choosing generalized velocity components as a function of generalized coordinates is used to influence the structure of the resulting dynamical equations. Initially, we describe how a congruency transformation can be formed that represents the transformation between generalized velocity components and generalized coordinate derivatives. It is shown that the proper choice for the congruency transformation will insure generation of first-order decoupled equations of motion for holonomic systems. In the case of nonholonomic systems, or more complex dynamical systems, where the appropriate congruency transformation may be difficult to obtain, we present a constraint relaxation method based on the use of orthogonal complements. The results are illustrated using several examples. Finally, we discuss numerical implementation of congruency transformations to achieve first-order decoupled equations for simulation purposes.
A Novel Design Procedure for Reducing Vibration and Noise in Gears
Authors: Yoon K. Y. , Rao S. S.
Published: March 2021

A new method is proposed for reducing vibration and noise of involute gears. The method is based on the use of cubic spline curves for gear tooth profile modification. The tooth profile is constrained to assume an involute shape during the loaded operation. Thus the new gear profile assures conjugate motion at all points along the line of action. The new profile is found to result in a more uniform static transmission error compared to standard involute profile thereby contributing to the improvement of vibration and noise characteristics of the gear.
Deriving Exploded Views by Graph Transformation for Assembly Planning
Authors: Mohammad Riaz , Kroll Ehud
Published: March 2021

An automatic assembly planner that is integrated with a CAD system is being developed. To facilitate computer understanding of the design, a high-level representation scheme based on features and mating conditions is used and briefly explained. The focus of this paper is on automatic reasoning about relative spatial locations of product components for the purpose of establishing assembly precedence. The key element in the initial product description is a graph of planar contacts (’against’ mating conditions) between parts. This graph is transformed by a rule-based procedure into a new graph representing an exploded-view of the product. In the process of transforming the graph, the program uses rules that encode assembly process knowledge and heuristics, and performs interference checks on feature-based descriptions rather than solid models. The exploded view and the mating conditions are used to generate selected assembly sequences of the product.
Assembly Representation Within a Product Data Framework
Authors: Henson Brian W. , Baxter James E. , Juster Neal P.
Published: March 2021

Recent research at the University of Leeds demonstrated how a product data model can integrate the information required and used during product design and manufacture. The product data framework developed during this research structured assemblies as lists of parts and did not consider information about the relationships between components necessary to support applications such as tolerance analysis and design for assembly. This paper describes how we intend to combine research in assembly representation, functional modeling and data modeling to describe the geometric and functional relationships between components of assemblies. Focus is provided by considering both the design process and the information requirements of a design for assembly analysis.
Compliance and Dynamic Analysis of Tendon-Driven Robotic Mechanisms
Authors: Chang Sun Lai
Published: March 2021

The stiffness and compliance matrices of tendon-driven robotic mechanisms have been derived in this paper. Position compensation for external force/moment based on the system compliance has also been developed. Using a stretchable tendon model, dynamic equations are systematically generated. Natural frequencies and mode shapes of this class of mechanisms have been analyzed through local linearization of its dynamic equations.
Kinematic Error, Compliance, and Friction in a Harmonic Drive Gear Transmission
Authors: Tuttle Timothy D. , Seering Warren P.
Published: March 2021

In this experimental examination, the behavior of harmonic-drive kinematic error, compliance, and friction was characterized. In particular, kinematic error was confirmed to appear primarily at frequencies that were multiples of the wave-generator rotational velocity, and static stiffness measurements were found to yield a range of profiles that could be highly nonlinear. Additional measurements of static and dynamic friction demonstrated that energy dissipation in harmonic drives varies nonlinearly with velocity and can escalate during system resonance. Due to the inseparable interaction between harmonic-drive kinematic error, compliance and friction, transmission properties often showed significant variation with operating conditions and were difficult to characterize accurately.
Dynamics of the Generalized Slider-Crank Mechanism
Authors: Fischer Ian S. , Rahman Sahidur
Published: March 2021

Dual-number techniques are used to analyze the dynamics of the slider crank mechanism generalized to consider the effects of the cylinder axis being offset and non-perpendicular to the crankshaft axis, conditions which result in reciprocating machinery such as engines and compressors from manufacturing tolerances. Results for various cases are shown and the implications for the design engineer are discussed.
An Efficient Genetic Algorithm for Large Scale Built-Up Structural Optimization
Authors: Wang Shigang , Cheng Xindu , Zhou Ji , Yu Jun
Published: March 2021

In this paper, a new zigzag method for plate structures and a genetic algorithm (GA) of dynamic source seed spaces are developed and a combination of them is used to deal with large scale built-up structural optimization. The new GA combined with the zigzag method can work efficiently to cope with large scale structural optimization with displacement and stress constraints. Examples show that this GA is robust and can be used for many complex structural optimization problems.