bluuebunny/crossref_metadata_2025 huggingface dataset:
An Isoparametric Four-Node Beam Element for the Analysis of Planar Robot Manipulators
Authors: Smaili Ahmad A. , Sannah Muhammad
Published: March 2021

Accurate determination of the dynamic response of high speed flexible manipulators requires that the dynamic model incorporates the influence of joint compliances, in addition to faithfully representing the physical characteristics of the links. A finite element model is herein presented for this purpose. The model is based on a 4-node isoparametric Timoshenko beam element to model the structural characteristics of the links including the effects of shear deformation and rotary inertia. It also includes the influence of the rigid body motion and the time derivatives of the elastic deformations of the manipulator on the characteristic matrices of the system, and accounts for the inertia of the drive units and payload and the damping of externally applied dampers. Quasistatic analysis, modal analysis, and linear and nonlinear vibrational responses of a 3-R planar manipulator are determined by solving the appropriate equations of equilibrium. The results of the analysis revealed that the compliance of the joints have a considerable influence on the manipulator response which is manifested by considerable increase in endpoint deflections and substantial decrease in fundamental natural frequency. Nonlinear transient response exhibited a behavior that differs drastically from that obtained when rigid joints are assumed.
Exploring Artificial Muscles As Actuators for Artificial Hands
Authors: Meghdari Ali , Jafarian Majid , Mojarrad Mehran , Shahinpoor Mohsen
Published: March 2021

This article presents a brief overview of current research and findings in developing artificial muscles. Furthermore, possibilities of applying such muscles as actuators in prosthetic hands (i.e. The Sharif Artificial Hand) have been proposed and investigated.
Spatial Filtering Characteristics of Distributed Piezoelectric Sensors
Authors: Tzou H. S. , Zhong J. P.
Published: March 2021

Distributed spatial filtering characteristics of distributed piezoelectric sensors are investigated. In general, a sensor output signal is contributed by a membrane strain and a bending strain. Depending on the sensor placement, a distributed sensor can be only sensitive to either membrane or bending modes — membrane or bending sensor. In addition, a piezoelectric sensor can be sensitive to a mode or a group of modes due to signal average of electrode surface, especially anti-symmetrical modes. Accordingly, the sensor layer can be spatially shaped such that its sensitivity can be specified. These filtering characteristics are discussed and examples demonstrated.
Analysis of a Piezoelectric Actuator and Receiver on an Elastic Half-Space Subjected to Harmonic Electric Excitation
Authors: Chang Shuo-Hung , Lin Ching-San
Published: March 2021

Analytical solutions are formulated for the displacement, stress, and electric potential in piezoelectric actuator and receiver on an elastic half-space. The surface wave is taken into account when the piezoelectric actuator is subjected to the harmonic electric excitation. The derived analytical formulas are used to compute the output potential of piezoelectric receiver. Experiment measurements are performed and compared with numerical results in good agreement. The influence of excitation frequency, material property and dimension of the piezoelectric material is presented.
An Introduction to Smart Fractal Structures and Mechanisms
Authors: Shahinpoor Mohsen
Published: March 2021

Fractal structures are unique in the sense that they are highly expandible or collapsible and yet they are capable of preserving their basic structural geometry in a dynamic fashion. This dynamic geometric invariance opens up a new territory in fractal solids, i.e., fractal structures, mechanisms and robot manipulators. Some of these structure are in the form of highly deployable mechanisms and possibly redundant, multi-axis, multi-arm, multi-finger robot manipulators whose kinematic structure is fractal. Thus, simple fractal structures, such as triadic cantor set, and fractal functions, such as the Weirstraus-Mandelbrot functions, govern the structural branching of such robots and essentially define their kinematic structure. These deployable fractal structures, mechanisms and robot manipulators are shown to be capable of generating unique, and yet unparalleled properties such as computer-controlled microsensing even down to molecular level (micromachining) and computer-controlled dynamics such as the creation of hypervelocity fractons with speeds in the range of hundreds of kilometers per second. A number of structures and mechanisms and their unique properties are presented in this paper and a simple kinematic model is presented and briefly discussed.
Eigenvalue Veering, Perturbed Bifurcation Theory and Modal Analysis of Mistuned Linear Systems
Authors: Happawana G. S. , Bajaj A. K. , Nwokah O. D. I.
Published: March 2021

Eigenloci crossing or veering in structural systems dependent on parameters, and having two nearly identical eigenvalues, is the subject of this paper. Utilizing some basic ideas from the perturbed bifurcation theory, a criterion for identifying eigenloci crossing or veering is presented along with a method for studying the modal properties of mistuned structural systems. Two classical continuous systems: a clamped rectangular membrane and a rotating guided circular string, have been chosen as illustrations. The analysis is performed by applying the singular perturbations technique for asymptotic expansions. These expansions are used to detect correctly, whether the eigenloci will cross over or veer away from a particular “singular” point under the influence of small parameter variations from nominal values. This is useful in the correct identification of the vibration behavior of mechanical systems subject to structural parameter variations, since it is known that only the eigenloci veering leads to modal bifurcations.
Theoretical and Experimental Analysis of the Forced Response of Sagged Cable/Mass Suspensions
Authors: Cheng S.-P. , Perkins N. C.
Published: March 2021

This study examines the forced response of a sagged elastic cable supporting an array of discrete masses. Such systems arise, for instance, in ocean engineering applications employing cable hydrophone arrays. The excitation considered is harmonic and normal to the cable and may, for instance, approximate prescribed environmental loading. An asymptotic model is presented that describes the linear forced response of a cable/mass suspension having small equilibrium curvature. Closed-form expressions for the Green’s function to an associated boundary-value problem are obtained using a transfer matrix formulation. The derived Green’s function is utilized to construct integral representations for steady-state response under boundary and/or domain excitation. Solutions obtained for a variety of domain loading distributions demonstrate the utility and efficiency of this solution strategy. The theoretical response predictions are verified through experimental measurements of the natural frequency spectrum and frequency response of laboratory cable/mass suspensions.
Moving Contact and Coupling in Belt Strand Vibration
Authors: Yue M. G.
Published: March 2021

Belt vibration behavior is analyzed, by considering moving contact between belt and pulley and the coupling between longitudinal and transverse motions. For typical belt drive parameters there is a very weak coupling on lateral vibration from longitudinal vibration but a moderate coupling the other way around. This coupling in combination with the moving contact increases the fundamental transverse natural frequency difference compared to the simply supported case.
Thermal/Mechanical Effect of Rotor-to-Stator Rubs in Rotating Machinery
Authors: Muszynska Agnes
Published: March 2021

The thermal effects of rotor-to-stator rubbing resulting in rotor bowing, and subsequent changes in rotor vibrational responses are discussed in this paper. The rotor thermal bow is modeled following relationships quoted in rotordynamic literature. The rotor model takes into account its first lateral mode in which the rubbing spot differs from the modal mass location. It is shown that the rotor responds to the rub thermal effect in a “spiraling/oscillating” mode which represents a form of rotor self-exciting vibrations. A simplified model explains physical phenomena occurring in the rubbing rotor system. An example of the field data illustrates the rotor dynamic behavior.
A Theoretical and Experimental Investigation of a Gas Operated Bearing Damper for Turbomachinery: Part II — Experimental Results and Comparison With Theory
Authors: Sundararajan Padmanabhan , Vance John M.
Published: March 2021

This is the second of two papers describing results of a research project directed at developing a gas operated vibration damper for high temperature turbomachinery applications. This part presents the experimental measurements made on three variations of the gas damper hardware and compares them with the theoretical predictions presented in Part I. It is found that the isentropic theoretical model predicts the damper characteristics quite well. A maximum damping of 13.2 Ib-s/in was measured for a single actuator at a natural frequency of 100 hz using the present design and the results suggest that significantly higher damping levels are possible with design modifications.
A Waved Journal Bearing Concept-Evaluating Steady-State and Dynamic Performance With a Potential Active Control Alternative
Authors: Dimofte Florin
Published: March 2021

Analysis of the waved journal bearing concept featuring a waved inner bearing diameter for use with a compressible lubricant (gas) is presented. The performance of generic waved bearings having either three or four waves is predicted for air lubricated bearings. Steady-state performance is discussed in terms of bearing load capacity, while the dynamic performance is discussed in terms of fluid film stability and dynamic coefficients.

It was found that the bearing wave amplitude has an important influence on both steady-state and dynamic performance of the waved journal bearing. For a fixed eccentricity ratio, the bearing steady-state load capacity and direct dynamic stiffness coefficient increase as the wave amplitude increases. Also, the waved bearing becomes more stable as the wave amplitude increases. In addition, increasing the number of waves (e.g., four waves instead of three waves) reduces the waved bearing’s sensitivity to the direction of the applied load relative to the wave. However, the range in which the bearing performance can be varied decreases as the number of waves increases. Therefore, both the number and the amplitude of the waves must be properly selected to optimize the waved bearing design for a specific application. Another possibility is to use the waved bearing to actively control the rotor-bearing system dynamic coefficients via actively controlling the wave amplitude.
Effect of Straight Through Labyrinth Seals on Rotordynamics
Authors: Vance John M. , Zierer J. J. , Conway E. M.
Published: March 2021

Experimental measurements have been made to evaluate the rotordynamic performance of straight-through labyrinth seals under conditions that are realistic for many turbomachines. Both teeth-on-rotor and teeth-on-stator gas seals were tested, each with twelve blades, 173 mm (6.8″) blade diameter, and 102 mm (4″) total length. The nominal blade tip clearance was 0.5 mm (20 mils). The teeth-on-stator seal was tested with the blade tip clearances diverging (in the direction of the flow), uniform, and converging. The teeth-on-rotor seal was tested with uniform clearances. The inlet air pressure to the seals was varied from 1.7 bar to 14.6 bar (25 psi to 200 psig) with the last blade exhausting to the atmosphere. Coastdown tests of all the seals were performed on a rotordynamic test rig to show their effect on synchronous response to imbalance when passing through a 3700 rpm critical speed. For the teeth-on-rotor seal, rap tests at 4500 rpm were also conducted to measure the effective damping coefficient for subsynchronous vibration.

The synchronous response to imbalance was generally increased by all the seals at inlet pressures up to about 11.2 bar (150 psig). The worst case was for the teeth-on-rotor seal at about 2.7 bar (35–45 psi) inlet pressure where the rotor whirl amplitude was increased from .1 mm (3.75 mils, peak to peak) to over .13 mm (5 mils). In most cases the rotor whirl amplitude was slightly decreased at inlet pressures above 13 bar (176 psig).

The teeth-on-rotor seal provided a small amount of damping to attenuate the 61 Hz subsynchronous vibration with the rotor running at 4500 rpm. A computer model which includes both the rotor and housing dynamics was developed to evaluate the possible range of values of the rotordynamic seal coefficients. Simulations show that the effective subsynchronous damping coefficient of the teeth-on-rotor seal ranges from 175 N-s/m at 5.1 bar inlet pressure (1 lb-s/in at 75 psi) to 876 N-s/m at 10.2 bar (5 lb-s/in at 150 psi). This corresponds to a range of 0.3% to 1.4% of critical damping added by the seal for subsynchronous vibration, even though the seal increased the synchronous response at the critical speed. It is shown that the orbit conditions for the synchronous and subsynchronous tests were radically different, as they likely will be in most turbomachines.
The Effect of Inlet Grooves and Swirl on the Dynamics of Long Annular Seals in Centrifugal Pumps
Authors: Ismail Mohamed , Brown R. David , France David
Published: March 2021

This paper describes additional results from a continuing research program which aims to identify the dynamics of long annular seals in centrifugal pumps. A seal test rig designed to experimentally identify dynamic coefficients using a least-squares technique based on the singular value decomposition method. The analysis is carried out in the time domain using a multifrequency forcing function. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. A rigid rotor supported in rolling element bearings runs through the stator. The only physical connection between shaft and stator is a pair of annular gaps filled with pressurised water discharged axially. The experimental coefficients obtained from the tests are compared with theoretical values.
An Eigenvalue Inclusion Principle for Simple, Rotationally Periodic Structures
Authors: Shen I. Y.
Published: March 2021

This paper describes an eigenvalue inclusion principle for a simple, rotationally periodic structure P whose i-th substructure Si is connected to a neighboring substructure Si+1 through a single-degree-of-freedom interface constraint Ii+1. The state vector vi+1 at the interface Ii+1, consisting of the displacement and the force at the interface, is represented in terms of the state vector vi at the interface Ii through transfer functions of the substructure Si. The periodicity of the structure P then requires that a linear combination of the transfer functions of Si be zero. As a consequence, a simple periodic structure P with period N will have exactly N eigenvalues lying between two consecutive eigenvalues of the substructure Si. Finally, this eigenvalue inclusion property is illustrated on a periodic structure with known exact eigensolutions.
Digital Measurement Method on Rotating Shaft Torsional Vibration
Authors: Fu Haizhong , Yan Puqiang
Published: March 2021

For many large scale rotating machines, torsional vibration is one of key factors affecting operation safety. Torsional vibration measurement of the rotating shaft is a difficult task in monitoring the machine operation. The non-contact measuring approach is considered to be a practical method for the torsional vibration measurement. However, because the measurement usually depends on the accuracy of on-shaft gears, it is neither easy to conduct nor can reach a high precision. A new digital measurement method is presented in this paper to overcome the difficulty. The principle of the new method is described Experimental measurements indicate that the measurement is easy to execute and its accuracy is higher than 0.01 degree.
Rotating, Axially Loaded Timoshenko Shaft: Modeling and Stability
Authors: Karch Gerald , Wauer Jörg
Published: March 2021

For studying the stability of a rotating shaft subject to axial load, the derivation of correct stability equations is the essential preliminary problem. Here, the model of a uniform non-circular Timoshenko shaft under a compressive end load of constant magnitude is dealt with. Starting point is the nonlinear boundary value problem for coupled extensional-bending-torsional oscillations where a finite strain beam theory in a floating reference frame following the rigid body rotation is applied. First, the equation set describing the stationary shaft configuration is deduced. Next, the variational equations for small superimposed perturbations are derived. The only interesting stability problem for usual properties of the shaft cross section is constituted by a linear boundary value problem describing the bending vibrations. The corresponding characteristic equation is evaluated finally to find the critical buckling load also for the case of an oval shaft not considered before.
Stability and Stability Degree of a Cracked Flexible Rotor Supported on Journal Bearings
Authors: Guang Meng , Gasch Robert
Published: March 2021

This paper investigates the stability and the stability degree of a flexible cracked rotor supported on different kinds of journal bearings. It is found that no matter what kind of bearings is used, the unstable zones caused by rotor crack locate always within the speed ratio 2N(1-△Kξ4)<Ω<2N when gravity parameter Wg > 1.0; and locate always within the speed ratio 2ΩαN(1-△Kξ4)<Ω<2ΩαN when Wg < 0.1, where ΔKξ is the crack stiffness ratio, N = 1, 2, 3, 4, 5 … and Ωα=(1+2α2α)1/2. When 0.1 < Wg < 1.0, there is a region, where no unstable zones caused by rotor crack exist.

Outside the crack ridge zones, the rotor crack has almost no influence on system’s stability and stability degree; while within the crack ridge zones, the stability and stability degree depend both on the crack and system’s parameters. In some cases, the system may still be stable even the crack is very large. For small gravity parameter (Wg < 0.1), the mass ratio α has large influence on the position of unstable region, but its influence on the stability degree is small. The influence of fixed Sommerfeld number So on the crack stability degree is small although So has large influence on the stability degree of uncracked rotor.
Dynamic Analysis of Flexible Rotors Subjected to Torque and Force
Authors: Yun Jong-Seop , Lee Chong-Won
Published: March 2021

The effect of the applied direction and magnitude of loads on the stability and natural frequency of flexible rotors is analyzed, when the rotors are subject to nonconservative torque and force. The stability criterion derived from the energy and variational principle is discussed and a general Galerkin’s method which utilizes admissible functions is employed for numerical analysis. Illustrative examples are treated to demonstrate the analytical developments.
On the Generation of Bending Vibration in a Drill Rod
Authors: Kaski Juha
Published: March 2021

In this paper, it is studied how much of the piston blow energy will be transformed to the bending energy of drill rod in a percussive rock drilling process. The mathematical model is based on one-dimensional wave theory and Euler-Bernoulli beam theory. The axial and the transverse motions of drill rod are assumed to be coupled at the boundary only. The rod is considered as semi-infinite in length, and the rod/rock contact condition is modelled with an eccentric linear spring element.

Two kind of problems will be considered. First, the one in which the piston eccentrically impacts on the rod end, thus causing bending vibration; and second, the one in which the purely axial incident pulse arrives at the eccentrically spring-supported rod end, reflects back and generates bending vibration. Using Laplace-transformation techniques, the closed form solution for these problems is discovered. The results show that the disturbances at the rod/rock boundary cause stronger bending effect than those at the piston/rod boundary.
Modeling of Coupled Bending and Torsion in Elastic Structures
Authors: Banks H. T. , Smith C. A.
Published: March 2021

In this presentation we will report on joint efforts with D.J. Inman and his colleagues at MSL, SUNY at Buffalo, to develop viable models for the analysis and control of elastic structures exhibiting coupled torsional and flexural vibrations. A model for coupled torsion and bending is developed which incorporates Kelvin Voigt damping and warping. Approximation techniques are introduced and preliminary numerical results are discussed. Experimental data is presented and used to test our computational results.
Axial Force Stabilization of Transverse Beam Vibration
Authors: Rahn Christopher D. , Mote C. D.
Published: March 2021

An axial force stabilizes the transverse vibration of a beam with translational and rotational boundary springs and arbitrary geometry. The nonlinearly coupled, longitudinal and transverse equations of motion of the beam with axial force control are derived and simplified using a quasistatic assumption. Lyapunov’s direct method and an invariance principle for distributed systems show that an axial damper can asymptotically and simultaneously stabilize all transverse vibration modes. Asymptotic stability is guaranteed if the eigenvalues are simple and nonzero and if there are no internal resonances between coupled modes.
Distributed Orthogonal Filtering of Piezoelectric Shell Actuators
Authors: Tzou H. S. , Zhong J. P.
Published: March 2021

Distributed control of elastic shell continua using spatially distributed piezoelectric actuators is proposed and a generic distributed velocity feedback algorithm with a spatial modal feedback function formulated. The generic distributed modal feedback function is further represented by a gain factor and a spatially distributed orthogonal (mode shape) function to achieve independent modal actuation capability. Based on this principle, distributed piezoelectric actuators can be spatially shaped to emulate the spatial orthogonal actuation of the distributed modal feedback function. Distributed orthogonal shaped modal actuators for ring shells are proposed and their modal actuations demonstrated. Analyses suggested that the primary control action came from the in-plane membrane (circumferential) forces and that contributed by the bending control moment is relatively insignificant for lower natural modes. Control effects due to thickness variation of the ring shell and the actuator are also investigated.
Characterization and Reduction of Reluctance Torque in Permanent Magnet D.C. Motors
Authors: Hwang Sangmoon , Lieu Dennis K.
Published: March 2021

For motors with low speeds and loads, torque pulsation by the reluctance torque is an important source of vibration and control difficulty. In this paper, the magnetic field of a motor is calculated by finite element method and the periodic reluctance torque is determined using Maxwell stress method and time stepping method, and then decomposed using Fourier series expansion. The purpose of this paper is to characterize design parameters on the reluctance torque and to design a permanent magnet motor with a reluctance torque less vulnerable to vibration, without sacrificing the motor performance. The design parameters include stator slot width, permanent magnet slot width, airgap length and magnetization direction. A new design with a less populated frequency spectrum of the reluctance torque is proposed after characterizing individual effect of design parameters. Gradual magnetization, by gradually increasing the thickness of the permanent magnets at edges, yields a smooth shape for the reluctance torque with reduced harmonics.
Free and Forced Vibration of Stepped Levy Plates
Authors: Lee Jinkyo , Bergman Lawrence A.
Published: March 2021

The study of the transverse vibration of thin rectangular plates has been mainly confined to plates of uniform thickness. There are few publications available on the vibration of plates with nonuniform thickness. These plates have application in various fields such as civil engineering and aerospace structures and are often found in high frequency acoustic transducers. Furthermore, it is sometimes possible to achieve minimum weight design of plates by having suitable variations in thickness. For the special case of a plate with two opposite edges simply supported and thickness discontinuities perpendicular to the simply supported edges, an analytical solution is possible using a dynamic flexibility method. Several examples are discussed.
Parametric Studies on Muffler Design With Applications to a Vacuum Pump
Authors: Sridhara B. S.
Published: March 2021

A computer simulation was employed to perform parametric studies on muffler design. Engine exhaust system parameters such as muffler diameter, source-muffler pipe length, number of mufflers, series and parallel installation of mufflers, and the source and termination impedances were considered during the studies. The muffler insertion loss and radiated sound pressure level were predicted for several values of each parameter. An acoustic model consisting of a lumped source-muffler-termination system was used. A scheme was developed using the pressure source model to predict the radiated sound pressure and a simplified expression for the predicted quantity was obtained as a sum of the measured, plane wave and monopole terms. The relationship between the insertion loss and radiated sound pressure level was established for a given set of conditions. A vacuum pump was used as the sound source. An expansion chamber was used as a muffler.
Vibration Analysis of a Partially Covered Double Sandwich Cantilever Beam With Concentrated Mass at the Free End
Authors: Levy C. , Chen Q.
Published: March 2021

The partially covered, sandwich-type cantilever with concentrated mass at the free end is studied. The equations of motion for the system modeled via Euler beam theory are derived and the resonant frequency and loss factor of the system are analyzed. The variations of resonance frequency and system loss factor for different geometrical and physical parameters are also discussed. Variation of these two parameters are found to strongly depend on the geometrical and physical properties of the constraining layers and the mass ratio.
Determination of the Position of Solid/Liquid Interface During Solidification and Melting of Metals With Vibrational Parameters
Authors: Fengquan Wang , Zhenghua Zhu , Shiyu Chen
Published: March 2021

The paper proposes the method to locate the solid / liquid interface with vibrational parameters during solidification for the first time. The sufficient difference in resistance to shear stresses between liquid and solid phases of metals and alloys permits the application of vibrational parameters to locate the interface in real time and in situation during solidification. Based on the solidification theory, continuum mechanics, vibrational modal analysis and sensitivity analysis, the author established the mechanical model and the dynamical equations of typical Bridgman solidifying system, derived the sensitivity of eigenvalues of the Bridgman system to the location of the solid / liquid interface as well as the calculating formulae concerned. The experimental results are quite accordant with those of computed ones.
A Simple Method for Extracting Normal Modes
Authors: Chen S. Y. , Ju M. S. , Tsuei Y. G.
Published: March 2021

A simple method for extracting the normal modes of structures is developed. The frequency response function relation between the complex and the normal modes is derived and a technique is developed to calculate the normal modes from the identified (damped) complex modes. In this method, only the magnitude and phase information at resonant frequencies are needed for extracting the normal mode shapes. A numerical example is employed to illustrate the theory. The results indicate that this method is more robust than other methods when the frequency response measurements are contaminated with noise.
A Holographic and BEM/FEM Analysis of a Fluid-Loaded Propeller
Authors: Rice John M. , Fennell William G.
Published: March 2021

The modal dynamic characteristics of an underwater propeller are investigated using a coupling of the Finite Element Method (FEM) to model the propeller and the Boundary Element Method (BEM) to model the fluid. Results of this numerical model are presented for a fluid-loaded propeller and are compared with experimental holographic results.

The FEM is known to yield very reliable solutions in the analysis of the modal dynamic characteristics of solid structures such as a propeller and the BEM is very attractive in dealing with infinite domain problems and the radiation condition, such as the infinite fluid field. Combining the two methods exploits the best attributes of both. The fluid/structural coupling is achieved by discretizing Kirchhoff’s integral with boundary elements and isolating the effective mass of the fluid. This effective mass is in the form of a mass matrix which is coupled by the degrees of freedom of the propeller. The effective mass is then input into a finite element program in the form of user elements along with the propeller’s geometry, material properties, and boundary conditions to simulate an underwater propeller in a hub.

An experiment using time averaged holographic interferometry was performed to identify the resonant modes of the propeller, identical in geometry to that used in the FEM model. In order to simulate the boundary conditions of the model the propeller was rigidly clamped in a vise at it’s root and submerged in water. Excitation of the propeller was provided by means of a mechanical shaker mounted to the vise.

Both the resonant frequencies and their respective mode shapes agreed favorably with numerical predictions.
Experimental Characterization of a Flexible Two-Link Manipulator Arm
Authors: Mayes Randall L. , Eisler G. Richard
Published: March 2021

Experiments were performed to verify the analytical models for a robotic manipulator with two flexible links. A finite element model (FEM) employing two-dimensional beam elements was used to model the structure. A proportional model relating input voltage to output torque was used for both hub and elbow joint motors. With some minor adjustments to the link stiffness, the FEM modal frequencies matched the experimentally extracted frequencies within 1.5%. However the voltage-torque relationship for the hub motor was found to exhibit dynamics in the frequency range of interest.
Linearization of Multibody Dynamic Systems Using Automatic Differentiation (AD) Tools
Authors: Lin Tsung-Chieh
Published: March 2021

This paper presents an automatic method to linearize the dynamics of multibody systems that are modeled through a recursive approach. The first-order approximation of the nonlinear dynamic systems is obtained by the use of an automatic differentiation (AD) tool (GRESS) and a 9,700 lines Fortran model for the dynamics. The efficiency and accuracy of this AD implementation is shown by two examples: a five-bar closed-chain robot manipulator and a 18 degrees of freedom tractor-trailer. This study successfully demonstrates how to create a general-purpose numerical tool that can provide accurate solutions and derivatives for multibody dynamic systems.
A Form Verification System for the Conceptual Design of Complex Mechanical Systems
Authors: Colton Jonathan S. , Ouellette Mark P.
Published: March 2021

This paper presents a summary of research into the development and implementation of a domain independent, computer-based model for the conceptual design of complex mechanical systems (Ouellette, 1992). The creation of such a design model includes the integration of four major concepts: (1) The use of a graphical display for visualizing the conceptual design attributes; (2) The proper representation of the complex data and diverse knowledge required to design the system; (3) The integration of quality design methods into the conceptual design; and (4) The modeling of the conceptual design process as a mapping between functions and forms.

Using the design of an automobile as a case study, a design environment was created which consisted of a distributed problem solving paradigm and a parametric graphical display. The requirements of the design problem with respect to data representation and design processing were evaluated and a process model was specified. The resulting vehicle design system consists of a tight integration between a blackboard system and a parametric design system. The completed system allows a designer to view graphical representations of the candidate conceptual designs that the blackboard system generates.
A Parametric and Experimental Study of a Power Construction Tool
Authors: Marinkovich Dragomir C. , Kremer John M. , Shabana A. A.
Published: March 2021

Power tools play a large role in the construction industry. From power nailers to circular saws, these tools provide an enormous and relatively untapped opportunity in the field of dynamic analysis. The intent of this paper is to analyze a unique power construction tool and then develop a computer model to simulate its dynamics. The study model used in this investigation is a nailer which utilizes a linear internal combustion engine to drive nails into wood and is completely cordless and portable. Analytical expressions for the forces acting on the system are developed and the obtained analytical results are verified experimentally. The computer model is then used to parametrically study the performance of this nailer under varying conditions. The parameters varied are the piston mass, by choosing materials with different densities, and the bumper material on which the piston impacts, to vary the coefficient of restitution between the bumper and piston. The jump discontinuity in the system velocities is predicted using a momentum balance and the restitution conditions. The coefficient of restitutions used in this study are determined experimentally using a simple impact test. It is found that there is an ideal piston mass that will provide the highest kinetic energy at the end of the stroke. It is also shown that the lower the coefficient of restitution between the piston and bumper, the lower the piston rebound height and velocity. The material chosen as having the lowest coefficient of restitution was not acceptable as an alternative material due to its low durometer, or hardness. In addition, the high elastic-energy-absorption capacity of this material may also result in increased heating of the bumper resulting in premature failure.
Suspension Design Optimization of a Washing Machine: Part II — Formulation and Implementation of Parametric Optimization
Authors: Kiray B. , Türkay O. S. , Tuğcu A. K. , Sümer I. T.
Published: March 2021

This paper presents an optimization methodology for determining the optimal suspension characteristics of an automatic washing machine.

Earlier publications by the authors have presented the modeling and experimental validation of the suspension dynamics of a horizontal-axis washing machine. That machine was characterized by the horizontal tub being suspended by three springs and supported by two dry-friction absorbers. A companion paper (Part I) assessed the modeling and validation of a different washing machine where the horizontal tub stands on four shock absorbers.

In this paper (Part II) various formulations for the optimization of the suspension system introduced in Part I are described and implemented by using a parametric grid optimization method. The primary objective of this effort is to determine the most suitable criteria that will be employed for future washing machine design optimization with different configurations. It is concluded that a weighted multiobjective function subject to washing machine cabinet motion constraint is appropriate for this purpose.

Future work will be toward the employment of an analytical optimization methodology in order to develop a complete design software that will be used by washing machine suspension design engineers.
Design of Smart Metal-Ceramic Composite Actuators for Macro-Motion Applications
Authors: Thirupathi Sridhar R. , Naganathan Nagi G.
Published: March 2021

Piezoceramic, electrostrictive, and magnetostrictive materials are being increasingly applied in active vibration control and are being investigated for other motion control and damage mitigation applications. Typically, motion ranges required in active vibration control are of the order of a few microns. On the other hand, many mechanical and electromechanical motion control applications require the point of application of the load to move through at least a few millimeters. In this research, a smart ceramic-elastic composite actuator is invented for such motion control applications. The work presented in this paper includes the concept, its illustration, development of a design geometry based on this concept, and its finite element analysis and results. It will be shown that by a proper synthesis of smart structure, a class of such actuators can be successfully designed and realized in practice.
Issues in Computer-Aided Process Planning for Parallel Machine Tools
Authors: Yip-Hoi Derek , Dutta Debasish
Published: March 2021

Parallel machines represent a new generation of machine tool. Through reducing the number of setups both the efficiency and the accuracy of the machining process is increased within the part domain. While Flexible Manufacturing Systems (FMSs) and Machining Cells (MCs) are said to be agile, the parallel machine is the first stand-alone machine which can claim to have this property. This makes them ideally suited for machining small batch sizes and for rapid prototyping. Unfortunately like FMSs and MCs these machines will be largely underutilized if agile data generation, processing and transfer mechanisms are not incorporated into CAD/CAM systems. One major hurdle to achieving this objective is the development of an automatic process planning system for parallel machines. This presents new challenges beyond those encountered in process planning for sequential machining. In this paper we discuss two aspects of parallel machines which impact on process planning. These are (1) the part domain for parallel machines and (2) the machine configuration.
Automation of Transient Flight Loads Estimation for Spacecraft Design
Authors: Kodiyalam Srinivas
Published: March 2021

Quick and effective estimation of transient dynamic flight loads is a critical part of the spacecraft design process. In this work, a transient base drive procedure is used to estimate the flight loads on a spacecraft, during the spacecraft design iterations. In this base drive procedure, only the spacecraft dynamic model is used as against a coupled spacecraft-launch vehicle dynamic model. The well established fixed interface modal model representation, with a determinate interface, is used for the spacecraft substructure. The second part of this paper is on a new, constrained optimization based procedure for notching the qualification level sine vibration loads, specified by the launch vehicle organization. Finally, the base drive and the sine vibration notch procedures are demonstrated on a spacecraft stick model and a spacecraft structure with solar arrays.
A Model for Performance-Intelligent Design Advisors
Authors: Reed R. Grant , Sturges Robert H.
Published: March 2021

We consider a design advisor to be performance-intelligent when its suggestions do not conflict with high level performance-related goals of the design under study. We address the problem of representing non-domain-specific design Information at a high level and describe coupling it to the inputs and outputs of design critics and their suggestion mechanisms. High level design Information represented in a function-based structure with linked allocations is shown to interact with a domain-specific design critic in three instances, viz.: allocation refinement, goal matching with a supported function, and performance-intelligent tradeoffs. Examples of manual and computer-based procedures are discussed.
Data-Conditioning in the Optimization of Function-Generating Linkages
Authors: Liu Zheng , Angeles Jorge
Published: March 2021

Rank-deficiencies and ill-conditioning of the synthesis matrix in the optimization of function-generating linkages are often caused by an improper selection of the input-output data points given by the {ψi,ϕi}1m pairs, where ψ and ϕ denote the input and output values, respectively. Ten basic cases of rank-deficiencies in the synthesis matrix are discussed in this paper, the associated curves, termed singularity curves, being plotted in the ψ-ϕ plane. Measures to remedy the ill-conditioning that arises in the optimization procedure and means to find the best-conditioned synthesis matrices by minimizing their condition number are also proposed.
A Stochastic Methodology for the Optimal Analytical Synthesis of Planar Mechanisms
Authors: Ogot Madara M. , Alag Satnam
Published: March 2021

This paper presents a stochastic based methodology for the optimal synthesis of planar mechanisms. The approach is fully automated, relatively simple to use and flexible. The methodology employs an analytical synthesis approach based on the complex number theory, to synthesize the desired mechanism based on a relatively small number of prescribed positions (hard precision points – satisfied exactly). The quality of the synthesized mechanism is then optimized at an arbitrary number of prescribed positions (soft precision points – approximately satisfied). In this manner, the number of design variables is kept relatively low without compromising on the quality of the final solution. A ‘global’ stochastic optimization approach is employed to assign values to the free choices in the analytical synthesis portion, thereby effectively guiding the design process through the often highly non-linear design space. Thus the problems associated with local minima are addressed and automation is achieved. In addition, this work investigates the feasibility of considering some of the hard precision points as design variables (variable hard precision points).
APPréCIE: A Computer Package for the Simulation and Design of Mechanical Grippers
Authors: Gosselin Clément M. , Lemieux Sylvain
Published: March 2021

This paper presents a simulation package developed for the computer-aided design of simple mechanical grippers. The program includes a relatively large database of gripper architectures which can be accessed interactively by the designer. The kinematic analysis of each of the generic architectures has been performed symbolically at the programming stage and explicit expressions of the input-output equations as well as the velocity relationships have been coded. This provides an accurate and fast interactive response. The kinematic dexterity and the gripping index can be plotted and are updated automatically when dimensional changes are made. Finally, a graphic animation of the grippers is available. An example is given here to illustrate the application of the design package to a practical problem. This CAD tool could be of great help in the context of the design of mechanical grippers which is one of the key challenges in advanced robotic applications.
Multilevel Parallelization Concepts for Structural Optimization Using Transputer Systems
Authors: Hartmann Dietrich , Leimbach Karl R.
Published: March 2021

Multilevel parallelization concepts for structural optimization provide potential to significantly improve the productivity in CAE. In particular, if large scale structural systems are to be designed with respect to a specified optimization criterion subject to a large set of constraints substantial speedup factors are achievable. This contribution is discussing generic as well as specific parallelization concepts of large structural optimization problems. Based upon these concepts transputer systems are applied as a platform for the transition from concepts to actual computer implementation.
The Direct Contact Problem in a Trochoidal-Type Machine
Authors: Shung John B. , Pennock Gordon R.
Published: March 2021

Reducing the contact forces in a trochoidal-type machine is important because the machine can not be adjusted for wear. The main difficulty in calculating the contact forces is to determine the forces that are transmitted through each contact point. Since there are many points of contact, at any instant, the problem is quasi-statically indeterminate and no satisfactory method of analysis is available in the current literature. The first part of this paper presents a simplified analytical model of a trochoidal-type machine when friction and deformation at the contact points are neglected. From this model, closed-form equations are derived for the normal contact forces. Then the second part of the paper presents a combined analytical and finite element model of the same machine. The analysis for the combined model includes the effects of friction and deformation at the contact points. The analysis for both models is for quasi-static conditions. The results from the two models are compared and important conclusions are drawn.
Determination of the Minimum Distance Between Moving Objects Including Velocity Information
Authors: Nahon Meyer
Published: March 2021

The rapid determination of the minimum distance between objects is of importance in collision avoidance for a robot maneuvering among obstacles. Currently, the fastest algorithms for the solution of this problem are based on the use of optimization techniques to minimize a distance function. Furthermore, to date this problem has been approached purely through the position kinematics of the two objects. However, although the minimum distance between two objects can be found quickly on state-of-the-art hardware, the modelling of realistic scenes entails the determination of the minimum distances between large numbers of pairs of objects, and the computation time to calculate the overall minimum distance between any two objects is significant, and introduces a delay which has serious repercussions on the real-time control of the robot. This paper presents a technique to modify the original optimization problem in order to include velocity information. In effect, the minimum distance calculation is performed at a future time step by projecting the effect of present velocity. This method has proven to give good results on a 6-dof robot maneuvering among obstacles, and has allowed a complete compensation of the lags incurred due to computational delays.
Application of the Monomial Method to Shape Optimization
Authors: Burns Scott A.
Published: March 2021

The monomial method is an alternative to Newton’s method for solving systems of nonlinear algebraic equations. It possesses several properties not shared by Newton’s method that enhance performance, yet does not require substantial computational effort beyond that required for Newton’s method. Previous work has demonstrated that the monomial method treats problems in structural design very effectively. This paper combines the monomial method with the method of generalized geometric programming to treat the problem of structural shape optimization of continuum structures modeled by finite elements.
Optimally Directed Truss Topology Generation Using Shape Annealing
Authors: Reddy Giridhar M. , Cagan Jonathan
Published: March 2021

This paper presents a technique for generation and optimization of truss structure topologies based on the shape annealing algorithm. Feasible truss topologies are generated through a shape grammar, in an optimally directed manner, using simulated annealing. The algorithm can incorporate a variety of constraints; stress and buckling constraints are employed in this paper.