bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Recovery Systems in a Bipedal Walking Robot
Authors: Dhandapani S. , Ogot M. M.
Published: March 2021

The minimization of energy consumption plays a key role in the design of walking machines. As these vehicles tend to carry their own energy source, a reduction in energy consumption results in machines which can not only travel further, but require smaller actuators that typically yield a reduction in vehicle weight and cost. This paper examines how spring-damper (SD) systems, incorporated within the limbs of walking machines, can be used to transfer a portion of the energy typically dissipated, from one step to the next. Unlike previous efforts which have concentrated on hopping machines, this paper examines walking machines which have a definite multi-limb support phase. Two methods, active and passive locking, are developed and applied to a five-link biped. Dynamic simulations demonstrate that energy consumption can be reduced by 34%.
A Linkage Type Map for Spherical 4 Position Synthesis
Authors: Murray Andrew P. , McCarthy J. Michael
Published: March 2021

This paper classifies and evaluates the solutions to the four orientation synthesis of spherical 4R linkages. Burmester’s result that a one-parameter set of planar RR dyads exists that guide a body through the four planar positions has an analogous form for spherical RR dyads given four orientations. The theory provides a two dimensional set of spherical 4R linkages that can be assembled in each of the four chosen orientations. A map of linkage types is obtained by classifying each spherical mechanism at the vertices of a finite grid on this set; Erdman titles this a “Map of Solutions” for the planar case. Each mechanism is then checked for input drivability, that is, whether or not the input link can drive the coupler smoothly through all four positions. The result is a map of the spherical 4R mechanisms that the designer can use to find practical solutions to the spherical synthesis problems.
A New Algorithm for the Determination of the Workspace of Complex Planar Kinematic Chains
Authors: Lê-Huu Pascal , Gosselin Clément M.
Published: March 2021

A new algorithm for the determination of the workspace of complex planar kinematic chains is presented in this paper. This algorithm is completely general since it can deal with any kind of topological graph and any set of parameters defined in a convention of notation. It uses the numerical solution of the inverse kinematics and is based on a wavefront expansion in the Cartesian space. Three examples are presented here, and lead to a dexterity mapping for two two-degree-of-freedom multi-loop manipulators and a three-degree-of-freedom hybrid manipulator.
An Inverse Dynamic Model of a Spherical Electrohydraulic Actuator for Use in a Dexterous Mechanical Hand
Authors: Sharma Shikha , Ogot Madara M.
Published: March 2021

The purpose of this paper is the development of an inverse dynamic model of a two degree of freedom electrohydraulic actuator. The actuator is to be incorporated at the base of each of three fingers of a nine degree of freedom mechanical hand, currently under development. Motion in the proposed actuator is facilitated about intersecting pitch and yaw axes, thus creating spherical actuation. The dynamic model incorporates frictional and hydraulic losses, commonly overlooked sources of energy dissipation. The model is to be used in the control scheme of the mechanical hand and in the optimal synthesis procedure of the actuator. The latter application, briefly described here, takes into account specified motion and torque requirements, pressure, peak input force and size constraints. Particular attention is paid to traditional performance indices, such as mechanical advantage.
Dynamic Non-Interference Constraints in Goal-Directed Geometry
Authors: Coulter Stewart , Bras Bert , Rosen David
Published: March 2021

Improvements in computer-aided design tools can significantly increase designer productivity. The ability to explore a variety of possible designs quickly and effectively is essential for a designer. In a previous paper, Goal Directed Geometry (GDG) was introduced as a computational framework for preliminary design, aiding the formulation of engineering models with geometric considerations, and the solution of these models with a multi-objective optimization package. The geometric considerations were limited to static noninterference constraints, introducing a metric and method for prevention of geometric interference between two subassemblies. In this paper, this metric and method are expanded to include the prevention of interference between moving subassemblies, or dynamic interference. Based on a series of repetitive static checks, this metric is intended to be accurate and simple for the designer to use. A case study is presented showing the GDG implementation for a linkage design problem, demonstrating the use of this metric. This parametric GDG model is then solved using an existing optimization program called DSIDES.
Finite Element Analysis Improves Design of Hot Metal Ladle Car
Authors: Suchora Daniel H. , Perrine Harry S. , Chamberlain Bradley
Published: March 2021

An electric powered Hot Metal Ladle Car was designed to safely transport a ladle filled with 160 metric tons of molten steel. The ladle geometry and space constraints within the use environment were specified. A final design was prepared and documented which met the design requirements and could be efficiently manufactured.

An initial design was developed using past designs of a similar nature as a basis. By hand stress calculations were performed and the design modified to get stress values to acceptable levels. Preliminary design drawings were developed.

At this stage of the design, some engineering personnel felt that the “by hand” stress analysis was sufBciently accurate to go ahead with fabrication. After much discussion it was decided to perform a Finite Element Analysis (FEA) to verify the design stresses calculated “by hand”. The FEA analysis predicted stresses that were significantly higher than indicated “by hand” in some critical change of section regions. These stress levels were much higher than the allowable stresses for this design.

The difference between the FEA stresses and “by hand” stresses were evaluated. After much discussion and thought an insight to the actual load flow was developed which was consistent with the FEA results.

With this insight, modifications were made to the design and incorporated into the FEA model. These changes needed to be practical from a manufacturing and end use viewpoint. After a few iterations on the design tire FEA stresses were reduced to an acceptable level. These changes were incorporated into the design.

The final design of the ladle car was fabricated. The design was significantly improved due to the ability to accurately calculate stresses in transition regions of the frame where “by hand” methods were not really applicable. The combination of “by hand” methods to ballpark a design and FEA methods to reftne a design proved to be a powerful method to get a truly good design.
On the Safety of Agricultural Disc Mowers
Authors: Brickman Dennis B.
Published: March 2021

A thrown object test protocol was developed and performed based on agricultural rotary mower safety standards to analyze the safety of an agricultural disc mower. Test results reveal a relationship between the guard to ground clearance and the quantity of thrown objects striking the operator zone target. Application of the Safety Hierarchy systematically explores safety strategies for mitigating the thrown object danger.
Structural Health Monitoring Using Modal Strain Energy
Authors: Ballinger Robert S. , Herrin David W.
Published: March 2021

This research combines analytical and experimental modal analysis techniques to verify the structural integrity or monitor the “health” of a dynamic structure. Central to the procedure is the development of a baseline dynamic fingerprint model of the structure. The dynamic fingerprint is verified with experimental modal analysis and correlation. After the structure is placed into service, damage can be determined by comparing the current dynamic response with the baseline dynamic fingerprint response. The unique aspect of this procedure is that the current dynamic response is enforced on the undamaged baseline dynamic fingerprint model. Should damage exist, the structure is forced to deform in an unnatural manner, and high strain energy results. Significant differences in the normalized modal or operating strain energy density identify structural regions where a loss of stiffness, weakening of the structure, and/or damage has occurred. This identification of a potentially “unhealthy” structural region allows a quick visual inspection of the region or further analytical and/or experimental submodelling of the area to precisely identify the damage. The method is ideally suited to CAE application. The method is demonstrated analytically and experimentally for two structures: an eight-bay cantilevered truss structure and a rectangular plate with various boundary conditions.
Finite Element Analysis of Dynamic Rigidity of Diesel Engine Housing
Authors: Maslov Igor V. , McCafferty Raymond , Rea James P.
Published: March 2021

High levels of dynamic loads in a modem diesel engine take place at low frequencies and are connected with the forced vibration of the engine under the action of excitation gas and inertia forces. The lower range of these frequencies are equivalent to the speed of the engine (two stroke) and half engine speed (four stroke). They lead to high stress levels and deformations and often cause internal damage or component failure as well as increasing vibration transmitted to the foundation. One of the most important factors in improving the reliability and durability of engine components and reducing the level of vibration is providing sufficient rigidity for the engine housing. Careful choice of the main dimensions and design parameters will greatly influence engine performance.

An engineering approach to the Finite Element analysis of low frequency forced vibration is proposed for the elastic system including crankshaft, engine housing, elastic mounting and foundation. This approach is applied to the analysis of medium speed marine diesel engines with particular attention being paid to the analysis of the rigidity of the engine housing.

A solution procedure is proposed to define the loads transmitted from the crankshaft to the main bearings. The procedure takes into account the reciprocal influence of elastic and inertial characteristics of the crankshaft and the engine housing mounting on the elastic foundation, alteration of load amplitudes according to the angular position of the crankshaft, and hydrodynamic behaviour of the lubricating oil film in the contact zone.
Plastic Deformation of a Solid Cylinder of Temperature Dependent Properties Subjected to Cyclic Loading
Authors: Jahanian Shahriar
Published: March 2021

There are many practical instances of structural behaviors where the incremental increase of deformation occurs under cyclic loading, such as ratcheting in nuclear fuel element cans, incremental growth of pressure vessels or turbine cases, etc. This increase of deformation may lead to the failure of structure. For an incremental collapse to occur, it is necessary for different parts of the structure to yield at different stages of loading and unloading cycle. When the thermal loading is present, the properties of the material are temperature dependent. Accordingly the yielding occur at the earlier stage. The situation may get worse when the thermal loading is coupled with the mechanical one. This paper presents a quasi-static, uncoupled thermo-elastoplastic analysis based on incremental theory of plasticity. The behavior of a solid cylinder subjected to torsion and transient thermal loading for one cycle is investigated. The influence upon behavior of nonlinear-strain hardening in the material is investigated.
A Transient Thermoelastoplastic Solution for a Hollow Sphere of Temperature Dependent Properties
Authors: Jahanian Shahriar
Published: March 2021

In this paper an analysis based on incremental theory of plasticity is formulated to predict the thermoelastoplastic stresses in a hollow sphere. The properties of the material are assumed to be temperature dependent, and the material was characterized by linear strain hardening. Mendeson’s method of successive elastic solution is presented for the analysis. The analysis shows that the stresses are not monotonic function of radius or temperature, they strongly depend on history of temperature distribution. In this analysis the problem is treated in a uncoupled, and quasi-static sense. The plastic stress and strain distribution on loading and the residual stress distribution on unloading is presented. The results are compared with the results of other investigators who used a different theory and a reasonable agreement is observed.
Estimating Errors in Concept Selection
Authors: Otto K. N. , Wood Kristin L.
Published: March 2021

Numerical concept selection methods are used throughout industry to determine which among several design alternatives should be further developed. The results, however, are rarely believed at face value. Uncertainties (or errors) in subjective choices, modeling assumptions, and measurement are fundamental causes of this disbelief. This paper describes a methodology developed to predict overall error ranges, in addition to estimating a confidence measure in the numerical evaluation results. Each numerical assignment is given an associated error tolerance, and then treated as a probability error to create a simple means to propagate the uncertainties. A degree of confidence is also derived, similar to a statistical t-test, to indicate an induced confidence level in the final decision. Two preliminary concept selections are shown, to illustrate the methodology. Results from these concept selections indicate that (1) uncertainties can be suitably captured and quantified; (2) critical design questions are addressed during the process of numerical concept selection with error propagation; and (3) designers can make more informed and confident decisions through error estimation.
A Jungian Theory for Constructing Creative Design Teams
Authors: Wilde Douglass J. , Berberet John
Published: March 2021

A novel coordinate system is proposed for the four-dimensional space of scores from the Myers-Briggs Type Indicator (MBTI), a psychological questionnaire increasingly used in education and business as well as in psycholgical counseling. The new normal orthogonal basis proposed is consistent with the Jungian personality theory upon which the MBTI is based. The immediate motive is to find ways of improving the composition of student design teams.
Elementary Education and Engineering Design: Concrete Experiences in Mathematics and Science
Authors: Crawford Richard H. , Wood Kristin L. , Fowler Marilyn L.
Published: March 2021

The education community has focused attention recently on a number of initiatives to evolve, and perhaps revolutionize, approaches for teaching science, mathematics, and engineering. In this paper, we present a new engineering and design technology program, initiated in 1992 and referred to as DTEACh, that focuses on the elementary grades. Two components comprise this new program: (1) open-ended design and exploration lessons that use hands-on models to teach integrated mathematics and science principles, and (2) a two-part teacher preparation program to provide teachers with the necessary engineering, mathematics, and science fundamentals for DTEACh. In this paper, we focus on a description of the teacher preparation program, including discussions of a novel teaching model, the subject matter for engineering and design fundamentals, and evaluation of the program. Results of the evaluation that teachers are more confident and equipped to facilitate the instruction of mathematics, science, and engineering principles.
Modeling the Information Access Methods of Engineering Designers
Authors: Court Andrew W. , Culley Stephen J. , McMahon Christopher A.
Published: March 2021

An information modeling approach is used to gain an understanding of the methods that engineering designers use when accessing design information. A new technique is presented that attempts to represent the key information sources used and to identify the information access paths or routes most frequently undertaken by engineering designers. This technique is termed Information Access Diagrams (IADs). Elements of the IADs were derived firstly, from observations of engineering designers in practice, and secondly, from the use of the IDEF1X modeling technique.

Using twenty case studies, the diagrams are demonstrated in real design situations. In particular, the paper focuses on the access paths or routes undertaken during a number of different design activities; for example, original, adaptive and variant design; simple and complex designs, design and selection tasks; and new and previously done designs. Subsequent observations are used to recommend areas for future research.
Engineering Decision Support System (EDSS)
Authors: Herling Derald , Ullman David G. , D’Ambrosio Bruce
Published: March 2021

Engineers, as well as other decision makers, are required to make many decisions as they are designing a product or resolving a problem. At these decision points there are many alternatives and criteria to be considered. Studies of design sessions show that most decisions made during these times are in an ad hoc manner. Greater understanding of the mechanical design process, data representation for collaborative design and probabilistic inferences have allowed the creation of a computer decision support program, called Engineering Decision Support System (EDSS), that addresses the special needs of design engineers.1 This paper introduces this work, which is still in the developmental stages.
A Consideration of Applying QFD to Concurrent Engineering Processes of Automobile Development
Authors: Tsuda Yasuhisa
Published: March 2021

As a tool to present the systematic application of QFD to product development, a “two-storied quality chart” model is conceived which the project team prepares with the support of functional departments. To consider the progress of time, this chart is further developed to contain two parts, one to be provided for the new development and the other relying on data accumulated in the past. Furthermore a “parallel flow quality chart” is conceived, considering the job sharing between the project team and functional departments. By means of these concept models it is made clear that the development activities pushed forward simultaneously by many departments can be separately treated as individual quality deployment in each department. In this way the application of QFD to a complicated product development, in which many departments are involved, is made much easier.
A Flexible, Interactive Integration Architecture for Extraction of CAPP Information From CAD
Authors: Hayes C. C.
Published: March 2021

This paper describes CHAMP, a conceptual architecture designed to support the task of passing information from computer-aided design systems to computer-aided process planning systems.1 Current integration systems are lacking in the flexibility of both their information-exchange mechanisms and in their control structures. The result is a sacrifice in the efficiency of solutions produced. The proposed architecture is based on models of human process planning, and aims to improve the effectiveness of CAD/CAPP integration by providing more flexible communications and control structures through shared blackboards, and by providing a mechanism for reasoning about intermediate solution states. The architecture is intended to summarize the current understanding of the CAD/CAPP integration task and to elucidate areas where further research is required.
Nonstationary Response of a Two-Degrees-of-Freedom Nonlinear Ship Model Under Modulated Excitation
Authors: Pan Ruigui , Davies Huw G.
Published: March 2021

Nonstationary response of a two-degrees-of-freedom system with quadratic coupling under a time varying modulated amplitude sinusoidal excitation is studied. The nonlinearly coupled pitch and roll ship model is based on Nayfeh, Mook and Marshall’s work for the case of stationary excitation. The ship model has a 2:1 internal resonance and is excited near the resonance of the pitch mode. The modulated excitation (F0 + F1 cos ωt) cosQt is used to model a narrow band sea-wave excitation. The response demonstrates a variety of bifurcations, loss of stability, and chaos phenomena that are not present in the stationary case. We consider here the periodically modulated response. Chaotic response of the system is discussed in a separate paper.

Several approximate solutions, under both small and large modulating amplitudes F1, are obtained and compared with the exact one. The stability of an exact solution with one mode having zero amplitude is studied. Loss of stability in this case involves either a rapid transition from one of two stable (in the stationary sense) branches to another, or a period doubling bifurcation. From Floquet theory, various stability boundary diagrams are obtained in F1 and F0 parameter space which can be used to predict the various transition phenomena and the period-2 bifurcations. The study shows that both the modulation parameters F1 and ω (the modulating frequency) have great effect on the stability boundaries. Because of the modulation, the stable area is greatly expanded, and the stationary bifurcation point can be exceeded without loss of stability. Decreasing ω can make the stability boundary very complicated. For very small ω the response can make periodic transitions between the two (pseudo) stable solutions.
The Applicability of Fuzzy Control for Flexible Mechanisms
Authors: Beale David G. , Lee Shyr Wen
Published: March 2021

The nonlinear nature of high speed, flexible rod mechanisms has been previously confirmed, both experimentally and analytically. Therefore, sound control system design of flexible mechanisms must necessarily be based on nonlinear control. Active control via fuzzy logic is assessed as a means to suppress the elastic transverse bending vibration of a flexible rod of a slider crank mechanism of a slider crank mechanism. Several pairs of piezoelectric elements are used to provide the control action. Sensor output of deflection is fed to the fuzzy controller, which determines the voltage input to the actuator. A three mode approximation is utilized in the simulation study. Computer simulation shows that fuzzy control can be used to suppress bending vibrations at high speeds.
Effects of Flexible Supports and Gyroscopic Moments on Passage of a Cracked Shaft Through a Critical Speed
Authors: Suherman Surjani , Plaut Raymond H.
Published: March 2021

The motion of a cracked shaft with a rigid disk is analyzed as the system is accelerated or decelerated past the lowest critical speed. New features are the inclusion of flexible supports at the ends of the shaft and the gyroscopic effects of the disk. The supports are modeled with elastic springs and dashpots. Eccentricity of the disk, gravitational forces, and internal and external damping are also included. The shaft contains a single transverse crack that is assumed to be either completely open or completely closed at any given time, depending on the curvature of the shaft at the cross section containing the crack. The maximum response is computed numerically, and the influence of the gyroscopic moments and the spring and damping coefficients at the supports is investigated.
Two-to-One Internal Resonances in Buckled Beams
Authors: Kreider Wayne , Nayfeh Ali H. , Chin Char-Ming
Published: March 2021

The vibrations of buckled beams with two-to-one internal resonances (ω2 ≈ 2ω1) about a static buckled position are analyzed. General boundary conditions and harmonic excitations (frequency Ω) in both the transverse and axial directions are considered. The analysis assumes a unimodal static buckled deflection, considers quadratic nonlinearities only, and determines the amplitude and phase modulation equations via the method of multiple scales. The following specific cases are treated: Ω ≈ 2ω2, Ω ≈ ω1 + ω2, and Ω ≈ ω1. From the modulation equations for a primary resonance of the second mode (i.e., Ω ≈ ω2), one-mode and two-mode stable equilibrium solutions are found in addition to dynamic solutions caused by Hopf bifurcations. In the region of dynamic solutions, a variety of phenomena are documented, including period-doubling bifurcations, intermittency, chaos, and crises.
Chaotic Amplitude Dynamics for Parametrically Excited Systems With Quadratic Nonlinearities
Authors: Banerjee Bappaditya , Bajaj Anil K.
Published: March 2021

Dynamical systems with two degrees-of-freedom, with quadratic nonlinearities and parametric excitations are studied in this analysis. The 1:2 superharmonic internal resonance case is analyzed. The method of harmonic balance is used to obtain a set of four first-order amplitude equations that govern the dynamics of the first-order approximation of the response. An analytical technique, based on Melnikov’s method is used to predict the parameter range for which chaotic dynamics exist in the undamped averaged system. Numerical studies show that chaotic responses are quite common in these quadratic systems and chaotic responses occur even in presence of damping.
Estimating Ljapunov-Exponents Using the Generalized Cell Mapping Method
Authors: Schaub Swen , Schiehlen Werner
Published: March 2021

Ljapunov-Exponents are widely used to characterize the local stability of dynamical systems. On the other hand, Cell Mapping methods provide an effective numerical tool for global study by a probabilistic description of the time evolution. Using this description together with powerful interpolation techniques, an iterative method for global stability analysis with estimated Ljapunov-Exponents for all coexisting attractors of nonlinear dynamical systems is presented.
Numerical Formulation of Nonlinear Vibrations of Elastically-Constrained Rotating Disks
Authors: Yang Longxiang , Hutton Stanley G.
Published: March 2021

An analysis of nonlinear vibrations of an elastically-constrained rotating disk is developed. The equations of motion, which are two coupled nonlinear partial differential equations corresponding to the transverse force equilibrium and to the deformation compatibility, are first developed by using von Karman thin plate theory. Then the stress function is analytically solved from the compatibility equation by assuming a multi-mode transverse displacement field. Galerkin’s method is applied to transform the force equilibrium equation into a set of coupled nonlinear ordinary differential equations in terms of time functions. Finally, numerical integration is used to solve the time governing equations, and the effects of nonlinearity on the vibrations of a rotating disk are discussed.
A Nonlinear Normal Mode Approach for Studying Waves in Nonlinear Monocoupled Periodic Systems
Authors: Vakakis A. F. , King M. E.
Published: March 2021

The free dynamics of a mono-coupled layered nonlinear periodic system of infinite extent is analyzed. It is shown that, in analogy to linear theory, the system possesses nonlinear attenuation and propagation zones (AZs and PZs) in the frequency domain. Responses in AZs correspond to standing waves with spatially attenuating, or expanding envelopes, and are synchronous motions of all points of the periodic system. These motions are analytically examined by employing the notion of “nonlinear normal mode,” thereby reducing the response problem to the solution of an infinite set of singular nonlinear partial differential equations. An asymptotic methodology is developed to solve this set. Numerical computations are carried out to complement the analytical findings. The methodology developed in this work can be extended to investigate synchronous attenuating motions of multi-coupled nonlinear periodic systems.
The Dynamics of Viscoelastic Links in Mechanisms
Authors: Buculei Mihai I. , Marghitu Dan B.
Published: March 2021

The main objective of this study is to develop an analytical model that incorporates the effect of the general motion on the vibration of elastic elements in kinematic mechanisms. Equations for the translational and rotational motions of the links are developed applying Hamilton’s principle. Kinetic energy that is required for the application of this principle has been derived by utilizing a generalized velocity field theory for elastic solids. This approach provides means to include the inertia terms directly in the equations of motion. Effects such as centrifugal stiffening and vibrations induced by Coriolis forces are accommodated automatically, rather than with the aid of ad hoc provisions. We use Alfrey and Lee analogy to solve the dynamic problem of viscoelasticity.
Safety Enhancement of Hysteretic Structures Through Active Control
Authors: Li Peng , Aug Alfredo H.-S.
Published: March 2021

A new control algorithm is developed for hysteretic structures. The performance function is chosen to minimize the structural damage. Numerical examples are presented to show the effectiveness of the proposed control algorithm. It is noted that the algorithm could improve the control efficiency in terms of reducing the required total control energy or maximum control forces without sacrificing the structural safety.
Stabilization by Random Vibration
Authors: Wihstutz Volker
Published: March 2021

We consider the control system ẋ = Ax + Bu with stochastic mean zero high gain feedback control u. The classes of stochastic processes which can stabilize the trivial solution x = 0 depend on the rank of B. For rank B = 1 we characterize, in particular, the class of noise which stabilizes the originally unstable equilibrium of the linearized inverted pendulum.
On the Identifiability of Structural Systems
Authors: Skelton Robert E. , Shi Guojun
Published: March 2021

An identifiability result determines whether there exists a linear time invariant model capable of matching the input/output data observed from experiments. If no match is possible, a method is presented to find the closest linear model to the data. A weighted q-Markov COVER method is introduced for identification.
Dynamic Reliability of Nonlinear Systems Under Random Excitation
Authors: Colonius Fritz , Häckl Gerhard , Kliemann Wolfgang
Published: March 2021

Reliability theory analyzes failure phenomena in systems, leading to maintenance and replacement schedules as well as risk assessment and other topics. Dynamic reliability takes into account the (possibly nonlinear) dynamics of the system and of the random excitation that may lead to failure. It is shown, how some of the concepts of reliability theory can be interpreted in the dynamical systems context. Analytical results are derived for failure probabilities, for life time distributions, asymptotic damage accumulation rates, and other relevant concepts. The Takens-Bogdanov oscillator and a model for ship roll motion are analyzed in detail, together with a thorough description of the numerical methods that are available for dynamic reliability studies.
Evaluation of Surface Vibrations in the Low and High Frequency Domain
Authors: Fischer Peter , Pradlwarter Helmut J. , Schuëller Gerhart I.
Published: March 2021

The frequency domain of many problems in structural dynamics encompasses a wide range, covering nearly static behavior up to vibration flow characteristics similar to heat transfer. This work presents an uniform approach for low and high frequency vibration analysis, which is based on Finite Element modeling of the structure. Vibrations in the low frequency range are determined by an efficient superposition technique of complex modes, which accounts accurately for any linear damping effect. The modal method is extended to the high frequency domain by applying different levels of averaging to the response and eigenfrequencies and by the introduction of random properties of modeshapes. The high frequency domain is defined by the size of the Finite Elements, i.e. short wave lengths of high frequency modeshapes cannot be represented by the FE-model. The response computation of isolated structures is extended to substructures of complex systems by prescribing stochastic multi-support base excitation at the substructure boundaries. It may be noted, that the presented approach of stochastic high frequency dynamics contains, as special cases, the expressions of the structural response of Statistical Energy Analysis, Bolotin’s integral method and the results of Asymptotic Modal Analysis.
Vibration-Induced Loosening and Tightening of Threaded Fasteners
Authors: Hess Daniel P.
Published: March 2021

Previous analyses of threaded fasteners under vibration are based on static equilibrium conditions with supporting data limited to low frequency loading. Such analyses predict only a net loosening action. This paper presents a dynamic model of a single-bolt assembly with moderate pre-load subjected to axial harmonic vibration. Simulations with this model predict that threaded fasteners can, on the average, loosen or tighten in the presence of vibration; and that the applied vibration, as well as other system parameters, can be tuned so that either action occurs. The model elucidates the nonlinear interaction of friction and vibration of such systems. Measurements from a single-bolt assembly apparatus are presented and compared with the simulations.
Friction-Induced Vibration of Multi-Degree of Freedom Sliding Subsystems
Authors: Rorrer Ronald A. L.
Published: March 2021

The purpose of this investigation is to develop an appropriate model for the friction-induced vibration of a tribological system, where there is at least an order of magnitude difference in the stiffness between the mating subsystems. The significance of this system is that neither system can analytically be considered rigid or aspects of the dynamics that are exhibited experimentally are lost. This leads to the necessity of creating a multi-degree of freedom model, where the multiple degrees of freedom are distributed between the two systems. Experiments have shown that both subsystems contribute to the dynamical response. The modeling starts with the simplest system model, in terms of degrees of freedom, and then progresses to the level required to demonstrate the experimentally observed behavior. An example of such a system is an elastomer sliding against a steel counterface. It has been observed on a variety of dissimilar test devices (linear and rotational) that the subsequent response contains similar dynamical behavior relative to friction-induced vibration. The striking similarities of the dynamic behavior is demonstrated in the friction(time) response, which is subsequently evidenced in the autospectra of friction with an identifiable characteristic form. Specifically, with the exception of scaling in amplitude and frequency, due to system differences, the autospectrum are contained within a characteristic envelope that is determined by both subsystems. While not specifically attempting to model any particular test device or system, representative values of stiffness and estimated friction (velocity) relationships have been incorporated to lend realism to the models.
Chain Dynamics
Authors: Pfeiffer Friedrich
Published: March 2021

Chains are important machine components being applied in cars, in gears and in armoured vehicles. The dynamics of chains typically is characterized by free motion and by contact processes, which may include impacts and friction. Therefore modeling by multibody theory augmented by methods of contact mechanics represents an appropriate way to evaluate the dynamical chain behaviour. Paper gives some examples.
On Self-Excited Friction Vibrations in Brakes
Authors: Gekker Fedor R. , Khairaliev Serik I.
Published: March 2021

Dynamic processes in machines resulting from the interaction between rough rubbing surfaces are called self-excited friction vibrations in the theory of vibrations. Such vibrations are generated in machines brakes, causing the instability of then-operation and various noise effects.
Pattern Changes of Time-Shifted Vibration Signals on Wavelet Time-Scale Maps
Authors: Chen Da Jun , Wang Wei Ji
Published: March 2021

As a multi-resolution signal decomposition and analysis technique, the wavelet transforms have been already introduced to vibration signal processing. In this paper, a comparison on the time-scale map analysis is made between the discrete and the continuous wavelet transform. The orthogonal wavelet transform decomposes the vibration signal onto a series of orthogonal wavelet functions and the number of wavelets on one wavelet level is different from those on the other levels. Since the grids are unevenly distributed on the time-scale map, it is shown that a representation pattern of a vibration component on the map may be significantly altered or even be broken down into pieces when the signal has a shift along the time axis. On contrary, there is no such uneven distribution of grids on the continuous wavelet time-scale map, so that the representation pattern of a vibration signal component will not change its shape when the signal component shifts along the time axis. Therefore, the patterns in the continuous wavelet time-scale map are more easily recognised by human visual inspection or computerised automatic diagnosis systems. Using a Gaussian enveloped oscillation wavelet, the wavelet transform is capable of retaining the frequency meaning used in the spectral analysis, while making the interpretation of patterns on the time-scale maps easier.
An Accelerated Retarded Potential Method for Time Dependent Acoustic Wave Scattering
Authors: Abboud Toufic S. , Gharib Joseph M. , Nédélec Jean Claude , Sayah Toni G.
Published: March 2021

We are interested in the numerical approximation of the problem of the scattering of a transient acoustic plane wave by a bounded obstacle in IR2 or IR3, using the boundary integral equation method. In the frequency domain it has been recently developed a boundary finite element method where the mesh size is like O(λ1/3) instead of O(λ) (λ is the wavelength) and where the obstacle is convex. This paper presents the implementation of the idea on the retarted potential representation.
Coupled Finite Element/Boundary Element Method for the Analysis of the Acoustic Scattering From Elastic Structures
Authors: Dubus Bertrand , Lavie Antoine , Decultot Dominique , Maze Gérard
Published: March 2021

Considerable interest has been expressed recently in the scattering of acoustic waves from elastic targets. For structures of arbitrary shapes, the numerical method relying upon a finite element description of the solid part and a boundary element description of the waves propagating in the infinite fluid medium is the most commonly used. This paper presents a coupling between the ATILA finite element code and the EQI boundary element code performed using a solid variable methodology. Results are presented for a thin cylindrical shell bounded by hemispherical endcaps which are insonified at axial and normal incidences. Comparisons are made with measurements of backscattered pressure spectra and angular patterns obtained with the quasi-harmonic MIIR (Method of Isolation and Identification of Resonances). Emphasis is put on post-processing techniques contributing to the interpretation of physical phenomena such as the extraction of resonant mode shapes.
Transient Infinite Elements for Acoustics and Shock
Authors: Cipolla Jeffrey L.
Published: March 2021

Many phenomena in acoustically loaded structural vibrations are better understood in the time domain, particularly transient radiation, shock, and problems involving nonlinearities and bulk structural motion. In addition, the geometric complexity of structures of interest drives the analyst toward domain-discretized solution methods, such as finite elements or finite differences, and large numbers of degrees of freedom. In such methods, efficient numerical enforcement of the Sommerfeld radiation condition in the time domain becomes difficult; although a great many methodologies for doing so have been demonstrated, there seems to exist no consensus on the optimal numerical implementation of this boundary condition in the time domain.

Here, we present theoretical development of several new boundary operators for conventional finite element codes. Each proceeds from successful domain-discretised, projected field-type harmonic solutions, in contrast to boundary integral equation operators or those derived from algebraic functions. We exploit the separable prolate-spheroidal coordinate system, which is sufficiently general for a large variety of problems of naval interest, to obtain finite element-like operators (matrices) for the boundary points. Use of this coordinate system results in element matrices that can be analytically inverse transformed from the frequency to the time domain, using appropriate approximations, without altering the Hilbert space in which the approximate solution resides. The inverse transformation introduces some additional theoretical issues involving time delays and Stieltjes-type integrals, which are easily resolved. In addition, use of element-like boundary operators does not alter the banded structure of the system matrices, which is of enormous importance for efficient solution of large problems.

Results presented here include theoretical derivation of the new “infinite elements”, the approximations for certain problematic frequency-domain terms, resolution of the inversion issues, and element matrices for the boundary operators which introduce no new continuity requirements on the fluid field variable.
Practical Applications of Scale Independent Elements
Authors: Ettouney Mohammed M. , Daddazio Raymond P. , Abboud Najib N.
Published: March 2021

Discrete deterministic methods such as finite elements offer great flexibility in analyzing the dynamic response of vibrating systems. However, these methods can easily grow beyond available computer resources as frequencies of interest grow higher. In this paper we present a new approach for the frequency domain dynamic analysis of structures. A theory is developed for the analysis of systems which are uniform along a single coordinate axis but otherwise arbitrary in geometry and material composition. This approach, termed the Scale Independent Element, is shown to be an accurate, efficient and general method for the analysis of vibrating systems. This technique extends the applicability of discrete deterministic finite element based modeling to higher frequencies and is capable of bridging the gap to frequency regimes where statistical energy methods become applicable.
Progress in Applying the Surface Variational Principle to Analyze Acoustic Radiation From Slender Elastic Bodies
Authors: Wu Kuangcheng , Ginsberg Jerry H.
Published: March 2021

The surface variational principle (SVP) has been developed as a method for gaining analytical-type results for radiation and scattering from submerged bodies whose shape does not suit classical techniques for analyzing the Helmholtz equation. The approach employs Ritz series expansions for surface pressure and velocity in the frequency domain. The relation between the series coefficients is obtained by extremizing the SVP functional. The present work extends the earlier developments to the case of an axisymmetric elastic shell that is subjected to an arbitrary excitation. The surface pressure and normal velocity are represented as a sequence of surface waves that are the trace of the waves in the surrounding fluid medium. SVP is used to determine the wavenumber spectrum of pressure amplitudes generated by a specific wave having unit velocity amplitude. The structural displacement field is represented by Ritz expansions, and equations governing the generalized coordinates associated with these series are obtained by invoking Hamilton’s principle. Difficulties in satisfying the continuity conditions at the apexes are circumvented by mapping the eigenmodes for a spherical shell into the variable representing position along the meridian of the shape generator. The structural dynamic equations are coupled to the SVP equations by matching the normal velocity in the fluid to the time derivative of the normal displacement, as well as using the series expansion for surface pressure to form the contribution of the pressure to the generalized forces. Results for a spherical shell subjected to a trans erse point force at the equator, which is a nonaxisymmetric representation of the excitation, are compared with analytic results. Predictions for a hemi-capped cylindrical shell are compared to those obtained from SARA-2D (Allik, 1991), which is a finite/infinite element program. In addition to providing validation of the SVP implementation, each set of results is used to illustrate the convergence and error measures provided by an SVP analysis.
Incorporating Compressional and Shear Wave Types Into Fuzzy Structure Models for Plates
Authors: Rochat Judith L. , Sparrow Victor W.
Published: March 2021

Although realistic complex structures are usually difficult to model theoretically, fuzzy structure theory enables one to produce such a model without a detailed knowledge of the entire structure. Using the theory established by Pierce et al. [A. D. Pierce, V. W. Sparrow, and D. A. Russell, J. Vib. Acoust. (to be published), also ASME 93-WA/NCA-17.] regarding fundamental structural-acoustic idealizations for structures with imprecisely known or fuzzy internals, the effects that fuzzy attachments have on different wave types in a primary (or master) structure are examined in this paper. In the theory by Pierce et al., the primary structure that undergoes vibrations is a thin plate mounted in an infinite baffle. On one side of the plate are fuzzy attachments, represented as an array of attached mass-spring-dashpot systems, which are excited by an incident plane pulse. This known theory explains the effects of these attachments on bending waves in the plate. In this paper, the theory is extended to isolated compressional and shear waves in a plate. While studying this new problem, it is discovered that coupling effects occur when the plate and attachment properties are not uniform in the direction perpendicular to the wave propagation. Hence, unlike the bending wave theory which models a finite thin plate with point attached oscillators, the new wave type theory uses a thin plate infinite in one direction with line attached oscillators also infinite in the same direction. For both the compressional and shear waves, it is found that the fuzzy attachments add an apparent frequency dependent mass and damping to the plate. These results are similar to those for the bending wave theory.
Signature Features in Returned Echoes From Submerged Targets Insonified by Short, Broadband Pulses: Comparison of Experiments and Theory
Authors: Ståhlsten Torbjörn , Strifors Hans C. , Gaunaurd Guillermo C.
Published: March 2021

Backscattered echoes are studied from submerged elastic targets in the frequency domain and combined time-frequency domain when the targets are insonified by short, broadband sound pulses. The targets are either an air-filled spherical shell or various solid brass or steel spheres. The incident waveform is generated by weighting a sinusoidal signal with a Blackman time-window of a few cycles width. The spectrum is computed from each recorded set of experimental data and the result is shown to agree well with the theoretical prediction for the corresponding target and interrogating waveform. An advantage of the time-frequency approach is that target signatures can show the time evolution of the resonance features that identify each target. Experimentally obtained data are processed in the time-frequency domain using a pseudo-Wigner distribution (PWD). The associated time-window is Gaussian, and its width is adjusted to suppress the interference of cross-terms in the PWD, yet retaining the desired property of time-frequency concentrating the extracted features.