bluuebunny/crossref_metadata_2025 huggingface dataset:
Bond durability of universal adhesives to intact enamel surface in different etching modes
Authors: Suzuki Miho , Takamizawa Toshiki , Hirokane Eizo , Ishii Ryo , Tsujimoto Akimasa , Barkmeier Wayne W , Latta Mark A , Miyazaki Masashi
Published: March 2021

This study aimed at determining the enamel bond durability of universal adhesives to intact enamel (IE) and ground enamel (GE) in different etching modes under thermal cycling (TC) and fatigue stresses. Two universal adhesives and a two‐step self‐etch adhesive were used. Enamel specimens were divided into four groups by treatment: (i) GE in etch‐and‐rinse, (ii) IE in etch‐and‐rinse, (iii) GE in self‐etch, and (iv) IE in self‐etch. Bonded specimens were subjected to TC, and then shear bond strengths (SBS) were conducted. SBS tests were also conducted after storage in 37°C water for 24 h (baseline). For shear fatigue strength (SFS) testing, bonded specimens were subjected to fatigue stress at a frequency of 10 Hz for 50,000 cycles. At baseline, all adhesives showed significantly higher SBS values with GE than IE in self‐etch mode in contrast to in etch‐and‐rinse mode. After TC, the universal adhesives with IE showed lower SBS values than the baseline, regardless of the etching mode. Universal adhesives showed significantly lower SFS values with IE in etch‐and‐rinse, but not in self‐etch mode. Phosphoric acid pre‐etching or grinding of the aprismatic enamel may be helpful in establishing reliable initial and long‐term bonds to enamel when using universal adhesives in self‐etch mode.
Avoidance of dental appointment due to cost and consequences for oral health‐related quality of life: 25‐yr follow‐up of Swedish adults
Authors: Åstrøm Anne Nordrehaug , Lie Stein Atle , Mastrovito Berit , Sannevik Josefin
Published: March 2021

We explored how socio‐demographic and personal characteristics contribute to avoidance of dental appointment due to cost over time from age 55 (in 1997) to 75 (in 2017) and assessed the implications for oral health‐related quality of life. In 1992, 6346 residents born in 1942 consented to participate in a prospective questionnaire survey, and 3060 (48.2%) of them completed postal follow‐ups every fifth year until 2017. Oral health‐related quality of life was assessed using the Oral Impact on Daily Performance inventory. The frequency of avoidance of dental appointment due to cost declined from 7.0% (in 1997) to 5.4% (in 2017), whereas the frequency of oral impacts declined from 26.0% in 2007 to 24.0% in 2017. Generalized Estimating Equation models revealed that avoidance of dental appointments due to cost was more likely reported in 1997 (OR: 1.5: 1.2–1.8) than in 2017, more likely in low educated people, and less likely in those using private dental care services. Avoidance of dental appointment due to cost was associated with impaired oral health‐related quality of life. Social inequalities in avoidance of dental appointment due to cost and oral impacts did not vary across time but persisted into older ages despite the dental health care reforms that had been implemented.
The effect of COVID‐19 stay‐at‐home order and campus closure on the prevalence of acute respiratory infection symptoms in college campus cohorts
Authors: Adenaiye Oluwasanmi , Bueno de Mesquita Paul Jacob , Wu Qiong , Hong Filbert , Lai Jianyu , Chen Shuo , Milton Donald K. ,   Prometheus@UMD Consortium
Published: March 2021

Evaluation of population‐based COVID‐19 control measures informs strategies to quell the current pandemic and reduce the impact of those yet to come. Effective COVID‐19 control measures may simultaneously reduce the incidence of other acute respiratory infections (ARIs) due to shared transmission modalities. To assess the impact of stay‐at‐home orders and other physical distancing measures on the prevalence of ARI‐related symptoms, we compared symptoms reported by prospective college cohorts enrolled during two consecutive academic years. ARI‐related symptoms declined following campus closure and implementation of stay‐at‐home orders, demonstrating the impact of population‐based physical distancing measures on control of a broad range of respiratory infections.
Frequency of rare, serious donor reactions: International perspective
Authors: Young Pampee , Crowder Lauren , Steele Whitney , Irving David , Pink Joanne , Kutner Jose Mauro , Yokoyama Ana Paula Hitomi , Van Buren Nancy , O'Sullivan Nicholas William , Sayers Merlyn , Alcantara Ramir Moreno , van den Hurk Katja , Wiersum‐Osselton Johanna , Shaz Beth ,   the Biomedical Excellence for Safer Transfusion (BEST) Collaborative
Published: March 2021

Background

Severe blood donor adverse events are rare, but due to their rarity studying them can be difficult. To get an accurate estimate of their frequency and rate in the donor population it may be necessary to combine donation data across countries.

Study Design and Methods

International blood collection organizations (BCOs) provided data on rare/severe donor reactions as well as denominator information for their donor populations from 2015 to 2017. Donor reactions were classified using standardized definitions.

Results

BCOs from six countries provided reaction data for more than 22 million donations. A total of 480 rare reactions were reported of which 76.7% were imputed as definite and 11% probable. Rates of rare reactions were higher in females and first‐time donors. Systemic rare reactions were the most common reaction type, accounting for over three quarters of reactions reported. Of systemic reactions, vasovagal reactions with loss of consciousness and injury or off‐site (n = 350) made up the majority and occurred 1.53 per 100,000 donations. For the 22.3% that were localized reactions, the majority of these were cellulitis (n = 71, 0.31 per 100,000 donations) followed by deep venous thrombosis (n = 21, 0.09 per 100,000 donations).

Conclusion

Pulling together data from multiple BCOs across countries allows for a better understanding of rare reactions, such as vasovagal reaction with injury or cellulitis, and for generating a reliable incidence rate for air embolism or compartment syndrome. However, gaps remain due to missing elements such as unknown donor status or location of reaction.
Approximation and Derivatives of Probability Functions in Probabilistic Structural Analysis and Design
Authors: Marti K.
Published: March 2021

Yield stresses, allowable stresses, moment capacities (plastic moments), external loadings, manufacturing errors are not given fixed quantities in practice, but have to be modelled as random variables with a certain joint probability distribution. Hence, problems from limit (collapse) load analysis or plastic analysis and from plastic and elastic design of structures are treated in the framework of stochastic optimization. Using especially reliability-oriented optimization methods, the behavioral constraints are quantified by means of the corresponding probability ps of survival. Lower bounds for ps are obtained by selecting certain redundants in the vector of internal forces; moreover, upper bounds for ps are constructed by considering a pair of dual linear pro-prams for the optimizational representation of the yield or safety conditions. Whereas ps can be computed e.g. by sampling methods or by asymptotic expansion techniques based on Laplace integral representations of certain multiple integrals, efficient techniques for the computation of the sensitivities (of various orders) of ps with respect to input or design variables have yet to be developed. Hence several new techniques are suggested for the numerical computation of derivatives of ps.
A New Algorithm for Combinatorial Optimization
Authors: Gadallah M. H. , ElMaraghy H. A.
Published: March 2021

A new algorithm for combinatorial search optimization is developed. This algorithm is based on orthogonal arrays as planning schemes and search graph techniques as representation schemes. Based on the algorithm, a discrete formulation is given to model two search domains. As an application, the algorithm is used to deal with the problem of least cost tolerance allocation with optimum process selection. Studies are performed to compare between different orthogonal array and column assignment and number of design levels with respect to optimum. The proposed algorithm is capable of dealing with continuous, discrete linear and nonlinear functions and is validated by test cases versus other local and global search methods.
PCB Layout Design Using a Genetic Algorithm
Authors: Jain Sakait , Gea Hae Chang
Published: March 2021

This paper presents an approach to find the optimal design layout of chips on a circuit board in a manner that minimizes the area covered on the board and the connections between the various chips. In addition, there are no major heat sources next to each other and certain physical constraints are satisfied while finding a layout design. In this approach, the whole circuit board area is divided into a finite number of cells for mapping it into a genetic algorithm chromosome. The mutation and crossover operators have been modified and are applied in conjunction with connectivity analysis for the chips to reduce the creation of a lot of faulty generations. Examples of GA based chip layout are presented to show how each of the objectives are attained separately followed by examples to arrive at layouts using multiple objectives.
Modelling Hard Stops and Joint Clearances in Multibody Systems
Authors: Mehra A. , Shivaswamy S. , Lankarani H. M.
Published: March 2021

Multibody mechanical systems that have hard stops or joint clearances, encounter changes in the system kinematic structure. Due to the joint clearances or hard stops, internal impacts within the joint geometry occur. As a result of these impacts, nonlinear contact forces of unknown nature are created, which act and disappear over a short period of time. These forces or their corresponding impulses are transmitted throughout the system. In this paper, a methodology for treatment of multibody mechanical systems with hard stops and joint clearances is discussed. The methodology is based on the development of different contact force models that include energy absorption, with which a continuous analysis of the system undergoing internal impact is performed. The concept of effective masses is used to take into account the effect of the entire system rather than the link or the joint that encounters a discontinuous motion. The methodology is more suitable than the conventional impulse / momentum formulation in its treatment of multiple impacts and it guarantees accurate solutions no matter how hard or soft the stops are. The method discussed is applied to a point follower mechanism and an aircraft landing gear latch mechanism.
Pipe Self-Reinforcing Outlets: Nonlinear Analysis Towards Rational Design
Authors: Carino Claudio , Carli Fabio , Cinquini Carlo , Gobbi Mauro
Published: March 2021

A class of self-reinforcing outlets addressed to a wide variety of plants and pipelines is analyzed in this paper in order to examine computer simulation in comparison with bursting tests commonly adopted in industry. Based on a specific pre-processor for mesh generation, finite element analysis is performed on a workstation by a software package suitably accounting for both geometrical and material nonlinearities. Besides stress distribution visualization, high-resolution post-processor capability allows to predict, with sufficient accuracy, plastic strain trend in critical area. This may provide, on the one hand, a powerful tool in view of anticipating proof testing results and, on the other hand, a useful guideline for design purposes in view of a more rational material usage and joint configuration, paying particular attention to the overall structural reliability and performance.
Design and Analysis of the Selective Compliance Device for Stacking Machine
Authors: Chang Sun-Lai
Published: March 2021

An innovative concept of the remote center semi-passive device for the material handling machine has been introduced. This device is used to adjust the final position and/or orientation of a package passively and quickly so that this package can fit into the package stack corner. In this paper, we have designed a double-pantograph mechanism to adjust the position of the package. We have also introduced the idea of using a four-bar linkage to remote the rotation center of the package so that the orientation can be adjusted passively. The workspace of such a device has been analyzed. The dimension has also been synthesized by optimization. Using this mechanism, the force control can be avoided and the control of this device becomes a feed-forward control. It is believed that its implementation will result in low cost, high speed, better stability and space efficiency of the package stack.
Probabilistic Design Methodology and the Application of Probabilistic Fault Tree Analysis to Machine Design
Authors: Onyebueke Landon C. , Onwubiko Chinyere , Chen Feng C.
Published: March 2021

This paper gives an overview of Probabilistic Design Methodology (PDM) with emphasis on quantification of the effects of uncertainties for structural variables and the evaluation of failure probability. The application of Probabilistic Fault Tree Analysis (PFTA) to the design of a shaft carrying a spur gear is also presented. The PFTA includes the development of a fault tree to represent the system, construction of an approximation function for bottom events, computation of sensitivity factors of design variables, and the calculation of the system reliability. The computer code employed for the analyses is known as “Numerical Evaluation of Stochastic Structures Under Stress” (NESSUS). NESSUS is developed under NASA probabilistic structural analysis program.
Modeling Manufacturing Quality Constraints for Product Development
Authors: Ho Christopher M. , Otto Kevin N.
Published: March 2021

When bringing a new or improved product to market, a design and manufacturing enterprise can speed the process and improve the result by understanding and designing within the manufacturing process used. We propose process characterization modeling and experiments aimed at uncovering their effect upon product functional requirement metrics. In a real industrial design and manufacturing enterprise, however, modeling and experiments are limited to activities that provide direct answers to short term real identified problems. This means that only a continuous improvement approach is practical to construct process constraint models. We demonstrate a methodology to quantify the quality constraints imposed on a product design by its manufacturing process.

We start with the sequence of operations transforming the incoming material into the final product, which is diagrammed into a topology of the operational sequence. Performance metrics are then identified which correspond to the customer requirements. Using engineering analysis, a basic model is developed relating known product and material variables to the metric. Production data, either from designed experiments or from natural variation occurring during production, are measured to validate the basic model. Next, each operation in the process topology is analyzed for potential effect upon the model. Modes of impact of each operation upon the metric are conceived, and quantified into the basic model. These modes become either supported or not by the production data. The methodology, therefore, is one of continuously improving the understanding of the process imposed constraints to improve the product. We demonstrate the methodology with a running example, characterizing the process imposed constraints upon a low temperature co-fired ceramic circuit assembly.
Turning Sketches Into Working Geometry
Authors: Stahovich Thomas F. , Davis Randall , Shrobe Howard
Published: March 2021

We describe a program called SketchIT that uses a description of desired behavior to transform a sketch of a mechanical device into a “BEP-Model,” a parametric model with constraints that ensure the device produces the desired behavior. The program also generates alternative implementations for the design, each of which is represented as a BEP-Model. The program is based on qualitative configuration space, a novel representation for mechanical behavior.
Kinematic Simulation Using Qualitative Mechanism Models
Authors: Liu Jihong , Igoshi Masanori , Arai Eiji
Published: March 2021

When trying to use computers to aid designers at the conceptual design stage, it becomes clear that many traditional methods and support tools are incompetent because they mainly deal with sufficient and quantitative information. However, at the conceptual design stage, information is insufficient and mostly qualitative. The focus of this paper is on representing and reasoning about the geometry and motion of physical objects for mechanical conceptual design. A new concept, called qualitative spatial relation space (QSRS), is introduced to describe mechanisms of mechanical products by referring to the qualitative spatial relations between their components. A qualitative kinematic simulation system has been implemented to enable verification of functions of products at the conceptual design stage. The system derives motions of components caused by other components’ specified motions from the qualitative structural descriptions of products, and puts brief and comprehensible functional interpretations of products.
Near Optimal Approach to General Manufacturing Feature Extraction
Authors: Dong Jian (John) , Vijayan Sreedharan
Published: March 2021

Computers are being used increasingly in the process planning function. The starting point of this function involves interpreting design data from a CAD model of the designed component Feature-based technology is becoming an important tool for this. Automatic recognition of features and extraction of feature information from CAD data can be used to drive a process planning system. In this paper a new approach to automatic feature extraction called the Blank-Surface Concave-edge (BS-CE) approach is illustrated. This approach attempts to remove as much of the blank material with a given machine setup as possible. Hence intuitively one can say that the manufacturing cost of material removal may be minimized if this technique is employed. This feature extraction method is explained along with examples of its implementation. An analysis of alternate feature extraction results is performed and the cost of manufacture is compared to demonstrate the near optimal performance of this technique.
Off-Line Robot Programming in a Virtual Environment
Authors: Troy James J. , Vanderploeg Martin J.
Published: March 2021

A robotic simulation and off-line programming package has been developed for use on Silicon Graphics workstations that has the capability of using several types commercially available virtual reality (VR) hardware devices. The software includes a library of 4, 5, and 6 degree-of-freedom (DOF) industrial robots with closed form inverse kinematics and translators that convert graphical simulation commands into the device control language that can be transferred to the robot control hardware. Forward kinematics, inverse kinematics, and joint space path planning methods used in the software development are discussed. The performance of three types of commercially available 6-DOF input devices are compared for use in interactive off-line programming. Stereo vision and external 6-DOF positioning devices were added to enhance programming efficiency and offer more realistic access to the virtual workcell environment.
Influence of Axial Excitations and of Boundary Conditions on the Parametric Instability of a Beam
Authors: Dufour Régis , Berlioz Alain , Streule Thomas
Published: March 2021

In this paper the stability of the lateral dynamic behavior of a pinned-pinned, clamped-pinned and clamped-clamped beam under axial periodic force or torque is studied. The time-varying parameter equations are derived using the Rayleigh-Ritz method. The stability analysis of the solution is based on Floquet’s theory and investigated in detail. The Rayleigh-Ritz results are compared to those of a finite element modal reduction. It shows that the lateral instabilities of the beam depend on the forcing frequency, the type of excitation and the boundary conditions. Several experimental tests enable the validation of the numerical results.
Nonlinear Dynamics of a Transversely Excited Flexible Cantilever Beam
Authors: Tabaddor Mahmood , Nayfeh Ali H.
Published: March 2021

Some experimental results concerning the nonlinear dynamics of a transversely excited beam are presented. The excitation is harmonic. A frequency sweep around the fourth natural frequency of the beam reveals some interesting modal interactions. The first phenomenon is the transfer of energy from the fourth mode, approximately 33.10 Hz, to the first mode, approximately 0.70 Hz. This interaction involves modulation of the amplitude and phase of the fourth mode. The second interaction involves the participation of the fourth mode and the second mode, approximately 5.80 Hz. The mechanism by which the second mode is activated as yet remains unidentified.
On the Parametrical Excitation of Nonlinearly Coupled Wave Equations
Authors: van der Burgh A. H. P. , Kuznetsov P. , Vavilov S. A.
Published: March 2021

In this paper a mathematical model for the study of the interaction of longitudinal and transversal vibrations in a stretched string is presented. The study implies an existence theory for time periodic transversal vibrations generated by a horizontal excitation of one of the end-points of the string. The conditions for the existence of this parametrically excited time periodic vibrations are evaluated in a practical application.

The innovative character of the results obtained concern the application of an operator method to a system of nonlinearly coupled wave equations modeling the dynamical behaviour of a strectched string where unite elasticity is taken into account.

It may be known that in the literature little attention has been paid to a rigorous analysis of time periodic solutions for systems of partial differential equations.
Finite Amplitude Dynamics of a Flexible Spinning Disc
Authors: Malhotra N. , Sri Namachchivaya N. , Whalen T.
Published: March 2021

The transverse dynamics of a high speed spinning disc which is clamped at the inner radius and rotating with a time-varying spin rate is examined in a space fixed frame of reference. The general nonlinear equations of motion governing the disc dynamics are systematically derived using displacement as well as stress function formulations. These equations of motion include the effects due to inherent bending rigidity, membrane stresses arising from centrifugal forces, non-axisymmetry of the in-plane and transverse displacements, geometric nonlinearities, aerodynamic damping arising from air stationary and moving with respect to the disc, parametric excitation due to time varying spin rate, etc. For the constant rotation case, the linearized equations of motion are solved by taking both membrane as well as flexural stiffness effects into account. This leads to a power series solution for the radial shape functions and harmonic solutions for the circumferential shape functions. The two-dimensional eigen-functions thus obtained can describe a disc mode with any number of nodal diameters and nodal circles, and the resulting eigen-frequencies match very well with the numerical results. The nonlinear and non-axisymmetric in-plane response is also determined, and a 2-DOF system of ODEs is obtained which governs the dynamic variation of the amplitudes of traveling waves associated with the dominant mode of the transverse motion.
Reduced Boring Bar Vibrations Using Damped Composite Structures
Authors: Trego Angela , Eastman Paul F. , Pratt William F. , Jensen C. G.
Published: March 2021

A new technology, called Stress Coupling Activated Damping (SCAD©), was applied successfully to a lathe boring bar. It reduced high frequency vibrations by up to 20 db. It can be applied to a wide range of structural designs. The geometries of the damped structures are not limited to thin plates but can be applied to tubes, I-beams, and complex structures. This allows SCAD© technology to be applied to several industry design problems, including the metrology, medical, aerospace, automotive and machine tool industries. SCAD© will also allow boring bars to: 1) be optimized for stiffness, frequency and loss factor, 2) be ‘tuned’ to a specific resonant frequency, 3) have improved damping regardless of boring bar diameter, 4) lengthen the usable tool length without a significant increase in cost, and 5) decrease cutting surface vibration induced pattern.
Nonlinear Normal Modes in the Presence of Internal Resonances: An Energy-Based Approach
Authors: King Melvin E. , Vakakis Alexander F.
Published: March 2021

In this work, modifications to existing energy-based nonlinear normal mode (NNM) methodologies are developed in order to investigate internal resonances. A formulation for computing resonant NNMs is developed for discrete, or discretized for continuous systems, sets of weakly nonlinear equations with uncoupled linear terms (i.e systems in modal, or canonical, form). By considering a canonical framework, internal resonance conditions are immediately recognized by identifying commensurable linearized natural frequencies. Additionally, the canonical formulation allows for a single (linearized modal) coordinate to parameterize all other (modal) coordinates during a resonant modal response. Energy-based NNM methodologies are then applied to the canonical equations and asymptotic solutions are sought. In order to account for the resonant modal interactions, it will be shown that high-order terms in the O(1) solutions must be considered. Two applications (‘3:1’ resonances in a two-degree-of-freedom system and ‘3:1’ resonance in a hinged-clamped beam) are then considered by which to demonstrate the application of the resonant NNM methodology. Resonant normal mode solutions are obtained and the stability characteristics of these computed modes are considered. It is shown that for some responses, nonlinear modal relations do not exist in the context of physical coordinates and thus the transformation to canonical coordinates is necessary in order to define appropriate NNM relations.
An Experimental Study of the Forced Response of Pre- and Post-Critical Plates
Authors: Murphy Kevin D. , Virgin Lawrence N. , Rizzi Stephen A.
Published: March 2021

Experimental results are presented which characterize the dynamic response of homogeneous, fully clamped, rectangular plates to narrow band acoustic excitation and uniform thermal loads. Using time series, pseudo-phase projections, power spectra and auto-correlation functions, small amplitude vibrations are considered about both the pre- and post-critical states. These techniques are then employed to investigate the snap-through response. The results for snap-through suggest that the motion is temporally complex and a Lyapunov exponent calculation confirms that the motion is chaotic. Finally, a snap-through boundary is mapped in the (ω, SPL) parameter space separating the regions of snap-through and no snap-through.
Random Response to Periodic Excitation With Correlated Disturbances
Authors: Hou Zhikun , Zhou Yunshen , Dimentberg Mikhail F. , Noori Mohammad N.
Published: March 2021

The paper addresses non-Gaussian stationary response of linear single-degree-of-freedom (SDOF) systems subject to a periodic excitation with correlated random amplitude and phase disturbances which are modeled as correlated Gaussian white noise processes. Correlation between amplitude and phase modulation is specified by the cross-correlation coefficient. Numerical results for the second and fourth moment responses are presented. The probability density function of the response is calculated based on the cumulant-neglect closure method. Non-Gaussianity of the response is discussed in terms of the excess factor. The results show that the moment responses generally increase with larger random amplitude disturbance and decrease with larger random phase modulation. The cross-correlation between amplitude and phase disturbances tend to reduce the system moment response. Large relative detuning results in smaller system moment responses. The response may become Gaussian in the sense of up to the fourth moment for sufficiently large relative detuning or random phase disturbances.
Phase-Space Reconstructions of Stick-Slip Systems
Authors: Feeny B. F. , Liang J. W.
Published: March 2021

Nonsmooth processes such as stick-slip may introduce problems with phase-space reconstructions. We examine chaotic single-degree-of-freedom stick-slip friction models and use the method of delays to reconstruct the phase space. We illustrate that this reconstruction process can cause pseudo trajectories to collapse in a way that is unlike, yet related to, the dimensional collapse in the original phase-space. As a result, the reconstructed attractor is not topologically similar to the real attractor. Standard dimensioning tools are applied in effort to recognize this situation. The use of additional observables is examined as a possible remedy for the problem.
Diagnosis of the Joint Backlash of a Mechanism: Wigner-Ville Distribution Combined With Correlation Techniques
Authors: Pan M.-C. , Verbeure B. , Van Brussel H. , Sas P.
Published: March 2021

The aim of this paper is to develop appropriate techniques to detect and classify the joint backlash of a robot by monitoring its vibration response during normal operating conditions. In this investigation, Wigner-Ville distributions combined with two-dimensional correlation techniques have been employed to diagnose various degrees of single-joint backlash. The method also allows to detect and to single out backlash present in two joints of a multi-link mechanism.

In the work reported here, the Wigner-Ville distribution based signal detection and the generalized symmetrical Itakura distance were proposed as tools for pattern differentiation. Initially the proposed methods have been applied to quantify the backlash of a single joint. Consecutively, the detection problem has been generalized to diagnose faults in two joints simultaneously. Due to the extra degree of freedom given by the 2D nature of the WVD’s, certain time-frequency regions were chosen as reference signatures in the case of single-joint backlash, and the signatures, spanning over two impact transients at the reverses of motion, were chosen in the cases of double-joint backlash. The proposed techniques have been successfully implemented on a two-link mechanism.
Finite Element Methods for the Interaction of Acoustic Fluids With Elastic Solids
Authors: Harari Isaac , Blejer Gabriel
Published: March 2021

Computation is essential to the solution of many problems of structural acoustics, particularly when wavelengths are of the same order as characteristic length scales. The development of finite element methods for large-scale computation of solutions to these problems should be preceded by a thorough analytical understanding of their performance in simplified settings in order to validate application to general configurations. Coupling such an analysis with the design of numerical methods that is based on understanding the underlying mathematical framework leads to the development of robust methods in which stability properties are enhanced while maintaining higher-order accuracy.

In this work we develop finite element methods for exterior problems of time-harmonic acoustic-structure interaction. Exterior boundary conditions are derived from an exact relation between the solution and its derivatives on an artificial boundary by the DtN method, yielding an equivalent problem in a bounded region that is suitable for domain-based computation. Solutions to the equivalent problem are unique, precluding singular behavior in finite element models.

Galerkin/least-squares technology is specialized to these problems in order to counter the numerical difficulties that result from employing traditional Galerkin methods. This is achieved by appending terms in least-squares form containing residuals of the Euler-Lagrange equations to the standard Galerkin formulation. The Galerkin/least-squares method is designed to yield dispersion-free finite element solutions to model problems, leading to superior performance on general, multi-dimensional configurations. Two one-dimensional model problems are investigated over a wide range of combinations of material properties of both media. In the first an exterior acoustic problem with impedance boundary conditions is analyzed, in order to study the influence of the elastic body on the acoustic medium. In the second, an elastic rod with an exterior acoustic medium is investigated in order to examine propagation from the solid to the fluid. The resulting method exhibits superior performance for fluid-solid interaction in multi-dimensional configurations. One version of the method offers particularly good representation of interface values.
A Slender-Body Theory in Acoustics
Authors: Van Nhieu Michel Tran
Published: March 2021

A new approach has been proposed to calculate the sound pressure field radiated or scattered from slender bodies. The theoretical analysis is based upon mathematical singular perturbation methods leading to the so-called slender-body approximation. The theory provides a practical method to compute the sound field as it allows a great simplification in the geometrical representation of the body surface and a reduced computation load. This paper summarizes the main results obtained with this approximation at the present state of investigation.
Main Principles of Vibrodamped Structure Scale Models for the Whole Sound Frequency Range
Authors: Ionov Alexei V.
Published: March 2021

At low and middle sound frequencies the physical modelling of vibro-absorbing constructions is interpreted as a reconstruction of a frequency dependence of an imaginary part of a full-scale construction dynamic rigidity which is shifted in frequency according to a scale factor. For the high sound frequency range there is a dimensionless form of a matrix energy equation. It allows the task of physical scale modeling to be formulated as a reconstruction of a vibration energy difference between structure elements excited by an external vibration load and the others its elements as in a full-scale object. The analysis is fulfilled in the specially selected frequency bands when the geometrical similarity between scale and full-scale constructions and a number of demands to their material and the loss factors are observed.
The Use of Radiation Resistance Measurements to Assess the Noise Characteristics of Machines
Authors: Paddock Everett H. , Koopmann Gary H.
Published: March 2021

An experimental method for assessing the noise characteristics of machines is developed. The method is based on a computation of the radiated sound power of a vibrating structure in terms of its acoustic surface radiation resistance and surface volume velocity. To measure acoustic surface radiation resistance, a probe is developed which consists of a low profile loudspeaker and a small microphone, both of which are moveable over the surface of the structure. As an application of the the method, the sound power produced by two valve covers of a 3.3L V6 internal combustion engine, a current production model and the prototype of a new design, is computed and compared. Based on the probe measurements made on a quiescent engine, a surface resistance matrix was generated for the two valve covers. Measurements of the volume velocity of the valve covers were made at two engine operating conditions: 1800 and 5300 RPM. After combining each of the velocity measurements with the resistance matrix, the results indicate that the prototype valve cover radiates significantly less sound power than the production cover at both operating conditions.
Structural Modification Software Development for Design Optimization
Authors: Gu Xiaoye , Flatau Alison B.
Published: March 2021

This paper presents a method for obtaining structural matrices from experimental frequency response function (FRF) data and using these structural matrices to predict the response of the structure to modifications at various locations. The approach taken is designed for subsequent use in optimizing structural modifications to efficiently reduce radiated acoustic power. A series of programs were written for identifying the structural matrices (mass matrices, stiffness matrices and damping matrices) from the measured FRF data. These matrices are used to obtain the modified response of the structure resulting from adding linear springs at different locations on the structure. Experimental results from a beam are presented to verify these programs. Work is in progress on extending this method to incorporate modifications to the structure produced by constrained-layer damping materials.

The programs for obtaining the structural matrices and the structural response are composed of approaches used by several prior authors. Potter and Richardson’s [1,2] method is used for obtaining the relative modal parameters (modal mass, modal stiffness and modal damping). Luk and Mitchell’s [3,4] pseudo-inverse method is employed to obtain the structural matrices for cases when the number of modes measured is much less than the number of test points. A method for deriving the absolute value of modal parameters from the measured FRF data is also developed using modal analysis theory. Linear springs are added at various positions to modify the structure. The structural matrices are used to predict the modified structural responses scaled to displacement per unit force. A series of linear spring modifications are modeled and implemented experimentally to verify these programs.
Physical Properties of Transfer Function Zeros for Collocated Control in Flexible Structure System
Authors: Chung Chingyei , Lin Chin-yuh
Published: March 2021

In this paper, the physical meaning of transfer function zeros for collocated control in a general flexible structure system is discussed. For a flexible structure system, we propose the “Zero Dynamic Theorem”. The theorem states that in a flexible structure system, the flexible structure can be a circulatory system (non-sysmetric stiffness matrix) with viscous and gyroscopic damping (non-symmetric damping matrix), if the sensor output (generalized displacement) and the actuator input (generalized force) are “dual type” and the transfer function is strict proper and coprime (no pole/zero cancellation); then, the transfer function zeros are the natural frequencies of constrained structure. Furthermore, with this theorem, the interlacing pole/zero property for the gyroscopic systems is presented.
Development of an Engine System Model for Predicting Structural Vibration
Authors: Sung S. H. , Nefske D. J.
Published: March 2021

A finite-element based engine system model is developed for predicting the structural vibration of the engine. The engine system model combines modal models of the major bolted-together sub-structures of the engine, with non-structural mass models of the remaining engine components added to bring the inertial properties to those of the running engine. The model is developed and experimentally evaluated with impact and shaker excitation tests. Comparisons are made of the predicted and measured vibration response for various partially assembled engine configurations, as well as for the fully assembled engine. The comparisons illustrate the accuracy of the model in predicting the narrow-band and one-third octave-band vibration response for excitation frequencies up to 2 kHz.
Chaos of a Flexible Rotor in Journal Bearings
Authors: Brown R. D. , Drummond G.
Published: March 2021

Nonlinear systems can give rise to chaotic behaviour, essentially unpredictable. Oil film forces arising from hydrodynamic bearings in rotating machinery can be extremely nonlinear under conditions of large unbalance. Chaotic response has been demonstrated in theoretical models of rigid rotors supported in hydrodynamic bearings.

The behaviour of a rigid rotor can be extended by looking at a flexible rotor model supported on journal bearings and subject to large unbalance levels. The introduction of a flexible shaft yields chaotic regions which are less extensive than those obtained from a rigid rotor model. This is not surprising as the nonlinearity in the model is confined to the oil films at the end of the shaft. However if this level of unbalance is experienced in service then shaft fatigue could occur because of the sustained nature of the non-synchronous response and the effect of the resulting stress reversals.
A New Approach to Machinery Monitoring and Diagnostics Using Self-Organizing Maps
Authors: Zhang Siyu , Ganesan R. , Sankar T. S.
Published: March 2021

The problem of estimating an unknown multivariate function from on-line vibration measurements, for determining the conditions of a machine system and for estimating its service life is considered. This problem is formulated into a multiple-index based trend analysis problem and the corresponding indices for trend analysis are extracted from the on-line vibration data. Selection of these indices is based on the simultaneous consideration of commonly-observed faults or malfunctions in the machine system being monitored. A neural network algorithm that has been developed by the present authors for multiple-index based regression is adapted to perform the trend analysis of a machine system. Applications of this neural network algorithm to the condition monitoring and life estimation of both a bearing system as well as a gearbox are fully demonstrated. The efficiency and computational supremacy of the new algorithm are established through comparing with the performance of Self-Organizing Mapping (SOM) and Constrained Topological Mapping (CTM) algorithms. Further, the usefulness of multiple-index based trend analysis in precisely predicting the condition and service life of a machine system is clearly demonstrated. Using on-line vibration signal to constitute the set of variables for trend analysis, and employing the newly-developed self-organizing neural algorithm for performing the trend analysis, a new approach is developed for machinery monitoring and diagnostics.
Damping Machine Tools With Imbedded Viscoelastic Materials Constrained by Shear Tubes
Authors: Marsh Eric R. , Hale Layton C.
Published: March 2021

This paper considers a passive damping method that can be applied to beam-like structures such as machine tool bases and columns. The method uses viscoelastic materials to dissipate energy in the manner of classic constrained-layer damping; however, the layers are embedded within the structure as opposed to being applied externally. This provides a robust means of incorporating damping without encountering several of the common disadvantages associated with external damping treatments. An analytical solution to the amount of damping that can be achieved using embedded layers is available, but is known to be inaccurate when the viscoelastic stiffness approaches that of the structural components. Therefore, a new prediction of the maximum damping level that can be expected in a structure is developed and presented here. This prediction gives good results in a wide variety of applications, and offers insight into the relationship between key design parameters. Finite element and experimental verification of the maximum damping predictor are also presented.
An Electromechanical Vibration Absorber
Authors: Nagem Raymond J. , Madanshetty Sameer , Medhi Gunajit
Published: March 2021

A conventional vibration absorber consists of a secondary mechanical oscillator whose properties are chosen to improve the dynamic response of a primary vibratory system. The improvement in the primary system is obtained at the expense of large amplitude mechanical oscillations of the secondary system. We propose an electromechanical absorber in which the secondary system consists of a resonant electric circuit capable of withstanding large amplitude electrical oscillations. The theoretical basis for the design of the electromechanical absorber is presented, and initial experiments to test the technique are described.
Frequency Domain Approach to Solve the Time-Optimal Control of a Distributed Parameter System
Authors: Alli Hasan , Singh Tarunraj
Published: March 2021

In this paper, the time-optimal control of the wave equation is derived in closed form. A frequency domain approach is used to obtain the time-optimal solution which is bang-off-bang. The system studied in this paper is a uniform flexible rod with a control input at each end, whose dynamics in axial vibration is represented by the wave equation. In order to verify the optimality of the control profile derived for the distributed parameter system, the system is discretized in space and a series of time-optimal control problems are solved for the finite dimensional model, with increasing number of flexible modes. In the limit, the controllers show the convergence of the first and final switch of the bang-bang controller of the finite dimensional system to the first and final switch of the bang-off-bang controller of the distributed parameter system, in addition to the convergence of the maneuver time. The number of switches in between the first and final switch is a function of the order of the finite dimensional system. The maneuver time of the distributed parameter system is compared to that of an equivalent rigid system and the coincidence of the time-optimal controller for the flexible and rigidized systems is illustrated for certain maneuvers.
Remarks on the Modelling of Active Structures With Colocated Piezoelectric Actuators and Sensors
Authors: Loix N. , Preumont A.
Published: March 2021

This paper aims to attract the attention of the designers of active structures on the importance of evaluating properly the feedthrough component of the open-loop transfer functions. It is shown that overlooking the feedthrough component can change significantly the location of the zeros of the open-loop system and, as a result, alter drastically the performance of the closed-loop system.

The feedthrough term may result from the quasi-static contribution of the high frequency modes or from local effects that are neglected by over-simplified modelling techniques (e.g. plate or beam instead of shell). The problem is illustrated with a cantilever beam provided with strain actuators.
The Modeling and Active Control of Flexible Plate Structure for Reducing Noise Radiation
Authors: Seto Kazuto , Miyata Takaharu , Ren Mingzhang , Doi Fumio
Published: March 2021

This paper shows a new method of active vibration control of a flexible plate structure with aim to reduce the radiated noise. It involves modeling the real structure into a reduced order lumped parameter model on the basis of modal analysis, and then adopting LQ control theory to control the vibration of selected multi-modes of the plate. In this paper the modeling procedure and the control strategy design is presented, in which suboptimal control theory and digital filtering technique have been used. Simulation and preliminary experimental results are given to demonstrate the effectiveness of the proposed method.
Optimal Design of a Truss Structure for a Segmented Reflector
Authors: Hahn Mark A. , Mirmirani Maj D. , Boussalis Helen R.
Published: March 2021

Design requirements for a support truss used in a segmented reflector telescope test-bed are identified. From these requirements a baseline model of the support truss is developed. Multicriteria optimization and Pareto optimality concepts are employed to obtain an optimal truss structure among variations of the baseline model that yields a correct balance between strength and flexibility. Modal analysis shows that the structure exhibits the characteristics of a large space-borne structure.