bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of organizational justice and decision latitude on expatriate organizational commitment and job performance
Authors: AlMazrouei Hanan , Zacca Robert
Published: March 2021

Purpose

The purpose of this paper is to study the influence of organizational justice and decision latitude on expatriate organization commitment and job performance.

Design/methodology/approach

Data were collected from 175 nonmanagerial-level expatriate employees in Dubai, UAE using a purposive sampling approach. A structural equation model with partial least squared analysis was utilized to test the hypotheses.

Findings

The results show that decision latitude partially mediates the relationship between organization justice and organizational commitment and fully mediates the relationship between organization justice and job performance.

Research limitations/implications

Data were collected from a cross sectional sample in UAE, and hence, the generalizability of the results to other contexts may be limited.

Practical implications

The research study suggests ways in which human resource managers and practitioners can develop a stronger awareness of the importance of decision latitude in employee decision-making and the role it plays in promoting employees' commitment and job performance given perceived organizational justice.

Originality/value

The present research is among the first of its kind to examine the study variables within the nonmanagerial expatriate context.
Global rising rates of caesarean sections
Authors: Chien Patrick
Published: March 2021

Deputy Editor‐in‐Chief, Dr Patrick Chien, discusses how top articles from this issue in an audio podcast available at: https://soundcloud.com/bjog/april‐editors‐choice‐2021.
Work Effort and Work Requirements for Food Assistance among U.S. Adults
Authors: Cuffey Joel , Beatty Timothy K. M. , Mykerezi Elton
Published: March 2021

We investigate the effect of Supplemental Nutrition Assistance Program (SNAP) work requirements on work effort for a particularly disadvantaged subgroup of potential SNAP participants. Individuals age out of SNAP work requirements at age fifty and requirements are occasionally waived in certain areas. We leverage this policy variation in a regression discontinuity research design and find that, for adults with low income and low education, aging out of work requirements decreases employment, hours worked, and the probability of working over twenty hours per week only when requirements are in effect. This drop in work effort is not apparent among low‐income adults in general and is driven by individuals leaving the labor force because they report being unable to work or because they retire. The drop is smaller when states do not provide qualifying work opportunities. Overall, although we find meaningful effects consistent with theory for a subset of low‐income adults, it is not clear that the overall number affected is sufficiently large to translate to noticeable labor market effects among low‐income adults without dependents in general.
Problems and Perspectives of a Theory of Transformational Processes of Bildung
Authors: Koller Hans‐Christoph
Published: March 2021

Abstract

In this essay, Hans‐Christoph Koller presents a concept of transformational processes of Bildung in an attempt to redefine the German notion of Bildung referring to actual social conditions of educational processes. According to this conception, Bildung is a transformation of world‐ and self‐relations that can come about when subjects are confronted with problems for which they have no established routines of engagement. With reference to theories of Pierre Bourdieu, Bernhard Waldenfels, and Ulrich Oevermann, Koller looks for answers to three questions: (1) Which concepts and theories are able to adequately grasp the world‐ and self‐relations of subjects going through processes of Bildung? (2) How can the problems that trigger processes of Bildung and that challenge subjects to transform be determined more precisely? (3) How exactly does the emergence of new figures of world‐ and self‐relations take place when we “successfully” complete a process of Bildung? Finally, the essay concludes with an attempt to clarify the normative implications of this theory.
Scale‐dependent patterns and drivers of plant diversity in steppe grasslands of the Central Alborz Mts., Iran
Authors: Talebi Amir , Attar Farideh , Naqinezhad Alireza , Dembicz Iwona , Dengler Jürgen
Published: March 2021

Questions

Which are the main environmental drivers of plot scale alpha‐diversity and beta‐diversity in arid steppes? Do they vary between functional groups and across grain sizes?

Location

Central Alborz Mts., N Iran.

Methods

We sampled vascular plants in 23 nested‐plot series with nine grain sizes from 0.0001 m2 to 1,000 m2 and 334 25‐m2 vegetation plots in different vegetation types of natural dry steppe grasslands. To assess beta‐diversity, we calculated overall and local z‐values of species–area relationships modelled with the power function. As potential drivers of species richness and z‐values, we used topographic, edaphic and climatic variables as well as management types. Generalised linear models (GLMs), and generalised linear mixed‐effect models (GLMMs) if spatial autocorrelation occurred, were used in a multi‐model inference framework to build statistical models.

Results

Mean annual temperature was the most important predictor for total species richness and richness of functional groups across grain sizes, with a unimodal relationship for grains of 25–100 m2, but mostly increasing for finer grain sizes. Precipitation of the driest month and cover of gravel were influential drivers at the smallest grains. The explanatory power of regression models increased towards larger grain sizes. The overall z‐values showed a high positive relationship with precipitation of the driest month, mean annual temperature and mean soil depth.

Conclusions

Related to our more than 3,000‐m elevational gradient, mean annual temperature (highly negatively correlated with elevation) was the most influential and consistent driver across functional groups and grain sizes with mostly unimodal relationships for alpha‐diversity and a positive effect on beta‐diversity. Findings for other drivers were less consistent, and overall the explained variance of our models was relatively low, calling for additional studies to determine whether in the arid grasslands of Iran stochasticity is just higher or there are additional important variables.
Sirtuin GdSir2.4 participates in the regulation of rRNA transcription in the Giardia duodenalis parasite
Authors: Lagunas‐Rangel Francisco Alejandro , Yee Janet , Bazán‐Tejeda María Luisa , García‐Villa Enrique , Bermúdez‐Cruz Rosa María
Published: March 2021

Giardia duodenalis is a parasite of great medical interest due to the number of infections it causes worldwide each year. Although research on epigenetic mechanisms in this protist has only begun recently, epigenetic regulation has already been shown to have important roles in encystation, antigenic variation, and resistance to antibiotics in Giardia. In this work, we show that a Giardia ortholog of Sir2, GdSir2.4, is involved in the silencing of rRNA expression. Our results demonstrate that GdSir2.4 localizes to the nucleolus, and its binding to the intergenic spacer region of the rDNA is associated with the deacetylation of the chromatin in this region. Given the importance of the regulation of rRNA expression to maintain adequate levels of ribosomes and genomic stability within the cells, GdSir2.4 can be considered a target to create new therapeutic agents against this parasite.
Validation of a novel patient‐operated device for measuring skin barrier function in atopic dermatitis
Authors: Grinich Erin E. , Topham Christina , Haynes Dylan , Chung Janice , Latour Emile , Simpson Eric L.
Published: March 2021

Background

Transepidermal water loss (TEWL) and capacitance are used in atopic dermatitis (AD) trials to provide objective data on clinical change and response to therapy. Many barrier devices are costly, limiting their utility. GPSkin is a novel low‐cost, patient‐operable device that measures both TEWL and capacitance via smartphone application.

Objective

This validation study investigated the correlation of GPSkin with the AquaFlux and Corneometer, and the reliability of these devices, in patients with AD.

Methods

Fifty AD patients with varying disease severity performed self‐measurements with GPSkin, while investigators collected data with all 3 devices, on both nonlesional and lesional skin.

Conclusion

GPSkin and AquaFlux demonstrated strong correlation for TEWL on nonlesional and lesional skin by Spearman's correlation (rs), independent of device user. For capacitance, GPSkin and the Corneometer showed moderate correlation when obtained by patients, yet a strong correlation when obtained by a clinician. Despite good correlation, GPSkin showed poor agreement with both the AquaFlux and Corneometer in Bland‐Altman plots. GPSkin underestimated both TEWL and capacitance. Overall, the devices had good test‐retest reliability. None of the devices could discriminate between AD severity states. While GPSkin marks an exciting advancement in barrier technology, further study is needed for validation on AD skin.
Thermal Design of Material Quality in Rapid Prototyping Techniques
Authors: Doumanidis Charalabos C. , Fourligkas Nikolaos
Published: March 2021

In thermal rapid prototyping of mechanically functional products, their geometric design must be also combined to specification of their material quality features. The material structure and properties of these parts are generated and can be specified through the dynamic temperature distribution history during the process. Such a desired thermal field cycle, prescribed by computational modeling or direct experimental measurement, can be implemented by proper scheduling of the power and motion trajectory of a heat source, usually supplied by time-sharing the thermal process torch (arc, Laser etc.). This article presents such an off-line thermal design methodology of the process conditions, based on a numerical simulation of the temperature distribution, which tracks the reference thermal field by guiding the torch to the areas of highest thermal demand. This strategy was successfully implemented in simple laminated object manufacturing on a plasma-arc laboratory setup with infrared thermal monitoring. The effects of equipment bandwidth and the potential for closed-loop thermal control of various thermal rapid prototyping methods are also addressed.
Stiffened CFRP-Panels Under Buckling Loads: Modeling, Analysis, Optimization
Authors: Eschenauer Hans A. , Weber Christof M.
Published: March 2021

The present paper addresses the optimal layout of stiffened fiber composite plates (Fig. 1) considering buckling constraints; these plates are increasingly applied in many fields of engineering (air- and spacecraft technology, automotive industries, boatbuilding etc.).

This particular area of structural optimization still requires substantial investigations into its fundamentals. The structural analysis alone for the treatment of this type of problems may increase to such a degree that the complete optimization process requires extremely long computation times due to the processing of a high amount of data, a fact that calls for the development of “intelligent” procedures in order to reduce the computation effort to a tolerable measure and to maintain reduplicability of the whole process. For this purpose, a so-called “constructive design model” is introduced.
Algebraic Representation of Geometric and Size Tolerances
Authors: Mullins S. H. , Anderson D. C.
Published: March 2021

Presented is a method for mathematically modeling mechanical component tolerances. The method translates the semantics of ANSI Y14.5M tolerances into an algebraic form. This algebraic form is suitable for either worst-case or statistical tolerance analysis and seeks to satisfy the requirements of both dimensional metrology and design analysis and synthesis. The method is illustrated by application to datum systems, position tolerances, orientation tolerances, and size tolerances.
Synthesis of Optimal Non-Orthogonal Routes
Authors: Szykman Simon , Cagan Jonathan
Published: March 2021

This paper introduces a novel approach to three dimensional routing optimization. Examples of routing tasks for engineering applications include routing of pipes, wires and air ducts. Traditionally, routing algorithms perform Manhattan, or orthogonal, routing. Non-orthogonal routing can be less costly than Manhattan routing and for applications such as automotive or aerospace design, Manhattan routing is impractical due to spatial limitations. The research presented in this paper uses simulated annealing as the basis of a non-orthogonal routing optimization algorithm that avoids the drawbacks associated with Manhattan routing. Several examples comparing the two approaches are given.
Operational Envelopes for Working Bodies of Mechanisms and Manipulators
Authors: Haug Edward J. , Adkins Frederick A. , Luh Chi-Mei
Published: March 2021

The set of all points in space that can be occupied by any point in the working body of a mechanism or manipulator is defined as its operational envelope. Criteria for points in and on the boundary of the operational envelope of working bodies with smooth boundaries are developed, for both parametric and equation representations of domains and boundaries of working bodies in two- or three-dimensional space. The criteria derived involve kinematic constraint equations for the underlying mechanism and equations that characterize the shape of the working body. A row rank deficiency condition is derived as a criterion for the boundary of the operational envelope, and numerical methods based on this condition for mapping the boundary are presented. An example involving a planar Stewart platform with a dome attached is analyzed numerically.
Automated Generation of Fixture Configuration Design
Authors: Bai Yong , Rong Yiming (Kevin)
Published: March 2021

Flexible fixturing is a necessary aspect of flexible manufacturing systems (FMS) and computer-integrated manufacturing systems (CIMS). Modular fixtures are most widely used in industry for job and small batch production. Computer-aided fixture design (CAFD) has become a research focus in implementing FMS and CIMS. Fixture configuration design is an important issue in CAFD. A review of the current research in CAFD indicates that one major problem impeding the automated generation of fixture configuration design is the negligence of study on fixture structures. This paper investigates fundamental structures of dowel-pin modular fixtures and fixturing characteristics of commonly-used modular fixture elements. A modular fixture element assembly relationship graph (MFEARG) is designed to represent combination relationships between fixture elements. Based on MFEARG, algorithms are developed to search all suitable fixturing unit candidates and mount them into appropriate positions on baseplate with an interference checking. A prototype system for automated design of dowel-pin modular fixture configurations is presented in this paper. Fixture design examples are given in the end of the paper.
Branching and Immovable Configurations
Authors: Holte Jennifer E. , Chase Thomas R.
Published: March 2021

Improvements to Chase and Mirth’s (1993) definition of branches of planar linkage mechanisms are proposed. The improvements extend the definition of branches to mechanisms where the earlier definition fails. The new definition utilizes immovable configurations and uncertainty configurations to divide a circuit into branches. Several examples are presented to demonstrate the added versatility of the new definition.
On the Optimal Robot Manipulator Motion Planning for Solid Freeform Fabrication by Thermal Spraying
Authors: Rastegar J. , Qin Y. , Tu Q.
Published: March 2021

A novel approach to optimal robot manipulator motion planning for Solid Freeform Fabrication (SFF) by thermal spraying is presented. In this approach, given the desired spatial geometry of the object, the motion of the spray gun relative to a forming platform is synthesized for minimal masking requirements considering the probabilistic nature of the thermal spraying process. The material build-up rate can be planned to achieve the desired distribution of the physical/material properties within the object volume. Examples of optimal motion planning for the generation of some basic solid objects and computer simulation of the effectiveness of the developed methodology are presented.
Inverse Kinematics of Serial Redundant Manipulators With Locked Articulations
Authors: Perreault Louis , Gosselin Clément M.
Published: March 2021

This paper presents an algorithm for the solution of the inverse kinematics of a serial redundant manipulator with one (or more) locked joint(s). To this end, a general procedure is developed for the determination of the equivalent Denavit-Hartenberg parameters of a serial manipulator with locked joints. This procedure can be applied to any serial architecture. The solution of the inverse kinematic problem for the three cases which can arise is then addressed. An example of the application of the method to a SARCOS 7-DOF manipulator is also given.
An Algorithm for Enveloping Linear Structural Response With Application to Spacecraft Stress Analysis
Authors: Kunt Cengiz O. , Mignosa Lawrence J. , Pontius James T.
Published: March 2021

An algorithm and a computer program are developed for spacecraft structural analysis to determine the maximum linear static response (stress, deformation, etc.) and the corresponding “worst direction” of the loading. Compared to the brute force approach of repeating the structural analysis to cover all the possible orientations of the load vector, the proposed approach is faster, more accurate, and computationally more efficient. Maximum structural response determination is illustrated through a case study of stress analysis conducted for the TRMM (Tropical Rainfall Measuring Mission) payload developed by NASA Goddard Space Flight Center and NASDA (National Space Development Agency of Japan). The paper includes part of the structural analysis conducted in sizing the Upper Instrument Support Platform, which provides support for two of TRMM’s major instruments.
The Study of Design Theory and Methodology in Mechanical Engineering: A Commentary
Authors: Karandikar Harshavardhan , Shupe Jon
Published: March 2021

Our aim in this paper is to examine the study of design theory and methodology (DTM) in the field of mechanical engineering design and to assess its impact. Rather than review the work of a growing number of individual researchers essential research themes have been distilled by an analysis of the conference papers in the area and through a survey of the research and practicing community. On the basis of the survey some commonly understood goals and products of the DTM research community are identified. We seek to understand the extent to which the goals of the research community been met and whether the products have benefited the customers. To maintain continuity and some perspective this commentary builds upon past reviews.
Managing Risk by Reordering Tasks in Engineering Design
Authors: Smith Robert P.
Published: March 2021

This paper describes a model of how reordering tasks in the engineering design and development process affects resource usage in a risky environment. All development projects are risky; their outcome and level of success is unpredictable. Many projects are canceled at some time during the development process, or never produce a working product or produce a product that fails in the marketplace. Doing engineering development is expensive; it requires high-cost labor as well as other potentially expensive resources. To some extent the magnitude of the risk is estimable; it is possible to predict now much resources (time, labor or other costs) any particular development task will consume as well as some estimate of whether or not an insurmountable technical problem is likely to be discovered. Also, development tasks are not independent; there are constraints on their ordering due to needed technical knowledge. The model presented in this paper uses those estimates to suggest an ordering of the tasks in an attempt to minimize the expected resource consumption for those projects that run a risk of cancellation.
A Study on Heredity and Evolution of Designs Considering Kansei by Using Genetic Algorithms
Authors: Yamakawa Hiroshi , Arakawa Masao , Katsuyama Nobuyuki
Published: March 2021

A new concept on the heredity and evolution of designs was proposed and an optimum design method based on the concept was developed newly by one of the authors. Several kinds of needs for designs may exist and users of some products are not satisfied with the functions of the products but also with their sensuous beauties or impressions of shapes and materials. To consider such sensous quality of the products was called “Kansei designs” in Japan and have become of interest and important lately (Nagamachi, 1989). In this study we introduce the same concept on heredity and evolution of designs as in the previous reports shown in Fig.1 (Yamakawa, 1994) and present a general design method to consider the Kansei design into ordinary, design process by making use of both SD (Semantic Differential) and the Genetic Algorithms. In order to support designer’s impressions, we also consider to take for other features Kansei estimation, which is similar to the original feature and easier to take “Kansei”, into account and developed an interface system which can show the transition of feature during GA process. Front view designs of a car are taken as simple numerical examples and the effectiveness of the proposed method is examined.
Frank Whittle and the Jet Engine
Authors: Smith Charles O.
Published: March 2021

The inertia of society is so stubborn that no one will move against it, if he cannot believe that it can be more easily overcome than is actually the case. And no one will suffer the perils and pains involved in the process of radical social change, if he cannot believe in the possibility of a purer and fairer society than will ever be established. These illusions are dangerous because they justify fanaticism, but their abandonment is perilous because it inclines to inertia.
Application of DFA to Telecommunications Equipment: One of the Most Successful Cases in AT&T
Authors: Kim B. Sung , Stanfill Karen Owens , Carus Bryce W.
Published: March 2021

A new telecommunications power distribution frame was developed to reduce costs, meet new international market requirements and enhance performance. DFA was thoroughly applied and resulted in a dramatic customer price reduction, fewer parts, less assembly time, and a lower defect rate.
Coding and Classification of Geometric Models
Authors: Qamhiyah A. Z. , Benhabib B. , Venter R. D.
Published: March 2021

For the efficient manipulation of information in support of design and manufacturing one would need to access large active databases. In this context, it is envisioned that 3-D object models must be easily retrieved for modification, or for simply reviewing related information. This paper addresses the development of a classification system for the efficient retrieval of 3-D object CAD models. For the design of a new object the user would access the database to locate the most similar object model and, if worthwhile, modify it to attain a model for the new object under consideration.

The proposed classification procedure comprises three main stages: First, 3-D geometrical data, sufficient for classification, is determined and extracted from a selected model of the object, and a primary representation domain is determined. Contours, were selected as the basic descriptive units. Based on this selection, relationships defined by descriptor elements were established between (a) two solid contours; (b) a solid and a hollow contour; and, (c) two hollow contours. In order to facilitate the use of the descriptor elements, a simple alpha-numeric coding system was developed.

In the second stage, the description of the object is mapped from the geometrical domain into a numerical-factor domain, where each contour is represented by a numerical value.

In the final stage, a code is generated based on the factor-domain representation in the form of a Fourier signature. Classification is then carried out according to the similarity of the generated Fourier signatures.
Experimental Analysis of the Finite Dynamics of a Suspended Cable
Authors: Benedettini F. , Rega G. , Alaggio R.
Published: March 2021

An experimental model of clastic cable carrying eight concentrated masses and hanging at vertically moving supports is considered. The system parameters are adjusted to realize multiple 1:1 e 2:1 internal resonance conditions involving planar and nonplanar, symmetric and antisymmetric, modes. Systematic response measurements are made in a large frequency range including meaningful external resonance conditions. Frequency-response plots and overall behaviour charts in the control parameter space highlight rich picture of often coexisting planar and nonplanar regular responses, as well as the occurrence of regions of quasiperiodic and chaotic motions which are characterized both qualitatively and quantitatively.
An Extrapolation Method to Compute Far-Field Pressures From Near-Field Pressures Obtained by Finite Element Method
Authors: Assaad Jamal , Bruneel Christian , Rouvaen Jean-Michel , Bossut Régis
Published: March 2021

The finite element method is widely used for the modeling of piezoelectric transducers. With respect to the radiation loading, the fluid is meshed and terminated by an external nonreflecting surface. This reflecting surface can be made up with dipolar damping elements that absorb approximately the outgoing acoustic wave. In fact, with dipolar dampers the fluid mesh can be quite limited. This method can provides a direct computation of the near-field pressure inside the selected external boundary. This paper describes an original extrapolation method to compute far-field pressures from near-field pressures in the two-dimensional (2-D) case. In fact, using the 2-D Helmholtz equation and its solution obeying the Sommerfeld radiation condition, the far-field directivity pattern can be expressed in terms of the near-field directivity pattern. These developments are valid for any radiation problem in 2D. One test example is described which consists of a finite width planar source mounted in a rigid or a soft baffle. Experimental results concerning the far-field directivity pattern of lithium niobate bars (Y-cut) are also presented.
Frequency Window Implementation of Adaptive Multi-Level Substructuring
Authors: Bennighof Jeffrey K. , Kaplan Matthew F.
Published: March 2021

Adaptive multi-level substructuring (AMLS) is a method for reducing the order of models of complex structures by orders of magnitude, while ensuring that the accuracy available from the original finite element model is preserved. A structure’s finite element model is transformed to a much more efficient representation in terms of approximate vibration modes for substructures on multiple levels. An adaptive procedure constructs an optimal model for satisfying a user-specified error tolerance, by determining which modes should be included in the model. In this paper, a frequency window implementation of AMLS is developed, in which frequency response analysis can be done over a frequency window at little additional cost beyond that of the solution at the center frequency. A numerical example is presented.
Control of Structure-Borne Sound Using Periodically Varying Rigidity
Authors: Hawwa Muhammad A. , Nayfeh Ali H.
Published: March 2021

Subsonic modes may cause significant radiation when they scatter at a discontinuity. In this study, we suggest an approach to filter out subsonic waves before they reach the discontinuities on the structure. This is done by imposing a material (parametric) periodicity in a fluid-loaded structure, which leads to a strong stopband interaction under a Bragg condition. The interaction is analytically described by the coupled-mode equations, derived using the method of multiple scales. Numerical illustrations are given in terms of the transmission loss for different fluid-loaded plates. The results can be utilized to suppress the undesired acoustic radiation generated by fluid-loaded structures.
Windowed-Transform Processing of Acoustic Beam Scattering From Fluid-Immersed Elastic Structures
Authors: Zeroug Smaine , Felsen Leopold B.
Published: March 2021

Acoustic beam scattering from submerged bulk and layered elastic structures is of interest for applications ranging from determining material properties to locating and identifying interior defects. Nonspecular reflection, which occurs when the incident beam is phase matched to leaky waves (LW) supported by the structure, constitutes an effective sensor for such applications. Forward frequency domain modeling based on a robust asymptotic hybrid beam-LW algorithm [Zeroug and Felsen, 1992] has shown that the nonspecular data, which is established by interference between specular reflection and LWs, depends strongly on the collimation of the incident beam, the number and leakage strengths of the excited LWs, and the curvature of the insonified structure. The present contribution addresses the inverse problem of extracting this phenomenology via wave-oriented processing, which is implemented by subjecting the scattered field data to a Gaussian-windowed Fourier transform (GWT) along spatial tracks parallel to the fluid-structure interface. For the fluid-immersed elastic configurations of: 1) solid half-spaces, 2) plates, 3) solid cylinders, and 4) cylindrical shells, the GWT-generated local wavenumber phase-space distributions footprint the correct wave physics, but with resolutions that are limited by the configuration-spectrum tradeoff. Examples demonstrate how the resolution is influenced by the GWT window size. The paper also includes preliminary results on application of a Prony superresolution algorithm for extraction of LW phase velocities and leakage rates.
Acoustic Behavior of Near Periodic Elastic Structures
Authors: Photiadis Douglas M.
Published: March 2021

Near periodic arrays of discontinuities have been predicted to have a significant impact on the acoustic properties of elastic structures. The discontinuities in the elastic properties of the structure produce a characteristic signature in the acoustic scattering cross section of the structure via two distinct mechanisms; a direct interaction producing acoustic Bragg scattering, and an indirect interaction wherein the discontinuities fundamentally alter the free waves of the structure. The locally propagating states of the pseudo-periodic system are Floquet or Bloch wave packets and the locations of the highlights in the cross section may be determined simply from the Bloch wavenumber via a phase matching argument. Predicting the resulting scattering levels requires an understanding of the propagation of the Bloch wave packets in the finite, pseudo-periodic structure. In the case of a thin ribbed cylindrical shell or plate this scattering mechanism can arise from flexural waves, and recent experimental results obtained at Naval Research Laboratory have demonstrated the importance of both this mechanism and Bragg scattering on the acoustic far field over a broad frequency range. In this paper, these results and the underlying theoretical development will be discussed.
Free Acoustic Oscillations Inside a Triaxial Ellipsoid
Authors: Levitina Tatyana V.
Published: March 2021

If a Dirichlet or Neumann condition is imposed on the surface of the ellipsoid, the variables are separated in the scalar wave equation in ellipsoidal coordinates, and the problem in hand is reduced to a system of three identical ordinary differential equations, each being defined on a separate interval and subject to its own boundary conditions. Thus, the three-parameter self-adjoint Sturm-Liouville problem arises: the equations are coupled by two separation constants and the eigen frequency of the ellipsoid, i. e., the spectral parameters, which must be so chosen that all the equations of the system have simultaneously nontrivial solutions, each satisfying the corresponding boundary conditions. The effective globally converging numerical algorithm is proposed for calculating eigen frequencies and separation constants. When the modes of an ellipsoid are found, the caustic surfaces can be easily determined. The merit of the method is illustrated on the example of several calculations of the sound field and caustic surfaces in an ellipsoid.
Selling, Designing, and Producing Products That Sound Good
Authors: Lyon Richard H.
Published: March 2021

“Sound Quality” has become a product feature that is becoming more important to customers and companies. Although the precise meaning of the term can vary, companies must respond when customers react to products that sound better. The purpose of this paper is to discuss some of the marketing and design issues involved in product sound, some tools that are available to determine what Sound Quality (SQ) is for any particular product, and how engineering design can be brought to bear on this product attribute. The author’s view is that SQ is amenable to good and rational procedures, just like the other methods used in product planning and engineering design.
The Method of Structure Dynamic Modification With Tested Modal Parameters: FEM Full Mode
Authors: Chen Shiyu , Dimentberg M. F. , Noori M. , Hou Zhikun , Wang Fengquan
Published: March 2021

This paper offers a new method for Structure Dynamic Modification, it is called the Modal Parameters–FEM Full Mode Method. With the FEM of the structure and the tested modal parameters, the rotational displacement information and the full mode can be got by full mode computation. After structure modification, the dynamic character of the modified structure can be calculated with the full mode.
Critical Speeds Resulting From Unbalance Excitation of Backward Whirl Modes
Authors: Greenhill Lyn M. , Cornejo Guillermo A.
Published: March 2021

Most rotordynamic analyses typically ignore the potential for critical speeds to be created by traversing a backward precessional whirl mode. While not commonly recognized, a backward mode can be excited using unbalance as the driving force. Based on the analysis of a Jeffcott rotor-bearing model, it was found that the condition for this response to occur is strongly dependent on stiffness asymmetry in the rotordynamic coefficients at the supports. To illustrate the application of this result, a rotordynamic analysis on actual hardware is presented, in which the unbalance excited backward mode resonance is calculated to occur. Test data is also given indicating the presence of the predicted critical speed. It is important to note that although the resonance is due to the backward mode, the precessional direction is forward. Several recommendations are offered with respect to rotor-bearing design so that this unique critical speed situation may be avoided.
A Numerical Method for the Dynamic Analysis of Rotating Flexible Blade-Disc-Shaft Assemblies
Authors: Jacquet-Richardet Georges , Ferraris Guy , Rieutord Pierre
Published: March 2021

A numerical method is proposed to compute the natural frequencies and mode shapes of rotating flexible blade-disc-shaft assemblies The formulation is based on a modal finite element analysis of the rotating system. The mode shapes used for the modal reduction are those associated to the global non-rotating undamped structure. To compute these modes, the size of the problem is reduced using both wave propagation and component mode techniques. An application is presented. The results obtained show that the chosen reductions do not reduce the quality of the model and illustrate its capability to deal with rotating shafts usually calculated using the rotordynamic approach. Finally, the possible dynamic interactions between shaft and disc components are described.
Modal Balancing of Quasi-Rigid Jet Engine Rotors With Exchangeable Rotor Modules
Authors: Schneider Hatto
Published: March 2021

Flexible rotor assemblies often consist of two or more rotor modules which are index-balanced against each other with the purpose of eliminating the need for re-balancing if a module should have to be exchanged. However, the index procedure may cause vibration problems because it ignores certain flexible rotor balancing requirements. This paper describes a modal balancing approach based on jet engine rotors which are typically balanced as ISO Class 2 (quasi-rigid) rotors. Appreciation is expressed to Prof. R. Gasch of TU Berlin for his valuable suggestions.
H2 Optimal Tuning of Passive Isolators and Absorbers
Authors: Van Pelt Tobin H. , Bernstein Dennis S.
Published: March 2021

Isolators and absorbers have been studied extensively as a means of passively suppressing vibration in mechanical systems. This paper derives the optimal tuning parameters for these passive suppression schemes with an H2 performance criterion. The H2 norm of a system is briefly reviewed, and its selection as a performance criterion is motivated. The optimal tuning scheme in the case of the absorber is then compared to the classical work of Den Hartog [1] and Snowdon [2]. The comparison shows little improvement in the H2 cost over the classical scheme, which suggests that the approximately optimal H∞ analysis of the absorber respects the optimal H2 cost. However, the reverse is generally not true, as in the case with increasing absorber masses.
Active Boundary Control of Elastic Cables
Authors: Baicu Catalin F. , Rahn Christopher D.
Published: March 2021

Cables are lightweight structural elements used in a variety of engineering applications. This paper introduces an active boundary control approach that damps undesirable vibrations in a cable. Using Hamilton’s principle, the governing nonlinear partial differential equations for an elastic cable are derived, including the natural boundary conditions associated with boundary force control. Based on Lyapunov theory, passive and active vibration controllers are developed. A Galerkin approach generates the linearized, closed loop, modal dynamics equations for out-of-plane vibration. Simulations demonstrate the improved damping provided by the passive and active controllers.
Optimum Structural Vibration Control With Bounds on Control Forces
Authors: Bolonkin Alexander A. , Veley Duane E. , Khot Narendra S.
Published: March 2021

This paper describes an approach for designing a structure-control system based on the linear quadratic regulator (LQR) which suppresses vibrations in structures. Bounds are placed on the control forces to simulate real actuators. The control system is optimized with an objective function of the total weight of the control devices. The design variables are the bounds (which are proportional to the weight of the control devices) on each control force with a constraint on the time to reduce the energy of the vibration to 5% of its initial value. As an example to illustrate the application of an approach, a wing box idealized by rod elements is used. Control systems are designed for this structure using four and eight actuators for several locations.
Control of a Slewing Motor-Beam System With Coulomb Friction
Authors: Crassidis Agamemnon L. , Mayne Roger W.
Published: March 2021

In this paper, a sliding mode controller is studied in the experimental control of a flexible undamped beam actuated by a DC motor and including Coulomb friction. A model of the system is described which includes a finite element representation for the beam and a representation for Coulomb friction. The model has been used in the study of closed-loop transient response of the slewing system and predicts the critical factors observed in slewing behavior. Development of the sliding mode controller is based on the nonlinear model of the system. The performance and characteristics of the controller are summarized in a simulation study. The sliding mode controller is particularly effective at eliminating the negative effects of shaft lock-up which tends to result from Coulomb friction and counteracts these nonlinear effects in the presence of modeling uncertainties. The system model includes the interaction that occurs between the DC motor and the slewing beam and a gear train that influences the motor-beam interaction. The effect of motor-beam dynamic interaction is studied for the nonlinear slewing system under sliding mode control. It is found that the motor-beam interaction continues to be an important factor in the closed-loop performance. The paper concludes with a summary of experimental results for the nonlinear control of the motor-beam system.
Bode Integral Constraints and the Zero Spillover Controller in Active Noise and Vibration Control
Authors: Hong Jeongho , Bernstein Dennis S.
Published: March 2021

With the success of feedforward techniques, feedback control researchers have begun to explore the relationship between these two control paradigms. The goal of the present paper is to further investigate the relationship between feedforward and feedback control techniques by means of the classical Bode integral constraint on achievable performance. These results provide insight into the phenomenon of spillover which has been widely discussed in the vibration control literature. Specifically, it is shown that a particular feedforward controller called the zero spillover controller avoids spillover by producing perfect disturbance cancellation at every frequency. For readability, we derive the approximate zero spillover controller which is shown to be an optimal feedback controller for an LQG problem with suitable cross weights. Finally, the results are illustrated by means of analytical and numerical examples.
Integrated Optimum Design of Structure and Control System by Modal Analysis
Authors: Kajiwara I. , Tsujioka K. , Nagamatsu A.
Published: March 2021

An approach for integrated optimum design of structure and control system is presented based on modal analysis. This approach consists of two process, namely the process by sensitivity analysis using optimal regulator theory and the process by the complex method in which a control system is composed of a small-order output feedback. In both processes, the design variables of the structural and the control parameters are optimized simultaneously in order to minimize the response due to disturbances of both white noise and colored noise. The integrated optimum design is performed by minimizing the objective function with respect to the response under the constraints of the control cost and the stability of the closed-loop system corresponding to high order natural modes. The validity and the usefulness of the present approach are verified by a vibration control experiment with a steel plate.
Stabilizing and Positioning Control of Inverted Flexible Pendulum by Means of H∞ Servo Control With Partial-State Feedback
Authors: Nishimura Hidekazu , Ohnuki Osamu , Nonami Kenzo , Totani Takayoshi
Published: March 2021

In this study we formulate H∞ servo compensator where displacement signals are used as the controlled variables and their time derivatives are used as partial-state feedback signals for stabilizing and positioning control of a cart and inverted flexible pendulum system. The feedback loop of the part of the state variables except the controlled variables is added to the feedback loop of the controlled variables in the design of the H∞ compensator. Through this formulation the order of the designed compensator is reduced by the order of the weighting functions for the time derivative signals. By numerical calculations and experiments, we investigate the settling characteristics and the robust stability against a disturbance to the pendulum with two kinds of controllers, the output feedback controller by the displacement feedback and the output feedback controller adding the cart velocity feedback. It is shown that although the displacement-output feedback controller has a big overshoot in the step response and the positioning of the cart is difficult, by means of the partial-state feedback controller with a cart velocity feedback the overshoot can be reduced and stable positioning control of the cart is possible. Also it is verified that the servo compensator is superior to the regulator-based compensator in the settling characteristics.
An ER Long-Stroke Damper: Performance Modelling Under Quasi-Steady Conditions
Authors: Peel David J. , Stanway Roger , Sproston John L. , Bullough William A.
Published: March 2021

A hydraulic piston/cylinder arrangement is connected to an externally located ER valve to provide a controllable vibration damper. This arrangement is analysed and a technique developed to predict the force/velocity characteristics under quasi-steady conditions. The basis of the technique is a generalised non-dimensional presentation of fluid-alone data. In the work described here fluid inertia, compressibility and temperature effects are not included. This limits the application of the results to cases where the excitation frequency is low whilst allowing a clear portrayal of the potential controllability of a long-stroke damping device.
Direct and Inverse Wave Propagation in the Frequency Domain via the Weyl Operator Symbol Calculus
Authors: Fishman Louis
Published: March 2021

Wave field splitting, invariant imbedding, and phase space methods reformulate the Helmholtz wave propagation problem in terms of an operator scattering matrix characteristic of the modeled environment. The equations for the reflection and transmission operators are first-order in range, nonlinear (Riccati-like), and, in general, nonlocal. The singularity structure of the corresponding Weyl operator symbols plays a crucial role in the development of both direct and inverse wave propagation algorithms.
Least Squares Estimation of Hydraulic Conductivity From Field Data
Authors: Bailey K. R. , Fitzpatrick B. G. , Jeffris M. A.
Published: March 2021

In this paper, we present some numerical results of the determination of flow parameters in a groundwater model. The data used in this parameter estimation is from the MADE experiments conducted on Columbus Air Force Base. Our results are based on least squares cost functional with a finite difference scheme used to solve the flow equation.
Nonsmooth Optimization Method for Image Restoration
Authors: Ito Kazufumi , Kunisch Karl
Published: March 2021

In this paper we discuss applications of the numerical optimization methods for nonsmooth optimization, developed in [IK1] for the variational formulation of image restoration problems involving bounded variation type energy criterion. The Uzawa’s algorithm, first order augmented Lagrangian methods and Newton-like update using the active set strategy are described.
Identification of the Polyharmonic Vibration From Combination With a Normal Random Noise by the Use of High-Order Moments of Instantaneous-Value Distribution
Authors: Steinwolf Alexander
Published: March 2021

Polyharmonic oscillation with multiple frequencies is inherent in many applied problems. However, it rarely exists in the pure form and is often accompanied by a random vibration. Separation of the periodic signal from the actual record measured is usually restricted to determining the harmonic amplitudes only. The paper presents a method for complete identification of polyharmonic process including the phase angles that were unattainable when its period is unknown a priori. The approach is based on the fact that the presence of a periodic component transforms the instantaneous-value probability distribution of the combined signal to the non-Gaussian form. The solution obtained is compared with the results of time domain averaging.