bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Pipes Containing Pulsative Flow
Authors: Szabó Zsolt , Sinha S. C. , Stépán Gábor
Published: February 2021

Several mechanical models exist on elastic pipes containing fluid flow. In this paper those models are considered, where the fluid is incompressible, frictionless and its velocity relative to the pipe has the same but time-periodic magnitude along the pipe at a certain time instant. The pipe can be modelled either as a chain of articulated rigid pipes or as a continuum. The dynamic behaviour of the system strongly depends on the different kinds of boundary conditions and on the fact whether the pipe is considered to be inextensible, i.e. the cross-sectional area of the pipe is constant. The equations of motion are derived via Lagrangian equations and Hamilton’s principle. These systems are non-conservative, and the amount of energy carried in and out by the flow appears in the model.

It is well-known, that intricate stability problems arise when the flow pulsates and the corresponding mathematical model, a system of ordinary or partial differential equations, becomes time-periodic. There are several standard techniques, like perturbation method, harmonic balance, finite difference, etc., to analyze these models. The method which constructs the state transition matrix used in Floquet theory in terms of the shifted Chebyshev polynomials of the first kind is especially effective for stability analysis of large systems. The implementation of this method using computer algebra enables us to obtain more accurate results and to investigate more complex models. The stability charts are created with respect to three important parameters: the forcing frequency ω, the perturbation amplitude υ and the mean flow velocity U.
Effect of Oil on the Dynamics of Compressor Suction Valve
Authors: Khalifa H. Ezzat , Liu Xin
Published: February 2021

The presence of oil on the suction valve of a reciprocating compressor has long been known to be responsible for the so-called valve stiction phenomenon. With stiction, the opening of the valve is delayed until later in the suction stroke, which results in a reduction in volumetric efficiency and increases the probability of valve failure. In this paper, a model is presented for analyzing the dynamic behavior of a round reed valve in the presence of oil. It is shown that the primary reason for stiction is the viscous force arising from dilating the oil film between the valve and its seat. This dilation takes place as the cylinder pressure on one side of the valve reed falls below the suction pressure in the intake plenum upstream of the valve. The viscous force delays the valve opening until later in the suction stroke. Because the film dilation resistance is directly proportional to the oil viscosity and decreases rapidly as the film thickens, the film eventually breaks and the valve begins to accelerate rapidly until it impacts the valve stop. The delayed rapid release of the valve and the associated impact are shown to subject the valve to much higher forces than would be experienced without the effect of stiction. The relative effect of oil viscosity and valve/seat contact area on valve force is presented for a representative reciprocating compressor equipped with suction valves.
Modification of the Craig-Bampton CMS Procedure for General Systems
Authors: de Kraker Bram , van Campen Dick H.
Published: February 2021

In this paper the Craig-Bampton CMS procedure for the reduction and successive coupling of undamped structural subsystems with symmetric system matrices will be modified for the case of general damping and nonsymmetric matrices. This leads to a Ritz-transformation matrix based on left- and right static and dynamic modes (complex vectors). The physical meaning of these modes will be illustrated and two examples (a damped beam system and a rotor-system with gyroscopy and a cross-coupling bearing model) will be presented and discussed showing the potential of this extension of the Craig-Bampton procedure.
Levitation and Torque Control of PM Synchronous and Induction Type Bearingless Motor
Authors: Okada Yohji , Miyamoto Shigenobu , Ueno Satoshi , Ohishi Tetsuo , Tan C. C.
Published: February 2021

General solution of levitation control applicable to PM synchronous and induction type rotating motor is presented. It is intended for a single rotor to have both functions of magnetic bearing and rotating motor. The rotational control is achieved with the traditional P pole magnetic flux, while the radial force is controlled with either P+2 or P−2 pole magnetic flux in the stator. In the previous work, the proposed general theory of levitated motor is successfully confirmed with no load experiments.

In this paper, the load capability of the levitated motor is tested using a horizontal type experimental setup. The stator has 8 concentrated wound electromagnets, each of which is controlled individually by a DSP and power amplifier. The radial load is the gravity of the rotor, while the produced rotating torque is measured with a noncontact variable torque load system. The results obtained are discussed in detail.
Analysis of Fabricated Gear Wheels Using Cyclic Symmetry in a PC Environment
Authors: Ramamurti V. , Bhattacharya A. , Manjula S.
Published: February 2021

A computer aided analysis of a heavy duty fabricated gear wheel is presented. The concept of CYCLIC SYMMETRY and the SKYLINE APPROACH are exploited to reduce the computer memory and time. Static and Eigen value analyses are conducted. This is followed by a Quasi Static analysis which gives an idea of the Dynamic behaviour of the gear wheel. The emphasis has been on the use of the PC for solving this industrial problem.
Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part I
Authors: Faulkner H. B. , Strong W. F. , Kirk R. G.
Published: February 2021

This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.
Coriolis Effect on Mode Localization in a Rotating Bladed Disk
Authors: Kuang J. H. , Huang B. W.
Published: February 2021

An investigation of the speed effect, i.e., the effects of centrifugal force and coriolis force, on the mode localization of a mistuned blade-disk is presented in this paper. A disk comprising of periodically shrouded blades is used to simulate the weakly coupled periodic structure. Galerkin method is employed to derive the mode localization equations of the mistuned system with the consideration of coriolis force. The blades are approximated as cantilever beams, and five axial and lateral modes of each blade are used to present the dynamic behavior of the system. Ten modal coordinates have been considered for each blade. The effects of coriolis force and the magnitude of disorder on the localization phenomenon of a rotating blade-disk system were investigated numerically. Numerical results obtained herein indicate that the coriolis force may enhance the localization phenomenon.
Analysis and Synthesis of Dynamic Response of a Flexibly Coupled Rotor Assembly
Authors: Chaika Valdas
Published: February 2021

Torsional vibration of two flexibly coupled reciprocating machines is investigated. The rotors of the machines are connected by elastic couplings of several types. The system is excited by a harmonic torque. The excitation frequency is proportional to the rotational speed which varies within a wide range. The motion of the system is described by nonlinear ordinary differential equations. These are linearized for the specific case of the rotor assembly design. Applying impedance functions, a closed-form solution of the equations of motion is derived. Three different cases of the system response are analyzed in the frequency domain. The passive vibration control of the rotor assembly using the centrifugal coupling is investigated. An analytical synthesis technique of the coupling parameters is devised.
Modeling and Analysis of Spinning Disk-Spindle Vibration
Authors: Parker Robert G.
Published: February 2021

This work develops the equations of motion for a spinning disk-spindle system. Furthermore, a formulation of the governing equations in terms of extended operators reveals the classical gyroscopic nature of the system. The disk and spindle are modeled as elastic continua coupled by a rigid clamp. System kinematics and dynamics are derived for steady rotation about the spindle axis. The analytical model consists of three partial differential equations for the disk and spindle vibration coupled by four dynamic momentum balances for the clamp translation and rotation. The inherent structure of the system is clarified with the definition of extended operators that collect the component equations into a compact analytical form. The extended operators are easily identified as the classical inertia, elastic bending stiffness, gyroscopic, and rotational stiffness operators. These extended operators possess the symmetry and definiteness characteristics that define gyroscopic continua. Consequently, classical methods for gyroscopic systems are readily applied to disk-spindle systems. The disk-spindle eigensolution, closed-form modal analysis, and discretization procedures that follow naturally from the structured formulation are discussed.
Comparison of Bending Models of Multiwire Strand
Authors: Jayakumar C. V. , Sathikh S. , Jebaraj C.
Published: February 2021

Nine discrete thin rod models are critically compared for their merit for studying the bending response of strands. Four bench marks employed for comparison are two (upper and lower) bounds of bending stiffness and two strand curvatures at slip initiation and completion. The strand configuration chosen, the way in which the lay angle is employed to describe the effective area of cross section as well as moments of inertia of the wire and the components of forces; the inclusion or omission of the wire interaction with the core through friction contact and the moment of inertia of the wire about its own diameter; and of wire couples in part or full are identified as factors that make the difference. Numerical values of the four bench marks for these models are presented.
Nonconservative Stability of a Friction Loaded Disk
Authors: Tseng Jung-Ge , Wickert Jonathan A.
Published: February 2021

This paper investigates the vibration of an annular disk that is subjected to rotation and in-plane frictional traction distributed over a sector of the disk’s two faces. Technical applications include noise, vibration, and harshness in automotive and aircraft disk brakes, and other rotating machine components. To the degree that the rotor-to-stator friction in such cases is directed along the disk’s deformable surface, it is treated here as a nonconservative follower-type load. The vibration model incorporates membrane stiffness which derives from rotation and the stresses established as a result of friction. The plane stress state is determined in closed form as a Fourier series, and that solution is compared with the companion, but computationally intensive, results from finite element analysis. For the cases of sector-shaped and full annular loading, the vibration model predicts the critical mode, which is defined as the one that becomes dynamically unstable at the lowest friction level. Vibration modes that fall into opposite symmetry classes, both with and without rotation, also have opposite stability-characteristics in the presence of frictional loading.
Design and Control of Shipboard Cranes
Authors: Yuan Guo Hui , Hunt Brian R. , Grebogi Celso , Ott Edward , Yorke James A. , Kostelich Eric J.
Published: February 2021

We propose a new cable rigging for a ship crane in order to control load pendulation. The “Maryland Rigging” involves the addition of a pulley-brake mechanism to the existing configuration. We show numerically that by applying friction in this rigging system we are able to reduce pendulation enormously.
Forced Oscillations of a Continuous Rotor With Geometric Nonlinearity: Internal Resonance Phenomena at Harmonic and Subharmonic Resonances
Authors: Ishida Yukio , Nagasaka Imao , Lee Seongwoo
Published: February 2021

Harmonic resonances and subharmonic resonances of order 1/2 and order 1/3 in a continuous rotating shaft with distributed mass are discussed. The restoring force of the shaft has geometric stiffening nonlinearity due to the extension of the shaft center line. It is supposed that a distributed bias force, such as the gravity, works. The possibility of their occurrences, the shapes of resonance curves, and internal resonance phenomena are investigated.
Some Interesting Characteristics of a Simple Autonomous Impact System With Symmetric Clearance
Authors: Mattos M. C. , Weber H. I.
Published: February 2021

The study of impact systems is gaining increased interest due to many practical situations where impact affects the overall dynamics. However, there are few results in the literature leading to a clear understanding about how the dynamics of MDOF systems with impacts changes, as several parameters are altered. In this work we investigate changes in the response of a 2-DOF impact system with symmetric clearance as the clearance is varied. The analyzed system is autonomous, so that the changes in its response are related only to the alteration in its “self dynamics”. As a second goal we investigate the occurrence or not of the migration of characteristic frequencies1 such as it was observed by Piccoli (1994) in a rotor with clearance and impact in one of its bearings.
Post-Critical Dynamics of an Axially Moving Beam
Authors: Vestroni Fabrizio , Pellicano Francesco
Published: February 2021

In the present paper, the dynamic behaviour of a beam subjected to an axial transport of mass is analyzed. The Galerkin method has been used to discretize the problem; a high dimensional system of ordinary differential equations with linear gyroscopic part and cubic nonlinearities is obtained. The system is studied in the sub and supercritical speed ranges with emphasis on the global dynamics that exhibits special features after the first bifurcation. A sample case of a physical beam is developed and numerical results are presented concerning linear subcritical behaviour, static bifurcation analysis including linear stability and direct simulation of global postcritical dynamics.
Identification of a Two Degree of Freedom Experimental System Using a Force Appropriation Approach
Authors: Atkins P. A. , Wright J. R.
Published: February 2021

The identification of nonlinear multi degree of freedom systems involves a significant number of nonlinear cross coupling terms, whether the identification is carried out in spatial or modal domains. One possible approach to reducing the order of each identification required is to use a suitable pattern of forces to drive any mode of interest. For a linear system, the force pattern required to drive a single mode is derived using a Force Appropriation method. This paper presents a method for determining the force pattern necessary to drive a mode of interest of a nonlinear system into the nonlinear region whilst the response is controlled to remain in proportion to the linear mode shape. Such an approach then allows the direct nonlinear modal terms for that mode to be identified using the Restoring Force method.

The method for determining the relevant force patterns is discussed. The implementation of the method for experimental systems is considered and experimental results from a two degree of freedom ‘benchmark structure’ are presented. Two methods of estimating the mass for a restoring force identification are compared.
Active Isolation Design for a Flexible Base
Authors: Sciulli Dino , Inman Daniel J.
Published: February 2021

It has been commonly assumed that the corner or mount frequency in an isolator should be designed as low as possible. This is one result of using a single-degree-of-freedom (SDOF) system to model isolation systems. However, for systems that have flexible or nonrigid foundations, a design point for the mount frequency can occur between the modes of the base. By implementing this type of design, a strong interaction will exist between the modes. When isolator damping is included, whether done passively or actively, more than one mode can be attenuated for this new mount design. Therefore, the effects of the mount frequency on isolation designs are discussed as well as using both passive and active damping in the isolator. For active damping, three commonly used control methodologies are discussed: a proportional-plus-integral-plus-derivative (PID) controller, a positive position feedback (PPF) controller, and a linear quadratic Gaussian (LQG) regulator.
Semiactive Control of Multiple Degree of Freedom Systems
Authors: Ahmadian Mehdi
Published: February 2021

Semiactive control of systems with multiple degrees of freedom is addressed. Two systems representing a pitch-plane model of a vehicle and a single suspension are used to illustrate the results. The dynamic simulations show the well-known compromise between resonance control and isolation, due to passive dampers. It is shown that semiactive dampers also compromise between controlling different bodies. For skyhook and groundhook control policies, the control of one body is achieved at the cost of less control on the other bodies. For instance, in a single suspension model, skyhook semiactive dampers better control the body resonance, but significantly increase the axle resonance (wheelhop). The groundhook dampers provide a better control of wheelhop at the expense of increasing body resonance. A hybrid control policy that combines the effect of skyhook and groundhook policies is introduced. This policy can be used to provide the proper control on all bodies, while using the hardware common to existing semiactive dampers.
Dynamics of CVT Chain Drives: Mechanichal Model and Verification
Authors: Srnik Jürgen , Pfeiffer Friedrich
Published: February 2021

This paper deals with the dynamics of continuously variable (CVT) chain drives. According to the discrete structure of the chain, which causes the polygonal actions, the mechanical model contains each chain link and pulley as a separate body. While a chain link is part of a strand, only joint forces including friction act on the chain links, whereas in the contact situation additional impulsive and frictional forces in the contact zones between the chain link’s rocker pins and the tapered surfaces of the cone pulleys have to be taken into account. For the calculation of the contact forces Coulomb’s friction law as well as a time sparing continuous approximation are applied.

Simulation results show the influence of the cone pulley’s deformation on the power transmission. They also show the repercussion of the polygonal action. Furthermore the chain’s pitch influence on the vibrational behavior of the transmission is discussed. A comparison of calculated and measured tensional forces verifies the model presented.
Wavelet Novelty Measure for Machinery Diagnostics
Authors: Staszewski Wiesław J.
Published: February 2021

The paper is concerned with wavelet analysis for fault detection in machinery diagnostics. A new approach based on novelty detection is presented. The method involves a wavelet compression algorithm to vibration data in order to extract a set of features which are related to the fault. The compression algorithm uses orthogonal Daubechies’ wavelets and a simple thresholding procedure. The wavelet based novelty measure is established as a statistical distance between decoded data representing different fault advancements.
Simultaneous Stiffness and Mass Change Detection Based on Reduced Measurements
Authors: Baruch Menahem
Published: February 2021

Simultaneous changes in the stiffness and mass matrices of a dynamic structure can be detected by using reduced measurements. In the method proposed here, both, the stiffness and the mass matrices, are assumed to be incorrect. The missing measurements can be calculated by utilizing the connection between the measured and unmeasured quantities trough the iterative process of identification of the tested structure. The missing measurements and to some extend the partial measurements obtained during the tests are treated as hidden functions of the parameters of the structure. This makes the Euclidean norm of the appropriate matrix to be minimized a nonlinear function of the parameters. This norm may have more than one minimum. The changes in the stiffness and mass matrices must be identified by looking for the global minimum of the Euclidean norm. The global minimum can be found by changing the initial values of the parameters or by changing some special coefficients, or both. A discussion of the minimal number of necessary measurements in connection with the number of the parameters of the stricture is included.

In order to identify the stiffness and mass parameters of the structure the measured and the supplied missing quantities are forced to comply with the general laws for a linear structure. This compliance is achieved during any step of the iterative process.

The structure is idealized to be a linear dynamic structure without damping. The reduced measured quantities are measured during the tests at discrete points of the Frequency Response Function.
Updating of Impact Models for Vibrating Cantilever Beams
Authors: Szwedowicz Dariusz , Sotelo Carlos A.
Published: February 2021

In the paper, the numerical technique for simulations of impact problems of stationary vibrating beams is proposed. Good qualitative agreements between the computed and measured impact forces and contact duration are obtained. For getting better quantitative agreements between the measurements and simulations, some improvements of the experimental set-up are discussed.
Updating Rotor-Bearing Finite Element Models
Authors: Mares Cristinel , Surace Cecilia
Published: February 2021

In this paper, the possibility of updating the finite element model of a rotor-bearing system by estimating the bearing stiffness and damping coefficients from a few measured Frequency Response Functions using a Genetic Algorithm is investigated. The issues of identifiability and parameters estimation errors, computational costs and algorithm tuning are addressed. A simulated example of a flexible rotor supported by orthotropic bearings is used for illustrating the method.
Damage Detection Based on Vibration Measurements and Inaccurate Models
Authors: Fritzen C.-P. , Jennewein D. , Kiefer Th.
Published: February 2021

The paper presents a model-based approach for the detection of structural damage with respect to location and extent from measured vibration test data. The method which is tolerant to small modeling errors is based upon an analytically redundant mathematical model approximately representing the undamaged structure.

The motivation was that in many practical cases it is not possible to obtain perfect correlation between the undamaged system and the original model due to modeling uncertainties or excessive modeling cost.

On the other hand, in the early phase of damage evolution the changes of the dynamical characteristics are very small. If the changes due to the damage are superimposed by the effects of mismodeling it is nearly impossible to get reliable diagnostic results. Therefore, an approach is presented here for the case that a perfect model cannot be obtained.

The resulting inverse problem usually is ill-posed, so that special attention must be paid to its accurate numerical solution. The application to damage detection problems requires the reduction of a large set of damage parameter candidates to a small subset of one or two parameters really describing the local change of the system. An orthogonalization strategy is given to reduce the parameter set and Akaike’s information criterion is used to confirm the correct size of the parametrization.

The method is applied to two laboratory structures: a multi-story frame and a damaged plate. The results show that the algorithm is able to localize and quantify the damage also in the presence of modeling errors.
The Application of Probability Theory to Model Updating
Authors: Papadopoulos Loukas , Garcia Ephrahim
Published: February 2021

A method is proposed for probabilistically model updating an initial deterministic finite element model using measured statistical changes in natural frequencies and mode shapes (i.e., modal parameters). The approach accounts for variations in the modal properties of a structure (due to experimental errors in the test procedure). A perturbation of the eigenvalue problem is performed to yield the relationship between the changes in eigenvalues and in the global stiffness matrix. This stiffness change is represented as a sum over every structural member by a product of a stiffness reduction factor and a stiffness submatrix. Monte Carlo simulations, in conjunction with the variations of the structural modal parameters, are used to determine the variations of the stiffness reduction factors. These values will subsequently be used to estimate statistics for the corrected stiffness parameters. The effectiveness of the proposed technique is illustrated using simulated data on an aluminum cantilever Euler-Bernoulli beam.
Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part II
Authors: Faulkner H. B. , Strong W. F. , Kirk R. G.
Published: February 2021

This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.
Critical Speeds of Shaft-Disk Systems Subjected to Longitudinal Forces
Authors: Chen Lien-Wen , Sheu Hong-Cheng
Published: February 2021

The critical speeds of a spinning Timoshenko shaft with an intermediate attached disk subjected to a longitudinal force are analytically solved. The expressions of whirl speed equations for hinged-hinged, hinged-clamped, clamped-hinged, and clamped-clamped rotors are given respectively. The critical speeds of each shaft-disk system are sought from its corresponding whirl speed equation by using simple numerical techniques. The effects of the disk location and the longitudinal force on the critical speeds of the shaft-disk systems are investigated. Numerical results reveal that if the disk locates in the left portion of the shaft, both the primary forward and backward critical speeds for the rotor subjected to a follower force are larger than those subjected to an axial force with the same magnitude. The results are contrary while the disk locates in the right portion of the shaft.
Nonlinear Dynamic Performance Analysis of Elastic Linkage Mechanisms
Authors: Xianmin Zhang , Xuemei Guo
Published: February 2021

In this paper, the generalized nonlinear equations of motion for elastic linkage mechanism systems are presented, in which the gross motion and elastic deformation coupling terms and the geometric nonlinearity effects are taken into account. The equations of motion are period and time-varying nonlinear equations. According to the characteristics, solution method for this kind nonlinear equations is investigated, and an efficient closed-form iterative procedure is presented. The effects of geometric nonlinearity on linkage mechanisms are studied. The results of this study are important for dynamic design of linkage mechanism systems.
Impact Analysis of Flexible Multi-Armed Terrestrial Robots
Authors: Bakr E. M.
Published: February 2021

A nonlinear formulation for the dynamic analysis of a flexible multi-armed terrestrial robot system which is subjected to a sudden collision during its functional use is presented. Finite rotations and large deformations of the arms are accounted for by using a Timoshenko beam theory of flexural vibration. Impacts and associated impulsive forces are incorporated into the formulation using a generalized impulse momentum balance. Numerical experimentations indicate that the use of a geometrically nonlinear Timoshenko beam model that can undergo large reference rotations could have a significant effect on the transient response of multi-armed robots subjected to impact loading.
Recovery of Joint Reaction Force for Real-Time Recursive Multibody Dynamics
Authors: Tsai Fuh-Feng , Mirtaheri Masoud
Published: February 2021

This paper proposes a formulation and parallel algorithm for the computation of all joint reaction forces in the recursive multibody dynamics. First, the Lagrange Multipliers associated with cut joints in each decoupled loop of a mechanical system are recovered. Then the joint reaction forces for the cut joints are computed directly using the obtained Lagrange Multipliers. After that, joint reaction forces associated with uncut joints are computed in backward computational paths, using synchronization in all junction nodes. A parallel algorithm for recovering reaction forces and torques for all cut joints and uncut joints is proposed. For validation, a space slider 3-D model is illustrated to compare the simulation results with those obtained from a commercial code DADS. Finally, A passenger car 14-body model is generated and simulated to obtain the joint reaction forces for the purpose of vehicle component design purpose.
Fault Identification for Rotating Machinery Using Adaptive Signal Processing and Time-Frequency Analysis
Authors: Lee Sang-Kwon , White Paul R.
Published: February 2021

Impulsive sound and vibration signals in rotating machinery are often associated with faults which lead to due to irregular impacting. Thus these impulsive sound and vibration signals can be used as indicators of machinery faults. However it is often difficult to make objective measurement of impulsive signals because of background noise signals. In order to ease the measurement of impulsive sounds embedded in background noise, we enhance the impulsive signals using adaptive signal processing and then analyze them in time and frequency domain by using time-frequency representation. This technique is applied to the diagnosis of faults within internal combustion engine and industrial gear.
Analysis of Dynamic Stress Responses in Structural Vibration
Authors: Huang Liping
Published: February 2021

This paper describes basic concepts and finite element method of dynamic stress response analysis. It provides basics of stress modal analysis and frequency response analysis. The paper defines concepts of normal mode stresses and complex stress frequency response functions for shell elements and shows that element stress responses in both time and frequency domains can be expressed as superposition of normal mode stresses. It demonstrates that element stress response solutions have the similar forms to those of node displacement responses and that normal mode stresses in stress analysis play the same role as mode shapes in normal vibration analysis.
Identification of Viscoelastic Properties of Finite Element Structures With Joints
Authors: Herrmann Torsten , Chaika Valdas
Published: February 2021

Identification of the damping and stiffness parameters of the composite joints in finite element structures is analyzed. For the modeling of the viscoelastic properties of the joints the classical Voigt-Kelvin and generalized Maxwell model (three parameter solid) are used. A time domain identification algorithm for classically and non-classically damped dynamic systems is developed. It is based on the application of an extended Kalman filter and least square technique. The algorithm uses complex modal analysis and sparse matrix technology. Both force and base excited systems are considered. Experimental verification of the identification results is carried out on a test structure. The accuracy of the modeling of damping in the joint using the Voigt-Kelvin and generalized Maxwell models is investigated.
Seabed type and source parameters predictions using ship spectrograms in convolutional neural networks
Authors: Van Komen David F. , Neilsen Tracianne B. , Mortenson Daniel B. , Acree Mason C. , Knobles David P. , Badiey Mohsen , Hodgkiss William S.
Published: February 2021

Broadband spectrograms from surface ships are employed in convolutional neural networks (CNNs) to predict the seabed type, ship speed, and closest point of approach (CPA) range. Three CNN architectures of differing size and depth are trained on different representations of the spectrograms. Multitask learning is employed; the seabed type prediction comes from classification, and the ship speed and CPA range are estimated via regression. Due to the lack of labeled field data, the CNNs are trained on synthetic data generated using measured sound speed profiles, four seabed types, and a random distribution of source parameters. Additional synthetic datasets are used to evaluate the ability of the trained CNNs to interpolate and extrapolate source parameters. The trained models are then applied to a measured data sample from the 2017 Seabed Characterization Experiment (SBCEX 2017). While the largest network provides slightly more accurate predictions on tests with synthetic data, the smallest network generalized better to the measured data sample. With regard to the input data type, complex pressure spectral values gave the most accurate and consistent results for the ship speed and CPA predictions with the smallest network, whereas using absolute values of the pressure provided more accurate results compared to the expected seabed types.
Remote sociophonetic data collection: Vowels and nasalization over video conferencing apps
Authors: Freeman Valerie , De Decker Paul
Published: February 2021

When the COVID-19 pandemic halted in-person data collection, many linguists adopted new online technologies to replace traditional methods, including video conferencing applications (apps) like Zoom (Zoom Video Communications, San Jose, CA), which allow live interaction with remote participants. This study evaluated the suitability of video calls for the phonetic analysis of vowel configurations, mergers, and nasalization by comparing simultaneous recordings from three popular video conferencing apps (Zoom; Microsoft Skype, Redmond, WA; Microsoft Teams, Redmond, WA) to those taken from professional equipment (H4n field recorder) and an offline iPad (Apple, Cupertino, CA) identical to those running the apps. All three apps conveyed vowel arrangements and nasalization patterns relatively faithfully, but absolute measurements varied, particularly for the female speaker and in the 750–1500 Hz range, which affected the locations (F1 × F2) of low and back vowels and reduced nasalization measurements (A1-P0) for the female's prenasal vowels. Based on these results, we assess the validity of remote recording using these apps and offer recommendations for the best practices for collecting high fidelity acoustic phonetic data from a distance.
Relationship Between Employment Status, Reported Physical Activity, and Sitting Time During COVID-19 Pandemic
Authors: Lindsey Bryndan W. , Boolani Ali , Merrigan Justin J. , Cortes Nelson , Caswell Shane V. , Martin Joel R.
Published: February 2021

Background: The COVID-19 pandemic has changed our working environment and divided workers into essential or nonessential statuses. Employment status is a major factor determining the amount of physical activity performed. Our purpose was to understand how employment status affects physical activity and sitting time. Methods: Between April 13 and May 4, 2020, 735 full-time employed individuals responded to a survey investigating daily life and overall health during the COVID-19 pandemic. Participants reported how much physical activity they had performed in the last 7 days. Multiple linear regressions were performed for physical activity and sitting time. Results: Physical activity was not associated with employment status. An interaction effect between hours worked and employment status was found for sitting time. Conclusions: Employment status was not related to physical activity; however, it did affect the amount of time spent sitting, with nonessential employees sitting more and working more hours than essential employees. Because greater amounts of daily total sitting time have been associated with increased risk of all-cause mortality, it is important that increased sitting time be attenuated by greater physical activity.
Structure and dynamics of the CGRP receptor in apo and peptide-bound forms
Authors: Josephs Tracy M. , Belousoff Matthew J. , Liang Yi-Lynn , Piper Sarah J. , Cao Jianjun , Garama Daniel J. , Leach Katie , Gregory Karen J. , Christopoulos Arthur , Hay Debbie L. , Danev Radostin , Wootten Denise , Sexton Patrick M.
Published: February 2021

Dynamic activation of a GPCR

G protein–coupled receptors (GPCRs) coordinate a complex information flow between the outside and inside of a cell. An increasing number of GPCR structures provide insight into function. However, the dynamics that link extracellular sensing to intracellular signaling are not completely understood, because GPCRs used in structure determination are generally modified to constrain their dynamics. Josephs
et al.
succeeded in determining the structures of an unmodified calcitonin gene–related peptide receptor, which is implicated in migraines, both alone and bound to its neuropeptide ligand. Based on the structures and data from complementary biophysical techniques, they show that initial binding of the peptide causes only minor conformational changes of the GPCR, but dynamically causes changes at the intracellular side that facilitate G protein binding and activation.

Science
, this issue p.
eabf7258
The Need for Dedicated Microbiology Leadership in the Clinical Microbiology Laboratory
Authors: Samuel Linoj P. , Hansen Glen T. , Kraft Colleen S. , Pritt Bobbi S.
Published: February 2021

Clinical microbiology laboratories play a crucial role in patient care using traditional and innovative diagnostics. Challenges faced by laboratories include emerging pathogens, rapidly evolving technologies, health care-acquired infections, antibiotic-resistant organisms, and diverse patient populations.
Supplemental Material: Segmentation of the Wassuk Range normal fault system, Nevada (USA): Implications for earthquake rupture and Walker Lane dynamics
Authors: Surpless Ben , Thorne Sarah
Published: February 2021

T-test results for comparison of footwall domain data.
Keeping young people connected during COVID-19: the role of online groups
Authors: Flannery Halina , Portnoy Sara , Daniildi Xeni , Kambakara Gedara Chandrika , Korchak Gina , Lambert Danielle , McParland James , Payne Lara , Salvo Tania , Valentino Charlotte , Christie Deborah
Published: February 2021

The COVID-19 pandemic has had a profound impact on young people, disrupting education, routines, hobbies and peer interactions and there is concern for longer term effects on physical and mental health outcomes. Young people living with chronic health conditions face additional challenges including reduced or no face-to-face contact with medical teams, shielding and the increased stressors of being in ‘at-risk’ groups and social isolation. In a climate of social isolation and disconnectedness, online groups could provide a method of delivering healthcare and support that strengthens social connectedness and reduces isolation. Despite the technology being available, uptake and evidence for online groups is limited. This article shares learnings from a paediatric and adolescent psychology service delivering online groups for young people with chronic health conditions and their healthcare teams. Ideas for how to transfer group process to online platforms are considered, with examples and tips. With sufficient staffing, preparation, thought, creativity and innovation, it is possible for face-to-face groups to successfully be offered online. Caution should be exercised trying to run online groups without these provisions in place, as the safety, comfort and experience of young people could be jeopardised. Further research is needed to better understand group processes online and to consider what is lost and what is gained when comparing online to face-to-face groups.
Endovascular mechanical thrombectomy and stenting in a case of central vein thrombosis
Authors: Vijayvergiya Rajesh , Kaur Navjyot , Sahoo Saroj K , Sharma Ashish
Published: February 2021

Central vein stenosis and thrombosis are frequent in patients on haemodialysis for end-stage renal disease. Its management includes anticoagulation, systemic or catheter-directed thrombolysis, mechanical thrombectomy and percutaneous transluminal angioplasty (PTA). Use of mechanical thrombectomy in central vein thrombosis has been scarcely reported. We hereby report a case of right brachiocephalic vein thrombosis with underlying stenosis, which was successfully treated by mechanical thrombectomy followed by PTA and stenting. The patient had a favourable 10 months of follow-up.
Q fever: a rare but potentially life-threatening zoonotic disease
Authors: Mahajan Pranav , Pant Kailash , Majdizadeh Shirin
Published: February 2021

Q fever can present as a fever of unknown aetiology and can be challenging to diagnose because of the rare incidence. It can present as an acute illness with manifestations, including influenza-like symptoms, hepatitis, pneumonia or chronic disease involving the cardiovascular system. We present a case of a 39-year-old woman in the USA, who developed acute Q fever with associated sepsis and severe hepatitis. She received treatment with recovery from acute infection but currently has symptoms of post Q fever syndrome.
Hyperbaric oxygen therapy for refractory pyoderma gangrenosum: a salvage treatment
Authors: de Sousa Magalhães Rui , Moreira Maria João , Rosa Bruno , Cotter José
Published: February 2021

A 42-year-old woman with left-side ulcerative colitis (E2 – rectum to splenic flexure) was diagnosed with pyoderma gangrenosum (PG) on a persistent ulcerated wound with peripheral erythema, in the left leg’s gemelar surface, associated with tenderness and pain. Due to incomplete response to wound care and oral prednisolone, treatment with infliximab was initiated. As PG remained unresponsive after 12 weeks, the patient was switched to adalimumab with concomitant oral prednisolone. Before the second induction dosage of adalimumab, the refractory PG complicated with a superinfection byPseudomonas aeruginosa. A course of wide spectrum antibiotic therapy, daily wound care including negative pressure bandages and a physiotherapy rehabilitation programme controlled the infection, but the pyoderma persisted non-healed, with visible deep muscle layers and tendons. We proposed hyperbaric oxygen therapy in addition to weekly adalimumab, achieving full remission of the PG and recovering of the left foot’s function.
Duplication of the internal jugular vein: a rare presentation during neck dissection
Authors: Burman Samriddhi , Pandey Sameer , Rao Sruthi , Rao Santhosh
Published: February 2021

The anatomical variations of the internal jugular vein (IJV) is a well-documented phenomenon which may depend on the course of drainage, fenestration in the vein, bifid formation, variations in the tributaries and so on. However, a true duplication of the IJV is a rare entity on its own and is seldom reported in the literature. We report a case of true duplication of IJV which is an incidental discovery during the course of neck dissection.
Painful, reappearing eruption in a medically complex 4-year-old
Authors: Sooy Meredith , Randell Rachel L , Tchapyjnikov Dmitry , Werner Klaus , Nazareth-Pidgeon Kristina
Published: February 2021

A 4-year-old boy with atypical, complete DiGeorge and CHARGE (coloboma, heart defects, atresia choanae, growth retardation, genital abnormalities and ear abnormalities) syndromes presented with frequent episodes of a painful, markedly erythematous eruption associated with swelling. Evaluation revealed non-specific findings on skin biopsy at the time of eruption and no pathogenic mutation in the SCN9A gene. The patient was diagnosed with secondary erythromelalgia based on clinical presentation. Erythromelalgia is a rare disorder characterised by recurrent episodes of pain and erythema typically affecting the distal extremities. This case represents the first case of erythromelalgia in the setting of DiGeorge and CHARGE syndromes.
Catatonia in a 10-year-old boy with early childhood neglect and disruptive behaviours in psychiatric residential treatment
Authors: Giggie Marisa A
Published: February 2021

Catatonia is a rare medical condition that can be fatal in paediatric patients if left untreated. It is often misdiagnosed or underdiagnosed. There are no published cases of catatonia in traumatised children living in long-term psychiatric care. However, there is some evidence that childhood maltreatment in its variant forms may be a risk for the development of catatonia in children and adolescents. In this case, a 10-year-old boy with intrauterine exposure to alcohol and multiple drugs and early childhood deprivation, developed neuroleptic-induced catatonia in an intensive psychiatric residential treatment centre approximately 24 hours after receiving a first-time intramuscular injection of haloperidol 5 mg for acute agitation. He had no known predisposing factors for catatonia such as psychosis, autism, neurological or general medical problems. This 10-year-old child’s early childhood trauma should be considered as a predisposing factor for catatonia.
Superiorly based subperiosteal orbital abscess: an uncommon presentation
Authors: Chrysovitsiotis Georgios , Kollia Paraskevi , Kyrodimos Efthymios , Chrysovergis Aristeidis
Published: February 2021

A 32-year-old female patient presented with severe facial pain, right eye proptosis and diplopia. Endoscopy revealed ipsilateral crusting, purulent discharge and bilateral nasal polyps. Imaging demonstrated a subperiosteal abscess on the roof of the right orbit. Due to patient’s significant ocular manifestations, surgical management was decided. The abscess was drained using combined endoscopic and external approach, via a Lynch-Howarth incision. Following rapid postoperative improvement, patient’s regular follow-up remains uneventful. A subperiosteal orbital abscess is a severe complication of rhinosinusitis that can ultimately endanger a patient’s vision. It is most commonly located on the medial orbital wall, resulting from direct spread of infection from the ethmoid cells. The rather uncommon superiorly based subperiosteal abscess occurs superiorly to the frontoethmoidal suture line, with frontal sinusitis being its main cause. Treating it solely endoscopically is more challenging than in medial wall abscesses, and a combined approach is often necessary.