bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flexural Vibration of Turbine Generator Rotors: Application of Modal Analysis to Predictions of the Effects of Light Rubs
Authors: Wilkinson Terence S. 
Published: March 2021

Abstract
Methods for calculating the effects of periodic contact between the stators and rotors of large turbine generator systems are discussed. The case of periodic contact between a stator and part of the LP turbine rotor of a modern turbine generator is selected for study. The rotor is part of a train which includes, in order, HP, IP, and (one) LP turbines, each supported by two journal bearings solidly coupled to each other and to an alternator which is supported by three bearings, one of which carries little load and is popularly known as a steady bearing. The periodic contact is supposed to be caused by poor alignment of the rotor relative to the stator and by vibration of the rotor due to unbalance. Comparisons are made between the effects predicted using modal analysis, using models of the LP turbine rotor of Jeffcott type (Wilkinson, 1987), and those obtained using more accurate methods. It is assumed that the normal forces generated during contact are proportional to the interference between rotor and stator and that the tangential force can be calculated with sufficient accuracy by using a coefficient of friction. It is shown that light rubs usually causes periodic synchronous responses but subharmonics may also appear. There is little doubt that chaotic vibration will ensue if rubs become heavier than those considered.
It is suggested mat modal analysis methods are probably best for long rotor systems, however, the simplest models reveal the correct qualitative behaviour.
The work forms part of a wider investigation of the effects of rotor/stator interaction and at the time of writing a test rig is being manufactured to facilitate the measurement of response to unbalance, the effects of misalignment and the response to light rubs. Aspects of the design of the six bearing rig, which is claimed to be a true scale model of a substantial fragment of the nine bearing turbine generator rotor system discussed earlier, are also described.
Calculated Rotordynamic Behaviour of a Twin Spool Engine and the Comparison With Test Results
Authors: Domes B. , Hartmüller H. , Tokar G. , Wang G. 
Published: March 2021

Abstract
The new BR 700 series of twin spool engines, of the thrust class of 15,000 to 20,000 pounds, is being developed for business jets. In this paper the rotordynamic vibration analysis is performed with a detailed whole engine model including both rotors, bearings with oil squeeze film dampers and squirrel cages, the engine structure, the mounts and the fuselage. The analytical method is described and some calculated results are presented. The effectiveness of the oil squeeze film dampers on all main bearings will be demonstrated. The comparison of the analytical and the measured results gives a good agreement in the resonance frequencies and in the damping characteristics. It also shows that a linear analysis can describe with sufficient accuracy the dynamic behaviour of such a complex structure like a twin spool engine under normal operating conditions.
Forced and Natural Vibration Analysis of Mistuned Practical Turbomachine Impellers Using Multifreedom Models
Authors: Petrov Evgueni P. 
Published: March 2021

Abstract
A computational technique is suggested to calculate forced and natural vibrations of axial flow turbomachine impellers having any kind of distortions of blading symmetry: as caused by blades’ mistuning due to inaccuracies of blade geometry within manufacturing tolerances and as caused by special design of blade connections by shrouds or wires. The impellers with flexible and stiff disk are examined. Multifreedom models are used for analysis. Peculiarities of excitation due to inhomogeneous aerodynamic loadings or rotor vibrations as well as damping in material, aerodamping are taken into account.
Passenger Ride Comfort Through Observer Based Control
Authors: Taghirad H. D. , Esmailzadeh E. 
Published: March 2021

Abstract
An analytical investigation of a half-car model including passenger dynamics, subjected to random road disturbances is performed, and the advantage of active over conventional passive suspension systems are examined. Two different performance indices for optimal controller design are proposed. The performance index is a quantification of both ride comfort and road handling. Due to practical limitations, all the states required for the state-feedback controller are not measurable, and thus must be estimated with an observer. Stochastic inputs are applied to simulate realistic road surface conditions, and statistical comparisons between passive system and the two controllers, with and without state estimator, are carried out to gain a clearer insight into the performance of the controllers. The simulation results demonstrate that an optimal observer-based controller, when including passenger acceleration in the performance index, retains both excellent ride comfort and road handling characteristics.
Rigid and Flexible Body Modeling for a Triaxial Shaker Control System
Authors: Dougherty John J. , El-Sherief Hossny , Nguyen Thanh 
Published: March 2021

Abstract
The modeling of a triaxial shaker system is discussed. The shaker system has eight inputs and six outputs. The models have been implemented in a computer simulation; both the rigid body and flexible body effects have been simulated. Results from the simulation have been compared to test data.
Dynamic Walk of a Quadruped Locomotion Robot Using Robust Optimal Tracking Control
Authors: Uchida Hiroaki , Nonami Kenzo 
Published: March 2021

Abstract
We propose a new control system design strategy that is called “frequency-shaped optimal tracking control method” in this paper. We make sure that the proposed method is very useful by creating the quasi-dynamic walk of a quadruped locomotion robot. During control of the locomotion robot, high feedback (FB) gains should be selected to work against the force and the moment from the body and the reaction force from the ground. However, if high FB gains are used, high frequency vibration comes out because of the backlash of the gear. Frequency-shaped optimal control is the control method to improve the robustness against the disturbance like high frequency vibration. Frequency-shaped optimal tracking control extends the frequency-shaped optimal control to the servo system like the trajectory following control of the robot. First, we’ll show the design scheme of the frequency-shaped optimal tracking control. Next, we’ll show how decentralized control is realized in order to apply frequency-shaped optimal tracking control. Finally, we’ll compare the frequency-shaped optimal tracking control with the optimal tracking control from the points of view of the simulations and the experiments.
Magnetically Induced Vibration in an 8-Pole, 9-Slot Brushless DC Motor
Authors: Chuang Thomas Y. , Lieu Dennis K. 
Published: March 2021

Abstract
A parametric study was conducted to determine the effect of motor geometry on the force imbalance in an 8-pole/9-slot motor. The study is based on a quasi-static finite element analysis in which the force calculations were made by integrating the Maxwell stresses along the center of the airgap. For small variations from the base motor geometry, the study revealed the following trends. The magnitude of the force imbalance decreases as the slot width decreases. The imbalance also decreases as the airgap length increases. A rotor/stator eccentricity introduces a constant force imbalance which increases proportionally to, and in the direction of, the eccentricity. As the size of the motor is scaled up uniformly, the mass increases faster than the imbalance. The results suggest that the force imbalance is caused predominantly by the stress concentrations at the corners of the stator teeth.
Optimal Length of Constrained Layers on a Substrate With Linearly Varying Strain
Authors: Demoret Kimberly B. , Torvik Peter J. 
Published: March 2021

Abstract
The performance of a constrained layer damping treatment is greatly affected by its length, and the damping effectiveness can be optimized by choosing a damping treatment length appropriate to the geometry and material properties of the viscoelastic and constraining layers. In this paper, the equilibrium equation and boundary conditions are formulated for a constraining layer on a substrate with a linearly varying strain distribution, and an analysis is developed that allows conclusions to be drawn about the optimal length of the constraining layer. Plunkett and Lee1 analyzed this problem for the special case of uniform strain in the substrate, and they showed that a loss coefficient depends only on the viscoelastic loss factor and a stiffness parameter that is a function of the material properties and thickness of the damping layers. In this paper, the uniform strain analysis is extended for the case of linearly varying substrate strain of the form ax+b, where a and b are arbitrary constants. The corresponding loss coefficient was shown to be a function of the parameters identified in the uniform strain problem, plus an additional parameter that accounts for the degree of non-uniformity of the substrate strain. It is shown that the non-uniformity of the substrate strain increases the length at which the damping treatment is optimized.
Optimal Damping of Vibrations in Multibody Systems Through Equivalent Friction Control Laws
Authors: Dakev Nikolay V. , Chipperfield Andrew J. , Fleming Peter J. 
Published: March 2021

Abstract
In the paper modelling and optimization of friction laws and energy exchange processes in multibody systems are considered. The multibody systems are regarded as chains of absolutely rigid bodies with compliance and friction concentrated at the connections. It is proposed to control the vibration level of such systems by introducing equivalent frictional forces. Such an approach enables modelling and optimization of passive and semi-active damping methods together with active control of vibrations in multibody systems within a unified framework. In particular, the equivalent friction laws can be regarded as controls minimizing deviations of the multibody system motion from the reference trajectory and used for total compensation of links cross interactions and stabilization of fast modes.
The corresponding optimal vibration control problem is formulated and reduced to a constrained optimization one in order to determine the optimal friction laws dissipating the oscillation energy. For linear vibration control problems numerical methods based on solving matrix Lyapunov and Riccati equations are discussed. Additionally, an approach employing a global search mechanism, the genetic algorithm, and parallel processing techniques, to alleviate the problem of computational burden, is proposed to solve general control problems for optimal vibration damping.
Two examples are presented in order to illustrate the proposed approach.
Experimental Identification of Structural Damage by Neural Networks
Authors: Ceravolo Rosario , De Stefano Alessandro , Grosjacques Michel , Sabia Donato 
Published: March 2021

Abstract
The problems involved in structural damage identification by means of pattern recognition neural techniques are addressed. As is known, mechanical system recognition can be achieved by making appropriate use of these connectionistic instruments. Recognition takes place on the basis of an incomplete set of data contained in the system’s dynamic response.
Some methods, previously developed by the authors on the basis of numerical models, are validated through the use of noisy data. To this end, an experimental research was carried out on simply supported beams. The tests made it possible to acquire a wealth of dynamic response data from beams damaged artificially to produce defects of varying entity and position. The data obtained, appropriately normalised, are used as inputs for supervised neural networks. In particular, frequency analysis data are able to provide a summary characterisation of the distortion in a structure’s dynamic behaviour.
Different signal processing and analysis procedures are compared in order to identify the best resolution and sensitivity capabilities in the diagnostic performance of neural networks.
Application of a Model Updating Technique for Health Condition Monitoring and Damage Detection of Flexible Structures
Authors: Pereira Joao A. , Heylen Ward , Lammens Stefan , Sas Paul 
Published: March 2021

Abstract
This paper discusses the application of a damage detection methodology to monitor the location and extent of partial structural damage. The methodology combines, in an iterative way, the model updating technique based on frequency response functions (FRF) with monitoring data aiming at identifying the damage area of the structure. After the updating procedure reaches a good correlation between the models, it compares the parameters of the damage structure with those of the undamaged one to find the deteriorated area. The influence of the FEM mesh size on the evaluation of the extent of the damage has also been discussed. The methodology is applied using real experimental data from a spatial frame structure.
Intensified Training Supersedes the Impact of Heat and/or Altitude for Increasing Performance in Elite Rugby Union Players
Authors: Racinais Sebastien , Périard Julien D. , Piscione Julien , Bourdon Pitre C. , Cocking Scott , Ihsan Mohammed , Lacome Mathieu , Nichols David , Townsend Nathan , Travers Gavin , Wilson Mathew G. , Girard Olivier 
Published: March 2021

Purpose: To investigate whether including heat and altitude exposures during an elite team-sport training camp induces similar or greater performance benefits. Methods: The study assessed 56 elite male rugby players for maximal oxygen uptake, repeated-sprint cycling, and Yo-Yo intermittent recovery level 2 (Yo-Yo) before and after a 2-week training camp, which included 5 endurance and 5 repeated-sprint cycling sessions in addition to daily rugby training. Players were separated into 4 groups: (1) control (all sessions in temperate conditions at sea level), (2) heat training (endurance sessions in the heat), (3) altitude (repeated-sprint sessions and sleeping in hypoxia), and (4) combined heat and altitude (endurance in the heat, repeated sprints, and sleeping in hypoxia). Results: Training increased maximal oxygen uptake (4% [10%], P = .017), maximal aerobic power (9% [8%], P < .001), and repeated-sprint peak (5% [10%], P = .004) and average power (12% [14%], P < .001) independent of training conditions. Yo-Yo distance increased (16% [17%], P < .001) but not in the altitude group (P = .562). Training in heat lowered core temperature and increased sweat rate during a heat-response test (P < .05). Conclusion: A 2-week intensified training camp improved maximal oxygen uptake, repeated-sprint ability, and aerobic performance in elite rugby players. Adding heat and/or altitude did not further enhance physical performance, and altitude appears to have been detrimental to improving Yo-Yo.
Parallel molecular mechanisms for enzyme temperature adaptation
Authors: Pinney Margaux M. , Mokhtari Daniel A. , Akiva Eyal , Yabukarski Filip , Sanchez David M. , Liang Ruibin , Doukov Tzanko , Martinez Todd J. , Babbitt Patricia C. , Herschlag Daniel 
Published: March 2021

Some like it hot, others notEnzymes strike a delicate balance between features that enhance chemical reactivity and those that contribute to stable structure. Both features are important and can be unrelated or antagonistic. Pinneyet al.combined rich experimental work on thermophilic and mesophilic variants of the enzyme ketosteroid isomerase (KSI) with bioinformatic data from a diverse set of bacterial enzymes to reveal the molecular determinants of thermal adaptation in enzymes. For KSI, they observed a trade-off between activity and thermal stability that comes down to a single active-site residue. With their larger dataset, they identified patterns of individual amino acid substitutions that are favored at higher temperatures, and also consider how networks of stabilizing interactions develop.Science, this issue p.eaay2784
Linear System of Differential Equations with a Quadratic Invariant as the Schrödinger Equation
Authors: Kozlov V. V. 
Published: March 2021

Abstract
Linear systems of differential equations with an invariant in the form of a positive definite quadratic form in a real Hilbert space are considered. It is assumed that the system has a simple spectrum and the eigenvectors form a complete orthonormal system. Under these assumptions, the linear system can be represented in the form of the Schrödinger equation by introducing a suitable complex structure. As an example, we present such a representation for the Maxwell equations without currents. In view of these observations, the dynamics defined by some linear partial differential equations can be treated in terms of the basic principles and methods of quantum mechanics.
Patients’ participation in government-sponsored guidelines in Latin America: a cross-sectional study
Authors: Garegnani Luis Ignacio , Meza Nicolás , Rosón-Rodriguez Pablo , Escobar-Liquitay Camila Micaela , Arancibia Marcelo , Madrid Eva , Franco Juan Victor Ariel 
Published: March 2021

BackgroundIt is recommended that patients actively participate in clinical practice guideline (CPG) development, which allows consideration of their values and preferences and improves adherence to recommendations. The development of CPGs throughout Latin America is variable and diverse, and the inclusion of patients’ participation is unknown.ObjectivesTo evaluate the methods of patients’ participation in government-sponsored CPGs in Latin America, the type of CPG development and the use of Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methods.DesignCross-sectional study. We included CPGs developed over the last 10 years through a comprehensive hand search in official national government websites and biomedical databases.Main outcome measureThe type of patients’ participation was coded according to five predefined categories. We also report the proportion of application of GRADE methods.ResultsWe included 408 CPGs from 10 countries: 74% (n=303) were de novo development, 13%(n=55) used an adaptation method and 10%(n=41) used both adaptation and de novo methods. Only 45% (n=185) applied the GRADE approach, ranging from 14% (n=12) of CPGs in Brazil to 89% (n=56) of CPGs in Colombia. Only 23% (n=95) of CPGs included at least one method of patients’ participation. Mexico was one of the largest CPG producers (100 CPGs), but none included methods of patients’ participation; in turn, in countries with lower production of government-sponsored CPGs, patients’ participation was found in almost 88%. Guidelines using the GRADE approach were more likely to use methods of patients’ participation. These methods were highly variable: 46% (n=44) incorporated patients in the panel, 81% (n=77) searched for evidence about patients’ values and preferences, 43% (n=39) used an external review of the draft recommendations by patients, 38% (n=36) used public comments, and 2% included other methods for stakeholders’ participation.ConclusionOnly one quarter of government-sponsored CPGs in the Latin American region incorporated a method for patients’ participation, which varied considerably across the selected countries. These findings highlight the need to improve CPG development methods to systematically incorporate patients’ values and preferences when drafting recommendations.
Validation of ICD-10-CM codes for injuries complicating pregnancy, childbirth and the puerperium: a medical record review
Authors: Hansen Anna , Quesinberry Dana , Akpunonu Peter , Martin Julia , Slavova Svetla 
Published: March 2021

IntroductionThe purpose of this study was to estimate the positive predictive value (PPV) of International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) codes for injury, poisoning, physical or sexual assault complicating pregnancy, childbirth and the puerperium (PCP) to capture injury encounters within both hospital and emergency department claims data.MethodsA medical record review was conducted on a sample (n=157) of inpatient and emergency department claims from one Kentucky healthcare system from 2015 to 2017, with any diagnosis in the ICD-10-CM range O9A.2-O9A.4. Study clinicians reviewed medical records for the sampled cases and used an abstraction form to collect information on documented presence of injury and PCP complications. The study estimated the PPVs and the 95% CIs of O9A.2-O9A.4 codes for (1) capturing injuries and (2) capturing injuries complicating PCP.ResultsThe estimated PPV for the codes O9A.2-O9A.4 to identify injury in the full sample was 79.6% (95% CI 73.3% to 85.9%) and the PPV for capturing injuries complicating PCP was 72.0% (95% CI 65.0% to 79.0%). The estimated PPV for an inpatient principal diagnosis O9A.2-O9A.4 to capture injuries was 90.7% (95% CI 82.0% to 99.4%) and the PPV for capturing injuries complicating PCP was 88.4% (95% CI 78.4% to 98.4%). The estimated PPV for any mention of O9A.2-O9A.4 in emergency department data to capture injuries was 95.2% (95% CI 90.6% to 99.9%) and the PPV for capturing injuries complicating PCP was 81.0% (95% CI 72.4% to 89.5%).DiscussionThe O9A.2-O9A.4 codes captured high percentage true injury cases among pregnant and puerperal women.
Exploring the implications of the new ICD-10-CM classification system for injury surveillance: analysis of dually coded data from two medical centres
Authors: Poltavskiy Eduard A , Fenton Susan H , Atolagbe Oluseun , Sadeghi Banafsheh , Bang Heejung , Romano Patrick S 
Published: March 2021

IntroductionExternal cause of injury matrices is used to classify mechanisms/causes of injuries for surveillance and research. Little is known about the performance of the Centers for Disease Control and Prevention’s new external cause of injury matrix for Clinical Modification of the 10th Revision of the International Classification of Diseases (ICD-10-CM), compared with the ICD-9-CM version.MethodsDually coded (ICD-9-CM and ICD-10-CM) administrative data were obtained from two major academic trauma centres. Injury-related cases were identified and categorised by mechanism/cause and manner/intent. Comparability ratios (CR) were used to estimate the net impact of changing from ICD-9-CM to ICD-10-CM on the number of cases classified to each mechanism/cause category. Chamberlain’s percent positive agreements (PPA) were calculated and McNemar’s test was used to assess the significance of observed classification differences.ResultsOf 4832 and 5211 dual-coded records from the two centres, 632 and 520 with injury-related principal diagnoses and external cause codes in both ICD-9-CM and ICD-10-CM were identified. CRs for the mechanisms/causes with at least 20 records ranged from 0.85 to 1.9 at one centre and from 0.97 to 1.07 at the other. Among these mechanisms/causes, PPAs ranged from 33% for ‘other transport’ to 94% for poisoning at one centre, and from 75% for ‘other transport’ to 100% for fires/burns at the other centre. Case assignment differed significantly for falls, motor vehicle traffic, other transport, and ‘struck by/against’ injuries at one centre, and for ‘other pedal cyclist’ at the other centre.ConclusionSwitching to ICD-10-CM and the new external cause of injury matrix may affect injury surveillance and research, especially for certain mechanisms/causes.