Tuning for Performance and Stability in Systems of Nearly Tautochronic Torsional Vibration Absorbers

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Steven W. Shaw ◽  
Bruce Geist
Keyword(s):  
Torsional Vibration ◽  
Center Of Mass ◽  
Vibration Absorbers ◽  
Nonlinear Perturbations ◽  
Operating Range ◽  
The Subject ◽  
And Performance ◽  
The Stability ◽  
Stability Results ◽  
Selection Of

This paper considers the dynamic response and performance characteristics of a special class of centrifugal pendulum torsional vibration absorbers. The absorbers of interest are designed by selection of the path that their center of mass follows, such that their dynamics are linear or nearly so, out to large amplitudes of motion, thereby avoiding the nonlinear-induced detuning that typically accompanies such responses. These order-tuned, tautochronic or isochronic, absorbers have been the subject of previous investigations, including analyses of the synchronous and certain nonsynchronous responses of systems comprised of a set of identical absorbers. The analysis and experiments have demonstrated that the synchronous response of such absorber systems can experience an instability that results in nonsynchronous responses in which a subset of absorbers have significantly larger amplitude than the corresponding synchronous response. In this study, we present results that generalize these stability results to include absorbers whose dynamics differ slightly from tautochronic by varying the absorber path such that both linear and nonlinear perturbations of perfect tuning are included. It is shown by analysis and verified by simulations that the perfect tuning case is quite special, specifically that the instability described above occurs for tunings very close to ideal and that the synchronous response can be made stable over the entire feasible operating range by employing small levels of linear and/or nonlinear detuning. Such detuning is known to have the additional benefit of resulting in smaller absorber responses and an attendant larger operating range albeit at the expense of absorber performance in terms of attenuating rotor torsional vibrations. The main conclusion of these results is that one can select a very small amount of detuning to avoid this undesirable instability and that such detuning does not have a significant effect on absorber effectiveness. The analytical results derived also provide a quantitative means of predicting synchronous absorber response amplitudes and the associated rotor torsional vibration levels, as well as the stability properties of these responses, results are very useful for the design of absorber systems.

scholarly journals Developments in the Design of Centrifugal Pendulum Vibration Absorbers

2020 ◽  
Vol 25 (2) ◽  
pp. 266-277
Author(s):  
David E. Newland
Keyword(s):  
Torsional Vibration ◽  
System Performance ◽  
Vibration Absorbers ◽  
Aircraft Engines ◽  
Current State ◽  
Practical Design ◽  
Centrifugal Pendulum Vibration Absorbers ◽  
Automobile Engines ◽  
The Subject ◽  
Design Requirements

For over 60 years, the torsional vibration of reciprocating aircraft engines has been controlled by centrifugal pendulum vibration absorbers. Loose weights attached to an engine's crankshaft act as tuned-mass absorbers by oscillating at a frequency in proportion to rotational speed. More recently, similar loose masses have been attached to the flywheels of automobile engines. The need to achieve increased power from fewer cylinders, while reducing weight and improving economy, has exacerbated torsional vibration of the drive train. The dynamics of a wheel carrying many centrifugal pendulums of bifilar design has been the subject of a growing literature, but much less has been written about roller-type pendulums and about overall system performance. This paper is a new analysis of bifilar and roller systems and their design requirements. The current state of knowledge about practical design limitations is explained and the need for further research discussed.

Exponential Stability for Uncertain Switched Neutral Systems with Nonlinear Perturbations

2011 ◽  
Vol 217-218 ◽  
pp. 668-673
Author(s):  
Xiu Liu ◽  
Shou Ming Zhong ◽  
Xiu Yong Ding
Keyword(s):  
Exponential Stability ◽  
Linear Matrix ◽  
Time Varying ◽  
Nonlinear Perturbations ◽  
Neutral Systems ◽  
Weighting Matrix ◽  
The Stability ◽  
Switched Neutral Systems ◽  
Delay Dependent ◽  
Stability Results

The global exponential stability for switched neutral systems with time-varying delays and nonlinear perturbations is investigated in this paper. LMI-based delay-dependent criterion is proposed to guarantee exponential stability for our considered systems under any switched signal. Lyapunov-Krasovskii functional and Leibniz-Newton formula are applied to find the stability results. Free weighting matrix and linear matrix inequality (LMI) approaches are used to solve the proposed conditions.

scholarly journals Body sway and performance at competition in male pistol and rifle Olympic shooters

2014 ◽  
Vol 6 (1) ◽  
Author(s):  
Daniel Mon ◽  
Maria Zakynthinaki ◽  
Carlos Cordente ◽  
Maria Barriopedro ◽  
Javier Sampedro
Keyword(s):  
Center Of Mass ◽  
National Level ◽  
The Body ◽  
Body Sway ◽  
Significant Relation ◽  
Parametric Test ◽  
Average Maximum ◽  
And Performance ◽  
Pearson Correlations ◽  
Selection Of

Summary Study aim: We examine the body sway differences between a) pistol and rifle and b) elite and national level senior male Olympic shooters, as well as the possible relation between body sway and performance at competition in Olympic shooting. Material and methods: Two body sway tests (feet together and feet apart) were performed by 28 Spanish male senior Olympic shooters just before competition. Performance was measured as the actual score at competition. Total center of mass (COM) areas and average/maximum COM velocities were calculated from force platform data. ANCOVA tests were implemented with age as a covariable. The non-parametric test U of Mann Whitney was used to study the differences between national and elite shooters. Pearson correlations were used to examine the relation between performance and total COM area. Results: At the feet apart position, rifle and elite shooters were found to have statistically less body sway than pistol and national level shooters respectively (total COM areas: F1,25 = 6.7; p < 0.05, and Z = 2.36; p < 0.01). No statistically significant differences were found regarding the feet together position, regardless the level or discipline (total COM areas: F1,25 = 1.49 ; p > 0.05; 1 – β = 0.22, average COM velocities: F1,25 = 0.58; p > 0.05; 1 – β = 0.11, maximum COM velocities: F1,25 = 0.03; p > 0.05; 1 – β = 0.05). No significant relation was found between body sway and performance at competition (feet together: r = 0.13, feet apart: r = 0.14, p > 0.05). Age and body sway were not found to be significantly correlated (F1,25 = 0.23; p > 0.05; 1 – β = 0.08). Conclusions: Easy to carry out, non-specific body sway tests can be used for the selection of novice shooters.

Production and properties of natural rubber glove using sustainable benign accelerator

2021 ◽  
pp. 147776062110194
Author(s):  
Vishantini Tangavaloo ◽  
Nor Yuliana Yuhana ◽  
Yu Lih Jiun
Keyword(s):  
Mechanical Properties ◽  
Manufacturing Industry ◽  
Maturation Time ◽  
Curing Characteristics ◽  
Link Density ◽  
Cross Link Density ◽  
And Performance ◽  
Time Required ◽  
Stability Results ◽  
Selection Of

In natural polyisoprene glove manufacturing industries, the selection of accelerators in the curing system is mainly determined by the curing characteristics, maturation time required, cross-link density and mechanical properties of gloves. In this study, a new accelerator replacing conventional ones in a typical glove manufacturing process, was studied in order to produce free carcinogen dipped article. The glove properties and performance prepared by using both conventional and new proposed accelerators were studied and compared. The use of a conventional accelerator tends to release carcinogenic chemicals namely N-nitrosamine and N-nitrosatable substances. These chemicals are restrained on dipped articles under the requirement of EN 71-12:2013. Xanthogen accelerators promote the reduction of carcinogenic chemicals, but they are associated with prolonged maturation hour, which is unfavourable in the manufacturing industry. This study used a mixture of a benign accelerator, namely, diisononyldithiocarbamate and diisopropyl xanthogen polysulfide, to substitute the usage of conventional accelerators zinc dibutyl dithiocarbamate and zinc diethyl dithiocarbamate. The effects of benign accelerator loading in latex compounds were studied by focusing on the swelling index, maturation hour, carcinogenic chemical released and mechanical properties, thermal degradation and stability. Results showed no presence of N-nitrosamines and N-nitrosatable substances in the final dipped products by using 0.3 and 0.5 phr of benign accelerator. This study showed that 0.5 phr of benign accelerator achieved a moderate pre-vulcanising rate and improved the pre-ageing tensile strength and elongation by 11% and 7.0%, respectively. Moreover, its thermal stability was higher and discolouration intensity was lower as compared with the conventional accelerator.

scholarly journals A State of Art Survey for OS Performance Improvement

2018 ◽  
Vol 6 (3) ◽  
pp. 118-123 ◽  
Author(s):  
Lailan M. Haji ◽  
Subhi R.M. Zeebaree ◽  
Karwan Jacksi ◽  
Diyar Q. Zeebaree
Keyword(s):  
Performance Improvement ◽  
Critical Issue ◽  
The Past ◽  
Performance Requirements ◽  
And Performance ◽  
Measurement And Evaluation ◽  
The Stability ◽  
High Level ◽  
Multiple Metrics ◽  
Selection Of

Through the huge growth of heavy computing applications which require a high level of performance, it is observed that the interest of monitoring operating system performance has also demanded to be grown widely. In the past several years since OS performance has become a critical issue, many research studies have been produced to investigate and evaluate the stability status of OSs performance. This paper presents a survey of the most important and state of the art approaches and models to be used for performance measurement and evaluation. Furthermore, the research marks the capabilities of the performance-improvement of different operating systems using multiple metrics. The selection of metrics which will be used for monitoring the performance depends on monitoring goals and performance requirements. Many previous works related to this subject have been addressed, explained in details, and compared to highlight the top important features that will very beneficial to be depended for the best approach selection.

Stability of the Unison Response for a Rotating System With Multiple Tautochronic Pendulum Vibration Absorbers

1997 ◽  
Vol 64 (1) ◽  
pp. 149-156 ◽  
Author(s):  
Chang-Po Chao ◽  
S. W. Shaw ◽  
Cheng-Tang Lee
Keyword(s):  
Equations Of Motion ◽  
Vibration Absorbers ◽  
Rotating System ◽  
Total Moment ◽  
Equivalent Viscous Damping ◽  
Future Paper ◽  
The Stability ◽  
The Individual ◽  
Special Case ◽  
Selection Of

Due to spatial and balancing considerations, the implementation of centrifugal pendulum absorbers (CPVA’s) invariably requires that the total absorber inertia be divided into several absorber masses and stationed about the center of rotation. To achieve the designed-for performance, the CPVA’s are expected to move in exact unison, since the selection of the total absorber mass is made by assuming an equivalent single absorber mass. In this paper, we determine the conditions under which the unison motion of a system of several identical CPVA’s is dynamically stable. This is done for the special case of tautochronic absorbers subjected to a purely harmonic torque. The stability criterion is obtained by an asymptotic method that exploits certain symmetries in the equations of motion and is based on the assumption that total moment of inertia of the absorbers is much smaller than that of the entire rotating system—an assumption that is almost always satisfied in practice. It is expressed in terms of a critical torque level that is proportional to the square root of the equivalent viscous damping of the individual absorbers. The result is verified by numerical simulations of the system near the critical parameter conditions. A future paper will consider the post-critical response of the system.

EFFECTS OF HELICOPTER HORIZONTAL TAIL CONFIGURATIONS ON AERODYNAMIC DRAG CHARACTERISTICS

2017 ◽  
Vol 79 (7-4) ◽  
Author(s):  
Iskandar Shah Ishak ◽  
Muhammad Fitri Mougamadou Zabaroulla
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Angle Of Attack ◽  
Aerodynamic Efficiency ◽  
Wind Tunnel Tests ◽  
Tunnel Model ◽  
The Subject ◽  
And Performance ◽  
Selection Of

Experimental aerodynamic investigations remain the subject of interest in rotorcraft community since the flow around the helicopter is dominated by complex aerodynamics and flow interaction phenomena. The objective of this study is to determine the aerodynamic drag characteristics of helicopter horizontal tail by conducting wind tunnel tests. To fulfil the objective, three of the most common helicopter horizontal tail configurations namely Forward Stabilizer, Low-aft Stabilizer and T-tail Stabilizer, were fabricated as a simplified scaled-down wind tunnel model mated with a standard ellipsoidal fuselage. The test wind speed for this experimental work was 30 m/s, determined from Reynolds sweep, which was corresponding to Reynolds number of 2.8 x 105. Wind tunnel tests were performed at variations angle of attack ranging from -15O to 15O with 5O interval. The results tell that at zero yaw and zero pitch angles, Forward Stabilizer contributed the least drag coefficient at 0.277 implying the configuration could be the best for cruising flight segment. Contrarily to T-tail Stabilizer, this configuration contributed the most drag coefficient at 0.303, which was 9% higher than the former. The T-tail Stabilizer was also found to be the most sensitive to the change of angle of attack where the drag was drastically increased up to 131.35% at -15O angle of attack compares to at zero angle of attack. These findings had successfully testified that the type of stabilizer configuration does significantly influencing the aerodynamic drag characteristics of helicopter. Subsequently, the selection of stabilizer must wisely be done to have the best aerodynamic efficiency and performance for the helicopter. 

Thomas More’s Correspondence in a Spanish Ambiance

Moreana ◽  
2002 ◽  
Vol 39 (Number 149) (1) ◽  
pp. 41-60 ◽  
Author(s):  
Eugenio M. Olivares Merino
Keyword(s):  
The Subject ◽  
Selection Of

The recent reprinting of Álvaro de Silva’s 1998 edition of a selection of More’s letters prompts the author to examine the subject of Spanish translations of More, and of de Silva’s general commentary on More’s correspondence and on his relationship to other humanists. The author reflects on aspects of More’s personality as exposed in his letters and uses what he finds as a corrective to several biographical misconceptions. He points out the strengths and weaknesses of de Silva’s work and compares it with that of other translators, particularly Elizabeth Rogers, and notes the particularly Spanish quality of de Silva’s edition.

TO THE STABILITY OF TANK VEHICLES IN THE BRAKE MODE

2019 ◽  
pp. 27-32
Author(s):  
Denys Popelysh ◽  
Yurii Seluk ◽  
Sergyi Tomchuk
Keyword(s):  
Mathematical Model ◽  
Control Systems ◽  
Distribution Systems ◽  
Traffic Accidents ◽  
Road Traffic ◽  
Center Of Mass ◽  
Dynamic Processes ◽  
Course Stability ◽  
The Stability ◽  
Tank Vehicles

This article discusses the question of the possibility of improving the roll stability of partially filled tank vehicles while braking. We consider the dangers associated with partially filled tank vehicles. We give examples of the severe consequences of road traffic accidents that have occurred with tank vehicles carrying dangerous goods. We conducted an analysis of the dynamic processes of fluid flow in the tank and their influence on the basic parameters of the stability of vehicle. When transporting a partially filled tank due to the comparability of the mass of the empty tank with the mass of the fluid being transported, the dynamic qualities of the vehicle change so that they differ significantly from the dynamic characteristics of other vehicles. Due to large displacements of the center of mass of cargo in the tank there are additional loads that act vehicle and significantly reduce the course stability and the drivability. We consider the dynamics of liquid sloshing in moving containers, and give examples of building a mechanical model of an oscillating fluid in a tank and a mathematical model of a vehicle with a tank. We also considered the method of improving the vehicle’s stability, which is based on the prediction of the moment of action and the nature of the dynamic processes of liquid cargo and the implementation of preventive actions by executive mechanisms. Modern automated control systems (anti-lock brake system, anti-slip control systems, stabilization systems, braking forces distribution systems, floor level systems, etc.) use a certain list of elements for collecting necessary parameters and actuators for their work. This gives the ability to influence the course stability properties without interfering with the design of the vehicle only by making changes to the software of these systems. Keywords: tank vehicle, roll stability, mathematical model, vehicle control systems.

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