DYNAMIC ANALYSIS AND FORMULATION OF THE SOLUTION FOR COMPLEX PROBLEM OF DURABILITY INCREASE FOR STRUCTURAL ELEMENTS IN A TURBULENT FLOW OF THE MEDIUM

When designing the structures of modern hydroelastic systems in power engineering, namely heat exchangers for various purposes, effective frequency tuning should be purposefully carried out to prevent intense vibration of individual elements. To do this, it is necessary, in accordance with the specified resource requirements, to provide reasonably defined ratios of various values of the natural oscillation frequencies of the structural elements and the characteristic nearest excitation frequencies in the flow. The optimal choice of the values of the frequency tuning coefficients is realized taking into account the characteristic known factors of hydroelastic systems, such as the effects of attached masses and the significant influence of damping on the intensity of vibrations of the structure in the fluid flow. The article provides a description and a general plan for solving the set complex problem based on the results of numerical and experimental studies known in this direction.

The Effects of Reynolds Number on Energy Harvesting from FIV by a Square Cylinder

Under the action of incoming flow, the square cylinder can generate more intense vibration responses than the circular cylinder, which is beneficial for energy harvesting. Numerical simulations for FIV of the square-cylinder energy conversion system are carried out. URANS equations are used in conjunction with the shear stress transport k-ω turbulence model to predict the flow, and the equations for vibrations are solved by the Newmark-β algorithm. The present numerical method is validated against the published data with good consistency. The Reduced velocity Ur is varied from 1-20, with corresponding Reynolds numbers of 24 000-160 000. The numerical results indicate that the Reynolds number significantly affects the frequency response, amplitude response, vortex shedding mode, and energy conversion efficiency. The highest efficiency point locates at Re=88 000, with a value of 7.156%. When Re>120 000, the system transits from vortex-induced vibration into galloping, and its vibration responses as well as energy harvesting characteristics change sharply. Fully developed galloping motion occurs when Re>144 000.

Modal Velocity Perturbation Method for Contact Fatigue at Blade Attachment Under Resonant Vibration

In a gas turbine engine, it is often impossible to have rotating components running free of resonance at all operating conditions. As such, blades may be subject to episodes of intense vibration, resulting in fatigue damage at the connection between blade and disk. This paper presents a novel finite element approach allowing to evaluate in the time domain the behavior at the disk fir-tree or dovetail contacts caused by a high response on a resonance. The method can be applied to simple bending or torsion modes as well as to higher modes with complex shapes. The application of a one-time velocity perturbation is an efficient way to initiate an oscillating motion at the frequency of interest. The behavior of the 3D-contact is then studied in the time domain, allowing non-linear behaviors to develop. The basic principle of this approach is described in this work. In the design of turbomachinery blade attachments, this approach can be used to study in the time domain the fretting effect of load, coefficient of friction and sliding distance at different frequency regimes. In conjunction with fretting criteria such as Ruiz and Smith-Watson-Topper, fretting fatigue life can then be predicted.

1192 The Accuracy of a Novel Sleep Ring Device for Estimating Sleep Onset with Good and Poor Sleepers

Introduction THIM is a new ring-like sleep device that, if found to accurately measure sleep onset, could be used for a variety of clinical purposes. These include administering a brief but effective treatment for insomnia called Intensive Sleep Retraining, facilitating the optimal 10-minute power nap, and administering Multiple Sleep Latency Tests (MSLTs) outside of the sleep laboratory. This study assessed the accuracy of THIM for measuring sleep onset latency compared to polysomnography (PSG). Methods Twenty healthy individuals aged 23.6 years (SD = 4.89) underwent overnight PSG recording whilst using THIM on two nights in the sleep laboratory, one week apart. On each night, participants completed sleep onset trials for four hours whilst monitored via PSG. In these trials, participants attempted to fall asleep whilst responding to vibrations emitted from THIM. Once they failed to respond to two consecutive stimuli, THIM woke them with an intense vibration. Participants had a short break before attempting the next trial. Results On average, THIM overestimated sleep onset on the first night by 0.24 minutes (SD = 0.90). On the second night, THIM overestimated sleep onset by 0.82 minutes (SD = 1.31) and this discrepancy was not significantly different to that obtained on the first night, p = .08. The accuracy of THIM did not differ between good sleepers (Insomnia Severity Index (ISI) score < 7) or poor sleepers (ISI score 8-15), p = .98. Conclusion The findings suggest that THIM is accurate at estimating sleep onset latency for both good and poor sleepers. The next step is to test THIM outside of the laboratory environment. The goal is to develop an accurate yet practical device that can translate laboratory-based procedures to the home environment, to the benefit of patients and clinicians wanting to improve sleep. Support The project was funded in-part by the manufacturers of THIM, Re-Time Pty. Ltd., with additional funding provided by Flinders University.

Vector Form Intrinsic Finite Element Method for Analysis of Train–Bridge Interaction Problems Considering The Coach-Coupler Effect

In this paper, the vector form intrinsic finite element (VFIFE) method is presented for analysis the train–bridge systems considering the coach-coupler effect. The bridge is discretized into a group of mass particles linked by massless beam elements and the multi-body coach with suspension systems is simulated as a set of mass particles connected by parallel spring-dashpot units. Then the equation of motion of each mass particle is solved individually and the internal forces induced by pure deformations in the massless beam elements are calculated by a fictitious reverse motion method, in which the structural stiffness matrices need not be updated or factorized. Though the vector-form equations resulting from the VFIFE method cannot be used to compute the structural frequencies by the eigenvalue approach, this study proposes a numerical free vibration test to identify the bridge frequencies for evaluating the bridge damping. Numerical verifications demonstrate that the present VFIFE method performs as accurately as previous numerical ones. The results show that the couplers play an energy-dissipating role in reducing the car bodies’ response due to the bridge-induced resonance, but not in their response due to the train-induced resonance because of the bridge’s intense vibration. Meanwhile, a dual-resonance phenomenon in the train–bridge system occurs when the coach-coupler effect is considered in the vehicle model.

Analysis of Vibration of Roadheader Rotary Table Based on Finite Element Method and Data from Underground Coalmine

The intense vibration of a roadheader rotary table damages the cutting system of the roadheader and reduces the efficiency. This paper analyzes the vibration of a rotary table by combining the finite element model with tested data from an underground coalmine. First, the force of the rotary table during the cutting procedure was analyzed, and the finite element model was built using Pro/E and ADAMS. The tested data were then imported into the model after selection, procession, and combination were conducted. Next, the six lowest-order parameters of the rotary table were calculated. A vibration analysis of the rotary table under certain working conditions was conducted, and the results were compared with those from a modal experiment using a single-point excitation method. According to the comparison between the simulation result and experiments, it is clear that this method is both reasonable and feasible. And it could supplement the theoretical foundation of the analysis of other roadheader components, providing reference for the improvement of the structure and dynamic properties of a roadheader. In addition, other vibration components of a roadheader such as the cutting head and the cutting arm could also be analyzed through the proposed method, with very reliable precision.