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lock-in phenomenon of tip clearance flow and its influence on aerodynamic damping under specified vibration on an axial transonic compressor rotor

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Chinese Journal of Aeronautics 2022年第3期35卷 185-200页

作者： Le HAN Dasheng WEI Yanrong WANG Mingchang FANG School of Energy and Power Engineering Beihang UniversityBeijing 100083China Collaborative Innovation Center for Advanced Aero-Engine Beijing 100083China

In this study,the lock-in phenomenon of Tip Clearance Flow(TCF)instabilities and their relationship to blade vibration are investigated numerically on an axial transonic rotor with a large tip *** capabilities of simulating instability flow and lock-in phenomenon are verified on a transonic rotor and a NACA0012 airfoil by comparing with the test data,*** lock-in phenomenon is first numerically confirmed that may occur to TCF instabilities when its frequency is close to the blade vibration *** lock-in region becomes wider with the vibration amplitude increasing,and it is also affected by modal *** the rotor at the simulation conditions in this study,the bending mode results in a wider lock-in region than the torsional *** the lock-in region,the phase difference between the Tip Clearance Vortex(TCV)and the blade vibration changes with the flow condition and the frequency ratio of the blade vibration and the TCV *** frequency of the TCV instabilities reduces with the mass flow ***,reducing mass flow and increasing frequency ratio have similar effects on the TCV phase,which causes a significant variation on the unsteady pressure amplitude in the blade tip ***,the aerodynamic damping changes significantly with the TCV *** aerodynamic damping displays a nonlinear relationship with the vibration amplitude,and it changes from negative to positive with the vibration amplitude increasing at the same frequency *** negative damping is mainly provided by the tip area of the *** unlocked conditions,the period of the TCF instabilities fluctuates over time,and it cannot be directly separated by their frequency *** Blade Phase Angle(IBPA)also has an important influence on the feature of the TCV *** occurrence of frequency lock-in also requires“appropriate”*** the examined working conditions,the frequency lock-in occurs under 0 ND(Nodal Diameter),but not un

关键词： Aerodynamic damping Inter blade phase angle lock-in Specified blade vibration Tip clearance flow instabilities

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Influence of fluid-structure interaction on vortex induced vibration and lock-in phenomena in long span bridges

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Frontiers of Structural and Civil Engineering 2016年第4期10卷 363-384页

作者： Nazim Abdui NARIMAN Institute of Structural Mechanics Faculty of Civil Engineering Bauhaus University Weimar Weimar 99423 Germany

In this paper, deck models of a cable stayed bridge are generated in ABAQUS-finite element program once using only CFD model （one-way fluid-structure interaction） and another by using both the CFD model and the CSD model together （two-way fluid-structure interaction） in a co-simulation. Shedding frequencies for the associated wind velocities in the lock-in region are calculated in both approaches. The results are validated with Simiu and Scanlan results. The lift and drag coefficients are determined for the two approaches and the latter results are validated with the flat plate theory results by Munson and coauthors. A decrease in the critical wind velocity and the shedding frequencies considering two-way approach was determined compared to those obtained in the one-way approach. The results of the lift and drag forces in the two-way approach showed appreciable decrease in their values. It was concluded that the two-way approach predicts earlier vortex induced vibration for lower critical wind velocities and lock-in phenomena will appear at lower natural frequencies of the long span bridges. This helps the designers to efficiently plan and consider for the design and safety of the long span bridge against this type of vibration.

关键词： vortex-induced vibration fluid-structure interaction Strouhal number lock-in kinetic energy

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Characteristic analysis of lock-in for an elastically suspended airfoil in transonic buffet flow

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Chinese Journal of Aeronautics 2016年第1期29卷 129-143页

作者： Quan Jingge Zhang Weiwei Gao Chuanqiang Ye Zhengyin School of Aeronautics Northwestern Ploytechnical University

Numerical simulations are performed to study the aeroelastic responses of an elastically suspended airfoil in transonic buffet flow, by coupling the unsteady Reynolds-averaged Navier- Stokes （RANS） equations and structural motion equation. The current work focuses on the char- acteristic analysis of the lock-in phenomenon. Great attentions are paid to studying the frequency range of lock-in and the effects of the three parameters, namely the structural natural frequency, mass ratio and structural damping, on lock-in characteristic of the elastic system in detail. It is found that when the structural natural frequency is close to the buffet frequency, the coupling fre- quency of the elastic system is no longer equal to the buffet frequency, but keeps the same value as the structural natural frequency. The frequency lock-in occurs and stays present until the structural nature frequency is near the double buffet frequency. It means that the lock-in presents within a broad range, of which the lower threshold is near the buffet frequency, while the upper threshold is near the double buffet frequency. Moreover, the frequency range of lock-in is affected by mass ratio and structural damping. The lower the mass ratio and structural damping are, the wider the range of lock-in will be. The upper threshold of lock-in grows with the mass ratio and structural damping decreasing, but the lower threshold always keeps the same.

关键词： Aeroelastic analysisBuffet Elastic airfoil lock-in Transonic flow

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No apparent lock-in depth of the Laschamp geomagnetic excursion: Evidence from the Malan loess

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Science China Earth Sciences 2006年第9期49卷 960-967页

作者： ZHU Rixiang1, LIU Qingsong1,2, PAN Yongxin1, DENG Chenglong1, ZHANG Rui1 & WANG Xianfeng3 1. Paleomagnetism and Geochronology Laboratory (SKL of Lithosphere Evolution), Institute of Geology and Geophysics, Chi- nese Academy of Sciences, Beijing 100029, China 2. Institute of Geophysics and Planetary Geophysics, University of California, Santa Cruz, CA 95064, USA 3. Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA Paleomagnetism and Geochronology Laboratory (SKL of Lithosphere Evolution) Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China Institute of Geophysics and Planetary Geophysics University of California Santa Cruz USA Department of Geology and Geophysics University of Minnesota Minneapolis USA

The first-order chronological framework of the long-term Chinese loess/paleosol sequences was based mainly on magnetostratigraphy. However, there remain arguments on the lock-in ages of the major geomagnetic reversals. This study systematically compared the stratigraphic locations of the Laschamp excursion and Henrich events (H4 at～39 ka and H5 at～48 ka) recorded by the Luochuan loess profile in the central Chinese Loess Plateau. Results show that the Lascchamp excursion is bracketed well by these two cold events, and the corresponding estimated age is between about 41.7-43.7 ka, which is close to the widely accepted age of ～40-41 ka for the ***, our new results do not suggest apparent lock-in effects in the last glacial Malan loess.

关键词： Chinese loess, Laschamp excursion, Henrich event, lock-in depth.

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An Approximate Method for Calculation of Fluid Force and Response of A Circular Cylinder at lock-in

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China Ocean Engineering 2008年第3期22卷 371-384页

作者：王艺 Division of Engineering Sciences Institute of MechanicsChinese Academy of Sciences

In this paper, equations calculating lift force of a rigid circular cylinder at lock-in in uniform flow are deduced in detail. Besides, equations calculating the lift force on a long flexible circular cylinder at lock-in are deduced based on mode analysis of a multi-degree freedom system. The simplified forms of these equations are also given. Furthemore, an approximate method to predict the forces and response of rigid circular cylinders and long flexible circular cylinders at lock-in is introduced in the case of low mass-damping ratio. A method to eliminate one deficiency of these equations is introduced. Comparison with experimental results shows the effectiveness of this approximate method.

关键词： vortex-induced vibraton circular cylinder lock-in phase lift amplitude

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Vortex Shedding lock-in on Tapered Poles with Polygonal Cross-Section

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Open Journal of Fluid Dynamics 2022年第2期12卷 127-153页

作者： Jaime A. Ocampo Steven H. Collicott Robert J. Connor School of Aeronautics and Astronautics Purdue University West Lafayette USA Lyles School of Civil Engineering Purdue University West Lafayette USA

A study to investigate the effects of taper on vortex shedding coherence on High Mast Lighting Towers (HMLT) with models of eight-, twelve-, and sixteen-sided polygonal cross-section was performed in Purdue’s Boeing Low-Speed Wind Tunnel. Partial tower models were mounted on springs to recreate a flutter phenomenon seen on high mast lighting towers and data was taken using a stationary configuration within the wind tunnel. The model was later oscillated at specified frequencies and amplitudes and the resulting wake and surface pressures were recorded and compared to the stationary cases. The researchers aim to study the characteristics of a “lock-in” phenomenon, that is, a region of pole height where there is a vortex cell with a single shedding frequency, instead of different shedding frequencies for different diameters as Strouhal theory dictates. Results show the existence of vortex cell shedding for clamped models. Using a motor and a forcing cam to recreate the elastic movement of the HMLT in ambient conditions has yielded a specific range of diameters to determine the size of the locked in vortex cells. According to standard Department of Transportation manufacturing standards for tapered HMLT, the lock in distance for small excitations (0.254 cm) would be approximately 305 cm in tower height.

关键词： Vortex Shedding lock-in Tower Aerodynamics

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“lock-in Effect” to Be Blamed for Regional Development Imbalances

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China Economist 2008年第3期3卷 53-64页

作者：陈飞翔黎开颜刘佳 Professor Institute of Economics Tongji University Ph.D School of Economics and Management Tongji University

Reform and opening up has made China’s economy develop faster than ever. But it has not succeeded in changing the regional disparity in China. In this article, we establish a model factor input called the "lock-in effect" and analyze the channel of the lock-in effect and how it influences the regional economy. On the analyses of thirty provinces’ panel data in China from 1990 to 2005, we find that the lock-in effect of factor inputs further exacerbates the developmental imbalance among regions.

关键词： lock-in effect Regional disparity Factor input Openness.

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NDI of Rail Squats and Estimating Defect Size and Location Using lock-in Thermography

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Engineering（科研） 2013年第1期5卷 29-38页

作者： Daren Peng Rhys Jones Department of Mechanical and Aerospace Engineering Monash University Melbourne Australia

Rail squats are a form of near surface rolling contact fatigue damage found in rail heads. Currently, the most popular method to detect the rail squats is utilizing ultrasonic techniques to determine their presence and measure their depths. This technique needs to be direct contact between the probe and the rail head, with a coupling fluid in at the interface. Other weaknesses of these ultrasonic techniques include false detections as well as missed detections. Infrared thermography is a relatively new non-destructive inspection technique used for a wide range of applications but is not used for rail squat detection. lock-in thermography is a non-destructive inspection technique that can be used for the detection of near surface defects. It utilizes an infrared camera to detect the thermal waves and then produces a thermal image, which displays the local thermal wave variation in phase or amplitude. In inhomogeneous materials, the amplitude and phase of the thermal wave carries information related to both the local thermal properties and the nature of the structure being inspected. This comparison is then used to determine the phase angle difference (Δf) between the input and the thermal response of the object. The aim of this paper is to determine whether lock-in thermography can be used to firstly locate squats in rails, and secondly measure their depths. It has demonstrated the feasibility for using such a technique in generating thermal responses that could be adequately utilized for the purpose of defect characterization.

关键词： lock-in Thermography Phase Contrast Infrared Camera Squat Non-Destructive Inspection

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Lightweight Virtualization Cluster How to Overcome Cloud Vendor lock-in

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Journal of Computer and Communications 2014年第12期2卷 1-7页

作者： Nane Kratzke Department for Electrical Engineering and Computer Science Center of Excellence CoSA Lübeck University of Applied Sciences Lübeck Germany

To overcome vendor lock-in obstacles in public cloud computing, the capability to define transferable cloud-based services is crucial but has not yet been solved satisfactorily. This is especially true for small and medium sized enterprises being typically not able to operate a vast staff of cloud service and IT experts. Actual state of the art cloud service design does not systematically deal with how to define, deploy and operate cross-platform capable cloud services. This is mainly due to inherent complexity of the field and differences in details between a plenty of existing public and private cloud infrastructures. One way to handle this complexity is to restrict cloud service design to a common subset of commodity features provided by existing public and private cloud infrastructures. Nevertheless these restrictions raise new service design questions and have to be answered in ongoing research in a pragmatic manner regarding the limited IT-operation capabilities of small and medium sized enterprises. By simplifying and harmonizing the use of cloud infrastructures using lightweight virtualization approaches, the transfer of cloud deployments between a variety of cloud service providers will become possible. This article will discuss several aspects like high availability, secure communication, elastic service design, transferability of services and formal descriptions of service deployments which have to be addressed and are investigated by our ongoing research.

关键词： Cloud Computing Vendor lock-in Cross-Platform Lightweight Virtualization Container

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Simplified Prediction Model for Vortex-Induced Vibrations of Top Tensioned Risers

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China Ocean Engineering 2008年第2期22卷 291-302页

作者：薛鸿祥唐文勇张圣坤 State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University

According to the characteristics of deepwater top tensioned risers, a simplified model is presented to predict the multi-modal response of vortex-induced vibration （VIV） in non-uniform flow based on energy equilibrium theory and the exporimental data from VIV self-excited and forced oscillations of rigid cylinders. The response amplitude of each mode is determined by a balance between the energy fed into the riser over the lock-in regions and the energy dissipated by the fluid damping over the remainders. Compared with the previous prediction models, this method can take fully account of the intrinsic nature of VIV for low mass ratio structures on lock-in regions, added mass and nonlinear fluid damping effect, etc. Moreover, it is the first time to propose the accurate calculating procedure for VIV amplitude correction factor by solving energy equilibrium equation and a closed form solution is presented for the case of a riser of uniform mass and cross-section oscillating in a uniform flow. The predicted values show a reasonable agreement with VIV experiments of riser models in stepped and sheared currents.

关键词： top-tensioned riser vortex-induced vibration lock-in simplified prediction model

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