Effect of Nonminimal Coupling on the Dynamics of Vacuum Bubbles

이범훈,Chul H. Lee,이원우,남시영,박찬용 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

The dynamics of true vacuum bubbles is studied by employing the junction conditions with nonminimal coupling. We concentrate on the effct of nonminimal coupling for tension on the wall. In this framework the effect of nonminimal coupling is interpreted as an additional positive tension on the wal of a true vacuum bubble. For a false vacuum bubble, it is interpreted as an additional negative tension.

Indirect displacement monitoring of high-speed railway box girders consider bending and torsion coupling effects

Xin Wang,Zhonglong Li,Yi Zhuo,Hao Di,Jianfeng Wei,Yuchen Li,Shunlong Li 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.28 No.6

The dynamic displacement is considered to be an important indicator of structural safety, and becomes an indispensable part of Structural Health Monitoring (SHM) system for high-speed railway bridges. This paper proposes an indirect strain based dynamic displacement reconstruction methodology for high-speed railway box girders. For the typical box girders under eccentric train load, the plane section assumption and elementary beam theory is no longer applicable due to the bend-torsion coupling effects. The monitored strain was decoupled into bend and torsion induced strain, pre-trained multi-output support vector regression (M-SVR) model was employed for such decoupling process considering the sensor layout cost and reconstruction accuracy. The decoupled strained based displacement could be reconstructed respectively using box girder plate element analysis and mode superposition principle. For the transformation modal matrix has a significant impact on the reconstructed displacement accuracy, the modal order would be optimized using particle swarm algorithm (PSO), aiming to minimize the ill conditioned degree of transformation modal matrix and the displacement reconstruction error. Numerical simulation and dynamic load testing results show that the reconstructed displacement was in good agreement with the simulated or measured results, which verifies the validity and accuracy of the algorithm proposed in this paper.

지지부 탄성효과를 고려한 회전 외팔 보의 진동해석

윤경재,유홍희 한국소음진동공학회 2000 소음 진동 Vol.10 No.6

This paper presents a modeling method for the vibration analysis of rotating cantilever beams considering the elastic foundation effect. Mass and stiffness matrices are derided explicitly by considering coupling effect between stretching and bonding motion. Numerical results show that the bending direction elastic foundation stiffness influences the vibration characteristics significantly in practical range of beam configuration. The ranges of elastic foundation stiffness to avoid the dynamic buckling are also presented. The method presented in this paper can be used to predict the variations of natural frequencies of rotating cantilever beams with elastically restrained root.

Performance changes of a floating offshore wind turbine with broken mooring line

Bae, Y.H.,Kim, M.H.,Kim, H.C. Elsevier 2017 RENEWABLE ENERGY Vol.101 No.-

<P><B>Abstract</B></P> <P>In the present study, a series of numerical simulations of the performance changes of a Floating Offshore Wind Turbine (FOWT) with broken mooring line was carried out. For this simulation, an aero-hydro-servo-elastic-mooring coupled dynamic analysis were carried out in the time domain. The OC4 DeepCwind semisubmersible with NREL's 5-MW baseline turbine was selected as a reference platform. One of the three mooring lines was intentionally disconnected from the floating platform at a certain time. The resulting transient/unsteady responses and steady-state responses after that, mooring line tensions, and turbine performance were checked. The accidental disconnection of one of the mooring lines changes the watch circle of the floating platform and the tensions of the remaining mooring lines. In addition, the changes in the platform orientation also cause nacelle yaw error, which is directly related to the power production and structural fatigue life. When horizontal offset becomes large, power-line is likely to be disconnected and its influence was also investigated. To ensure the sustainability of a series of FOWTs associated with farm development, the influence of mooring line failure and resulting changes to the turbine performance should be checked in advance. Otherwise, successive failure of neighboring FOWTs could take place.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated the dynamic responses of the OC4 semi-submersible floating offshore wind turbine with broken mooring line. </LI> <LI> We developed the coupled dynamic analysis tool for FOWT with broken mooring lines and large-offset-position effects. </LI> <LI> We demonstrated the platform drifting route after one-mooring-line failure in wind-wave environment. </LI> <LI> We examined the platform motion and wind turbine responses after the disconnection of the specific mooring line. </LI> </UL> </P>

증속 기어 전동 로터-베어링 시스템의 횡-비틀림 연성 유한요소 로터다이나믹 해석

이안성,하진웅,최동훈 한국소음진동공학회 2001 소음 진동 Vol.11 No.1

In a transmission or geared rotor system a coupled phenomenon of lateral and torsional vibrations may occur due to the gear meshing effect. Particularly, in high speed or low vibration and low noise applications of geared rotor systems a coupled rotordynamic analysis is required to precisely predict their dynamic characteristics. In this paper a generalized finite element model of a gear pair element is developed, which actively couples the lateral and torsional vibrations due to the gear meshing effect. In the modeling the generalized forces due to the transmission error. geometrical eccentricities. and unbalances in the gear system are also considered. Then. using the developed gear pair element model a coupled unforced rotordynamic analysis is performed with a prototype 800 RT turbo-chiller rotor-bearing system having a hull-pinion speed increasing gear. Results show that the torsional vibration characteristics experience some changes due to the gear meshing and lateral dynamic coupling effect, but that they have no adverse effect and the lateral ones have no practical changes in an operating speed range.

구조물과 부계통간의 연계방법에 따른 지진응답 분석

정광섭,곽신영,최인길,임승현,Jung, Kwangsub,Kwag, Shinyoung,Choi, In-Kil,Eem, Seunghyun 한국지진공학회 2020 한국지진공학회논문집 Vol.24 No.2

Seismic responses due to the dynamic coupling between a primary structure and secondary system connected to a structure are analyzed in this study. The seismic responses are compared based on dynamic coupling criteria and according to the error level in the natural frequency, with the recent criteria being reliant on the error level in the spectral displacement response. The acceleration responses and relative displacement responses of a primary structure and a secondary system for a coupled model and two different decoupled models of two degrees-of-freedom system are calculated by means of the time integration method. Errors in seismic responses of the uncoupled models are reduced with the recent criteria. As the natural frequency of the secondary system increases, error in the natural frequency decreases, but seismic responses of uncoupled models can be underestimated compared to that of coupled model. Results in this paper can help determine dynamic coupling and predict uncoupled models' response conservatism.

Numerical study on the cavitating flow through poppet valves concerning the influence of flow instability on cavitation dynamics

Cong Yuan,Lisha Zhu,Shiqi Liu,Du Zunling,He Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2

The flow dynamics of the cavitating jet through poppet valves inevitably suffers from the influence of varying openness, but the relevant mechanism remains unclear. Hence, the present study conducts a numerical study on the cavitating flow phenomenon inside poppet valves with two valve seat structures, in order to examine the flow mechanisms underlying varying cavitation phenomenon at different openness. According to the results, the overall cavitation distribution as well as the morphology feature follows a similar pattern due to the same inception mechanism irrelevant of the openness amount. However, examination of the dynamic behaviors confirms discernable variation in 2 coupling effects between flow instability and cavitation. The flow separation at the poppet trailing edge produces non-cavitation flow instability at 0.4 mm openness and attached cavitation at 0.8 mm, which amalgamate with upstream-shed vortex cavitation. The stably attached cavitation within the chamfered groove at 0.4 mm, as the source of non-cavitation flow instability, and the detached cavitation at 0.6 and 0.8 mm openness produce vortex cavitation at the free shearing side. The substantial variation in these two coupling effects contributes sensibly to the increase in the overall cavitation intensity. Meanwhile, the weakened coupling effect between the free shearing vortex and wall shearing vortex, as a consequence of increased potential core thickness at larger openness, leads to the attenuated vortex cavitation at the wall poppet side. Additionally, the vortex cavitation at free shearing side has a larger size in the chamfered valve seat case, due to the coupling of shed flow instability with the Kelvin-Helmholtz instability. As a conclusion, the inception mechanism for the cavitation remains unchanged with openness, while the difference in flow instabilities as well as the associated coupling effects with cavitation contributes to the variation in cavitation intensity.

Numerical and experimental investigation on electromechanical aileron actuation system with joint clearance

Qi Wan,Geng Liu,Yong Zhou,Shangjun Ma,Ruiting Tong 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.2

A closed-loop coupling model at the system-level is developed to analyze the effects of joint clearance on the dynamic responses of electromechanical aileron actuation system. The proposed model considers the coupling effects between the electromechanical actuator (EMA) control performance and dynamic characteristics of linkage mechanism with joint clearance. Besides, the experiments are conducted in a test rig, which verifies the effectiveness of the proposed closed-loop coupling model. The nonlinear contact force model and modified Coulomb friction model are adopted in the joint clearance of the linkage mechanism, and the influences of clearance size on the dynamic behaviors of electromechanical aileron actuation system are studied. The numerical and experimental results indicate that the novel closed-loop coupling model, considering the EMA control performance and dynamics of linkage mechanism with joint clearance at the same time, is an effective model to predict the dynamic characteristics of electromechanical aileron actuation with joint clearance, which provides a practical method to analyze the dynamic performance of electromechanical coupling multibody systems with joint clearance.

Trajectory planning of multi-degree-of-freedom robot with coupling effect

Kunming Zheng,You-Min Hu,Bo Wu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1

For a multi-degree-of-freedom (MDOF) robot with flexible components, vibration errors can easily occur during operation. Thus, the position of the end effector inevitably deviates from its desired value and causes failure of the precise trajectory tracking task. To solve this problem, an MDOF KUKA robot is introduced in the present study. We propose a new methodology to investigate the dynamic coupling effect and trajectory planning for the robot. The dynamic coupling effect index is defined for the first time, thereby providing a theoretical basis for the trajectory planning. Moreover, a new trajectory plan is adopted to reduce the vibration errors caused by the coupling effect in the Cartesian coordinate and joint coordinate systems. The advantages of the proposed methodology in improving accuracy and stability are validated by experiments. In addition, the chaos phenomenon is observed, which is the focus of our future study.

Mechanism of Controllable Force Generated by Coupling Inverse Effect of Piezoelectricity and Magnetostriction

Aiqun Xu,Qianxing Gu,Haikuo Yu 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.4

A method based on piezoelectric and magnetostrictive coupling inverse effect to generate precise controllable force is proposed to meet the requirement of manipulation force control in ultra-precision machining and assembly process. According to the principle of magnetic flux continuity, combine with the characteristics of piezoelectric and magnetostrictive inverse effects, the working mechanism of force generation is analyzed, and the theoretical model of the relationship between output force and parameters which include material characteristics, geometric parameters, working voltage of piezoelectric ceramics is established. An experimental device consisting of piezoelectric ceramic driving power supply, strain gauge, static strain tester, micro laser displacement sensor, force sensor, data acquisition card and magnetic force control component is developed. The relationship between output magnetic force and air gap or working voltage are studied by experiment and simulation. The results show that the output force variations of simulation and experiment are close. The output magnetic force fluctuation is small and with good stability. It verifies the consistency and correctness of the theoretical, simulation and experimental results.