Experi mental Study on Vortex-Induced Vibrations of Submarine Pipeline near Seabed Boundary in Ocean Currents

Unlike most previous studies on vortex-induced vibrations of a cylinder far from a boundary, this paper focuses on the influences of close proximity of a submarine pipeline to a rigid seabed boundary upon the dynamic responses of the pipeline in ocean currents. The effects of gap-to-diameter ratio and those of the stability parameter on the amplitude and frequency responses of a pipeline are investigated experimentally with a novel hydro-elastic facility. A comparison is made between the present experimental results of the amplitude and frequency responses for the pipes with seabed boundary effects and those for wall-free cylinders given by Govardhan and Williamson （2000） and Anand （1985）. The comparison shows that the close proximity of a pipeline to seabed has much influence on the vortex-induced vibrations of the pipeline. Both the width of the lock-in ranges in terms of Vr and the dimensionless amplitude ratio Amax/D become larger with the decrease of the gap-to-diameter ratio e/D, Moreover, the vibration of the pipeline becomes easier to occur and its amplitude response becomes more intensive with the decrease of the stability parameter, while tire pipeline frequency responses are affected slightly by the stability parameter.

Faster vortex core switching with lower current density using three-nanocontact spin-polarized currents in a confined structure

We perform micromagnetic simulations on the switching of magnetic vortex core by using spin-polarized currents through a three-nanocontact geometry. Our simulation results show that the current combination with an appropriate current flow direction destroys the symmetry of the total effective energy of the system so that the vortex core can be easier to excite,resulting in less critical current density and a faster switching process. Besides its fundamental significance, our findings provide an additional route to incorporating magnetic vortex phenomena into data storage devices.

NONLINEAR DYNAMICS RESPONSE OF CASING PIPE UNDER COMBINED WAVE-CURRENT

The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison’s nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin’s method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.

载流等离子体中的静磁Vortex

研究载流等离子体中的静磁对流胞模,导出了描述非线性静磁对流胞横的方程。并且利用方法求得该方程的偶极Vortex 解。

NONLINEAR DYNAMICS RESPONSE OF CASING PIPE UNDER COMBINED WAVE-CURRENT

The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison＇s nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin＇s method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160 m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wavecurrent.

Magnetic vortex gyration mediated by point-contact position

Micromagnetic simulation is employed to study the gyration motion of magnetic vortices in distinct permalloy nanodisks driven by a spin-polarized current. The critical current density for magnetic vortex gyration, eigenfrequency, trajectory, velocity and the time for a magnetic vortex to obtain the steady gyration are analyzed. Simulation results reveal that the magnetic vortices in larger and thinner nanodisks can achieve a lower-frequency gyration at a lower current density in a shorter time. However, the magnetic vortices in thicker nanodisks need a higher current density and longer time to attain steady gyration but with a higher eigenfrequency. We also find that the point-contact position exerts different influences on these parameters in different nanodisks, which contributes to the control of the magnetic vortex gyration. The conclusions of this paper can serve as a theoretical basis for designing nano-oscillators and microwave frequency modulators.

Wave-current interaction with a vertical square cylinder at different Reynolds numbers

Large eddy simulation is performed to study three-dimensional wave-current interaction with a square cylinder at different Reynolds numbers, ranging from 1,000 to 600,000. The Keulegan-Carpenter number is relevantly a constant of 0.6 for all cases. The Strouhal number, the mean and the RMS values of the effective drag coefficient in the streamwise and transverse directions are computed for various Reynolds numbers, and the velocity of a rep- resentative point in the turbulent zone is simulated to find the turbulent feature. It is found that the wave-current interaction should be considered as three-dimensional flow when the Reynolds number is high; under wave-current effect, there exists a critical Reynolds number, and when the Reynolds number is smaller than the critical one, current effect on wave can be nearly neglected; conversely, with the Reynolds number increasing, wave-currentstructure interaction is sensitive to the Reynolds number.

Experiments on Interaction Between Current-Induced Vibration and Scour of Submarine Pipelines on Sandy Bottom

In order to understand the dynamic behavior of submarine pipelines exposed to current and the mechanism of the interaction between current-induced vibration and scour of pipelines on a sandy bottom, an experimental investigation is conducted with a small scale model A test model which can be tested in the flume is set up by taking into account the typical working conditions of the pipelines and by applying the similarity theory. The interactions between the shape of the scour hole and the behavior of the pipeline as well as the flow patterns of the current are detailed, and the interaction mechanism outlined. The effect of vibration of the pipeline on the development of dynamic scour at different stages is found out. The proposed experimental method and test results provide an effective means for design of marine pipelines against scouring.

Trajectory and frequency of vortex gyration in a multi-nanocontact geometry

Nonlinear vortex gyrotropic motion in a three-nanocontacts system is investigated by micromagnetic slmulations and analytical calculations. Three out-of-plane spin-polarized currents are injected into a nanodisk through a centered nanocontact and two off-centered nanocontacts, respectively. For current combination （ipl, ip0, ip2） = （-1,1, -1）, the trajectory of the vortex core is a peanut-like orbit, but it is an elliptical orbit for （ip1, ip0, ip2） = （1, 1, -1）. Moreover, the gyrotropic frequency displays peaks for both current combinations. Analytical calculations based on the Thiele equation show that the changes of frequency can be ascribed mainly to the forces generated by the Oersted field accompanying the currents. We also demonstrate a dependence of eigenfrequency shifts on the direction and distance of the applied currents.

Vortex lines in a ferromagnetic spin-triplet superconductor

Based on Duan＇s topological current theory,we show that in a ferromagnetic spin-triplet superconductor there is a topological defect of string structures which can be interpreted as vortex lines.Such defects are different from the Abrikosov vortices in one-component condensate systems.We investigate the inner topological structure of the vortex lines.The topological charge density,velocity,and topological current of the vortex lines can all be expressed in terms of 未 function,which indicates that the vortices can only arise from the zero points of an order parameter field.The topological charges of vortex lines are quantized in terms of the Hopf indices and Brouwer degrees of-mapping.The divergence of the self-induced magnetic field can be rigorously determined by the corresponding order parameter fields and its expression also takes the form of a 未-like function.Finally,based on the implicit function theorem and the Taylor expansion,we conduct detailed studies on the bifurcation of vortex topological current and find different directions of the bifurcation.

Influence of Additional Device on Performance of the Marine Current Turbine

To investigate the influence of additional device on the flow in marine current turbine, two additional devices for ma- rine current turbine including short diffuser and long diffuser types are studied based on the test data of original marine current turbine. The results of numerical simulation show that the additional device with flange structure, compared to marine current turbine without additional device, can obtain more output power. However, it brings the inhomogeneity of additional device force as the increasing of effective output power. At same time, due to existence of the flange, two karman vortices are found behind the flange. The low pressure region produced by additional device and flange struc- ture can speed up the flow around the marine current turbine, so as to improve the output power.

Experimental Investigation on Vortex-Induced Vibration of Steel Catenary Riser

Steel catenary riser（SCR） is the transmission device between the seabed and the floating production facilities. As developments move into deeper water, the fatigue life of the riser can become critical to the whole production system, especially due to the vortex-induced vibration（VIV）, which is the key factor to operational longevity. As a result, experimental investigation about VIV of the riser was performed in a large plane pool which is 60 m long, 36 m wide and 6.5 m deep. Experiments were developed to study the influence of current speed and seabed on VIV of SCR. The results show that amplitudes of strain and response frequencies increase with the current speed both in cross-flow（CF） and in-line（IL）. When the current speed is high, multi-mode response is observed in the VIV motion. The amplitudes of strain in IL direction are not much smaller than those in CF direction. The seabed has influence on the response frequencies of riser and the positions of damage for riser.

Dynamics of vortex–antivortex pair in a superconducting thin strip with narrow slits

In the framework of phenomenological time-dependent Ginzburg-Landau（TDGL） formalism,the dynamical properties of vortex-antivortex（V-Av） pair in a superconductor film with a narrow slit was studied.The slit position and length can have a great impact not only on the vortex dynamical behavior but also the current-voltage（Ⅰ-Ⅴ） characteristics of the sample.Kinematic vortex lines can be predominated by the location of the slit.In the range of relatively low applied currents for a constant weak magnetic field,kinematic vortex line appears at right or left side of the slit by turns periodically.We found such single-side kinematic vortex line cannot lead to a jump in the Ⅰ-Ⅴ curve.At higher applied currents the phase-slip lines can be observed at left and right sides of the slit simultaneously.The competition between the vortex created at the lateral edge of the sample and the V-Av pair in the slit will result in three distinctly different scenarios of vortex dynamics depending on slit length：the lateral vortex penetrates the sample to annihilate the antivortex in the slit;the V-Av pair in the slit are driven off and expelled laterally;both the lateral vortex and the slit antivortex are depinned and driven together to annihilation in the halfway.

波流环境中多孔射流三维数值模拟

建立了波流环境中多孔射流的三维大涡数学模型,探讨了波流共同作用下多孔射流的扩散和稀释机制,分析了孔间距对双孔射流、射流与环境水体相互作用的影响,并给出了最优相对孔间距。模拟结果表明:在波谷相位时刻,由于横流与波浪相互作用强烈,流场内的三维涡旋结构丰富、尺度较大、数目众多,有利于射流与环境水体、射流与射流之间的掺混,这是波流环境比单一横流环境中多孔射流运动扩散效果更佳的主要原因;随着孔间距的增大,双孔射流之间的相互作用慢慢削弱,而射流与环境水体之间的相互作用却在不断增强;双孔射流在孔间距为7.0倍管口直径时扩散效果最好。

Vortex lines in a ferromagnetic spin-triplet superconductor

Based on Duan’s topological current theory,we show that in a ferromagnetic spin-triplet superconductor there is a topological defect of string structures which can be interpreted as vortex lines.Such defects are different from the Abrikosov vortices in one-component condensate systems.We investigate the inner topological structure of the vortex lines.The topological charge density,velocity,and topological current of the vortex lines can all be expressed in terms of δ function,which indicates that the vortices can only arise from the zero points of an order parameter field.The topological charges of vortex lines are quantized in terms of the Hopf indices and Brouwer degrees of-mapping.The divergence of the self-induced magnetic field can be rigorously determined by the corresponding order parameter fields and its expression also takes the form of a δ-like function.Finally,based on the implicit function theorem and the Taylor expansion,we conduct detailed studies on the bifurcation of vortex topological current and find different directions of the bifurcation.

考虑质量比影响的双圆柱涡激振动发电装置数值模拟研究

双圆柱涡激振动发电装置是一种利用海流能发电的新型能源装置。该研究使用Fluent软件模拟了双圆柱涡激振动发电装置的水动力特性。利用用户自定义函数和动网格技术实现了圆柱振子的流固耦合模拟,分析圆柱振子的涡激振动特性。首先,进行网格和时间步长的无关性验证,证明了该数值模拟的准确性;其次,从位移时程曲线、幅值、频率三个方面分析圆柱振子的涡激振动特性;最后,通过对等质量比下串列双圆柱涡激振动发电装置圆柱振子的获能功率及能量转换效率的分析,研究质量比对双圆柱涡激振动发电装置的俘获能特性的影响。研究表明:当质量比m^(*)=3、4、5时,下游圆柱的横流向振幅随约化速度的增加而逐渐大于上游圆柱的横流向振幅;不同质量比下双圆柱振子的横流向无量纲振幅均呈现先随约化速度的增加而增加,然后又减小的趋势;当质量比m^(*)=4时,上、下游圆柱的能量转换效率最高,分别为32.6%、22.8%;当质量比m^(*)=5时,下游圆柱的能量转换效率最高,为30.5%。

流动控制组合对潮流能水轮机翼型水动力学的特性影响研究

为全面提升潮流能水轮机叶片的水动力学性能,将格尼襟翼(GF)和涡流发生器(VGs)的附加件组合引入到潮流能水轮机领域,研究附加件组合对改善水轮机叶片水动力性能的作用机理。以NACA4418翼型为研究对象,分别建立加装格尼襟翼、涡流发生器和二者流动控制组合的水轮机翼型三维模型,应用数值模拟方法研究流动控制组合对水轮机叶片水动力性能的影响机理。结果表明:安装GF可有效提高翼型段的升力系数,但会降低翼型的失速角;安装VGs可抑制翼型段吸力面的流动分离、增大翼型段的失速角,但攻角越小水动力学性能改善效果越不明显;GF和VGs的流动控制组合则可将二者优势充分结合,在全面提高翼型段升力系数的同时,还可抑制翼型表面的流动分离、增大翼型的失速角,从而获得最佳的流动控制效果。

综合实验试题C:永磁铁通过金属管所产生的涡旋电流损耗功率及累计损耗测量

第9届全国大学生物理实验竞赛珠海赛区综合实验试题C为测量永磁铁通过金属管所产生的涡旋电流损耗功率及累计损耗.选手需设计并搭建光电门测量装置,测量磁铁下落速度,计算出能量损耗.本文给出了详细的试题设计和参考解答,并结合选手成绩和竞赛调研的统计结果,分析出选手的知识薄弱点和不足能力,为大学物理实验的教学与改革提供参考.

组合三棱柱振子流致振动运动特性分析

以流致振动能量转换系统(flow induced motion energy conversion system,FIMECS)为基础,以截面形式和刚度为变量针对组合三棱柱振子进行试验,评估振幅、频率等指标。试验选取了组合三棱柱振子进行了模型试验,通过改变截面排布形式以及系统刚度来研究截面布局、刚度对组合三棱柱振子的影响。该研究旨在探究组合振子流致振动的最佳振动条件,为后续多振子流致振动研究扩展思路。试验结果表明:三种不同排布形式的组合振子,在不同刚度工况下都有较好的振动效果,Ⅰ型和Ⅲ型振子振动随流速变化表现为典型的涡激振动,Ⅰ型排布振子具有最好的振动表现。

悬浮隧道锚索的涡激动力响应分析

参考斜拉桥拉索的振动微分方程,利用动力学方程和莫里森方程,建立了锚索涡激振动方程,计算并讨论了锚索倾角、张力和长度的改变对其横向振动的影响。计算结果表明:锚索拉力和倾角的减小将引起振动幅值的增加和一阶固有频率、引起涡激流速锁定的流速、最大响应时的参数激励频率的减小;锚索垂直深度的减小将引起振动幅值的减小和一阶固有频率、引起涡激流速锁定的流速、最大响应时的参数激励频率的增加。