水下加肋双层圆柱壳体振动传递特性分析

研究水下双层圆柱壳体振动传递特性具有重要的工程意义,尤其对于水下结构噪声快速预报和外壳表面速度场实时重构.以此为出发点,通过双层加肋圆柱壳体模型水下振动试验研究了不同激励条件下内外壳体振动特性;然后建立了水下双层圆柱壳体有限元模型,计算分析了壳体在流固耦条件下的振动路径及特性,找出了不同激励方向、流体耦合方式和内外壳体连接方式等典型因素下内、外壳体间振动传递规律,为速度场重构和水下噪声预报提供了一定的理论指导.     

突然开孔结构风致瞬态内压极值研究

基于经典内压控制方程,对特定开孔时刻下的瞬态内压峰值响应进行了详细研究,分析孔口开启时间对结构瞬态内压峰值的影响。提出突然开孔结构瞬态内压极值的估算方法,并与精确算法进行对比。结果表明:门窗开启时刻的外压值越大,瞬态内压峰值越大,但两者最大值之间存在着一定的时差;瞬态内压极值与外压达极值时的瞬态内压峰值之间的比值可用放大因子G=1.17来描述;提出的极值计算方法能有效地估算突然开孔结构瞬态内压极值。     

芯材增强对夹层圆柱壳动力学性能影响的有限元分析

将表层、增强材料与芯材分开,应用有限元分析软件ANSYS,采用8节点SOLID45实体单元,对增强型夹层圆柱壳建立物理模型,进行自由振动及瞬态动力学过程分析。考虑树脂材性、尺寸以及分布等参数的变化,分析了点阵增强和齿槽增强对夹层圆柱壳动力学性能的影响,将两种增强方式进行了对比。结果显示,树脂柱及树脂齿槽均可改变圆柱壳的振动特性,对降低瞬态荷载下的动力响应有积极作用。其中树脂材性的影响较小,而点阵和齿槽的尺寸与分布对圆柱壳动力学性能的影响较为明显,分析显示,点阵增强对于提高结构固有频率比齿槽增强更好一些,而齿槽增强对于降低端部受冲击荷载时的动力位移比点阵增强更好一些。     

点探头涡流无损检测中磁介质作用机理研究

结合实际涡流无损检测应用中的含磁介质点探头的特点,分析了探头中磁介质引入的各种附加效应及其对缺陷阻抗的影响。通过引入等效电流的概念,讨论了磁介质对涡流场的作用,建立含磁介质点探头涡流无损检测模型,并给出含磁介质探头周围的电磁场方程,求得均匀半无限导体系统的磁矢量势分布和导体中涡流、电场强度分布。通过实例,计算了非铁磁性导体中无缺陷时探头信号与提离高度的关系、存在缺陷时探头阻抗变化的特点。理论计算与实验结果基本吻合。     

考虑圆柱铰链间隙的多刚体系统动力学计算方法

为了研究含圆柱铰链间隙的多刚体系统动力学计算方法,针对三维圆柱铰链的结构特点,给出了一种改进的接触对确定方法,构造了空间间隙圆柱铰链接触分离切换点的判别方法。法向接触力采用Lankarani与Nikravesh的连续接触力模型计算,切向摩擦力采用修正的Coulomb模型计算,综合考虑接触分离状态建立了统一形式的动力学方程。最后对比间隙铰链机构和理想铰链机构运动,结果表明圆柱铰链间隙在短时间内对其他构件的运动影响很小,但严重增大了铰链内部的碰撞力,长时间运动后机构的位移、速度、加速度与理想铰链偏差变大,但接触摩擦力使圆柱铰链的轴向运动受到抑制。间隙圆柱铰链的研究方法和结果为相关和更复杂的含间隙圆柱铰链机构的运动分析提供了理论参考。     

引入减基法的压电层合板瞬态响应分析

摘要：用减基法（RBM）结合有限元法、傅里叶变换和Newmark直接积分法,研究了压电层合板在机电耦合载荷下的瞬态响应。用层单元将层合板沿厚度方向进行离散,得到时间域内的运动方程,通过傅里叶变换得到波数域内的控制方程。应用Newmark直接积分法求解波数域内的位移和电势,并在Newmark法求解过程嵌入减基法,构造减基空间,把结构的等效刚度矩阵、质量矩阵和载荷列向量映射到减基空间降阶,得到减缩的Newmark增量式,从而快速求解得到原结构波数域响应,通过傅里叶逆变换得到时域内的响应。以PZT-5A/0°PVDF铺层两相材料复合压电层合板为算例,分析了机电耦合线载荷激励下,位移场和电势场的瞬态响应情况。计算结果表明,求解过程引入减基法能更快得到结构的瞬态响应,并保证了精度。     

新型装配式竖向电涡流TMD试验研究

针对城市大跨度钢结构人行天桥的减振需求,研制了一种结构紧凑、装配简单的新型装配式竖向永磁式电涡流TMD样机,综合TMD样机阻尼参数测试与电涡流阻尼磁场有限元分析结果提出了电涡流阻尼的初步设计方法与磁路优化布置。结果表明:新型TMD具有优良的阻尼特性、耐久性,且易于装配,工程应用可行性强。研究得到了用于竖向TMD的电涡流阻尼磁路优选构造:导体铜板两侧的矩形永磁铁宜采用同侧极性相同、不同侧极性相反的布置方式;永磁铁宜以水平单排布置为主,间距控制在永磁铁边长的一半以内;永磁铁必须安装2排或多排时,上下2排间距不宜小于永磁铁边长。     

时变等离子体覆盖导体圆柱的双站散射特性分析

研究时变等离子体覆盖导体圆柱的双站散射特性对等离子体隐身技术和太空再入体的跟踪识别技术具有重要的意义。以非磁化不均匀等离子体覆盖导体圆柱的模型为基础,采用分段线性电流密度递归卷积时域有限差分方法计算了不均匀时变等离子体覆盖导体圆柱的双站雷达散射特性。结果表明:不均匀等离子体覆盖导体圆柱能成功地缩减目标的雷达散射截面。     

反射导体参数对涡流栅传感器非线性误差影响的仿真分析

涡流栅传感器基于横向电涡流效应设计,其反射导体参数变化对传感器测量准确度的影响比较明显,因此需要对反射导体尺寸、形状参数进行分析和优化,使其能够适应更多高准确度的测量场合。利用有限元分析方法(Maxwell软件)建立涡流栅传感器的线圈、反射导体模型,对不同尺寸、形状参数的反射导体进行仿真计算,分析反射导体长度、宽度、形状变化对涡流栅传感器的影响。分析结果表明:为提高传感器的准确度,反射导体选用略大于线圈长度和尽可能大宽度的两边半圆导体,为传感器选择合理的反射导体参数提供有利参考。     

磁流变液阻尼器响应时间的试验研究及其动态磁场有限元分析

摘 要：首先,试验测试了不同速度和电流变化下,大吨位磁流变液阻尼器的响应时间;然后,对激励电流变化时阻尼器的磁场变化进行了有限元模拟,基于阻尼器间隙内磁流变液剪切屈服强度的变化考察了阻尼器的响应时间,并与试验数据做了比较。最后,研究了涡流和阻尼器电磁回路中电流响应时间对阻尼力响应时间的影响。结果表明,可以用有限元模拟得到的间隙内磁流变液的平均有效剪切屈服强度的时程曲线来研究磁流变液阻尼器的响应时间;电磁响应时间是阻尼力响应时间的决定因素,减小阻尼器中的涡流是缩短磁流变液阻尼器响应时间的重要途径;电流下降时涡流对阻尼器磁路的影响要大于电流上升的情况;无论是上升还是下降,电流初值越小,涡流对阻尼器磁路的影响越大,阻尼力响应时间也越长。研究还表明,缩短电流的响应时间,会带来更大的涡流,并不一定能缩短阻尼力的响应时间。     

Braking forces and damping coefficients of eddy current brakes consisting of cylindrical magnets and plate conductors of arbitrary shape

A method for analyzing a magnetic damper (eddy current brake) consisting of a cylindrical magnet and a plate conductor of arbitrary shape is considered. Since the magnetic flux is a function of the position, the analytical solution to obtain the eddy current, braking force, and damping coefficient is obtained by dividing the magnetic flux into the narrow circular bands, and the unit step function is applied to solve the differential equation of the electromagnetic fields. The boundary condition of the plate conductor of arbitrary shape is satisfied directly by making use of the Fourier expansion collocation method. Numerical calculations have been carried out for the conductor of rectangular plates, circular plates with eccentric fluxes. The theoretical results are in very good agreement with the experimental ones.     

Remote Field Eddy Current Control Using Rotating Magnetic Field Transducer: Application to Pressure Tubes Examination

The remote field eddy current (RFEC) technique is used to investigate the possibility of detecting the discontinuities practiced on pressure tubes samples from nuclear reactors, pressurized heavy water reactors (PHWR) type. In this article, we propose to develop the RFEC using the technique of rotating magnetic field (RMF). A method for calculating the field generated by the eddy current transducer with RMF using propagator matrix was developed. The experimental measurements are realized for artificial discontinuities practiced in pressure tubes samples.     

Propagation velocity of normal zones in a SC braid

Propagation velocities of normal zones are obtained experimentally in a superconducting (SC) braid which is wound into a coil to simulate the SC pulsed dipole magnet for a synchrotron from the viewpoint of cooling. A numerical calculation to determine this velocity is carried out by using a modified thermal conduction equation. The equation eliminates a troublesome problem on the boundary condition reported previously by defining a new variable of the square of the heat flux along the conductor. A velocity dependent correction factor is used for cooling to take account of the transient effect. The values calculated are a representation of the experimental dependence of the velocity on both current and magnetic field and this indicates that the correction factor is applicable to the winding of the braid if modified properly. Discussion is also made on the transient cooling in the coil.     

Pulsed Eddy Current Testing of Carbon Steel Pipes’ Wall-thinning Through Insulation and Cladding

Pulsed eddy current testing of wall-thinning through cladding and insulation was studied from both theoretical and experimental aspects. The analytical solution was derived for a simplified four-layered structure and was used to conduct simulations to ascertain the feasibility of this method. A pulsed eddy current testing probe consisting of a circular excitation coil and an AMR-sensor-embedded differential detector was fabricated to measure the time-varying magnetic field signals on the axisymmetric excitation coil??s axis. The measurement system was able to measure magnetic field down to a few hundred micro-Gausses in an unshielded environment. Simulation and test results showed that over a certain time after turning off the excitation current the magnetic field signal??s decay behavior is almost merely relevant to the pipe??s wall thickness. Future development of a carbon steel pipe??s wall-thinning can be evaluated by using decay coefficients estimated from previously obtained test data.     

Heat transfer from plates to conductors: from toroidal field model coil tests analysis to ITER model

During a safety discharge of toroidal field type magnets, eddy currents and associated heat generation are induced in the plates. A model has been developed from the thermohydraulic code Gandalf with introduction of the equations of the heat diffusion from plates to conductors through the steel and insulation. The comparison of calculation and experimental results for the ITER toroidal field model coil is presented.Preliminary analysis for the ITER toroidal field coils is also presented, taking into account the conductor parameters, the magnetic field and the external hydraulic circuit. The possible quench of the magnetic system is discussed.     

Theoretical Analysis and Numerical Simulation of the Feasibility of Inspecting Nonferromagnetic Conductors by an MFL Testing Apparatus

ABSTRACT

It has been widely accepted that the magnetic flux leakage (MFL) testing system can be applied only to the inspection of ferromagnetic materials. The possibility of using the MFL testing apparatus to inspect nonferromagnetic metals is discussed in this article. According to Faraday’s law of induction, eddy current rises in the conductor passing through the MFL magnetizer. The perturbation of eddy current and its corresponding magnetic field caused by defects are theoretically analyzed. Then, the finite element method is carried out to verify the theoretical analyses and extract the perturbed magnetic field signals. Furthermore, the influences of specimen conductivity and moving velocity on the detection signal amplitude are also simulated. The results show that the nonferromagnetic conductors are possible to be inspected by the MFL apparatus, and higher conductivity or inspection speed will facilitate the inspection.     

Magneto-thermo-elastic problem of a conducting rectangular cylinder subjected to sinusoidal change in time of magnetic field

This study is concerned with a magneto-thermo-elastic problem of a conducting rectangular cylinder in an external magnetic field which varies sinusoidally in time. Analytical solutions of eddy currents induced in the cylinder are derived on the basis of a theory of the quasi-stationary current. Two-dimensional transient temperature change produced by the eddy current loss is derived by means of the Green’s function method. The stresses in the infinitely long cylinder in a plane state are derived by making use of the Airy’s stress function. The effect of a frequency in a sinusoidal change in time of the external magnetic field on behaviors of eddy current loss, temperature change and stresses in the cylinder is examined by numerical calculation. The skin effect with an increase in a frequency of the external magnetic field on the transient response of temperature change and stresses in the cylinder is discussed.     

脉冲强磁体导体材料研究

在脉冲强磁体设计中,磁应力是我们面临的最大挑战,当磁场强度达到100T时,磁体绕组中的磁应力高达4GPa,这是目前任何实用导体材料都无法承受的,因此,脉冲强磁体的发展在很大程度上取决于磁应力的解决情况.文章从提高导体材料机械强度的角度出发,介绍了目前各种导体材料的加工过程和技术参数,包括铜、铜宏复合导体材料、铜微复合导体材料、多层绞线复合导体材料等.     

Effective thermal conductivity of the conductor insulation of the ITER toroidal field model coil at operation temperature

During current transients in the toroidal field model coil (TFMC), the radial plates carry eddy currents that generate Joule heat. The heat sink is the forced flow helium cooling of the conductor. Vice versa, during accidents, the radial plates act as a heat sink during the heat up of the conductor. In both cases, the time constant of heat transfer is given by the thermal conductivity of the insulation of the conductor. The code system MAGS (magnet system) is used to recalculate fast discharge experiments of the TFMC at the TOSKA facility. The model takes into account the transient magnetic field, the current in the conductor circuit, in the radial plates and coil case, the ac-losses in the conductor and the helium flow. The results clearly indicate that the power distribution in the radial plate should be taken into account and the thermal conductivity of the insulation is considerably lower than assumed up to now.