三维隔震单层球面网壳结构频率相关变阻尼半主动控制

在不同频率特征的地震动作用下,三维隔震单层球面网壳结构隔震层最优阻尼设计不同.文中基于单自由度体系加速度传递率函数,提出一种地震动主频相关的加速度阈值变阻尼半主动控制方法以及地震动主频分区识别方法.基于ABAQUS软件的DLOAD子程序,开展了三维隔震单层球面网壳被动控制与半主动控制有限元计算,对节点加速度、杆件轴力进...     

Gravitational potential energy of terrestrial planets

Summary The gravitational potential energies of Mercury, Venus and Mars have been computed on the basis of density models and compared to that of the Earth. It has been stated that the specific potential energy per unit mass is very close as regards the pair Earth and Venus, as well as the pair Mercury and Mars.Dedicated to the Memory of K. P     

Gravitational potential energy of the Sun

Summary The gravitational potential energy of the Sun and its corresponding internal energy have been estimated on the basis of the standard model of the Sun's internal structure. It is demonstrated that the principal moment of inertia of the Sun, computed from the model, does not fit the hydrostatic equilibrium limit.     

Radial vibration of a composite spherical shell

Summary This paper deals with radial vibration of a composite spherical shell made up of orthotropic materials by the application of a periodic shearing stress on the outer surface. Two cases have been discussed. In the first the elastic constants of the material of the composite body are assumed to remain constant while in the second they are proportional to the distance from the centre of the composite body. Results were obtained in terms of Bessel functions.     

Taylor cylinder and convection in a spherical shell

The successive development of thermal convection in a rotating spherical shell heated from below has been studied. It has been indicated that the convection properties strongly differ within and outside a Taylor cylinder. The distributions of the kinetic energy, helicity, temperature, and differential rotation in these regions are presented. The consequences for the geodynamo theory and interpretation of geomagnetic observations are considered.     

凯威特单层球面网壳结构隔震分析

将凯威特网壳结构的固定支座设置成隔震支座,分别采用弹簧支座和粘弹阻尼支座对结构进行了隔震控制。在有控和无控状态下,计算了凯威特网壳结构的自振频率,初步分析了凯威特网壳结构的隔震控制机理。分别在常遇和罕遇各三种地震作用下,对网壳结构进行了时程分析,对网壳结构的最大水平位移、隔震支座的最大水平位移、最大支座反力和网壳结构的杆件轴力进行了数值计算。研究结果表明：两种隔震装置均有效地控制了凯威特网壳结构的支座反力和杆件轴力,粘弹阻尼支座还明显地减少了隔震支座的水平位移和隔震结构的水平位移。隔震方法对于大跨网壳结构的减振是有效的。     

双层球面网壳结构的阻尼替代杆件减振控制研究

采用阻尼杆件替代双层网壳结构中的部分下弦杆件,既不改变原结构的网格形式,又对其进行有效的减振控制。在ANSYS软件中建立粘弹性阻尼杆件的数值模型,采用阻尼杆件对网壳部分下弦杆件进行替换,建立网壳减振结构数值模型;分别采用8种阻尼杆件替换方式对结构进行控制,进行结构的三维地震作用分析,在三种常用II类场地地震作用下考察替换杆件布局对结构控制效果的影响。研究表明:阻尼杆件布局方式对结构动力响应的控制效果有较大影响,合理布置阻尼替换杆件可以有效降低结构最大节点位移、最大节点加速度、最大杆件轴力等响应,控制效果可以达到20%～30%。     

Dielectrophoretic,thermal instability in a spherical shell of fluid

Abstract

This paper is concerned with the dielectrophoretic instability of a spherical shell of fluid. A dielectric fluid, contained in a spherical shell, with rigid boundaries is subjected to a simultaneous radial temperature gradient and radial a.c. electric field. Through the dependence of the dielectric constant on temperature, the fluid experiences a body force somewhat analogous to that of gravity acting on a fluid with density variations. Linear perturbation theory and the assumption of exchange of stabilities lead to an eighth order differential equation in radial dependence of the perturbation temperature. The solution to this equation, satisfying appropriate boundary conditions, yields a critical value of the electrical Rayleigh number and corresponding critical wave number at which convective motion begins. The dependence of each critical number is presented as a function of the gap size and temperature gradient. In the limit of zero shell thickness both the critical Rayleigh number and critical wave number agree with results for the case in the infinite plane problem.     

Nonlinear dynamics of a stellar dynamo in a spherical shell

Abstract

A simple mean-field model of a nonlinear stellar dynamo is considered, in which dynamo action is supposed to occur in a spherical shell, and where the only nonlinearity retained is the influence of the Lorentz forces on the zonal flow field. The equations are simplified by truncating in the radial direction, while full latitudinal dependence is retained. The resulting nonlinear p.d.e.'s in latitude and time are solved numerically, and it is found that while regular dynamo wave type solutions are stable when the dynamo number D is sufficiently close to its critical value, there is a wide variety of stable solutions at larger values of D. Furthermore, two different types of dynamo can coexist at the same parameter values. Implications for fields in late-type stars are discussed.     

半刚性连接焊接空心球网壳弹塑性分析的短杆模型

提出了一种考虑焊接空心球节点半刚性网壳弹塑性分析的"短杆模型",即采用等效短杆模拟焊接空心球节点,通过对质量、横截面积及惯性矩的折算来模拟球的质量及初始刚度,并利用自定义PMM塑性铰模拟焊接空心球节点塑性工作阶段随轴力变化的弯曲刚度。在SAP2000有限元软件中实现了该计算模型的导入,并通过算例证明了采用该模型进行弹塑性分析的可行性。"短杆模型"适用于半刚性连接焊接空心球网壳的静动力弹塑性分析,借助它可以更准确地分析半刚性连接焊接空心球网壳塑性阶段的真实反应和实际工作性能。     

球面网壳结构的分段式多维隔震控制

球面网壳结构是典型的大跨度空间结构,地震时水平和竖向地面运动分量对其地震响应的影响均十分显著。为了提高网壳结构的抗震性能,可采用支座型隔震装置形成分段式多维隔震机制。在这类多维隔震体系中,碟形弹簧支座可用于结构的竖向隔震,同时,可将其与适用于水平隔震的摩擦摆(FPS)或SMA-橡胶支座配合使用。基于上述概念设计,提出了水平和竖向隔震装置的构造和计算模型。进而,根据网壳结构多维隔震的动力方程,开展了El Centro波作用下双层球面网壳和单层球面网壳结构多维隔震控制的数值模拟。计算结果表明,多维隔震球面网壳结构的杆件内力、加速度和位移的减振效果能达到50%以上,验证了所提多维隔震技术对保护球面网壳结构免遭地震破坏的有效性。     

双层球面网壳动力失效分析及地震损失评估

双层球面网壳结构是一种缺陷敏感型结构,影响结构动力失效的初始缺陷主要有杆件的初弯曲、杆件的残余应力和结构节点的初始安装偏差3种。本文首先利用有限元软件ANSYS的二次开发功能开发了可以考虑初始弯曲和残余应力的杆单元,接着利用动力增量法(IDA)系统地研究了这3种缺陷对结构动力失效的影响,最后总结提出了考虑缺陷的双层球面网壳结构的抗震损失评估方法。     

中国大陆现今地应力场黏弹性球壳数值模拟综合研究

中国大陆现今实测地应力场的状态与板块构造环境、活动断裂带分布、地形地貌以及地壳结构呈现一定相关性. 在中国大陆西缘,印度洋板块与欧亚板块陆发生陆碰撞,在中国大陆东缘,菲律宾海板块、太平洋板块俯冲到欧亚板块之下. 中国大陆内部被大型活动断裂带分割为多个块体,各个块体的地壳结构和厚度呈不均匀分布,地形地貌起伏具有很大的差异. 笔者以中国大陆块体模型为基础,把板块构造作用和重力势作为主要影响地应力状态的两个主要要素,在现今活动构造、GPS和实测地应力等成果的约束下,利用线性黏弹体球壳有限元模拟分析了中国大陆现今地应力场的分布特征和控制因素. 结果表明: (1)构造应力场总体上呈现出西部挤压,东部拉张的特征,印度板块与欧亚板块的持续碰撞形成了青藏高原及其周缘的挤压性质的构造应力场,而东部菲律宾板块与太平洋板块的俯冲形成了黄海、东海和环渤海区域的拉张性质的构造应力场,中间为拉张环境和挤压环境的过渡,最大主应力的方向受到板块构造环境和活动构造分布的控制;(2)重力的影响主要体现在地形梯度大和地壳厚度结构变化大的地壳浅部区域,在藏南、滇西北局部地区的地壳浅部由于受到重力势控制,呈现为张性应力场,在塔里木地区由于重力势引起的应力场与构造应力场同为挤压性质,因此该区的挤压强度得以增加;(3)中国大陆浅部地应力场的状态主要受到区域板块构造环境、块体边界活动构造带的展布和地形的控制,总体上以南北构造带为界,西部以较强的压性构造环境为主,东部为较弱的压性构造环境,藏南和滇西北局部地区存在有张性构造环境;构造应力对地应力的贡献比重随着深度增加而增加;(4)采用黏弹性模型的构造应力场模拟结果比完全弹性模型的模拟结果能够更好地与实测地应力场相吻合,利用完全弹性模型分析由地震等诱发的地应力瞬时变化是有效的;(5)青藏高原东南缘最大主应力方向发生了较大的偏转,其主要控制因素有:印度板块持续的碰撞、中下地壳对上地壳拖曳以及印度板块通过实皆断裂对欧亚板块的剪切拉伸作用. 中国大陆现今地应力场是整个地壳岩石黏弹特性长期演化和断裂活动的结果,是地应力场动态演化过程中在现今时间点上的状态,受到板块构造环境、大陆内部活动断裂分布、地形地貌和地壳结构等因素不同程度的控制,模拟结果为中国大陆地应力场提供了一个定量的参考模型.     

摩擦摆隔震双层球面网壳结构的多维地震响应

将摩擦摆(FPS)引入到网壳结构的隔震控制中。文中首先阐明了FPS的工作机理和本构关系,建立了FPS隔震网壳结构的振动方程。通过双层球面网壳结构的数值算例考察了隔震和无控结构在单向和三向地震作用下的振动响应以及FPS的控制效果。研究结果表明,FPS具有良好的隔震和耗能效果,可有效地应用于球面网壳结构的振动控制。     

Finite amplitude convection and magnetic field generation in a rotating spherical shell

Abstract

Finite amplitude solutions for convection in a rotating spherical fluid shell with a radius ratio of η=0.4 are obtained numerically by the Galerkin method. The case of the azimuthal wavenumber m=2 is emphasized, but solutions with m=4 are also considered. The pronounced distinction between different modes at low Prandtl numbers found in a preceding linear analysis (Zhang and Busse, 1987) is also found with respect to nonlinear properties. Only the positive-ω-mode exhibits subcritical finite amplitude convection. The stability of the stationary drifting solutions with respect to hydrodynamic disturbances is analyzed and regions of stability are presented. A major part of the paper is concerned with the growth of magnetic disturbances. The critical magnetic Prandtl number for the onset of dynamo action has been determined as function of the Rayleigh and Taylor numbers for the Prandtl numbers P=0.1 and P=1.0. Stationary and oscillatory dynamos with both, dipolar and quadrupolar, symmetries are close competitors in the parameter space of the problem.     

Magnetic dipole moment of a spherical shell with TRM acquired in a field of internal origin

The acquisition of thermoremanent magnetization (TRM) by a cooling spherical shell is studied for internal magnetizing dipole fields, using Runcorn's new theorems on magnetostatics. If the shell cools progressively inward, inner regions acquire TRM in a net field composed of the dipole source term plus a uniform field due to the outer magnetized layers. In this case the global dipole moment and thus external remanent field are non-zero when the whole shell has cooled below the Curie point and the source dipole has disappeared. The remanent field outside the shell is found to depend on the thickness, radii, and cooling rate of the shell, as well as the coefficient of TRM and the intensity of the magnetizing field. Some implications for the Moon's remanent dipole moment are discussed.     

Rotatory vibration of a thick spherical shell of isotropic non-homogeneous elastic material

Summary Rotatory vibrations of a thick spherical shell of isotropic non-homogeneous material with rigidity and density given by (i) = ₀ r ^-2 withQ =Q ₀ r ^-2 e ^2mr and (ii) = ₀ r ^m with =Q ₀ r ⁿ have been discussed and the frequency equation is derived with numerical enumeration of frequency in each case.     

横向黏度变化对球层中热对流的影响

本文在常黏度的基础上,加上横向黏度变化,纯粹研究了横向黏度变化对球层中热对流的影响.结果表明,横向黏度变化可以加速或阻碍球层中的热对流,并对球层中热传输方式有调节作用,但是横向黏度变化对球层中热对流的影响会限制在一定的强度范围内,并且难以改变球层中热对流的格局.横向黏度变化所产生的环型场速度占总速度场的比例最多为十几个百分点,难以解释观测到的地表板块运动中的环型场能量大小.     

The patterns of high-degree thermal free convection and its features in a spherical shell

Introduction Mantle convection is thought to be the most effective way of heat transportation in the earth and the source of driving lithospheric plates (Elasser, 1971). The velocity field of plate motion can be split into poloidal and toroidal parts, which are corresponding to the vertical (i.e. radial) and horizontal motions, respectively, in global model. The toroidal component is manifested in the existences of transform faults and the poloidal one in the presences of convergence and diver…