Uniform Stabilization of aNonlinear Axially Moving String by a Boundary Control of Memory Type

A nonlinear problem modeling a moving string with memory condition at the boundary is considered. This work aims at establishing reasonable sufficient conditions capable of suppressing the transversal vibrations that occur during the movement of the string. Unlike the fixed strings case here we need to employ the Reynold Transport Theorem to compute the ”total” derivative. This results in the appearance of several boundary terms which necessitates appropriate handling. We shall prove that the motion of the string plays an important role in determining the rate of the decay of solutions.     

On the Spatial Behavior of the Steady-State Vibrations in Thermoviscoelastic Porous Materials

This paper reviews the spatial behavior of the amplitude of the steady-state vibrations in an anisotropic and homogeneous thermoviscoelastic porous beam. Here, we take into account the effects of the viscoelastic and thermal dissipation energies upon the corresponding harmonic vibrations in a right cylinder made of an anisotropic thermoviscoelastic porous material. In fact, we prove that the positiveness of the viscoelastic and thermal dissipation energies is sufficient for characterizing the spatial decay and growth properties of the harmonic vibrations in a cylinder, without any limiting restriction upon their frequencies.     

呼图壁储气库气井冲蚀规律初探

对于地下储气库而言,由于强注强采,高速流动的气体对管柱产生的冲蚀磨损是影响气井管柱寿命的重要因素。针对气井冲蚀问题,研究了材料冲蚀的不同内在机理,包括微切削理论、基于单点冲蚀的切削模型、锻造挤压理论、变形磨损理论、二次冲蚀理论和弹塑性压痕破裂理论。结合呼图壁储气库气井实际管柱结构与生产状况,认为微切削理论和变形磨损理论是主要的冲蚀破坏机理,并指出了管柱和井下工具不同部位所适用的不同的破坏机理。分析了造成气井冲蚀的影响因素,主要包括粒子的冲蚀角度、冲蚀速度、粒度、砂粒含量以及材料的硬度、弹性模量、类型、腐蚀对冲蚀的影响、环境温度等,并针对呼图壁储气库的实际情况,提出了减少甚至避免气井冲蚀的具体防护措施。呼图壁储气库优选的改良型13Cr气井管柱,具有良好的耐冲蚀性能。     

The vibration characteristics of drillstring with positive displacement motor in compound drilling Part 2: Transient dynamics and bit control force analysis

The transient dynamics of a drill string and the dynamic characteristics of bit control force during compound drilling have not been elucidated yet. A numerical simulation model of drill string with a positive displacement motor was established to analyze the transient dynamics of drill string. The calculation model of dynamic bit control force was proposed based on the results of the transient dynamics of drill string. The results show that, when compared with conventional drilling, the impact frequency and the mean and peak values of drill string–wellbore interaction were larger. The effect of compound drilling on the lateral vibration acceleration of drill string was greater than that on the longitudinal vibration acceleration. A heightened build-up effect was caused by the increase of weight on bit. The larger bend angle and higher position of the stabilizer were not conducive to the stable control of the well trajectory. The increased outer diameter of the stabilizer could reduce the build-up effect of the bottom hole assemble to a certain extent. The driller in the field control of a well trajectory should be based on the complex dynamics of the numerical model of the bottom hole assemble during compound drilling.     

Stability of an Axially Moving Viscoelastic Beam

In this paper, we consider a viscoelastic flexible structure modeled as an Euler-Bernoulli beam. The beam is moving in the direction of its axis. This is one of the main features of this work. We will be dealing with variable intervals of integration and therefore the standard computation using differentiation under the integral sign is no longer valid. The boundary conditions are of ‘cantilever’ type: there is no displacement at one end and the other end is free. In fact, it is subject to a nonlinear force acting there. We prove that when the velocity of the beam is smaller than a critical value, the dissipation produced by the viscoelastic material is sufficient to suppress the transversal vibrations that occur during the axial motion of the beam. The rate of decay is shown to be exponential.     

Analytical Solution for Thermomechanical Vibration of Double-Viscoelastic Nanoplate-Systems Made of Functionally Graded Materials

In this article, based on the nonlocal elasticity theory of Eringen, dynamic characteristics of a double-FGM viscoelastic nanoplates-system subjected to temperature change with considering surface effects (surface elasticity, tension and density) is studied. Two Kirchhoff nanoplates are coupled by an internal Kelvin–Voigt viscoelastic medium and also are limited to the external Pasternak elastic foundation. The material properties of the simply supported functionally graded nanoplates are assumed to follow power law distribution in the thickness direction. The governing equations of motion for three cases (out-of-phase vibration, in-phase vibration and one nanoplate fixed) are derived from Hamilton's principle. The analytical approach is employed to determine explicit closed-form expression for complex natural frequencies of the system. Numerical results are presented to show variations of the frequency of double-FGM viscoelastic nanoplates corresponding to various values of the nonlocal parameter, temperature change, power law index, aspect ratio and transverse and shear stiffness coefficients of the Pasternak elastic foundation. Moreover, influence of higher order modes, viscoelastic structural damping and damping coefficient of the viscoelastic medium on vibration characteristics are investigated. Numerical results show that natural frequency is greatly influenced by surface elastic modulus and residual surface stress.     

覆冰不平衡张力计算分析

为计算输电线路不均匀覆冰后所产生的不平衡张力,并分析各种线路参数对其产生的影响以便为覆冰设计提供指导。根据耐张段内串偏移量及档距变化量建立非线性方程组,采用牛顿法求解输电线路不均匀覆冰所产生的不平衡张力并分析了线路各种参数对其产生的影响。大量计算表明:增大导地线安全系数能增大不平衡张力;增加悬垂串串长和减小高差能有效减小覆冰时的不平衡张力;档距分布不均将有利于减小不均匀覆冰时的不平衡张力;适当增加耐张段内的档距数,覆冰不平衡张力将得到明显改善。     

Vibration Control of a Viscoelastic Translational Euler-Bernoulli Beam

In this paper, we consider a viscoelastic Euler-Bernoulli beam fixed to a base in a translational motion at one end and to a tip mass at its free end. Under a suitable control force applied at the base, we prove an arbitrary decay of the energy of the system. This is established for a large class of relaxation functions.     

Computer simulation of shading effects in photovoltaic arrays

A simulation of shading effects in arrays with different string configurations has been done. Simulation has been performed using as the basic unit the solar cell, modelled in direct bias by the conventional one exponential model, and in reverse bias by an equation previously validated in different types of photovoltaic cells reverse characteristics. The influence of the amount of shading, the type of reverse characteristic of the cell, the string length and the number of shaded cells has been analysed, and some recommendations are extracted.     

A POD-Galerkin reduced-order model for isotropic viscoelastic turbulent flow

In this article, a proper orthogonal decomposition (POD) reduced-order model for isotropic turbulent flow of viscoelastic fluid is established for the first time. Particularly, since the present studies about viscoleastic fluid are mainly for revealing the mechanism of turbulence, we try to establish the reduced-order model for momentum equations and constitutive equations, finally get both velocities and deformation rates calculated. Through decomposing the sampling matrices which are obtained by direct numerical simulation (DNS) using finite volume method (FVM), the velocity basis functions and deformation rate basis functions are generated respectively. According to the Galerkin projection method, the equations for velocity spectrum coefficients and deformation rate spectrum coefficients are deducted, which are coupled pluralistic nonlinear equations and solved iteratively by the Newton–Raphson method. To illustrate the performance of the proposed model for the viscoelastic fluid flow, a two-dimensional decaying isotropic turbulence testing case is designed in Example 1. It is found that the established reduced-order model obtains good accuracy when the decaying flow is at its early stage, but the errors get considerable when the flow steps into transition flow. In addition, a three-dimensional forced isotropic viscoelastic turbulence testing case is designed in Example 2. It is indicated that the errors of viscoelastic forced isotropic turbulent flow are acceptable. Finally, the calculation speed of the established reduced-order model is found to be much faster than that of DNS.     

Stability of Viscoelastic Fluid Flowing Through Porous Medium Down Non‐uniformly Heated Inclined Plane

The stability of a thin layer of viscoelastic fluid flowing through a porous medium down a non‐uniformly heated inclined plane with a constant temperature gradient along the plane is considered. The film flow system is influenced by gravity, mean surface tension, thermocapillary forces, viscoelastic forces, porosity, and permeability of porous medium. We seek a solution of the stability problem in a series in small wave numbers, and the obtained results, when the plane is heated in the downstream direction, show that the Marangoni, Galileo, and Biot numbers, porosity, and permeability of the porous medium have dual roles in the stability of the flow system, while the viscoelastic parameter and angle of inclination have stabilizing effects, and the Prandtl number has a destabilizing effect. The effects of these physical parameters are also discussed in the case when the plane is cooled in the downstream direction, and we found that their effects are opposite to those of the previous case. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21105     

Enhanced heat transfer using oscillatory flows in solar collectors

In this work, we propose the use of oscillatory laminar flows to enhance the transfer of heat from solar collectors. The idea is to explore the possibility of transferring the heat collected from a solar device to a storage tank by means of a zero-mean oscillating fluid contained in a tube. This method takes advantage of the fact that the effective thermal diffusivity of a fluid in oscillatory motion is several orders of magnitude higher than the fluid molecular diffusivity. Therefore, the axial transport of heat along the tube is substantially higher when the fluid oscillates than when the fluid is static. Also, preliminary estimations show a dramatic heat transfer enhancement using oscillatory flows compared with the forced convection of heat by standard unidirectional flows. We explore the behavior of the effective thermal diffusivity using both Newtonian and viscoelastic fluids. For the Newtonian fluid a single maximum value of this quantity is exhibited for a given oscillation frequency. In contrast, several maxima for different resonant frequencies are observed for the viscoelastic fluid. Further, the absolute maximum of the enhanced thermal diffusivity for the viscoelastic fluid is several orders of magnitude larger than that of the Newtonian fluid.     

220 kV输电线路耐雷水平仿真研究

针对用规程法计算输电线路耐雷水平偏于保守的问题,借助电磁暂态分析程序ATP EMTP对一个实际的输电线路进行建模,将仿真计算结果与规程法计算结果进行比较,并分析两个不同的绝缘子串模型和雷击塔顶两个不同的避雷线支架对反击耐雷水平的影响。结果表明,ATP EMTP法计算耐雷水平比规程法更具合理性,有利于节省防雷造价,雷击塔顶OPGW光缆侧的反击耐雷水平比普通铝包钢绞线侧大,采用IEEE绝缘子串模型得到的反击耐雷水平要比采用武汉高压研究所绝缘子串模型小。     

水平井机械隔离上提分段压裂工艺研究与应用

低渗透油田水平井开发是一项复杂而又有实际价值的工程技术。吉林油田4.6×108t探明未动用储量中,低渗透油藏超过90%,但产量普遍较低。为改变低渗透油藏"多井低产"的局面,开展低渗透油藏水平井开发试验。针对目前国内外低渗透油田水平井压裂改造工艺复杂、工艺可靠性差的现状,在环空分压和桥塞压裂工艺基础上,对工具和管柱结构进行改进,提出一种利用油管对水平井进行一趟管柱、双封单卡压裂施工多段的水平井上提分段压裂工艺及配套技术,同时,通过地面模拟试验,对研制的上提压裂管柱的水平状态冲砂性能和工具配件性能进行验证。经现场试验及应用,该管柱性能可靠,满足水平井分段压裂要求。水平井压裂工具,由其组成的工艺管柱入井工具少,性能稳定,全过程防卡控制,使施工更加安全可靠,是一种先进的水平井分段改造工艺技术。     

The vibration characteristics of drillstring with positive displacement motor in compound drilling Part1: Dynamical modelling and monitoring validation

The storage of hydrogen energy is one of the key difficulties in the efficient use of hydrogen. The most important thing for different storage methods is to establish the aisles of the hydrogen to storage space, and efficiently drill a few high-quality well holes. Compound drilling is one of the alternative technologies. However, the bit-rock interaction and the drill string-borehole interaction make the movement of bottom hold assembly more complex and increase the difficulty of well trajectory control. The vibration characteristics of drill string during compound drilling are not clear. The numerical simulation model of drill string with positive displacement motor is established by considering the bit-rock interaction, the rock failure behavior, the drill string-borehole interaction and the drill string structural. The mechanical parameters of shale for the numerical model are measured by wave velocities method. The simulation model is verified by the measuring and motoring data of axial force in the field. The rock element damage failure rate of compound drilling is greater than conventional drilling. The axial force and torque of bit of drill string in compound drilling is greater than that in the conventional drilling. The drill string is in contact with the wellbore in a more complicated way during compound drilling. The research results are benefit for optimal design of borehole quality.     

Electrohydrodynamic capillary instability of Rivlin–Ericksen viscoelastic fluid film with mass and heat transfer

This paper presents an analysis of viscous fluids and a Rivlin–Ericksen (R-E) viscoelastic fluid interface under the influence of heat and mass transfer, while both fluids are exposed to an axial electric field. The fluids are restricted within an annular region that is enclosed by two rigid cylinders. The outer section of the annular region holds the R-E viscoelastic fluid, while the inner section is filled with the viscous fluid. To ascertain the correlation between perturbation growth and wavenumber, the theory of potential flow on viscoelastic–viscous fluids is applied, and the result is represented as a second-order polynomial. This correlation is numerically solved using the Newton–Raphson method. Variables of viscous flow, such as electric field strength, heat transfer coefficient, viscoelasticity, viscosity, and so forth, are numerically studied. With an increase in electric field strength, the perturbation growth decays and expands for the particular combinations of permittivity and conductivity ratio, showing the dual effect of the axial electric field.     

钻头-钻柱系统振动特性分析

针对钻柱振动引起的钻具失效问题,综合考虑钻柱弹性变形及钻柱与井筒的碰撞摩擦相互作用,研究了钻头与下部钻柱的振动特性。根据哈密顿原理和有限单元法,建立了全井钻柱纵、横、扭耦合振动动力学模型;将钻头、钻柱、井筒视为一个完整的系统,以川渝地区某中深井实钻操作参数、下部钻具组合(BHA)和井筒参数作为基本输入数据,采用非线性仿真技术,研究了不同井段钻柱以及钻头的振动规律,分析了钻头处的动态钻压、扭矩及转速波动情况。结果表明,钻头处振动剧烈,跳动幅度较大,因此有必要研究振动控制工具和方法,以减少振动对钻头的伤害,改善钻头的工作环境并提高钻进效率。形成的钻头-钻柱-井筒系统非线性仿真技术,为下部钻具组合优化、钻井操作参数优选、钻具失效预防乃至钻头优化设计,提供了可行的分析手段,为研究振动控制策略提供了基础技术支持。     

STRESS FIELD GENERATED IN A VISCOELASTIC AEOLOTROPIC CONTINUUM BY A DISTRIBUTED HEAT SOURCE

The induced temperature, displacement, and stress fields in an infinite nonhomoge neous viscoelastic aeolotropic solid having a spherical cavity are obtained. The medium considered is heated by a distributed heat source in such a way that the flux changes exponentially in the radial direction. The type of nonhomogeneity is such that the elastic constants and the coefficient of linear thermal expansion are proportional to the nth power of the radial distance. The viscoelastic nature of the material is characterized by a model where the elastic constants are replaced by appropriate differential operators. The problem is solved analytically employing the integral transform technique. Numeri cal values of the field quantities at different points of the medium at different instants of time are computed for an exemplary case.