深厚表土层冻结壁厚度计算方法研究

针对冻结法凿井工程面临的表土层厚度不断增加,而现有冻结壁的设计理论滞后于工程实践的问题,目前冻结壁的设计和计算多数是将冻结壁视为均质和各向同性的厚壁圆筒,基于弹性和弹塑性理论进行计算的结果已经不能适用于未来深厚表土层的冻结法凿井工程,文章综述了冻结壁厚度设计理论的研究现状和存在的问题,并提出了考虑冻结壁径向非均匀的粘弹性分层计算模型,考虑径向非均质条件,井帮的径向变形较均质冻结壁小25%～30%,可以充分发挥冻结壁的承载和变形性能,有效减小冻结壁的厚度,具有一定的的工程应用价值。     

剪切变形与转动惯量对层合金属厚壁短管振动模态的影响EI北大核心CSCD

对层合金属厚壁短管进行振动分析必须考虑非匀质、剪切变形和转动惯量效应。基于Timoshenko理论,推导了两端简支、两端固支、两端自由和悬臂四种边界条件下,层合金属厚壁短管弯曲振动的频率函数与模态振型函数的表达式。采用计算机代数系统MAPLE对四种边界条件下铜钢层合厚壁短管的固有频率进行求解,并绘制振型曲线。采用锤击实验法并结合有限元模态分析法,测得了铜钢层合厚壁短管在两端自由条件下弯曲振动的固有频率。理论解与实测值相比的最大误差为-4.56%,理论解与有限元解相比的最大误差为-0.76%。求解了剪切变形与转动惯量对铜钢层合厚壁短管固有频率的影响系数,并分析了该频率影响系数与管子的振型曲线随边界条件、阶序、层合管长径比、以及壁厚比等参数的变化规律。     

剪切变形与转动惯量对层合金属厚壁短管振动模态的影响

对层合金属厚壁短管进行振动分析必须考虑非匀质、剪切变形和转动惯量效应。基于Timoshenko理论,推导了两端简支、两端固支、两端自由和悬臂四种边界条件下,层合金属厚壁短管弯曲振动的频率函数与模态振型函数的表达式。采用计算机代数系统MAPLE对四种边界条件下铜钢层合厚壁短管的固有频率进行求解,并绘制振型曲线。采用锤击实验法并结合有限元模态分析法,测得了铜钢层合厚壁短管在两端自由条件下弯曲振动的固有频率。理论解与实测值相比的最大误差为-4.56%,理论解与有限元解相比的最大误差为-0.76%。求解了剪切变形与转动惯量对铜钢层合厚壁短管固有频率的影响系数,并分析了该频率影响系数与管子的振型曲线随边界条件、阶序、层合管长径比、以及壁厚比等参数的变化规律。     

单层厚壁圆筒弹性动应力的简化计算方法

厚壁圆筒在爆炸领域被广泛应用,经典厚壁圆筒弹性动应力公式计算十分复杂,不利于工程直接应用。为了得到有效的精度较高的单层厚壁圆筒弹性动应力的简化计算公式,从经典动应力公式出发,通过求取频率特征方程的特征值,再将其代入动应力公式中进行简化计算,结合对动应力公式的级数表达式的讨论,最后得到了简化的厚壁圆筒内壁和外壁处动应力计算公式。数值计算结果表明,在圆筒外直径和内直径之比K不超过2时,简化计算结果和精确解的相对误差不大于6%。     

正交各向异性厚壁圆筒扭转冲击的一种解法

本文利用特征函数的方法，得到了满足混合边界条件下正交各向异性厚壁圆筒在扭转冲击作用下的动态剪应力的解析表达式。在实例计算中，求解了正交各向异性厚壁圆筒在不同的扭转载荷作用下，两种厚壁结构的剪应力响应历程和分布规律。     

热冲击下带裂纹功能梯度厚壁圆筒的分析

针对功能梯度材料热冲击下的断裂问题,对功能梯度材料的材料参数分类进行加权处理,建立带裂纹功能梯度厚壁圆筒的模型;给出热量平衡方程与边界条件,建立相关问题的有限元分析格式;改进Calahan算法以适用于带状稀疏矩阵的一阶非齐次常微分方程组,完善温度场的求解过程,计算了裂纹尖端的温度应力强度因子,并且分析功能梯度材料组分构成对温度应力强度因子的影响。以上研究为带裂纹功能梯度厚壁圆筒的可靠性分析及结构优化设计提供了参考。     

双层组合厚壁圆筒弹脆塑性极限内压统一解

基于三剪统一强度准则和弹脆塑性软化模型,考虑材料的脆性软化和中间主应力效应,推导了双层组合厚壁圆筒弹脆塑性极限内压统一解,探讨了粘聚力、内摩擦角、半径比、强度理论参数和中间主应力系数的影响特性,克服了以往基于Tresca屈服准则、Mises屈服准则或双剪强度理论的理想弹塑性解的不足。研究结果表明:中间主应力、材料模型和脆性软化对厚壁圆筒的极限内压均有显著影响。该文所得统一解具有广泛的适用性和理论意义,不但可退化为现有公式,而且还能得到系列化的新解答,对组合厚壁圆筒的设计及工程应用有重要参考价值。     

深表土冻结壁变形规律

利用ANSYS软件建立数学模型,分析不同地压、不同冻结壁厚度、不同冻结壁平均温度、不同开挖段高与冻结壁变形之间的关系。通过研究发现,井帮位移随冻结壁平均温度的降低、冻结壁厚度的增大而减小,随施工段高增大、地层地压值的增大而增大,且地压值的变化对冻结壁的变形影响最为显著。据此提出了深表土冻结壁应按变形条件进行设计,且施工段高是影响冻结壁稳定性的极为重要的参数,在施工中应严格控制。研究提出当冻结壁厚度为10 m左右,平均温度达到-20℃时,采取降低冻结壁平均温度的方式比增加冻结壁厚度能更加有效地提高冻结壁的稳定性。研究成果对于指导深表土冻结工程设计与施工,实现矿井冻结工程安全、优质、高效、节能,具有重要的参考价值。     

Drucker-Prager弹塑性本构关系积分:考虑非关联流动与各向同性硬化

考虑非关联流动法则以及各向同性硬化条件,采用广义中点法(Generalized Midpoint Method,GMM)进行Drucker-Prager(DP)弹塑性本构关系数值积分,给出调整后最终应力的解析解.GMM 属于隐式算法,具有良好的计算精度与数值稳定性;最近点投影法(Closest Point Project Method,CPPM)是其特例,具有一阶精度并且无条件稳定.DP 塑性势函数的特殊性质导致上述GMM 解由初始应力状态与应变增量显式确定,无需迭代求解,因此计算效率大幅提高,同时避免了迭代过程的收敛性问题.数值算例证明:当加载偏离角度较大时,GMM(ξ=1/2)的计算精度高于CPPM,可适应更大的加载步长;而对于比例加载,任意GMM 等同于精确解,采用CPPM 可获得最高的计算效率.推导了满足DP 屈服准则厚壁圆筒的弹塑性理论解,对比验证算法精度.采用非关联流动各向同性线性硬化DP 材料模拟厚壁圆筒变形局部化效应.     

巴彦高勒风井冻结管断裂应急预案及处理新技术

在全深冻结井筒施工中,基岩段施工打锚杆或放炮掘进期间,由于冻结管偏斜等原因,极容易将冻结管打穿或炸裂,严重影响冻结工程的安全施工。尤其是地质条件复杂、井筒涌水量大的井筒,在井筒不具备抗水灾能力的条件下,需要延期冻结,通过巴彦高勒风井冻结管处理新技术实施,提高解决类似问题的能力,为冻结管穿过硐室施工具有借鉴意义。     

Characteristics of waves in a functionally graded cylinder

An analytical‐numerical method is presented for analysing characteristics of waves in a cylinder composed of functionally graded material (FGM). In this method, the FGM cylinder is divided into a number of annular elements with three‐nodal‐lines in the wall thickness. The elemental material properties are assumed to vary linearly in the thickness direction so as to better model the spatial variation of material properties of FGM. The Hamilton principle is used to develop the dispersion equations for the cylinder, and the frequency and the group velocity are established in terms of the Rayleigh quotient. The method is applied to analyse several FGM cylinders, and its efficiency is demonstrated. Numerical results demonstrate that the ratio of radius to thickness has a stronger influence on the frequency spectra in the circumferential wave than on that in the axial wave, that negative group velocity presents at a range of smaller wave numbers and that the range varies as the wave normal and the ratio of radius to thickness of FGM cylinders. Copyright © 2001 John Wiley & Sons, Ltd.     

Vibro-acoustic behavior of a hollow FGM cylinder excited by on-surface mechanical drives

The linear three-dimensional elasticity theory in conjunction with the powerful transfer matrix solution technique is employed to investigate the steady-state nonaxisymmetric sound radiation characteristics of an arbitrarily thick functionally graded hollow cylinder of infinite length subjected to arbitrary time-harmonic on-surface concentrated mechanical drives. A formal integral expression for the radiated pressure field in the frequency domain is obtained by utilizing the spatial Fourier transform along the shell axis and Fourier series expansion in the circumferential direction. The method of stationary phase is subsequently employed to evaluate the integral for an observation point in the far-field. The analytical results are illustrated with numerical examples in which water-submerged metal-ceramic FGM cylinders are driven by harmonic concentrated radial/transverse surface forces and circumferential moment. The far-field radiated pressure amplitudes and directivities are calculated and compared with those of equivalent bi-laminate hollow cylinders with comparable volume fractions of constituent materials. The effects of FGM material profile, cylinder thickness, excitation frequency and type on the radiated far-field are examined. Limiting cases are considered and the validity of results is established by comparison with the data in the existing literature as well as with the aid of a commercial finite element package.     

Analysis of apparent fracture toughness of a thick-walled FGM cylinder with two diametrically opposed edge cracks

This study focuses on the analysis of apparent fracture toughness of a thick-walled functionally graded material (FGM) cylinder with two diametrically opposed edge cracks emanating from the inner surface of the cylinder. The crack surfaces and the inner surface of the cylinder are subjected to an internal pressure. The incompatible eigenstrain developed in the cylinder due to non-uniform coefficient of thermal expansion after cooling from sintering temperature is taken into account. Based on a generalized method of evaluating stress-intensity factor developed in our previous study, an approach is presented to evaluate apparent fracture toughness. To demonstrate the approach, some numerical results of apparent fracture toughness are presented for a TiC/Al₂O₃ FGM cylinder. The effects of material distribution, cylinder wall thickness, application temperature and number of cracks on apparent fracture toughness are investigated in details. It is found that all these factors play an important role in controlling apparent fracture toughness of a thick-walled FGM cylinder.     

Inverse problem of material distribution for desired fracture characteristics in a thick-walled functionally graded material cylinder with two diametrically-opposed edge cracks

This study concerns the inverse problem of evaluating the optimum material distribution for desired fracture characteristics in a thick-walled functionally graded material (FGM) cylinder containing two diametrically-opposed edge cracks emanating from the inner surface of the cylinder. The thermal eigenstrain developed in the cylinder material due to nonuniform coefficient of thermal expansion as a result of cooling from sintering temperature is taken into account. Based on a generalized method of evaluating stress intensity factors developed in a previous study, an inverse method is developed to optimize material distribution intending to realize prescribed apparent fracture toughness in the FGM cylinder. To present some numerical results, a TiC/Al₂O₃ FGM cylinder is considered and the inverse problems are solved to evaluate material distributions for two examples of prescribed apparent fracture toughness. The effect of cylinder wall thickness on the material distribution and comparison of material distributions corresponding to a single and two cracks are also discussed. The numerical results reveal that the apparent fracture toughness of FGM cylinders can be controlled by choosing the material distributions properly.     

Stress intensity factors of two diametrically opposed edge cracks in a thick-walled functionally graded material cylinder

A method is developed to evaluate stress intensity factors for two diametrically-opposed edge cracks emanating from the inner surface of a thick-walled functionally graded material (FGM) cylinder. The crack and the cylinder inner surfaces are subjected to an internal pressure. The thermal eigenstrain induced in the cylinder material due to nonuniform coefficient of thermal expansion after cooling from the sintering temperature is taken into account. First, the FGM cylinder is homogenized by simulating its nonhomogeneous material properties by an equivalent eigenstrain, whereby the problem is reduced to the solution of a cracked homogenized cylinder with an induced thermal and an equivalent eigenstrains and under an internal pressure. Then, representing the cracks by a continuous distribution of edge dislocations and using their complex potential functions, generalized formulations are developed to calculate stress intensity factors for the cracks in the homogenized cylinder. The stress intensity factors calculated for the cracks in homogenized cylinder represents the stress intensity factors for the same cracks in the FGM cylinder. The application of the formulations are demonstrated for a thick-walled TiC/Al₂O₃ FGM cylinder and some numerical results of stress intensity factors are presented for different profiles of material distribution in the FGM cylinder.     

立井冻土爆破技术的研究

建立了冻土爆破冻结管震动破坏准则,进行了冻土爆破性的分析,根据冻土掏槽参数和光面爆破参数的模型试验进行冻土爆破参数的设计,并结合冻土爆破实际,提出了冻土爆破前的准备工作,如详细分析爆破作业区内冻结管的偏斜情况,计算每根冻结管距井帮的最短距离,根据井筒断面及冻结土层的特性,选择钻眼设备等。经过实践,既保证施工安全,又提高了效率。     

Development of freezing–thawing processes of foundation soils surrounding the China–Russia Crude Oil Pipeline in the permafrost areas under a warming climate

The proposed China–Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing–thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas, and the variations in the maximum freezing depths under the pipeline in taliks and thawing depths in different permafrost regions near Mo'he station, the first pumping station in China, were studied in detail using numerical methods in this paper. The inlet oil temperature at Mo'he station was assumed to vary from 10 to − 6 °C in a sine wave form during the preliminary design phase. Research results showed that the freezing–thawing processes of soils surrounding the buried pipeline had distinct differences from those in the undisturbed ground profile in permafrost areas. In summer, there was downward thawing from the ground surface and upward and downward thawing from the pipeline's surface once the temperature of the oil rose above 0 °C. In winter, downward freezing began from the ground surface but upward and downward cooling of the cylinder around the pipeline didn't begin until the temperature of the oil dropped below 0 °C. However, in the undisturbed ground profile, downward thawing from the ground surface occurred in summer and downward freezing from the ground surface and upward freezing from the permafrost table occurred in winter. The maximum thawing depths and thawed cylinder around the pipeline in warm permafrost enlarged with elapsing time and decreasing water content of the soils. In taliks, the maximum freezing depths and frozen cylinder around the pipeline kept shrinking with elapsing time and increasing water content of the soils. The freezing–thawing processes and development of the thawed and frozen cylinders around the pipeline were muted by any insulation layer surrounding the pipeline. Insulation had better thermal moderating on the heat exchange between the pipeline and the surrounding soils during the early operating period. But its role slowly weakened after a long-term operating. Research results will provide the basis for assessment and forecasting of engineering geological conditions, analysis of mechanical stability of the pipeline, foundation design, and pipeline construction and maintenance.     

Development of freezing-thawing processes of foundation soils surrounding the China-Russia Crude Oil Pipeline in the permafrost areas under a warming climate

The proposed China-Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing-thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas, and the variations in the maximum freezing depths under the pipeline in taliks and thawing depths in different permafrost regions near Mo'he station, the first pumping station in China, were studied in detail using numerical methods in this paper. The inlet oil temperature at Mo'he station was assumed to vary from 10 to − 6 °C in a sine wave form during the preliminary design phase. Research results showed that the freezing-thawing processes of soils surrounding the buried pipeline had distinct differences from those in the undisturbed ground profile in permafrost areas. In summer, there was downward thawing from the ground surface and upward and downward thawing from the pipeline's surface once the temperature of the oil rose above 0 °C. In winter, downward freezing began from the ground surface but upward and downward cooling of the cylinder around the pipeline didn't begin until the temperature of the oil dropped below 0 °C. However, in the undisturbed ground profile, downward thawing from the ground surface occurred in summer and downward freezing from the ground surface and upward freezing from the permafrost table occurred in winter. The maximum thawing depths and thawed cylinder around the pipeline in warm permafrost enlarged with elapsing time and decreasing water content of the soils. In taliks, the maximum freezing depths and frozen cylinder around the pipeline kept shrinking with elapsing time and increasing water content of the soils. The freezing-thawing processes and development of the thawed and frozen cylinders around the pipeline were muted by any insulation layer surrounding the pipeline. Insulation had better thermal moderating on the heat exchange between the pipeline and the surrounding soils during the early operating period. But its role slowly weakened after a long-term operating. Research results will provide the basis for assessment and forecasting of engineering geological conditions, analysis of mechanical stability of the pipeline, foundation design, and pipeline construction and maintenance.