共查询到20条相似文献,搜索用时 31 毫秒
1.
针对浅埋高压输气管道爆炸产生的地面振动效应,采用现场试验结合数值模拟的方法展开研究。组织实施了全尺寸天然气管道爆炸试验,掌握了高压输气管道爆炸地面振动的量级范围以及衰减规律。经试验数据分析得到,埋地高压天然气管道爆炸造成的地面振动主要产生于物理爆炸过程中,随后发生的天然气爆燃过程并未产生明显的地面振动。基于非线性有限元程序 LS-Dyna建立了高压输气管道爆炸试验计算模型,计算结果与试验现象吻合较好,验证了模型参数设计的合理性。进一步分析了管道爆炸瞬间管内气体-管壁-土体的相互作用机理、应力分布以及裂纹扩展规律。由计算结果分析得到,管道开裂是由于内部高压气体推动管壁向两侧扩展在裂纹尖端处形成了应力集中,管壁冲击土体的速度可达50 m/s,冲击产生的塑性状态向远处传播逐渐衰减为弹性应力波,即形成了地面振动效应。研究成果揭示了高压气体管道爆炸地面振动的主要成因,可为爆炸事故振动预防提供理论参考和技术支持。 相似文献
2.
《International Journal of Solids and Structures》2006,43(7-8):2378-2397
Accurate prediction of crack-driving force equations is important in any pipeline fracture assessment program. In highly ductile materials, such as pipeline steel, a considerable amount of stable crack growth can be tolerated before the failure of the structure. The existing methods use simplified analytical procedures to account for ductile tearing, and they often result in conservative critical crack sizes. Further, none of the published numerical tools for modelling crack growth is suitable for engineering applications. This work describes a simple method for simulating through-thickness ductile tearing in surface cracked pipes, using line-spring finite elements. The crack growth resistance curve is used to advance the crack front. The line-spring results are verified using crack growth simulations employing the Gurson damage model. Finally, a detailed parametric study is carried out to examine the effect of ductile tearing on crack driving force relationships in circumferentially surface cracked pipes. The results demonstrate that considering ductile tearing is important in fracture assessment procedures for pipelines. 相似文献
3.
基于典型城市燃气管道直埋地层特点,通过全尺寸直埋燃气管道爆破地震实验,并结合LS-DYNA动力有限元数值计算软件建立不同爆源距离的无接口和法兰接口的燃气管道模型,分析研究了爆破地震波作用下法兰接口燃气管道动力响应特征及其失效机制。研究结果表明:管道截面应变以轴向拉伸应变为主,环向应变为辅;不同爆破工况下,无接口管道和法兰接口管道及地表峰值振动速度随爆源距离减小而增大;沿管道轴线方向,无接口管道、地表峰值振动速度以管道中心截面为对称面沿两端不断减小,法兰接口管道峰值振速由两侧向中间逐渐增大,在法兰接口处突然减小;法兰接口处出现明显的应力集中现象;管道法兰接口处是爆破地震作用下研究的关键点,螺栓的峰值有效应力、垫片轴向压力、法兰峰值有效应力、法兰偏转角随爆源距离增大而减小;法兰管道偏转角与地表峰值振动速度具有对应关系,法兰接口燃气管道中心正上方地表的控制振速(13.82 cm/s)可作为邻近燃气管道爆破工程地表的安全控制值。 相似文献
4.
5.
承插式管道接口更易受到外界荷载破坏导致管道失效,为保证爆破开挖过程中邻近承插式高密度聚乙烯(high-density polyethylene,HDPE)波纹管道的安全运营,控制爆破振动荷载对管道的影响是重点关注内容。通过全尺度预埋单段HDPE波纹管道现场试验,得到管道的振动速度和动应变响应数据,结合LS-DYNA数值模拟软件分别建立了无承插接口管道与含弹性密封圈的承插式HDPE波纹管道;利用现场试验数据验证了无承插口管道模型参数的可靠性,并对比分析了承插式管道的结构位移、振动速度、有效应力的响应规律与失效机制;结合现行规范,根据管道响应规律与接口允许旋转角度计算得到了承插式管道的安全振动速度。研究结果表明:有承插口管道的合振速、合位移和有效应力大于无承插口管道;在同一截面上,有承插口管道迎爆侧的合振速和有效应力更大,而最大合位移出现在截面的背爆侧;管道合位移与合振速在轴线中心处截面最大,并向两端不断减小,有承插口管道中心合位移更大;通过接口允许旋转角度得到此类工况条件下的承插式管道的安全振速为24.77 cm/s。
相似文献6.
高韧性管道动态断裂的气体减压模式和材料韧性研究 总被引:5,自引:0,他引:5
天然气管道上动态裂纹扩展包含气体、结构和断裂的相互作用.因此,分析射流场分布特性及其与管壁开裂变形的相互作用是数值模拟过程的关键问题.随着钢管韧性等级的迅速提升和气体压力的不断提高,原有的经验公式乃至算法多数不再适用,亟需通过理论、试验和数值模拟给出新的扩展与止裂判据,以控制裂纹在管道上扩展的速度和距离.本文通过一系列的韧性试验校正了现行的管材韧性判定办法,并对不同工况下的裂纹动态扩展以及超声速射流场进行了数值仿真,以建立一套工程适用的评价体系。 相似文献
7.
The total energy release and the length of interfacial crack growth associated with an earthquake are analyzed based on a horizontal one-dimensional semi-infinite elastic model of fault of uniform rectangular cross section between two rigid rocks. Initial interfacial cracks of finite length are assumed to exist on the top and bottom surfaces of the fault. A compressive force is applied at the end of the fault and uniform frictional forces are exerted on the crack surfaces. When the compressive force reaches a critical value, fault slip against the surrounding rock occurs and the frictional force changes from a static value to a dynamic value within a short time interval. The change in frictional force generates longitudinal wave propagation in the fault. As a result, a large amount of energy release takes place. The total amount of energy release and the length of crack growth can be analyzed based on the balance of energy. 相似文献
8.
Analysis model to simulate the cracked pipe buried in soil 总被引:1,自引:0,他引:1
This paper describes the use of the finite element method to simulate crack propagation in a pipeline in the presence of soil
backfill. Since typical values for soil modulus are known, a spring element can be used to simulate the effects of backfilled
soil on crack propagation. This consists of the relationship between the soil property and the stiffness of the spring element,
and the effect of backfill depth on the crack propagation in the pipes. By equating crack driving force,G, in the presence of soil, to the dynamic fracture toughness of the pipeline material, a theoretical predictive capability
is obtained for the first time for the gas transmission and distribution pipelines. Numerical calculations have also been
carried out for the cracked pipe with backfill and without backfill. 相似文献
9.
10.
《International Journal of Solids and Structures》1999,36(7):1045-1079
An Element Free Galerkin (EFG) method based formulation for steady dynamic crack growth in elastic–plastic materials is developed. A domain convecting parallel to the steadily moving crack tip is employed. The EFG methodology eliminates the stringent mesh requirements of the Finite Element Method (FEM) for such problems. Both rate-independent materials and rate-dependent materials are considered. The material is characterized by von Mises yielding condition and an associated flow rule. For rate-independent materials, both the influence of crack speeds and that of strain hardening on the mechanics of steady dynamic crack growth are investigated. For rate-dependent materials, only a non-hardening material is considered with emphasis on determining the influence of viscous properties of materials and crack speeds. The influence of strain hardening on steady dynamic crack growth shows the same trends as for steady quasi-static crack growth. The simplifications used in the literature in deriving analytical solutions for high strain-rate crack growth have been examined thoroughly using the numerical results. 相似文献
11.
含偏置裂纹三点弯曲梁的动态断裂行为研究 总被引:15,自引:0,他引:15
采用动态焦散线方法,对含偏置裂纹三点弯曲梁承受横向冲击的弯曲断裂行为进行了一系列动态断裂力学实验研究,分析了无量纲量a/l的改变(a——初始裂纹偏离梁中心线的距离;l——梁长度的一半)对于裂纹动态扩展行为(裂纹起始状态、裂纹尖端的复合应力强度因子、裂纹扩展速度、裂纹扩展轨迹)的影响,并借助动态光弹性应力分析,对应力波与扩展裂纹的相互作用以及应力波传播规律进行探讨.给出了裂纹尖端复合应力强度因子、裂纹扩展速度的变化、裂纹曲裂轨迹以及方向与梁中应力波传播的相互关系 相似文献
12.
We investigate damage detection in a simply-supported pre-stressed beam. A crack was propagated by fatigue loads, which were
applied up to two million cycles. Both fast Fourier transform (FFT) and continuous wavelet transform (CWT) are used in the
analysis of the structural response to impulse loads. The acceleration response of the full-scale beam was measured each time
a certain number of cycles of fatigue loads were applied. The results of this study show that both methods can clearly identify
the crack growth induced by fatigue loads. The natural frequencies found by FFT are sensitive to the crack progression. The
results from the CWT analysis show a clear difference in structural responses between the initial and damaged states of the
structure. The response accelerations are de-noised by a soft-thresholding method before they are analyzed by CWT. In addition
to the frequency components, the CWT shows the moment in time when particular frequencies occur. Therefore, wavelet analysis
has the potential of becoming an effective tool for damage detection and health monitoring of structures for which the natural
frequencies are irregularly changing. As the crack grows, the magnitude of ridges obtained by CWT analysis decreases significantly,
which indicates the reduction in structural stiffness. 相似文献
13.
14.
动态压缩荷载作用下,脆性岩石内部动态细观裂纹扩展特性,对岩石宏观动态力学特性有着重要的影响。然而,对岩石内部动态细观裂纹扩展与宏观动态力学特性的关系研究较少。基于准静态裂纹扩展作用下的应力-应变本构模型、准静态与动态裂纹扩展断裂韧度关系、裂纹速率与应变率关系模型及应变率与动态断裂韧度关系,提出了一种基于细观力学的动态应力-应变本构模型。其中裂纹速率与应变率关系,是根据裂纹长度与应变关系的时间导数推出;应变率与动态断裂韧度关系,是根据推出的裂纹速率及应变率关系,与裂纹速率及断裂韧度关系相结合而得到。研究了应变率对应力-应变本构关系及动态压缩强度影响。并通过试验结果验证了模型的合理性。讨论了岩石初始损伤、围压、模型中参数m、ε0和R对应力-应变关系、动态压缩强度和动态弹性模量的影响。研究结果可为动态压缩荷载作用下深部地下工程脆性围岩稳定性分析提供了一定的理论支持。 相似文献
15.
N. Jacques S. Mercier A. Molinari 《Journal of the mechanics and physics of solids》2012,60(4):665-690
The aim of this paper is to investigate the role of microscale inertia in dynamic ductile crack growth. A constitutive model for porous solids that accounts for dynamic effects due to void growth is proposed. The model has been implemented in a finite element code and simulations of crack growth in a notched bar and in an edge cracked specimen have been performed. Results are compared to predictions obtained via the Gurson–Tvergaard–Needleman (GTN) model where micro-inertia effects are not accounted for. It is found that microscale inertia has a significant influence on the crack growth. In particular, it is shown that micro-inertia plays an important role during the strain localisation process by impeding void growth. Therefore, the resulting damage accumulation occurs in a more progressive manner. For this reason, simulations based on the proposed modelling exhibit much less mesh sensitivity than those based on the viscoplastic GTN model. Microscale inertia is also found to lead to lower crack speeds. Effects of micro-inertia on fracture toughness are evaluated. 相似文献
16.
《International Journal of Solids and Structures》2003,40(21):5819-5837
Mode I steady-state dynamic crack growth in rate-dependent viscoplastic solids containing damage, under small scale yielding conditions, is analyzed based on a modified cohesive zone model. A multi-scale approach is used to describe the entire non-linear zone consisting of a plastic region and a damage region, each of which has its own constitutive law. Traction in the damage region is characterized by a softening power-law, in terms of the ultimate strength, a softening index and a rate sensitivity factor. In the plastic region, the cohesive law is assumed to be both strain hardening and rate dependent. The critical crack opening displacement at the physical crack-tip controls crack growth. The governing integral equations are derived and solved by a collocation method combined with associated boundary conditions. Numerical results are presented for the traction and opening profiles along the cohesive zone, the fracture energy and lengths of the damage and non-linear zones at different crack speeds and for different material parameters. The importance of factors, such as material softening, plastic deformation, crack speed and viscosity, is identified by parametric studies. In addition, the competition of plastic flow and material damage, and its effect on crack growth, are discussed. 相似文献
17.
18.
《应用数学和力学(英文版)》2017,(2)
The dynamic behavior of a rectangular crack in a three-dimensional(3D)orthotropic elastic medium is investigated under a harmonic stress wave based on the non-local theory. The two-dimensional(2D) Fourier transform is applied, and the mixedboundary value problems are converted into three pairs of dual integral equations with the unknown variables being the displacement jumps across the crack surfaces. The effects of the geometric shape of the rectangular crack, the circular frequency of the incident waves,and the lattice parameter of the orthotropic elastic medium on the dynamic stress field near the crack edges are analyzed. The present solution exhibits no stress singularity at the rectangular crack edges, and the dynamic stress field near the rectangular crack edges is finite. 相似文献
19.
Effects of fractal crack 总被引:1,自引:0,他引:1
Experimental results indicate that propagation paths of cracks in geomaterials are often irregular, producing rough fracture surfaces which are fractal. In this paper, crack tip motion along a fractal crack trace is discussed. A fractal kinking model of the crack extension path is established to describe irregular crack growth. The length, velocity and kinking effects of the fractal crack are analysed. A formula is derived to describe the effects of fractal crack propagation on the dynamic stress intensity factor and on crack velocity. Finally, expressions of stress and displacement fields near the fractal crack tip are given. 相似文献
20.
研究了考虑腐蚀和海生物附着作用的海洋管道在海波激励下的动力学响应.采用欧拉-伯努利梁模型建立细长海洋管道动力学模型,利用格林函数法得到了该受迫振动问题的稳态响应.首先,推导了未腐蚀且考虑海生物附着的海洋管道在海波激励作用下的动力学响应.其次在考虑腐蚀、海生物附着情况下,利用前面未腐蚀模型的解得到腐蚀管道的动力学响应解析解.最后进行了数值讨论,分析了不同腐蚀深度、不同生物质量对管道固有频率的影响.研究了三种输流截面面积相同的环(圆、矩形、三角)模型在同一海波激励作用下的稳态位移响应.分析了不同海波高度、不同海波数目、不同海洋深度及腐蚀深度对管道模型位移的影响;对比了未腐蚀和有腐蚀深度时,某点随时间变化的位移效果.研究结果对海波激励下的管道响应分析和保护具有重要意义. 相似文献