Deformation and Stress Analysis of the Deepwater Steel Lazy Wave Riser Subjected to Internal Solitary Waves

The dynamic response of the steel lazy wave riser(SLWR)subjected to the internal solitary wave is a key to assessing its application feasibility.The innovation of this paper is to study the dynamic response properties of the SLWR with large deformation characteristics under internal wave excitation.A numerical scheme of the SLWR is constructed using the slender-rod theory,and the internal solitary wave(ISW)with a two-layer seawater model is simulated by the extended Korteweg-deVries equation.The finite element method combined with the Newmark-βmethod is applied to discretize the equations and update the time integration.The ISW excitation combined with vessel motion on the dynamic deformation and stress of the SLWR is investigated,and extensive simulations of the ISW parameters,including the interface depth ratio and density difference,are carried out.Case calculation reveals that the displacement of the riser in the lower interface layer increases significantly under the ISW excitation,and the stresses at a part of both ends grow evidently.Moreover,the mean value of riser responses under a combination of vessel motion and ISW coincides with the ISW-induced ones.Furthermore,the dynamic responses along the whole riser,including the displacement amplitudes,bending moment amplitudes,and stress amplitudes,almost increase with the increase in interface depth ratios and density differences.

Vertical variations of wave-induced radiation stress tensor

The distributions of the wave-induced radiation stress tensor over depth are studied by us- ing the linear wave theory, which are divided into three regions, i. e., above the mean water level, be- low the wave trough level, and between these two levels. The computational expressions of the wave-in- duced radiation stress tensor at the arbitrary wave angle are established by means of the Eulerian coordi- nate transformation, and the asymptotic forms for deep and shallow water are also presented. The verti- cal variations of a 30°incident wave-induced radiation stress tensor in deep water, intermediate water and shallow water are calculated respectively. The following conclusions are obtained from computations. The wave-induced radiation stress tensor below the wave trough level is induced by the water wave parti- cle velocities only, whereas both the water wave particle velocities and the wave pressure contribute to the tensor above the wave trough level. The vertical variations of the wave-induced radiation stress ten- sor are influenced substantially by the velocity component in the direction of wave propagation. The dis- tributions of the wave-induced radiation stress tensor over depth are nonuiniform and the proportion of the tensor below the wave trough level becomes considerable in the shallow water. From the water surface to the seabed, the reversed variations occur for the predominant tensor components.

Study on pile drivability with one dimensional wave propagation theory

Pile drivability is a key problem during the stage of design and construction installation of pile foundations. The solution to the one dimensional wave equation was used to determine the impact force at the top of a concrete pile for a given ram mass, cushion stiffness, and pile impedance. The kinematic equation of pile toe was established and solved based on wave equation theory. The movements of the pile top and pile toe were presented, which clearly showed the dynamic displacement, including rebound and penetration of pile top and toe. A parametric study was made with a full range of practical values of ram weight, cushion stiffness, dropheight, and pile impedance. Suggestions for optimizing the parameters were also presented. Comparisons between the results obtained by the present solution and in-situ measurements indicated the reliability and validity of the method.

The Mathematical Modelling for Studying the Influence of the Initial Stresses and Relaxation Times on Reflection and Refraction Waves in Piezothermoelastic Half-Space

The present paper concentrates on the study of reflection and refraction phenomena of waves in pyroelectric and piezo-electric media under initial stresses and two relaxation times influence by apply suitable conditions. The generalized theories of linear piezo-thermoelasticity have been employed to investigate the problem. In two-dimensional model of transversely isotropic piezothermoelastic medium, there are four types of plane waves quasi-longitudinal (qP), quasi-transverse (qSV), thermal wave (T-mode), and potential electric waves (φ-mode) The amplitude ratios of reflection and refraction waves have been obtained. Finally, the results in each case are presented graphically.

Stress Waves in Polymeric Fluids

This paper demonstrates the existence, propagation, transmission, reflection, and interaction of deviatoric stress waves in polymeric fluids for which the mathematical models are derived using conservation and balance laws (CBL) of Classical Continuum Mechanics (CCM) and the constitutive theories are based on the entropy inequality and representation theorem. The physical mechanisms of deformation in polymeric liquids that enable the stress wave physics are identified and are demonstrated to be valid using Maxwell, Oldroyd-B, and Giesekus polymeric fluids, and are illustrated using model problem studies. We assume polymeric fluids to be isotropic and homogeneous at the macro scale so that the CBL of the CCM can be used to derive their mathematical models. For simplicity, we assume the polymeric fluids to be incompressible in the present work.

动静载作用下充填节理砂岩应力波传播特性研究

为研究节理角度和不同围压作用下的充填节理岩石的动态力学特性和应力波传播规律,利用改造后的动静组合加载霍普金森压杆(split Hopkinson pressure bar, SHPB)装置,对充填节理厚度为8 mm的砂岩试样进行冲击试验,研究不同围压等级(0、4、6和8 MPa)和不同节理倾角(0°、15°、30°、45°)下充填节理试样的动态力学特性和应力波传播的规律,采用应力波斜射理论并进行验证。试验结果表明:(1)完整砂岩的反射波幅值最小,以0 MPa为例,反射波幅值从0.194×10^(-3)增长到0.299×10^(-3),与倾角成正相关,透射波幅值与倾角成负相关,且从0.169×10^(-3)减小到0.053×10^(-3);以0°为例,反射波幅值与围压呈负相关,且从0.194×10^(-3)减小到0.074×10^(-3),透射波幅值相反从0.169×10^(-3)增长到0.257×10^(-3);(2)在冲击动载作用下,一定程度围压可以起到限制变形,抑制胶结面分离,提高承载能力;节理倾角越大的充填节理产生的变形越大,承载状态越差;(3)倾角试件随着围压增大反射能力降低,透射能力提高,0°倾角试件的反射系数从0.603减小到0.147,透射系数从0.569均匀增加到0.789,围压试件随着倾角的增大反射能力增大,透射能力降低与理论分析规律一致;(4)节理倾角与试样吸收能密度呈负相关,围压与试样吸收能密度呈正相关,与围压作用下的透反射规律一致。

The nonlocal solution of two parallel cracks in functionally graded materials subjected to harmonic anti-plane shear waves

In this paper, the dynamic interaction of two parallel cracks in functionally graded materials （FGMs） is investigated by means of the non-local theory. To make the analysis tractable, the shear modulus and the material density are assumed to vary exponentially with the coordinate vertical to the crack. To reduce mathematical difficulties, a one-dimensional non-local kernel is used instead of a twodimensional one for the dynamic problem to obtain stress fields near the crack tips. By use of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations, in which the unknown variables are the jumps of displacements across the crack surfaces. To solve the dual integral equations, the jumps of displacements across the crack surfaces are expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularity is present at the crack tips. The non-local elastic solutions yield a finite hoop stress at the crack tips. The present result provides theoretical references helpful for evaluating relevant strength and preventing material failure of FGMs with initial cracks. The magnitude of the finite stress field depends on relevant parameters, such as the crack length, the distance between two parallel cracks, the parameter describing the FGMs, the frequency of the incident waves and the lattice parameter of materials.

Nonlinear Model of Mean Free Surface of Waves

A nonlinear model of mean free surface of waves or wave set-up is presented. The model is based on that of Roelvink (1993), but the numerical techniques used in the solution are based on the Weighted-Average Flux (WAF) method (Watson el al., 1992), with Time-Operator-Splitting (TOS) used for the treatment of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modeling wave set-up. The short wave (or primary wave) energy equation is solved by use of a more traditional Lax-Wendroff technique. A nonlinear wave theory (James, 1974) is introduced. The model described in this paper is found to be satisfactory in most respects when compared with the measurements conducted by Stive (1983) except in modeling the mean free surface very close to the mean shoreline.

Improvements on Mean Free Wave Surface Modeling

Some new results of the modeling of mean free surface of waves or wave set-up are presented. The stream function wave theory is applied to incident short waves. The limiting wave steepness is adopted as the wave breaker index in the calculation of wave breaking dissipation. The model is based on Roelvink (1993), but the numerical techniques used in the solution are based on the Weighted-Average Flux (WAF) method (Watson et al., 1992), with Time-Operator-Splitting (TOS) used for the treatment of the source terms. This method allows a small number of computational points to be used, and is particularly efficient in modeling wave set-up. The short wave (or incident primary wave) energy equation is solved by use of a traditional Lax-Wendroff technique. The present model is found to be satisfactory compared with the measurements conducted by Stive (1983).

Nonlinear Waves in Solid Continua with Finite Deformation

This work considers initiation of nonlinear waves, their propagation, reflection, and their interactions in thermoelastic solids and thermoviscoelastic solids with and without memory. The conservation and balance laws constituting the mathematical models as well as the constitutive theories are derived for finite deformation and finite strain using second Piola-Kirchoff stress tensor and Green’s strain tensor and their material derivatives [1]. Fourier heat conduction law with constant conductivity is used as the constitutive theory for heat vector. Numerical studies are performed using space-time variationally consistent finite element formulations derived using space-time residual functionals and the non-linear equations resulting from the first variation of the residual functional are solved using Newton’s Linear Method with line search. Space-time local approximations are considered in higher order scalar product spaces that permit desired order of global differentiability in space and time. Computed results for non-linear wave propagation, reflection, and interaction are compared with linear wave propagation to demonstrate significant differences between the two, the importance of the nonlinear wave propagation over linear wave propagation as well as to illustrate the meritorious features of the mathematical models and the space-time variationally consistent space-time finite element process with time marching in obtaining the numerical solutions of the evolutions.

近接隧道开挖卸荷与爆破振动的叠加效应研究

为研究近接新建隧道开挖卸荷和爆破应力波振动的叠加作用对既有隧道结构的影响,结合现场试验和数值模拟手段,研究0.05 B~1.0 B先行隧道衬砌的力学响应、围岩塑性区分布,并分析后行隧道开挖不同应力释比的影响。研究结果表明:受爆破P波作用,衬砌拉应力峰值与振速峰值呈线性正比关系;围岩级别差、净距较小时,开挖卸荷与爆破振动作用叠加,衬砌拉应力大于弹性波动理论计算值;应力释放率的增加会加剧爆破应力波的动力作用;基于上述分析,提出Ⅳ、Ⅴ级围岩下2种作用的叠加影响区范围,针对小于0.25 B的近接隧道施工,应加强支护措施以防护叠加作用对隧道结构安全的影响。

平面P波入射软弱结构面传播特征研究

软弱结构面在动载作用下易发生失稳破坏,影响工程与场地安全。基于软弱结构面理论模型,采用应力波理论,分别考虑粘结与滑移边界条件,推导了P波入射软弱结构面的透反射系数表达式,并采用数值方法对理论结果进行对比验证。讨论了P波入射角、频率等因素对应力波传播的影响。研究结果表明:粘结与滑移边界应力波透反射特性相近,但滑移状态下应力波存在能量损耗;软弱结构面存在高频滤波特性,需要关注低频时结构面的稳定性;软弱结构面等效摩擦角越大越难发生剪切变形;波阻抗比对应力波透反射系数的影响存在一个阈值,超过这个阈值则透射系数保持恒定;应力波透反射系数随着充填材料厚度增大呈现周期波动变化,该周期可能与入射P波波长相关。研究结论有助于在岩土工程中确定潜在滑移软弱结构面,为抗震加固、岩土爆破工程等提供理论依据。

Stress dependence of elastic wave dispersion and attenuation in fluid-saturated porous layered media

The fluid-saturated porous layered(FSPL)media widely exist in the Earth's subsurface and their overall mechanical properties,microscopic pore structure and wave propagation characteristics are highly relevant to the in-situ stress.However,the effect of in-situ stress on wave propagation in FSPL media cannot be well explained with the existing theories.To fill this gap,we propose the dynamic equations for FSPL media under the effect of in-situ stress based on the theories of poroacoustoelasticity and anisotropic elasticity.Biot loss mechanism is considered to account for the stress-dependent wave dispersion and attenuation induced by global wave-induced fluid flow.Thomsen's elastic anisotropy parameters are used to represent the anisotropy of the skeleton.A plane-wave analysis is implemented on dynamic equations yields the analytic solutions for fast and slow P waves and two S waves.Modelling results show that the elastic anisotropy parameters significantly determine the stress dependence of wave velocities.Vertical tortuosity and permeability have remarkable effects on fast and slow P-wave velocity curves and the corresponding attenuation peaks but have little effect on S-wave velocity.The difference in velocities of two S waves occurs when the FSPL medium is subjected to horizontal uniaxial stress,and the S wave along the stress direction has a larger velocity,which implies that the additional anisotropy other than that induced by the beddings appears due to horizontal stress.Besides,the predicted velocity results have the reasonable agreement with laboratory measurements.Our equations and results are relevant to a better understanding of wave propagation in deep strata,which provide some new theoretical insights in the rock physics,hydrocarbon exploration and stress detection in deep-strata shale reservoirs.

Influence of the Radial Inertia Effect on the Propagation Law of Stress Waves in Thin-Walled Tubes

This investigation focused on the influence of the radial inertia effect on the propagation behavior of stress waves in thin-walled tubes subjected to combined longitudinal and torsional impact loads.Generalized characteristics theory was used to analyze the main features of the characteristic wave speeds and simple wave solutions in thin-walled tubes.The incremental elastic-plastic constitutive relations described by the rate-independent plasticity were adopted,and the finite difference method was used to investigate the evolution and propagation behaviors of combined elasticplastic stress waves in thin-walled tubes when the radial inertial effect was considered.The numerical results were compared with those obtained when the radial inertia effect was not considered.The results showed that the speed of the coupled stress wave increased when the radial inertia effect was considered.The hardening modulus of the material in the plastic stage had a greater impact on the coupled slow waves than on the coupled fast waves.

基于行为转变理论的健康指导结合正念音乐干预对体外冲击波碎石术患者恐惧情绪、心理弹性及应激反应的影响

目的探讨基于行为转变理论的健康指导结合正念音乐干预对体外冲击波碎石术患者恐惧情绪、心理弹性及应激反应的影响。方法选取2019年1月至2021年1月我院收治的90例行体外冲击波碎石术治疗的患者为研究对象,根据入院顺序将其分为对照组和观察组,各45例。对照组实施常规护理,观察组在对照组基础上应用基于行为转变理论的健康指导结合正念音乐干预。比较两组的干预效果。结果干预后,观察组的生理健康、社会家庭评分低于对照组(P<0.05)。干预后,观察组的坚韧、自强、乐观评分高于对照组(P<0.05)。干预后,观察组的皮质醇(Cor)及促血管生成素-Ⅱ(Ang-Ⅱ)水平低于对照组(P<0.05)。结论基于行为转变理论的健康指导结合正念音乐干预有助于改善体外冲击波碎石术患者恐惧情绪,提升心理弹性,减轻应激反应,值得推广。

螺栓拉应力超声无损检测方法

本文依据声弹性原理中超声波传播速度与应力之间的对应关系,利用横波与纵波联合测量的办法,给出栓体长度未知的紧固螺栓轴向应力测量办法。针对螺栓在低载荷与高载荷不同情况下的栓体轴向应力测量系数不同的状况,分类进行了讨论,并给出对应载荷条件下应力测量系数的计算办法。文章讨论了A2-70奥氏体不锈钢与强度等级4.8低碳钢两种不从材质螺栓的轴向应力测量结果,实际测量与理论测量平均误差小于2.9367%,提高了横纵波轴向应力测量的精度。

预制桩可打性的分析

为进一步分析预制桩的可打性问题,在一维应力波传播理论的基础上,建立了锤-桩-土三者之间相互作用模型,获得了桩端的动位移和速度的解析解,研究了施工工艺参数、桩的设计参数以及地质条件等对冲击力、桩顶贯入度和桩顶回弹等的影响,分析表明,桩垫刚度、桩锤质量对桩的贯入影响非常大.经过对两个工程实例的对比分析表明,按照本文方法计算的贯入度、锤击数和实测贯入度、锤击数之间非常吻合.

水炮泥合理填塞长度的试验研究

分析了炮孔装药爆破时水炮泥的受力情况,利用爆破理论和应力波理论,对水炮泥填塞作用机理及其在孔内的运动规律进行了分析。基于水炮泥填塞的模型试验,通过对水炮泥合理填塞长度的选取进行试验研究,并对试验模型表面和底面裂纹扩展情况作统计分析,得出了合理的水炮泥填塞长度为7.0~8.5 cm,根据BCM模型,认为裂纹扩展至自由面的时间为合理的破岩时间,由此建立了合理的填塞长度计算公式,计算得出的合理填塞长度为7.75 cm。最后将实验值与理论计算值进行对比分析,试验值与理论计算值较吻合,证明了试验模型具有一定的合理性。

SHPB数据处理中的二波法与三波法

分析了传统的分离式霍普金森压杆测试数据处理方法(二波法)及其他被提出的改进方法的误差及优缺点,给出了传统二波处理方法在不同被测材料情况下所带来的误差。分析结果表明,基于绝对时间下的试件应力及应变计算的三波处理法具有最好的可信度且能最大程度地避免数据处理过程中的人为因素。传统二波法在不同测试情况下均不是优选的方法。对于三波测试无法进行的情况,也提出了一种简化三波处理方法。

基于赫兹接触的板中微裂纹非线性兰姆波检测方法研究

针对金属板结构中微裂纹检测问题,进行基于二次谐波的非线性兰姆波检测方法研究。基于赫兹接触理论,进行板中二次谐波非线性兰姆波理论研究,建立板中兰姆波二次谐波与微裂纹尺寸的关系模型。进行板中微裂纹非线性兰姆波数值仿真,研究不同长度和宽度的微裂纹对兰姆波二次谐波非线性效应的影响。结果表明,随着微裂纹长度增加,二次谐波幅值呈增加趋势;随着微裂纹宽度增加,二次谐波幅值呈减小趋势。在以上研究基础上,进行板中微裂纹非线性兰姆波检测试验研究。结果表明,通过测量结构的兰姆波二次谐波非线性系数,可用于结构中微裂纹检测与定量评价。研究工作为板中微裂纹定量检测做了有益探索。