Experimental Investigation of Irregular Wave Uplift Force on Deck of Exposed High-Pile Jetties

A laboratory setup was developed to investigate irregular wave uplift loads on exposed high-pile jetties. It is shown that the dimensionless uplift load increases to the maximum with an increasing relative clearance and then decreases. The relative clearance corresponding to the peak force is linked to a range from 0.4 to 0.8. When the relative clearance exceeds a certain value, the wave can not reach the underside of the deck and the force becomes zero. Distinct trends of dimensionless force with a relative width of deck show that the force tends to decrease as the relative deck width increases, and then the decrease slows down after the relative deck width increases or decreases to a certain value. The pressure distribution length associated with the maximum uplift force is equivalent to the wave contact width x. When x is larger than the width of deck B, it is taken as B. The statistical distribution of loads obeys the Weibull distribution. The results from the analyses of the real data suggest a new dimensionless prediction model on wave-in-deck uplift loads and the conversion ratio between wave loads at different exceedance probabilities. A comparison is made between the new prediction model and the existing widely used three prediction models. These results are used as useful references for structural design of the jetty.

A Method for the Damage Detection of Pile Foundation in High-Pile Wharf Based on A Curvature Mode Deletion Model

As the top of the pile foundation in high-pile wharf is connected to the superstructure and most of the pile bodies are located below the water surface, traditional damage detection methods are greatly limited in their application to pile foundation in service. In the present study, a new method for pile foundation damage detection is developed based on the curve shape of the curvature mode difference(CMD) before and after damage. In the method, the influence at each node on the overall CMD curve shape is analyzed through a data deletion model, statistical characteristic indexes are established to reflect the difference between damaged and undamaged units, and structural damage is accurately detected. The effectiveness and robustness of the method are verified by a finite element model(FEM) of high-pile wharf under different damage conditions and different intensities of Gaussian white noise. The applicability of the method is then experimentally validated by a physical model of high-pile wharf. Both the FEM and the experimental results show that the method is capable of detecting pile foundation damage in noisy curvature mode and has strong application potential.

The Research on Safety Evaluation of High-pile Wharf Structure

Due to a combination of the sea erosion,the ship collision,the change of ground condition,the effect of alternative static and dynamic load and the material deterioration,the structure of high-pile wharf is easily damaged.Once the structure of high-pile wharf destroyed,it is bound to be a great threat to the safety of various facilities and personnel in the port.Given all of that,the multi-level comprehensive evaluation method based on the extension theory is proposed in this paper.Using this method to assess the safety of high-pile wharf structure,the reasonable advice on its maintenance and reinforcement can be given in time.What’s more,the method is simple and can give more objective result of the evaluation.

Application of Converted Displacement for Modal Parameter Identification of Offshore Wind Turbines with High-Pile Foundation

In the actual measurement of offshore wind turbines(OWTs),the measured accelerations usually contain a large amount of noise due to the complex and harsh marine environment,which is not conducive to the identification of structural modal parameters.For OWTs with remarkably low structural modal frequencies,displacements can effectively suppress the high-frequency vibration noise and amplify the low-frequency vibration of the structure.However,finding a reference point to measure structural displacements at sea is difficult.Therefore,only a few studies on the use of dynamic displacements to identify the modal parameters of OWTs with high-pile foundations are available.Hence,this paper develops a displacement conversion strategy to study the modal parameter identification of OWTs with high-pile foundations.The developed strategy can be divided into the following three parts:zero-order correction of measured acceleration,high-pass filtering by the Butterworth polynomial,and modal parameter identification using the calculated displacement.The superiority of the proposed strategy is verified by analyzing a numerical OWT with a high-pile foundation and the measured accelerations from an OWT with a high-pile foundation.The results show that for OWTs with high-pile foundations dominated by low frequencies,the developed strategy of converting accelerations into displacements and then performing modal parameter identification is advantageous to the identification of modal parameters,and the results have high accuracy.

A three-dimensional feature extraction-based method for coal cleat characterization using X-ray μCT and its application to a Bowen Basin coal specimen

Cleats are the dominant micro-fracture network controlling the macro-mechanical behavior of coal.Improved understanding of the spatial characteristics of cleat networks is therefore important to the coal mining industry.Discrete fracture networks(DFNs)are increasingly used in engineering analyses to spatially model fractures at various scales.The reliability of coal DFNs largely depends on the confidence in the input cleat statistics.Estimates of these parameters can be made from image-based three-dimensional(3D)characterization of coal cleats using X-ray micro-computed tomography(m CT).One key step in this process,after cleat extraction,is the separation of individual cleats,without which the cleats are a connected network and statistics for different cleat sets cannot be measured.In this paper,a feature extraction-based image processing method is introduced to identify and separate distinct cleat groups from 3D X-ray m CT images.Kernels(filters)representing explicit cleat features of coal are built and cleat separation is successfully achieved by convolutional operations on 3D coal images.The new method is applied to a coal specimen with 80 mm in diameter and 100 mm in length acquired from an Anglo American Steelmaking Coal mine in the Bowen Basin,Queensland,Australia.It is demonstrated that the new method produces reliable cleat separation capable of defining individual cleats and preserving 3D topology after separation.Bedding-parallel fractures are also identified and separated,which has his-torically been challenging to delineate and rarely reported.A variety of cleat/fracture statistics is measured which not only can quantitatively characterize the cleat/fracture system but also can be used for DFN modeling.Finally,variability and heterogeneity with respect to the core axis are investigated.Significant heterogeneity is observed and suggests that the representative elementary volume(REV)of the cleat groups for engineering purposes may be a complex problem requiring careful consideration.

The impact of cleats on hydraulic fracture initiation and propagation in coal seams

Cleats are systematic, natural fractures in coal seams. They account for most of the permeability and much of the porosity of coalbed methane reservoirs and can have a significant effect on the success of hydraulic fracturing stimulation. Laboratory hydraulic fracturing experiments were conducted on coal blocks under true tri-axial stress to simulate fracturing stimulation of coal seams. Fractures were initiated by injecting a water gel with luminous yellow fluorescent dye into an open hole section of a wellbore. The impact of cleats on initiation and propagation of hydraulic fractures in coal seams is discussed. Three types of hydraulic fracture initiation and propagation pattern were observed in this study： 1） The hydraulic fracture initiated and then grew along the cleat. 2） The hydraulic fracture initiated along a butt cleat or a fracture （natural or induced by drilling） oriented roughly in the minimum horizontal stress direction, then turned to propagate along the first face cleat that it encountered or gradually turned towards the maximum horizontal stress direction. 3） The hydraulic fracture initiated perpendicular to the minimum stress and, when it encountered a face cleat, tended to propagate along the cleats if the extension direction does not deviate greatly （〈20° as determined in this paper） from the maximum horizontal stress direction. When a coal seam is hydraulically fractured, the resulting fracture network is controlled by the combined effect of several factors： cleats determine the initiation and extension path of the fracture, the in-situ stress state dominates the main direction of the fracture zone and bedding planes impede fracture height growth.

Mathematical Simulation of Cleat Porosity in Coal Reservoir

Cleat system of coal reservoir is one of the main migrating passage of coalbed methane (CBM). The development of cleat system has important influence on both the preservation of CBM in geological history and surface CBM exploitation. The relationship among cleat porosity, net confine pressure, rock mechanics, coal seam’s occurrence and other factors of coal reservoir is established and simulated based on the energy conservation law. The result indicates that the net confine pressure and buried depth of coalbed are the major control factors of cleat porosity. The extensive stress and abnormal high reservoir pressure can make cleats open thus increase tbe cleat porosity; while the overburden pressure and compressive stress make cleats close and decrease the cleat porosity. The influence of occurrence (dip and dip angle) of coalbed on cleat porosity depends on the change of the above mentioned factors. It is also affected by rock mechanics parameters to some extent, while water-gas saturation and reservoir temperature have little effect on cleat porosity. The above conclusions are of great significance in geological exploration and surface exploitation region determination of CBM.

Dependence of fluid flow on cleat aperture distribution and aperture–length scaling: a case study from Gondwana coal seams of Raniganj Formation, Eastern India

Dimensions and mutual relationships amongst fracture(cleat)parameters such as maximum aperture width,average aperture width,length,spacing etc.control the connectivity within a fracture network and the fluid flow in a coal seam as the matrix permeability,here,is negligible.In this paper,we document cleat size distributions and investigate length–aperture relationships from coals of Raniganj coalfield in Eastern India.This coalfield has a proven extractable reserve of six billion tons of coal and holds immense potential to be one of the largest coal bed methane fields serving India’s growing energy needs.Here,cleat length(L)correlates with corresponding maximum aperture width(Dmax)in a power-law function with an exponent of 0.84(DmaxαL0.84)instead of the commonly observed exponents of 1 or 0.5 applicable for other natural‘opening-mode’fractures.The conventional wisdom pertains that laminar fluid flow(Q)through an isolated,smooth-walled,parallel-plate fracture,embedded in an impermeable matrix,is directly proportional to the cube of its aperture width(b,equivalent to Davg;cubic law:Qαb3).This assumes a linear relationship between length and fracture aperture.However,the modified relationship between cleat length and average aperture width changes the cubic law applicable for Raniganj coal seam and now fluid flow correlates with aperture width in a power-law function with an exponent of 4.25(Qαb4.25)instead of 3(cube).Such simplifications will come handy for the modeling and estimation of fluid flow as it will reduce the effort of cleat length measurement which is anyway difficult and can be misleading due to the risk of undersampling.

The coal cleat system:A new approach to its study

After a general analysis regarding the concept of coal ＂cleat system＂, its genetic origin and practical applications to coalbed methane （CBM） commercial production and to C02 geological sequestration projects, the authors have developed a method to answer, quickly and accurately in accordance with the industrial practice and needs, the following yet unanswered questions： （1） how to define the spatial orientation of the different classes of cleats presented in a coal seam and （2） how to determine the frequency of their connectivites. The new available and presented techniques to answer these questions have a strong computer based tool （geographic information system, GIS）, able to build a complete georeferentiated database, which will allow to three-dimensionally locate the laboratory samples in the coalfield. It will also allow to better understand the coal cleat system and consequently to recognize the best pathways to gas flow through the coal seam. Such knowledge is considered crucial for understanding what is likely to be the most efficient opening of cleat network, then allowing the injection with the right spatial orientation, of pressurized fluids in order to directly drain the maximum amount of gas flow to a CBM exploitation well. The method is also applicable to the CO2 geological sequestration technologies and operations corresponding to the injection of CO2 sequestered from industrial plants in coal seams of abandoned coal mines or deep coal seams.

鄂尔多斯盆地石炭系本溪组煤岩气地质特征与勘探突破

通过对鄂尔多斯盆地石炭系本溪组煤岩分布、煤岩储层特征、煤质特征、煤岩气特征以及煤岩气资源和富集规律等方面开展系统研究,评价其勘探潜力。研究表明:①煤岩气是有别于煤层气的优质天然气资源,在埋深、气源、储层、含气性、碳同位素组成等方面具有独特特征;②本溪组煤岩分布面积达16×10^(4)km^(2),厚度2~25m,以原生结构的光亮和半亮煤为主,挥发分和灰分含量低,煤质好;③中高阶煤岩TOC值为33.49%~86.11%,平均值为75.16%,演化程度高(Ro为1.2%~2.8%),生气能力强,气体稳定碳同位素值高(δ^(13)C_(1)值为-37.6‰~-16.0‰,δ^(13)C_(2)值为-21.7‰~-14.3‰);④深层煤岩发育气孔、有机质孔和无机矿物孔等基质孔隙,与割理、裂缝共同构成良好储集空间,储层孔隙度为0.54%~10.67%,平均值为5.42%,渗透率为(0.001~14.600)×10^(-3)μm^(2),平均值为2.32×10^(-3)μm^(2);⑤纵向上发育5种煤岩气聚散组合,其中煤岩-泥岩聚气组合与煤岩-灰岩聚气组合最为重要,封闭条件好,录井全烃气测峰值高;⑥构建了广覆式分布的中高阶煤岩持续生气、煤岩基质孔和割理裂缝规模储集、源-储一体赋存、致密岩盖层密闭封堵的煤岩气富集模式,存在煤岩侧向尖灭体、透镜体、低幅度构造、鼻状构造和岩性自封闭5种高效聚气类型。⑦依据煤岩气地质特征评价划分出8个区带,估算埋深超过2000m的煤岩气资源量超过12.33×10^(12)m^(3)。上述认识指导风险勘探部署,两口井实施后分别获得工业气流,推动进一步部署预探井和评价井,获得规模突破,提交超万亿方预测储量和超千亿方探明储量,对中国天然气效益增储和高效开发具有重大意义。

钢筋增强钢夹板-螺栓连接胶合木梁受力性能试验研究

为改善钢夹板-螺栓连接胶合木梁的刚度在到达极限荷载55%~70%区间内存在减小的问题,设计制作了3组共12根钢筋增强钢夹板-螺栓连接胶合木梁,通过改变配筋率进行三分点加载试验,并与相同设计参数的胶合木梁和钢夹板-螺栓连接胶合木梁进行对比试验。观察记录试件的受力过程和破坏现象,实测各组试件的极限承载力、荷载位移曲线和应变曲线,对比分析增强筋对各组试件破坏机理、抗弯刚度和极限承载力的影响规律。试验结果表明:与钢夹板-螺栓连接胶合木梁相比,钢筋增强钢夹板-螺栓连接胶合木梁的抗弯承载力和整体弯曲刚度在增强筋的作用下均有显著提高,钢夹板-螺栓连接试验梁在到达极限荷载55%~70%区间内刚度减少问题得到明显改善。钢筋增强钢夹板-螺栓连接试验梁的破坏形式随着配筋率的增大,逐渐由受拉脆性破坏向受拉延性破坏再到受压延性破坏进行转变。增强梁截面应变沿高度方向的分布基本符合平截面假定。依据试验数据和理论推导,得出了钢筋增强钢夹板-螺栓连接试验梁抗弯计算公式,其理论结果与试验结果吻合较好。研究表明,在钢夹板-螺栓连接胶合木梁受拉区配置增强筋可以有效改善其后期刚度减少的问题,并提升其抗弯性能,可为此类连接木梁的增强提供理论依据和试验支撑。

基于分段压裂水平井的临兴区块煤层气开发数值模拟

煤层气作为非常规天然气的重要组成部分,其高效开发技术已引起广泛关注,而水平井分段压裂技术是目前非常规天然气开发的关键技术之一,因而有必要对基于分段压裂水平井的区块煤层气开发进行数值模拟,以期提高煤层气的开发效果以及实现工艺优化。基于煤层气开发流固耦合数学模型,考虑煤储层中割理系统发育与分布,以临兴区块为研究对象,建立水平井分段压裂物理模型,开展煤层气储层压力与产能数值模拟,并对煤层压力变化以及产气效果影响因素进行分析。结果表明:水平井分段压裂开发煤层气在365 d左右可实现较远区域控制,且水平井井周压力较稳定。割理条数、裂缝参数的增加可提高煤层气的产气效果,但需考虑水平井分段压裂技术的开发成本以及井间干扰等因素的影响。基于分段压裂水平井的区块煤层气开发数值模拟模型可为实现煤层气高效开发的水平井分段压裂技术提供参考与指导。

割理结构对WW盆地煤层气井井壁稳定性影响研究

煤层气作为清洁的非常规能源在我国储量丰富,成为增储上产的重要补充来源,且煤层气的开采能有效防止瓦斯泄露爆炸,但煤岩弹性模量和强度低,割理结构发育,煤层气井井壁常发生掉块卡钻,制约了煤层气的高效开发。文章首先研究了煤岩微观结构,建立了同时考虑面割理和端割理影响的煤岩强度准则,结合双孔双渗井周应力模型,研究了割理结构对WW盆地井壁稳定性的影响。结果表明:该区块煤岩黏土矿物含量较少,水化作用较弱;面割理端割理与面割理相互垂直交错切割煤岩,严重削弱了煤岩强度;割理结构对煤岩井壁坍塌压力具有显著影响,若不考虑割理影响,将得到错误的坍塌压力随井眼轨迹的变化规律。割理产状对三种井型坍塌压力影响研究表明,直井坍塌压力不随割理倾角的变化而变化,受割理倾向的影响较大;当割理倾角较大时,沿水平最小地应力方向的水平井稳定性较好;在特定的割理方位情况下,沿水平最大地应力方向的水平井不会沿割理发生剪切滑移破坏。

Geological characteristics and exploration breakthroughs of coal rock gas in Carboniferous Benxi Formation,Ordos Basin,NW China

To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin,this paper presents a systematic research on the coal rock distribution,coal rock reservoirs,coal rock quality,and coal rock gas features,resources and enrichment.Coal rock gas is a high-quality resource distinct from coalbed methane,and it has unique features in terms of burial depth,gas source,reservoir,gas content,and carbon isotopic composition.The Benxi Formation coal rocks cover an area of 16×104km^(2),with thicknesses ranging from 2 m to 25 m,primarily consisting of bright and semi-bright coals with primitive structures and low volatile and ash contents,indicating a good coal quality.The medium-to-high rank coal rocks have the total organic carbon(TOC)content ranging from 33.49%to 86.11%,averaging75.16%.They have a high degree of thermal evolution(Roof 1.2%-2.8%),and a high gas-generating capacity.They also have high stable carbon isotopic values(δ13C1of-37.6‰to-16‰;δ13C2of-21.7‰to-14.3‰).Deep coal rocks develop matrix pores such as gas bubble pores,organic pores,and inorganic mineral pores,which,together with cleats and fractures,form good reservoir spaces.The coal rock reservoirs exhibit the porosity of 0.54%-10.67%(averaging 5.42%)and the permeability of(0.001-14.600)×10^(-3)μm^(2)(averaging 2.32×10^(-3)μm^(2)).Vertically,there are five types of coal rock gas accumulation and dissipation combinations,among which the coal rock-mudstone gas accumulation combination and the coal rock-limestone gas accumulation combination are the most important,with good sealing conditions and high peak values of total hydrocarbon in gas logging.A model of coal rock gas accumulation has been constructed,which includes widespread distribution of medium-to-high rank coal rocks continually generating gas,matrix pores and cleats/fractures in coal rocks acting as large-scale reservoir spaces,tight cap rocks providing sealing,source-reservoir integration,and five types of efficient enrichment patterns(lateral pinchout complex,lenses,low-amplitude structures,nose-like structures,and lithologically self-sealing).According to the geological characteristics of coal rock gas,the Benxi Formation is divided into 8 plays,and the estimated coal rock gas resources with a buried depth of more than 2000 m are more than 12.33×10^(12)m^(3).The above understandings guide the deployment of risk exploration.Two wells drilled accordingly obtained an industrial gas flow,driving the further deployment of exploratory and appraisal wells.Substantial breakthroughs have been achieved,with the possible reserves over a trillion cubic meters and the proved reserves over a hundred billion cubic meters,which is of great significance for the reserves increase and efficient development of natural gas in China.

考虑割理的深煤层水平井多段分簇间距优化研究

为研究水平井多段多簇裂缝在割理发育的深部煤储层扩展情况,基于扩展有限元,考虑缝间干扰和诱导应力场,创建了多段多簇裂缝扩展模型;借助Python语言的前处理二次开发,在模型中加入大量近似正交的割理裂隙,分析了簇间距、压裂顺序和段间距对多裂缝扩展的影响,通过查询裂缝沟通割理组数,来验证压裂效果的优劣。模拟结果表明:簇间距在20 m,段间距控制在40~45 m时,裂缝沟通割理组数相对较多,且受到缝间干扰和诱导应力场影响较小,裂缝长度最优;在不同压裂顺序对多裂缝扩展的影响方面,压裂效果由优到劣排列为:顺序压裂>交替压裂>同步压裂;模型计算结果与现场应用吻合度较高,第2段压裂施工与模拟结果综合符合率为96.5%,第3段压裂施工与模拟结果综合符合率为93.4%。

考虑煤层割理的多分支水平井煤层气开发数值模拟研究

开发煤层气的多分支水平井形态多样且在对开发过程中割理的作用认识不清,有必要探究煤层中离散割理分布特征和多分支水平井形态对气井产能的影响。根据煤层中面割理和端割理的发育情况和正交特性,采用随机方法在煤层中分别构建了低密度、中密度和高密度的离散割理系统,并与等长型、纺锤型、交错型和哑铃型4种不同形态的多分支水平井结合,构建出多分支水平井开发煤层气的物理模型。在考虑开发过程中煤层有效应力变化和基质收缩效应的条件下建立了煤层基质和割理系统的应力敏感模型,并采用Langmuir定理计算煤层气的解吸附,建立了一种可压缩煤层气在煤层基质–割理系统–多分支水平井耦合中流动的开发模型,进而研究了多分支水平井形态和割理密度对煤层气开发的影响。结果表明:煤层中的离散割理可以极大地增加多分支水平井在短时间内对煤层的动用范围,但是仅限于与多分支水平井直接联通的割理及周围基质区域,未与多分支水平井联通的部分则需要较长的开发时间,这也是气井在较短的时间获得峰值产量并迅速减产的重要原因;等长型多分支水平井控制的储层范围最大,交错型、哑铃型和纺锤型的控制范围依次减小;在煤层中割理密度相同时,等长型多分支水平井的煤层气峰值日产量和20 a内的累积产量均高于其他3种类型的多分支水平井,可以取得更好的开发效果;增大多分支水平井主次井筒的夹角,等长型多分支水平井开发效果更好,同时纺锤型分支水平井的峰值日产量提高显著;交错型和哑铃型多分支水平井的峰值日产量对分支数量更加敏感,纺锤型多分支水平井的分支数量应不少于8条,而哑铃型多分支井的分支数量不多于6条。

轿车子午线轮胎瞬态冲击特性的仿真研究

以轿车子午线轮胎(简称轮胎)为研究对象,建立轮胎-转鼓有限元模型,并采用隐式-显式仿真分析方法对轮胎瞬态冲击特性进行仿真研究。结果表明:轮胎从较低速度向较高速度转变时,对障碍条的包覆行为存在由完全包覆向非完全包覆转移的现象;随着轮胎速度的增大,轮胎径向力最大幅值变化趋势为增大-减小-增大-减小,周向力最大幅值变化趋势与之相反;径向力衰减特性是轮胎固有属性,不随轮胎速度的变化而变化;在较低速度下负荷越小的轮胎行驶舒适性越好,在中等速度下适量负荷可以保证轮胎行驶舒适性最好,在较高速度下负荷越大的轮胎行驶舒适性越好。

考虑割理面时煤层造斜段坍塌压力变化规律研究

在武威盆地太原组水平井钻进作业时,依据井史数据调研发现,煤层段卡钻、井径扩大、钻具掉落等井壁坍塌导致的井下复杂事故发生,严重制约了煤层气勘探开发的进程。由于煤岩交错割理性(面割理、端割理)弱结构面发育,使煤岩在造斜钻进时井壁破坏在力学上呈现为非连续性和非均质性。建立了考虑弱面的井壁坍塌数学模型。通过分析煤岩矿物成分、微宏观结构,确定煤岩井壁坍塌为力学机制占主导因素,得出割理导致的煤岩碎裂成块是井壁失稳的根本原因,建议在后续煤层钻井中优化井眼轨迹、优化钻井液性能进行井壁防塌,并引入煤岩井壁坍塌实时监测系统。

基于相控阵超声的线路带夹板焊缝轨底检测研究

为解决带夹板焊缝线路探伤检测效率较低的问题,提出了一种基于相控阵超声的线路带夹板焊缝轨底检测方法,通过将相控阵探头放置于轨底下表面来避免夹板的拆装,同时利用相控阵探头多角度扫查来减少轨底焊缝扫查工序,从而提高检测效率。首先利用仿真研究该方法对轨底缺陷的检测覆盖性,然后针对轨底焊缝检测特点设计相控阵探头,将探头放置于轨底下表面来完成轨底焊缝检测,随后基于设计的钢轨缺陷试块进行试验测试。结果表明:该探头可实现对轨底焊缝位置7个缺陷的全覆盖检测,且检测信噪比均大于17dB。

煤层割理与煤级的关系

通过对煤中割理的宏观观测、光学显微镜、扫描电镜观测等实验 ,详细研究了割理与煤级的关系 .指出煤中割理密度随煤级的增高存在 3种变化趋势 :①随煤级增高割理密度增加 ,在中煤级阶段达极大值 ,之后逐渐降低 ;②随煤级增高密度增加 ,在中煤级阶段达极大值后 ,随煤级进一步增加密度保持不变 ;③在中煤级阶段密度达极大值后 ,随煤级增高逐渐降低 ,但在反射率大于 4 %时 ,保持不变 .同时探讨了割理的成因与闭合机理 .