透空结构与半潜式风机集成系统耦合运动响应特性分析

A novel semi-submersible platform is proposed for 5 MW wind turbines.This concept focuses on an integrated system formed by combining porous shells with a semi-submersible platform.A coupled aerodynamic–hydrodynamic–mooring analysis of the new system is performed.The motion responses of the novel platform system and the traditional platform are compared.The differences in hydrodynamic performance between the two platforms are also evaluated.The influence of the geometric parameters(porosity,diameter,and wall thickness)of porous shells on the motion response behavior of the new system is studied.Overall,the new semi-submersible platform exhibits superior stability in terms of pitch and heave degrees of freedom,demonstrating minimal effects on the motion response in the surge degree of freedom.

一个新的压气储能多层预应力内衬洞室多目标优化模型

地下多层洞室是压气储能(CAES)工程的关键环节,其优化设计对提高压气储能工程的效率至关重要,而大多数压气储能工程的洞室优化模型只考虑强度指标,未考虑经济性指标。本文采用有限元方法模拟了高温高压作用下的CAES多层洞室,计算了各层的应力场和应变场(通过试验验证了εθ_(max)出现在衬砌层的顶部),并论证了衬砌层εθ_(max)受结构参数的影响较小,以及预应力衬砌的必要性。预应力衬砌洞室的数值计算结果表明,施加预应力可以有效地减小εθ_(max),提高CAES预应力衬砌洞室的稳定性。建立了一种新的CAES预应力内衬洞室的多目标优化模型,该模型考虑了安全性(最小化预应力以满足其强度条件)和经济性(最小化洞室表面积以降低施工成本)。计算结果表明,多目标优化模型比单目标优化模型(仅考虑强度指标)更安全、更经济地获得CAES多层洞室结构。

单轴压缩下基于轴向塑性应变的岩石裂纹闭合应力与损伤应力阈值的评估方法

量化裂纹应力阈值对认识岩石材料的变形与破坏具有重要意义。本文首先提出了一种基于轴向塑性应变评估岩石裂纹闭合应力和损伤应力阈值的新模型。随后,通过比较提出方法与已有方法的估计结果,验证了本文提出方法的准确性。最后,讨论了弹性模量取值误差对应力阈值计算结果的影响。结果表明,提出方法计算结果与已有方法计算结果非常接近,说明提出方法可以准确识别岩石材料的裂纹闭合应力和损伤应力阈值。此外,本文提出方法能显著降低弹性参数取值对岩石应力阈值计算结果的影响,能够更客观地确定岩石材料的裂纹闭合应力和损伤应力阈值。基于以上结果,本文还提供了详细的计算流程图以消除弹性模量误差造成的影响。

超大浮体与OWC集成系统的水动力性能:半解析研究

Responses of the very large floating Structures(VLFS)can be mitigated by implementing oscillating water columns(OWCs).This paper explores the fundamental mechanism of present wave interactions with both structures and examines the hydrodynamic performance of VLFS equipped with OWCs(VLFS-OWCs).Under the linear potential flow theory framework,the semi-analytical model of wave interaction with VLFS-OWCs is developed using the eigenfunction matching method.The semi-analytical model is verified using the Haskind relationship and wave energy conservation law.Results show that the system with dual-chamber OWCs has a wider frequency bandwidth in wave power extraction and hydroelastic response mitigation of VLFS.It is worth noting that the presence of Bragg resonance can be trigged due to wave interaction with the chamber walls and the VLFS,which is not beneficial for the wave power extraction performance and the protection of VLFS.

Comparison of Pile-Soil-Structure Interaction Modeling Techniques for A 10-MW Large-Scale Monopile Wind Turbine Model Under Wind and Wave Conditions

Considering the large diameter effect of piles,the influence of different pile-soil analysis methods on the design of monopile foundations for offshore wind turbines has become an urgent problem to be solved.Three different pile-soil models were used to study a large 10 MW monopile wind turbine.By modeling the three models in the SACS software,this paper analyzed the motion response of the overall structure under the conditions of wind and waves.According to the given working conditions,this paper concludes that under the condition of independent wind,the average value of the tower top x-displacement of the rigid connection method is the smalle st,and the standard deviation is the smallest under the condition of independent wave.The results obtained by the p-y curve method are the most conservative.

Economic feasibility of large-scale hydro–solar hybrid power including long distance transmission

Solar PV is expected to become the most cost-competitive renewable energy owing to the rapidly decreasing cost of the system. On the other hand, hydropower is a high-quality and reliable regulating power source that can be bundled with solar PV to improve the economic feasibility of long-distance transmitted power. In this paper, a quantification model is established taking into account the regulating capacity of the reservoir, the characteristics of solar generation, and cost of hydro and solar PV with long-distance transmission based on the installed capacity ratio of hydro–solar hybrid power. Results indicate that for hydropower stations with high regulating capacity and generation factor of approximately 0.5, a hydro–solar installed capacity ratio of 1:1 will yield overall optimal economic performance, whereas for hydropower stations with daily regulating capacity reservoir and capacity factor of approximately 0.65, the optimal hydro–solar installed capacity ratio is approximately 1:0.3. In addition, the accuracy of the approach used in this study is verified through operation simulation of a hydro–solar hybrid system including ultra high-voltage direct current(UHVDC) transmission using two case studies in Africa.

An elasto-plastic constitutive model incorporating strain softening and dilatancy for interface thin-layer element and its verification

The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the interfaces both without slurry and with bentonite slurry were analyzed.The experimental results show that different slurries exert much influence on the strength and deformation of soil/structure interface.Under mixed soil slurry,strain softening and shear dilatation are observed,while shear dilatation appears under the small normal stress of the interface without slurry,and shear contraction is significant under the condition of the bentonite slurry.The thickness of the interface was determined by analyzing the disturbed height of the sample with both simple shear test and particle flow code (PFC).An elasto-plastic constitutive model incorporating strain softening and dilatancy for thin layer element of interface was formulated in the framework of generalized potential theory.The relation curves of shear stress and shear strain,as well as the relation curves of normal strain and shear strain,were fitted by a piecewise function composed by hyperbolic functions and resembling normal functions.The entire model parameters can be identified by tests.The new model is verified by comparing the measured data of indoor cut-off wall model tests with the predictions from finite element method (FEM).The FEM results indicate that the stress of wall calculated by using Goodman element is too large,and the maximum deviation between the test data and prediction is about 45%.While the prediction from the proposed model is close to the measured data,and the error is generally less than 10%.

Rock borehole shear tests in dam foundation of Xiangjiaba hydropower station

Xiangjiaba hydropowcr station is one of the complicated geological conditions of its dam foundation, parameters of rock masses are very important issues. To cascade power stations on the Jinsha River, China. Due to the evaluating the rock mass quality and determining the mechanical address these issues, several groups of rock borehole shear tests （RBSTs） were conducted on the black mudstone in the dam foundation of Xiangjiaba hydropower station in the second construction phase. Forty three groups of shear strengths of black mudstone samples were obtained from RBSTs, and the shear strength parameters （c and f） were calculated using the least squares method. In addition, the limitations and merits of RBST employed in the Xiangjiaba hydropower station were discussed. Test results indicate that the shear strength parameters obtained from RBST have a good correlation with the results from sotmd wave test in borehole. It is believed that RBST has a good adaptability and applicability in geotechnical engineering.

Coupled hydro-mechanical effect of a fractured rock mass under high water pressure

To explore the variation of permeability and deformation behaviors of a fractured rock mass in high water pressure,a high pressure permeability test（HPPT）,including measuring sensors of pore water pressure and displacement of the rock mass,was designed according to the hydrogeological condition of Heimifeng pumped storage power station.With the assumption of radial water flow pattern in the rock mass during the HPPT,a theoretical formula was presented to estimate the coefficient of permeability of the rock mass using water pressures in injection and measuring boreholes.The variation in permeability of the rock mass with the injected water pressure was studied according to the suggested formula.By fitting the relationship between the coefficient of permeability and the injected water pressure,a mathematical expression was obtained and used in the numerical simulations.For a better understanding of the relationship between the pore water pressure and the displacement of the rock mass,a 3D numerical method based on a coupled hydro-mechanical theory was employed to simulate the response of the rock mass during the test.By comparison of the calculated and measured data of pore water pressure and displacement,the deformation behaviors of the rock mass were analyzed.It is shown that the variation of displacement in the fractured rock mass is caused by water flow passing through it under high water pressure,and the rock deformation during the test could be calculated by using the coupled hydro-mechanical model.

Structural bonding-breakage constitutive model for natural unsaturated clayey soils

The natural clayey soils are usually structural and unsaturated,which makes their mechanical properties quite different from the remolded saturated soils.A structural constitutive model is proposed to simulate the bonding-breakage micro-mechanism.In this model,the unsaturated soil element is divided into a cementation element and a friction element according to the binary medium theory,and the stress-strain coordination for these two elements is obtained. The cementation element is regarded as elastic,whereas the friction element is regarded as elastoplastic which can be described with the Gallipoli＇s model.The theoretical formulation is verified with the comparative experiments of isotropic compressions on the saturated and unsaturated structural soils.Parametric analyses of the effects of damage variables on the model predictions are further carried out,which show that breakage deformation of natural clayey soils increases with the rising amount of initial defects.

个性化采暖对热舒适的影响:综述

个性化空调因其同时具备节能潜力和满足个性化热舒适需求的能力而备受关注。作为个性化空调的重要组成,个性化采暖能在寒冷环境中维持人体热舒适,因而具备成为冬季重要采暖方式的潜力。为更好地促进个性化采暖的应用与发展,本文对现有研究成果进行了综述。将个性化采暖按其主要的热量传递方式划分为传导式、对流式、辐射式和组合式四类。总结了各方式的原理、具体形式及特点。比较了主要的三类(传导、对流和辐射)个性化采暖方式对热舒适影响的特点,并将其影响规律定量化。总结和归纳了基于环境参数和生理参数的人体局部热舒适评价模型,同时为用户在冬季选择合适的采暖设备提供了理论依据。

Microanalysis of supersaturated gas release based on wall-attached bubbles

Supersaturation of dissolved gases in natural water,due to spillage from high dams and other factors,may cause fish mortality.In previous experiments,the dissipation coefficient has been used to denote the degassing process of total dissolved gas(TDG)saturation.These experiments mainly analyzed supersaturated TDG dissipation from a macroscopic view.To precisely clarify the mechanism of supersaturated TDG release,this study investigated bubble adsorption at a wall surface from a microscopic view.The experiment was conducted in a Plexiglas-wall container filled with supersaturated TDG water.A model that calculates the adsorption flux of supersaturated TDG by a solid wall,and helps describe construction for a contact angle at a three-phase intersection,was developed according to Young's equation.This model was used to investigate the formation process of bubbles adsorbed on a solid polymethyl methacrylate(PMMA)surface in supersaturated TDG water.The adsorption effect of a solid wall on TDG release was analyzed based on the experimental data.The modeling results were compared with observations under different wall area conditions,and it was found that TDG release tended to increase with wall area.This study helps improve our understanding of the mechanisms of supersaturated TDG release and provides an important theoretical method for accurate calculation of the release process.The adsorption flux model of the solid wall provides mitigation measures to combat the adverse effects of TDG supersaturation,which will be beneficial to the protection of aquatic organisms in hydropower-regulated rivers.

Response of air gap and slamming loadings on semi-submersible platform

The present research deals with the numerical prediction of the air gap within the 6th generation of deepwater drilling floating semi-submersible platform and the experimental studies on the slamming loadings onto the structure. The survivability of the floating model with a mooring system was tested under extreme wave of 10-year return period. In the numerical simulation of the Gaussian method,the narrow band model was applied to obtain the first-order wave surface equation and the modified second-order wave surface equation. The hydrodynamic responses of the floating body,i.e. radiation damping,added mass,second-order wave excitation force and drifting force,were computed by using the potential flow theory based on higher order boundary element method in frequent domain. In the experimental analysis,high-frequency sensors were installed at the lower deck to measure the wave slamming loads. Equivalent truncated mooring system was applied to make sure position of the floating body in the wave tank. The comparison between the numerical and experimental results showed the numerical model underestimated the air gap of the floating body. Nevertheless,the predictions of the high risk spots underneath the floating deck that is prone to wave slamming obtained from both models were agreeable to each other. The experimental results also revealed that the wave slamming events often occurred at the connection point between the rear columns and the lower deck.

Grouping-Based Optimal Design of Collector System Topology for a Large-Scale Offshore Wind Farm by Improved Simulated Annealing

During the construction of an offshore wind farm(OWF),the capital cost of the collector cable system accounts for a large proportion of the total cost.Consequently,the optimal design of the collector system topology(CST)is one of the most crucial tasks in OWF planning.However,for a large-scale OWF,the optimal design of CST is a complex integer programming problem with high-dimension variables and various constraints.Therefore,it is difficult to acquire a high-quality optimal design scheme.To address this issue,this paper proposes a new grouping-based optimal design of CST for a large-scale OWF.First,all the wind turbines are divided into multiple groups according to their geographical locations and the maximum allowed connected wind turbines by each cable.This not only reduces the optimization dimension and difficulty,but also effectively satisfies the‘no cross’constraint by putting the geographically closed wind turbines into the same group.Secondly,the electrical topology among different wind turbines in each group is initially generated by an improved dynamic minimum spanning tree(DMST).The division groups of the OWF are then adjusted to further reduce the capital cost by improved simulated annealing.To verify the proposed technique,comparison case studies are carried out with five algorithms on two different OWF.

Finite volume method-based numerical simulation method for hydraulic fracture initiation in rock around a perforation

1 Introduction Hydraulic fracturing is a technique for increasing permeability in oil and gas resource development,grouting reinforcement in mine management,and geostress measurement.For the purpose of enhancing hydraulic fracturing in horizontal wells,oriented perforating methods have been developed(Kurdi,2018;Michael and Gupta,2020a;Yan et al.,2020).Fluid is injected into the rock through perforations,which increases fluid pressure within rock and decreases rock temperature.Then,the rock around the perforation is fractured.Therefore,fracture initiation pressure is intimately connected to the reservoir’s physical and mechanical properties,geo-stress,and temperature(Morgan and Aral,2015).

Failure Mechanism and Stability Analysis of an Active Landslide in the Xiangjiaba Reservoir Area,Southwest China

Dam construction for hydropower development is a very important subject all around the world, especially in developing countries due to energy crises. Filling of reservoir lakes may trigger or reactivate landslides in reservoir area. Active landslides in populated districts in the Xiangjiaba Reservoir area have become a striking problem for residents, local government and construction engineers. The key objective of this study is to analyze the role of reservoir filling and fluctuation in the activation/reactivation of the landslide as well as the mechanism of landslide from microstructures of pre-sheared slip surface. A large active landslide with a total volume of 1.25 Mm^3 at the left margin of Jinsha River in Pingshan County of Sichuan Province, Southwest China, was selected as a case study. Field investigation, field monitoring and laboratory tests were carried out to find out the failure mechanism and the stability of the active landslide. The shear strength test and stability analysis confirm that the water level fluctuations have an adverse effect on slope stability. It is obvious from microstructure analysis that the clay minerals contribute to down-slope movement at micro-scale as well as presence of expansive minerals （e.g., montmorillonite） decreases the strength of soil due to water level rise.

Hydraulic Characteristics of Multi-Stage Orifice Plate

Energy dissipater of multi-stage orifice plate, as a kind of effective energy dissipater with characteristics of high energy dissipation ratio and low cavitations risk, has become welcomed more and more by hydraulics researchers. The relationship between the contraction ratio of upper stage orifice plate and the lower one's under the principle of equal-cavitation characteristics, and the reasonable distance between upper stage orifice plate and the lower one under the condition of complying with this principle, are two important factors to be considered for multi-stage energy dissipater design. In the present paper, these two factors were analyzed by theoretical consideration and numerical simulations, and solving methods were put forward. The conclusion in this paper was proved to be reasonable by model experiment.

Effects of different soil amendments on physicochemical property of soda saline-alkali soil and crop yield in Northeast China

Soil amendment is one of the most effective methods to improve saline-alkali soil.In this study,laboratory experiments were conducted to verify the effect of 13 kinds of amendments and their combinations(Citric acid(NM),Phosphogypsum(LS),Aluminum sulfate+citric acid(AL+NM),Aluminum sulfate+phosphogypsum(AL+LS),Aluminum sulfate+citric acid+phosphogypsum(HH),Zeolite(Z),Acidified zeolite(ZH),Aluminum sulfate(AL),Aluminum sulfate+zeolite(AL+Z),Aluminum sulfate+acidified zeolite(AL+ZH),Poly Aluminum chloride(ALCL),Polyaluminium chloride+zeolite(ALCL+Z),Polyaluminium chloride+acidified zeolite(ALCL+ZH))on soil pH,metal cations content,exchangeable Na+,exchangeable sodium percentage(ESP)in the lab.And then the five most effective amendments(Z,ZH,AL,AL+Z,and AL+ZH)were chosen applying both in dry field(maize field)and paddy field to evaluate their improvement on soda saline-alkali soil and crop yield in the northeast Songnen Plain,China.The lab results showed that AL,AL+Z and AL+ZH treatments could significantly reduce the pH in soil solution and increase the content of metal cations.Z and ZH treatments could adsorb metal cations in soil.Both in dry and paddy fields,all five treatments could increase the soil saturated hydraulic conductivity(Ks),increased from 9.63 to 60.02 mm/d and 0.18 to 33.25 mm/d,respectively,of which the AL treatment was the best;all five treatments could reduce the content of exchangeable Na+in soil,and decrease by 38.62%-61.33%and 25.24%-71.53%,respectively,of which the AL+ZH treatment was the best;all treatments could reduce soil exchangeable sodium percentage,and decrease by 0.14-0.22 and 0.14-0.41,respectively,of which the AL+ZH treatment was the best;AL,AL+Z and AL+ZH treatments could improve soil organic matter content;all treatments could effectively improve the yield of crops,and increase 23.98%-60.75%and 52.51%-260.21%,respectively,of which the AL treatment was the best in dry field and the AL+ZH treatment was the best in paddy field.The effect of AL treatment was the best in dry field and AL+ZH treatment was the best in paddy field of soda saline-alkali soil.This study could provide instructive information for the chemical improvement and agricultural utilization of soda saline-alkali soils in the world.