Numerical experiment rock fragmentation by combined dynamic and static loads under dual-cutter head

This paper puts forward a new rock fragmentation loading method of dual-cutter head combined dynamic and static loads. By applying the numerical simulation software - RFPA2D, we have done numerical experiment about the sihstone＇ s crushing effect by dynamic load on single cutter head without confining pressure, dynamic load on single cut- ter head with confining pressure 10 MPa and different dual-cutter heads spacing by combined dynamic and static loads with confining pressure 10 MPa. Experimental results show that the confining pressure can obviously affect the rock frag- mentation effect. Combined dynamic and static loads can greatly improve the rock fragmentation effect. There exists an optimal spacing of dual-cutter head that can make the rock fragmentation achieve the desired effect. Through analyzing the acoustic emission accumulative energy and quantity, the authors make a conclusion that the optimum spacing is 30 mm.

Experimental study on desorption of soluble matter as influenced by cations in static water

With variation of drainage basin environments, desorption of soluble matter has become one of the significant erosion processes in rivers. It has a considerable impact on flow and sediment transport, as well as processes of river bed deformation and landform evolution throughout a watershed. In this study, considering influences on sediment movement, especially on cohesive sediment transport, Ca^2＋ and H^＋ were chosen as characteristic ions of soluble matter, and the total desorption quantity of Ca^2＋ and pH value when the desorption equilibrium is reached were employed as two indexes representing the desorption of soluble matter. By means of an indoor experiment, desorption of soluble matter as influenced by cations in static water was investigated. The results show that the total desorption quantity of soluble matter increases with the initial cation concentration until a maximum desorption quantity value is obtained and maintained. The total desorption quantity of soluble matter depends on properties of the specific cations in static water, and the stronger the affinity is between the cation and sediment surface, the higher the total desorption quantity will be. Finally, a strong approximate linear relationship between desorption quantities for different kinds of soluble matters was obtained, which means that variation of pH values can accurately reflect the desorption results of soluble matter.

Design and Experiment of Triangular Prism Mast with Tape-Spring Hyperelastic Hinges

Because of the limited space of the launch rockets, deployable mechanisms are always used to solve the phenomenon. One dimensional deployable mast can deploy and support antenna, solar sail and space optical camera. Tape-spring hyperelastic hinges can be folded and extended into a rod like configuration. It utilizes the strain energy to realize self-deploying and drive the other structures. One kind of triangular prism mast with tape-spring hyperelastic hinges is proposed and developed. Stretching and compression stiffness theoretical model are established with considering the tape-spring hyperelastic hinges based on static theory. The finite element model of ten-module triangular prism mast is set up by ABAQUS with the tape-spring hyperelastic hinge and parameter study is performed to investigate the influence of thickness, section angle and radius. Two-module TPM is processed and tested the compression stiffness by the laser displacement sensor, deploying repeat accuracy by the high speed camera, modal shape and fundamental frequency at cantilever position by LMS multi-channel vibration test and analysis system, which are used to verify precision of the theoretical and finite element models of ten-module triangular prism mast with the tape-spring hyperelastic hinges. This research proposes an innovative one dimensional triangular prism with tape-spring hyperelastic hinge which has great application value to the space deployable mechanisms.

Mechanical behaviour analysis and support system field experiment of confined concrete arches

Soft rock control is a big challenge in underground engineering.As for this problem,a high-strength support technique of confined concrete(CC)arches is proposed and studied in this paper.Based on full-scale mechanical test system of arch,research is made on the failure mechanism and mechanical properties of CC arch.Then,a mechanical calculation model of circular section is established for the arches with arbitrary section and unequal rigidity;a calculation formula is deduced for the internal force of the arch;an analysis is made on the influence of different factors on the internal force of the arch;and a calculation formula is got for the bearing capacity of CC arch through the strength criterion of bearing capacity.With numerical calculation and laboratory experiment,the ultimate bearing capacity and internal force distribution is analyzed for CC arches.The research results show that:1)CC arch is 2.31 times higher in strength than the U-shaped steel arch and has better stability;2)The key damage position of the arch is the two sides;3)Theoretical analysis,numerical calculation and laboratory experiment have good consistency in the internal force distribution,bearing capacity,and deformation and failure modes of the arch.All of that verifies the correctness of the theoretical calculation.Based on the above results,a field experiment is carried out in Liangjia Mine.Compared with the U-shaped steel arch support,CC arch support is more effective in surrounding rock deformation control.The research results can provide a basis for the design of CC arch support in underground engineering.

Centrifuge experiment on the penetration test for evaluating undrained strength of deep-sea surface soils

Rapid advances in deep-sea mining engineering have created an urgent need for the accurate evaluation of the undrained strength of marine soils,especially surface soils.Significant achievements have been made using full-flow penetration penetrometers to evaluate marine soil strength in the deep penetration;however,a method considering the effect of ambient water on the surface penetration needs to be established urgently.In this study,penetrometers with multiple probes were developed and used to conduct centrifuge experiments on South China Sea soil and kaolin clay.First,the forces on the probes throughout the penetration process were systematically analyzed and quantified.Second,the spatial influence zone was determined by capturing the resistance changes and sample crack development,and the penetration depth for a sample to reach a stable failure mode was given.Third,the vane shear strength was used to invert the penetration resistance factor of the ball and determine the range of the penetration resistance factor values.Furthermore,a methodology to determine the penetration resistance factors for surface marine soils was established.Finally,the effect of the water cavity above various probes in the surface penetration was used to formulate an internal mechanism for variations in the penetration resistance factor.

Experimental study on interaction between simulated sandstone and acidic fluid

In order to investigate the controlling mechanism of temperature, fluid and other factors on water-rock interaction in the diagenetic process, we performed a series of simulated experiments on the interaction between two kinds of fluids with different salinity and a composite mineral system （simulated sandstone）, which contains albite, K-feldspar and other minerals. The experimental results showed that acidity was the most important factor that affected the dissolution of minerals in the composite mineral system. The lower the pH value, the more easily the minerals dissolved. At the same pH value, the dissolution abilities of different acids for various mineral components were also different. Compared to hydrochloric acid （inorganic acid）, oxalic acid （organic acid） was more able to dissolve aluminosilicate minerals. However, the dissolution ability of oxalic acid for carbonate minerals was lower than that of hydrochloric acid. In the process of fluid-rock interaction, dissolution of feldspar was relatively complicated. Increase of temperature would accelerate the dissolution of feldspar. Under acidic conditions, albite had a higher dissolution rate than K-feldspar. K-feldspar could dissolve and convert into montmorillonite and kaolinite, while albite could dissolve and convert into kaolinite both at 40℃ and 80℃. Presence of organic acid, and decrease of pH value and water salinity were all favorable for the dissolution of feldspar, but weakened the ability to form clay minerals.

Experimental and Numerical Study on the Gas Explosion in Urban Regulator Station

Regulator station is an important part in the urban gas transmission and distribution system.Once gas explosion occurs,the real explosion process and consequences of methane gas explosion in the regulator station were not revealed systematically.In this study,a full-scale experiment was carried out to simulate the regulator station explosion process,and some numerical simulations with a commercial CFD software called FLACS were conducted to analyze the effect of ignition and vent conditions on the blast overpressure and flame propagation.The experimental results demonstrated that the peak overpressure increased as the distance from the vent increased within a certain distance.And the maximum overpressure appeared 3 m away from the door,which was about 36.6 kPa.It was found that the pressure-time rising curves obtained from the simulation are basically the same as the ones from the experiment,however,the time of reaching the peak pressure was much shorter.The numerical simulation results show that the peak overpressures show an increase trend as the ignition height decreased and the vent relief pressure increased.It indicates that the damage and peak overpressure of gas explosion could be well predicted by FLACS in different styles of regulator station.In addition,the results help us to understand the internal mechanism and development process of gas explosion better.It also offers technical support for the safety protection of the urban regulator station.

Large scale sand saltation over hard surface:a controlled experiment in still air

Saltation is the major particle movement type in wind erosion process.Saltating sand grains can rebound up to tens of times larger in length and height over hard surface(such as gravel surface)than over loose sand surface.Gravels usually have different faces,causing distinct response of the impacting grains,but the effects of the grain and gravel-surface contact angle on grain rebound are not yet well quantified.We performed full-range controlled experiments of grain saltation using different contact angles,grain sizes and impact speeds in still air,to show that contact angle increases the height of representative saltation path but decreases particle travel length.The results were compared with outputs from the COMprehensive numerical model of SALTation(COMSALT).Large saltation height of 4.8 m and length of 9.0 m were recorded.The maximum and representative saltation height over the gravel surface were found to be about 4.9 times and 12.8 times those over the loose sandy surface,respectively.The maximum saltation length may be reduced by 58%and the representative saltation height may be increased by 77%as contact angle increases from 20°to 40°.We further showed that the collision inertia contributes 60%of the saltation length,and wind contributes to the other 40%.These quantitative findings have important implications for modeling saltation trajectory over gravel surface.

Flexural failure experiment on cracked PC simply supported box girders

Long-term load and flexural failure experiments are carried out on two prestressed concrete(PC) simply supported box girders. In the long-term load experiment, girder-1(G1) is in an elastic state, while girder-2(G2) is in a cracking state. To investigate the influence of cracking on the flexural behaviors of PC simply supported box beams, the experiment results are analyzed from many aspects, such as load–deflection, load–strain, and failure mode. Experiment results show the following: 1) the shrinkage and creep of concrete have considerable influences on the long-term deflection and strain of the two girders; 2) in the flexural failure experiment, the cracks and ultimate loads of the two girders are close. The rigidity degeneration of G2 is significantly faster than that of G1, and thus G2 shows nonlinear characteristics earlier; 3) to prove the validity and rationality of the current code, the cracking load and ultimate load of the two girders are calculated according to the current code.

Experiments on Large-Diameter Welded Hollow Spherical Joint

We experimented on welded hollow spherical joint of a stadium steel roof to investigate the stress and strain distributions on the surface of the joint and determine the ultimate bearing capacity. Then, finite element analysis was made to experimental results. When the test load was 140% of the design load, the stress at the bottom of the fourth wimble pipe reached the yield point. The experimental results agree with the analytical results well.

Experimental Research and Finite Element Analysis on Setting Stiffening Rib of Corner Joints in Gabled Frames

In order to clear constructional design of corner joint, it is necessary to further investi-gate mechanical property of corner joint in gabled frames. Through static test and finite element software analysis of comparing the panel zone with and without inclined stiffener. Some conclusions are given in the article. The load displacement curves show that the capacity of oblique nodes installed within stiffening rib components is enhanced i.e. 40% more than those without stiffening rib nodes. The results reveal that in the gabled frames, the corner node with the inclined stiffening rib can improve the bearing capacity of the specimens. When the extraterritorial flange is tension, the erection of the inclined stiffening rib can prevent structural failure and improve effectually the ductility of the structure.

Experiment study on RC frame retrofitted by the external structure

A new retrofitting method is proposed herein for reinforced concrete （RC） structures through attachment of an external structure. The external structure consists of a fiber concrete encased steel frame, connection slab and transverse beams. The external structure is connected to the existing structure through a connection slab and transverse beams. Pseudo- static experiments were carried out on one unretrofitted specimen and three retrofitted frame specimens. The characteristics, including failure mode, crack pattern, hysteresis loops behavior, relationship of strain and displacement of the concrete slab, are demonstrated. The results show that the load carrying capacity is obviously increased, and the extension length of the slab and the number of columns within the external frame are important influence factors on the working performance of the existing structure. In addition, the displacement difference between the existing structure and the outer structure was caused mainly by three factors： shear deformation of the slab, extraction of transverse beams, and drift of the conjunction part between the slab and the existing frame. Furthermore, the total deformation determined by the first two factors accounted for approximately 80% of the damage, therefore these factors should be carefully considered in engineering practice to enhance the effects of this new retrofitting method.

Static load test and load transfer mechanism study of squeezed branch and plate pile in collapsible loess foundation

As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundation failure. Pile is a popular foundation used in collapsible loess. The squeezed branch and plate pile is a new type of pile developed in recent years and has not be used in a project before. In this paper three squeezed branch and plate piles are tested in collapsible loess after immersion processing. The results may be used for reference in similar construction project, and to provide theoretical references for de- signing of the squeezed branch and plate piles in engineering practice.

Full-scale experiment for segmental linings of deep-buried shield tunnels bearing high inner water pressure:Comparison of mechanical behaviors of continuous-and stagger-jointed structures

Full-scale loading tests were performed on shield segmental linings bearing a high earth pressure and high inner water pressure,focus-ing on the effects of the inner water load and assembly manner on the mechanical properties of the segmental linings.The test results indicate that the deep-buried segmental linings without inner pressure have a high safety reserve.After the action of high inner water pressure,the lining deformation will increase with the reduction of the safety reserve,caused by the significant decrease in the axial force in the linings.Because the bending moment at the segmental joints is transferred to the segment sections in the adjacent ling rings,the convergence deformation,openings of segmental joints,and bolt strains are smaller for the stagger-jointed lining than those for the continuous-jointed lining;however,dislocations appear in the circumferential joints owing to the stagger-jointed assembly.Although it significantly improves the mechanical performance of the segmental lining,stagger-jointed assembly results in compromising the water-proofing safety of circumferential joints.The stagger-jointed assembly manner can be considered to improve the service performance of shield tunnels bearing high inner water pressure on the premise that circumferential joint waterproofing is satisfied.

Static inelastic analysis of RC shear walls

A macro-model of a reinforced concrete (RC) shear wall is developed for static inelastic analysis.The model is composed of RC column elements and RC membrane elements.The column elements are used to model the boundary zone and the membrane elements are used to model the wall panel.Various types of constitutive relationships of concrete could be adopted for the two kinds of elements.To perform analysis,the wall is divided into layers along its height.Two adjacent layers are connected with a rigid beam.There are only three unknown displacement components for each layer.A method called single degree of freedom compensation is adopted to solve the peak value of the capacity curve.The post-peak stage analysis is performed using a forced iteration approach.The macro-model developed in the study and the complete process analysis methodology are verified by the experimental and static inelastic analytical results of four RC shear wall specimens.

Study on smoke propagation in tunnel construction of a hydropower station: A full-scale fire experiment

In this study,full-scale fire experiments were conducted in a hydropower station to investigate smoke propagation during tunnel construction.The flame height,smoke temperature and stratification,smoke descent and spread velocity were analyzed via measurements and on-site observations.The initial combustion stage was largely affected by ignition source during tunnel construction for diesel pool fire,and the average flame height in the fully developed stage could reach 1.4-2.1 m in experimental fire scenarios.The gradient of the smoke temperature evolution near the fire was the opposite for the upstream and downstream regions.The longitudinal temperature distribution was concentrated in a small range at the heights of the smoke layer,and gradually decreased by air entrainment as the height decreased,while further increasing in the lower half of the tunnel height in the near-fire region under heat radiation from the fire source.Moreover,distinct and stable smoke stratification formed during the fully developed combustion stage,and the smoke layer interface was at approximately half the tunnel height.Smoke descent was aggravated in the decay stage of combustion,and the fire risk remained high after the fully developed period.The smoke front spread velocity was empirically determined for the full-scale tunnel fire scenarios.Conclusions from full-scale experiments can support smoke control design and on-site fire emergency response plans for hydropower stations.

基于双层极值法的储能系统锂离子电池均衡实验设计

储能系统初始参数和运行环境的差异性,会导致电池单体荷电状态(state of charge,SOC)的不一致性,降低储能系统能量利用率。为解决上述问题,设计了基于双层极值法的锂离子电池均衡实验。采用耦合电感与Flyback变换器搭建均衡系统双层架构,建立电池组端电压、均衡电流及占空比间的关联特性;以储能电池端电压作为均衡目标,提出基于双层极值法的锂离子电池快速均衡方法;搭建电池均衡实验教学平台,设计充放电及静置均衡实验,通过仿真分析和实验数据验证所提方法的有效性。该教学实验将理论知识、实验操作及数据分析相结合,有助于提升电气工程专业相关课程实验的质量和效果。

共享铁塔单/双挂载连接件承载性能研究

为研究挂载数量对挂载连接件承载能力和刚度的影响,设计了单挂载与双挂载两种挂载连接件。通过单调拟静力试验研究挂载连接件的承载能力、刚度及其破坏模式,采用有限元软件分析了螺栓直径、钢管宽度、双板件厚度、抗滑移系数和螺栓预紧力对单/双挂载连接件承载力和刚度的影响。结果表明:单/双挂载连接件的破坏模式均为钢管底部加劲肋处断裂,双挂载连接件的极限承载力和初始刚度相比于单挂载连接件分别增加了108.48%和104.27%,可通过加强钢管的上下端部提高连接件的承载力;当抗滑移系数小于等于0.1时,单挂载连接件出现滑移破坏,当抗滑移系数小于等于0.15时,双挂载连接件出现滑移破坏,在其他参数下连接件均未出现滑移破坏;相比于螺栓预紧力和抗滑移系数,螺栓直径、钢管宽度和双板件厚度对连接件的承载力和刚度影响更大;推导出的连接件极限承载力和极限位移计算公式可为同类工程设计提供参考。

任意静定桁架内力分析仿真实验设计

提出了描述桁架几何结构、载荷和支座约束的平衡方程,构建了桁架系统平衡方程的统一矩阵形式,基于MATLAB开发了静定桁架内力分析仿真实验软件。通过该软件,学生可以自主搭建任意静定平面桁架和空间桁架,并完成结构的内力分析实验。实践表明,将仿真实验引入理论力学课程教学,不仅激发了学生的学习兴趣,加深了学生对基本概念的理解;而且培养了学生的高阶思维,提升了学生利用计算机求解问题的能力。

SP08-20先导式螺纹插装比例方向阀静态特性仿真与试验

SP08-20是一种用于方向控制的先导式螺纹插装比例方向阀,断电时,用作单向阀,通电时,用作节流阀,通过控制先导阀芯及主阀芯位置变化实现对阀的流量控制。此阀流道形状较为复杂,控制腔压力分布规律难以确定,且传统的液动力与流量经验公式本身准确性较差,导致在通过由经验公式构成的数学模型求解阀的静态特性时,模型计算结果与试验结果有较大的差异。故采用Fluent软件对SP08-20进行流场仿真得到其阀芯受力规律,利用曲线拟合的方式得到阀芯受力拟合式,据此求解静态数学模型,得到此阀的静态特性。试验结果表明,利用流场仿真的方式求解所得静态特性曲线与试验曲线具有较高的吻合度。