Flume Experiment Investigation on Propagation Characteristics of Tidal Bore in A Curved Channel

Tidal bore is a special and intensive form of flow movement induced by tidal effect in estuary areas, which has complex characteristics of profile, propagation and flow velocity. Although it has been widely studied for the generation mechanism, propagation features and influencing factors, the curved channel will complicate the characteristics of tidal bore propagation, which need further investigation compared with straight channel. In this study, the flume experiments for both undular and breaking bores’ propagation in curved channel are performed to measure the freesurface elevation and flow velocity by ultrasonic sensors and ADV respectively. The propagation characteristics,including tidal bore height, cross-section surface gradient, tidal bore propagation celerity, and flow velocity are obtained for both sides of the curved channel. And three bore intensities are set for each type of tidal bores. The freesurface gradients are consistently enlarged in high-curvature section for undular and breaking bores, but have distinct behaviors in low-curvature section. The spatial distributions of tidal bore propagation celerity and flow velocity are compared between concave and convex banks. This work will provide experimental reference for engineering design of beach and seawall protection, erosion reduction and siltation promotion in estuary areas with the existence of tidal bores.

Experimental Study on the Aerodynamic Performance of Swept-Curved Blade

Compared with a straight blade, a unique compressor blade integratedforward-swept and positive-curved stacking line is studied experimentally. Aerodynamic parameters ofthe two cascades are measured by a five-hole probe at different positions and ink trace flowvisualization is conducted on blade surfaces. The result shows that the swept-curved cascade haslower endwall loss and higher midspan loss as compared with the straight cascade. However, lowerloss is accompanied with lower diffusion factor. Opposite 'C' shape static pressure distribution isestablished on the suction surface of the swept-curved blade, which is helpful for avoiding theaccumulation of low energy fluid in the endwall corner region. Anyhow the studies support theconclusion that the swept-curved blade conduces to not only the reduction of overall loss but alsothe improvement of stable operation in the endwall corner region.

Industrially Experimental Investigations and Development of the Curve-ROD Baffle Heat Exchanger

The conventional heat exchanger with segmental baffles is prone to bring forth fluid-induced vibration of heat transfer tubes and increase the pressure drop of shell-side greatly at higher fluid flow velocity. In order to avoid the above defects, the ROD-baffle heat exchanger has been developed. However, its collocation of heat transfer tubes is conventionally in square, which leads to fewer heat transfer area per unit volume. Based on the ROD-baffle heat exchanger, a new type curve-ROD baffle has been developed, and an industrial investigation of the curve-ROD baffle heat exchanger with normal triangular collocation has been carried into execution. In this paper, two equations using the Reynolds number were acquired to predict the heat transfer coefficients of the shell-side and tube-side. The experimental results show that the shell-side heat transfer and pressure drop characteristics of the curve-ROD baffle heat exchanger are superior to those of the segmental baffle one.

Impact of backwater on water surface profile in curved channels

Owing to extensive construction of dams, the impact of backwater on flow may lead to navigation or flood control issues in curved channels. To date, the impact of backwater on the water surface profile in curved channels remains unknown and requires investigation. In this study, experiments were conducted in a glass-walled recirculating flume with a length of 19.4 m, a width of 0.6 m, and a depth of 0.8 m, and the impact of backwater on the water surface profile in a 90° channel bend was investigated. The experimental results showed that the backwater degree had a significant impact on the transverse and longitudinal flow depth distributions in the bend. The transverse slope of the flow (Jr) increased linearly with an increase in the Froude number of the approach flow upstream of the bend. Jr increased with the longitudinal location parameter ξ when −0.2 < ξ < 0.5, and decreased with ξ when 0.5 < ξ < 1.2. Furthermore, the results showed that Jr asymptotically decreased to zero with an increase in the degree of backwater. An equation was formulated to estimate the transverse slope of the flow in a 90° bend in backwater zones.

Prediction of Load-Displacement Curve of Flexible Pipe Carcass Under Radial Compression Based on Residual Neural Network

The carcass layer of flexible pipe comprises a large-angle spiral structure with a complex interlocked stainless steel cross-section profile, which is mainly used to resist radial load. With the complex structure of the carcass layer, an equivalent simplified model is used to study the mechanical properties of the carcass layer. However, the current equivalent carcass model only considers the elastic deformation, and this simplification leads to huge errors in the calculation results. In this study, radial compression experiments were carried out to make the carcasses to undergo plastic deformation. Subsequently, a residual neural network based on the experimental data was established to predict the load-displacement curves of carcasses with different inner diameter in plastic states under radial compression.The established neural network model’s high precision was verified by experimental data, and the influence of the number of input variables on the accuracy of the neural network was discussed. The conclusion shows that the residual neural network model established based on the experimental data of the small-diameter carcass layer can predict the load-displacement curve of the large-diameter carcass layer in the plastic stage. With the decrease of input data, the prediction accuracy of residual network model in plasticity stage will decrease.

Experimental investigation and analytically modeling of hysteretic behavior of rigid bus-flexible connectors of 220 kV electrical substations

This paper describes the quasi-static testing and analytical modelling of the hysteretic behavior of aluminum alloy rigid bus-flexible connectors of 220 kV electrical substations.The main objective of the study is to experimentally investigate the hysteretic behavior of six different types of rigid bus-flexible connectors 220 kV electrical substations when subjected to cyclic loading.Another objective is to theoretically study the flexibility and effectiveness of a previously proposed analytical model in fitting the experimental hysteresis loops of the tested rigid bus-flexible connectors.The experimental investigation indicates that the tested rigid bus-flexible connectors exhibit highly asymmetric hysteresis behavior along with tension stiffening effect.The theoretical study demonstrates that the generalized Bouc-Wen model has high flexibility and is effective in fitting the experimental hysteresis resisting force-displacement curves of the six tested rigid bus-flexible connectors.

Flow Structure and Short-Term Riverbed Evolution in Curved Flumes

River bending is the major effect responsible for bed topography and bank changes.In this study,fluid velocity(measured by a three-dimensional Doppler advanced point current meter)and bed topographical data have been collected in 40 sections of an experimental model.The whole flume was composed of an organic glass bend,upstream and downstream water tanks,two transition straight sections,a circulation pump,and a connection pipeline.Each section has been found to be characterized by a primary circulation and a small reverse circulation,with some sections even presenting three more or more circulation structures.The minimum circulation intensity has been detected in proximity to the top of the curved channel,while a region with small longitudinal velocity has been observed near the concave bank of each bend,corresponding to the flat bed formed after a short period of scouring.The maximum sediment deposition and scour depth in the presence of a uniform distribution of living flexible vegetation within 10 cm of the flume wall have been found to be smaller than those observed in the tests conducted without vegetation.

Error Model of Curves in GIS and Digitization Experiment

A stochastic error process of curves is proposed as the error model to describe the errors of curves in GIS. In terms of the stochastic process, four characteristics concerning the local error of curves, namely, mean error function, standard error function, absolute error function, and the correlation function of errors , are put forward. The total error of a curve is expressed by a mean square integral of the stochastic error process. The probabilistic meanings and geometric meanings of the characteristics mentioned above are also discussed. A scan digitization experiment is designed to check the efficiency of the model. In the experiment, a piece of contour line is digitized for more than 100 times and lots of sample functions are derived from the experiment. Finally, all the error characteristics are estimated on the basis of sample functions. The experiment results show that the systematic error in digitized map data is not negligible, and the errors of points on curves are chiefly dependent on the curvature and the concavity of the curves.

Influence analysis of chevron alignment signs on drivers' speed choices at horizontal curves on highways

Using a driving simulator,the effects of Chinese chevrons on drivers’actual and perceived safe speeds at horizontal curves on two-lane rural highways are tested. Twelve horizontal curves with different roadway geometries are designed and used as the simulated scenarios.The results show that, regardless of the curve radius, chevrons at horizontal curves provide advance warning and speed control for vehicles on the nearside of chevrons.Besides,chevrons can be used as an addition to speed limit signs in preventing excessive speed at horizontal curves and, therefore, can contribute to a reduction in run-off-road crashes.Moreover, Chinese chevrons can also serve to provide an improved sense of safety while driving around sharp curves.These study results lay a foundation for setting Chinese chevrons more reasonably.

Experimental investigation on rainfall infiltration and solute transport in layered porous and fractured media

Layered structures with upper porous and lower fractured media are widely distributed in the world. An experimen- tal investigation on rainfall infiltration and solute transport in such layered structures can provide the necessary foundation for effectively preventing and forecasting water bursting in mines, controlling contamination of mine water, and accomplishing ecological restoration of mining areas. A typical physical model of the layered structures with porous and fractured media was created in this study. Then rainfall infiltration experiments were conducted after salt solution was sprayed on the surface of the layered structure. The volumetric water content and concentration of chlorine ions at different specified positions along the profile of the experiment system were measured in real-time. The experimental results showed that the lower fractured media, with a considerably higher permeability than that of the upper porous media, had significant effects on preventing water infil- tration. Moreover, although the porous media were homogeneous statistically in the whole domain, spatial variations in the features of effluent concentrations with regards to time, or so called breakthrough curves, at various sampling points located at the horizontal plane in the porous media near the porous-fractured interface were observed, indicating the diversity of solute transport at small scales. Furthermore, the breakthrough curves of the outflow at the bottom, located beneath the underlying fractured rock, were able to capture and integrate features of the breakthrough curves of both the upper porous and fractured media, which exhibited multiple peaks, while the peak values were reduced one by one with time.

Biomimetic Experimental Research on Hexapod Robot's Locomotion Planning

To provide hexapod robots with strategies of locomotion planning, observation experiments were operated on a kind of ant with the use of high speed digital photography and computer assistant analysis. Through digitalization of original analog video, locomotion characters of ants were obtained, the biomimetic foundation was laid for polynomial trajectory planning of multi-legged robots, which was deduced with mathematics method. In addition, five rules were concluded, which apply to hexapod robots marching locomotion planning. The first one is the fundamental strategy of multi-legged robots＇ leg trajectory planning. The second one helps to enhance the static and dynamic stability of multi-legged robots. The third one can improve the validity and feasibility of legs＇ falling points. The last two give criterions of multi-legged robots＇ toe trajectory figures and practical recommendatory constraints. These five rules give a good method for marching locomotion planning of multi-legged robots, and can be expended to turning planning and any other special locomotion.

Tests and numerical simulation on curved blade of super-critical adjust stage

Tests and numerical simulations of super-critical adjust stage blade were carried out and the effect of bowed blade on flow characteristics and the secondary flow were analyzed. The simulation and test results show that the adjust stage blade with aft-loading and big front-edge radius has good flow characteristics by meridian shrink. The numerical studies were carried out with software of NUMECA in order to investigate the aerodynamic characteristics of adjust stage blades,which include prototype blade(tested blade) ,positive curved blade (15°) and negative curved blade(-15°) . The simulation results show that the positive curved blade forms a negative static pressure gradient in the lower region of the cascade along the blade height and a positive static pressure gradient in the upper region. This leads to the reduction of the streamwise vortices intensity and the aerodynamic load on both sides of the blade and the endwall. Therefore,the crosswise secondary flow losses of endwall can be decreased considerably.

EXPERIMENTAL STUDY ON FUSION OF TIN-BEARING GRANITES IN GUANGXI,SOUTHERN CHINA

Experiments have been carried out for studying the melting characteristics of two representative types of granite complexes relating to tin ore deposits in Guangxi. The curves of the beginning melting of the Longxiangai porphyritic biotite granite (LPBG), the Longxiangai granular biotite granite (LGBG), the margin phase and central phase of the rocks of the Pinyin granite (MPPG and CPPG) are determined by the experiments. The results of the experiments show that the temperature of the beginning melting points of the tin -bearing granite not only depends on the type and features of the rocks, but also varies with the total water vapour pressure (PH2O) and the one of the different granites decrease with the increasing pressure. In different ranges of the pressure,the variance gradient of the beginning melting points sharply varies. When PH2O is less than or equal to 136 MPa, the beginning melting temperatures of LPBG somewhat lower than those of LGBG ;Whe P H2O is larger than 136MPa,The beginning temperatures of LPBG are higher than those of LGBG. The beginning teperatures of CPPG are always higher than those of MPFG at the conditions of PH2O from 75 to 250 MPa.

Experimental and Numerical Research on Strengthening the Performance of Wave Rotor Equipment with Curved Passages

The wave rotor technology is an energy exchanging approach that achieves efficient energy transfer between gases without using mechanical components.The wave rotor technology has been successfully utilized in gas turbine cycle systems,gas expansion refrigeration and a variety of other industrial domains,yielding numerous researches and application outcomes.The structure of wave rotor passages inside which the energy exchange between gases is realized has an important impact on the equipment performance.In this study,based on gas wave ejection technology,the first application trials of an expansion wave rotor with curved passages were conducted.Additionally,the performance enhancing effect and mechanism of curved passages on the energy exchanging process were studied precisely by the combination of experimental and three-dimensional numerical simulation methods.The experimental results demonstrate that the curved passage rotor(CIR rotor)employed in this research has a maximum isentropic efficiency of 61.6%,and the CIR rotor achieves higher efficiency than the straight passage rotor(STR rotor)on all working conditions in this study.Compared with the STR rotor,the maximum efficiency improving ratio of CIR rotor can exceed 14.2%at each experimental expansion ratio,and the maximum relative increments of ejection rate are more than 5%.In addition,the CIR rotor can also effectively increase the proportion of static pressure in total pressure of the medium-pressure gas,and reduce the device power consumption.The three-dimensional numerical investigations revealed the principle of gas ejection in the wave rotors and explained why the CIR rotor performed better.According to the numerical findings,the curved passages of the CIR rotor may effectively minimize various energy losses created in the processes of high-pressure gas incidence,exhausting flow in nozzle,and high-speed gas flow in the passages.

Geometric nonlinear formulation for curved beams with varying curvature

Based on exact Green strain of spatial curved beam, the relation for plane curved beam with varying curvature is derived nonlinear strain-displacement Instead of using the previous straight beam elements, curved beam elements are used to approximate the curved beam with varying curvature. Based on virtual work principle, rigid-flexible coupling dynamic equations are obtained. Physical experiments were carried out to capture the large overall motion and the strain of curved beam to verify the present rigid-flexible coupling formulation for curved beam based on curved beam element. Numerical results obtained from simulations were compared with those results from the physical experiments. In order to illustrate the effectiveness of the curved beam element methodology, the simulation results of present curved beam elements are compared with those obtained by previous straight beam elements. The dynamic behavior of a slider-crank mechanism with an initially curved elastic connecting rod is investigated. The advantage of employing generalized-or method is pointed out and the special nonlinear dynamic characteristics of the curved beam are concluded.

底部双排配筋单孔空心预制梁力学性能试验研究

为了研究新型装配式单孔空心预制梁的抗弯承载力和变形性能,并提高其工作性能。试验共设计并制作了3根单孔空心预制梁和1根实心预制梁,通过试验和理论计算相结合的分析手段,重点研究单孔空心预制梁和实心预制梁的破坏机理、裂缝发展、荷载-挠度曲线、变形性能及抗弯承载力等。结果表明:单孔空心预制梁与普通实心预制梁的破坏特征相似,且其裂缝分布较均匀、间距小,延性好;在相同荷载作用下,单孔空心预制梁挠度大于实心预制梁,其整体受力变形性能相对优越。提出了截面有效面积等效法和混凝土轴心抗压强度等效法2种计算方法,通过对比分析发现,混凝土轴心抗压强度等效法计算值误差仅为0.82%,满足工程要求,而且单孔空心预制梁与实心梁相比还可节约材料8.72%。因此,单孔空心预制梁具有良好的应用前景。

L型隔板弧形双钢板组合墙板抗爆性能试验与数值研究

弧形双钢板混凝土组合墙板结构具有和拱结构相同的传力机理,可以充分发挥混凝土优异的抗压性能,极大地提高了结构的承载力。该文开展了L型隔板弧形双钢板混凝土组合墙板(L-shaped-Curved Double Steel Concrete Composite Wallboard,L-CDSCW)在近场爆炸作用下的试验研究,通过混凝土的损伤分析和结构变形分析探究其抗爆性能。基于ANSYS/LS-DYNA软件进行了L-CDSCW试件爆炸响应的数值分析,参数化分析了不同关键参数对L-CDSCW试件抗爆性能的影响规律。结果表明:近场爆炸作用下,L-CDSCW试件未出现倒塌或崩塌现象,具有较强的抗爆性能;增加钢板厚度可以减小混凝土跨中凹陷深度和混凝土塑性破坏;增加TNT当量和降低爆距会显著增加底部钢板跨中最大挠度,同时也会增加混凝土跨中凹陷深度和混凝土损伤。研究结果可以为弧形双钢板混凝土组合板的应用提供一定的技术参考。

三重四极杆电感耦合等离子体质谱仪测定铼含量

铼(Re)是自然界中最稀有的元素之一,因其含量低而测定较为困难。三重四极杆电感耦合等离子体质谱仪(ICP-MS/MS)为解决该难题提供了技术支持。本文利用ICP-MS/MS建立了快速分析Re含量的方法。结果表明,ICP-MS/MS的灵敏度较传统的单杆ICP-MS显著提高,能够准确分析Re含量低至0.5 pg/mL的样品;样品中基体(Ca、K、Mg、Na)浓度在较低时对Re的分析没有影响,浓度高于2000μg/mL时基体干扰会降低分析结果的准确性。因此,分析时可先通过离子交换纯化或稀释以减小基体效应的影响再进行样品测试。采用该方法对河水标样SLRS-6、岩石标样BHVO-2和BCR-2的Re含量进行分析,其结果分别为(14.4±0.4)pg/mL、(0.59±0.05)ng/g和(12.46±1.21)ng/g,均与报道结果一致。最后,利用建立的方法分析常见的自然样品(如河水、岩石、土壤、沉积物等)的Re含量,获得了与前人报道一致的分析结果,这些结果丰富了自然界Re含量储库,也增加了对自然界Re变化的认识。

基于低频简化频散方程的充流管道泄漏固体声波波速计算方法

由充流管道泄漏引致并在管壁上传播的声波被称为泄漏固体声波,其中波速的确定是实现管道泄漏定位的关键。针对适合泄漏定位的低频段的T(0,1)模态、L(0,1)模态和F(1,1)模态,该文提出了一种基于低频简化频散方程的声波波速计算方法。该方法将低频简化的流体荷载和土体荷载施加于管道,从而建立了流体-管道-土体的耦合方程。不同模态的波速可以通过求解耦合方程来得到。以钢管、HDPE管和球墨铸铁管为对象进行算例研究,得到了三种管道在不同流体和土体工况下的频散曲线。结果表明,流体性质对波速的影响较小,而土体性质会对波速产生显著且复杂的影响。该文通过标定实验获取了埋地充水DN200球墨铸铁管的频散曲线。标定结果与所提出的计算方法的结果较为一致,这支撑了所提出方法的工程应用价值。

城市轨道交通S型曲线夹直线与长直线地段振动对比试验研究

夹直线在一定程度上可以保证线型连续和行车平顺,但过短的夹直线长度会导致振动叠加,影响旅客舒适度和列车运行的稳定性,增加运营维护成本。本文通过对城市轨道交通S型曲线夹直线与长直线地段振动对比试验研究,从时域、时频域、振动加速度级及地面Z振级等方面对获得的数据进行分析,解释了夹直线段振动叠加的产生机理,验证了车体垂向加速度峰值在缓直点处会出现峰值提前现象,并阐述了夹直线段的振动叠加现象对地面环境振动的影响。结论如下:车辆在通过S型曲线线形变化点时产生的冲击振动会通过钢轨以弹性波的形式向前传播,与车辆在夹直线段行驶产生的振动叠加;由于弹性波的形式传播的速度远高于车辆行驶速度,因此会导致夹直线段出现振动加速度峰值提前现象;S型曲线夹直线的垂向振动加速度的优势频率要高于长直线段,且更向高频分散;S型曲线夹直线产生的振动叠加现象不会对地面环境振动产生影响。