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Flow pattern is an important factor affecting fish collective behavior. In the reproductive season, schizothorax prenati will choose suitable flow area for migration, but the water conservancy project caused serious damage to its migration channel. The purpose of this study was to study the response of the collective behavior of Schizothorax prenati to the flow velocity and turbulent kinetic energy, to optimize the flow pattern and water management of the fish crossing facilities. In this paper, the Nearest Neighbor Distance (NND) and collective area were used to evaluate the cohesion of fish, and the Separation Swimming Index (SSI) was used to evaluate the repulsion of fish. In the experiment, 10 Schizothorax prenati with an average age of 3 years were selected from each group, a total of two groups, and each group was tested for 6 times. Each time allowed the fish to swim in a 3 m×14 m rectangular flume physical model (flow velocity decreased from 0.17 m/s on the left to 2.5 m/s on the right, and the turbulent energy was 0-0.225 m² /s2 ) and (16±1) ℃ water temperature. After shooting with the camera, the graph was collected to extract and analyze the swimming trajectory of the fish, at the same time, we observed the formation of fish in moving water and all collective indicators were calculated at 10-second intervals during the analysis of the fish. All coordinates recorded in a total of 12 tests were plotted as heat map, the darker the color, the more likely the fish were to cluster in that area, meanwhile, we calculated the NND, collective area and SSI of fish at all recorded times. Finally, by coupling the above three collective indexes with flow velocity and turbulent kinetic energy, the collective indexes under different hydraulics conditions were analyzed to evaluate the collective behavior of fish. The results showed that Schizothorax prenati had obvious collective behavior under specific hydraulic conditions, and its collective behavior was closely related to hydraulic factors. In this experiment, the fish mainly swam in the formation of “schooling” mode, and fish usually swam in a single partition in the experimental flume, showing a neatly arranged polar structure, and all individuals tended to swim in the same direction when the flow velocity was 0.27-0.70 m/s and the turbulent kinetic energy was 0.004-0.018 m² /s², the NND, collective area and SSI of the fish were 0-0.80 m, 0-5.00 m² and 0-1.20, and the collective behavior was the most compact and close, with better cohesion and repulsion. In the two typical swimming upstream routes, the average flow velocity and turbulence kinetic energy were basically consistent with the compact collective behavior hydraulic conditions of the Schizothorax prenati summarized in this paper, which verified the accuracy of this study. Therefore, it is recommended that engineering measures be taken to create a flow velocity of 0.27-0.70 m/s and a kinetic energy of 0.004-0.018 m² /s² in order to make the Schizothorax prenati mass migration, which allowed for a smaller flow velocity range than traditional fishway design methods. [ABSTRACT FROM AUTHOR]

The structure and flow pattern of traditional fishway are relatively simple, which is usually suitable for specific fish to pass through. However, there are many types of fish to be protected in rivers. Near natural fishway simulates natural form of fish and is expected to improve fish passing efficiency. Therefore, in order to enhance the meandering and naturalness of fish passing facilities, a swirling fishway structure with curved sidewall and diversion bank was proposed in this paper. The side wall of the swirl fishway adopted circular curve, and the contraction area between the chambers was smoothly connected by the reverse circular arc, which made the water flow close to the natural sinuous channel. The swirling fishway was obtained by improving Taiji fishway. Compared to Taiji fishway, it omitted the Taiji disc and was cheaper. At the same time, the water flow in the pond could be rapid and slow, or deep and shallow, highlighting the effect of Yin and Yang and enriching the flow pattern. Through the combination of numerical simulation and physical model test, the hydraulic characteristics of swirling fishway under different working conditions were explored. First of all, through physical model test, the water depth along the wall and the flow pattern distribution of the two sides of the fishway under different working conditions were obtained, and the effect of fish passing was observed. The accuracy and rationality of the numerical calculation were verified by comparing the water depth data obtained from the physical model test and the numerical calculation results. The CFD numerical calculation method was applied to simulate distribution of surface velocity field and internal velocity field that were difficult to be measured by physical model. The free surface flow velocity, the velocity near the bottom slope and the velocity distribution in key cross section of the swirl fishway were further analyzed. According to the design guidelines of fishway, the basic points of hydraulic design and the gravity similarity criteria, the physical test model was established. After the establishment of the physical model, the water flow test under different conditions was carried out, and the water depth of the measuring point was measured by the water level probe. The results showed that the swirling flow in the fishway was zigzag and the flow pattern was rich. The maximum relative error of simulated and measured water depth was 14.2%, less than the allowable value of 15%. The variation trend of the measured and numerical water depth along the wall was approximately the same. It indicated that the simulated method was reliable. The velocity in the main flow area of the fish passage was not higher than 0.84 m/s, meeting the requirements of fish passage. The fish passage object could be traced smoothly in the fish passage. The slow flow or return area on both sides of the main flow could be used for fish rest, which showed the rationality of the fish passage shape. The depth of the shallowest water increased from 1 cm without diversion sill to 2.4 cm with diversion sill. After scarification, although the upper water flow could still overflow the diversion scarp and enter the pool chamber, the shallowest water depth on the left side of the pool chamber was about 0.5 cm higher than that on the right side, and the water depth growth was smaller. The fishway proposed in this paper enriches the form of fishway and can guide design and construction of similar fishways. [ABSTRACT FROM AUTHOR]

The plants in the river not only purify the water quality, but also increase the resistance of the river and raise the water level. Therefore, the resistance of river with plants is one of the current research hot spots. Plastic grass was used to simulate vegetation, and an open channel with trapezoid cross section was built to study the influence of water depth, velocity and plant spacing to the resistance of open channel with submerged vegetation in this paper. Through the force analysis of the research water body, the calculation formula of the average shear stress of the bed surface was derived. According to the test results, the average shear stress of the boundary under different conditions was calculated and the change rule of the shear stress of the open channel under different flow conditions and different plant densities was analyzed. The results show that the flow velocity and plant spacing have a great influence to the boundary shear stress, while the water depth has a relatively smaller influence to the boundary shear stress. [ABSTRACT FROM AUTHOR]

The natural-like fishway has a similar flow pattern to the natural river, and it has more ecological functions comparing to the traditional technical fishways. It is more conducive to fish migration. However, it is difficult to deviate from the design concept of the traditional technical fishway in China. In order to obtain a fishway with comprehensive ecological functions, a type of vegetative fishway constructed by plant modules was presented, and its hydraulic characteristics and fish passing performance were studied by experiments. Before we conducted the experiment, we need to select a proper type of plants to construct the fishway. The biological characteristics and growth cycle of the target plants should match with the migration season of the target fish. Four major domestic fish (green, grass, silver carp, bighead carp) were selected as the target fish, and the fishway was designed based on their swimming ability and migration season. Generally speaking, the four major domestic fish have similar biological index: the body length ranges from 0.2 to 0.9 m, the induced flow velocity is generally 0.1 to 0.2 m/s, the sustained swimming speed is 0.8 to 1.3 m/s, and the burst swimming speed is more than 1.3 m/s. According to the current fishway design practice in China, the control section velocity of the fishway was controlled at 1.1 m/s. The migration season of the four major domestic fish is also comparatively consistent, from April to August. Upon comprehensive consideration, reed was selected to build the fishway. Reed is widely distributed in China and has strong vitality. Its biological characteristics and growth cycle can match the migration season of the target fish. The physical model test was designed to verify the water-blocking effect of the emergent plants in the channel, so as to form a proper flow structure. In the model, the reed plants were simplified firstly, and then the individual plants were arranged to form the plant module. In this paper, the reed was simplified to single stem, and the water-blocking effect of the plants was weakened to some extent because of the removal of leaves. The physical model was designed according to the gravity similarity, and the length scale was 1:5. Firstly, the prototype reed was scale down according to the length scale. Two schemes were carried out to the physical model. The plant with full arrangement schemes was used to test the water-blocking effect of a reed plant module with 156 plants/m2 density. The staggered arrangement of plant modules was carried out for analyzing whether the flow structure can meet the requirements of fish from the view of hydraulics. The results showed that the reed plant module with 156 plants/m2 density had good water blocking effect, and the plant module could decelerate the flow velocity effectively. The staggered arrangement of plant modules could form a meandering flow in the fishway. The flow pattern was rich and changeable, and the flow velocity was effectively controlled to less than 1.1 m/s, which can meet the needs of fish migration. Fish passing test were carried out to check out the feasibility of the designed nature-like fishway in this paper. The juvenile grass carp was selected as the test fish. Considering the size of the fish path and the velocity of flow, juvenile grass carp with body length of (10±2) cm was selected. The critical swimming speed of juvenile grass carp in this experiment was about 0.95 m/s and the penetrating swimming speed was about 1.17 m/s. We carried the fish passing test in two cases, with different water depth in the fishway, the fish performance in the designed fishway was recorded. The results showed that, the success passing rate was 90% in the first case, with an average passing time of 66 s, and 100% in the second case, with an average passing time of 67 s. Through the fish passing test, it was proved that the fish can pass smoothly in the fishway with staggered arrangement of plant modules, and the plant modules can provide rest areas in the downstream side for the migration fish. The good performance of the migration fish verifies staggered arrangement of plant modules was reasonable. This paper had positive reference value to the design and reconstruction of the existing natural-like fishway. The nature-like fishway constructed by reed in this paper enriches the fishway form, which can guide the design and construction of similar fishways in the future. [ABSTRACT FROM AUTHOR]

In this paper, the causes of mass loss of throwing materials in flood control of the Yellow River were analyzed and the stress analysis model of throwing body in moving water was established with gabion as the research object. Based on the force analysis of gabion, the influence of the velocity and depth of the dangerous section to the stability of the throwing materials was studied. The results show that increasing velocity and water depth can lead to poor stability of the throwing materials in the dynamic water and increasing weight (size) of throwing materials can effectively reduce the displacement and enhance its stability. Finally, some measures are put forward, such as designing a reasonable weight throwing materials, reserving enough throwing distance or using linked gabion system to ensure the stability. [ABSTRACT FROM AUTHOR]

In order to solve effectively the problems of lower transport efficiency and higher utilization cost during the process of the long-distance transportation for the agricultural products, a kind of agricultural mechanical transport mode having a wide and great application prospect is proposed and known as the technique of tube-contained raw materials pipelines hydraulic transportation. The technique of tube-contained raw materials pipelines hydraulic transportation is the freight transportation mode that uses a fluid to suspend (float) and pull (drive) the pipe vehicle filled with the agricultural products from one location to another through a pressurized pipeline. According to the kinetic mechanism of the pipe vehicle, the mathematical models of the cyclical slit flow with the moving boundary under the different cyclical slit widths in the technique of tube-contained raw materials pipelines hydraulic transportation were established in this paper. The mathematical models were solved by adopting the RNG k-ε turbulent model, the 6DoF coupling model and the PISO algorithm of the commercial software Fluent. The effects of the cyclical slit width on the internal hydraulic characteristics of the flow velocity and the pressure in the cyclical slit flow with the moving boundary were obtained. At the same time, through a wide of experimental investigations, the cyclical slit flow with 4 widths of 0.025, 0.02, 0.015, 0.01 m respectively were studied by using the Laser Doppler velocimeter (LDV) when the pipe vehicle moved within the pipelines. The experiment was carried out in the parallel straight pipe section of the test piping system, whose the control flow was 50 m3/h, carrying the loading of 800 g. The flow field characteristics such as the instantaneous velocity of the pipe vehicle with the moving boundary, the average axial velocity of the cyclical slit flow, the pressure distributions through the static wall of the pipeline and the velocity distributions of several typical sections were obtained. Comparing with the numerical results and experimental results, it was shown that the simulated results and the experimental results on the instantaneous velocity of the pipe vehicle with the moving boundary, the pressure distributions and the velocity distributions of the cyclical slit flow in the technique of the tube-contained raw materials pipelines hydraulic transportation were in substantial agreement, and the maximum relative error did not exceed 5.3%, which further indicated that using the commercial software Fluent was feasible for solving the hydraulic characteristics of the cyclical slit flow with the moving boundary in the technique of tube-contained raw materials pipelines hydraulic transportation; The overall pressure of the cyclical slit flow with the moving boundary within the pipelines showed a decreasing trend at the inlet of the cyclical slit areas, an increasing trend in the central location of the cyclical slit areas and a precipitous decline trend again at the outlet of the cyclical slit areas along the static boundary of the pipeline. The near-wall pressure of the moving boundary of the pipe vehicle was slightly higher than that of the static boundary of the pipeline. With the increasing of the cyclical slit width, the range in distributions of the low-velocity areas formed by the near-wall of the moving boundary at the inlet of the cyclical slit space increased gradually. As the cyclical slit width increased, the pressure drop increased gradually at the inlet of the cyclical slit areas while the pressure drop at the central location of the cyclical slit areas decreased significantly. The hydraulic characteristics of the cyclical slit flow with the moving boundary was affected not only by the structural parameters of the pipe vehicle, but also by the flow field of the upstream and the downstream of the pipe vehicle with the moving boundary within the pipelines. The study of this paper not only improved the relevant theories of the cyclical slit flow with the moving boundary, but also provided a feasible method for further study on the hydraulic characteristics of the cyclical slit flow with the moving boundary in the technique of tube-contained raw materials pipelines hydraulic transportation. [ABSTRACT FROM AUTHOR]

In order to study the diversion effect of repeatedly assembled diversion pile dam in the lower Yellow River and to control the abnormal river regime in the lower Yellow River, the paper took an impervious pipe pile dam as the research object and adopted the method of moving bed model test to analyze the velocity distribution and the shape of the main flow line of the impervious pile dam under different flood conditions (Q=800, 4 000,8 000 and 12 000 m3/s)and the position of top wash. The results show that with the increase of peak discharge, the velocity of the river section is increased, and the top scour position of the flow is gradually moved downward and the main flow is close to the pile dam. The impervious pipe pile dam can control and guide the river regime of the lower Yellow River. [ABSTRACT FROM AUTHOR]

In order to prevent the severe corrosion damage ca used by direct contact between base material of the pipeline and conveying medium, internal coating is widely applied in the development of acidic gas wells in Sichuan Chongqing gas field. Factors such as corrosion characteristics of the conveying medium and high flow rate can impact on the internal wall coating of pipelines, and flow rate plays the most crucial role. In this paper, the erosion resistance and electrochemical corrosion resistance of three different inner coatings were tested under the set conditions. The outcome suggests that the corrosion resistance of the coating decreases with the increases of corrosive medium velocity under the condition of erosion. When the flow rate increases, the spectral radius of three coatings decrease, which indicates that the erosion resistance of coatings decreases with the increase of velocity [ABSTRACT FROM AUTHOR]

In recent years, most researches focus on the same height at the bottom of both main and side canal to study the hydraulic performance of water diversion. However, in practice, the height of main and side canal bottom are different in most irrigation districts. In this paper, the effect of the height of the side canal bottom on the hydraulic performance of bleeder was studied. The prototype test was carried out in Northwest A & F University in Yangling, Shannxi of China. In the prototype test, both the main channel and side channel were rectangular. The length of the main channel was 12-m long and 0.46-m wide. The length of the side channel was 2.5 m, and the width was adjustable in the range of 0.46-0.14 m. The elevation of the side channel was 0.06, 0.08 and 0.1 m higher than the bottom elevation of the main channel. A total of 8 flow sections were set up, 5 of which were at the water inlet. In order to analyze the water surface variation at the water diversion of the main channel, 3 measuring points at section I, section II, section III, section IV, section V, section VI were taken. The 3 measuring points were on the center line and 5 cm away from the wall of the main channel on both sides. The variables in the test were the side channel width and the flow rate. The water depth and velocity were determined at the measuring point. To eliminate the influence of boundary conditions, this study simplified the experimental channels. The width of the simulated main and side channels was the same as the actual width of the main and side channels. However, the lengths of the main and side channels were correspondingly extended on the basis of the actual channel length, which were 12 and 5m respectively. Because the flow field near the water-diversion changed drastically, the grid interval at the area was decreased, the cell length was 0.01 m, the remaining area cell grid was 0.02 m, and the total grid number was about 900 000. In the channel model, the inlet boundary of the main channel was set to several volume flow rates, which were 19.96, 25.2, 30.2, 36.5 and 45.32 L/s, respectively; the outlets of the main channel and the side channel were set to be free; the side wall of the channel was selected to have no sliding wall; the air above the free surface was air, and the relative pressure was 0. Based on experiments, FLOW-3D was used to simulate and calculate several flow rate and heights on the rectangular channel water diversion, compared to the measured water depths and velocity. The results showed that the variation of velocity was basically consistent with the measured value and relative error was less than 10%. It was reliable to make numerical analysis on water diversion by using FLOW-3D. The numerical simulation showed that the fluctuation of water surface at the water diversion was affected by the flow rates from the main channel. With the increasing of the bottom height, the maximum velocity and water depth of the side channel inlet section gradually decreased. At the entrance of the side channel, the turbulent kinetic energy near the upstream end was large, while at the downstream end of the branch, the turbulent kinetic energy near the bottom was small. The study provides information on water distribution and water-quantity control in irrigation area. [ABSTRACT FROM AUTHOR]

In order to solve the nonlinear problem of runoff concentration caused by excess rainfall intensity,a method deriving time-variant distributed unit hydrograph (TVDUH) based on the SCS's velocity equation was presented in this paper. A reference rainfall intensity is introduced to represent the hydraulic conditions corresponding to k values. A dimensionless factor formed by the ratio of duration excess rainfall intensity to reference rainfall intensity is added in SCS's equation to make up a new velocity equation that can take into account of the influence of excess rainfall intensity on flow velocity. The modified SCS's equation is used to derive the TVDUH of each rainfall duration during a rainfall event. A rainfall-runoff hydrological model is constructed of TVDUH and the runoff generation module of Xin'anjiang model. The rainfall-runoff hydrological model is used in Peihe River basin to calibrate the reference rainfall intensity. Application is performed in Tanjiahe River basin for validation. Results show that the number of events whose coefficient of efficiency being greater than or equal to 0.9 increases from 42% of time-invariant unit hydrograph to 83%. It is concluded that the presented method can contribute to increase the rainfall-runoff simulation capabilities of watershed hydrologic models observably. [ABSTRACT FROM AUTHOR]

In this paper, The FLUNET numerical simulation software was used to establish two-dimensional model, loading velocity, pressure and wall roughness. The flow field of the channel was calculated by using FLUENT numerical simulation software to calculate the flow field of the same flow rate and section velocity profile. The relationship between flow rate, flow velocity and roughness was studied in order to provide the basis for choosing the roughness coefficient correctly in practice. The results show that for the concrete bag lining channel, flow velocity and discharge are the factors of roughness. Through data correlation analysis, roughness is negatively correlated with velocity and discharge,the velocity gradually increases along the direction of the channel's bottom, but the maximum velocity occurs below the water surface and the lateral flow from the channel wall to the central flow, resulting in a larger velocity concentrated in the middle area. [ABSTRACT FROM AUTHOR]

As a special means of river restoration in hydraulic engineering construction, the basic function of culvertnot only provides water channels for the system of roads and bridges, but also to ensure the successful passage through the barrier for various local aquatic animal. Since there are few literature referring to the hydraulic design of culvert fish passage in China, so the theoretical basis that can provide reference for the construction of culvert fishway is limited. In this paper, the characteristics of hydraulics and flow fields for the classical baffle systems of culvert fishway, which include the following three baffles; spoiler baffle, Alberta fish-weir (AFW) and Alberta fish baffles, were summarized on the basis of summarizing the foreign experimental data and the relational expressions between flow rate, water depth, slope and velocity were obtained, the working performance of the baffles was compared and analyzed as well. Relative data and conclusion could provide a theoretical basis and reference for the internal transformation and hydraulic design of domestic culvert fishway. [ABSTRACT FROM AUTHOR]

Owing to low cost and long operational life span, screen filter is widely used in chemical industry, pharmaceutical engineering, and agricultural irrigation. In order to study the motion and spatial distribution of particles in the filter and reduce the harm of local clogging，in this paper we simulated the particles' motion under different flow rates and diameters by the method of CFD-DEM, and analyzed the effects on the particles' spatial distribution caused by flow rate and particle size. The correctness of theoretical analysis and the validity of methods were verified in experimental filtration with both clean water and muddy water under different inlet pressure. According to the velocity vector distribution and streamlines, there is a jet-flow and backflow in the filter, this causes the uneven flow field. The uneven flow field in screen filter leads to local clogging whose distribution is influenced by flow rate, particle size, streamlines and etc. Pressure and velocity distribution directly reflects the resistance characteristics of mesh which results in 77 percentage of total pressure drop. The charts about the flow rate on different mesh sections, with stepped distribution characteristics, show that flux differences are obvious on account of filter shells. The lowest flow rate is located in the middle of screen close to inlet while the highest in the upper of screen close to outlet, and the former is as high as 5.9 times that of the latter. Therefore, it is necessary to optimize the filter shell for better performance. Particles' motion and distribution shows sieve effect of mesh on the movement and distribution of sediment. Although particles which can pass through the screen will not attach themselves to the mesh surface, they will aggravate clogging when the porous medium forms on mesh surface. The higher the flow rate is, the more concentrative the particles pass through the screen and the more serious the local clogging is. For the clogged particles which are the essential factor of clogging on mesh surface, bigger ratios of filter pore size to particle size cause the particles cycling in the housing, while the smaller firmly adhere to mesh surface and are more heavily agglomerated on the mesh with the rise of flow rate. So the smaller particles can lead more serious clogging and higher pressure drop than the bigger one under the same mass. The motion of both passing particles and smaller clogging particles is closely related to streamlines and surface velocity on mesh. Along streamline, particles can easily adhere to mesh surface or pass through mesh pore in lower surface velocity. When particles move with a high-velocity or the flow field speed up by the increase of inlet velocity, the kinetic energy of particles increase and the collision becomes more frequent. This decreases the possibility through the screen and weakens particles' stability. Particles prefer to adhere to the mesh in low velocity, but rarely adhere to the mesh where the streamline does not skim over regardless of the surface velocity. When the overall velocity rises，a great deal of particles amass on the section lying on end of streamlines because of the lower velocity. In most cases, adopting high inlet velocity can increase the work efficiency, but when the ratios of filter pore size to particle size is slightly greater than 1, high inlet velocity will sharply increase the harm of local clogging. In this situation, reducing the inlet velocity can increase the uniformity of particle distribution, enhance the auxiliary effect of filter cake, prolong the effective time and the operational life span of filter, and reduce the difficulty of flushing at the cost of efficiency loss. So, in practice, the filtering accuracy and inlet pressure of the filter should be adjusted according to the particle size of irrigation water for better perform. [ABSTRACT FROM AUTHOR]

The study of flow velocity on grassland slope is of great significance to understand dynamic of erosion deeply and to make scientific decision on soil and water conservation and ecological construction in Loess Plateau. In order to study the variation of flow velocity with rainfall intensity and slope on grassland slope, in the paper, we adopted artificial rainfall experiment to study flow velocity. The results show that: a) under five different rainfall intensities and slopes, variation of flow velocities with time first increase rapidly after becoming increase slowly or stably and relationships between them can be described by the power function equations; b) average runoff velocities on grassland slopes increase with the increase of rainfall intensities and slopes respectively, which can be described by the logarithmic function equation; c) average velocities of grassland slope with rainfall intensities and slopes can be described by the dual logarithmic function equation and in the experiment, the influence of slope on grassland average velocity is greater than the influence of rainfall intensity to the grassland average velocity. [ABSTRACT FROM AUTHOR]

Once the fishway is completed in the traditional style and the flow condition is basically fixed. It will be hard for a variety of fish to go through it at the same time. To solve the problem, in this paper, we developed a Tai Chi fish-way, which can form a rich flow regime and adapt to the migration of many fishes. Based on the ancient Taoist philosophy of “Tai Chi Eight Diagrams”, Tai Chi fishway created a flow changing environment when the eight diagrams rolled, which can offset the general fishway's shortcoming, “once built, water conditions were basically fixed”. The pool room of the Tai Chi fishway was arc-shaped, which was connected by a reverse arc smoothly. Through the diffusion and aggregation of water, it can help the water flow more smoothly, and reduce the adverse effects of turbulence, vortex and so on. The wall of the pool room was provided with external eight diagrams (groyne type clapboards), which offered resistance to the water flow and helped change its direction when flowing through. The migratory fishes may rest below the external eight diagrams. Tai Chi disk was also set in the pool room and the S shaped channel on the disk had the function of dispersing water flow and dissipating energy. The Tai Chi disk and internal eight diagrams partition can rotate in certain cycles which were combined into different operating conditions at different times to create conditions for the polymorphism of the stream. For Tai Chi fishway had its unique pool room structure, the physical model test alone was difficult to capture the flow structure in detail, and it was time-consuming, too. We used a method combined with the physical model test and numerical simulation to study the flow characteristics of Tai Chi fishway in different conditions. Physical model test was used to study the variation of water level along the course and the basic flow pattern of water flow, and the CFD numerical simulation method was applied to determine the distribution of the surface and internal flow fields which were difficult to be measured by the physical model. Then the water level and flow pattern were compared and verified with each other after being obtained via the two methods. In accordance with the relevant norms of fishway designs and gravity similarity criteria, the fishway physical test models were made. Before the installation of the Tai Chi disc and external and internal eight diagrams, a water test and a measurement of the water depth along the center line were conducted. After the installation of Tai Chi disc, the test was divided into two groups to measure the water depth along the center line. The S shaped channel was approximately parallel and vertical to the flow. In each case, Tai Chi disk placement angle was consistent. The above three situations were simulated by numerical calculation. The results showed that they had a same trend. The maximum error was 13.6%, within the allowable range of 15%. Therefore, the calculation model was reliable and can be used to simulate the complex flow field of the pool room. Therefore, the surface velocity, bottom velocity and critical cross section velocity were further analyzed. The results showed that the Tai Chi fishway had significant energy dissipation reduction effect. The shallowest water depth was twice of that of the corresponding shallowest water depth without the Taichi disk. Average maximum velocity of cross section decreased by more than 50%, the flow presented polymorphism, Tai Chi disk's different positions also made flow change, which can provide more suitable conditions for migratory fish. [ABSTRACT FROM AUTHOR]

The nature-like fish way is one of the most promising layouts of fish pass structures, its remarkable characteristics are that the individual cobblestone weirs from local river bed substrates are adopted in the fishway construction to imitate as closely as possible the flow pattern of Natural River. Therefore it has higher running efficiency for fish migration than traditional technical fishways. In order to identify the differences of the hydraulic characteristics between the nature-like fishway and the traditional fishway, we conducted comparative studies. The three-dimensional mathematical models of the fishways with cobblestone weirs and water proof weirs were developed respectively. The cobblestone weirs had porosity about 12%. It was defined as the ratio of pervious area to total area of the vertical section along with the longitudinal direction. Each mathematical cobblestone feature was defined as obstacles with special shapes as the natural one. The gaps between the cobblestones allowed water to pass through existing calculation elements. A hydraulic model of the fishway with cobblestone weirs was designed based on the law of gravity similarity at a scale of 1:5. The fishway structure of the model test was consistent with the mathematical model. The water depth and velocity at typical measurement points were recorded. The results were used to verify the numerical model. In the scenario that the fish way upstream and downstream water depth was 1.4 m, the hydraulic characteristics in the fish ways, such as flow pattern, flow velocity, turbulence kinetic energy, and flow rate were compared. The results showed that the currents coming from the cobblestone gaps improved the flow dynamics conditions in the pools. The velocity distributions of the gaps in the staggered weirs appeared as the velocities of the surface were smaller than the bottom; the velocities of the sides were smaller than that of the middle. Obviously, using permeable weir fishway, the abundance of velocity distribution for fish was quite obvious, and the velocity distribution of impervious weir fishway was close to uniform. Turbulence in the mainstream can attract fish back to migration, the turbulence kinetic energy (TKE) was considered as a potential index to assess the suitability of the fishway structure. The turbulent intensity preferred by fish may depend on their swimming capabilities. In the fishways with cobblestone weirs, the TKE had greatly increased; the TKE on the surface was higher than that near the bottom. As the water surface of each of the pool was kept at the same level, the water consumption flow is very different between the impervious weir and cobblestone weir fishway. The consumption flow of the impervious weir fishway was Q=1.39 m3/s, while the consumption flow of the cobblestone weir fishway was Q=2.86 m3/s, which was increased to about twice. Thus, the nature-like fishways with cobblestone weirs needed more water flow in operating. The flow pattern of the nature-like fishway was rich and varied, and it was closer to the natural river; environment. As such it provided abundant hydrodynamic conditions for different types of migration fish. The effecting factors on the hydraulic characteristics of the nature-like fishway were analyzed, such as partition type, bottom slope, and different operation depth and so on. In general, the simulation technique of nature-like fishway was still at the exploratory stage, and the study should be further developed with a consideration with special life habits of migratory fish. The approach used in this paper can provide reference for the hydraulic design and optimization of nature-like fishway. [ABSTRACT FROM AUTHOR]

The characteristics of microfluidic devices are different from those of ordinary fluid devices. One of the most important features of microfluidic devices is the decrease of their characteristic scale. This feature leads to a lot of differences in microfluidic device. Two major differences are included. There are the flow law of the fluid and the physical properties of fluid. The flow law of the fluid in a microfluidic device is different from that in an ordinary fluid device. The physical properties of the fluid in a microfluidic device also differ from that in an ordinary fluid device. The emitter channel is small in size from the point view of its width. As a result, the emitter belongs to the microfluidic device. Therefore, the applicability of Navier-Stokes (NS) equations has been controversial in the analysis of the flow characteristics in the emitter channel. In order to verify the suitability of the continuity medium hypothesis in design of the emitter, the lattice Boltzmann method (LBM) was used to study the flow characteristics of the emitter in this paper. The flow rate field on a specific plane obtained by different numerical methods was analyzed. The numerical methods were LBM and the computational fluid dynamics (CFD) method which was based on the finite volume method. The flow rate field obtained by using the two numerical methods was also compared with the experimental results. The flow rate with larger flow rate gradient of the straight line on the specific plane was also compared and analyzed. Firstly, the mesh independent analysis was made in order to guarantee the numerical accuracy of numerical results. Secondly, the numerical results were compared with those obtained by the finite volume method (FVM) based on the assumption of continuous medium. The numerical results were also made a comparison with the particle image velocimetry (PIV) experimental results. The average relative deviations of the results of the LBM calculation from the experimental values of PIV were analyzed. In addition, the average relative errors of the results of the FVM calculation from the experimental values of the PIV were also analyzed. By comparing flow rate contours, the results showed that the overall flow rate field calculated by the LBM in the specified cross section was in good agreement with the flow rate field measurement by the experiment, and the results also showed that the flow rate field calculated by the CFD method in the specified cross section was in good agreement with the flow rate field measurement by the experiment. The flow rate contour which was calculated by the LBM or CFD showed a large flow rate gradient at the corner of the contraction section. Comparing the flow rate on the specified measurement line, CFD reached its maximum flow rate on the measurement line where the distance was 0.482 mm, and the flow rate obtained by using the computational fluid dynamics method which was based on the finite volume method was 1.176 m/s. The flow rate of PIV experimental results was 1.09 m/s. The flow rate obtained by using the LBM reached its maximum value, and the result of the flow rate obtained by using the LBM was 1.06 m/s. Therefore, the relative error of flow rate obtained by using the CFD from the experimental result at 0.482 mm was 7.8%, which was larger than that of LBM which had the relative error of 2.7%. In view of the arithmetic mean of the relative deviation, the results showed that the arithmetic mean of the relative deviation of the CFD deviation from the PIV experiment was 0.139%, while the arithmetic mean of the relative deviation of LBM deviation was 0.115%. The results were very close. Therefore, the computational fluid dynamics method based on the assumption of continuous medium is applicable for analysis of the flow field in the emitter which has the characteristic size of 1 mm. [ABSTRACT FROM AUTHOR]

Soil crust plays an important role in rainfall, runoff and erosion process. When it comes to the present situation, most studies analyze the impact mechanism of soil erosion on the existence of soil surface crust, through comparison analysis of sediment yield, runoff producing and characteristic of hydrodynamic under the crust and no crust slope. However, limited studies report on the characteristic of soil sediment yield, runoff produced and the rule of feature variation for hydrodynamic, also, no quantitative evaluation about the hydraulics parameter's influence on sediment yield. Therefore, in our research, according to crust strength variation and hydrodynamic characteristic under different crust strength, we conducted quantitative analysis on the impact of crust on slope erosion, and through comparison analysis for characteristic of slope sediment yield, under different crust intensities. We further analyzed the change features of hydraulics parameter under slope erosion, and described strength of effect quantitatively under influence factor, for providing important material to predicate accurately and effectively slope soil erosion. In this paper, the impact mechanism of soil crust on slope erosion was reported using quantitative analysis method. The strength of soil crust change of 4 soil types (Lou soil, Loess soil, Heilu soils and Huangshan soil) under 3 rainfall intensities (60, 90, 120 mm/h) was analyzed. Our results showed that the relationship between the crust strength and rainfall intensity was complex when soil water content was more than 30%. However, when soil water content was less than 30%, crust strength increased with the increase of rainfall intensity. Taking the 10° slope of Lou soil as an example, sediment yield, shear stress, resistance coefficient and flow velocity of different crust strength under artificial rainfall experiments were determined and analyzed. The existence of crust could reduce slope sediment yield effectively, and the sediment yield of no crust slope was 1.24-8.72 times more than crust slope's. The crust on slope effectively reduced the erosion and sediment yield. The greater the crust strength was, the stronger the reduction was. The flow shear stress, stream power, resistance coefficient of no crust slope were all larger than the crust slope, but for crust slope, flow shear stress of various crust strength was not significant different (P>0.05). Stream power and flow shear stress were enhanced with increase of crust strength. The larger crust strength was, the smoother surface was, the larger flow velocity was, the smaller resistance was, which improved the stream power. The stream power of high strength crust was larger than low strength crust, but with the smaller sediment yield, its resistance of slope was large. Therefore, the formation of soil erosion was synthetic result of erosion dynamic, slope resistance and soil anti-erodibility. The grey correlation analysis showed that with the increase of the soil crust strength, the influence of the stream power on the erosion of the soil was decreased, and the effect of the resistance coefficient was increased. Therefore, there was a positive effect of water flow on sediment reduction, and the soil erosion resistance of the soil was enhanced with the increase of crust strength, so the erosion amount of soil would decrease greatly. [ABSTRACT FROM AUTHOR]