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.

Sedimentary characteristics and internal architecture of a river-dominated delta controlled by autogenic process:implications from a flume tank experiment

Autogenic processes are widely found in various sedimentary systems and they play an important role in the depositional evolution and corresponding sedimentary architecture.However,autogenic processes are often affected by changing allogenic factors and are difficult to be identified and analyzed from modern and ancient records.Through the flume tank experiment under constant boundary conditions,the depositional process,evolution principles,and the sedimentary architecture of a river-dominated delta was presented,and a corresponding sedimentary architecture model was constructed.The evolution of river-dominated delta controlled only by autogenic process is obviously periodic,and each autogenic cycle can be divided into an initial progradational stage,a middle retrogratational stage,and a late aggradational–progradational stage.In the initial progradational stage,one feeder channel incised into the delta plain,mouth bar(s)was formed in front of the channel mouth,and small-scale crevasse splays were formed on the delta plain.In the middle retrogradational stage,the feeder channel was blocked by the mouth bar(s)which grew out of water at the end of the initial stage,and a set of large-scale distributary splay complexes were formed on the delta plain.These distributary splay complexes were retrogradationally overlapped due to the continuous migration of the bifurcation point of the feeder channel.In the late aggradational–progradational stage,the feeder channel branched into several radial distributary channels,overlapped distributary channels were formed on the delta plain,and terminal lobe complexes were formed at the end of distributary channels.The three sedimentary layers formed in the three stages constituted an autogenic succession.The experimental delta consisted of six autogenic depositional successions.Dynamic allocation of accommodation space and the following adaptive sediments filling were the two main driving factors of the autogenic evolution of deltas.

Flume Experiment on Stream Blockage by the Debris Flow From Tributary

Stream blockage by the debris flow from tributary valleys is a common phenomenon in mountainous area,which takes place when large quantities of sediment transported by debris flow reaches a river channel causing its complete or partial blockage.The dam formed by debris flow may causes upstream and downstream flooding,and presents great threat to people and property.Because of the catastrophic influence on people and property,debris-flow dam has attracted many attentions from the researchers and local adm...

Hydrodynamic Characteristics of the Biplane-Type Otter Board with the Canvas Through Flume−Tank Experiment

Hydrodynamic characteristics of a biplane-type otter board,equipped with nylon canvas of 2 mm in thickness was investigated through flume-tank experiment in this study.A series of predesigned structures with different gap-chord ratios G/c(0.75,0.90,1.05),stagger anglesθ(30°,45°,60°),and proportions of flexible area relative to the whole wing areaƒr(0,55%,65%,75%),at an aspect ratio of 2.0 and a camber ratio of 15%,were experimentally carried out.The results showed the solution referring to the usage of flexible canvas replacing part of rigid structure for the biplane-type otter board was efficient for the trawling in the middle or shallow water area.The improvement of lift and stability for the biplane-type otter board was concluded,and drag of the structure was reduced by 1.9%atƒr=55%.In addition,the coefficient of variation of the lift and drag coefficient at different current velocities were 2.69%and 2.28%,respectively,which was smaller than those at relatively large proportion of the flexible area.Compared with the other tested structures,the frame-type flexible structure with the gap-chord ratio of 0.9 and a stagger angle of 45°and the proportion of the flexible area of 55%,performed best,and its drag was reduced by 5.72%and lift increased by 4.8%,compared with the rigid biplane-type otter board at the angles of attack from 18°to 28°.

Modeling of breaching parameters for debris flow dams

The debris flow dam is a common type of barrier dams,which shows significant differences from other types of barrier dam such as landslide dam,moraine dam in their formation processes,dam body shapes,and internal compositions.The basic breaching parameters such as flood peak discharge are vital indicators of risk assessment.In this study,we elucidated the failure process of the debris flow dam through the flume experiment,and built the calculation equation of the breaching parameters by selecting critical factors.The result shows that the overtopping failure process of the debris flow dam is capable of forming significantly retrogressive scarps,and the failure process experiences three stages,the formation of the retrogressive scarp,the erosion of the retrogressive scarp,and the decline of the retrogressive scarp.Five factors used for establishing the calculation equations for peak discharge(Qp),final width(Wb)of the breach,and duration(T)of the debris flow dam failure are dam height(h),reservoir capacity(V),the fine grain content(P0.075)of the soil,the nonuniformity coefficient(Cu)of the soil,and the upper limit grain size(D90)of the soil,respectively.In the three equations,the correlation coefficients between Qp,Wb,T and the five factors were 0.86,0.70,0.63,respectively.The equations still need to be modified and verified in actual cases.

A new statistical model of wave heights based on the concept of wave breaking critical zone

When waves propagate from deep water to shallow water, wave heights and steepness increase and then waves roll back and break. This phenomenon is called surf. Currently, the present statistical calculation model of surf was derived mainly from the wave energy conservation equation and the linear wave dispersion relation, but it cannot reflect accurately the process which is a rapid increasing in wave height near the broken point. So, the concept of a surf breaking critical zone is presented. And the nearshore is divided as deep water zone, shallow water zone, surf breaking critical zone and after breaking zone. Besides, the calculation formula for the height of the surf breaking critical zone has founded based on flume experiments, thereby a new statistical calculation model on the surf has been established. Using the new model, the calculation error of wave height maximum is reduced from 17.62% to 6.43%.

和水文地理模式相关的淤积三角洲前积层沉积速率的水槽实验（英文）

Foreset profiles of deltaic topography change corresponding to hydraulic conditions,and are influenced by water discharge and change rates of water discharge.To investigate the correlation between the transition of deposition rates on the foreset and the change rate of water discharge of temporary waxing and subsequent waning flows,we perform experiments on silty deltas that developed under several different hydrographic patterns.The findings are as follows:(1) Under flows with constant discharge,the deposition rate on the foreset was low at high water discharge and high at low water discharge because the separated flow became vigorous at high water discharge and prevented sediment supply onto the foreset.If the water discharge is not constant,the deposition rate shifted concurrently with water discharge only at extremely low change rate.(2i) In a waxing flow at low(but not extremely low) increase rate,the deposition rate gradually decreased with some time lag.(2ii) In the case of high increase discharge,intense erosion on the topset caused by rapid waxing made a large amount of silt move onto the foreset and the deposition rate temporary increased.(3) With ample time after waning stage,the deposition rate recovered to that at constant low water discharge in all runs.However,the transitional processes depended on not only waning rate but also waxing rate at before waning stage.(3i) In the case of high decrease rate of water discharge,the deposition rate abruptly decreased regardless of increase rate.(3ii) Even in the case of low decrease rate of water discharge,if the increase rate before waning stage was high,the deposition rate abruptly decreased.(3iii) Only in the case where both the increase rate and the decrease rate were low,deposition rate gradually increased.

Natural consolidation characteristics of viscous debris flow deposition

Pore water pressure and water content are important indicators to both deposition and consolidation of debris flows, enabling a direct assessment of consolidation degree. This article gained a more comprehensive understanding about the entire consolidation process and focused on exploring pore water pressure and volumetric water content variations of the deposit body during natural consolidation under different conditions taking the viscous debris flow mass as a study subject and by flume experiments. The results indicate that, as the color of the debris changed from initial dark green to grayish-white color, the initial deposit thickness declined by 3% and 2.8% over a permeable and impermeable sand bed, respectively. A positive correlation was observed between pore water pressure and depth in the deposit for both scenarios, with deeper depths being related to greater pore water pressure. For the permeable environment, the average dissipation rate of pore water pressure measured at depths of 0.10 m and 0.05 m were 0.0172 Pa/d and 0.0144 Pa/d, respectively, showing a positivechanging trend with increasing depth. Under impermeable conditions, the average dissipation rates at different depths were similar, while the volumetric water content in the deposit had a positive correlation with depth. The reduction of water content in the deposit accelerated with depth under impermeable sand bed boundary conditions, but was not considerably correlated with depth under permeable sand bed boundary conditions. However, the amount of discharged water from the deposit was greater and consolidation occurred faster in permeable conditions. This indicates that the permeability of the boundary sand bed has a significant impact on the progress of consolidation. This research demonstrates that pore water and pressure dissipations are present during the entire viscous debris consolidation process. Contrasting with dilute flows, pore pressure dissipation in viscous flows cannot be completed in a matter of minutes or even hours, requiring longer completion time — 3 to 5 days and even more. Additionally, the dissipation of the pore water pressure lagged the reduction of the water content. During the experiment, the dissipation rate fluctuated substantially, indicating a close relationship betweenthe dissipation process and the physical properties of broadly graded soils.

Experimental Study of Pore Water Pressure and Bed Profile Change Under Regular Breaking Waves

There lies a close relationship between the seabed destruction and the distribution of pore water pressure under the action of breaking wave. The experiments were carried out in a wave flume with a 1：30 sloping sandy seabed to study regular breaking wave induced pore water pressure. A wide range of measurements from the regular wave runs were reported, including time series of wave heights, pore pressures. The video records were analysed to measure the time development of the seabed form and the characteristics of the orbital motion of the sand in the wave breaking region. The pore water pressure in the breaker zone showed the time variation depending on the wave phases including wave breaking and bore propagation. The time-averaged pore water pressure was higher near the seabed surface. The peak values of pore water pressure increase significantly at the breaking point. The direction of pore water pressure difference forces in the breaker zone is of fundamental importance for a correct description of the sediment dynamics. The upwards- directed pressure differences may increase sand transport by reducing the effective weight of the sediment, thereby increasing the bed form evolution. The seabed configuration changed greatly at the wave breaking zone and a sand bar was generated remarkably. The amplitude of the pore water pressure changed with the seabed surface. The results are to improve the understanding of sand transport mechanisms and seabed responses due to breaking regular waves over a sloping sandy bed.

Numerical and Experimental Analysis of A Vertical-Axis Eccentric-disc Variable-Pitch Turbine(VEVT)

A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on doubleblock mechanism is proposed.The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine,and the three-dimensional model of the turbine is established.Kinematics analysis of the eccentric disc pitch control mechanism is carried out.Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived.Kinematics analysis and simulation are carried out,and the motion law of the corresponding mechanical system is obtained.By analyzing the force and motion of blade of VEVT,the expressions of the important parameters such as deflection angle,attack angle and energy utilization coefficient are obtained.The lateral induced velocity coefficient is acquired by momentum theorem,the hydrodynamic parameters such as energy utilization coefficient are derived,and the hydrodynamic characteristics of VEVT are also obtained.The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions,which verifies that VEVT has good self-startup performance and high energy capture efficiency.

Experimental Investigation of the Response of Monopiles in Silty Seabed to Regular Wave Action

Excessive displacement responses of monopiles affect the serviceability of offshore structures.Related to complicated pile−seabed−wave interactions,the actual behavior of monopiles in silty seabed under periodic wave action remains unclear,and relevant studies in the literature are limited.A series of experiments were conducted in a wave flume containing single piles in silty seabed with relative density of 0.77 subjected to regular waves.Two stages of wave loading were applied successively,accompanied by data recording which included pore water pressure,water surface elevation,pile head displacement,and pile strain.Development of pile-head displacement and pore pressure in silty seabed was the main focus,but the effects of pile diameter,pile type,and pile stiffness were also investigated.The experimental results indicate that,in silty seabed,piles of large diameter or with fins accelerate soil liquefaction,resulting in strengthened soil which allows a higher upper boundary of pore pressure.Using fins at deeper locations led to a quick failure of the piles,but the opposite result was observed with an increase in fin dimensions.Once pile-head displacement entered its rapid development period,the wave load calculated via the pile moment was an overestimation,especially for the piles of large diameter.

Scour around submarine pipes due to high-amplitude transient waves

Estimation of scour dimensions below submarine pipelines is a vital step in designing offshore infrastructure.Extreme events like tsunami waves produce strong erosive forces below the underwater pipes,apt to create scour holes,jeopardizing the safety of the structure.Despite the importance of this issue,previous studies have mainly focused on steady flow cases,and the scour pattern below submarine pipes induced by high-amplitude transient waves has rarely been investigated.This paper reports the results of 40 experimental runs on transient wave-induced scour below a model pipe in a laboratory flume under a variety of initial conditions.The variables included the bed particle size and gradation,initial water depth,wave height,and slope of the bed layer.Waves were generated by a sudden release of water from a sluice gate,installed in the middle of the flume.A pressure transducer data acquisition system was used to record the wave heights at different time steps.The results indicate that,with a shallower initial depth of flow,the scour depth is relatively large.It was also found that there exists a direct correlation between the induced wave height and the size of the scour hole.It was observed that,in clear water conditions,the size of the scour hole in coarse sediments is smaller,while in live-bed conditions,larger scour holes are created in coarser sediments.It was also observed that at high wave amplitudes,the live-bed conditions are dominant,and consequently the bed elevation is altered.

Experimental Simulation Study of the Dominant Enrichment Area of Terrestrial Organic Matter in the Shallow-Delta Sedimentary System of the Yacheng Formation in the Qiongdongnan Basin

Shallow-delta sedimentary systems receive both terrestrial and marine organic matter. As oil and gas exploration activities determine that the source rocks of the deep-water area of the Qiongdongnan Basin, northern South China Sea, are generally rich in and even dominated by terrestrial organic matter, this has led many researchers to examine the rules governing terrestrial organic matter enrichment in shallow-delta sea sedimentary systems. However, the deep burial of source rocks in deep-water areas and the relatively small amount of drilling undertaken have greatly restricted the study of these rules. In this study, the ‘forward modeling' research method was used to observe and analyze the deposition and preservation of terrestrial organic matter through flume experiments, where the depositional results were carefully depicted and sampled. The total organic carbon content of selected samples was measured and when combined with qualitative observations and quantitative comparison results, the dominant enrichment areas of terrestrial organic matter were identified. The experimental results show that the overbank parts of the delta front, the dune countercurrent surface, the low-lying parts, the delta front slope area and the shallow-prodelta sea area are where terrestrial organic matter is predominantly enriched. This provides an important basis and guidance for the prediction of the development areas of marine source rocks with terrestrial input in the deep-water areas of the Qiongdongnan Basin.

A STUDY OF DRAG COEFFICIENT RELATED WITH VEGETATION BASED ON THE FLUME EXPERIMENT

This study is focused on the effects of ecological factors （diameter and flexibility） and vegetation community composition on the drag coefficient related with vegetation. The single leafy shrub and three mixed communities （including shrub-grass, shrub-reed and reed-grass community） were studied. The flow velocity and water level were measured and used to calculate the drag coefficient based on the Bernoulli＇s equation, Darcy drag formula and the expression for the drag coefficient related with Darcy drag factor. The trend of the drag coefficient in the vertical direction was analyzed against flow depth, diameter, diameter P（eynolds number, flow depth Reynolds number and relative roughness height in different discharges. The results show that beside the dense leafy shrubs community, the vertical trend of the drag coefficient among other cases against flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height can be approximately expressed by power law functions under different flow discharges. Moreover, in a mixed community with two plants with distinctly different ecological factors, the one with the most distinct variations of ecological factors determines the vertical trend of the drag coefficient; the other one only affects the magnitude of the drag coefficient. Furthermore, if the ecological factors of the vegetation in the vertical direction are kept almost not changed, the drag coefficient can be approximately regarded as a constant.

SOME NEW DATA AND FORMULAS FOR RESISTANCE FLOW IN FLUVIAL OPEN CHANNELS

Flow resistance in fluvial open channels, especially in steep gravel-bed channels, still presents challenges to researchers and engineers. This article presents some new data from both the flume experiments and field measurements. Data analysis using the divided hydraulic radius approach shows that the relative roughness plays a significant role in the bed form resistance. A new set of formulas that incorporate the relative roughness are proposed. As compared with several existing formulas, the proposed formulas can be used to better estimate the bed form resistance.

Measuring Internal Velocity of Debris Flows by Temporally Correlated Shear Forces

Debris flow is a kind of geological hazard occurring in mountain areas.Its velocity is very important for debris flow dynamics research and designing debris flow control works.However,most of past researches focused on surface velocity and mean velocity of debris flow,while few researches involve its internal velocity because there is no available method for measuring the internal velocity for its destructive power.In this paper,a method of temporally correlated shear forces（TCSF） for meas-uring the internal velocity of debris flows is proposed.The principle of this method is to calculate the internal velocity of a debris flow using the distance between two detecting sections and the time differ-ence between the two waveforms of shear forces measured at both sections.This measuring method has been tested in 14 lab-based flume experiments.

Study of bedload transport in backwater flow

This paper studies the flow structure and the bedload transport regime in backwater flows, to provide a theoretical support for solving the sediment transport and bed scour problems in rivers or reservoirs with backwater. The bedload transport rates under different conditions are analyzed first on the basis of theoretical analysis, measurement comparison and flume experiment, and it is pointed out that the existing formulas for the bedload transport rate are not applicable for the bedload transport rate in backwater flows. Next, the flow structure in a non-uniform flow is observed by flume experiments, and by introducing the backwater degree index, the quantitative relation between the relative bed shear stress and the backwater degree is obtained. Finally, the formula for the bedload transport rate applicable for the reservoir channel segment with backwater flows is obtained through measurements and flume experiments.