Hydraulic Model Experiments Research Articles

Evaluation of the Hydraulic Performance of a Rear-Parapet Vertical Breakwater under Regular Waves through Hydraulic Experiments

Climate change has resulted in increased intensity and frequency of typhoons and storm surges. Accordingly, attention has been paid to securing the breakwater’s stability to protect the safety of the port. Herein, hydraulic model experiments were conducted to evaluate the hydraulic performance of a vertical breakwater having a rear parapet. For comparison, cases in which the parapet was placed on the seaside, the harborside, and at the center of the breakwater were considered. Regular waves were used for convenient performance analysis. Five wave gauges and nine pressure transducers were installed to secure physical data for hydraulic performance evaluation. Results showed that a rear parapet can reduce the maximum wave force acting on the breakwater. Even though impulsive pressure was generated, it did not affect the stability of the breakwater owing to the phase difference between the maximum wave pressures acting on the caisson and parapet. By decreasing the maximum wave force, the required self-weight that satisfies the safety factor of 1.2 was reduced by up to 82.7%; the maximum bearing pressure was reduced by up to 47.6% compared with that of the parapet located on the seaside. Thus, the rear parapet was found to be more suitable for actual applications.

Wave Control by Tide-Adapting Submerged Breakwater

A submerged breakwater is a coastal structure built under water with excellent landscape. The depth of the crest of the breakwater should be maintained at more than a certain level in order for the submerged breakwater to control waves properly. This means that the effect of blocking waves deceases sharply at high tide in coastal areas with large tidal differences. In this study, we proposed a Tide-Adapting Submerged Breakwater (TA-SB) to overcome this problem, and then we conducted hydraulic model experiments to evaluate the performance of the TA-SB for controlling waves. The experimental results showed that the tapered wings attached to the crest of the TA-SB helped induce forced breaking waves. In particular, they were very effective in blocking waves and attenuating wave energy at high tide. In addition, the wave control performance of the proposed TA-SB was far superior to the Tide-Adapting Low-Crested Structure (TA-LCS) of the previous study.

Experimental and Numerical Investigation of Self-Burial Mechanism of Pipeline with Spoiler under Steady Flow Conditions

Herein, hydraulic model experiments and numerical simulations were performed to understand the self-burial mechanism of subsea pipelines with spoilers under steady flow conditions. First, scour characteristics and self-burial functions according to the spoiler length-to-pipe diameter ratio (S/D) were investigated through hydraulic experiments. Further, the Navier–Stokes solver was verified. The experimental values of the velocity at the bottom of the pipeline with a spoiler and the pressure on the sand foundation where the pipeline rested were represented with the degree of conformity. Scour characteristics of a sand foundation were investigated from the numerical analysis results of the velocity and vorticity surrounding the pipelines with spoilers. The compilation of results from the hydraulic experiment and numerical analysis showed that the projected area increased when a spoiler was attached to the subsea pipes. This consequently increased the velocity of fluid leaving the top and bottom of the pipe, and high vorticity was formed within and above the sand foundation. This aggravated scouring at the pipe base and increased the top and bottom asymmetry of the dynamic pressure field, which developed a downward force on the pipeline. These two primary effects acting simultaneously under steady flow conditions explained the self-burial of pipelines with a spoiler attachment.

The Reproduction Ability of a Numerical Model for Simulating the Outflow Rate of Backfilling Materials from a Coastal Structure

In very shallow areas, the frequency by which coastal structures (like dikes and seawalls) are directly broken by large wave forces is low because large waves are broken in deeper areas. The main cause for such destruction is ground scour in front of the structures and outflow of backfilling materials by middle-scale waves; therefore, the scour and the outflow should be considered when designing a coastal structure in a very shallow area. In this paper, a numerical model consisting of CADMAS-SURF, which can calculate fluid motion in porous media, and empirical equations for simulating the outflow phenomena are introduced; thereafter, practical calculations on field cases in Thailand and Japan are demonstrated. Additionally, since the effects of wave periods and water depth to the outflow rate have never been clarified, hydraulic model experiments, empirical calculations using an existing formula, and numerical simulations are performed in order to examine these effects on the outflow rate. The simulated results using the numerical model align well with the experimental results. Moreover, both results show that the outflow rate is proportional to the wave period and inversely proportional to water depth.

Experimental and Numerical Analysis on Hydraulic Characteristics of Coastal Aquifers with Seawall

In this study, hydraulic model experiments were conducted to measure the saltwater–freshwater equilibrium interface in a coastal aquifer with underground obstructions such as an impermeable seawall. To analyse the hydraulic characteristics inside the coastal aquifer, numerical analysis was conducted using a non-hydrostatic Navier-Stokes solver based on the Porous Body Model (PBM), which can directly analyse groundwater flow. A unique saltwater–freshwater equilibrium interface that does not appear in typical coastal aquifer analyses was observed in a sandy tank experiment. In the experiment, the rise of the groundwater level behind the seawall increased the pressure gradient and groundwater flow rate, causing the saltwater–freshwater interface to move towards the sea and a freshwater region to form on the seabed in front of the seawall. The numerical analysis enabled close examination of the groundwater level distribution, groundwater flow, seawater–freshwater interface, and pore water pressure characteristics of the coastal aquifer with underground obstructions. The sandy tank experiment also provided an understanding of the hydraulic characteristics of groundwater in the coastal aquifer with a seawall, which previously could not be accurately analysed. The experimental and analytical results demonstrated that the rise of groundwater level due to underground obstructions in the coastal aquifer increased the pressure gradient and groundwater flow rate and slowed seawater intrusion. This principle can be employed to sufficiently reduce seawater intrusion of coastal aquifers.

Wave Control Performance of Tide-Adapting Low-Crested Structure

Hur, D.S.; Jung, K.H.; Park, J.R., and Lee, W.D., 2019. Wave control performance of tide-adapting low-crested structure. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 116-120. Coconut Creek (Florida), ISSN 0749-0208.Low-Crested Structures (LCSs) are aesthetically apt coastal structures with wave and sand drift control functions. However, they are inappropriate in waters where the tidal range is large because the crest width and height must be above certain levels to allow the breakwater to carry out these functions. Forced wave breaking cannot be induced during high tide because the crest depth increases. Therefore, a Tide-Adapting Low-Crested Structure (TA-LCS) is proposed to overcome the problems caused by large tidal ranges. The hydraulic performance of the proposed LCS was evaluated and compared with that of a typical LCS via hydraulic model experiments. The typical LCS showed an excellent wave screening effect with an average transmission coefficient of 0.4 under the conditions of Fb/Hi=0.29–0.67 and B/Li=0.09–0.15. The wave screening performance of the new type of LCS was 9.5–28.8 % lower than that of the typical LCS. However, the wave screening performance of the new type of LCS decreased only by 9.1–10.4 % under the condition of Fb/Hi≤1 and only by 24.3 % under the condition of Fb/Hi=4. Therefore, the new type of LCS proposed in this study is expected to exhibit its wave control functions during high tide even when installed in a coastal area with a large tidal range.

Sand Suction Characteristics in the Rear Side of a Revetment Using DEM-WASS-2D

Hur, D.S.; Cho, W.C.; Lee, J.L., and Jeong, Y.M., 2019. Sand suction characteristics in the rear side of a revetment using DEM-WASS-2D. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 66-70. Coconut Creek (Florida), ISSN 0749-0208.The coupled analysis of a particle method and a wave field model was conducted to examine numerically the characteristics of sand behaviors at the bottom and in the rear side of a revetment. The two-way coupled analysis used in this study can not only consider the interaction among the wave, revetment, and ground but also represent sand behaviors at the bottom and in the rear side of a revetment under waves. The validity and usefulness of the two-way coupled analysis was ensured by comparing hydraulic characteristics around an impermeable revetment with the results of a hydraulic model experiment. In the coupled analysis, characteristics of sand behaviors at the bottom and in the rear side of a revetment were numerically analyzed according to the installation of an incident wave and submerged breakwater. As the wave energy increased, the sand transport from the bottom of the revetment also increased. The transport rates of sand from the bottom of the revetment to the open sea decreased by 14-93% when a submerged breakwater was installed under the tidal condition of this study. In addition, the two-way coupled analysis was also effective in numerically examining the stability of the bottom and rear side of a revetment according to the characteristics of sand behaviors.

STABILITY ESTIMATION METHOD FOR ARMOR UNITS FOR BREAKWATERS WITH PARAPETS AGAINST TSUNAMI OVERFLOW

This paper presents a stability estimation method for armor units to cover a rubble mound on the rear side of a caisson breakwater against tsunami overflow while taking into account the influence of the shape of the superstructures of the caisson. In this method, the required mass of the armor units is obtained from the impinging velocity onto the rear side mound. This is calculated by using the overflow depth. Accordingly, the influence of the shape of the superstructure is taken into account directly. This method also takes the influence of the slope angle into account properly by using the formula by Isbash. In addition, the influence of the impingement position of the overflow nappe and the influence of the thickness of the water jet are considered. The validity of this method is confirmed by comparing with the results of hydraulic model experiments conducted in a wide range of conditions.

Effect of the armor crest freeboard relative to the crown wall freeboard on wave overtopping for simple rubble mound slopes

Several studies have been carried out to investigate the effect of crest parameters on the wave overtopping for armored slopes with crown walls. However, the effect of the armor crest freeboard is still under question. In this study, for the first time, a series of hydraulic model experiments are conducted specifically to investigate how the armor crest freeboard relative to the crown wall freeboard affects the wave overtopping rate. Experimental results indicate that while the armor crest freeboard lower than the crown wall freeboard is giving larger overtopping, higher armor crest freeboard is reducing the overtopping. However, this reduction is not same as the reduction due to the increase in the crown wall freeboard. The reason may be the porosity of the armor crest. For the first time, a new correction factor is proposed to describe the change in the wave overtopping due to the armor crest freeboard by using experimental results. The correction factor CAc is applied to cover the effect of armor crest freeboard in the predictions of EurOtop (2016). The verification study present that overtopping rate predictions of corrected EurOtop (2016) are more consistent with the measured rate results compared to the predictions of the original formula, if the armor crest freeboard is not equal to the crown wall freeboard.

Experimental Studies on the Stability Assessment of a Levee Using Reinforced Soil Based on a Biopolymer

Cement and other similar compounds have been used to prevent a levee breach during a flood. However, the demand is increasing for eco-friendly and sustainable alternatives to replace the conventional method for levee stabilization and strengthening. To improve the durability and environmental friendliness of a levee, the Andong River Experiment Center applied a biopolymer, which is a new eco-friendly substance, to fabricate a levee model, and conducted a hydraulic model experiment to evaluate the reliability and stability of the new type of levee. An image analysis was applied to calculate the scale of the breaches of the levee slopes. Based on the experimental results obtained, the characteristics of the breach between an earthen levee and the proposed levee were compared. The stability of the levee body was also evaluated according to the thickness of the new substance. The ultimate aim of this study was to derive the optimal conditions by verifying the performance and effectiveness of the new substance in terms of levee breach factors such as overflow, seepage, or piping in a series of hydraulic experiments. In the future, the field application of these optimal conditions will be verified through a real-scale experiment.

Energy Generation Efficiency due to Wave Overtopping on Floating-Overflow-Type Wave Energy Converter

Hur, D.S.; Jeong, Y.M.; Lee, J.L.; Kim, I.H., and Lee, W.D., 2018. Energy generation efficiency due to wave overtopping on floating-overflow-type wave energy converter. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1341–1345. Coconut Creek (Florida), ISSN 0749-0208.The current heightened interest in renewable energy motivated this investigation into the efficiency of wave power generation, which can produce electricity from the infinite energy source of ocean waves. The subject chosen was a floating-overflow-type wave energy converter (FOWEC), which is a comparatively simple type of power generation equipment among the various types of wave power equipment. Because FOWEC is a floating body, it functions not only for power generation, but also as a floating breakwater. In this study's hydraulic model experiments, FOWEC time waveforms were measured, and the reflection and transmission coefficients were computed. In addition, the outflow velocity from the FOWEC overtopping water tank was measured and compared with the theoretical value. The results confirmed that the FOWEC exhibited some degree of wave control in its role as a floating breakwater. The freeboard for the overtopping waves on the lowest FOWEC had an average wave reflection coefficient of 0.43 and an average wave transmission coefficient of 0.21. As wave overtopping increased (as the freeboard decreased and the incident wave height increased), the effective velocity ratio of the outflow from the overtopping tank increased. However, as the freeboard decreased, the effective head decreased, and therefore the energy that could be received was smaller than when the freeboard was higher. In order to maximize the generation efficiency, conditions that allow for overtopping should be implemented with a FOWEC that can maintain an optimal freeboard for appropriate wave overtopping and effective head.

Clarification of Pumping Characteristics and Method for Utilization of Irrigation Water Wheel by Hydraulic Model Experiment

Clarification of Pumping Characteristics and Method for Utilization of Irrigation Water Wheel by Hydraulic Model Experiment

Wave Power Generation by Piezoelectric Sensor Attached to a Coastal Structure

The characteristics of a new wave power generating system have been proposed by installing a piezoelectric sensor to the seaward position of an existing coastal structure. By installing the sensor to the structure, waves will hit the piezoelectric sensor to generate wave energy; at the same time, the structure acts as a wave breaker. This technique can be applied to various coastal structures to converge the functions of renewable energy generator and the wave reducing structure. This technique of using piezoelectric sensor is relatively inexpensive that can be used for economic purposes as well. Throughout the study, usability of the existing coastal structure and characteristics of current research trend in the ocean wave energy retrieval of the wave power generators have been analyzed. Hydrographic analysis of this technique has been conducted by hydraulic model experiment using 2D wave flume and confirmed that the wave pressure and voltages maximize when higher wave with longer period of wave induces. Throughout the experiment, correlations of generation volume and wave conditions have been found.

Teaching Exploration of Hydraulic Structure Model Experiment Course

This paper deepens the teaching mode, teaching method and teaching content of the reform experimental model of hydraulic structure model, aiming to mobilize the enthusiasm and creativity of students to participate in teaching and research activities, and comprehensively developing the innovative spirits of students. The article comprehensively sorts out the teaching content, experimental teaching links and teaching objects of the hydraulic structure model experiment, and improves the experimental practice teaching system by exploring experimental teaching cases and experimental teaching methods. The article explores new experimental teaching methods combining scientific research with teaching experiments. This article strengthens the construction of multimedia courseware, network platform and digital teaching methods through the study of experimental textbooks and experimental teaching, and improves teaching methods.

Analysis on Scour Characteristics under River Bed Variation in Weir Downstream

Various river projects are underway in small rivers in Korea that typically have natural flows. However, recent findings have shown that damages could be aggravated by structures such as weirs and drop structures during flood incidents. Experimental studies for securing the stability of flood control for these artificial structures have been insufficient, and designs applying the existing domestic design standards would not be suitable for the steep flow sections such as the actual small rivers, possibly aggravating the damages. The present study involved hydraulic model experiments conducted in a laboratory to investigate the surrounding flow patterns according to the river bed slope at the downstream part of the weir model. Further, the scour characteristics in the apron section during the overflow of the structure were analyzed to determine the appropriateness of the apron length. Thus, as the upstream river bed slope gradually increased, the experimental scour length deviated more from the design criteria formula. The results suggest that both the formula suggested by the National Construction Research Institute and Bligh’s formula presented in the River Design Criteria are not suitable for steep-slope rivers, such as small rivers in Korea, because both formulas were proposed based on the seepage line distance and river bed materials without considering the slope of the river bed. Thus, in designing the apron and bed pitching of weirs and drop structures, the river bed slope, scour characteristics of weir overflow, and existing design factors should be comprehensively considered to devise a design formula appropriate for environment of the small rivers in Korea.

A Study on Evacuation Safety at Inundated Stairs by using Real-scale Hydraulic Model Experiment

In recent years, sudden and local downpours in Korea have become more frequent. These rainfall patterns increase load on drainage system and reduce ability to exclude inland water, leading to flooding. If such rainfall patterns lead to flash floods especially in dense urban areas, sudden submergence of underground spaces by floods can be a fatal threat to life. Therefore, it is very important to secure evacuation routes in case of inundated underground spaces. In this study, we tried to determine evacuation safety by understanding hydraulic characteristics of inundated stairs that could become evacuation routes in underground spaces. For this purpose, water depth and volume flow rate were measured at each point of inundated stairs, and data obtained from results were used to evaluate evacuation safety at each step.

Applications of ultrasound imaging system for measuring water-sand parameters during sediment transport process in hydraulic model experiments

Abstract Moving particles and the topographic bed under muddy water or in sediment-laden flow are often clouded by suspended sediments, making it hard to detect or analyze for visualization. This paper concerns applications of ultrasound imaging measurement method for the visual measurement of related water-sand parameters during sediment transport process in hydraulic model experiments. We use a B-mode ultrasound imaging system to measure the related parameters of suspended sediment concentration (SSC), underwater topographic riverbed, flow velocity and sediment incipient motion, conducted at a water channel. A comprehensive measuring system for the visualization of multiple water-sand parameters is established. Results show that the measurement and analysis of SSC and its space distribution, topography bedform, flow velocity and flow field, and sediment incipient velocity can be realized. Ultrasound imaging measurements of SSC and their space distribution can be shown in real time, and also dynamic monitoring and analysis of sediment incipient motion and topography bedform during the sediment transport process. This method realizes the experimental visualization of the topographic bed and sediment-laden flow. Application of an ultrasound imaging measurement system has promoted the development of sediment movement law research and related hydraulic model experiment measurement technique.

An Experimental Study on Water Surface Profiles of High Froude Number Flows

Motivated by need to study supercritical overbank flows on floodplain, we experimentally investigate if initially supercritical flow in a rectangular flume would maintain its state throughout. Varying upstream gate opening, flow rate and angle of the slope, a total of 37 experimental cases were carried out. The experimental results are compared to two existing theories: an inviscid theory based on nonlinear shallow water equations and jump conditions and a hydraulic theory that takes friction into account. The experimental data are consistent with the two theories. Flows on downward slope were stable, while those on upward slope had unstable hydraulic jump and transformed into subcritical flow. The reported results should serve well in designing a laboratory flume with the supercritical inflow and in conducting hydraulic model experiments on overbank flows.

Simulation study of anisotropic flow resistance of farmland vegetation

Farmland vegetation is commonly cultivated with uniform planting spacing and heights. The effect of these features on resistance to hydraulic erosion is unclear. Hydraulic model experiments with the angle between the crop rows and the water flow direction set at 15°, 30°, 45° or 90° were conducted to analyze variation in the law of water flow resistance under partial or complete submergence of the crop. Cultivation can impact the flow resistance on slopes and this effect was greater when the crop was partially submerged. When planting spacing, slope, and water depth were constant, the change of the water flow Darcy-Weisbach resistance coefficient f with crop row-water flow angle was f<sub>15</sub>° > f<sub>30</sub>° > f<sub>45</sub>° > f<sub>90</sub>°. This suggests that flow resistance of farmland vegetation is anisotropic. The water flow resistance coefficient of crops that were partly submerged increased with water depth, but decreased with water depth when the crop was completely submerged. At the critical change from partial submergence to complete submergence, the water flow resistance coefficient was the highest when water depth was equal to crop height. These results may be useful for optimizing farmland planting and soil and water conservation.

ESTIMATION OF TSUNAMI FORCE ACTING ON THE BLOCK ARMORED BREAKWATER DUE TO SOLITON FISSION

A series of hydraulic model experiments were performed to verify the effect of armoring concrete blocks on tsunami pressure reduction in a state of soliton fission. Applicable ranges for the Tanimoto and modified Tanimoto formulas for wave pressures acting on a caisson have been determined in terms of the ratio of tsunami height to water depth. An estimation formula for the tsunami pressure reduction factor of the armoring blocks was proposed as a result of a comparison of tsunami force between the states without and with the armoring blocks. The calculated tsunami forces acting on a caisson armored with blocks agreed well with the corresponding experimental ones. Sufficient stability of the armoring blocks against tsunamis was also confirmed by the experiments.