Hydraulic Model Test Results Research Articles

NWT-DEM Coupled Numerical Analysis on Wave Attenuation due to Vegetation

Jeong, Y.M.; Jeon, H.S.; Park, J.R.; Jeong, Y.H., and Hur, D.S., 2019. NWT-DEM coupled numerical analysis on wave attenuation due to vegetation. 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. 146-150. Coconut Creek (Florida), ISSN 0749-0208.In this study, the numerical wave tank (NWT) and discrete element method (DEM) coupled analysis method was used to investigate the wave control characteristics of eco-friendly and natural vegetation. To examine the effectiveness and validity of the coupled analysis method, the results were compared with the existing hydraulic model test results. Most of the existing studies used numerical analysis methods that cannot consider the kinetic characteristics of vegetation owing to the drag coefficient (CD) of vegetation. As such, this study reproduced the kinetic characteristics of vegetation (which have not numerically examined but can be seen in the hydraulic model tests) using the coupled analysis method, and examined the wave control characteristics of vegetation by comparing its behavior according to its characteristics (flexible and rigid). Through the coupled analysis method, it was confirmed that rigid vegetation has a 1.2%–12.2% higher transmission coefficient (KT) than flexible vegetation in terms of wave attenuation of the vegetation zone due to the kinetic characteristics of vegetation.

Laboratory Flume Experiments on the Formation of Spanwise Large Wood Accumulations: I. Effect on Backwater Rise

AbstractTransported large wood (LW) in rivers may lead to accumulations at natural or artificial obstructions. The hydraulic and geomorphic conditions change due to these accumulations. Backwater rise as well as scour can evolve in the vicinity of such an accumulation. In this first companion paper, results of hydraulic model tests are presented on backwater rise due to spanwise LW accumulations in combination with a movable bed. The findings are summarized in design equations and allow the estimation of (1) characteristic LW volume generating the primary backwater rise, (2) effect of LW accumulation shape and bed material on resulting backwater rise, and (3) effect of LW volume on backwater rise. Compared to a fixed bed, movable bed reduces backwater rise as the open cross‐section area and thus discharge capacity increase. This work improves the understanding and predictability of the formation and impact of spanwise LW accumulations at natural or artificial obstructions (e.g., LW retention racks).

피복공법 적용 시 파랑에 의한 피복재 침식 실험 연구

피복공법의 설계에서 피복재의 선정은 중요한 설계 변수로 파랑에너지로 발생하는 해저면 유속에도 피복재가 침식되지 않게 설계되어야 한다. 피복공법 관련된 기존 연구는 파랑에너지에 따른 깊이별 유속과 유효입경을 주로 시공경험과 수치해석에 의존하여 수행되었기 때문에 현장에서 시공경험이 미흡한 기술자가 사용하기에는 어려움이 예상된다. 본 연구에서는 파랑에너지에 따른 깊이별 유속과 피복재의 입경에 따른 침식을 판단할 수 있는 간편식을 제시하고 모형수조를 이용한 실내실험을 통해 신뢰성을 확인하고자 한다. 실내실험에서 측정된 깊이별 유속은 이론식과 상당히 일치하며, 유속추정 이론식을 침식 해석에 적용하여 유효입경을 예측하면 침식 유무 판단이 가능하다. The determination of in-situ capping materials is one of the most important factors to design in-situ capping in order to protect capping materials from erosion. Previous studies have established relationship between the velocity induced by wave energy and effective diameter of sediments, but they are mostly empirical and numerical researches which is too complicated for field engineers to analyze the erosion of in-situ capping materials. This study provides simple analytical solutions and reliability based on hydraulic model test results. Experimental results show that measured flow velocities with respect to depth induced by wave energy are almost the same as estimated velocities and the erosion resistances of the different effective particle diameters can be estimated.

Hydraulic model test results of baffle–brush fish pass

The flow characteristics (depth, velocity, energy dissipation) of a new baffle–brush fish pass were investigated experimentally in a 2 m wide rectangular flume which has a bed slope of 4% for discharges of 100–550 l/s. In all the experiments, quasi-uniform and sub-critical flow conditions and Froude numbers between 0·17 and 0·23 were observed. The Darcy–Weisbach friction factor was negatively correlated with the relative submergence of the brush elements. Two different characteristic velocity regions were identified, namely the baffle region and the brush region. The turbulence intensities were in the range 38–79% in the baffle zone and 13–31% in the brush zone. The hydraulic test results showed that this type of fish pass can produce adequate flow depth and favourable local flow velocities for the design discharge of 0·2 m2/s (relative submergence of brushes = 1·03), which is suitable for different fish species.

The effect of dynamic amplification due to a structure׳s vibration on breaking wave impact

In this paper, breaking wave impact forces on vertical and inclined piles are studied by using a 3D numerical model. A method for obtaining net breaking wave impact forces from the measured response time history is also investigated. The computed forces are compared with the results of hydraulic model tests. However, because the piles installed in the numerical model are modeled as rigid objects, it is not possible to make a direct comparison between the CFD (Computational Fluid Dynamic) results and the experimental data. A force separation procedure is used for the experimental data. A low pass filter and EMD (Empirical Mode Decomposition) are employed for removing the effect of dynamic amplification in the experimental data, and the filtered results are compared with the numerical results. Based on the results, DAFs (Dynamic Amplification Factor) are estimated for these particular structures. Moreover, Duhamel integral is used to reproduce dynamic breaking wave forces (i.e., net breaking wave force+the force which is the amplified component due to the structure׳s vibration) based on the breaking wave forces calculated by the CFD model. The reproduced results are compared with the unfiltered experimental data for the verification of the method stated above.

A Study on Physical Model Test for Cheongpyeong Dam Discharge Recalculation

Cheongpyeong Dam was built in 1943 for the purpose of power generation. Since its construction, discharge flow data based on a theoretical formula have been used to the present times and this leads to a problem of accurate discharge flow information not being available. In particular, Cheongpyeong Dam has been partially repaired and modified to maintain the dam structure over a long period of time and is not being properly reflected with changes at the downstream of the river caused by river improvement projects and sedimentation in reservoir. With a goal to improve Cheongpyeong Dam discharge flow calculation, this study aimed at verifying discharge capability and discharge flow by damper opening in relation to the previously suggested discharge flow through a hydraulic model test based on an accurate reproduction of the dam structure and surrounding topographies as in the present conditions. In this study, a hydraulic model test was conducted to examine the discharge flow of Cheongpyeong Dam. In addition, a comparative examination was carried out against the existing discharge flow proposed using theoretical equations. As a verification of the discharge flow of Cheongpyeong Dam, discharge flows in all sluices and a single sluice were examined. Then, the impact of sluice interference caused by the dam structure consisting with 24 sluices was investigated. As a result of the examination, it was found that the difference between discharge flow calculated using the existing theoretical equations and discharge flow derived from the hydraulic model test was insignificant. Based on the results of hydraulic model test, a formula to estimate stage-discharge flow at a sluice was derived and suggested.

陸上構造物に作用する津波持続波圧に関する水理学的考察

Hydraulic mechanism of sustained tsunami wave pressure acting on land structures was investigated theoretically. The effect of wave pressure amplification due to wave reflection was estimated based on momentum conservation law. On the other hand, backwater effect was modeled by energy conservation law. The formulas which indicate wave pressure on 2D wall and 3D structure were derived. The theoretical result was compared with the hydraulic model test results and numerical computation results and good agreement was found out.

Stability Formula for Tetrapods

A stability formula has been developed for Tetrapods armoring rubble mound breakwaters based on hydraulic model test results of the present and previous studies. The formula is applicable to breakwaters with various slope angles. It is also applicable to low-crested breakwaters and different packing densities if the corresponding terms are incorporated in the formula. The uncertainty of the formula is also described.

Design weight of armour stone considering the effect of extreme waves

In this study, waves with the heights higher than H 1/3 in an irregular wave train are called as extreme waves and defined with the help of extreme wave parameter, α extreme. In order to see the effect of extreme waves on the design weight of armour stone, stability analysis is carried out based on the hydraulic model test results. The test results of high α extreme cases (HE) and low α extreme cases (LE) are compared with currently used van der Meer's formulae with permeability factor P=0.4 and 0.45 and Hudson formula by using H 1/3 and H 1/10 in terms of the design weight of armour stone. As a result of the comparison, it is found that Hudson formula by using H 1/3 underestimates the necessary armour weight. Usage of H 1/10 instead of H 1/3 in Hudson formula doubles the weight which seems overestimated when Irribaren number is away from the transition zone in which both wave run-up and run-down forces become effective. However, it seems underestimated near the transition zone where experiment case HE gives higher armour weights. When the design weight of armour stone is calculated by van der Meer's formulae with P=0.4, it may be necessary to increase the weight up to 30% in the case of high extreme waves. On the other hand, van der Meer's formulae may overestimate the weight 14% when the extreme waves are low.

Coastal erosion prevention by geotextile tube technology

Recently, geotextile tube technology has changed from being an alternative construction technique and, in fact, has advanced to become the prime solution of choice. This paper presents the various issues related to the geotextile tube technology and case history of shore protection at Young-Jin beach on the east coast of Korea. A stability analysis by the two-dimensional limit equilibrium theory is highlighted and the hydraulic model test results are described. Based on the results of stability analysis and hydraulic model tests, a double-lined geotextile tube installed with zero-water depth above crest was found to be the most stable and effective for wave absorption than other design plans. Also, the shoreline at Young-Jin beach was extended by about 2.4–7.6 m seaward, and seabed sand was gradually accumulated around areas covered by the geotextile tube.

Evaluation of Influence of Isahaya Wan Sea Dike by Hydraulic Model Test

Influences on the tidal current off the coast of Shimabara due to the construction of the sea dike in the Isahaya wan land reclamation project was evaluated by a hydraulic model test. The results of hydraulic model test were as follows. On the line connecting Ariake and Nagasu, strong currents occurred near the Shimabara Peninsula. Tidal current changed complexity at a point near the Shimabara Peninsula at the ebb tide, especially in the spring tide. Tidal current decreased approximately 5% due to the construction of the sea dike in average on the Ariake-Nagasu line, which corresponds to the amount of decrease of tidal discharge by the closing of the Isahaya bay.

Using submerged geotextile tubes in the protection of the E. Korean shore

Shore erosion is currently causing millions of dollars worth of damage to shorelines and public properties not only along the east coast of Korea but also around the world. Little else needs to be said to emphasize that, without adequate protection, a very significant part of our coastline will fall prey to the ravages of the sea and to man himself. In recent years, because of the shortage of natural rock, traditional forms of river and coastal structures have become very expensive to build and maintain. Therefore, the materials used in hydraulic and coastal structures are changing from the traditional rubble and concrete systems to cheaper materials and systems. One of these alternatives employs geotextile tube technology in the construction of shore protection structures, such as groins, jetties, detached breakwaters and so on. Recently, geotextile tube technology has changed from being an alternative construction technique and, in fact, has advanced to become the most effective solution of choice. This paper presents the various issues related to the geotextile tube construction for shore protection at Young-Jin beach on the east coast of Korea. A new approach to a stability analysis by 2-dimensional limit equilibrium theory is highlighted and the hydraulic model test results and case history of Young-Jin beach projects are described. Based on the results of stability analysis and hydraulic model tests, a two line geotextile tube installed with zero water depth above crest was found to be more stable and effective for wave absorption than other design plans. Also, the shoreline at Young-Jin beach was extended by about 2.4–7.6 m seaward, and seabed sand was gradually accumulated around areas covered by the geotextile tube.

直線翼垂直軸型水流タービンの海洋環境下への適用検討

The tidal and sea current turbines are one of potential utilization of renewable energies as well as offshore wind ones. Although they possibly produce electricity efficiently because of high density of water to air and more steadiness of flow to winds, hydro turbine generation system is less employed than wind one. We are studying an application of Straight Wing Vertical Axis Hydro Turbine Generation Systems in the tidal current and waves. This paper presents the results of hydraulic model tests using 2-dimensional channel.

直線翼垂直軸型水流発電システムの検討

The tidal and sea current turbines are one of potential utilization of renewableenergies as well as offshore wind ones. However they possibly produce efficiently electricity because of high density of water to air and more steadiness of flow to winds, hydro turbine generation system is less employed than wind one. We are studying an application of Straight Wing Vertical Axis Hydro Turbine Generation Systems in the tidal current. This paper presents the results of hydraulic model test using 2-dimensional channel and field test.

Elastic response characteristics of a very large floating structure in waves moored inside a reef

This article describes the results of hydraulic model tests of the elastic response of a very large floating structure (VLFS) moored inside a reef in an isolated island. The distributions of strains and vertical displacements due to the elastic response of the VLFS were measured. The response characteristics were strongly affected by deformed nonlinear waves inside the reef. A two-step analytical method to compute the elastic response of a VLFS is proposed, and its validity is verified using the results of the hydraulic model tests.

Warning system against Wave Overtopping on Promenade Breakwaters

A newly developed device, which is to be installed on the seaward side of promenade breakwaters, can be used as a warning system against wave overtopping. This system generates wave splashing and sounds before wave overtopping occurs, warning people nearby of possible danger on the promenade breakwater.The run-up height of wave splashing and characteristics of the sounds from this system are studied based on the results of hydraulic model tests. According to these tests, this system has been constructed at the Port of Mombetsu.

DEVELOPMENT OF THE DOUBLE CYLINDER CAISSON BREAKWATER

A double cylinder caisson breakwater was recently developed to create a calm sea area in deep and high wave open sea areas. In order to confirm some subjects on design method and construction work, we conducted a field test in an actual sea area. This paper reports the results of that field test, mainly from the viewpoint of the hydraulic property of this new type of caisson, and the results of hydraulic model tests conducted to complement and verify the results of the sliding tests.

Incipient wave breaking

This paper studies incipient wave breaking in 225 hydraulic model test results. The measured values of breaking wave height are compared with earlier data and earlier expressions. It is found that the present measured values are substantially lower, because the tests used irregular waves on a natural beach. These results are more representative of field conditions and should bring about selection of lower values for design breaking wave height. The paper provides some relatively simple expressions to calculate breaking wave height.

Design, Testing and Operation of Grit Chambers with Hydraulic Roll

The Soreq biological treatment plant has been recently brought into operation, after a comprehensive start-up and testing program. The plant's preliminary treatment facilities include four grit chambers 40 m long, equipped for both grit removal and scum skimming. The variable energy input required to control the deposition of the grit and the floating of the scum, is provided by a hydraulic jet system, using pumped recycled wastewater to generate the necessary motive power. The basic concept in designing grit chambers equipped with a hydraulic jet system, instead of a bubble aeration system, is to avoid the release of noxious odours and corrosive gases which are often associated with the conventional aerated grit chambers. Experiments were conducted on a hydraulic model of the grit chamber to develop the necessary design criteria for the full scale jet system. During the initial start-up program of the Soreq plant, the grit chambers and the related equipment were tested with clear water, and the actual transversal velocities were measured through a range of simulated operating conditions. This paper summarizes the hydraulic model test results, the upscaling approach used for design of the prototype system, and the on-site full-scale tests with clear water. A follow-up program under actual operating conditions is now in progress to establish the variable parameters for optimal operation of the hydraulically powered grit chambers with wastewater.

Floating Breakwater Design

Floating breakwaters are inventoried. The various types are separated into 4 general categories, which are Box, Pontoon, Mat, and Tethered Float. The Tethered Float was identified as a special category but lacked sufficient prototype experience for detailed analysis. Advantages and disadvantages of the Box, Pontoon and Mat are presented. Hydraulic model test results and prototype experience for these 3 types are presented. Alternative mooring systems and anchorage methods are summarized. The engineering studies usually needed for a suitable design are outlined. Costs and design data for selected prototype installations are tabulated.