Curtain-walled Breakwater Research Articles

Dissipative potential flow models and energy evolution characteristics for curtain-wall caisson breakwaters under wave action

Curtain-wall caisson breakwaters are a kind of coastal protection structure, which is composed of semi-submersible vertical thin curtain walls, a rear vertical caisson, and wave chambers formed by the curtain walls and rear caisson. When water waves interact with the curtain-wall caisson breakwater, the wave energy may be partially dissipated owing to the flow separation and vortex formation near the edges of curtain walls. The conventional potential flow solution without considering wave energy dissipation gives unreasonable results of full wave reflection by the curtain-wall caisson breakwater. To address this issue, this study develops a dissipative potential flow model for predicting the hydrodynamic performance of the curtain-wall caisson breakwaters. The wave energy dissipation near the breakwater is considered by introducing a quadratic pressure loss condition at the entrances of wave chambers. By adopting appropriate dimensionless dissipation coefficients, the analytical predictions of the reflection coefficient and the wave amplitude inside chambers are in good agreement with published experimental results. The differences in the hydrodynamic quantities predicted by the dissipative and conventional potential flow solutions are examined, and further discussion based on the dissipative analytical solution is performed. Moreover, viscous numerical simulations based on a meshless particle method are carried out to clarify the characteristics of wave energy evolution, wave energy dissipation, and local fluid motion near the curtain-wall caisson breakwaters. The results show that the front curtain wall plays the leading role in the wave energy dissipation process of the whole double-chamber curtain-wall breakwater.

Transmission and reflection of waves on curtain wall breakwater

Judul: Gelombang transmisi dan refleksi pada pemecah gelombang dinding tirai Title: Transmission and reflection of waves on curtain wall breakwater Pemecah gelombang sangat dibutuhkan pada kolam pelabuhan untuk mendapatkan perairan yang tenang sehingga kapal dapat naik/turunkan penumpang dan bongkar-muat barang secara aman dan nyaman. Pemecah gelombang dinding tirai merupakan salah satu pemecah gelombang yang hemat material jika dibandingkan dengan tipe pemecah gelombang tipe urugan. Tujuan penelitian ini adalah mengetahui pengaruh kedalaman dinding pada pemecah gelombang dinding tirai dan kecuraman gelombang datang terhadap nilai gelombang transmisi dan gelombang refleksi. Penelitian ini dilakukan dengan model fisik pada saluran gelombang. Berdasarkan hasil penelitian menunjukkan bahwa semakin dalam dinding terendam relative terhadap kedalaman (h/d) pemecah gelombang dinding tirai maka nilai koefisien gelombang transmisi ( K t ) semakin rendah dan semakin tinggi nilai wavestepness (H i /L) dari gelombang datang makanilai koefisien transmisi gelombang semakin rendah juga. Adapun koefisien gelombang refleksi ( K r ) berlaku sebaliknya. Breakwaters are needed in harbour pools to get calm waters so that ships can board/unload passengers and load and unload goods safely and comfortably. The curtain wall breakwater is one of the material-efficient breakwaters when compared to the fill type breakwater. This research aimed to ascertain the influence of the wall's depth on the curtain wall breakwater and the steepness of the incident wave on the transmission and reflection wave values. This research was conducted with a physical model on the wave channel. Based on the results of the study indicate that the more profound the submerged wall relative to the depth (h/d) of the curtain wall breakwater, the lower the value of the wave transmission coefficient (K t ) and the higher the wave steepness (H i /L) value of the incident wave, the lower the wave transmission coefficient value too. The reflection wave coefficient (K r ) is the opposite.

Hydrodynamic Performance of Wave Interaction with Curtain-Wall Breakwater: Using the MPS Model

Iddy, I.; Jiang, Q., and Zhang, C., 2020. Hydrodynamic performance of wave interaction with curtain-wall breakwater: Using the MPS model. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 76–80. Coconut Creek (Florida), ISSN 0749-0208.This paper examines the hydrodynamic performance of wave interactions with double curtain-wall breakwater by the laboratory experiment and numerical model. A vertical two-dimensional moving particle semi-implicit (MPS) numerical model is developed and verified by comparison of the simulated and experimental results. Then it is applied to investigate wave interaction with partially immersed double curtain walls at different immersion depths, porosity of perforated front wall, and chamber width. A good agreement is shown between the numerical results and the experimental data, indicating that the proposed MPS numerical model can successfully capture the essential aspects of wave interactions with breakwater structure and can be a useful predictive tool.

Numerical Modeling of Wave Interaction with Double Curtain-wall Breakwater

A numerical wave tank (NWT) based on the RANS equations is established by adding source terms into the momentum equation for generating wave and absorbing the reflected waves effectively. The wave dissipation induced by double curtain-wall breakwater and the flow field nearby under the action of regular wave are simulated. The effects of relative immersed depth of barrier on transmission coefficient are analyzed. The numerical results are identical with the experimental data, while they are different a lot from the results of the Lapa formula. The effects of relative width of horizontal plate, relative depth, wave slope are investigated, and a revised formula is presented based on comprehensive verification with both the experiment and numerical results.

Wave interaction with a wave absorbing double curtain-wall breakwater

This study examines the hydrodynamic performance of a wave absorbing double curtain-wall breakwater. The breakwater consists of a seaward perforated wall and a shoreward impermeable wall. Both walls extend from above the seawater to some distance above the seabed. Then the below gap allows the seawater exchange, the sediment transport and the fish passage. By means of the eigenfunction expansion method and a least square approach, a linear analytical solution is developed for the interaction of water waves with the breakwater. Then the reflection coefficient, the transmission coefficient and the wave forces acting on the walls are calculated. The numerical results obtained for limiting cases agree very well with previous predictions for a single partially immersed impermeable wall, the double partially immersed impermeable walls and the bottom-standing Jarlan-type breakwater. The predicted reflection coefficients for the present breakwater also agree reasonable with previous experimental results. Numerical results show that with appropriate structure parameters, the reflection and transmission coefficients of the breakwater may be both below 0.5 at a wide range of the relative water depth. At the same time, the magnitude of wave force acting on each wall is small. This is significant for practical engineering.

Performance of a Jacket-Type Breakwater with Water Chambers in Deep Sea

In comparatively deep sea, under which soft grounds exist and also comparatively long waves like swells attack, a curtain-walled breakwater has been adopted as a possible structure for simplicity. However, horizontal wave forces on such curtain-walled breakwaters become very large because of deep draft depth. For the economical construction of breakwaters in those deep sea ports, it has been newly proposed that a jacket-type breakwater with water chambers consisting of two vertical walls and one submerged horizontal plate. The effectiveness of a newly proposed breakwater has been examined extensively, especially focusing on the reduction rate of transmitted waves and wave forces.

Effectiveness of a Pile-Supported Breakwater with an Inclined-Plate-Array and a Submerged Plate in a Harbor

We have proposed a new type breakwater supported by piles, which consists of three major parts, i. e., an inclined plate array as a front wall, a vertical rear wall and a submerged plate at the base. It has been confirmed by the two-dimensional experiment that it enables to reduce both reflected and transmitted waves and also induce the mean current about the breakwater. In this study, we have carried out experiments on the performance of this type of breakwater in the three dimensional fields. For the comparisons, conventional breakwaters, such as a curtain-walled breakwater and also a vertical breakwater, were also used as a breakwater model. For the theoretical prediction of nearshore circulation around the harbor, applicability of the numerical analysis based on the Multi-Layered model was extensively examined.

傾斜版列を前面壁とする遊水室型杭式防波堤の港湾域における効果について

We have proposed a new type breakwater supported by piles, which consists of three major parts, i. e., an inclined plate array as a front wall, a vertical rear wall and a submerged plate at the bottom. It has been confirmed by the two dimensional study of vertical plane that the breakwater enables to reduce both reflected and transmitted waves for comparatively wide range of wave frequency, and also to generate mean current by wave actions in the offshore direction. In this study, we have examined the performance of this type of breakwater in the three dimensional wave fields, such as a harbor model basin. For the comparisons, conventional breakwaters, such as a curtain-walled breakwater and also a vertical impermeable breakwater, were also used as a harbor breakwater model. For the theoretical prediction of wave height distributions around the harbor, applicability of the numerical analysis based on the vertical line source Green's function method was extensively examined.

Hydrodynamic Characteristics of Pile-Supported Vertical Wall Breakwaters

This paper describes the hydrodynamic characteristics of a pile-supported vertical wall breakwater, the upper part of which is a vertical wall, and the lower part consisting of an array of vertical piles. For regular waves, using the eigenfunction expansion method, a numerical model has been developed that can compute wave transmission, reflection, and run-up, and wave force acting on the breakwater. For irregular waves, the regular wave model is repeatedly used for each frequency component of the irregular wave spectrum. The wave period is determined according to the frequency of the component wave, while the root-mean-squared wave height is used for all the component waves to compute the energy dissipation between piles. To examine the validity of the developed models, large-scale laboratory experiments have been conducted for pile-supported vertical wall breakwaters with a constant spacing between piles but various drafts of the upper vertical wall. Comparisons between measurement and prediction show that the numerical model adequately reproduces most of the important features of the experimental results for both regular and irregular waves. The pile-supported vertical wall breakwater always gives smaller transmission and larger reflection than a curtain wall breakwater with the same draft as that of the upper wall, or a pile breakwater with the same porosity as that of the lower part, of the pile-supported vertical wall breakwater.

INFLUENCE OF A SUPERSTRUCTURE ON THE PERFORMANCE OF A PILESUPPORTED BREAKWATER WITH DISSIPATIVE FRONT WALLS

In order to mitigate secondary effects caused by high reflection waves from a conventional curtainwalled breakwater, a new type of breakwater consisting of two different walls was proposed. One wall is an impermeable curtain wall and located on the shore side of the breakwater. The other is consisted of an array of inclined plates with the same gap and located on the offshore side. For the practicalapplication of the new breakwater, the influence of a super structure on the performance was examined extensively. Furthermore, presuming the sea area with significant tidal difference such as the Seto Inland Sea, effect of water levels on the performance of the breakwater was also clarified. The dissipation mechanism used here is to enhance the generation of vortex flows from the plate-array front wall. By using the Helmholtz mode wave resonance between the two walls, enhancement of the vortex flow is realized.

WAVE FORCES ON A GRAVITY-TYPE CURTAIN-WALLED BREAKWATER AND STABILITY AGAINST WAVES

Wave forces on a curtain-walled breakwater of gravity-type were dealt with experimentally and theoretically. Using the two different super structures such as a rectangular body and a thin wall, characteristics of wave forces on these super structures and submerged mound structures were examined extensively. The thin-wall super structure is adopted as a simplified model of a curtain-walled breakwater. Stability test of the breakwater against waves was also carried out.From the comparison between the two results regarding wave forces and breakwater displacements, major factors relating to the stability of the breakwater were clarified.

PERFORMANCE OF A DOUBLE-CURTAIN-WALLED BREAKWATER WITH A FRONT WALL OF INCLINED PLATE ARRAY

In order to mitigate secondary effects caused by high reflection waves from a curtain-walled breakwater, a new type of curtain-walled breakwater was proposed. It consists of two vertical walls with different draft depths. The distance between the two walls is comparatively narrow, e. g., having a similar size to the width of its super structure. The mechanism of effective dissipation of wave energy is to enhance the generation of vortex flows from the curtain walls, especially from the front curtain wall placed on the offshore side, which consists of an array of inclined plates with the same gap. By using the wave resonance of Helmholtz mode between the two walls, enhancement of the vortex flow is realized. In the experimental and theoretical examinations, changing the water depth and the distance between the two walls, important hydraulic properties of a double curtain-walled breakwater, such as reflection and transmission coefficients, wave energy dissipation rates and so on, are clarified.

WAVE REFLECTION AND TRANSMISSION ABOUT A GRAVITY-TYPE CURTAIN-WALLED BREAKWATER FOR IRREGULAR WAVES

Wave reflection and transmission characteristics about a curtain-walled breakwater of gravity-type were examined in both regular and irregular wave environments. At first, the representative wave analysis for a group of irregular waves with different statistical properties was adopted to examine reflection and transmission coefficients of the breakwater. These coefficients were also obtained for regular waves and compared with each other. Secondary, frequency characteristics of reflected and transmitted waves about the breakwater were examined through the use of spectral analysis. Reflection and transmission coefficients as a system function of a linear system were obtained and again compared with those of regular waves. It was confirmed that the reflection and transmission coefficients for regular waves can be used for the case of irregular waves if the significant wave is used as a representative wave. However, it must be noted that frequency characteristics of incident and transmitted waves are different about the breakwater.

Analysis on Wave Transformations and Wave Forces about an Angular Body Considering Wave Energy Dissipations

Concerning wave energy dissipations caused by flow separations and resultant vortex formations from sharp edges of an angular body, a twodimensional analysis on wave transformations and wave forces on an angular body has been developed. In the analysis, a damping wave model was newly proposed to account for the wave energy dissipation approximately. An equivalent linear damping coefficient of fluid and a spatial range of the damping fluid are necessary in the analysis. In order to figure out these factors, wave tank tests were carried out. Two different structural models, i.e., a curtain-walled breakwater and a semi-submerged rectangular body, were used in the experiment. It was confirmed that the numerical analysis developed here is useful for estimating wave transformations and wave forces about an angular body including the effects of wave energy dissipation due to vortex formations around the body.