Pile Breakwater Research Articles

シルト質内湾での現地特性を活かした海岸侵食対策の検討

In many coasts of Thailand, serious coastal erosion has occurred and breakwaters for preventing it have been constructed. Especially since many coasts in the gulf of Thailand consist of very fine bed materials, wave dissipation breakwaters made of bamboo piles and detached breakwaters made of geotextile bags which were packed bed materials have been constructed instead of concrete block breakwaters. However, these arrangement plans were based on empirical techniques. This research examines the validity of the effect evaluation method of the coastal erosion prevention using a numerical prediction model. Moreover, the comparison of the bamboo pile breakwater and the geotextile detached breakwater shows that the former can acquire sufficient effect for the erosion prevention with construction costs cheaper a little than the latter.

AN EXPERIMENTAL STUDY OF WAVE AND CURRENT-INDUCED FORCES ON A COMPACT LINEAR ARRAY OF VERTICAL CYLINDERS IN SHALLOW WATER

Arrays of vertical cylinders are essential components of many coastal structures, such as bridge piers, platform legs, and pile breakwaters. Thus, estimating the maximum wave and current-induced forces and moments on such structures is most important. Following a thorough literature review, the authors proceeded with an experimental study in order to investigate the forces exerted by random waves and a superimposed current on an array of three vertical cylinders as a function of the inter-cylinder gap and the angle of wave incidence over a wide range of wave and current conditions in shallow water.

Hydrodynamic characteristics of a single-row pile breakwater

The present paper extends the impedance analytical method to the study of the interaction of regular plane waves with a row of rectangular piles. The dissipative energy is estimated from the flow resistance for the row of piles. Formulas of wave reflection and transmission coefficients and the wave force for the row of piles are derived. Predictions obtained using the present model agree with experimental data in the literature.

Numerical investigation of the interactions between solitary waves and pile breakwaters using BGK-based methods

The interactions between a solitary wave, which can be used to model a leading tsunami wave, and a pile breakwater made of circular cylinders are numerically investigated. We use the depth-averaged shallow water equations, which are solved by the finite volume method based on the Bhatnagar–Gross–Krook (BGK) model. The numerical results are compared with the experimental data, which yields very good agreement between them when the ratio of wave height to water depth is small (<0.25). As this ratio exceeds the value of 0.25, the larger the ratio is, the bigger deviation of numerical results from experimental data is observed, the possible reasons for this observation are discussed. Both numerical and experimental results indicate that the transmission of the solitary wave decreases and the reflection of the wave increases with reducing gaps between the adjacent cylinders, and that both transmission and reflection coefficients are not very sensitive to the variation in wave height.

Laboratory and Numerical Studies of Hydrodynamics Near Jetties

Numerical and physical modeling studies were performed by the Coastal Inlets Research Program (CIRP) of the U.S. Army Corps of Engineers to investigate the spatial and temporal behavior of waves and wave-induced currents near jetties of an idealized coastal inlet. Hydrodynamics were examined in the vicinity of two extreme types of jetty structure: a highly absorbing jetty (resembling fairly porous rock rubble structure) and a fully reflective jetty (resembling a vertical sheet pile or caisson type breakwater). Laboratory experiments in a Froude scale of 1:50 were conducted with regular and irregular shore-normal (0°) and obliquely incident (20°) unidirectional waves. Current and wave measurements were made on the up-wave side and inside the inlet as well as in the bay, along a number of cross-shore and along-shore transects. Wave directions were measured by a remote-sensing video-camera system and Acoustic Doppler Velocimeters (ADV). Numerical modeling was performed with the Coastal Modeling System (CMS) consisting of a two-dimensional circulation model coupled to a spectral wave model. Calculated current and wave fields from CMS in the area around and between absorbing or reflected jetties were compared to measurements. The highly reflecting jetty created a circulation cell on the up-wave side of the inlet, whereas the absorbing jetty did not.

Wave reflection and transmission by curtainwall–pile breakwaters using circular piles

This paper presents a mathematical model which computes the hydrodynamic characteristics of a curtainwall–pile breakwater (CPB) using circular piles, by modifying the model developed for rectangular piles by Suh et al. [2006. Hydrodynamic characteristics of pile-supported vertical wall breakwaters. Journal of Waterway, Port, Coastal and Ocean Engineering 132(2), 83–96]. To examine the validity of the model, laboratory experiments have been conducted for CPB with various values of draft of curtain wall, spacing between piles, and wave height and period. Comparisons between measurement and prediction show that the mathematical model adequately reproduces most of the important features of the experimental results. The mathematical model based on linear wave theory tends to over-predict the reflection coefficient as the wave height increases. As the draft of the curtain wall increases and the porosity between piles decreases, the reflection and transmission coefficient increases and decreases, respectively, as expected. As the relative water depth increases, however, the effect of porosity disappears because the wave motion is minimal in the lower part of a water column for short waves.

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.

Hydrodynamic pressures and forces on quadrant front face pile supported breakwater

Quadrant front face pile supported breakwater is a combination of semicircular and closely spaced pile breakwaters which couples the advantages of these two types. This type of structure consists of two parts. The bottom portion consists of closely spaced piles and the top portion consists of a quadrant solid front face on the seaside. The leeward side of the top portion with a vertical face would facilitate the berthing of vessels. An experimental investigation on this breakwater model in a wave flume is carried out for three water depths. For each water depth, three different spacings between the piles were adopted for the investigation. The dynamic pressures exerted along the quadrant front face due to regular waves were measured. The variation of dimensionless pressures with respect to scattering parameter for different gap ratio (spacing between the piles/diameter of pile) and for relative pile depth (water depth/pile height) are presented and discussed. In addition, the dimensionless total forces exerted on the breakwater model as well as its reflection characteristics as a function of scattering parameter are reported.

Wave Transmission by Suspended Pipe Breakwater

A suspended pipe breakwater was designed specifically for fishery/pleasure-craft harbors where moderate wave agitations in the harbor basin are admissible. The present breakwater consists of a row of closely spaced pipes mounted onto a frame and suspended between the support piles spaced far apart. Experimental studies conducted to determine the wave transmission characteristics indicate that by suspending a row of closely spaced pipes (with a gap to diameter ratio of 0.22 and draft to water depth ratio of 0.46), a 50% reduction in incident-wave height can be achieved. The cost and performance of conventionally adopted pile breakwater (involving a row of closely spaced piles driven on the seabed) were compared with the present system. The comparison revealed that the present system can reduce the investment cost by about 40% and can attenuate waves with the same efficiency as that of a row of closely spaced piles.

TRANSMISSION OF RANDOM WAVES THROUGH PILE BREAKWATERS

Several previous investigators have conducted experiments leading to expressions for predicting the transformation of waves passing through closely-spaced pile breakwaters. The present study extends those earlier experiments using monochromatic waves to the case of a spectrum of random waves. Records of incident waves and of waves after transmission through a model pile breakwater were compared to determine a coefficient of transmission. Results are presented for several cases of pile spacing and pile diameter. Good agreement is found between observed transmission coefficients and those predicted using the expression proposed by Hayashi et al. (1966).

CASE HISTORY OF A SPACED PILE BREAKWATER AT HALF MOON BAY MARINA AUCKLAND, NEW ZEALAND

Half Moon Bay Marina is a privately owned small boat harbour located on the Tamaki Estuary of the Auckland Harbour. The marina was built in 1970 for 485 boats moored to floating marina berths, Fig. 1, and is sheltered by a spaced pile breakwater.

Closely Spaced Pile Breakwater as a Protection Structure Against Beach Erosion

Closely Spaced Pile Breakwater as a Protection Structure Against Beach Erosion

CLOSELY SPACED PILE BREAKWATER AS A PROTECTION STRUCTURE AGAINST BEACH EROSION

The theory for the transmission and reflection of the waves at the closely spaced pile breakwater has been developed by the use of shallow water wave theory of small amplitude. Experiment on the hydraulic characteristics of the breakwater has been performed in a two dimensional wave flume. The agreement between the theory and the experiment is pretty good with respect to the coefficients of transmission and reflection of waves, and also to the shoreward velocity of the jet discharged from a space between any two adjacent piles. Experiment was also made on the local scouring at the foot of the clocely spaced pile breakwater. The maximrai scouring depth at the foot of the breakwater relates closely to the ratio of the velocity of the jet to the mean fall velocity of bed material. The relation between the maximum scouring depth and the power of the jet is discussed.

Hydraulic Research on the Closely Spaced Pile Breakwater

Hydraulic Research on the Closely Spaced Pile Breakwater