The Oscillating Water Column(OWC) wave energy convertor with the advantage of its simple geometrical construction and excellent stability is widely employed.Recently,perforated breakwaters have been often used as they...The Oscillating Water Column(OWC) wave energy convertor with the advantage of its simple geometrical construction and excellent stability is widely employed.Recently,perforated breakwaters have been often used as they can effectively reduce the wave reflection from and wave forces acting on the structures.Considering the similarity between the compartment of perforated caisson and the air chamber of OWC wave energy convertor,a new perforated caisson of breakwater is designed in this paper.The ordinary caisson is modified by installing facilities similar to the air chamber of OWC converter,but here they are utilized to dissipate the wave energy inside the caisson.Such an arrangement improves the stability of the caisson and reduces the construction cost by using the compartment of perforated caisson like using an air chamber.This innovation has both academic significance and important engineering value.For a new type of caisson,reliability analysis of the structure is necessary.Linear potential flow theory is applied to calculate the horizontal wave force acting on the caisson.The calculated results are compared with experimental data,showing the feasibility of the method.The Importance Sampling Procedure(ISP) is used to analyse the reliability of this caisson breakwater.展开更多
This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes seco...This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes second-order waves. The numerical results obtained for limiting cases of double-row and triple-row walls are in good agreement with results of previous studies and experimental results. Comparisons with experimental measurements of the reflection, transmission, and dissipation coefficients （CR, Cr, and CE） for double-row walls show that the proposed mathematical model adequately reproduces most of the important features. We found that for double-row walls, the CR increases with increasing wave number, kd, and with a decreasing permeable wall part, din. The Cr follows the opposite trend. The CE slowly increases with an increasing kd for lower kd values, reaches a maximum, and then decreases again. In addition, an increasing porosity of dm would significantly decrease the CR while increasing the Cr. At lower values of kd, a decreasing porosity increases the CE, but for high values of kd, a decreasing porosity reduces the Ce. The numerical results indicate that, for triple-row walls, the effect of the arrangement of the chamber widths on hydrodynamic characteristics is not significant, except when kd〈0.5 Double-row slotted breakwaters may exhibit a good wave-absorbing performance at kd〉0.5, where by the horizontal wave force may be smaller than that of a single wall. On the other hand, the difference between double-row and triple-row vertical slotted breakwaters is marginal.展开更多
The comb-type breakwater(CTB)has been proposed and investigated in recent years due to its advantages in terms of deep-water adaptability,material saving and water exchanges.All existing empirical formulae for CTBs ha...The comb-type breakwater(CTB)has been proposed and investigated in recent years due to its advantages in terms of deep-water adaptability,material saving and water exchanges.All existing empirical formulae for CTBs have been so far restricted to the water level above the bottom of the superstructure,which mainly occurs under the high tides or storm tides.However,based on recent engineering applications and experimental observations,the most severe conditions for CTBs are more likely to occur under a medium water level,because impulsive wave pressure may occur due to interactions between waves and the special chamber in CTBs.Meanwhile,during the most of construction and operation periods,the CTBs are mainly working under the medium water levels,i.e.,water levels below the bottom of the superstructure.In this study,the effects of main influence parameters on the horizontal wave force coefficient and wave transmission coefficient for open CTBs(with partially immersed side plates)under medium water levels were investigated based on a 3D numerical wave flume and corresponding empirical formulae were proposed.It is indicated that the location of the side plate related to the main caisson has significant influence on the hydrodynamic performance of CTBs.In engineering applications,the location of the side plate can be designed at b/L≤0.15 or b/L≥0.3(where b is the distance between the side plate and the front face of the main caisson and L is the incident wave length)for efficiently lowering the horizontal wave force and wave transmission.The flow mechanism of impulsive wave force on CTBs was revealed based on synchronous analyses of flow fields and pressure distribution.Through appropriate design of the height of the superstructure according to H/hD≤1.0 or H/hD≥1.5(where H is the incident wave height and hD is the distance between the still water level and the bottom of the superstructure),the likely impulsive wave pressure on the side plate can also be diminished.展开更多
基金supported by the National Natural Science Foundation of China (Grant No 4087-6047)
文摘The Oscillating Water Column(OWC) wave energy convertor with the advantage of its simple geometrical construction and excellent stability is widely employed.Recently,perforated breakwaters have been often used as they can effectively reduce the wave reflection from and wave forces acting on the structures.Considering the similarity between the compartment of perforated caisson and the air chamber of OWC wave energy convertor,a new perforated caisson of breakwater is designed in this paper.The ordinary caisson is modified by installing facilities similar to the air chamber of OWC converter,but here they are utilized to dissipate the wave energy inside the caisson.Such an arrangement improves the stability of the caisson and reduces the construction cost by using the compartment of perforated caisson like using an air chamber.This innovation has both academic significance and important engineering value.For a new type of caisson,reliability analysis of the structure is necessary.Linear potential flow theory is applied to calculate the horizontal wave force acting on the caisson.The calculated results are compared with experimental data,showing the feasibility of the method.The Importance Sampling Procedure(ISP) is used to analyse the reliability of this caisson breakwater.
文摘This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes second-order waves. The numerical results obtained for limiting cases of double-row and triple-row walls are in good agreement with results of previous studies and experimental results. Comparisons with experimental measurements of the reflection, transmission, and dissipation coefficients （CR, Cr, and CE） for double-row walls show that the proposed mathematical model adequately reproduces most of the important features. We found that for double-row walls, the CR increases with increasing wave number, kd, and with a decreasing permeable wall part, din. The Cr follows the opposite trend. The CE slowly increases with an increasing kd for lower kd values, reaches a maximum, and then decreases again. In addition, an increasing porosity of dm would significantly decrease the CR while increasing the Cr. At lower values of kd, a decreasing porosity increases the CE, but for high values of kd, a decreasing porosity reduces the Ce. The numerical results indicate that, for triple-row walls, the effect of the arrangement of the chamber widths on hydrodynamic characteristics is not significant, except when kd〈0.5 Double-row slotted breakwaters may exhibit a good wave-absorbing performance at kd〉0.5, where by the horizontal wave force may be smaller than that of a single wall. On the other hand, the difference between double-row and triple-row vertical slotted breakwaters is marginal.
基金financially supported by the General Program of the National Natural Science Foundation of China(Grant No.51979192)the National Key Rsearch and Development Program of China(Grant Nos.2020YFE0201200 and 2021YFB2600700)the Program of China Communications Construction Company Limited(Grant No.2018-ZJKJ-01).
文摘The comb-type breakwater(CTB)has been proposed and investigated in recent years due to its advantages in terms of deep-water adaptability,material saving and water exchanges.All existing empirical formulae for CTBs have been so far restricted to the water level above the bottom of the superstructure,which mainly occurs under the high tides or storm tides.However,based on recent engineering applications and experimental observations,the most severe conditions for CTBs are more likely to occur under a medium water level,because impulsive wave pressure may occur due to interactions between waves and the special chamber in CTBs.Meanwhile,during the most of construction and operation periods,the CTBs are mainly working under the medium water levels,i.e.,water levels below the bottom of the superstructure.In this study,the effects of main influence parameters on the horizontal wave force coefficient and wave transmission coefficient for open CTBs(with partially immersed side plates)under medium water levels were investigated based on a 3D numerical wave flume and corresponding empirical formulae were proposed.It is indicated that the location of the side plate related to the main caisson has significant influence on the hydrodynamic performance of CTBs.In engineering applications,the location of the side plate can be designed at b/L≤0.15 or b/L≥0.3(where b is the distance between the side plate and the front face of the main caisson and L is the incident wave length)for efficiently lowering the horizontal wave force and wave transmission.The flow mechanism of impulsive wave force on CTBs was revealed based on synchronous analyses of flow fields and pressure distribution.Through appropriate design of the height of the superstructure according to H/hD≤1.0 or H/hD≥1.5(where H is the incident wave height and hD is the distance between the still water level and the bottom of the superstructure),the likely impulsive wave pressure on the side plate can also be diminished.
