The occurrence of a buried submarine pipeline crossing a channel becoming damaged by the impact of a falling anchor is becoming more common. It is important to analyze the dynamic response of pipelines exposed to such impact and develop effective protection methods to ensure the safe operation of the pipelines exposed to the impact of falling anchors. In this study, different protection methods, including pure rock, concrete mattress + rock, concrete mattress + rock + rubber pad, and compound flexible pad + rock, are physically tested. The strains at the impacting point and along the pipeline were measured with the fiber Bragg grating (FBG) sensors. The effectiveness of the protection methods is analyzed based on the maximum strain and its affected length on the pipeline. Then, a theoretical model is established to analyze the deformation and strain of a pipeline. Through curve-fitting the experimental results, the bearing capacity coefficients for different protection methods are determined. The protection method of compound flexible pad + rock has the best performance to protect the pipeline from the impact of a falling anchor.
A three-dimensional numerical model was established based on ANSYS-AQWA (R19.0) software for the purpose of analyzing the hydrodynamic characteristics of a floating breakwater. This study examines three distinct floating breakwaters with different cross-sectional designs in order to evaluate their respective wave dissipation capabilities. It is suggested that the horizontal multi-cylinder floating breakwater exhibits a superior ability to dissipate waves when compared to both the single-cylinder and square pontoon configurations and can be deemed the most advantageous shielding strategy for potential engineering applications. Subsequently, this study examines the effects of influential parameters, including a large cylinder diameter, a small cylinder diameter, the angular position of the small cylinder, and the height and period of the incident wave, on the wave transmission coefficient. An empirical formula for the wave transmission coefficient was derived based on the numerical results. Additionally, the effects of influential parameters, including wind speed, current velocity, incident wave height and period, and water depth, on the maximum total mooring force were investigated. Furthermore, an empirical formula for the maximum total mooring force is proposed for practical implementation in engineering.
Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves.
The flapwise bending vibrational equations of tapered Rayleigh beam are derived based on Hamilton's principle. The corresponding vibrational characteristics of rotating tapered Rayleigh beams are investigated via variational iteration method (VIM). Natural frequencies and corresponding mode shapes are examined under various rotation speed, taper ratio and slenderness ratio focusing on two types of tapered beam. The convergence of VIM is examined as part of the paper. Validation of VIM solution is made by referring to results available in other literature and corresponding results show that VIM is capable of yielding precise results in a very efficient way.
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.
Based on the assumption that the crest lines of sandwaves are perpendicular to the main flow direction, the formation and migration of submarine sandwaves are simulated in a 2 D flume under wave-only and combined wave-current conditions. The effects of various flow parameters, including the wave height and current velocity, on the characteristic dimensions and migration rates of sandwaves are discussed. Measured morphological data indicate that the seabed is composed of both large-scale sandwaves and small-scale sand ripples, and sandwaves are dominant in shaping the seabed form. Starting from a flat seabed, the height of sandwaves increases gradually and tends to become dynamically stable, while the wave length of sandwaves reaches a constant value at the initial stage. Under wave-only conditions, the characteristic wave heights and wave lengths of sandwaves increase with increasing incident wave height. The relative locations of the sandwave peak and trough are almost constant, indicating that sandwaves scarcely migrate under wave-only conditions. Under combined wave-current conditions, the characteristic heights and lengths of sandwaves also increase with increasing current velocity. The migration direction of sandwaves coincides with the direction of the residual current, and the migration rate increases with increasing current velocity. Finally, the characteristic dimensions of sand ripples are also analyzed, revealing that the Reynolds number (based on the particle size) is dominant in determining the size of a sand ripple. Both the characteristic wave lengths and the characteristic wave heights of sand ripples decrease with increasing Reynolds numbers.
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