In coastal waters, algal blooms (the rapid growth of microscopic phytoplankton) are often observed. The resulting oxygen depletion and even poisoning make local fisheries suffer severe damages. The dynamics of harmful algal blooms (HABs) are poorly understood. Novel models applying unstructured grids, e.g. Delft3D Flexible Mesh (Delft3D-FM), offer a good tool for a better representation of the hydrodynamics of coastal waters. In this paper, the performance of Delft3D-FM in hydrodynamic simulation of coastal waters was examined by a series of benchmark tests. At the end, the simulated tidal flushing processes in Hong Kong harbours were compared with previous studies.
The sea state plays an important role in offshore-and marine operations. It affects both direct costs as well as risks for human and/or material loss. A better understanding of the present-, near-future-, and far-future sea states will increase efficiency and safety in shipping since it allow a ship to reroute to a safer and/or more cost effective route. In the offshore industry it allows for minimizing downtime and aids in planning the construction of new offshore sites. Due to the complex nature of the sea state, its spatial distribution over a large region of ocean should be modeled using a probabilistic model. In this way, uncertainties due to lack of information and/or computing power can be quantified and decisions can be taken based on both what is known and what is not known. We analyze such a spatial probabilistic model in order to assess its ability to predict the significant wave height in the whole north Atlantic based only on measurements on a small line path, i.e., conditional prediction. This work is relevant for several applications, for instance data assimilation, oceanographic forecasting, and routing of ships.
In this paper, we introduce a semi-empirical head wave added resistance calculation formula. The formula considers the ship hull forms as well as the main particulars and was verified by the available experimental data in the regular wave. One PCTC full-scale measurements were carried out to perform the added resistance validation in the irregular sea, with a newly proposed wave height correction factor. The encountered weather conditions were extracted from the reanalysis metocean data. The result indicated that the proposed formula has achieved reasonable accuracy with fast calculation, and was discussed with regards to uncertainties and prediction capacity.
Targeted on grain refinement, the effects of different rolling process conditions on mechanical property of 460MPa class steel plate, in terms of tensile and yield strength, low-temperature toughness, arrestability and microstructure, are studied. The rolling process conditions are surface-layer with ultrafine grains process (SUF) and traditional thermo mechanical control process (TMCP). As for SUF process, better surface strength and toughness can be achieved. Yield strength is generally higher than 540MPa.-60℃ impact value of SUF2 is higher than 280J. The surface nil-ductility transition temperature (NDTT) of SUF condition have reached less than-80℃. The fine grain microstructure formed at the surface layer, which is about 4mm thick, contributes to better mechanical property than that in other layers. The microstructure varies gradually from the surface to the centre. There are proeutectoid ferrite and bainite at 1~4mm thickness of surface layer. The microstructure in the 4~10mm thickness layer consists of polygonal ferrite and a considerable amount of bainite. As for the TMCP process, relatively homogenous strength and toughness can be achieved across thickness direction, featuring with higher strength and lower toughness at the surface layer, and lower strength and higher toughness at centre layer, when compared to that of SUF process. The microstructure of the TMCP sample varies gradually from the surface to the centre.
With the rapid development of marine transport in recent years, container ships are becoming larger. In this paper, crack arrest steel plates are developed in micro alloyed route. Uniformly enhanced cooling TMCP technology is used and the rolling technology was controlled at a lower rolling temperature. The grain size of acicular ferrite and bainite are refined to a very low level, which has a advantage effect to the toughness of the matrix. The impact absorbed energy at –40° Care more than 300 J and the Kca value at-10°C are exceeding 8,000N/mm, which represent a high crack arrestability.
Due to the global warming and the continuous decline of Arctic sea ice, maritime transport in the Arctic region has been increased dramatically. While operating in the Arctic area, ships face regular environment loads and ice loads synchronously, the consideration of ice resistance is essential for the fuel consumption estimation in the ice-covered water voyage. In this paper, a theoretical fuel consumption model is proposed based on empirical method for ship sailing through the Arctic route. The results are compared with the full-scale measurements in a real Arctic ship navigation, and discussed with regards to uncertainties and the prediction capacity of the fuel consumption model. The encountered sea states and ice thickness are constructed by hindcast reanalysis data and climate model projections.
Waves penetrate deep into the ice covered seas, inducing breakup of the ice cover. Concomitantly, the ice cover attenuates the wave energy over distance, so that wave impacts die out eventually. Observations of wave attenuation and concurrent wave-induced breakup in the literature are serendipitous due to difficulties in making measurements in ice covered seas. Hence understanding of wave-ice interactions remain uncertain. Here we present measurements of wave propagation through ice covered waters in the new experimental wave-ice facility at the University of Melbourne. The facility comprises of a 14m long and 0.76m wide flume in a refrigerated chamber, where temperatures can be lowered down to −12 degrees Celsius to generate a continuous ice cover on the water surface. A wave maker, installed at one end, is used to generate regular waves, ranging from gently-sloping to storm-like conditions. Wave attenuation rates are determined from video-camera images of the displacements of markers embedded in the ice cover. The experiments investigated wave propagation through the continuous ice cover, breakup, and propagation through the broken ice cover. Spatial evolution of the breakup and geometrical properties of floes are monitored and correlated with incident wave properties. Wave attenuation over broken ice is investigated and compared against the continuous ice case.
Conventional voyage optimization algorithms often follow similar estimation procedures to design a ship’s optimal sailing courses and schedules, through first generate waypoints/grids along a ship’s sailing area, construct candidate routes, and implement a searching method to find the optimal route with respect to specific objectives. One important variable to control a ship’s operation is the navigation condition, which may lead to the fact that the planned optimum route is only a locally optimal solution for a ship’s route planning. In this paper, a hybrid optimization algorithm is proposed to provide globally optimum route planning using Dijkstra’s algorithm and genetic algorithm.
The coast of Yantai in China has often been ravaged by severe coastal storms together with high elevated water levels, resulting in severe beach erosion and inundation hazards. This study is undertaken to collect essential field data on beach transect profile, beach slope, maximum wave runup level and sediment grain size to assess coastal erosion hazard on Yantai Beach. There are 20 permanent beach transect profiles surveyed every month with RTK-GPS, and three sediment samples were collected from the dune/seawall, beach berm and swash zone. This study has found that the sandy beach backed by the vertical seawall is often flooded at daily high tides, while the beach backed by the sand dune is generally stable. A conceptual model is also applied to estimate shoreline setback distance in n years.
Wave-by-wave and cumulative overtopping data from fixed planar impermeable smooth beaches will be presented from random wave experiments and compared with predictions from two nonlinear shallow water equations (NLSWE) models, Australian National University and Geoscience Australia (ANUGA) and Simulating WAves till SHore (SWASH). These models have been tested and used by many researchers in various coastal processes studies. However, the capability of the models has not been tested when modeling wave-by-wave overtopping processes, and there is relatively limited validation for cumulative or time-averaged overtopping. The verified numerical models will be used to perform a parametric study on the relationship between overtopping and beach slope (beta), which has not been well resolved in the literature. This paper shows that the models provide reliable estimates of nearshore wave transformation and run-up, which includes the shoreline motion on a nontruncated beach, with SWASH modeling wave shoaling accurately. For the experimental configuration of a beach that was truncated with a sharp vertical edge, ANUGA provided more reliable estimates of wave-by-wave and cumulative overtopping and predicted total overtopping volumes without bias and within a few percent on the average overall. For wave-by-wave and cumulative overtopping SWASH is sensitive to the bathymetry at the overtopping edge, under predicting total overtopping volumes by approximately 25% for a sharp vertical edge but overpredicting by approximately 20% for a flat crest followed by a downward slope. A detailed investigation indicated that partial reflection occurred at the overtopping edge in the SWASH model for some configurations of the bathymetry, which lead to overestimated depths but reduced durations for positive discharge. The influence of beta on the ANUGA model run-up predictions and overtopping will be investigated and compared with empirical formulations. The ANUGA predictions for run-up were consistent with the empirical formulations for low beta and were linearly proportional to beta (tan beta), but were proportional to beta at a smaller power for a higher beta, which differed from the relationship given in some empirical models. For a given beach crest elevation (z(c)) with a sharp vertical edge and fixed wave conditions, the numerical ANUGA model and empirical model predictions for overtopping were approximately linearly proportional to tan beta, but the exact power varied depending on the chosen model. This was in contrast to some of the existing empirical models (when this dependency was explicit), but it was consistent with the analytical SWASH solution when written for positive volume flux (V-o) and deficit in the freeboard (R-z(c)) scaling. The numerical predictions from ANUGA agreed well with the empirical models. The modeling provided a new interpretation of the influence of the beta on overtopping in the empirical EurOtop formulation, where the complete influence of beta is not explicitly provided. (C) 2021 American Society of Civil Engineers.
The mainland coast of China is 18,000km long and often ravaged by major tropical cyclones, resulting in severe damage to the coastal economy and also heavy losses of human lives. This paper is designated to review on major coastal hazards occurred along the coast of China, and assess their impacts and causes. In analyzing the available long-term coastal hazard data, it is found that high storm tides and large coastal waves are responsible for causing annual damage of about US$2.68 billion to the coastal economy and also annual losses of 258 people's lives and that most of the fatalities are caused by the large waves. The intensity of the coastal hazards is also found to generally increase from the north to south on the coast of China.
