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The traditional neighborhood rough set model has low noise immunity and computational efficiency for mixed data. This paper establishes a local variable-precision neighborhood rough set model with dynamic change of attributes based on matrix theory. Firstly, on the basis of the updating law of local diagonal matrix and transition matrix, the dynamic updating mechanism of approximation under the local variable-precision neighborhood rough set of mixed information system is constructed; secondly, according to this dynamic updating mechanism, a new dynamic algorithm of local variable-precision neighborhood rough set with attribute change is proposed; finally, through the experimental analysis, it can be seen that the proposed dynamic algorithm has a high computational efficiency and a good robustness. [ABSTRACT FROM AUTHOR]

The efficiency of beach recovery during a time of moderate waves following storm waves is closely related to the interaction between dynamics, sediment, and the landform. The existing studies mainly focus on the description of erosion and accretion characteristics, while the response and feedback mechanism of beach berm sediment have not been elucidated. The main controlling factors of recovery efficiency are not clear. In this paper, field observation and the XBeach numerical model are utilized on the sandy beach in Puqian Bay, China, to capture high-frequency cross-shore data during the post-storm recovery period. The variation characteristics and rules of berm elements, including berm ridge height and slope on two sides of the berm ridge, are analyzed. It is observed that the berm constantly changes to adapt to dynamic conditions. Additionally, a correlation between volume change and certain landform parameters is proposed, leading to the identification of a new relationship in wave run-up. The new forum reflects berm influence and considers the berm ridge and berm width. [ABSTRACT FROM AUTHOR]

This paper addresses the current existence of attribute reduction algorithms for incomplete hybrid decision-making systems, including low attribute reduction efficiency, low classification accuracy and lack of consideration of unlabeled data types. To address these issues, this paper first redefines the weakly labeled relative neighborhood discernibility degree and develops a non-dynamic attribute reduction algorithm. In addition, this paper proposes an incremental update mechanism for weakly tagged relative neighborhood discernibility degree and introduces a new dynamic attribute reduction algorithm for increasing the set of objects based on it. Meanwhile, this paper also compares and analyses the improved algorithm proposed in this study with two existing attribute reduction algorithms using 8 data sets in the UCI database. The results show that the dynamic attribute reduction algorithm proposed in this paper achieves higher attribute reduction efficiency and classification accuracy, which further validates the effectiveness of the algorithm proposed in this paper. [ABSTRACT FROM AUTHOR]

Variable and complex marine environmental loads combined with wave resistance and the insufficient controllability of large caisson structures pose serious challenges during maritime towing. Cable breakage events are common, and improper behaviors could give rise to a variety of accidents. This work explored the dynamic responses of large caisson structures following towing cable breakage under irregular waves combined with harsh currents. Two types of cable breakage, i.e., main bridle and towing bridle breakage, were taken into account. Four potential wave–current combinations were assumed for each situation according to direction. The obtained results show that drag rope breakage could give rise to lateral shifts in the structure, which can become a serious condition when exposed to angled waves. Additionally, following breakage, significant force fluctuations took place in the remaining intact cables. For main cable breakage, both lateral and backward displacements were observed in the structure, which gradually entered a 'flowing with the wave' state. Furthermore, under the two abovementioned cable breakage conditions, the structure air gap consistently exceeded 2.3 m, ignoring the possibility of a wave slamming event. [ABSTRACT FROM AUTHOR]

The traditional neighborhood rough set model has low noise immunity and computational efficiency for mixed data. This paper establishes a local variable-precision neighborhood rough set model with dynamic change of attributes based on matrix theory. Firstly, on the basis of the updating law of local diagonal matrix and transition matrix, the dynamic updating mechanism of approximation under the local variable-precision neighborhood rough set of mixed information system is constructed; secondly, according to this dynamic updating mechanism, a new dynamic algorithm of local variable-precision neighborhood rough set with attribute change is proposed; finally, through the experimental analysis, it can be seen that the proposed dynamic algorithm has a high computational efficiency and a good robustness. [ABSTRACT FROM AUTHOR]

In this paper, a novel method to construct non-intrusive reduced order model (ROM) is proposed. The method is based on proper orthogonal decomposition and transformer neural network. Proper orthogonal decomposition is used to generate the basis functions of the low-dimensional flow field, and the coefficients are taken as low-dimensional flow field features. Transformer network is used to extract temporal feature relationships from low-dimensional features. Compared with recurrent neural network and convolutional neural network, transformer network can better capture flow dynamics. At online stage, the input temporal flow sequences are calculated in parallel and can effectively reduce online calculation time. The model proposed in this paper has been verified in two scenarios: two-dimensional flow past a cylinder and two-dimensional flow past a building group. Experimental results show that our model can better capture the flowing change details and has higher accuracy. Compared with the ROM based on long short-term memory and temporal convolutional network, the prediction error is reduced by 35% and 60%, and the time cost is reduced by 65% and 60%. Finally, we apply the ROMs to a practical three-dimensional complicated scenario, flow past London South Bank University, and discuss future development of ROMs. [ABSTRACT FROM AUTHOR]

In this paper, a novel reduced order model based on a convolutional auto-encoder with self-attention (SACAE ROM) is proposed. The proposed model is a non-intrusive reduced order model, which uses a convolutional neural network and a long short-term memory network to extract temporal feature relationships from high-fidelity numerical solutions. The self-attention is introduced into the convolutional neural network to enhance the non-local information perception ability of the convolutional neural network and improve the feature extraction ability of the network. The model adopts a joint construction method, which overcomes the problem of propagating error in each process of the model. The model proposed in this paper has been verified on the problem of the flow around a cylinder. The experimental results indicate that the SACAE ROM has higher robustness and accuracy. Compared with the ROM based on a convolutional auto-encoder, the prediction error of the SACAE ROM is reduced by 42.9%. As with other ROMs based on deep neural networks, the SACAE ROM takes a long time to train. To solve this problem, the transfer and generalization ability of the model is studied in this paper. In the experiment, the flow velocity and spoiler of the flow around the cylinder were changed, and the training time of the transfer model was reduced by about 50% to 60%. This result demonstrates that the problem of too long training time can be solved by transfer learning. [ABSTRACT FROM AUTHOR]

Quantifying how tides evolve with coupling between future sea level rise (SLR) and different coastline configurations is imperative for proposing appropriate coastal defense strategies. By using numerical models, we investigated tidal changes and determined a realistic trend of SLR on the Jiangsu coastal area and adjacent sea on the Yellow Sea shelf. A notable decrease in tidal range occurs in the northern shelf, and the tide increases mainly in the southern shelf. Tidal changes are of both signs, while the increase in sea level is unidirectional. Thus, the SLR effect on tide is not additive in all locations. We also explored the nonlinearity and spatial similarity in tidal range in response to the SLR considering uniform SLR scenarios with multiple levels and allowing inundation of the natural coastline. The patterns of change in tide evolution on the study domain remain linear until the SLR exceeds 2.0 m. Simulations and comparisons are further conducted between the responses of hardened and natural shoreline configurations to SLR. Hardened shoreline introduces both local and remote spatial variability in tidal responses. On the regional scale, SLR induces a shift in the tidal system in the offshore region, which controls the net energy flux into the embayment upon the coast. On the local scale, tidal dynamics are mainly a competition between net energy flux and tidal dissipation and are plausibly influenced by tidal reflection, which depends on whether a basin is tidally reflective. Plain Language Summary: China has experienced rapid economic growth and irreversible pressures from sea level rise (SLR) in the eastern coastal region. To provide future coastal defense strategies, we conduct multiple experiments to simulate how tides evolve with future SLR scenarios as well as how tides respond to different coastline configurations. We found that the future SLR can adjust the entire tidal system and control how much tidal energy flows into the local area from the deep ocean. Whether to build up or maintain a seawall for coastal defense depends on local conditions. By preserving the natural coast and removing the impermeable seawall from the radial sand ridges of China, tidal waves become more progressive on the shoals. Key Points: Tidal change remains linear under a 2.0‐m sea level rise within which a large spatial similarity was achieved on the Yellow Sea shelfDisplacement in the amphidromic point on the northern Yellow Sea shelf dominates the tidal range evolution for the Jiangsu coastal areaThe seawall of Jiangsu with SLR enlarges the tidal range where the tide is reflective but functions opposite where the tide is parallel to the coast [ABSTRACT FROM AUTHOR]

ABSTRACT Ni X.; Huang S.; Feng W., and Yao W., 2018. Numerical simulation of tidal bores using SPH method. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 951–956. Coconut Creek (Florida), ISSN 0749-0208. A tidal bore is a natural hydraulic phenomenon normally formed in funnel-shaped estuaries with large tidal ranges. Water levels and flow velocities change rapidly in both magnitude and direction when a tidal bore arrives. These strongly nonlinear water body movements have significant influences on scouring and deposition processes along the riverbed and produce hydrodynamic impacts on piers and dikes. In this paper, a mesh-free numerical method known as the smoothed particle hydrodynamics (SPH) method is used to implement a numerical model capable of handling complex free-surface flows and solve the Navier-Stokes equations with a large-eddy simulation. A tidal bore generation scheme suited for a mesh-free numerical method is also proposed based on the SPH open boundary technique. Various types of tidal bores, including undular bores, weakly breaking bores and breaking bores, are simulated and validated with measured data. The numerical results represent the evolutionary processes and hydrodynamic characteristics of tidal bores ranging from weak to strong intensities. The generation and evolution of dipole substructures in breaking tidal bores are also discussed. By studying the bed shear stresses and depth-averaged vorticities of the tidal bores, it can be concluded that the sediment incipience intensity grows nonlinearly in the second order with an increase in the tidal bore intensity, while the sediment transportation intensity grows linearly. [ABSTRACT FROM AUTHOR]

Ni X.; Huang S.; Feng W., and Yao W., 2018. Numerical simulation of tidal bores using SPH method. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 951–956. Coconut Creek (Florida), ISSN 0749-0208. A tidal bore is a natural hydraulic phenomenon normally formed in funnel-shaped estuaries with large tidal ranges. Water levels and flow velocities change rapidly in both magnitude and direction when a tidal bore arrives. These strongly nonlinear water body movements have significant influences on scouring and deposition processes along the riverbed and produce hydrodynamic impacts on piers and dikes. In this paper, a mesh-free numerical method known as the smoothed particle hydrodynamics (SPH) method is used to implement a numerical model capable of handling complex free-surface flows and solve the Navier-Stokes equations with a large-eddy simulation. A tidal bore generation scheme suited for a mesh-free numerical method is also proposed based on the SPH open boundary technique. Various types of tidal bores, including undular bores, weakly breaking bores and breaking bores, are simulated and validated with measured data. The numerical results represent the evolutionary processes and hydrodynamic characteristics of tidal bores ranging from weak to strong intensities. The generation and evolution of dipole substructures in breaking tidal bores are also discussed. By studying the bed shear stresses and depth-averaged vorticities of the tidal bores, it can be concluded that the sediment incipience intensity grows nonlinearly in the second order with an increase in the tidal bore intensity, while the sediment transportation intensity grows linearly. [ABSTRACT FROM AUTHOR]

Analytical and numerical investigations are carried out for harbor oscillations on a piecewise bottom of two different slopes. With the shallow water approximation, the longitudinal and transverse oscillations are analyzed by coupling the solutions on each segment of the bottom with the coupling conditions at the point of inflection in ignoring the nonlinear interactions between them. The longitudinal ones are the combinations of the Bessel functions of the first and second kinds, and the transverse ones are expressed with Kummer's equations. As the transverse oscillations trapped within the harbor are typically standing edge waves, their dispersion relationship is also derived for the two-slope-piecewise bottom. With the analytical predictions of the oscillation behaviors and based on Boussinesq equations, a range of numerical tests are made for the oscillations induced by seafloor motions on this type of piecewise bottom. Different combinations of the two slopes of the bottom are firstly tested and the numerical eigenfrequencies and wave profiles are compared with analytical ones. The transverse oscillations are revealed to be sensitive to the positions of the seafloor movements, and the importance of the position of the seafloor motions is manifested in their relative positions against the nodal lines and anti-nodal lines of the transverse modes. Although the longitudinal oscillations generated by seafloor motions of harbor width may not reach a steady state without forcing terms at the entrance, some patterns of several low-mode ones occur and are also sensitive to the position of the moveable seafloor. Wavelet spectra are used to analyze their evolutions and comparisons are made with theoretical predictions for the three principle longitudinal modes. [ABSTRACT FROM AUTHOR]

Oscillations within a rectangular harbor of parabolic bottom induced by small-scale landslides are investigated numerically based on Boussinesq-type equations and the results are used to reveal the characteristics of the oscillations generated on this type of bottom profile. Relatively, local and small-scale landslides within the harbor may induce obvious transverse oscillations. The predominant transverse components are those with small mode numbers m and n when the solid slides start moving from the backwall. The augmentation of the velocity of the slides along the parabolic seafloor may shift the amplitudes of the oscillation components to larger values, which corresponds to the physical understandings of the waves generated by landslides. In comparing the oscillations induced by the slides of constant velocity and those accelerated by gravity force with bottom friction, it is observed that the movements accelerated by gravity force may facilitate the development of certain oscillation modes while those with constant velocity may be in favor of others. While the landslides may not act on an isolated point of the bottom but follow a certain trajectory along the harbor, the transverse oscillations induced by landslides are sensitive to their position of departure both in the cross-harbor direction and in the offshore direction. The numerical result of each transverse eigenfrequency is very close to the theoretical prediction and the spatial structure of each mode may also be well captured by the existing analytical solutions based on shallow water equations. Although longitudinal oscillations may not be steadily generated with landslide movements on a parabolic bottom within the harbor, some patterns of several low-mode ones occur and are also sensitive to the initial location and trajectory of the slides. Wavelet spectra are used to analyze their evolutions and comparisons are made with theoretical predictions. [ABSTRACT FROM AUTHOR]

The smoothed particle hydrodynamics (SPH) technique is a mesh-free numerical method that has great potential to be used in the development of the next generation of numerical ocean models. The implementation of open and solid boundary conditions in the SPH method, however, is not as straightforward as the mesh-based numerical methods. Two types of open boundary conditions are considered in this study: the adaptive open boundary condition (AOBC) and Flather's open boundary condition (FOBC). These two open boundary conditions are implemented in the SPH-based shallow-water equation (SWE) circulation model for simulating sea surface elevations and depth-mean currents over a limited area with open boundaries. The performance of these two open boundaries is assessed in four numerical test cases. In comparison with the conventional characteristic open boundary condition, both the AOBC and the FOBC allow perturbations to propagate out more effectively and are easy to implement with the specification of external flow conditions at the model open boundaries. The model results also demonstrate that the AOBC requires an accurate estimation of the phase speed of perturbations and could lead to a small drift in the mean water level. By comparison, the FOBC is computationally more efficient without any model drift. The SPH-based SWE circulation model is also used in simulating the laboratory observations of the 1993 Okushiri Tsunami. The numerical results in this case demonstrate the feasibility and capability of the SPH-based SWE model for simulating free-surface flows in regions with complicated bathymetry and irregular coastline. [ABSTRACT FROM AUTHOR]

Cao, H.; Chen, Y.; Tian, Y., and Feng, W., 2016. Field investigation into wave attenuation in the mangrove environment of the South China Sea coast. Coastal mangroves form the land-sea interface and face an increasingly aggressive threat from ocean waves as a result of sea-level rise. This study investigates the buffering effect of mangroves on the coast of Leizhou Bay in the South China Sea under two different climates (normal windy weather and storm). By doing this, we aim to establish the exact wave damping rate due to the presence of mangroves and to study the wave and spectral characteristics of wave energy in the vegetated area. Wave gauges are mounted along a cross-shore transect to monitor the wave conditions during particular time periods. From the data analysis, we found that the recorded maximum significant wave height is 22.3 cm at the outermost station and remarkable wave damping was experienced within the mangrove troops of 100 meters. To evaluate the wave dissipation on the mudflat, an empirical expression is proposed on the basis of the field data. In this way, the net vegetation-induced wave dissipation is quantified separately. The spectral analysis of wave energy shows the modalities of frequency-dependent wave energy dissipation under different weather conditions. From the results, we conclude that the wave height was strictly subjected to the concurrent water depth even under the storm condition. The relative water depth (to the wave height) determined wave generation or dissipation on the mudflat. Despite the existence of dissipation by the mudflat, wave energy was majorly attenuated by the mangrove system. The wind growth of wave energy is of great significance when studying the spectral characteristics of wave energy during storm conditions. [ABSTRACT FROM AUTHOR]

Based on the linear shallow water approximation, longitudinal and transverse oscillations in a rectangular harbor with a parabolic bottom are analyzed. The longitudinal ones are combinations of the Legendre functions of the first and second kinds and the transverse ones are expressed with modified Bessel equations. Analytic results for longitudinal oscillations show that the augmentation of rapidity of variation of the water depth shifts the resonant wave frequencies to larger values and slightly changes the positions of the nodes for the resonant modes. For the transverse oscillations trapped within the harbor which are typically standing edge waves, the dispersion relationship is derived and the spatial structures of the first four modes are presented. The solutions illustrate that all the trapped modes are affected by the varying water depth parameters, especially for the higher modes whose profiles extend farther and the distribution of the energy of transverse oscillations is influenced by the rapidity of variation of the bottom within the harbor. [ABSTRACT FROM AUTHOR]

Cao, H.; Feng, W., and Chen, Y., 2016. Numerical modeling of wave transformation and runup reduction by the coastal vegetation of the South China Sea. Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 830-835. Coconut Creek (Florida), ISSN 0749-0208. The aim of this study is to examine wave transformation and runup using a numerical model of coastal conditions including vegetation. Based on the previous field study, the drag coefficient was estimated using an analytical model. After that, numerical modeling of wave dissipation in SWASH (Simulating WAves until SHore) was conducted and validated with the observed data. Furthermore, calibrated SWASH was used to inspect the wave runup under vegetated and non-vegetated cases. For the flexibility of numerical modeling, We also used the numerical model to assess various vegetation parameters and beach slopes to inform the characteristics of wave runup reduction. The results of the model indicate that SWASH with proper parameters accurately simulated wave dissipation. Wave runup and setup were significantly reduced by the coastal vegetation. The numerical results suggest that vegetation parameters and beach slope are important factors when analyzing the wave runup reduction rate. [ABSTRACT FROM AUTHOR]

Large caissons are extensively applied as deep-water foundations in marine engineering. In fact, caissons are generally prefabricated and transported to project site by wet towing. Motion responses of large caissons and those occurring during the towing process were investigated, and CO2 emissions under various conditions were calculated. These are all considered to ensure towing safety and environmental protection. The caisson resistance coefficient was simulated via Ansys Fluent software. The effects of towrope length, towing speed, and drift depth on the motion responses of caissons under the combined action of wind and wave were evaluated via Ansys AQWA software. Maximum heave value was dominantly affected by rope length and draft depth, and its fluctuation was highly influenced by towing speed and draft depth. However, all of the above mentioned factors had insignificant influences on pitch response. When towing existed, rope tension was rapidly increased from zero to a constant value that depended on towing speed and drift depth. However, the speed of achieving this stable phase depended on the length of the towrope. [ABSTRACT FROM AUTHOR]

Feng, X.; Dong, B.X.; Ma, G.F., and Feng, W.B., 2020. Topographic and hydrodynamic influence on rip currents and alongshore currents on headland beaches in China. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 468–473. Coconut Creek (Florida), ISSN 0749-0208. Headland beaches are one of the most typical beaches in southern China. Meanwhile, southern China seas experienced severe rip current hazards. In this paper, numerical simulations were carried out by utilizing Delft 3D Flow-Wave coupling model. Ideal topography of different headland beaches was established and the variabilities in the rip currents' forms and the hydrodynamics from the major headland beach patterns were discussed, including the relative headland length (α= Lhead/Lbeach), the curvature of shoreline (k = Ls/Lc), the wave direction (θ) and the wave height (hs). Results revealed that four factors, including α, k, θ and hs, all have some influences on the nearshore circulation. The shape of the coastline influenced the position of alongshore current and the appearance of headland rip. The length of headland and the wave height influenced the intensity and the spatial distribution of nearshore circulation mainly. Besides, wave direction was the most important factor for channel rip. Because it played a decisive role in the generation of channel rip. [ABSTRACT FROM AUTHOR]