Irregular Waves Research Articles

Effects of different wave calculation methods on groundwater flow and salt transport in coastal aquifers under irregular waves

Experimental study on added resistance of KSUPRAMAX-O in regular and irregular waves considering nonlinear effects of wave height

Numerical investigation of coupled responses of a mining vessel and moonpool in regular and irregular waves with varying moonpool aspect ratios using SPH

The performance of bow foils in irregular and oblique waves

Floating offshore wind–wave hybrid systems, as a novel structural form integrating floating wind turbine foundations and WECs, can effectively enhance the efficiency of renewable energy utilization when properly designed. A numerical model is established to investigate the dynamic responses of a wind–wave hybrid system comprising a semi-submersible FOWT and PA wave energy converters. The optimal damping values of the PTO system for the wind–wave hybrid system are determined based on an NSGA-II. Subsequently, a comparative analysis of dynamic responses is carried out for the PTO system with different states: latching, fully released, and optimal damping. Under the same extreme irregular wave conditions, the pitch motion of the FOWT with optimal damping is reduced to 71% and 50% compared to the latching and fully released states, respectively. The maximum mooring line tension in the optimal damping state is similar to that in the fully released state, but nearly 40% lower than in the latching state. This optimal control strategy not only sustains power generation but also enhances structural stability and efficiency compared to traditional survival strategies, offering a promising approach for cost-effective offshore wind and wave energy utilization.

Dispersion, nonlinearity, and waves-wave interactions are some of the important aspects of two-dimensional wave behaviour that are captured by the mathematical model known as the ion sound and Langmuir wave system. This study uses the truncated Painlevé technique to examine the (1+1) dimensional integrable ion Sound and Langmuir wave system. Various localised solutions, such as rogue or irregular waves, dromion-pair, and dromions can be produced via applying random functions to the findings. The collisional interaction of these solutions are produced, investigated, and visually displayed as a result of selecting suitable starting values for the arbitrary functions. We discover that dromions interact inelastically, exchanging both energy and phase, but rogue waves are inherently erratic. These findings advance our understanding of complex wave dynamics and have important implications for the study of non-linear occurrences in a variety of disciplines such as physical mechanisms, fluid dynamics, oceanography and nonlinear optics. It’s crucial to remember that all computations and visualisations are generated and their reliability and accuracy verified using Mathematica software. All things taken into account this work enhances our knowledge of complexities nonlinear systems and how their behaviour is influenced by their initial conditions. The study’s findings will aid in our comprehension of how waves behave in higher dimensional controlling models.

Dose optimization of NMDA for rat model of infantile spasms: Approach using EEG, behavior (Seizure) and histopathology.

Controlled laboratory wave flume experiments of dune erosion can assist researchers to explore the physical processes of dune erosion and improve numerical predictive models. This paper presents a dataset of controlled laboratory measurements of unvegetated dune erosion under vary waves, water levels, and initial dune moisture contents. Three different water levels in the wave flume, two irregular wave conditions, and three initial dune pore-moisture contents were explored. In total, twenty-nine (29) tests were conducted in a 36 m long by 1.6 m high and 0.9 m wide wave flume. Bathymetry, dune morphology, offshore and onshore wave conditions, wave runup, water table and volumetric water content data within the dune were recorded across all tests, as well as video footage for qualitative purposes. This combined dataset can be used to: (1) explore nearshore morphodynamic processes under varied forcing conditions, (2) elucidate dune face erosion and failure mechanisms tying the observed erosion to internal groundwater dynamics and external wave and water level forcing, and (3) validate numerical models of dune erosion processes.

The study of stabilisation performance is a crucial consideration in the design of offshore floating platforms. For large floating structures, incorporating passive anti-roll tanks is a common technique for roll reduction. To investigate the feasibility of using ballast tanks for roll attenuation on the “Guo Hai Shi 1” platform, this study employs the internal tank theory to analyze the influence of four independent empty tanks, located around the platform, acting as anti-roll tanks with varying ballast water volumes. The results indicate that: (1) Different ballast water volumes within a single tank do not significantly affect the static stability parameters of the platform. (2) In regular wave simulations, the ballast tanks show limited effectiveness in reducing pitch motion along the wave incidence direction but effectively suppress coupled responses in other degrees of freedom. In the resonance case (Case 3), the minimum pitch occurs in Condition 1 at 10.56°, while the maximum pitch reaches 11.45° in Condition 2. Nevertheless, a 40% reduction in roll motion is achieved (3.36° in Condition 4 vs. 5.60° in Condition 1), along with a 24.5% reduction in yaw motion (39.22° in Condition 4 vs. 51.94° in Condition 1). (3) In irregular wave simulations, the ballast tanks effectively reduce the heave amplitude by up to 8.34% in sea state level 4 and 6.06% in sea state level 8, thereby enhancing its wave-following performance in the heave degree of freedom. (4) A CNN_BiLSTM_Attention algorithm is developed using hydrodynamic analysis generated datasets to predict the pitch motion time series of the platform under different ballast water conditions and sea states, while the model has a superior prediction performance (R² = 0.9658, RMSE = 0.5343, MAE = 0.3188, representing a 4.82% increase in R² and 30.31% reduction in RMSE compared to the original model). Future work will further explore the application of ballast tanks on floating platforms, with a focus on performance optimization and the development of advanced neural network models capable of predicting motion responses under various ballast configurations. Moreover, appropriate evaluation metrics will be established to assess the effectiveness of ballast tank designs. Efforts will also be directed towards integrating time-domain motion prediction using neural networks with control theories aimed at dynamically regulating ballast water volume to enhance platform stability.

ABSTRACT This paper presents an irregular wave simulation using the Moving Particle Semi-implicit (MPS) method. Irregular waves consist of component waves with a variety of frequencies and wave heights; however, a numerical model with sufficiently high energy conservation must be applied to reproduce them effectively in a numerical simulation. In general, conventional particle methods do not have sufficient energy conservation, and they cannot successfully realize irregular waves propagating a sufficiently long distance. Therefore, in this study, we propose an MPS-based numerical model with high energy conservation. We clarify that the standard algorithm of the original MPS method is not strictly based on the projection method and propose a modified algorithm to resolve this problem completely, namely Accurate Projection Algorithm (APA). The proposed model implementing APA and several enhanced MPS-based discretization schemes, including the Improved Dynamic Stabilization (IDS) scheme has high energy conservation. The model was verified and validated through three types of benchmark tests: a plane 2D oscillating drop test, a vertical 2D standing wave test, and a solitary wave test. Subsequently, we conducted an irregular wave simulation in a wave flume with a flat bottom. It was demonstrated that the proposed model can simulate irregular waves without wave height attenuation.

Abstract A visual operational guidance, known as a polar chart, shows considerable potential for preventing excessive roll motion caused by parametric roll. This study utilizes a method based on the extended Grim’s effective wave (EGEW) theory for preparing a polar chart and validates it using experimental data. Although it can also be prepared by nonlinear seakeeping simulation in irregular waves, the proposed approach is computationally more efficient. The study compared experimental data and estimated parametric roll under both longitudinal and quartering wave conditions, the latter being particularly critical for large container ships. Additionally, a 6-degree-of-freedom (6-DOF) motion simulation based on three-dimensional potential theory was employed for comparison. The results demonstrated that the polar chart yield more conservative estimates than both the experimental data and the 6-DOF simulation, effectively covering the range where parametric roll is likely to occur. The findings could contribute to the development of safer operation, thereby reducing the risk of parametric roll.

In the field of wave energy, multi-axis wave energy converters (WECs) have emerged as a research priority owing to their enhanced energy absorption, leading to increased computational complexity. Conventional model predictive control (MPC) approaches have demonstrated limitations in the trade-off between real-time requirements and control performance. This paper proposes a bi-layer MPC strategy, including a long-term energy maximization layer and a short-term trajectory-tracking layer. First, a multi-axis underactuated WEC (MU-WEC) is proposed, which incorporates an inertial cable-driven parallel mechanism to absorb energy from multiple directions. In addition, a control-oriented dynamic model of a MU-WEC is established. Then, a bi-layer MPC strategy is proposed, which decouples computationally intensive optimization processes from time-sensitive real-time control, alleviating the computational burden significantly. Therefore, the upper layer achieves enhanced control performance by enabling extended prediction horizons, whereas the lower layer serves to ensure real-time requirements. Moreover, numerical simulations under irregular wave conditions demonstrate the performance of the proposed bi-layer MPC: under different waves, bi-layer MPC improves energy absorption by 127–311% over conventional MPC. This performance enhancement stems from the 5 times extension of the prediction horizon enabled by the reduced computational burden.

Abstract A numerical model is developed to examine the hydrodynamic interaction of irregular waves with a dual-wing
floating breakwater (DWFB) using the boundary element method (BEM). The linear water wave theory has been
adopted to investigate the wave scattering problem. For this analysis, three distinct configurations of DWFB
geometries are examined. Initially, the numerical results are compared with established analytical solutions from
the previous studies under regular wave conditions to validate the proposed numerical method. Subsequently,
the reflection (Kr) and transmission (Kt) coefficients of the DWFB, regardless of the shape configuration, were
calculated. After the study was extended to the irregular wave conditions to further examine the influence of
incident wave characteristics and certain geometrical factors, such as the DWFBs length and submergence depth,
on its performance efficiency. To assess the impact of irregular waves on the DWFB, the Pierson-Moskowitz
spectrum is considered in the frequency domain, and the incident wave spectra are analyzed to obtain the
response spectra for reflection and transmission. This study can aid in evaluating the effectiveness of wave
attenuation performance and refining breakwater design to ensure effective coastal protection under various
wave conditions.

A non-axisymmetric floating oscillating water column (OWC) wave energy converter (WEC) is proposed in this paper. In contrast to the traditional bottom opening used in axisymmetric OWCs, the newly proposed OWC WEC has a submerged opening positioned on the front cylindrical wall. A semi-analytical coupled hydrodynamic–pneumatic model is developed to investigate the power extraction of the proposed OWC, where the hydrodynamic model is established using the matching eigenfunction expansions and method of separation of variables. Following the model validation against general theoretical identities, the model is first applied to a stationary offshore OWC to study the effects of the chamber breadth and submerged opening geometry on power extraction under a series of regular waves with varying wave periods and incident directions, and then to an elastically constrained floating OWC WEC with six degree-of-freedom motion under both regular and irregular waves. The numerical results show that in comparison with axisymmetric OWCs, the proposed non-axisymmetric configuration significantly broadens the effective frequency bandwidth and increases the capture width ratio by up to three times with normal incidence of both regular and irregular waves. For floating OWCs, the free-sway motion emerges as a detrimental factor, negatively affecting both power extraction and safe operation.

Performance analysis of two-body wave energy converters with a bistable mechanism and a mechanical motion rectifier in irregular waves

ABSTRACT To improve hydrodynamic performance of semi-submersible platforms, influence of a bilge keel on moonpool responses and six degrees of freedom (6-DOFs) motion characteristics of a conceptual semi-submersible platform equipped with a hollow moonpool were investigated experimentally in this work. Results indicate that moonpool responses are predominantly dominated by piston-mode motion and green-water phenomena occur with incident wave period of 14 s. The intensity of piston-mode motion of the platform with bilge keel is significantly reduced compared to the platform without bilge keel under same incident waves. Furthermore, Response Amplitude Operators (RAO) indicate that hydrodynamic performance of the platform equipped with bilge keel is better with respect to reduced heave and pitch amplitudes due to increased viscous damping. Amplitudes of sway and roll motions of the platform with bilge keel are also decreased in irregular waves.

The hydrodynamic response of closed and semi-closed (open-bottom) rigid cylindrical aquaculture platforms was examined through combined model tests and numerical simulations. Free decay tests in calm water quantified natural periods and damping ratios for heave and pitch motions. Subsequent regular wave testing characterized response amplitude operators (RAOs) and wave elevations at interior and exterior wave gauges. Finally, the motion and wave elevation characteristics of the two types of aquaculture platforms under irregular waves were analyzed under extreme sea conditions. Results demonstrated that bottom openings significantly altered hydrodynamic responses of aquaculture platforms, with a 59% enhancement in heave damping ratio and a 47% reduction in heave natural period. Semi-closed cages exhibited asymmetric internal sloshing profiles along the mid-transverse axis, with lateral sloshing amplitudes increasing by 200–300% at lateral wave gauges. Under irregular wave conditions, compared to closed aquaculture platform, semi-closed aquaculture platform increased the heave, pitch motion, and internal sloshing response but reduced run-up on the outer wave-facing side.

Abstract Model-scale testing of floating wind turbine substructures is an integral part of design verification. Yet, both the test-facility and Froude-scales used, raise questions over the suitability of the hydrodynamic coefficients obtained. In this study, experimental measurements from towing tank tests with a 1:100 scale model of the INO WINDMOOR semi-submersible are directly compared to those from ocean basin tests of a 1:40 scale model. Dry inertial parameters for the two physical models are maintained within approximately 10% and very similar motion responses were found in the wave- and low-frequency ranges for the main degrees-of-freedom in a variety of irregular wave cases. Some significant discrepancies on mooring loads were obtained in the low-frequency range, thought to be due to differences in low-frequency incident energy.

Latching control of a point absorber wave energy converter in irregular wave environments coupling computational fluid dynamics and deep reinforcement learning

Abstract This paper deals with the dynamic responses of a semi-submersible floating wind turbine (FWT) under various environmental conditions with a particular focus on the wave-induced high-frequency (WIHF) structural responses. Experimental results are used to validate that WIHF structural loads are significant to the total structural loads under irregular wave conditions, and increases with the severity of sea conditions. Furthermore, ten typical wind and wave combined environmental conditions are selected for further numerical load effect analysis. The aero-hydro-servo-elastic fully coupled dynamic analysis of the semi-submerisible FWT system is conducted in SIMA. Two numerical model, Linear hydrodynamic model (LHM) and nonlinear hydrodynamic model (NHM), are built for the comparison of structural responses of tower and aerodynamic force. Moreover, four unfavourable environmental conditions are selected based on the statistic results to further investigate the effects of second-order sum-frequency wave loads on the ultimate limit state (ULS) check of critical tower section.