Explore the vast range of titles available.

Floating vertical−axis wind turbines present unique advantages for deep−water offshore deployments, but their basin model testing encounters significant challenges in aerodynamic load simulation due to Reynolds scaling effects. While Froude−scaled experiments accurately replicate hydrodynamic behaviors, the drastic reduction in Reynolds numbers at the model scale leads to substantial discrepancies in aerodynamic forces compared to full−scale conditions. This study proposed two methodologies to address these challenges. Fully physical model tests adopt a “physical wind field + rotor model + floating foundation” approach, realistically simulating aerodynamic loads during rotor rotation. Semi−physical model tests employ a “numerical wind field + rotor model + physical floating foundation” configuration, where theoretical aerodynamic loads are obtained through numerical calculations and then reproduced using controllable actuator structures. For fully physical model tests, a blade reconstruction framework integrated airfoil optimization, chord length adjustments, and twist angle modifications through Taylor expansion−based sensitivity analysis. The method achieved thrust coefficient similarity across the operational tip−speed ratio range. For semi−physical tests, a cruciform−arranged rotor system with eight dynamically controlled rotors and constrained thrust allocation algorithms enabled the simultaneous reproduction of periodic streamwise/crosswind thrusts and vertical−axis torque. Numerical case studies demonstrated that the system effectively simulates six−degree−of−freedom aerodynamic loads under turbulent conditions while maintaining thrust variation rates below 9.3% between adjacent time steps. These solutions addressed VAWTs’ distinct aerodynamic complexities, including azimuth−dependent Reynolds number fluctuations and multidirectional force coupling, which conventional methods fail to accommodate. The developed techniques enhanced the fidelity of floating VAWT basin tests, providing critical experimental validation tools for emerging offshore wind technologies.

The determination of ice loads on polar vessels and offshore structures is important for ice-resistant design, safe operation, and management of structural integrity in ice-infested waters. Physical model testing carried out in an ice tank/basin is usually an important technical approach for evaluating the ice loads. However, the high cost and time consumption make it difficult to perform multiple repetitions or numerous trials. Recently, the rapid development of high-performance computation techniques provides a usable alternative where the numerical methods represented by the discrete element method (DEM) have made remarkable contributions to the ice load predictions. Based on DEM simulations validated by physical model tests, numerical ice tanks can be developed as an effective complement to their counterparts. In this paper, a numerical ice tank based on 3D spherical DEM was established with respect to the small ice model basin of China Ship Scientific Research Center (CSSRC-SIMB). Based on spherical DEM with parallel bond model, the model tests of typical structures (vertical cylinder and inclined plate) in level ice sheets were established in the numerical ice tank, and the ice–structure interaction process under the same initial conditions was simulated. The accuracy of the simulations is verified by comparing the simulated ice loads with the measured ice loads from the model tests in the CSSRC-SIMB. Furthermore, the application of the numerical ice tank was extended to simulate the navigation of a Wass bow in level ice and broken ice conditions. The value of the break resistance of the Wass bow in level ice was evaluated, and the numerical ice tank produced results that were found to be consistent with those obtained from Lindqvist’s formula. The statistical properties of the bow load for different broken ice fields with the same initial physical conditions are analyzed by performing a repeatability test on the broken ice fields.

The formation control of multiple autonomous underwater vehicles (AUVs) is increasingly becoming a vital factor in enhancing the efficiency of ocean resources exploration. However, it is currently difficult to deploy such a package of AUVs for operation at sea because of their large size. The aim of our study is to create a demonstration system for formation control algorithms using actual hardware. To implement a prototype system, we developed a testbed AUV usable in a test basin and performed a simple formation control test in the Actual Sea Model Basin of the National Maritime Research Institute, Japan. Two AUVs, the simulated “virtual” leader and the developed “real” follower, communicate through an acoustic link and hence cruise to maintain a constant distance between them. Tests for more sophisticated formation control algorithms will be enabled using the system; consequently rapid implementation at sea will be realized.

Introduction Resource managers need spatially explicit models of hydrologic response to changes in key climatic drivers across variable landscape conditions. We demonstrate the utility of a Basin Characterization Model for California (CA-BCM) to integrate high-resolution data on physical watershed characteristics with historical or projected climate data to predict watershed-specific hydrologic responses. Methods The CA-BCM applies a monthly regional water-balance model to simulate hydrologic responses to climate at the spatial resolution of a 270-m grid. The model has been calibrated using a total of 159 relatively unimpaired watersheds for the California region. Results As a result of calibration, predicted basin discharge closely matches measured data for validation watersheds. The CA-BCM recharge and runoff estimates, combined with estimates of snowpack and timing of snowmelt, provide a basis for assessing variations in water availability. Another important output variable, climatic water deficit , integrates the combined effects of temperature and rainfall on site-specific soil moisture, a factor that plants may respond to more directly than air temperature and precipitation alone. Model outputs are calculated for each grid cell, allowing results to be summarized for a variety of planning units including hillslopes, watersheds, ecoregions, or political boundaries. Conclusions The ability to confidently calculate hydrologic outputs at fine spatial scales provides a new suite of hydrologic predictor variables that can be used for a variety of purposes, such as projections of changes in water availability, environmental demand, or distribution of plants and habitats. Here we present the framework of the CA-BCM model for the California hydrologic region, a test of model performance on 159 watersheds, summary results for the region for the 1981–2010 time period, and changes since the 1951–1980 time period.

In coarse resolution ocean models, eddy diffusive effects are parameterized using an isopycnal mixing coefficient, which controls mixing strength along isopycnals. Recent high‐resolution simulations show that increasing the wind stress over the Southern Ocean leads to increased local isopycnal mixing. In this work, we investigate how wind and isopycnal mixing affect surface temperature and salinity in the Southern Ocean and the buoyancy of waters near Antarctica. Using an idealized Massachusetts Institute of Technology general circulation model basin‐channel model, we vary both Southern Ocean wind stress and the isopycnal mixing coefficient independently. We find that when the wind and isopycnal mixing coefficient are small, a strong halocline in the far south prevents AABW formation. Increasing the wind stress and/or isopycnal mixing brings warmer, saltier water to the surface of the Southern Ocean, where it cools, becomes denser, and forms AABW. Increasing the isopycnal mixing coefficient also increases the latitudinal extent of the source waters for AABW formation. Plain Language Summary Ocean mixing refers to the small‐scale processes that redistribute ocean properties such as heat and salt. This mixing can be categorized into two types: mixing along layers of constant density and mixing between these layers. A wide range of values for mixing along layers (50–5,000 m2/s${\\mathrm{m}}^{2}/\\mathrm{s}$ ) are used in research and observed in the real world. Wind also influences heat and salt at the surface of the Southern Ocean. This paper looks at the effects of changing the mixing strength along the layers and at the effects of varied wind over the Southern Ocean in an idealized model. With sufficient strength of both the mixing along the layers and the wind over the Southern Ocean, our model has sinking in both the far south and far north. The sinking in the far south is turned off as a result of having both weak mixing strength along the layers and weak wind over the Southern Ocean. When increasing the mixing strength the sinking in the far south covers more area because it reaches further north. Key Points The isopycnal mixing coefficient and the Southern Ocean winds are varied in an idealized‐geometry single‐basin model Increasing the isopycnal mixing coefficient increases the latitudinal span of Southern Ocean negative surface buoyancy flux As a result, the Southern Ocean sinking is fed by southward flow from a wider range of latitudes when isopycnal mixing is larger

150 years ago, the first modern icebreaker in the world was designed by the naval architect Carl Ferdinand Steinhaus and built for purpose of removing ice barriers on the river Elbe in Hamburg, Germany. No model tests were performed at that time. Later, in the first half of the 20 th century, “model tests” for ships were carried out in natural ice on lakes. In the 1950 th the first-generation ice model basins were put in operation and ice model testing became a standard method in the icebreaker design process. This paper discusses the influence of the economic and environmental development in arctic regions, driven by shipping and offshore activities in environmental changing Arctic Waters, on the ice model basin design, equipment and testing methods. The developments will be presented with examples from The Hamburg Ship Model Basin (HSVA ). To complete the overview, an outlook to future trends is attempted.

This paper aims to cost-effectively improve the energy efficiency of large vessels in shipping by the optimum design of propeller boss cap fins (PBCFs). First, a model propeller of the modern four-blade propeller in a Ro-Ro ship, with no boss cap fin in its original design, is experimentally and numerically investigated. The computational fluid dynamics (CFD) model reproduced all the experiments very well. Then, the CFD model is used to conduct a comprehensive optimum design of PBCFs for the down-scaled propeller. Besides the commonly used rectangular PBCFs, nine airfoils are investigated, due to their favorable lift-to-drag ratio and great potential of being effective PBCFs. The best performing profile, among the 10 shapes, is chosen as the PBCF for further optimization. Finally, the optimum design of the PBCFs for the propeller/rudder system is achieved. It was found to yield remarkable efficiency gains for the modern propeller/rudder system under both design and off-design operation conditions, mainly due to the suppressed hub vortex and partly due to the extra thrust. The yield strength analysis confirmed that the optimum design is feasible in practice and can be used in industrial vessels. The generalized criteria for the optimum design of PBCFs also benefit other propeller/rudder systems for cost-effective energy saving.

In the process of ship motion control system design, it is necessary to take into account the impact of environmental disturbances such as winds, waves and sea currents. The commonly used representatives of wave influences in this area are the unidirectional wave power spectral density functions describing sea waves of different form: long-crested, fully developed waves, developing wind waves or multi-modal waves (e.g., with swell). The existing standard PSD models describe the surge of open sea or ocean. However, they are inadequate in the case of control system testing of scale ship models for sailing in open water areas such as lakes or test pools. This paper presents a study of wind-generated wave PSD estimations for a small lake used as a test area for free-running scale ships. The publication provides a brief overview of the wave spectral density functions commonly used for control system design. A measurement instrument using the idea of a water-induced variable capacitance that works synchronously with the wind sensors is also described. The process of collected data analysis is presented. As a result of the study, a series of empirical spectral density functions of lake waves for different wind speeds are obtained. They correspond to the rescaled, two-parametric ITTC model.

In this paper, we provide new experimental data of the wave-induced steady forces (the added resistance, wave-induced steady lateral force, and yaw moment) acting on a full hull ship in regular waves, and we verify the validity of existing prediction methods for wave-induced steady forces by performing comparisons with results obtained experimentally. For the prediction methods, we consider the zero-speed three-dimensional panel method (3DPM) and the method based on formulas of the wave-induced steady forces that are expressed using the Kochin-function assuming a slender ship (strip theory-based Kochin-function method: SKFM). The results show that the calculation accuracy obtained using 3DPM and SKFM for added resistance and steady lateral force is acceptable for practical purposes although the accuracy is insufficient for the steady yaw moment. In order to confirm the applicability of both methods to the problem of maneuvering in waves, we predict the turning motions of the ship in irregular waves using the calculation results obtained by 3DPM and SKFM for the wave-induced steady forces, and we compare the turning motions with the free-running model test results. Both methods are useful for predicting turning motions in irregular waves.

The strong nonlinearity of shallow-water waves significantly affects the dynamic response of floating offshore wind turbines (FOWTs), introducing additional complexity in motion behavior. This study presents a series of 1:80-scale experiments conducted on a 5 MW FOWT at a 50 m water depth, under regular, irregular, and focused wave conditions. The tests were conducted under regular, irregular, and focused wave conditions. The results show that, under both regular and irregular wave conditions, the platform’s motion and mooring tension increased as the wave period became longer, indicating a greater energy transfer and stronger coupling effects at lower wave frequencies. Specifically, in irregular seas, mooring tension increased by 16% between moderate and high sea states, with pronounced surge–pitch coupling near the natural frequency. Under focused wave conditions, the platform experienced significant surge displacement due to the impact of large wave crests, followed by free-decay behavior. Meanwhile, the pitch amplitude increased by up to 27%, and mooring line tension rose by 16% as the wave steepness intensified. These findings provide valuable insights for the design and optimization of FOWTs in complex marine environments, particularly under extreme wave conditions. Additionally, they contribute to the refinement of relevant numerical simulation methods.