Search Results (66)

The high cost of mooring systems, driven by extreme peak tensions during storm conditions, remains a significant barrier to the commercialization of floating offshore wind turbines (FOWTs). This paper proposes an innovative active tension-regulating joint (TRJ) for FOWT mooring lines. The TRJ consists of nested cylinders and an actively controlled accumulator, designed to release additional line length under high tension and to recover it under low tension, thereby reducing extreme dynamic peaks. A finite element scheme is also developed for efficient line dynamics analysis. The TRJ concept is applied to a benchmark IEA 15-MW semi-submersible FOWT in 100 m water depth under 50-year return period environmental conditions. The simulation results demonstrate that the TRJ reduces the maximum mooring line tension by approximately 53% and the maximum suspended line length by over 23%. This active control technique enables the downsizing of mooring components and a significant cost reduction. Full article

Curves constructed directly on point clouds are a core primitive in reverse engineering, product design, and point-based CAD; many workflows additionally require the curve to lie in a plane—e.g., as a section profile, inspection path, or design reference. This paper presents an algorithmic framework for computing free and plane-constrained geodesic curves directly on oriented point clouds, without any intermediate surface or mesh reconstruction. A geodesic-curvature-minimizing solver that combines a Newton/conjugate-gradient flow with directed projection, elliptic Gabriel neighborhoods, and Taubin smoothing forms the backbone; the plane-constrained problem is then reduced to a one-parameter pencil of planes through the endpoint chord and solved per plane by alternating projection onto the cloud and the plane, with a projection-only pre-lift and a penalized length objective that rejects sections floating off the cloud; the returned section is the best found over a sampled pencil of candidate planes. The returned sections are attached to the cloud within a small fraction of the mean sampling distance. All algorithms are given in pseudocode with convergence criteria and complexity estimates. Two parallel realizations of the plane search are developed and measured: a multithreaded CPU backend (about 3× over the serial scan) and a WebGPU backend that evaluates the whole plane pencil in a single compute dispatch. Accuracy is validated against the analytic conic sections of a cone and against cylinder and sphere benchmarks whose optimal plane is known in closed form; robustness is assessed under noise, non-uniform sampling, missing regions, outliers, and perturbed normals, and against both a slab-projection baseline and the conventional reconstruct-then-slice route. Five applications—shoe-last reverse engineering with a C² surface reconstruction, anthropometric girth measurement, medical transverse sectioning, dimensional metrology on industrial mold scans, and cleaning-path planning for a robotic surface-treatment task—demonstrate the plane-constrained geodesic curves in practice. Full article

Two methods of accounting for the motion of the bodies—the deforming mesh method and the method of overlapping meshes (or overset mesh method)—are compared using problems with floating bodies, which are typical for the shipbuilding industry. Three problems are considered: oscillation of the cylinder on the water surface, movement of the box under the influence of waves, and heaving and pitching of the ship model in head waves. Numerical computations are carried out in the LOGOS software package, the simulation methodology used is based on the solution of a system of Reynolds-averaged Navier-Stokes equations, and the Volume of fluid (VOF) method to take into account the free surface. In all problems, the characteristics of the movement of bodies are evaluated; the resistance force of the ship model is also determined in the third problem; control values obtained using two methods of accounting for moving bodies are compared with the available experimental data. The results of numerical simulation have shown that both methods predict body movement parameters well; the accuracy in determining the resistance force in the task of streamlining the ship’s hull is also comparable: the difference between the maximum deviations of the resistance coefficient in the computations with deformation and overlapping computation meshes is 0.5%. In the case of computations of the three-dimensional problem, the time spent when using the mesh-deformation method turned out to be 10% more; therefore, the method of overlapping meshes can be considered more optimal when solving such shipbuilding tasks as self-propelled tests and streamlining the ship’s hull with and without wind and wave loads. Full article

This study establishes a triangular numerical wave tank based on the viscous incompressible Navier–Stokes equations. The model is implemented in STAR-CCM+, employing the Reynolds-Averaged Navier–Stokes equations and the Volume of Fluid method, combined with velocity boundary wave-making and momentum source wave-making techniques for wave generation. On this basis, systematic numerical simulations of oblique and head-on waves were conducted, along with simulation studies of wave interactions with both fixed and floating circular cylinders. The accuracy and reliability of the model were validated by comparing simulation results with theoretical solutions and existing literature data. The results demonstrate that the performance of this triangular wave tank is not affected by the wave incident direction. It can stably generate high-quality oblique and head-on waves, making it suitable for numerical simulation studies of wave–structure interactions. Full article

Phase-resolved wave estimation during operation of floating structures based on motion measurements provides an efficient, low-cost approach to enhancing operations. Prolate spheroidal wave functions (PSWFs) enable the reconstruction of wave profiles in short time windows with the help of a wave-to-motion response amplitude operator (RAO). Although fully linear hydrodynamic modeling can efficiently derive the RAO of floating structures, its applicability is highly limited to rather linear operation conditions. This study extends the PSWF methodology for wave estimation by combining it with the statistical linearization approach, which allows nonlinearities to be incorporated into the RAO based on the measured motion. The combined methodology is verified with motions for a floating cylinder and sphere, whose motions were calculated using a time domain simulation based on Cummins equation. Viscous drag and nonlinear hydrostatic forces were investigated. The results showed that the combined methodology increased the accuracy of the resulting wave profiles, measured in terms of correlation and spectral differences. Combining PSWFs and statistical linearization reproduced wave profiles with correlation values above 0.9 in waves with periods greater than 9 s. Combining both nonlinear effects for the sphere slightly increased the method’s accuracy due to the reduced motion amplitudes. Full article

Axial floating piston pumps (AFPPs) have been proposed as a promising solution to address the increasingly demanding operating conditions of hydraulic pumps, including wide speed ranges, high-pressure environments, and low-viscosity media. To systematically investigate the displacement characteristics and flow pulsation rate of AFPPs, this study develops a mathematical model via the coordinate transformation method to precisely determine the coordinates of each cylinder. Based on this model, analytical formulas for displacement and flow pulsation rate were derived. Furthermore, the influence trends of diverse geometric parameters on these two metrics were analyzed, accounting for variations in installation methods and structural configurations. Validation was conducted through simulations and experimental tests on an AFPP prototype with specific parameters, confirming the accuracy of the theoretical analysis. This work provides a robust theoretical foundation for the optimal design and performance improvement of AFPPs in practical engineering applications. Full article

Reducing friction in the piston ring–cylinder liner contact is a key area for improving the efficiency of internal combustion engines. While tribological studies commonly focus on the top dead centre region using linear tribometers, the mid-stroke regime—with its higher sliding velocities—remains experimentally inaccessible to most conventional test methods. This study presents a rotating ring-on-liner tribometer that enables investigations at constant relative speed by transitioning the motion from oscillating to rotating. A cylindrical substitution geometry for the piston ring specimen is derived through a coupled elastohydrodynamic and asperity contact simulation approach to reproduce realistic load-sharing behaviour. Experimental results from starved lubrication tests demonstrate stable contact conditions with a low coefficient of variation in wear, confirming good reproducibility. Stepwise performed Stribeck tests at 40 °C and 100 °C reveal characteristic friction–velocity behaviour, including the transition from mixed to hydrodynamic lubrication. Although the test rig’s maximum sliding speed and steady-state thermal conditions differ from fired engine environments, the methodology closes an important gap between low-speed linear tribometers and complex floating-liner systems. The presented approach provides a flexible and robust platform for controlled parametric studies of ring-on-liner contacts under application-relevant lubrication regimes. Full article

This paper presents an extensive experimental study on the hydrodynamic behavior of vertical cylinders representative of the structural elements of offshore floating photovoltaic (OFPV) platforms under both wave and steady-current conditions. The objectives are to determine reliable hydrodynamic coefficients for Morison-type formulations and to analyze the wake effects between cylinders for modular floating configurations. Tests under regular waves are conducted in a 25 m long wave flume at the Energy Engineering Department of the Bilbao School of Engineering. The obtained inertia and drag coefficients follow the expected trends for a wide range of Keulegan–Carpenter (KC) numbers, aligning well with classical experimental studies. Steady-current experiments are conducted in the same flume using a towing tank method. Again, the obtained drag coefficients align well with previous studies. As for the wake provoked by the first cylinder on the second cylinder located downstream at one of four different distances, in the wave cases, the wake attenuation is minimal and rapid recovery of the flow is observed for a wide range of KC values, while in the steady-current cases, the wake is stronger and affects the forces acting on the second cylinder. Full article

Robot grinding requires a constant interaction force between the tool and the workpiece, even under inclination changes. This paper proposes a compact single-axis pneumatic constant-force floating compensator (CFFC) to achieve constant force output. The proportional pressure valve and pressure sensor are used to regulate the cylinder’s pressure. Pneumatic components and sensors are integrated into the narrow space between the cylinder and the slide rail. Embedded controller, power, and communication modules are developed and integrated into a control box and interact with the operator by a touch screen. The mathematical models of the compensator are established and the stability and response dynamics are analyzed through transfer functions. A dual-loop force controller based on active disturbance rejection control (ADRC) is designed to address bias load, inclination change, friction, and the sealing cover spring effect. The outer loop is compensated by displacement, tilt, and pressure sensors, and the unmodeled dynamics are estimated by an extended state observer (ESO) and a recursive least square (RLS). Finally, the CFFC is installed on a testing platform to simulate grinding conditions. The experimental results show that even under large floating stroke, inclination changes, and biased load, the CFFC can still quickly and stably output the desired grinding force. Full article

In recent years, due to the growing imbalance between energy consumption and available resources, as well as strict CO₂ emission regulations, turbochargers have become increasingly important in applications such as automobiles, ships, and aerospace. Turbochargers can effectively increase the intake volume of engine cylinders, improving fuel combustion efficiency and engine power. In order to meet the growing demand for more energy-efficient, lower-carbon-emission systems, it is necessary to design more compact, efficient, durable, and affordable supercharging systems. Compared with traditional floating ring bearings, rolling bearing turbochargers have become a greater focus of research due to their excellent transient performance, low friction loss, and strong load-bearing capacity. Due to the large number of components, complex structure, lightweight high-load rotor, complicated operating conditions, and unclear nonlinear vibration mechanism of rolling bearing turbochargers, it is necessary to establish a refined model to clarify how factors such as bearing and squeeze film damper parameters and rotor operating parameters affect the system response. Therefore, this study reviews relevant research in this field from the perspectives of modeling and system characteristics and points out directions for future research. Full article

Direct injection of hydrogen at high pressures into an otherwise unmodified heavy-duty diesel engine offers a near-term pathway to near-zero greenhouse gas emissions for commercial vehicles. Hydrogen direct-injection engines maintain diesel-like performance with equal or better thermal efficiency. Supplying the hydrogen for injection pressures of ~30 MPa requires a high-pressure supply. Onboard hydrogen compression enables more complete utilization of the stored compressed hydrogen; however, it introduces a significant parasitic load on the engine. The magnitude of this load depends on factors such as the compressor’s configuration, capacity, pressure ratio, efficiency, and the engine’s operating conditions. This paper presents an exergy analysis of an onboard hydrogen compression system that uses hydraulically driven free-floating pistons, sized for heavy-duty commercial vehicles. Minimizing the parasitic loads from the compressor is essential to retain vehicle performance and maximize system-wide efficiency. The exergy analysis approach provides a comprehensive understanding of the whole compression system by comparably quantifying the losses across all components. A one-dimensional model of the compression system, developed in GT-SUITE^TM and validated with experimental data, is used to quantify the main exergy loss components. Exergy efficiency ranges from 12% to 45% under varying pressure ratios and cycle frequencies, with a pronounced increase in efficiency observed at higher cycle frequencies. Major exergy losses occur in the hydraulic driving system up to 79%, especially during retracting and idle phases for lower pressure ratios and cycle frequencies. Within the compression cylinder, exergy destructions account for less than 10% of the total work input, wherein heat transfer and piston friction are identified as the dominant contributors to exergy destruction, with their effects intensifying at higher pressure ratios. This work highlights the challenges of onboard gas compression and develops a systematic framework that can compare compressor design alternatives for different driving cycles. Full article

Focusing on an energy-saving winch-type heave compensation system applicable to real working conditions, with the objective of enhancing compensation accuracy, a wavelet neural network was employed for platform velocity prediction, and the prediction results were applied to velocity disturbance compensation control. Initially, the ITTC two-parameter spectrum was utilized to generate wave spectral diagrams under different sea conditions, along with displacement and velocity data of the floating platform’s heave motion. Subsequently, a time-series-based wavelet neural network velocity prediction model was developed, trained, and tested. Comparative analyses were performed on prediction performance differences across varying prediction steps and sea condition levels. Then, the effectiveness of the time-series-based wavelet neural network prediction model was validated through a valve-controlled hydraulic cylinder heave motion simulation system. Experimental results indicated that the wavelet neural network-based velocity prediction method effectively improved the compensation accuracy of the winch-type heave compensation system. Finally, after verifying the effectiveness of the wavelet neural network prediction model based on time series, the compensation performance of the system after adding the velocity prediction module was tested and verified using the winch-type heave compensation simulation test bench built by the research team. After experimental verification, after adding velocity prediction, the compensation accuracy of the system was improved by 19% compared with that without velocity prediction. Full article

This paper presents a quantitative investigation into the hydrodynamic characteristics of a floating breakwater system encompassing an artificial floating island. The floating breakwater’s cross-section is configured as a collection of multiple buoys, with a large main horizontal cylinder and two small cylinders. A navigation channel opening is incorporated into the floating breakwater, fortified by a floating gate positioned externally. The wave patterns surrounding the floating breakwater system are simulated and analyzed using ANSYS-AQWA (R19.0) software. The research investigates the mean transmission coefficients in the area encompassed by the floating breakwaters, considering a range of influential parameters. These parameters include the dimensions of the navigation channel opening, the planar dimensions of the floating breakwater system, the type of mooring chains, as well as the incident wave height, wave period, and wave directions, among others. Additionally, this study evaluates the impact of the navigation channel’s floating gate shape on the wave dissipation performance of the floating breakwater system. An opening angle of 75° for the navigation channel has been determined as optimal, balancing wave dissipation performance with the structural complexity of the harbor gate. The ideal distance between the floating breakwater system and the central floating island is identified as 300 m. The tensioned mooring system demonstrated superior performance compared to the catenary system. Furthermore, the arc-shaped harbor gate achieved a 26% reduction in wave transmission relative to the linear gate. These findings offer practical design guidelines for improving the stability and cost-effectiveness of floating breakwater systems in open-sea environments. Full article

Predicting the roll damping coefficient of a ship is a crucial factor in determining the dynamic stability of the vessel. However, a nonlinear analysis that considers the viscosity of the fluid is required to accurately estimate the roll damping coefficient. This study numerically analyzed the hydrodynamic coefficients related to the roll motion of ships, focusing on the eddy-making damping coefficient. A series of forced vibration tests were conducted on a two-dimensional triangular cylinder floating on the water surface. The overset method and the volume-of-fluid method were applied, and the governing equations were solved using the open-source software OpenFOAM v2106. Uncertainties in the grid size and time intervals were identified through the International Towing Tank Conference (ITTC) procedure, and the obtained hydrodynamic coefficients were compared with available experimental data and potential flow results. Additionally, eddy-making damping was extracted from the shed vortex for various excitation frequencies and amplitudes. The study found that the uncertainty in the roll damping coefficient was less than 8%, with eddy-making damping being the dominant factor influencing the results. Numerical results showed a good agreement with experimental data, with an average deviation of 4.4%, highlighting the importance of considering nonlinear effects at higher excitation amplitudes. Comparison with experimental data and empirical formulas revealed that the nonlinearity due to the excitation amplitude must be considered in empirical formulations. Full article

The interaction between naval structures and underwater shock waves generated by explosions is critical in marine engineering. Numerical analysis is pivotal in investigating the effects of reflected waves from the free surface and the seabed on submerged or floating structures. This topic still needs to be explored in the marine engineering literature despite its significance. Understanding the complex dynamics of shock wave reflections is paramount for ensuring marine installations’ structural integrity and safety, including submarines, offshore platforms, and surface vessels. This paper aims to fill this gap by presenting a preliminary numerical study focused on analyzing the influence of reflected waves caused by the seabed on a simple ship-like structure, where the free-surface effects are negligible. A Coupled Eulerian–Lagrangian approach based on the suite MSC Dytran was used to investigate the interaction between shock waves and the seabed, considering a structure represented by an underwater cylinder and several seabed compositions. A deeper understanding of this phenomenon is crucial for enhancing the resilience and safety of marine installations, thereby mitigating potential risks and ensuring sustainable maritime operations. The simulations presented in this work represent the starting point for the creation of datasets to be used in Machine Learning applications. Full article