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The effects of on-road disturbances on the aerodynamic drag are attracting attention in order to accurately evaluate the fuel efficiency of an automobile on a road. The present study investigated the effects of cornering motion on automobile aerodynamics, especially focusing on the aerodynamic drag. Using a towing tank facility, measurements of the fluid-dynamic force acting on Ahmed models during steady-state cornering were conducted in water. The investigation included Ahmed models with slant angles θ = 25° and 35°, reproducing the wake structures of two different types of automobiles. The drag increase due to steady-state cornering motion was experimentally measured, and showed good agreement with previous numerical research, with the measurements conducted at a Reynolds number of 6 × 105, based on the model length. The Ahmed model with θ = 35° showed a greater drag increase due to the steady-state cornering motion than that with θ = 25°, and it reached 15% of the total drag at a corner with a radius that was 10 times the vehicle length. The results indicated that the effect of the cornering motion on the automobile aerodynamics would be more important, depending on the type of automobile and its wake characteristics.

During the towing of semisubmersible platforms, waves impact and superpose in front of the platform to form a ridge shaped “water ridge”, which protrudes near the platform and produces a large slamming pressure. The water ridges occur frequently in the towing conditions of semisubmersible platforms. The wave–slamming on the braces and columns of platform is aggravated due to the water ridges, particularly in rough sea conditions. The effect of water ridges is usually ignored in slamming pressure analysis, which is used to check the structural strengths of the braces and columns. In this paper, the characteristics of the water ridge at the braces of a semisubmersible platform are studied by experimental tests and numerical simulations. In addition, the sensitivity of the water ridge to the wave height and period is studied. The numerical simulations are conducted by a Computational Fluid Dynamics (CFD) method, and their accuracy is validated based on experimental tests. The characteristics of the water ridge and slamming pressure on the braces and columns are studied in different wave conditions based on the validated numerical model. It is found that the wave extrusion is the main reason of water ridge. The wave–slamming pressure caused by the water ridge has an approximately linear increase with the wave height and is sensitive to the wave period. With the increase of the wave period, the wave–slamming pressure on the brace and column of the platform increases first and then decreases. The maximum wave–slamming pressure is found when the wave period is 10 s and the slamming pressure reduces rapidly with an increase of wave period.

Multiple pipes bundled with a certain distance are used for deep ocean development for such as lifting seafloor massive sulfides (SMS), pumping up a large amount of cooling water for onboard natural gas liquefaction, and production of oil/gas. To understand the vortex-induced phenomenon of fluids and the structural mutual interference among pipes in a steady flow, a towing tank test using a model of two vertical elastic pipes in tandem is performed. The parameters of this test are: the distance between the two pipes, the incident angle of crossflow with the inline direction of the pipes, the flow velocity (towing speed), and the boundary conditions of the tops of the pipes. The two horizontal accelerations of the towing direction and perpendicular direction are measured with synchronization. Then, the motion of the two pipes in each direction was measured, and the influence of the distance between the two pipes on the motion from the amplitude and phase information was analyzed. The results are investigated relatively in detail about the tandem arrangements of the two pipes to the incident flow. It is found that the major motion pattern of the two pipes in the tandem case is a rotational motion around the midpoint of two pipes.

Recently, the demand for floating solar power farms in lakes and coasts (rather than on land) has been increasing rapidly. It is important to develop a numerical analysis technique that considers environmental conditions to predict structural stability and accurate motion response while designing a floating solar power farm. In this study, we performed a comparison under conditions similar to those of the Inha University towing tank (IUTT) model test to verify the numerical analysis method. The results revealed that heave and pitch movements were dominant under head sea conditions. Relative behavior occurred because of the hinge connection of each unit, and complex motion characteristics appeared depending on the wave conditions. The numerical method was verified based on the motion response and load of the floating solar farm. The validity of the results was also confirmed.

In the current article, the hydrodynamic forces of single-stepped planing hulls were evaluated by an analytical method and compared against towing tank tests. Using the 2D + T theory, the pressure distribution over the wedge section entering the water and the normal forces acting on the 2D sections have been computed. By integrating the 2D sectional normal forces over the entire wetted length of the vessel, the lift force acting on it has been obtained. Using lift forces as well as the consequence pitch moment, the equilibrium condition for the single-stepped planing hull is found and then resistance, dynamic trim, and the wetted surface are computed. The obtained hydrodynamic results have been compared against the experimental data and it has been observed that the presented mathematical model has reasonable accuracy, in particular, up to Froude number 2.0. Furthermore, this mathematical model can be a useful and fast tool for the stepped hull designers in the early design stage in order to compare the different hull configurations. It should also be noted that the mathematical model has been developed in such a way that it has the potential to model the sweep-back step and transverse the vertical motions of single-stepped planing hulls in future studies.

This study explores the hydrodynamic performance of three different underwater towing vehicle designs (Models 1, 2 and 3) for underwater survey applications, focusing on the impact of varying angles of attack on the vehicle's performance. Computational fluid dynamics (CFD) simulations were conducted at four angles of attack (0°, 5°, 10° and 15°) to evaluate key performance parameters, including drag force, lift force, lifi-to-drag (L/D) ratio, stability and manoeuvrability. The results show that Model 3 consistently outperformed the other two models, especially at higher angles of attack, showing the highest lifi-to-drag ratio and optimised drag performance for high-resistance underwater tasks. Static pressure contours also revealed that Model 3 experiences more uniform pressure distribution, contributing to its superior stability. In contrast, Model 1 demonstrated superior performance at low angles of attack with moderate lift and drag resistance. Model 2, while showing improvement at higher angles, lagged in overall efficiency and requires further optimisation. Steady-state CFD analysis was employed to derive the hydrodynamic coefficients and assess the impact of different towing conditions on each model's stability and efficiency. The findings suggest that Model 3 is the most efficient design for underwater towing, with each model offering distinct advantages based on operational requirements.

This study presents a model experiment on the oblique maneuvering of a ship in a floating ice environment. A series of captive model tests was conducted in both open-water and synthetic ice fields at concentrations of 60%, 70%, and 80%. The model was tested in a conventional towing tank using non-refrigerated polypropylene ice floes to simulate a broken ice field. Surge force, sway force, and yaw moment on the hull were measured under various drift angles and three speeds. Results show that in oblique motion, ice floes around the hull experience significant overturning and piling up, especially on the drift side, leading to random collisions with the hull. These interactions markedly affect the hydrodynamic forces. As the drift angle increases, the surge, sway, and yaw forces on the hull increase nonlinearly. The comparison between open-water and ice conditions indicates that floating ice can significantly increase the resistance and maneuvering forces. Higher ice concentrations lead to more frequent and more extensive contact between the hull and the ice floes, thereby further amplifying all components of the hydrodynamic forces. This work provides experimental data for validating calculation methods of ship resistance and maneuvering in broken ice. It demonstrates a feasible experimental approach for studying ship maneuvers in a floating ice channel.

It is known that the toughest stage of operation of a tractor with massive towed objects is the takeoff regime. This is because it is necessary to overcome the force of friction of rest that substantially exceeds the force of friction of motion. As a variant of solution of this problem, the initial kinetic energy of the tractor can be considered, which can evolve when boundedly elastically deformed towing couplers are used. To optimize the mathematical model, the following assumptions are made: towing force at the hook of the tractor is an invariable quantity; the inert masses of the tractor and towed objects are identical and equal to . The initial conditions are as follows: for t = 0 because the towing coupler is undeformed, and no force is applied to the towed object. Period during which the towing coupler experiences the maximal strain is determined. For estimating the effectiveness of application of elastically deformed towing couplers, the obtained results must be compared with analogous results corresponding to absolutely rigid towing couplers. Comparison of displacements, velocities, and energies indicates the high efficiency of application of elastically deformed towing coupler. The use of elastically deformed towing couplers makes it possible to accumulate the initial kinetic energy of an airport tractor, which makes it possible to overcome the force of friction of rest and to ensure the takeoff of heavy objects being towed. Comparison of kinematic and dynamic parameters of the tractor and towed objects in variants with absolutely rigid and elastically deformed towing couplers shows that the efficiency for the latter variant increases with increasing number of towed objects. Elastically deformed towing couplers can cause vibrations of the tractor–towed object system. To prevent such vibrations, towing couplers should be blocked at the instant of their highest straining.

This paper investigates a calculation method for the heave and pitch motion of a trimaran, which includes direct and indirect calculation methods. In the direct calculation method, Computational Fluid Dynamics (CFD) simulation is applied to calculate trimaran motion. In the indirect calculation method, there exist three steps to achieve motion calculation: first, a standard wave spectrum is chosen to excite the wave force and moment acting on the trimaran; second, particle swarm optimization (PSO) and polynomial fitting methods are adopted to identify the function of wave force and moment; finally, the mathematical model of the trimaran is established. To compare the effectiveness of the direct and indirect methods, the model test of the trimaran is performed in a towing tank. The results of the model test proved that the direct and indirect methods are all effective for calculating the heave and pitch motions of a trimaran.

This study addresses the question: “Does the towing tank water temperature affect the result of model-ship extrapolation?” While it is well-established that temperature variations affect Reynolds numbers and consequently frictional and viscous resistance, this study examines whether the ITTC 1978 extrapolation method properly compensates for these effects. Although current procedures consider temperature indirectly through the Reynolds number, they assume that the form factor depends solely on the Froude number and is insensitive to viscosity changes. Our analysis reveals that the form factor is also temperature-sensitive, indicating a fundamental limitation in the conventional approach. This sensitivity arises from the limitations of the ITTC 1957 friction curve and the method’s neglect of temperature-induced variations in the form factor. To quantify the effect of temperature, model-scale CFD simulations were conducted for two ship models (KCS and KVLCC2) at different water temperatures using the ITTC 1978 procedure with Prohaska’s method. The results show that the ship-scale total resistance coefficient (CT) can vary by up to 2.8% depending on the water temperature and friction line selection. This demonstrates that the ITTC 1978 performance prediction method fails to adequately compensate for the temperature-induced changes in resistance, which leads to systematic errors in the extrapolated results.