Bow Wave Research Articles

Mechanism analysis and prediction of longitudinal cut wave pattern resistance based on CFD simulation

Inspired by ITTC 2021 (International Towing Tank Conference), this paper implements the Longitudinal Cut Method (LCM), a methodology to predict wave pattern resistance (Rwp), within Computational Fluid Dynamics (CFD) simulation to explore its mechanism and feasibility in predicting wave resistance (Rw). To accurately predict the free surface, a validation study, including the grid convergence index (GCI), wave profile, and wave pattern, is conducted for a Series 60 ship model. Next, Rwp is appropriately evaluated and compared with the experiment. The influence of the transverse wave component on the LCM analysis is also discussed. Furthermore, a comparison between the EFD (Experimental Fluid Dynamics) and CFD-based LCM is made through the analysis of the Wigley Catamaran, highlighting the advantages of the present approach. Finally, the limitations of the LCM theory are systematically discussed with the nonlinear bow wave analysis of a wall-sided ship model by introducing the local adaptive mesh refinement (LAMR) approach. For the fine hull form, LCM has been validated as a suitable methodology for directly predicting Rw and consequently the other primary resistance components (frictional resistance Rf and viscous pressure resistance Rpv) by one simulation. In contrast, due to energy dissipation of the non-negligible nonlinear local field wave component in the downstream wake region, Rw could be underestimated for the full hull form.

Numerical investigation on nonlinear ship waves by LCM and WSAM

This paper investigates the nonlinear ship waves by implementing the longitudinal cut method (LCM) and wake survey analysis method (WSAM) in the computational fluid dynamics (CFD) simulation. LCM is first implemented and validated for a Series 60, Cb = 0.6 ship model to guarantee accurate prediction of the wave pattern resistance (Rwp). To illustrate the reliability, WSAM is performed for a wall-sided model, incorporating the local adaptive mesh refinement (LAMR) and surface tension models to capture nonlinear bow waves. Far and near-field wave patterns and momentum loss resistance (RML) are compared with the experiment.With the well-predicted nonlinear bow waves, the velocity discontinuity property across the nonlinear wavefront and the vortex motion beneath the nonlinear waves are clearly observed by velocity vector and Q-criteria iso-surface visualization. By LCM and WSAM analysis, the discrepancy between wave resistance (Rw) and Rwp is attributed to the nonlinearity in ship waves, and expression to evaluate this part of resistance (Rnw) is discussed and summarized. Finally, the influence of velocity and draft on Rnw and bow wave angle (β) is systematically analyzed and discussed. This study hopes to provide insights to evaluate the nonlinearity in ship waves and further understand its underlying mechanism.

Study on initiation characteristics of oblique detonation induced by hydrogen jets in acetylene-air mixtures

In this paper, effects of hydrogen jets in acetylene-air mixtures on the initiation characteristics of oblique detonation wave (ODW) are investigated, the two-dimensional (2D) multi-component NS equations considering detailed chemical reactions are solved. Influences of the transverse jet on flow field characteristics of the ODW are studied, including the initiation characteristics, the wave structures, and the state parameters. The existence of the jet changes the ignited mode of the ODW from double Mach interaction to single Mach interaction. Several wave configurations and their transitions induced by the jets are observed, including deflagration-to-detonation transition (DDT), jet-induced bow shock wave (BSW) in front of the transverse jet and rapidly develops into ODW, and ODW that generated directly in front of the transverse jet. The structure of these three wave systems is mainly influenced by the flow discharge of the hydrogen jet. When the hydrogen jet is small, no combustion is induced by the BSW in front of the jet. ODW is induced by the action of the deflagration wave and OSW. Increasing the hydrogen jet, BSW induces combustion and rapidly develops into ODW. When the hydrogen jet is large enough, the BSW disappears and direct detonation combustion occurs to produce ODW. Two types of relationships are obtained between the initiated position and the position of the transverse jet: the U-shaped curve at low flow discharge and the positive correlation at high flow discharge. When the flow discharge is small and no shock wave-induced combustion occurs, the initiated position is influenced by the position of the deflagration wave interacting with the OSW, which forms a U-shaped curve with the position of hydrogen jet. When the flow discharge is high and shock wave induced combustion occurs, ODW is rapidly developed behind the jet, resulting in a positive correlation between the initiated position and the position of hydrogen jet. Furthermore, the viscous effect has significant influence on the flow field characteristics of ODW, it promotes the transition between these initiation modes and shortens the initiation distance of oblique detonation. The findings of this study can better help understand the effect of transverse hydrogen jets on ODW initiation and contribute to theoretical studies and engineering applications of oblique detonation engines.

A numerical study on the added resistance and motion of a ship in bow quartering waves using a soft spring system

The prediction of resistance performance in oblique waves have been a key issue for the accurate estimation of added resistance of ships in the actual operating state. Therefore, in this paper, the added resistance of a large tanker in the bow quartering waves (180⁰, 150⁰, 120⁰) was studied by applying a computational fluid dynamics (CFD) solver based on the unsteady Reynolds-averaged Navier-Stokes equations. In addition, the forces and motion responses in bow quartering waves according to the captive test (heave, roll, and pitch free) and soft spring test (6 DOF) were investigated. To validate the CFD results, it was compared with the model test results showing good agreement. The maximum value of the added resistance was observed between 180⁰ and 150⁰, and it decreased sharply at 120⁰. The peak of the added resistance moved to a shorter wave region. The differences in added resistance, heave, and pitch motions in oblique wave according to the degree of freedom were insignificant. However, the discrepancy in roll motion occurred due to the forces and moments differences caused by the degree of freedom. The tendency of added resistance in the bow quartering waves and the forces and motion responses according to the degree of freedom were also investigated.

Numerical study of energy capture equipment using tanker rolling motion for different wave heights and encounter angles

ABSTRACT An energy capture equipment is proposed, which can harvest the mechanical energy generated by the rolling motion of a tanker, and the structure of the equipment is designed. The mass-spring-damping mathematical model of the slider is established. Then, a numerical wave tank is created by Fluent to simulate the rolling motion of a typical ship equipped with equipment. According to the data of ship rolling motion and the mathematical model solved by the Newmark-β method in MATLAB, the equipment's power is obtained. Specifically, when the encounter angle is beam wave condition (90 degree), the rolling motion is violent and the equipment power reached the maximum value (187.16 W). Besides, the power generation with the quartering wave is better by comparing the equipment's power under the conditions of the bow and quartering wave. Finally, the wave height becomes bigger, the ship's rolling angular displacement and the equipment's power become larger.

Oblique shock wave in turbulent flow

Abstract The main attention is paid to the analytical analysis of an oblique shock wave in a turbulent adiabatic gas flow. For this purpose, a modified Rankine–Hugoniot model was obtained. On its basis, a solution was derived for the Rankine–Hugoniot conditions for a gas flow with various degrees of turbulence, as well as the equation of the modified Hugoniot adiabat. The behavior of the velocity of an adiabatic turbulent gas flow during its passage through an oblique shock wave at different levels of turbulence is demonstrated. A modification of Prandtl’s law for the velocity coefficients was obtained. The shock polar was also analyzed. The relationship between the angular gas flow and the angle of the shock wave was derived. Finally, the condition for the appearance of an outgoing bow shock wave was obtained.

CFD Investigation for Sonar Dome with Bulbous Bow Effect

The objective of this study is to design a hull-mounted sonar dome of a ship using OpenFOAM with a bulbous bow effect at cruise speed in calm water. Verification and validation for the original sonar dome simulation are conducted. Next, the 1.44 million grid size is selected to study different dome lengths. By protruding the dome forward 7.5% of the ship’s length, the optimal 17% resistance reduction is achieved and is mainly caused by the pressure resistance decrease. The optimal sonar dome not only functions in the same way as a bulbous bow, but the viscous flow behaviors are also improved. The protrusion corresponding to 90 deg phase lag reduces the bow wave amplitude. The flow acceleration outside the boundary layer and ship wake velocity are higher coinciding with the much lower total resistance. A smaller flow separation and thinner boundary layer are also observed behind the sonar dome because its back slope is less steep. The high pressure covers a smaller area around the bow, and the smaller bow wave crest does not hit the ship’s flare to form high pressure. Consequently, the lower high pressure on the dome front and higher low pressure on the dome back result in the decreases in pressure resistance. The vortical structures are also improved.

High Energy Cosmic Generation Form Collisionless Shock Wave Acceleration

The collision less shock wave one of the shock waves that is more likely to detect in the plasma that come from the magnetosphere, interplanetary space and so far. The most significance difference between other shock wave is the direct collision between particle is almost not exist. To be specific, the bow shock wave that occur by the interact of magnetosphere of an astrophysical object and solar wind is one of the collisions less shock wave. The collision-less shock wave in the universe could accelerate the particle in to high energy and form cosmic rays. In this essay, the basic reorganization of collision-less shock wave will be illustrated. On this basis, this paper is going to analysis a few mechanism of how the collision-less shock wave accelerate the particle and the recent experiment about the shock wave. According to the analysis, lots of state-of-art observations can be explained. These results shed light on guiding further exploration of high energy cosmic ray.

A Cartesian grid-based two-dimensional plus time method for simulating ship bow waves

Numerical modeling of ship bow waves is still hard work, partly due to their multiscale features. Direct three-dimensional (3D) computational fluid dynamics simulation could be an appropriate choice to investigate the problem. However, limited by computational resources, small scale phenomena such as spraying and wave breaking that could be observed during the ship wave generation process are usually simplified or not fully distinguished in a 3D simulation. In order to accurately capture the small scales flow field information with the available computational resource, a new Cartesian grid-based two-dimensional plus time (2D+t) method is developed in this paper, which is suitable for 3D slender ships. With this method, a 3D steady ship wave-making problem is transformed into a 2D unsteady wave-making problem of a deformable body. The boundary velocity of the deformable body is obtained with a novel interpolation algorithm, which is then enforced on the background Cartesian grid by a newly proposed immersed boundary method. The pressure boundary condition on the surface of the deformable body is explicitly considered in the solution of the pressure Poisson equation. Moreover, an extra open boundary condition is applied to the upper boundary of the computational domain to achieve a better conservation. The proposed model is validated with selected cases, showing that the model is capable of simulating both non-wave-breaking and wave-breaking problems.

Assessment of added resistance estimates based on monitoring data from a fleet of container vessels

A practical estimation methodology of the mean added resistance in irregular waves is shown, and the present paper provides statistical analyses of estimates for ships in actual conditions. The study merges telemetry data of more than 200 in-service container vessels with ocean re-analysis data from ERA5. Theoretical estimates relying on spectral calculations of added resistance are made for both long- and short-crested waves and are based on a combination of a parametric expression for the wave spectrum and a semi-empirical formula for the added resistance transfer function. The theoretical estimates are compared to predictions from an indirect calculation of added resistance relying on shaft power measurements and empirical estimates of the remaining resistance components. Overall, the comparison reveals a bias in bow oblique waves and higher sea states of the spectral estimates as well as a large variance of the empirically derived predictions — particularly in beam-to-following waves. One of the study’s main findings, confirming previous studies but based on a much larger dataset than in earlier similar studies, is that added resistance assessment based on in-service data is complex due to significant associated uncertainties.

Numerical investigation of jet-wedge combinatorial initiation for oblique detonation wave in supersonic premixed mixture

The jet-wedge combinatorial initiation (JWCI) is a novel functional form for initiating an oblique detonation wave (ODW) with reduced total drag within the oblique detonation combustor under the conditions of a low Mach number and low static pressure inflow. It can suppress the instability of the detached ODW. The evolution of the combustion wave during combinatorial initiation is dominated by the intersection between the bow shock wave and the oblique shock wave and consists of four stages: the shock-induced combustion stage, the shock–deflagration coupling stage, the hybrid combustion stage, and the oblique detonation stage. Three combustion regimes can be formed by using the JWCI: the shock-induced combustion regime, the hybrid combustion regime, and the oblique detonation combustion regime. These regimes have distinct characteristics of combustion and flow structure that can be controlled by changing two non-dimensional variables: the ratio of momentum flux (J) and the penetration ratio (PR). This is significant as it can facilitate the application of different combustion regimes under a variety of realistic flight conditions. In this study, the criterion for the transformation of the combustion regime is quantitatively investigated, and it is shown that the structure of the combustion wave does not transform until both non-dimensional variables have reached their respective thresholds. J is crucial for determining the combustion regime and facilitating its transformation, but the PR accounts only for the height of the combustion wave structure. The work is beneficial for research on the initiation of the ODW in applications of oblique detonation engines.

Numerical Studies on Bow Waves in Intense Laser-Plasma Interaction

Laser-driven wakefield acceleration (LWFA) has attracted lots of attention in recent years. However, few writers have been able to make systematic research into the bow waves generated along with the wake waves. Research about the bow waves will help to improve the understanding about the motion of the electrons near the wake waves. In addition, the relativistic energetic electron density peaks have great potential in electron acceleration and reflecting flying mirrors. In this paper, the bow waves generated in laser-plasma interactions as well as the effects of different laser and plasma parameters are investigated. Multidimensional particle-in-cell simulations are made to present the wake waves and bow waves by showing the electron density and momentum distribution as well as the electric field along x and y directions. The evolution of the bow wave structure is investigated by measuring the open angle between the bow wave and the wake wave cavity. The angle as well as the peak electron density and transverse momentum is demonstrated with respect to different laser intensities, spot sizes, plasma densities, and preplasma lengths. The density peak emits high-order harmonics up to 150 orders and can be a new kind of “flying mirror” to generate higher order harmonics. The study on the bow waves is important for further investigation on the electron motion around the wake waves, generation of dense electron beams, generation of high-order harmonics, and other research and applications based on the bow waves.

Numerička analiza tegljajućeg nadzvučnog dvokrilca u uslovima van projektovanja sa zaklopkom zadnje ivice

Supersonic biplanes can achieve low-boom and low-drag supersonic flights. In the present study, aerodynamic analysis of a two-dimensional stagger Bussmann biplane (staggered upper element by 0.5c) at zero degrees angle of attack with trailing edge flap was investigated with the help of computational fluid dynamics (CFD) tools. Due to the wave cancellation effect, the Busemann biplane delivers a positive drag reduction at design supersonic Mach values. However, when operating outside of its intended parameters, it performs worse, and the wave cancellation effect has no beneficial effects on reducing drag. Another issue with the Busemann biplane is flow chocking, which produces a potent bow shock wave in front of the aircraft. This paper attempts to address low aerodynamics efficiency problems during take-off through numerical simulation of a staggered Busemann biplane with trailing edge flaps at zero degrees angle of attack. It was confirmed that the staggered biplane airfoil with flap has better aerodynamic performance during take-off at lower subsonic free stream Mach numbers. In 2D wings, the effect of flow chocking and hysteresis as starting problems, which arise when the biplanes accelerate from low Mach numbers, is reduced by using the suitable dimension and angle of rotation of the flap, and the flap is effective in settling these issues.

Characterisation of Flow Regimes in the Bow Wave of a Surface Piercing Cylinder

Characterisation of Flow Regimes in the Bow Wave of a Surface Piercing Cylinder

Dynamic Hull Vane—A Solution for Active Pitch Motion Reduction and Resistance Reduction of Ships

_ The Dynamic Hull Vane® is an actively controlled version of the Hull Vane®, a patented energy-saving and seakeeping device which consists of a submerged wing mounted on the aft ship. The Hull Vane is positioned in the upward flow aft of the ship, to develop forward thrust and reduce the stern wave. Naiad Dynamics US Inc, is a supplier of ride control systems and has worked with Hull Vane BV to develop the Dynamic Hull Vane®. By enabling the Hull Vane® to rotate, it can produce variable lift forces which when suitably controlled can reduce the pitching motions of a vessel in a seaway. This paper describes some of the research carried out on the AMECRC series 13, a generic fast displacement hull. Introduction Among other characteristics, two main performance parameters of a ship are fuel consumption and ship motions. Besides a well-designed hull, several appendages can be used to increase the performance. One of this is the Hull Vane. The Hull Vane is a fixed hydrofoil behind the transom of the ship. The Hull Vane has the potential to create large lift forces on the aft ship, thereby changing the resistance and the dynamic position of the vessel (Uithof et al. 2014). Ship motion reduction has long been a topic of research, and this has led to a number of solutions, which are widely applied. Most of the study work and products have been related to the rolling motions of ships, and there are indeed various effective solutions available, such as fin stabilizers, gyrostabilizers, interceptors, trim tabs, and antiroll tanks. The pitching motion of ships has been studied less, and while there are systems on the market to actively dampen the pitching motions of fast (planing) vessels, it has always been a challenge to dampen the pitch and heave motions of displacement ships, due to their inertia and limited speed. The pitch and heave motions are the prime source of vertical accelerations on board and these in turn are one of the main contributors in the Motion Sickness Incidence (MSI). Passive systems to reduce pitch motions exist, such as bow foils, which are preferably retractable to avoid their resistance penalty in calm water. There are two passive systems which dampen pitching motions while not adding calm-water resistance on specific ship types, because they reduce the wavemaking resistance of the ship: the bulbous bow and Hull Vane®. The pitch dampening effect of the passive Hull Vane has been demonstrated on naval vessels in computational fluid dynamics (CFD) (Bouckaert 2016) and in model tests (Ferré 2019).

Thermal effects on the wall surfaces of transonic evacuated tube maglev transportation

Shock waves and expansion fan hierarchies in complex flows induced by transonic evacuated tube maglev transportation (ETMT) cause a unique thermal environment, which can increase the aerodynamic heating on the wall surfaces of the train and tube with the possibility of structural damage. In this study, the thermal effects on the wall surfaces of transonic ETMT were numerically investigated using a density-based computational fluid dynamics (CFD) solver. The results show different thermal effects for choked and unchoked flows in the tube. For the train, the extreme hot or cold environment, which is non-uniformly distributed on the surface, occurs more easily in the choked flow. For the tube, the instantaneous thermal impact is severe on the wall at supersonic speeds in the choked flow, reaching a maximum of 43.2 kW/m2 at Mach 1.5 with a blockage ratio of 0.2. The spectrum of the heat flux fluctuation on the tube wall is divided into the low-frequency band (main frequency) subjected to the normal or bow shock wave and secondary-frequency band induced by the downstream reflected shock trains. In addition, the amount of heat accumulated on the tube is insignificant owing to the interaction between the expansion fans and shock waves with alternating action on the boundary layer. Adoption of these findings, including the thermal control techniques and thermal-impact-resistant materials, for different ETMT systems can promote high-efficiency and low-redundancy designs of thermal protection systems.

Investigation of a Cabin Suspended and Articulated Rescue Vessel in Terms of Motion Reduction

To solve the problem that small rescue vessels are seriously affected by waves when working at sea, which causes damage to the crew and equipment, a catamaran with a suspended and articulated cabin is designed. The multi-body dynamic model of the whole vessel based on SimMechanics is built, and the prototype is tested on the water. The correctness of the model is verified based on the three aspects of the roll motion, pitch motion, and heave motion of the rescue platform. The motion of the rescue platform is simulated under the conditions of bow waves and large heave waves, and the RMS value of the vertical acceleration of the rescue platform is taken as the response target to analyze the influence of the suspension system parameters of the whole vessel. The suspension system has good buffering and motion reduction effects under various working conditions, and it has an obvious reduction effect on the vertical acceleration at the rescue platform. The larger the amplitude of the wave impact, the more obvious the effect. The articulated system reduces the roll angle and the heave amplitude under the conditions of bow waves.

Basics of Control of the Bow Shock Wave, Drag and Lift Forces, and Stability in a Steady Supersonic Flow Past an AD Body Using Permanently Operating Thermally Stratified Energy Deposition

A new method of high-speed flow control using permanently operating thermally stratified energy deposition is presented. The paper focuses on the analysis of the dependence of the characteristics of a steady supersonic flow and an aerodynamic (AD) body on the temperature values in the layers of a stratified source and the possibility of making the transition from one steady flow mode to another by changing the temperature in the layers. A detailed visualization of the dynamics of the fields of density, pressure, temperature, and local Mach number is presented during the controlled establishment of steady flow modes. Multiple generation of the Richtmyer–Meshkov instability is shown. The sharp peaks accompanying the development of the Richtmyer–Meshkov instabilities were obtained, which remain in the steady flow mode established under the action of a stratified energy source. Basic approaches for controlling the bow shock wave, drag and lift (pitch) forces (at zero angle of attack), and the stability in a steady supersonic flow past an AD body using permanently operating thermally stratified energy source were developed. The possibility of initiating and damping self-sustained flow pulsations as well as the formation of a steady flow with oppositely directed constantly acting lift forces due to temperature changes in the layers of a thermally stratified energy source is shown.

Detonation simulations in supersonic flow under circumstances of injection and mixing

The unsteady, reactive Navier-Stokes equations with a detailed chemical mechanism of 11 species and 27 steps were employed to simulate the mixing, flame acceleration and deflagration-to-detonation transition (DDT) triggered by transverse jet obstacles. Results show that multiple transverse jet obstacles ejecting into the chamber can be used to activate DDT. But the occurrence of DDT is tremendously difficult in a non-uniform supersonic mixture so that it required several groups of transverse jets with increasing stagnation pressure. The jets introduce flow turbulence and produce oblique and bow shock waves even in an inhomogeneous supersonic mixture. The DDT is enhanced by multiple explosion points that are generated by the intense shock wave focusing of the leading flame front. It is found that the partial detonation front decouples into shock and flame, which is mainly caused by the fuel deficiency, nevertheless the decoupled shock wave is strong enough to reignite the mixture to detonation conditions. The resulting transverse wave leads to further mixing and burning of the downstream non-equilibrium chemical reaction, resulting in a high combustion temperature and intense flow instabilities. Additionally, the longitudinal and transverse gradients of the non-uniform supersonic mixture induce highly dynamic behaviors with sudden propagation speed increase and detonation front instabilities.

Study on the surf-riding and broaching of trimaran in oblique stern waves

The trimaran is a high-performance ship of excellent seakeeping performance and stability, which makes it less vulnerable to capsizing. In recent years, strong survivability has increased the applicability of trimaran in unmanned ships. However, compared with the stability and seakeeping, side hulls and the larger width make the trimaran's maneuverability not as good as the traditional monohull. The unified study on trimaran's course keeping and broaching in waves is still limited. In this paper, the navigation of trimaran in oblique stern waves is simulated, and the force and moment by the water-jet impetus and nozzle reflection are simplified. The hybrid method coupling FNPT and CFD is applied to simulate the process of surf-riding and broaching. The characteristics of the surf-riding and broaching of the autopilot trimaran in oblique stern waves are analyzed by changing the working condition of initial forward speed, wave parameters, and initial wave heading.