_ An improved emergency blow model is proposed, which is based on the traditional emergency blow model and takes into account the influence of compressed air overflows from flood holes in the later stage of blowing. In order to verify the prediction accuracy of the improved emergency blow model for tank blowing, the full-scale model experiment of tank blowing was conducted to investigate the effects of air source volume, air source initial pressure, and flood holes diameters on blowing. The process of air release from bottle and main ballast tank drainage can be accurately simulated by the improved emergency blow model, and the prediction error of tank air peak pressure is shown to be <10%. Additionally, it is found that the air source volume has no effect on the tank’s air peak pressure or tank drainage rate. By analyzing the dynamic characteristics of tank air pressure, it is found that the dynamic change trend of air pressure differs between flood holes with small and large diameters. In the small diameter conditions, the air pressure reaches the maximum when the compressed air just enters the tank; however, under large diameter conditions, the peak pressure comes before the accumulated air pressure is released. The experiment and simulation demonstrate that increasing the area of the flood holes has a decreasing effect on the amount of air accumulated in the tank, and that the decreasing effect becomes more pronounced as the air source initial pressure increases. Introduction To carry out military operations, submarines are deployed both underwater and close to the open surface. About 170 submarines have sunk since they were originally created as a result of an accident, such as a fire, explosion, malfunction, grounding, or collision (Park & Kim 2017). Submarines run the risk of losing safety control in these critical situations. The best method of self-rescue is emergency floating to the surface to prevent bottoming or going deeper than allowed (Liu et al. 2009). A key factor in emergency rising to the water’s surface is the compressed air blowing mechanism. In such an operation, supplying air to the main ballast tank and blowing out ballast water should be used to achieve positive buoyancy or recover a positive pitching moment, which can be used to restore the safe depth of the submarine. Emergency blow is the term used to describe the process of directly supplying air to the main ballast tank without using a high-pressure valve column. The emergency blow is explored in this work because its influence is significantly greater than that of usual blowing, or traditional blowing.

_ Considering the main structures of typical underwater vehicles, three types of numerical model are established, including the beam model, the shell-beam model, and the whole shell model. The results of the three models are compared during the analyses of global vibration, local vibration of cabins, and underwater acoustic radiation. Giving consideration to both the computational cost and accuracy, the proposed shell-beam model is appropriate for the calculation of low-medium frequency acoustic radiation of the main structures of underwater vehicles. The rationality and the frequency range of application of the shell-beam model are verified by calculating the fluid-structure coupling vibration response and the underwater acoustic radiation of the hull subjected to the transverse load excitation, which also demonstrate the significance of this model in engineering practice. Introduction The calculation research on the acoustic radiation of typical underwater vehicle structures can be generally divided into three types based on the calculation methods: analytical methods (Caresta & Kessissoglou 2009), numerical methods, and analytical-numerical hybrid methods (Zhu et al. 2014; Meyer et al. 2016; Qu et al. 2017). The analytical methods can be used for the study of basic laws and mechanisms, and can also be treated as benchmarks for numerical algorithms. However, when it comes to real ships with complex structures, it is difficult to accurately predict the forced vibration and underwater acoustic radiation characteristics by analytical methods. Previously, due to the limitation of the computer hardware, a whole ship was usually simplified as a free–free beam of variable cross section (the hull beam) when conducting the analysis of global vibration. In recent years, with the development of computer technology, whole shell models are usually established during analyses of the low-medium frequency vibration and acoustic radiation of underwater vehicles.

_ The interaction between the structural response and hydrodynamic loading (hydroelasticity) must be considered for design and operation purposes of high-speed planing craft made of composites that are prone to frequent water impact (slamming). A computational approach was proposed to study the hydroelastic slamming of a flexible wedge. The computational approach is a loose two-way coupling between a Wagner-based hydrodynamic solution and a linear finite element plate model. Verification and validation (V&V) was performed on this coupled model. It was found that the model overpredicts rigid-body/spray root kinematics by <15% and hydrodynamic loading/ structural response by <26%. Introduction One of the primary constraints on the operational envelope of high-speed craft is slamming (water impact). Slamming occurs between the hull body and the water surface when a portion/whole of the craft exits the water and then reenters at high-enough velocity (Lloyd 1989; Faltinsen 2005). The frequent water impacts, which work like “water hammers,” along with their induced acceleration pose great jeopardy on hull structures as well as crew and instrument on-board (Yamamoto et al. 1985; Ensign et al. 2000; Hirdaris et al. 2014). With the growing use of lightweight materials, the interaction between the structural deformation and the hydrodynamic loading (hydroelasticity) becomes more prevalent. The current design criteria of high-speed craft are based on empirical procedures with no regard to hydroelasticity due to the lack of understanding of this complex phenomenon (DNV 2013; ABS 2016). Therefore, a better comprehension of hydroelastic slamming is the first step to designing more high-performance craft (Fu et al. 2014; Judge et al. 2020).

_ 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).

_ The International Maritime Organization (IMO) provides criteria to assess the vulnerability of ships toward the phenomenon of parametric roll. Such long-term vulnerability assessments permit to qualify statistically the ships vulnerability regarding parametric roll. However, it does not permit to assess the risk of parametric roll in real time. Thus, researchers and private company have developed methods and software to evaluate this risk using the real-time ship motions provided by the onboard inertial unit. Those methods detect parametric roll events when it appears and warn the officer of the watch of the immediate danger. This paper presents an innovative real-time detection method and its validation. The detection method considers physical conditions required for parametric roll to appear. Especially, it considers the coupling between the roll and pitch motions. The method and its associated parametric roll alarm are entirely described. The results show that the method correctly identifies parametric roll in regular longitudinal waves and do not lead to false detection in regular beam waves. A statistical study in irregular waves based on simulated data presents very promising results with a parametric roll detection rate in head seas above 80% when heavy roll motions appear and a false detection rate in beam seas below 4%. Finally, a 2.5-day full-scale validation on a container ship provides promising results. Introduction The container ships, with typical hull shape presenting flat stern and pronounced bow flare, are especially subject to parametric roll. Operationally, several accidents which have led to the loss of containers at sea may be imputed to this phenomenon (France et al. 2003; Carmel 2006; MAIB 2020; DMAIB 2022). Following the accidents of the C11-class container ship (France et al. 2003) and of the Maersk Carolina (Carmel 2006), both due to parametric roll, insurers asked the shipowners to take measures to avoid such failure to appear (Dølhie 2006). Two solutions are rapidly developed to answer this request. The first one is developed by SeaSense and named SeaSense Monitoring (Nielsen et al. 2006).

_ A practical criterion which can be used for assessing the course-keeping capability of a ship in following waves, is proposed and evaluated. Presently, it accounts for regular waves and it accrued from an analytical estimation of the course instability region’s boundary by applying the method of harmonic balance. The calculation is performed with regard to the third-order yaw equation, derived from a classic sway-yaw-rudder model of ship maneuvering motions, with time-dependent coefficients at two places, which is like a Mathieu-type equation extended to third order. The proposed analytical criterion was evaluated thoroughly against simulations with regard to this sway-yaw model and it was found to be adequately accurate. A supplementary quasi-static yaw stability criterion (fitting to ship operation with frequency of encounter, with respect to the waves, close to zero) was also considered in order to determine which one yields more stringent requirements, for various operating conditions. The proposed criterion could be an extra vulnerability check for broaching-to, in the context of the Second Generation Intact Stability Criteria. Introduction The difficulties of steering of ships in following seas have received the attention of the research community since more than 70 years ago (Davidson 1948). A relevant direction of research refers to the avoidance of the broaching-to instability and, in particular, to the development of practical criteria that could ensure sufficient course-keeping capability for a ship encountering steep following waves. Some classic works on this topic, such as those of DuCane and Goodrich (1962), Wahab and Swaan (1964), and Motora et al. (1981), were focused on the quasi-static condition of a ship on the wave which could be practically realized if the ship was advancing with speed equal to the wave celerity (zero frequency of encounter). As implied, these works were essentially focused on the avoidance of a type of broaching-to instability that is preceded by the realization of surf-riding, a phenomenon where the ship is forced to move with the wave, usually riding a downslope.

The performance of a two-dimensional hydrofoil of arbitrary camber, moving at arbitrary Froude number at a constant depth below a free surface, is considered. The treatment is based upon the use of singularity distributions and thin foil theory. By assuming an appropriate series form for the vortex distribution representing the hydrofoil, it is shown that the problem can be reduced to the solution of a set of linear algebraic equations. These are solved by a collocation procedure. Numerical results for the performance characteristics are then given for several hydrofoil configurations, submergence depths, and Froude numbers. These indicate that operation at Froude numbers greater than about ten is practically equivalent to operation at infinite Froude number. However, at lower values of the Froude number and for all the configurations considered, Froude number effects are important, even at submergence depths of several chord lengths.

_ We present experimental results of resonant free surface oscillations within three circular moonpools arranged in tandem at forward, central, and aft positions of a fixed rectangular vessel in head waves. The piston mode resonance frequency is primarily captured, which decreases with the increase in the vessel draft. The aim is to study the effect of body diffraction on the free surface amplitude and phase of the oscillating water columns at the three locations. The results indicate that, in general, the forward moonpool has the highest response amplitude, whereas the relative amplitudes of the central and aft moonpools depend on the wave frequency. It is observed that the nondimensional response amplitude increases nonlinearly with decreasing wave steepness close to the resonance frequency, while the effect diminishes at lower wave frequencies. The oscillation phase differences between the moonpools show effects of wave-body interaction, a phenomenon dependent on the vessel draft and wave frequency. Finally, the study includes a comparison of the responses at the three moonpool locations between multiple and single configurations. Introduction A moonpool is a vertical opening through the ship deck and open to the sea at the bottom, which is installed in vessels specialized in certain offshore operations. Resonant water column oscillations are encountered in moonpools (Aalbers 1984) due to vessel operations in waves. On the other hand, oscillating water columns (OWCs) have been extensively researched, primarily due to their potential for ocean wave energy conversion (Evans 1978; Heath 2012; Falcão & Henriques 2016). Now, considering design perspectives, the focus of the studies on water column resonance in waves depends on the specific marine application. For example, wave energy converters would require maximized OWC responses for efficient energy capture (Evans & Porter 1995; Morris-Thomas et al. 2007), while large free surface oscillations within moonpools of drillships have adverse effects on the vessel dynamics (Fakuda 1977).

_ Hydrofoils made of metal alloys were broadly used on high-speed boats in the past. Nowadays, much lighter hydrofoils made of composite materials are finding increasingly more applications on sailing yachts and powerboats. However, these hydrofoils are usually rather flexible, and their design requires computationally demanding analysis, involving hydroelastic calculations. In this study, exploratory high-fidelity simulations have been carried out for surface-piercing hydrofoils in unsteady conditions with help of a computational fluid dynamics solver for fluid flow coupled with a finite element solver for the foil structure. To model unsteady foil deformations, the morphing mesh approach was utilized, and the volume-of-fluid method was applied for multiphase flow simulations. The computational setup, as well as verification and validation study, is described in this paper. Three hydrofoils of different stiffness, including a perfectly rigid foil, were simulated in both calm water conditions and regular head waves. Representative examples of foil deflections and wave patterns, as well as time-dependent structural and hydrodynamic characteristics, are presented. Introduction Hydrofoils are efficient lift-generating devices intended for application in water flows. Hydrofoils have streamlined shapes, and when operating at small incidence angles, they can produce high lift forces at relatively low drag, when moving in a certain speed range. Due to this ability, hydrofoils and their derivatives are commonly used as control and propulsive devices, e.g., as rudders, fins, and propeller sections. In the second half of the last century, hydrofoils found broad applications on fast boats, such as passenger ferries and military ships (McLeavy 1976; Matveev & Duncan 2005). These craft were able to achieve high speeds at lift–drag ratios (LDR) around 12–15, significantly higher than LDR of other hulls, such as planing boats. However, due to rather limited favorable operational conditions with regard to speed and payload, popularity of hydrofoils somewhat receded. One of drawbacks was that hydrofoils were usually made of metal alloys, thus being relatively heavy and difficult to service.

_ Accurate prediction of planing hull resistance is a difficult task due to complex hydrodynamic interactions at high speeds and is often performed by three methods: model testing, empirical formulas, and computational fluid dynamics (CFD). Model testing provides the most accurate results, but is usually only used in cases of necessity due to time and cost, whereas empirical formulas and the CFD method do not always provide results with the expected accuracy and reliability. Therefore, this paper will present methods to improve and ensure the accuracy of planing hull resistance values predicted by Savitsky’s empirical formula based on using our modified computation procedure, and by the CFD method based on ensuring the quality of 3D hull mesh and defining the simulation parameters suitable for a study planing hull. This study has been applied to Vietnam’s large displacement high speed passenger vessel with design symbol K88 and obtained good results with the deviations between the resistance model test data and the corresponding values predicted by the Savitsky method using our modified computation procedure, and by the XFlow CFD software using our suitable inputs in calculation cases are within ±5% and ±3%, respectively. Introduction In planing hull design, accurate prediction of its resistance is a difficult task due to complex hydrodynamic interactions at high speeds and is often performed by three methods: model testing, empirical formulas, and computational fluid dynamics (CFD). Model testing is the most reliable approach but it is expensive and time-consuming, so it is often used in cases where it is necessary, or used to verify and validate the results predicted by others. Also, since dynamic similarity cannot be fulfilled in model tests, it is necessary to use Froude or Prohaska methods to extrapolate results from model scale to full scale, which causes certain errors. Empirical formulas or graphs are established based on the systematization of resistance data of series model tests with hull form similarities (Holtrop & Mennen 1982; Faltinsen 2006). As a result, there are many different empirical resistance formulas and graphs depending on the type of ship used in the model tests. Table 1 shows some common empirical formulas or graphs for planing hull resistance with different ranges of hull parameters that can be found in related documents, such as Kafali (1959), Nordstrom (1951), Groot (1951), Almeter (1993), etc.