Hull Pressure Research Articles

Direct measurements and CFD simulations on ice-induced hull pressure of a ship in floe ice fields

Floe ice fields are expected to replace level ice to be the most common environment for future polar sea transportation under the long-term trend of global warming. In this study, the authors aim to develop a viable analysis procedure to predict the ice-induced hull pressure characteristics for ships navigating in floe ice fields. A novel ice model test procedure is established, which is characterized by making use of non-refrigerated synthetic model ice and tactile pressure sensors to measure the hull pressure. The numerical tool is based on a state-of-the-art CFD-DEM numerical framework; a novel method to monitor the hull pressure during the interaction between the hull and ice floes during the CFD-DEM simulations. Statistical analysis indicates the probability distributions of the ice pressure from the experiment and the numerical results are comparable. Besides, the impacts of ship speed and ice floe concentration on the hull pressure distribution are also examined. Increasing speed and ice concentration will make the probability distribution of ice pressure shift towards the high-pressure going interval, resulting in an increased mean of ice pressure. It is also found that increased speed leads to a smaller variance, while increased ice concentration results in a larger variance.

Numerical Investigation on the Hydrodynamic Response of Pentamaran—Resistance Analysis of Different Outrigger Inclination Angles

Due to the interference between the main hull and the outrigger of the pentamaran, resistance is greatly affected. Therefore, research on the pentamaran front outrigger inclination angle has further practical significance for reducing resistance. In this study, the pentamaran front outrigger inclination angle was analyzed by CFD method, the ship motion in waves was simulated by overlapping grid technology, and the resistance of the pentamaran in static water and waves was predicted by using the unsteady RANS equation. First, a series of validation studies were carried out for the numerical methods used in the study. Then, the influence of the front outrigger inclination angle on the pentamaran resistance performance under different working conditions is calculated and discussed. In order to analyze the influence of the change of the front outrigger inclination angle on the resistance, free surface wave-making and hull pressure are further discussed. The results show that the influence of the front outrigger inclination angle change on the resistance of the pentamaran has a certain rule, and the resistance of the pentamaran can be reduced by adjusting the front outrigger inclination angle.

Analyzing the Influence of Water Depth on Total Resistance in Ulstein X-Bow Configuration: A Numerical Study

Considering resistance is a vital factor during ship design, especially when the vessel navigates through shallow waters. This situation leads to increased hull pressure as the ship advances. The ship can increase sinkage and trim, affecting the total drag of the vessel. It is important to predict resistance in water conditions with different surface heights accurately. This study aims to analyze the resistance at sea level. Testing the X-bow shape on the bow is predicted to affect the resistance analysis results. This study predicts ship resistance using the overset mesh technique in the Computational Fluid Dynamics method. According to the study's findings, utilising Ulstein X-Bow in deep water may reduce the total resistance value by 4.85%, followed by a change in sinkage angle by 2.32% and trim by 0.40%. Unfavourable outcomes are shown by the overall resistance value in moderate shallow water situations, and this happens as a result of the squat phenomenon, which is caused by a drop in pressure along the ship's bottom interacting with the water.

Numerical prediction of propeller-induced noise in open water and ship behind conditions

In this article, the underwater noise of non-cavitating propellers is investigated using a boundary element method (BEM) coupled with the Ffowcs Williams–Hawkings (FW–H) formulation in the presence of the hull. The propeller is mounted on the vessel with an infinite plane assumed at the design draft to consider the free surface or tunnel wall effect. The hydrodynamic BEM solves the flow field for the analysis of propeller performance, then the time-dependent surface pressures are taken as the known noise sources for the FW–H equation in the form proposed by Farassat. The hull geometry and its disturbance to the medium are considered by solving the boundary integral equations, and the half-space medium is modeled by adding an additional term to the full space Green’s function for an image body beyond the infinite plane. The propeller performance in open water condition is first investigated to validate BEM predictions against experimental measurements. Along with the overall noise patterns in the flow field, decay rates of noise with the distance from the propeller and limited influence of the linear noise terms of the FW–H equation are discussed. Afterward, the propeller-induced hull pressure fluctuations are investigated, and the time history of acoustic pressures shows reasonable agreement with experimental measurements. Direct noise from the propeller, its scattered noise by the hull, and their sums as the total noise are discussed. This study identifies the dominating noise source around the hull, which could provide a basis for the noise control strategy for a ship propulsion system.

Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input

Ship noise predictions using FWH acoustic analogy with incompressible flow solution inputs are investigated for a model scale container vessel with a cavitating propeller. Numerical predictions of cavitation and hull pressure pulse predictions are validated first, comparing simulations performed for the tunnel test section and experimental measurements inside a large-size cavitation tunnel. The predictions agree well including the sheet cavitation development, tip vortex cavitation (TVC) bursting, convex shaped sheet cavitation closure line and the traveling re-entrant jet underneath the sheet cavity triggers the TVC bursting behavior.Noise predictions are performed within a large open simulation domain instead of the cavitation tunnel test section. With incompressible solutions, noise levels are predicted based on two different placements of Permeable/Porous Data Surfaces (PDS) where one encloses the cavitating propeller, rudder and downstream wake (PDS−L1) and one encloses the whole ship as a rectangular box (PDS−L2). The FWH noise predictions with impermeable surfaces (S−FWH) are also studied. Differences between predictions using PDS−L1, PDS−L2, and S−FWH are discussed.To compare calculated noise source level (Ls) at different noise receivers at varying distances, normalization assuming spherical spreading acoustic wave is used. In certain combinations of receiver point and method of acoustic computation, the predicted Ls agreed well comparing to experimental measurements, including the prediction with PDS−L2 and receiver close to the PDS and direct probed incompressible hydrodynamic pressure at similar receiver locations. However, with increasing distance to the receiver, the predicted Ls increases for higher frequencies and levels out at unrealistically high levels. To study this phenomenon, a free-field monopole representing the cavity structure dynamics is tested with different combination of PDS and receiver placements, using both incompressible and compressible input. This analysis gives a clear indication that the origin of this erroneous effect is the combination of the FWH acoustic analogy with an incompressible solver.

Numerical investigation of the influence of vortex generator on propeller cavitation and hull pressure fluctuation by DDES

Numerical investigation of the influence of vortex generator on propeller cavitation and hull pressure fluctuation by DDES

Numerical prediction of propeller induced hull pressure pulses using RANS and IDDES

Numerical prediction of propeller induced hull pressure pulses using RANS and IDDES

Design and analysis of low-cost underwater glider for shallow water

This paper aims to design a low-cost underwater glider to operate in shallow water. The proposed design was developed by manufacturing engineering software. Analysis of the hull using manufacturing engineering software and 3D computer-aided design (CAD). The analysis of hydrodynamics using computational fluid dynamics (CFD). This glider was designed to operate in shallow water, coastal, lake and river for a maximum depth of 10 m and a maximum speed of current 12,96 km/h, or 3,6 m/s. To reduce and minimize the cost to manufacture this underwater glider, the mechanics, electrical, electronics, and power source were using common tools on the market, not on demand. Based on numerical model, the hull pressure had 30,127 psi or 0,2077162 MPa for maximum depth 10 m and max speed 12,96 km/h. Maximum pressure occurs on the nose and behind the wings. This unmanned vehicle was designed to be in 9 compartments. The first compartment and 8th compartment are used for ballast tanks. The others for: mechanics of ballast system, altimeter and attitude controller, payload, battery pack, main controller part, propulsion system, and propulsor.

Roll characteristics contributed by a bilge keel using a high-order fractional step finite volume solver

This paper follows the previous work [Ocean Eng 199: 1–15] to study roll characteristics contributed by a bilge keel through investigating the differences between roll characteristics of the naked mid-section of a KVLCC2 and the ones of the hull fitted with a bilge keel. Harmonic excited rolls are simulated by a high-order fractional step finite volume solver. Roll moment, roll damping, added mass moment of inertia, hull pressure are explored. Besides, two damping components of a bilge keel, due to the force normal to the bilge keel and the additional pressure on the hull induced by the bilge keel, are studied. Five parameters, namely roll amplitude, roll frequency, ship draught, height and thickness of the bilge keel, are concerned. In results, the additional roll moment due to the bilge keel exhibits a strong nonlinearity. The two components contribute to the additional roll moment quite the same amount, whereas wave radiation contributes little and negligible. Added mass moment of inertia is saturated when roll amplitude becomes large. Hull pressure induced by the bilge keel is normally positive at the front of bilge keel and negative at the back side and attains maximum approximately right at the base of the bilge keel.

Research on hull pressure distribution of amphibious landing on water based on RANS method

Aiming at the strength problem of amphibious landing on water, the pressure distribution of ship bottom is studied. RANS multi-phase flow method is used to solve the coupling problem of gas, liquid and solid in the process of amphibious landing on the water surface. Overlapping grid technology is used to simulate the landing under different initial horizontal velocity and vertical velocity. The influence of initial conditions on the motion response of amphibious is analyzed, and the variation law of pressure on each section of ship bottom with time is obtained, This paper analyzes the variation of pressure with time and position, and provides technical reference for the design and application of water loads in the development of amphibious.

Empirical mode decomposition of ship hull pressure fluctuation induced by cavitating propeller

We report for the first time a cavitation-induced pressure fluctuation decomposition developed from empirical mode decomposition (EMD) [Huang et al., Proc. R. Soc. London, Ser. A 454, 903–995 (1998)]. The idea is to decompose the nonlinear and non-stationary time series data into a finite and usually small number of “intrinsic mode functions” based on the local properties of the signal, which admit a well-behaved Fourier transform. With this transform, we can obtain frequency characteristics that give sharp identifications of imbedded structures. The cavitation evolution and excited pressure fluctuation around a cavitating propeller in the nonuniform wake are investigated using high-speed imaging and pressure sensors. By the EMD method, we separate the pressure fluctuations induced by different types of cavitation. The high frequency components of the pressure fluctuations are mainly caused by the collapse of sheet cavitation, followed by the shrinking and growth of sheet cavitation. Furthermore, the tip vortex cavitation leads to higher frequency but contributes less to pressure fluctuations. The periodical motion of the propeller contributes to the first blade frequency, and the pressure fluctuations induced by cavitation are superimposed on it.

Application of Large Eddy Simulation to Predict Underwater Noise of Marine Propulsors. Part 2: Noise Generation

Methods to predict underwater acoustics are gaining increased significance, as the propulsion industry is required to confirm noise spectrum limits, for instance in compliance with classification society rules. Propeller–ship interaction is a main contributing factor to the underwater noise emissions by a vessel, demanding improved methods for both hydrodynamic and high-quality noise prediction. Implicit large eddy simulation applying volume-of-fluid phase modeling with the Schnerr-Sauer cavitation model is confirmed to be a capable tool for propeller cavitation simulation in part 1. In this part, the near field sound pressure of the hydrodynamic solution of the finite volume method is examined. The sound level spectra for free-running propeller test cases and pressure pulses on the hull for propellers under behind ship conditions are compared with the experimental measurements. For a propeller-free running case with priory mesh refinement in regions of high vorticity to improve the tip vortex cavity representation, good agreement is reached with respect to the spectral signature. For behind ship cases without additional refinements, partial agreement was achieved for the incompressible hull pressure fluctuations. Thus, meshing strategies require improvements for this approach to be widely applicable in an industrial environment, especially for non-uniform propeller inflow.

Prediction of cavitating performance of a tip loaded propeller and its induced hull pressures

A numerical method solving for the diffraction potential on the hull is coupled with a boundary element method (BEM) to evaluate the propeller-induced hull pressures. The BEM is first implemented for the hydrodynamic analysis of non-cavitating/cavitating propellers in the absence of the hull, and the predicted solutions are taken as the known unbounded potentials in the hull pressure calculations. A tip loaded propeller (TLP) is adopted as the model propeller and mounted under the flat hull subject to uniform inflow. The TLP is operated close to the hull so that infinite speed of sound can be assumed, reducing the frequency domain Helmholtz equation to Laplace's equation which can be solved by a BEM solver. Unsteady sheet cavitation and developed tip vortex cavitation are predicted on the propeller by the hydrodynamic BEM and considered in the calculation of the hull pressures. Several loading conditions are imposed on the propeller and the corresponding pressure predictions and cavitation patterns are compared to published experimental data and to those from unsteady full-blown Reynolds-averaged Navier–Stokes (RANS) simulations. Very good agreement is achieved between the predicted and measured results, especially under moderately loaded condition.

Numerical Study of Hydrodynamics of Heavily Loaded Hard-Chine Hulls in Calm Water

Hard-chine boats are usually intended for high-speed regimes where they operate in the planing mode. These boats are often designed to be relatively light, but there are special applications that may occasionally require fast boats to be heavily loaded. In this study, steady-state hydrodynamic performance of nominal-weight and overloaded hard-chine hulls in calm water is investigated with computational fluid dynamics solver program STAR-CCM+. The resistance and attitude values of a constant-deadrise reference hull and its modifications with more pronounced bows of concave and convex shapes are obtained from numerical simulations. On average, 40% heavier hulls showed about 30% larger drag over the speed range from the displacement to planing modes. Among the studied configurations, the hull with a concave bow is found to have 5–12% lower resistance than the other hulls in the semi-displacement regime and heavy loadings and 2–10% lower drag in the displacement regime and nominal loading, while this hull is also capable of achieving fast planing speeds at the nominal weight with typical available thrust. The near-hull wave patterns and hull pressure distributions for selected conditions are presented and discussed as well.

Estimation of the Noise Source Level of a Commercial Ship Using On-Board Pressure Sensors

The dominant underwater noise source of a ship is known to be propeller cavitation. Recently, attempts have been made to quantify the source strength using on-board pressure sensors near the propeller, as this has advantages over conventional noise measurement. In this study, a beamforming method was used to estimate the source strength of a cavitating propeller. The method was validated against a model-scale measurement in a cavitation tunnel, which showed good agreement between the measured and estimated source levels. The method was also applied to a full-scale measurement, in which the source level was measured using an external hydrophone array. The estimated source level using the hull pressure sensors showed good agreement with the measured one above 400 Hz, which shows potential for noise monitoring using on-board sensors. A parametric study was carried out to check the practicality of the method. From the results, it was shown that a sufficient recording time is required to obtain a consistent level at high frequencies. Changing the frequency resolution had little effect on the result, as long as enough data were provided for the one-third octave band conversion. The number of sensors affected the mid- to low-frequency data.

Investigation on RANS prediction of propeller induced pressure pulses and sheet-tip cavitation interactions in behind hull condition

This paper investigates the numerical prediction of cavitation and hull pressure pulses induced by a marine propeller operating in behind-hull conditions of a container vessel in model scale. Simulations are performed using commercial package Star-CCM+ and opensource package OpenFOAM using RANS approach and predictions are compared with experimental measurements. A mesh dependency study with respect to wake prediction is also presented. Operating conditions scaled to two different Reynolds numbers with the same propulsion characteristics and cavitation number are considered to study scaling effect. Simulations using tip refined mesh are performed and compared with using base mesh to study the tip vortex generation, tip vortex cavitation, its interaction with sheet cavity and induced pressure pulses. The influence of time step length is also investigated.Star-CCM+ and OpenFOAM predict consistent results. The predicted cavitation patterns agree well compared to experimental measurements as well as pressure pulse levels up to 3~4 times blade passing frequency (BPF) especially for the predictions with tip refined mesh. The sheet cavitation is the major contribution to 1st and 2nd order BPF pressure pulses and its closure has significant contributions to higher-order pressure pulses. Deduced pressure pulses by tip vortex cavitation (TVC) are significant ranging from 3rd order to 10th order of BPFs. The TVC induced pressure pulses are related to its violent bursting behavior which is influenced by the closure of the sheet cavity.

A comparison between fully-unsteady and quasi-steady approach for the prediction of the propeller performance in waves

Maritime transport is the most energy-effective mode to move large amounts of goods around the world. Hauling cargo via waterway produces an enormous quantity of greenhouse gas emissions. Vessel fuel efficiency directly influences ship emissions by affecting the amount of burnt fuel. Optimizing ships operating in waves rather than in calm water conditions could decrease the fuel consumption of vessels. In particular, ship propellers are traditionally designed neglecting dynamic conditions such as time-varying wake distribution and propulsion factors, propeller speed fluctuations, ship motions, and speed loss.The effect of waves on the propeller performance can be evaluated using both a quasi-steady and a fully-unsteady approach. The former is a fast computational approximation method based on the assumption that the ratio of propeller angular frequency to wave encounter frequency is sufficiently large. The latter provides a complete representation of the propeller dynamics, but it is computationally expensive.The purpose of this paper is to compare the propeller performance in the presence of waves using the quasi-steady and the fully unsteady approach. This analysis is performed by observing the differences in unsteady propeller forces, cavitation volume, and hull pressure pulses between the two approaches. The full-scale KVLCC2 propeller is utilized for the investigation.Results show a good agreement between the quasi-steady and the fully-unsteady approach in the prediction of the temporal mean and the fluctuation amplitude of KT and KQ, the cavity volume variation, and the hull pressure pulses. Therefore, for the considered operating conditions, the quasi-steady approach can be used to compute the propeller performance in waves.

Prediction of Unsteady Developed Tip Vortex Cavitation and Its Effect on the Induced Hull Pressures

Reducing the on-board noise and fluctuating pressures on the ship hull has been challenging and represent added value research tasks in the maritime industry. Among the possible sources for the unpalatable vibrations on the hull, propeller-induced pressures have been one of the main causes due to the inherent rotational motion of propeller and its proximity to the hull. In previous work, a boundary element method, which solves for the diffraction potentials on the ship hull due to the propeller, has been used to determine the propeller induced hull pressures. The flow around the propeller was evaluated via a panel method which solves in time for the propeller loading, trailing wake, and the sheet cavities. In this article, the propeller panel method is extended so that it also solves for the shape of developed tip vortex cavities, the effects of which are also included in the evaluation of the hull pressures. The employed unsteady wake alignment scheme is first applied, in the absence of cavitation, to investigate the propeller performance in non-axisymmetric inflow, such as the inclined-shaft flow or the flow behind an upstream body. In the latter case, the propeller panel method is coupled with a Reynolds-Averaged Navier–Stokes (RANS) solver to determine the effective wake at the propeller plane. The results, including the propeller induced hull pressures, are compared with those measured in the experiments as well as with those from RANS, where the propeller is also simulated as a solid boundary. Then the methods are applied in the cases where partial cavities and developed tip vortex cavities coexist. The predicted cavity patterns, the developed tip vortex trajectories, and the propeller-induced hull pressures are compared with those measured in the experiments.

Bilge keel load and hull pressure distribution on a rolling ship section with a high-order fractional step finite volume solver

Bilge keel load and hull pressure distribution are investigated. For this purpose, harmonic excited rolls of the mid-section of a KVLCC2 fitted with one bilge keel are simulated by means of a high-order fractional step finite volume solver. Fourier analysis is employed to derive drag and inertia coefficients in Morison equation and the corresponding higher harmonic terms from bilge keel load. The calculated drag and inertia coefficients as well as positive and negative pressure coefficients are validated with some published numerical and experimental results. Influence of the roll amplitude and circular frequency, height and thickness of the bilge keel, and draught is presented. In results, drag and inertia coefficients is solely determined by KC number. Effect of draught, circular frequency and thickness of bilge keel is minuscule and negligible. Bilge keel load shows pronounced nonlinearity, which reveals the importance of the higher harmonic terms. Besides, drag coefficient and jump of the pressure coefficient satisfy the relationship assumed by Ikeda et al. (1977a). Positive pressure coefficient in front of bilge keel is KC-dependent at low KC number especially when KC < 6. The empirical method underestimates the positive pressure at low KC number and overestimates the negative pressure.

Experimental investigation of vortex generator influences on propeller cavitation and hull pressure fluctuations

In this paper, the transient turbulent cavitating flow around a marine propeller behind a ship was investigated experimentally with emphasis on how vortex generator (VG) influences propeller cavitation and hull pressure fluctuations. The experiments were carried out in China Large Cavitation Channel with the closed test section covering 10.5 m in length and cross-section of 2.2 m2 ϗ 2.0 m2. The experiment recorded instantaneous cavitation photos of the propeller and pressure fluctuations on the hull surface. The results demonstrate that without vortex generator, the sheet cavitation inception begins at −50° (310°), and then from −50° (310°) to 30°, the extent and area of sheet cavitation increase. When vortex generator installed on the hull, the sheet cavitation inception occurs in advance at −60° (300°), and the sheet cavitation expands to larger rotation range due to the vortex generator. It is shown that the vortex generator with proper geometry and installed location may contribute the highly nonuniform wake to be more uniform, and can make the change of propeller cavitation to be milder, which decrease the pressure fluctuations in this study. Further analysis indicates that the vortex generator may promote the energy distribution to be more uniform in physical and spectral space in some degree.