Ship Pitch Research Articles

URANS simulations for a flooded ship in calm water and regular beam waves

CFD simulations are conducted for zero-speed damaged passenger ship SSRC in calm water and waves with 6DOF motions including flooding procedure in calm water, roll decay in calm water and motions in regular beam waves for various wavelengths. The simulations model the 6DOF soft spring experimental mount, the one- and two-room flooding compartment configurations, including both intact and damaged conditions. For flooding and roll decay, simulations show ability to predict the trend of increases in roll period and damping due to flooding, as reported in ITTC. The damping magnitudes were often under-predicted with large errors while the roll period and compartment water height were well predicted. Two-room compartment simulation showed three times larger damping than one-room compartment cases whereas the roll period was similar for both conditions. For wave cases, all motions show primarily 1st order responses, except for parametric roll condition which shows large ½ harmonic responses for the intact ship. The 2nd order responses are small for both damaged and intact ship. The larger roll period and damping for the damaged ship shift the peak of responses to smaller wave frequency and reduce the amplitude of responses. The average error is often large for 1st order intact ship pitch and damaged ship surge and pitch. The errors are larger for most ½ and 2nd order responses. Large errors could be partially due to the complex mounting system in the experiment. Overall, current CFD results show better predictions than those reported for potential flow solvers even though the computational cost is larger.

Study of HTS Machine System Cooling With a Closed-Loop Thermosyphon: Stability of Unsteady Heat Load and Transient Conduction

Thermosyphoning (TS) is a heat exchange mechanism that uses a circulating refrigerant based on natural convection with no need for a mechanical pump. This cooling technique has been employed to circulate liquid coolant and gaseous coolant for high-temperature superconductor (HTS) rotating machine systems. These machines operate with an HTS field pole in the temperature range from 25 to 40 K, which are suitable temperatures for the survivability of HTS wires. The cryomechanical components are simple; there are a condenser, an evaporator, and adiabatic tubes located between the condenser and the evaporator. For applications to ship propulsion motors or generators of the radial gap type, the liquid/gas coolant flow along the adiabatic tube inside the rotating shaft may be considerably affected by the ship's rolling and/or pitching motion. In this work, we studied the temperature stability and heat load survivability of cryogenic TS, by constructing a 100 W @ 30 K-grade model. We investigated the temperature, thermal resistance, and heat flux, with a maximum load up to 60 W, of ground and onboard tests. The observed TS behavior indicates that there is sufficient survivability to assemble megawatt-class ship propulsion systems.

Augmenting Ship Propulsion in Waves Using Flapping Foils Initially Designed for Roll Stabilization

Abstract Biomimetic flapping foils attached on ship hull are studied for wave-energy extraction, stored in ship motions, and direct conversion to propulsive power. We examine a pair of roll-stabilization wings located at the side of the hull, in horizontal arrangement. The fins gain their linear oscillation (heaving) from ship pitching and heaving responses in irregular waves, while wing's rotation (pitching) is properly controlled with respect to its vertical motion history. A method, developed in our previous works, is applied for that purpose. The system operates in realistic sea conditions modeled by using parametric spectra, taking into account the coupling between ship responses and the hydrodynamics of the lifting appendages. We present numerical calculations concerning the operation of the augmenting system indicating that, although the present arrangement is designed for roll reduction purposes it can obtain significant amount of thrust. Also it is illustrated that, after reposition of the fins near the bow, the performance of the system can be further enhanced.

Water Hammer Characteristic of the Pipeline in Ship Pitch Balance System

In ship pitch balance system, serious flow impact and water hammer occur because of the turning on and off of valve during the procedure of water-shift. Flow area of the ball valve used most on ship was derived, and mathematical models of pressure lost before and after valve were formulated. Besides, considering the fact of water-shift balance system, an AMESim model was established based on improved traditional throttle model. And the validity of AMESim model was ascertained by comparing simulation results of stable pressure before and after valve with calculated values from mathematical models. Then, with the AMESim model, impact characteristics of water-shift pipeline were investigated when adopting various valve switch rules, length of pipelines before and after valve and using an accumulator in system. From that, methods to reduce pipeline impact were proposed, which make good references for noise control of ship pitch balance system.

Accuracy improvement in depth measurements taken using one-beam echosounder under ship pitching and rolling

In order to ensure accuracy of depth measurements on small hydrographic ships in the paper an analysis of errors in depth measurements, taken with a one-beam echosounder under ship rolling and pitching is made, along with the comparison of methods used to decrease the impact of pitching and rolling on the accuracy of those measurements. Data obtained as a result of the analysis made indicate that depth measurement error induced by ship pitching and rolling depending on pitch and roll angles can take on a value up to 3,1% on a flat bottom; in order to ensure that error value is acceptable for precise measurements, the magnitude of pitching and rolling angles should be less than 2°. On a basis of the comparison of three basic methods used to decrease impact of pitching and rolling on depth measurements (i.e. using of ship stabilizers, gyrostabilization of echo sounder measurement head and electronic stabilization of an acoustic beam) it’s evident, that in the view of cost-effectiveness and acoustic noise reduction, use of a gyrostabilized echo sounder measurement head is optimal for small hydrographic ships. In the paper author proposes the scheme of mounting of such a head on the ship, and also recommends the method for gyrostabilizer synthesis.

Seakeeping prediction of KVLCC2 in head waves with RANS

The present work is devoted to the prediction of added resistance and ship motion of KVLCC2 in head waves. Systematic validation and verification of the numerical computation demonstrate that reliable numerical results can be obtained in calm water as well as in head waves. The numerical results are analyzed in terms of added resistance, ship motions and wake flow. Both free to heave and pitch and fixed model are studied to investigate the contribution to added resistance from ship motion at different wavelengths, and the results show that ship motion induced added resistance is negligible when the wavelength λ<0.6Lpp. The comparison with theoretical calculation based on strip theory and experimental results shows that RANS predicts the added resistance better in all wavelengths. Ship pitch and heave motion in regular head waves can be estimated accurately by both CFD and strip theory. Finally, wake flow at the propeller plane in waves is discussed, and the numerical results show that the change of axial velocity due to one studied incoming head waves is at most over 30% of the ship forward speed.

Aeroelastic analysis of a shipboard helicopter rotor with ship motions during engagement and disengagement operations

An aeroelastic simulation of a shipboard helicopter rotor with ship motions during engagement and disengagement operations is investigated to explore the coupled dynamic behavior between the rotor and the ship. A finite element analysis based on a moderate deflection beam model is employed to capture the flap, lag and torsion deflections of the rotor blade. The ship is treated as a six-degree-of-freedom rigid body. By using the Hamiltonʼs principle, system equations of motion are derived based on the generalized force formulation. The responses agree well with the test data of the rotor blade droop stop impact and the transient aeroelastic response of the shipboard teetering model rotor. Parametric investigations illustrate that the ship pitch motion has significant influence on the maximum negative displacement of the blade tip. Additional over 25% increase of the tip deflection can be introduced by the ship pitch motion. The aerodynamic and inertial couplings between the ship motion and the rotor have significantly nonlinear influence on the transient aeroelastic response. Both terms should be taken into account in the coupled helicopter–ship dynamics model.

Three-Dimensional Imaging of the High Sea-State Wave Field Encompassing Ship Slamming Events

Abstract Understanding and modeling ship wave slamming necessitates characterizing the surface wave field that results in slamming events. Shipboard measurements of the incoming wave field were made during sea trials of the twin-hull Sea Fighter (FSF-1), using a three-dimensional (3D), stereo-optic imaging system. The data obtained were processed using an image matching algorithm resulting in 3D video sequences of the incoming wave field at forward speeds of 16–40 kt in head seas at sea state 4. Six wave slamming events were captured, characterized, and compared to the average wave field properties. It was found that the salient properties of the individual waves that resulted in ship slamming occurred in groups of two or more, were approximately 30% larger than the significant wave heights during the ∼2-min period encompassing the slamming events, and had wave slopes at least 2 times that of the preceding wave slope. Additionally, wave slamming corresponded to large ship pitching motions resulting from the incident waveforms.

Basic Study of Body Sway in Artificial Ship Rolling and Pitching by Visual and Motion Platform -Toward Efficient Simulator-Based Training-

A navigator guides a ship for safe and efficient navigation, and s/he gets navigational information through the five senses. Visual information is most important because it is said to occupy more than eighty percents to whole information. We are researching the relationship between the visual image of seascape and the physiological/body response using ship bridge simulator, which is used to train and educate ship handling and how to handle a navigational instrument. The simulator-based training is popular worldwide. The simulator is able to control the traffic situation and to do the same scenarios for trainees. On the merchant ship simulator-based training, the ship movements- rolling, pitching, yawing, etc., never simulate by visual or motion platform. However, the ship movement is an important factor for the simulator-based training, and we need to confirm the influence of body and mental workload for the simulated ship movements. The purpose of this paper is to find characteristics of body response to artificial ship movements by visual and motion platform. The result shows characteristics of body response to artificial rolling and pitching by visual and motion platform differ.

Three-Dimensional Imaging of the High Sea-State Wavefield Encompassing Ship Slamming Events

Understanding and modeling ship wave slamming necessitates characterizing the surface wave field that results in slamming events. Shipboard measurements of the incoming wave field were made during sea trials of the twin-hull Sea Fighter (FSF-1), using a three-dimensional (3D), stereo-optic imaging system. The data obtained were processed using an image matching algorithm resulting in 3D video sequences of the incoming wave field at forward speeds of 16–40 kt in head seas at sea state 4. Six wave slamming events were captured, characterized, and compared to the average wave field properties. It was found that the salient properties of the individual waves that resulted in ship slamming occurred in groups of two or more, were approximately 30% larger than the significant wave heights during the ∼2-min period encompassing the slamming events, and had wave slopes at least 2 times that of the preceding wave slope. Additionally, wave slamming corresponded to large ship pitching motions resulting from the incident waveforms.

Experimental Study on the Behavior of a Swimming Pool Onboard a Large Passenger Ship

The water in a swimming pool on the top deck of a large passenger ship can be excited to a resonant motion, even in a moderate sea state. The motion of the water in the pool is mainly caused by longitudinal acceleration, resulting from the ship's pitch and surge motions. At resonance, there can be high waves in the pool and splashing of water. In this study the behavior of the Solarium Pool of the Freedom of the Seas was examined in various sea states and operating conditions. The motions of the pool were calculated on the basis of a linear seakeeping method, and the behavior of the water in the pool was studied with experimental model tests. A large-scale model of the pool was constructed and fitted to a purpose-built test bench that could be axially moved by a computer-controlled hydraulic cylinder. Water elevation in the pool was measured, and all tests were video recorded. Different modifications of the pool were tested to improve the behavior of the pool. A strong correlation between the longitudinal motion and the behavior of the water in the pool was found.

Application of the Grey topological method to predict the effects of ship pitching

Ship motion, with six degrees of freedom, is a complex stochastic process. Sea wind and waves are the primary influencing factors. Prediction of ship motion is significant for ship navigation. To eliminate errors, a path prediction model incorporating ship pitching was developed using the Gray topological method, after analyzing ship pitching motions. With the help of simple introduction to Gray system theory, we selected a group of threshold values. Based on an analysis of ship pitch angle sequences over 40 second intervals, a Grey metabolism GM(1,1) model was established according to the time-series which every threshold corresponded to. Forecasting future ship motion with the GM (1,1) model allowed drawing of the forecast curve with effective forecasting points. The precision of the test results show that the model is accurate, and the forecast results are reliable.

Ship motion extreme short time prediction of ship pitch based on diagonal recurrent neural network

A DRNN (diagonal recurrent neural network) and its RPE (recurrent prediction error) learning algorithm are proposed in this paper. Using of the simple structure of DRNN can reduce the capacity of calculation. The principle of RPE learning algorithm is to adjust weights along the direction of Gauss-Newton. Meanwhile, it is unnecessary to calculate the second local derivative and the inverse matrixes, whose unbiasedness is proved. With application to the extremely short time prediction of large ship pitch, satisfactory results are obtained. Prediction effect of this algorithm is compared with that of auto-regression and periodical diagram method, and comparison results show that the proposed algorithm is feasible.

Laivo supimosi vizualizavimo uždavinys

In this article the research and algorithms for calculation of longitudinal ship motion are evaluated. The program for ship's pitching and heaving modelling based of these algorithms is presented. Applying of this makes possible to determine ship's seakeeping characteristics mostly using data of the ship's bodyplan. It is created with Visual Lisp programming language what insures good visual results and good combination with the stages of ship design. The application can be used for training of naval architecture and informatics engineering students, and also in research field helping to create analytical models.

On the use of permanent symmetric scatterers for ship characterization

The symmetric scattering characterization method (SSCM) has been recently introduced for high-resolution characterization of certain targets under coherent conditions. SSCM is based on the Poincare/spl acute/ sphere representation, which supports a high-resolution decomposition of symmetric target scattering, as well as assessment and validation of the backscatter coherence. In this paper, the SSCM is investigated for ship characterization using Convair-580 polarimetric synthetic aperture radar (SAR) data. It is shown that the target Poincare/spl acute/ parameters permit identification of dominant scatterers with a significant symmetric scattering component. The polarization orientation angle of these quasi-symmetric scatterers is used to derive an estimate of the ship's pitch angle, under certain conditions. The effect of SAR system focus setting errors and Doppler centroid mistracking on the SSCM performance is investigated. It is shown that the SSCM is sensitive to the system focus setting and Doppler centroid shift. The first-order effects of these errors can be removed prior to the application of the SSCM method.

Ship detection and characterization using polarimetric SAR

Polarimetric information is investigated for ship detection and characterization at operational satellite synthetic aperture radar (SAR) incidence angles (20°‐60°). It is shown that among the conventional single-channel polarizations (HH, VV, or HV), HV provides the best ship‐sea contrast at incidence angles smaller than 50°. Furthermore, HH polarization permits the best ship‐sea contrast at near-grazing incidence angles. The wave polarization anisotropy is used for optimal information extraction from polarimetric SAR data. It is shown that fully polarimetric information permits a significant improvement in the ship‐sea contrast for relatively calm wind conditions, in comparison with conventional (i.e., scalar) single-channel polarizations (i.e., HH, VV, or HV). For rougher sea conditions, the effectiveness of polarimetric tools may be significantly degraded. Ship characterization is also investigated using the symmetric scattering characterization method (SSCM). Identification of ship targets with significant symmetric scattering can provide a useful ship pitch angle estimate under certain conditions.

Optimization parameter of transformation of parallel translation for ship pitch simulation

The transformation of parallel translation can improve the smoothness of discrete series sometimes. In this paper, for ship pitch, a method to modify the system error is proposed via the transformation of parallel translation, which can give the optimize parameters using the Method of Minimum Squares. The series in the method can fit white exponential law better, and then be applied in GM(1,1) very well. The numerical experiments imply that the method is practical, which make the ship pitch system model more accurate than GM(1,1).

Wave — Jet Converters

The possibilities of conversion of the energy of gravitational surface waves in liquid into a constant reactive flow due to special nonlinear mechanical floating devices (wave-jet converters) are investigated. The last ensure rectification of wave pressure and the effect of wave traction. Physical problems of radiation and scattering wave pressure rectification are considered separately using the examples of concrete devices. A ship model of special construction has been designed and tested. This model effectively converts ship's pitching immediately into a constant jet flow without using any external sources of energy. The ship's motion is characterized by an average Froude number Fr=0.14 and average forward velocity exceeding the velocities of liquid particles in the wave field. This ship presents a uniflow wave jet propulsive device.

Construction of GM(2, 1) model for oscillating pitch angle series

GM(1, 1) is generally used in Grey System Theory which constructs an Ordinary Differential Equation for given series. It is effective for monotone series, and its simulating effect is good and error is small. However, If the series doesn’t have a property of monotone, the simulating effect of GM(1, 1) is not fine, and its error gets bigger. In this paper, we use GM(2, 1) to handle the oscillation series, which uses the Method of Minimum Squares in determining the uncertain parameters. The method avoids a big error while choosing an initial value of O.D.E., and we get good results. Finally, we solve a real problem — the simulation of ship pitch, and obtain satisfactory results.

Surface meteorological instrumentation for BOBMEX

Although India has a long experience in ship-borne experiments and oceanographic instrumentation, the atmospheric component has not received much attention in the past. In this paper, the basis of the atmospheric instrumentation system assembled for use on board ORV Sagar Kanya for the BOBMEX-Pilot experiment is described along with some representative results. Wherever possible, Woods Hole's IMET recommendations for meteorological sensors for applications in the marine environment have been followed to keep our measurements in par with international standards. The sensors were tested during the BOBMEX-Pilot experiment and all sensors worked well. Velocity, humidity and temperature data have been successfully collected using fast sensors. It is shown that the component due to the ship's pitching motion can be removed from the measured vertical velocity by making use of an accelerometer. This makes it possible to calculate the surface fluxes by direct methods.