Estimation of Added Resistance for Large Blunt Ship in Waves

Under the background of the energy saving and emission reduction, more and more attention has been placed on investigating the energy efficiency of ships. The added resistance has been noted for being crucial in predicting the decrease of speed on a ship operating at sea. Furthermore, it is also significant to investigate the added resistance for a ship functioning in short waves of large modern ships. The researcher presents an estimation formula for the calculation of an added resistance study in short waves derived from the reflection law. An improved method has been proposed to calculate the added resistance due to ship motions, which applies the radiated energy theory along with the strip method. This procedure is based on an extended integral equation （EIE） method, which was used for solving the hydrodynamic coefficients without effects of the irregular frequency. Next, a combined method was recommended for the estimation of added resistance for a ship in the whole wave length range. The comparison data with other experiments indicate the method presented in the paper provides satisfactory results for large blunt ship.

Study on Wave Added Resistance of a Deep-V Hybrid Monohull Based on Panel Method

In this paper, a panel method based on three dimensional potential flow theory is used to study the problem of wave added resistance. The time-domain motion response of Wigely III ship in head waves is calculated by AQWA, and then the wave added resistance of ship is obtained by near-field pressure integration method. By comparing the calculated results with the experimental data in literature, it is shown that the variation trend and peak value are in good agreement, and the accuracy and efficiency meet the research requirements. Based on the above mentioned method, the wave added resistance of a deep-V hybrid monohull in head waves is studied. The motions and wave added resistances of the deep-V hybrid monohull and the deep-V original ship advancing in head waves with various forward speed and wave frequencies are calculated and analyzed. The results show that the longitudinal motion response of the deep-V hybrid monohull is effectively suppressed and the wave added resistance is obviously reduced, the new type of ship has good engineering application prospects. The present method provides an approach of satisfactory accuracy and efficiency to predict wave added resistance of ships voyaging in waves.

Study on Wave Added Resistance of Ships in Oblique Waves Based on Panel Method

When the ship is sailing at sea,wave added resistance has great influence on the rapidity and economy of the ship.With the increasing pressure of energy and environmental protection,IMO has proposed the EEDI formula of the newly built ships,which restricts the energy consumption standard of civil ships more strictly.Therefore,a panel method based on three dimensional potential flow theory is proposed to study the problem of wave added resistance in this paper.Firstly,the method solves the motion responses of the ship in the time domain,and then calculates the wave added resistance of the ship by near-field pressure integration method.The wave added resistance of S175 container ship in head and oblique waves are calculated and compared with the experimental data,and the accuracy of the proposed method are verified.At last,the influence of Froude number and wave direction angle on wave added resistance is studied.The proposed method provides an approach of satisfactory accuracy and efficiency for the development of high-performance new ship forms,optimization of ship hull lines,comprehensive performance evaluation of ships and practical navigation guidance.

Parametric Hull Form Optimization of Containerships for Minimum Resistance in Calm Water and in Waves

This paper described the process of generating the optimal parametric hull shape with a fully parametric modeling method for three containerships of diferent sizes.The newly created parametric ship hull was applied to another ship with a similar shape,which greatly saved time cost.A process of selecting design variables was developed,and during this process,the infuence of these variables on calm water resistance was analyzed.After we obtained the optimal hulls,the wave added resistance and motions of original hulls and optimal hulls in regular head waves were analyzed and compared with experi-mental results.Computations of the fow around the hulls were obtained from a validated nonlinear potential fow boundary element method.Using the multi-objective optimization algorithm,surrogate-based global optimization(SBGO)reduced the computational efort.Compared with the original hull,wave resistance of the optimal hulls was signifcantly reduced for the two larger ships at Froude numbers corresponding to their design speeds.Optimizing the hull of the containerships slightly reduced their wave added resistance and total resistance in regular head waves,while optimization of their hulls hardly afected wave-induced motions.

Analysis of Wave Added Drag and Motion Response of Mid-high-speed Ship against Waves

In order to accurately predict the on-wave resistance and responses to hull motions of ships in actual sea conditions,the k-εmethod of the RNG model is adopted on the basis of the unsteady RANS method.The two-formula turbulence model deals with the viscous flow,the VOF method captures the free surface,the velocity boundary method makes waves,the artificial damping method is used to eliminate waves,and the nested grid technology is used to deal with the motion response of ships on waves.Combined with the 6-DOF motion formula,a three-dimensional numerical wave cell for regular waves is established.For one example,taking a KCS Container ship and fishing boat sailing at a mid-high-speed,the increase of wave resistance and motion response at different wavelengths are analyzed,and the simulation results are compared with the experimental value,the content of strip theory in potential flow theory and the panel method to prove the reliability of CFD method in predicting ship motion.

A Practical Speed Loss Prediction Model at Arbitrary Wave Heading for Ship Voyage Optimization

This paper proposes a semi-empirical model to predict a ship’s speed loss at arbitrary wave heading.In the model,the formulas that estimate a ship’s added resistance due to waves attacking from different heading angles have been further developed.A correction factor is proposed to consider the nonlinear effect due to large waves in power estimation.The formulas are developed and verified by model tests of 5 ships in regular waves with various heading angles.The full-scale measurements from three different types of ships,i.e.,a PCTC,a container ship,and a chemical tanker,are used to validate the proposed model for speed loss prediction in irregular waves.The effect of the improved model for speed loss prediction on a ship’s voyage optimization is also investigated.The results indicate that a ship’s voyage optimization solutions can be significantly affected by the prediction accuracy of speed loss caused by waves.

Tank Tests with a Scaled Model of a BOC-50 Sailing Yacht Model in Calm Water and in Regular and Random Head Waves

In this paper the performance of a BOC-50＇ sailing yacht model in calm water and in realistic sea states is investigated experimentally. A scaled model of the hull form with the keel-bulb configuration has been tested in the towing tank of the LSMH of NTUA. During the tests the calm water resistance and the dynamic responses, including the added resistance in waves were recorded. Results referring to the resistance, the side force, the CG displacement, the pitch as well as the vertical accelerations of the model at the bow, the CG and the stern are presented. Moreover, by using a Velocity Prediction Program the polar and the stability diagram of the tested sailing yacht were calculated. Useful conclusions about the dynamic behavior of the model were obtained.

Prediction of added resistance of a ship in waves at low speed

This paper presents predictions of the added resistance of a ship in waves at a low speed according to the IMO minimum propulsion power requirement by a hybrid Taylor expansion boundary element method(TEBEM).The flow domain is divided into two parts:the inner domain and the outer domain.The first-order TEBEM with a simple Green function is used for the solution in the inner domain and the zero order TEBEM with a transient free surface Green function is used for the solution in the outer domain.The TEBEM is applied in the numerical prediction of the motions and the added resistance in waves for three new designed commercial ships.The numerical results are compared with those obtained from the seakeeping model tests.It is shown that the prediction of the ship motions and the added resistance in waves are in good agreement with the experimental results.The comparison also indicates that the accuracy of the motion estimation is crucial for the prediction of the wave added resistance.In general,the TEBEM enjoys a satisfactory accuracy and efficiency to predict the added resistance in waves at a low speed according to the IMO minimum propulsion power requirement.

A Practical Hull Form Design of Ferry Using Hybrid Scheme Method and Performing Experiment

Prediction of ship performance in preliminary ship design is an important consideration. It could guarantee ship in safe and comfort. However, many design works did not involve simultaneously ship performances predictions in preliminary design. Moreover, ship designers sometimes modified a ship form to obtain proper design without ship performance consideration. Therefore, this study concerns on predictions of total resistance and added wave resistance of a ferry using a hybrid particle-grid method and then its motions response after modifying bow and stern parts by conducting experiment. Research results show total resistance and added wave resistance have a significant different, therefore, it would be an important consideration in determining ship powering in preliminary ship design. The non-dimensional added wave resistance increases in increasing wave length from λ/Lpp = 0.5 to 1.0 and it decreases after L/λ = 1.0. In addition, it tends to decrease caused by increasing ship speed. The comparison of averaged heave and pitch amplitudes between basic forms after modifying bow and stem parts is quiet similar. However, the rolling amplitude of the modified form is significantly higher comparing with the basic form. We conclude that a ship could be design in preliminary design take into account performances predictions by using numerical method and experimental work.

Numerical study on ship-generated unsteady waves based on a Cartesian-grid method

The added resistance of a ship in waves can be related to ship-generated unsteady waves.In the present study,the unsteady wave-pattern analysis is applied to calculate the added resistance in waves for two modified Wigley models using a Cartesian-grid method.In the present numerical method,a first-order fractional-step method is applied to the velocity-pressure coupling in the fluid domain,and one of volume-of-fluid(VOF)methods is adopted to capture the fluid interface.A ship is embedded in a Cartesian grid,and the volume fraction of the ship inside the grid is calculated by identifying whether each grid is occupied by liquid,gas,and solid body.The sensitivity to the location of measuring position of unsteady waves as well as the number of solution grids is examined.The added resistance computed by direct pressure integration and wave pattern analysis is compared with experimental data.In addition,nonlinear characteristics of the added resistance in waves are investigated by detailed analyses of unsteady flow field and resulting wave pattern.