Thrust Deduction Factor Research Articles

Propeller-hull Interaction In Inland Navigation Vessel

The author presents a computational model of propeller operating in the wake of inland navigation flat-bottomed vessel. Using this model it is possible to compute propeller performance as well as propeller-hull interaction coefficients (wake fraction and thrust deduction factor) with limited depth of waterway taken into account. The surface distribution technique was applied to solve a flow over nozzle (part of ducted propeller) and potential component of flow between hull and waterway bottom. Vortex lattice model was used for screw propeller or impeller. Simplified Reynolds equation is being solved to determine axial velocity in flow domain. Results of performed calculations exhibit good agreement with available results of model tests.

Application of EKF technique to ship resistance measurement

The measurement of ship resistance is important in naval architecture and marine hydrodynamics research. The method of predicting ship resistance from scaled model tests has been used for over 100 years but the results suffer from “scale effect”. This paper presents a new method of “measuring” the resistance of full size ships by using a system identification technique. Extended Kalman Filtering is used for estimating intermediate coefficients in the ship's surge motion equation, then the ship resistance coefficient is derived from the identified results. This method only requires a simple sea trial during a ship's regular voyage. The ship resistance coefficient as well as the wake fraction and the thrust deduction factor were obtained with excellent accuracy. The success of this method should impact the design of ship hulls and propellers and also research in marine hydrodynamics.

係留けん引時の推力減少率

The Bollard pull test for “Fukae maru” was carried out with the varied pitch angle under constant propeller revolution. Making use of measured values, the torque and thrust coefficients of a actual propeller were calculated at advance coefficient of zero. These coefficients were compared with the both results of open water test with a model propeller and open water propeller series test.The actual torque coefficients were consequently between the both results. On the other hand, the actual thrust coefficients are smaller than those of open water test and nearly equal to those of propeller series test.If those of open water test were considered standard, the thrust deduction ratio become 0.13-0.15. As these values are larger than generally estimated value and the deduction ratio is different by the analized method, the thrust on bollard pull condition ought to be estimated carefully.*: The thrust deduction ratio is not the thrust deduction factor which is defined on advanced ship. It is the deductive rate of the actual thrust from the designed thrust at advanced coefficient of zero.

Numerical Solutions of Interaction Problem between Hull and Propeller of a Ship Considering the Effect of Free Surface

The present paper deals with the interaction problem between the hull and the propeller of a ship advancing at a constant speed on the still water surface. The Rankine source method has been employed in order to take into consideration the effect of the free surface on the hull and the propeller. The vortex lattice lifting surface method has been applied to the propeller. The interaction problem between the hull and the propeller has been solved numerically by an iterative procedure, starting from the Hess & Smith solution for the source distribution on the hull surface of the double model approximated ship as the basic flow. The effect of the interaction of the propeller has appeared on the closest hull surface as the pressure reduction and on the upper free surface as the increase of the wave just above the propeller. The calculated thrust deduction factor has showed a fairly good agreement with measured ones for 4 m and 6 m model ships.

Self-propulsion Test of a Semi-displacement Craft Model with a Waterjet Propulsor

In this paper explanations are made on experimental procedures of self-propulsion tests of a semi-displacement craft model with a combined propulsion system of twin screw propellers and a waterjet at center. First, self-propulsion tests only by a pair of screw propellers were conducted and then tests by the combined propulsion system were conducted. By using both test results self-propulsion factors, inlet drag and trim change associated with the installation of waterjet propulsor were determined. As a result it was found that the thrust deduction factor for waterjet system in operating condition was small negative value.

Study on the relation between propulsion factors and velocity field of flow in the propeller disk behind the hull1

The grounding and break-up of the ARGO MERCHANT on the propulsion factors, which are effective wake factor, thrust deduction factor and relative rotative efficiency, and other elements of ship performance, and the non-uniform velocity field of flow in the propeller disk behind the hull. This is based on a calculation method employing a mathematical model of the hydrodynamical action of a propeller. This study has made it possible to understand the physical meanings of the effective wake and the relative rotative efficiency, and to consider the scale effects on all propulsion factors in a practical way. Subsequently the effects of the non-uniformity of flow on the propuslion factors have been made clear. When the wake pattern of the full scale ship is estimated by the Sasaiima-Tanaka method or other estimation method, the thrust, torque and power generated by the actual propeller behind the full scale ship can be predicted. The predicted results of a numerical example for a large oil tanker have shown a good agreement cleanup. The report also suggests that improvements in ship

Forces on a Submarine Hull Induced by the Propeller

The induced-flow field generated by a propeller operating in the wake of a submarine can exert forces on the submarine in some arbitrary mode of motion in two ways: Either by pressures applied to the propeller blades and resulting in the conventional propeller thrust or by pressures applied to the hull surface. The ratio of these forces is shown, by theoretical analysis, to depend most strongly on the flow velocity which the particular hull mode of motion would generate at the propeller, to be slightly dependent on the shape of the propeller, and to be negligibly dependent on the magnitude or distribution of the submarine wake. The derived relations are valid for both the inertial and quasi-steady components of the induced-pressure field. The predominant factor in the force ratio is evaluated by a numerical technique which is applicable to any surface of revolution moving in almost any pattern of motion. As one application, it is shown that the steady longitudinal force on the hull is 8 to 1 2 percent of the steady component of the propeller thrust, in good agreement with measurements of the thrust-deduction factor. As another application, it is shown that a particular vibratory component of the hull force, tending to vibrate the hull in the accordion-vibration mode, is 6 to 8 percent of the same component of the propeller thrust.

On the Effects of the Leading Model upon the Following One of the Same Type when the Models are running in Tandem

The resu'ts of model experiments of naked hull for the above case have been presented before this institution in 1920.The present paper deals with the further investigation of the case for models with all appendages and also with propellers to find the effect of waves as well as propeller race of the leading model.A short account of the apparatus used for “behind” experiment is given. The results obtained are : (1) Wave making resistance of the following model is greatly affected by the distance, the maximum occurring at D/λ =0.85, 1.85, …, and the minimum at D/λ=1.35, 2.35, …, as in the case of naked hull. The propeller race of the leading model affects the resistance of the following model in similar way as waves produced by the leading one but in less significant degree.(2) The number of revolutions of propeller, thrust deduction factor, &c. are affected by the speed as well as the distance of the models. The ratio of propeller revolutions of the two models seems to be represented by single curve for any speed and distance within the range experimented with, having maximum & minimum at 1.35 & 1.85 respectively.(3) Finally it may be said that the following model is unstable to keep the distance constant when the model lies between the values of D/λ=1.351.85, and D/λ =2.352.85 and stable between D/λ =0.851.35 and D/λ=1.852.35.