Marine Propellers and Propulsion, Second Edition

Asian Journal of Applied Sciences (ISSN: 2321 - 0893)
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In this prior art, because the sectional shape of the duct is located on the outer surface of the front end of the duct during high-speed navigation, the thruster has a portion expanding with a circular section outward from a standard airfoil to inhibit pressure change, and an open angle of which the direction of leading edge is widened to generate a predefined towing force in low-speed operation.

However, the prior art does not disclose the distance from the parallel portion on the inner side of the duct which is in parallel with the duct axis e. In the prior art, important design variables are not described about what numerical ranges the front portion and the rear portion in the parallel portion belong to on the basis of the position of thruster plane drawn by the rotating end of the propeller blade plane Y-Z: the plane of propeller rotation.

Therefore, the effect of the aforementioned important design variables on total thrust, the torque of a propeller and the exclusive efficiency of an entire thruster is not known. The aforementioned prior art document does not provide enough description to develop a propulsion apparatus that offers even higher propulsive efficiency, while implementing precise maneuverability and highly-efficient towing.

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In addition, the prior art mentions just the outward expansion and the open angle of which the leading edge direction is widened, but does not describe any technology for reducing vortices taking place by propellers. In this context, it may be difficult to absorb the rotational component of propeller wake in the bollard condition in which just the propeller rotates at a rated RPM while a vessel or marine structure almost stands still.

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In view of the above, an embodiment of the present disclosure provides a vessel propulsion apparatus for improving vessel operation performance, positioning performance and towing performance, and reducing vortices left around a hub in the bollard condition. In accordance with an aspect of the present disclosure, there is provided a vessel propulsion apparatus including: a duct having a nose as a front vertex of an airfoil section, and a tail as a rear vertex of the airfoil section, wherein the sectional shape of the duct includes: an outer surface formed convex upward at the front end of the duct, and formed concave downward at the back end of the duct; and an inner surface having an inner front portion of the duct formed convex downward at the front end of the duct, an inner rear portion of the duct formed convex downward at the back end of the duct, and a parallel portion seamlessly connecting the inner front portion of the duct with the inner rear portion of the duct.

In accordance with another aspect of the present disclosure, there is provided a vessel propulsion apparatus including: a hub arranged on and receiving power through a main shaft; main blades installed on the outer circumferential surface of the hub; sub-blades spaced and placed toward the back of the main shaft from the main blades and installed inclined toward the back of the main shaft; and a duct installed around the main blades, and having an airfoil section.

The duct for propulsion apparatus in accordance with an embodiment of the present disclosure improves performance by improving flows around the duct. For example, the embodiment of the present disclosure may meet all of general operational conditions, positioning and towing conditions by optimizing first and second distances between the parallel portion on the inner side of the duct and the nose or the tail, and improve vessel operation performance, positioning and towing performance.

Further, the embodiment of the present disclosure has a parallel portion defined by the front portion and the rear portion thereof with reference to the position propeller position of the thruster plane plane Y-Z to improve thrust in the bollard condition. The parallel portion contributes to improving general operation performance while maximizing the performance of generating thrust in starting from the state of standstill, for example, ice jams, positioning performance in the state of standstill, or the performance of towing other vessels immobile in frozen seas.

Further, the embodiment of the present disclosure provides main blades and sub-blades for the hub to improve flows around the duct and the propeller to reduce vortices taking place by the propeller and also torque required to rotate the propeller, improving propulsive efficiency. In addition, the embodiment of the present disclosure improves thrust in the bollard condition to effectively reduce vortices left around the hub and also the torque of the main shaft to improve propulsive efficiency.

Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, when the detailed description of the relevant known function or configuration is determined to unnecessarily obscure the important point of the present invention, the detailed description will be omitted.

A comparative example against an embodiment of the present disclosure employs a standard airfoil, which is a marine 19A airfoil hereinafter, referred to as a comparative example generally used because of its high manufacturability for the duct of the ducted azimuth thrusters. Referring to FIG.

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The sectional shape of the duct may be the same along the entire circumference of the duct with reference to the rotation axis X-axis of the propeller For example, in terms of the sectional shape, the duct may include an outer surface G1 and an inner surface G2 of the duct having optimized design variables to improve the efficiency of the ducted propulsion apparatus in consideration of operation characteristics of vessels, for example, drill ships or marine structures, and characteristics of positioning vessels and towing other vessels immobile in frozen seas.

In the sectional shape, the duct , which has an airfoil section to generate lift in accordance with the Bernoulli's theorem, may include: a nose which is a front vertex of the airfoil section of the duct ; a tail which is a rear vertex of the airfoil section; and a chord line which is a straight line segment connecting the nose with the tail In the sectional shape, the duct may include an outer surface G1 having a front portion formed convex above the front end of the chord line , and a rear portion formed concave below the back end of the chord line The front portion of the outer surface G1 of the duct may be a curved surface from the point where the chord line meets the outer surface G1 of the duct to the nose In addition, the rear portion of the outer surface G1 of the duct may be a curved surface from the point where the chord line meets the outer surface G1 of the duct to the tail The front portion and the rear portion may be seamlessly connected each other at the point where the chord line meets the outer surface G1 of the duct As described above, the front portion of the outer surface G1 of the duct is formed convex above the front end of the chord line Therefore, it is shown that the front portion of the outer surface of the duct formed convex above the chord line accelerates flows into the propeller.

This effect of acceleration contributes to improving duct thrust and reducing propeller torque. On the other hand, referring to FIG. In addition, referring to FIG. Also, in the sectional shape, the duct may include an inner surface G2 of the duct composed of: a parallel portion running parallel with the rotation axis X-axis of the propeller ; an inner front portion of the duct which is a curved surface gently projected from the start point of the parallel portion to the nose in a range equivalent to a first distance F in the direction of Y-axis from the parallel portion to the nose ; and an inner rear portion of the duct which is a curved surface gently projected from the end point of the parallel portion to the tail in a range equivalent to a second distance K, in the direction of Y-axis from the parallel portion to the tail , the second distance being smaller than the first distance F.

In addition, the parallel portion has a front portion M and a rear portion N with reference to the position of propeller plane Y-Z-plane that is a circular plane drawn when the propeller rotates. Referring FIGs. In FIG. In this case, figures with a minus sign - imply the minus - direction where the position of the propeller plane is the origin in the axial direction X-axis.

Marine Propellers and Propulsion - 2nd Edition

In particular, a constant length of the parallel portion close to the propeller in the duct may improve efficiency. Also, referring to FIG. The vertical axis of the graph shown in FIG.

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The horizontal axis of the graph shown in FIG. Referring to FIGs. The airfoil section of the duct described above was used to derive the result shown in FIG. An examination of the aforementioned bollard performance curve POWER-THRUST reveals that the airfoil section of the duct in accordance with this embodiment improves thrust in the bollard condition by about 6. As shown from the curves for a correlation of the linear velocity and required horsepower for the comparative example and this embodiment shown in FIG. For example, with the same delivered horsepower DHP, it is shown that this embodiment may achieve faster speed than the comparative example, or, with the same speed, may require smaller DHP than the comparative example to result in improved performance.

In the graph shown in FIG. In the area of advance ratio J not smaller than 0. That is, the increased attractive force of the duct contributes to increasing flows into the propeller, to result in reducing propeller torque 10Kq and thus improving efficiency in all areas of the advance ratio J.

MARINE PROPELLERS AND PROPULSION

Specifically, the hub is coupled with the gear case 10 in which the main shaft of the hull is built in to be rotatable by means of the main shaft, and receives power from the main engine not shown of the hull through the main shaft to provide thrust to the propeller The hub may be tapered toward the back of the propulsion apparatus with its radius gradually being reduced, and the back end of the hub may be coupled with a cap The cap is tapered backward to smoothly pass the fluid through the propeller along the side thereof.

The propeller may be installed on the outer circumferential surface of the hub for effectively reducing vortices W left around the hub The propeller may include the main blades and the sub-blades spaced and arranged along the axial direction x-axis of the main shaft on the outer surface of the hub The main blades may be a plurality of wings spaced and arranged in the radial direction on the front outer circumferential surface of the hub The main blades may have an airfoil section, and the shape and the number of main blades may be varied depending on thruster efficiency, cavitation resulting from loads and the surrounding environment.

The sub-blades may be a plurality of wings spaced and arranged in the radial direction on the rear circumferential surface of the hub spaced toward the back of the main shaft from the main blades , to be disposed alternately with the main blade However, the sub-blade may be installed anywhere, for example, on the cap or in the space between the hub and the cap , as well as the hub , provided that the location is spaced toward the back of the main shaft from the main blade The sub-blades may be composed of wings smaller than the main blades , and be installed inclined toward the back of the main shaft.

In this case, installation inclined toward the back means that the back end rather than the front end of the sub-blades is positioned in the back of the main shaft. Since the aforementioned sub-blades may absorb rotational components in the condition of low advance ratios like the bollard condition in which just the propeller rotates at a rated RPM, it may effectively reduce vortices W left around the hub and also improve propulsive efficiency by the reduced torque of the hub For example, the sub-blades may have an inclination angle B inclined in a range from 0.

The hub may have an inclination angle H inclined in a range from 0.

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In particular, referring to FIG. Therefore, the effect of improved thruster efficiency may be insignificant. It can be seen from FIG. In this case, the position E may be defined as a position of the sub-blade in the X-axis direction. E P may be defined as a position of the main blade in the X-axis direction, and C as the full length of the duct As shown in FIG.

In addition, if the sub-blades are provided as in this embodiment, it is shown that the torque of propeller is reduced across all advance ratios while keeping entire thrust of a thruster. In particular, the propulsion apparatus of this embodiment generates about 2. That is, increased attractive forces of the sub-blade and duct increase flows into the propeller , contributing to reducing the torque Kq of the propeller to improve efficiency across all advance ratios J.

brazexalexat.ml As described above, the present disclosure has advantages of improving propulsive efficiency by providing the hub with the main blade and the sub-blade to improve flows around the duct and the propeller, in order to reduce vortices taking place by means of the propeller and also torque required to rotate the propeller. Another advantage of the present disclosure is propulsive efficiency improved through reduced main shaft torque while effectively reducing vortices left around the hub by improving thrust in the bollard condition.

Further, the duct may have the same sectional shape along the entire circumference thereof. The duct may include an outer surface G1 and an inner surface G2 thereof having optimized design variables to improve the efficiency of ducted propulsion apparatuses in consideration of operation characteristics of vessels, for example, drill ships or marine structures, and characteristics of positioning vessels and towing other vessels immobile in frozen seas.

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In particular, in the sectional shape, the duct may include a nose which is a front vertex of the airfoil section, a tail which is a rear vertex of the airfoil section, and a chord line which is a straight line segment connecting the nose with the tail The sectional shape of the duct may include an outer surface G1 having a front portion formed convex above the front end of the chord line , and a rear portion formed concave below the back end of the chord line In this case, the front portion of the outer surface G1 of the duct may be a curved surface from the point where the chord line meets the outer surface G1 of the duct to the nose The rear portion of the outer surface G1 of the duct may be a curved surface from the point where the chord line meets the outer surface G1 of the duct to the tail As such, the front portion of the outer surface G1 of the duct is formed convex above the front end of the chord line As described above, the front portion of the outer surface of the duct convex upward above the chord line may accelerate flows into the propeller This effect of acceleration may improve the thrust of the duct and reduce the torque of the propeller The rear portion of the outer surface G1 of the duct formed concave below the back end of the chord line may enable flows in the rear outer side to smoothly flow into the tail direction of the duct to form vortices around the tail, improving the thrust of duct Also, in the sectional shape, the duct may include an inner surface G2 of the duct composed of: a parallel portion running parallel with the axial direction x-axis of the main shaft; an inner front portion of the duct which is a curved surface gently projected from the start point of the parallel portion to the nose within a range equivalent to a first distance F in the direction of Y-axis from the parallel portion to the nose ; and an inner rear portion of the duct which is a curved surface gently projected from the end point of the parallel portion to the tail within a range equivalent to a second distance K in the direction of Y-axis from the parallel portion to the tail , the second distance being smaller than the first distance F.

A constant length of the parallel portion close to the propeller in the duct may enhance efficiency. While the embodiments of the present disclosure have been described with reference to the accompanying drawings, it will be understood by those skilled in the art that various changes and modifications may be made without changing the scope or essential characteristics of the present disclosure as defined in the following claims. For example, those skilled in the art may change material or size of each component depending on applications, or combine or substitute embodied types into the types not explicitly described in the embodiments of the present disclosure, which are not out of the scope of the present disclosure.

Therefore, the embodiments described above are exemplary in all respects, not intended limiting, and the modified embodiments shall be covered by the claims of the present disclosure. A vessel propulsion apparatus comprising: a duct having a nose as a front vertex of an airfoil section, and a tail as a rear vertex of the airfoil section,. The vessel propulsion apparatus of claim 1, wherein the outer surface comprises: a front portion formed convex above the front end of a chord line which is a straight line segment connecting the nose with the tail; and. In the case of high Reynolds number flow, a propulsive force can be obtained by the pressure force with the sinusoidal motion, while the portion of frictional force becomes larger to act as a larger drag at lower Reynolds number.

The tendency is almost the same as that confirmed for the unbounded case. The computed velocity vectors and the pressure contours for the sinusoidal motion at are shown in Fig. The pressure difference between on the downhill and on the uphill produces a propulsive force. In the sinusoidal motion, the flow on the moving surface is not rotated.

This phenomenon is different from that of the trochoidal motion. The computed mean forces for the trochoidal motion are also shown in Table 5. The tendency according to the variation of Reynolds number is completely reverse to the case of sinusoidal motion. The portion of frictional force is smaller than that of unbounded fluid case on the whole and the frictional force can act as a propulsive force even in highly viscous flow.

Computed velocity vectors and pressure contours at are plotted in Fig. The rotated flow by the trochoidal motion of surface is clearly seen in the profile of velocity vectors.

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It can be concluded that the propulsive force is also obtained in highly viscous fluid of narrow channel by the firctional force if the trochoidal motion is applied to the waving surface. Table 5 Computed results of x-directional forces of the body in narrow channel. A propulsion system by peristaltic motion in highly viscous fluid is studied by experimentally and numerically. The experimental results of self propulsion test show that if the phase velocity of sinusoidal motion of the body surface is over 20 times the model speed, the model can successfully advance in highly viscous fluid by peristaltic motion.

The velocity measurement by the particle tracking velocimetry disclosed that fluids are more effectively transported for the case of narrower clearnce between the body surface and the bottom because the difference of pressure plays a role in transportation. This is clearly proved by numerical computation also.

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It is experimentally concluded that a propulsion system by peristaltic motion can be applied as a propulsor in highly viscous fluid. Numerical studies carried out to investigate the mechanism of peristaltic motion more closely show that the pressure force is acting as a propulsive force in the peristaltic motion.

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The interaction between the wake and the tip vortex decreases as the flow moves downstream. Figure 9. Shipping to: United States. The horizontal probe utilized the green The panel arrangement for CS4 used in the panel method is shown in Fig.

Although some quantitative difference is found between the computation and the experiment, the tendency is rather similiar each other. For the application to the micro-hydro machine, the present study is extended to a contractive and dilative motion of body. Propulsive force can be obtained in highly viscous fluid by a contractive and dilative motion of body.

The trochoidal motion makes the fluid rotate to obtain propulsive force, while the sinusoidal motion makes the difference of pressure by which propulsive force is obtained. In highly viscous flow, the frictional force acts as propulsive force in a narrow channel. By the present study, it is clearly mentioned that a propulsive force can be obtained in highly viscous fluid either by sinusoidal or trochoidal motion.

The sinusoidal motion is effective in the case of shallow water, while the trochoidal is in extremely low Reynolds number fluid. The present study is expected to be applied for the development of a propulsor for micro-hydro machine and further studies may provide more efficient way of motion for the production of thrusting force. Yin and Y. Ninomiya and T.