阅读说明：本技术 半悬挂舵舵叶、半悬挂舵及船体 (Half-suspension rudder blade, half-suspension rudder and ship body ) 是由 耿继文 夏玉涛 李博 戴玛丽 莫继华 匡岩 于 2021-01-15 设计创作，主要内容包括：本发明提供了一种半悬挂舵舵叶、半悬挂舵及船体,涉及船舶技术领域,半悬挂舵舵叶包括舵叶上部分和舵叶下部分,舵叶下部分的上端面的外边沿包括左右对称设置的两个第一线型结构,第一线型结构包括自舵叶下部分的后端到最宽位置处的第一后段线型结构；舵叶上部分的下端面的外边沿包括左右对称设置的两个第二线型结构,第二线型结构包括自舵叶上部分的后端到最宽位置处的第二后段线型结构,舵叶上部分的上端面的外边沿包括左右对称的第三线型结构,第三线型结构包括自舵叶上部分的后端到最宽位置处的第三后段线型结构；第三后段线型结构和第二后段线型结构分别在舵叶下部分的上端面上的投影均与第一后段线型结构重合。(The invention provides a rudder blade of a semi-suspension rudder, a semi-suspension rudder and a ship body, and relates to the technical field of ships, wherein the rudder blade of the semi-suspension rudder comprises an upper rudder blade part and a lower rudder blade part, the outer edge of the upper end surface of the lower rudder blade part comprises two first linear structures which are arranged in bilateral symmetry, and the first linear structures comprise first rear-section linear structures from the rear end of the lower rudder blade part to the widest position; the outer edge of the lower end face of the upper part of the rudder blade comprises two second linear structures which are arranged in a bilateral symmetry mode, the second linear structures comprise second rear-section linear structures from the rear end of the upper part of the rudder blade to the widest position, the outer edge of the upper end face of the upper part of the rudder blade comprises third left-right symmetric linear structures, and the third linear structures comprise third rear-section linear structures from the rear end of the upper part of the rudder blade to the widest position; the projections of the third rear section linear structure and the second rear section linear structure on the upper end face of the lower part of the rudder blade are coincided with the first rear section linear structure.)

1. A semi-suspended rudder blade characterised in that it comprises: an upper rudder blade part (100) and a lower rudder blade part (200); the lower end of the rudder blade upper part (100) is connected with the upper end of the rudder blade lower part (200);

the outer edge of the upper end face of the lower rudder blade part (200) comprises two first linear structures which are arranged in bilateral symmetry, and the first linear structures extend to the front end along the rear end of the outer edge of the upper end face of the lower rudder blade part (200); the first linear structure comprises a first rear section linear structure (211) from the rear end of the lower rudder blade part (200) to the widest position of the lower rudder blade part (200);

the outer edge of the lower end face of the rudder blade upper part (100) comprises two second linear structures which are arranged in bilateral symmetry, and the second linear structures extend to the front end along the rear end of the outer edge of the lower end face of the rudder blade upper part (100); the second linear structure comprises a second rear section linear structure (111) from the rear end of the rudder blade upper part (100) to the widest position of the rudder blade upper part (100); the lower end of the upper rudder blade part (100) comprises a stepped structure, the stepped structure comprises a first stepped surface connected with the lower rudder blade part (200) and a second stepped surface with a gap with the lower rudder blade part (200), and a combined graph of projections of the outer edge of the first stepped surface and the outer edge of the second stepped surface on a horizontal plane encloses the outer edge of the lower end face of the upper rudder blade part (100);

the outer edge of the upper end face of the rudder blade upper part (100) comprises a third line-shaped structure which is bilaterally symmetrical, and the third line-shaped structure extends to the front end along the rear end of the outer edge of the upper end face of the rudder blade upper part (100); the third linear structure comprises a third rear section linear structure (121) from the rear end of the rudder blade upper part (100) to the widest position of the rudder blade upper part (100);

and along the height direction of the semi-suspended rudder blade, the projections of the third rear section linear structure (121) and the second rear section linear structure (111) on the upper end face of the lower part (200) of the rudder blade are overlapped with the first rear section linear structure (211).

2. A semi-suspended rudder, characterized in that it comprises a semi-suspended rudder blade according to claim 1;

the semi-suspension rudder further comprises a rudder horn (300), and the rudder horn (300) is connected with the ladder structure of the upper part (100) of the rudder blade.

3. Semi-suspended rudder according to claim 2, characterised in that the left and right sides of the rudder horn (300) are aligned with the left and right sides of the rudder blade upper part (100), respectively; the first linear structure further comprises a first front section linear structure (212) from the widest position of the lower rudder blade part (200) to the front end of the lower rudder blade part (200);

the area of the cross section of the arm part of the rudder horn (300) is gradually increased from bottom to top, and the length of the upper end surface of the semi-suspension rudder is greater than that of the upper end surface of the lower rudder blade part (200) along the front and back directions of the semi-suspension rudder;

the outer edge of the upper end surface of the rudder horn (300) comprises two fourth linear structures which are arranged symmetrically left and right, the fourth linear structure comprises a fourth rear section linear structure (311) extending along the front end of the outer edge of the upper end surface of the rudder horn (300) towards the rear end of the rudder horn (300), and the fourth posterior segment linear structure (311) is identical to the first anterior segment linear structure (212), the fourth linear structure further comprises a straight line section (312) extending from the tail end of the fourth rear linear structure (311) to the direction of the rudder blade, the straight line section (312) is parallel to the front-rear direction of the rudder blade, and the interval distance between the straight line segments (312) at the left side and the right side is equal to the maximum width value of the rudder blade, the straight line section (312) is aligned with the end of a third rear section linear structure (121) of the outer edge of the rudder blade upper part (100);

the outer edge of the lower end face of the rudder horn (300) comprises two fifth linear structures which are arranged in bilateral symmetry, each fifth linear structure comprises a fifth front-section linear structure (320) which extends to the maximum width of the semi-suspension rudder along the front end of the rudder horn (300), the fifth front-section linear structure (320) is in butt joint with the end part of a second rear-section linear structure (111) of the outer edge of the lower end face of the upper rudder blade part (100) in the height direction, and the outer edge of the lower end face formed after the rudder horn (300) is hung on the upper rudder blade part (100) is consistent with the outer edge of the upper end face of the lower rudder blade part (200).

4. Half-suspended rudder according to claim 3, characterised in that the two first line structures that are left-right symmetrical enclose a NACA type structure.

5. The semi-suspended rudder according to claim 3, wherein the two first line structures in bilateral symmetry enclose an HSVA type structure.

6. The semi-suspended rudder according to claim 3, wherein the first two line structures with bilateral symmetry enclose an JfS type structure.

7. Semi-suspended rudder according to claim 3, characterised in that the rear end surface of the arm of the rudder horn (300) is curved facing away from the rudder blade, and the rear end surface of the rudder blade is curved facing towards the rudder horn (300).

8. A ship hull, characterized in that it comprises a semi-suspended rudder according to any one of claims 2-7.

Technical Field

The invention relates to the technical field of ships, in particular to a rudder blade of a semi-suspension rudder, the semi-suspension rudder and a ship body.

Background

As shown in fig. 1 and 2, the rudder blade is an important device for ensuring the steering turning performance and the heading stability of the ship, so a reasonable rudder blade side projected area needs to be considered in the design. The design method of a part of semi-suspension rudder blade is to make the rudder blade positioned at the lower part of the rudder horn into a rectangle, and the cross section of the rudder blade usually adopts HSVA, NACA and the like. However, no matter which profile is selected, the relative coordinate value of the thickness ratio is fixed relative to the distance of the leading edge of the blade. The shapes of the respective sections of the lower rudder blade part 200, which is located below the rudder horn and has a constant thickness in the height direction, are identical. The non-rectangular rudder portion of the upper rudder blade portion 100 has different chord lengths in each cross section, but generally has the same thickness ratio, and thus has similar shapes in each cross section. Because the area of the cross section of the rudder horn of the half-suspension rudder is gradually increased from bottom to top, the length of the upper half part of the half-suspension rudder is longer than that of the lower half part, and in order to ensure that the line type of the side surfaces of the upper half part and the lower half part of the half-suspension rudder are consistent, the line type size of the upper end surface of the upper half part of the half-suspension rudder is amplified in equal proportion to the line type size of the upper end surface of the lower half part, therefore, the line type of the upper end surface of the rudder blade corresponding to the rudder blade part is not consistent with the line type of the lower end surface of the upper part of the rudder blade, and the vertical section of the upper part of the rudder blade.

Because rudder blade planking itself has been the bent plate, has certain degree of difficulty when processing the preparation, if a break point appears again along rudder blade direction of height, this kind of bent plate processing is more difficult, and along with the increase of planking thickness, especially at the difficult processing of break point department.

Disclosure of Invention

The invention aims to provide a rudder blade of a semi-suspension rudder, the semi-suspension rudder and a ship body, which are used for relieving the technical problem that the existing rudder blade is difficult to process.

In a first aspect, an embodiment of the present invention provides a semi-suspension rudder blade, where the semi-suspension rudder blade includes: the upper rudder blade part and the lower rudder blade part; the lower end of the upper part of the rudder blade is connected with the upper end of the lower part of the rudder blade;

the outer edge of the upper end surface of the lower rudder blade part comprises two first linear structures which are arranged in bilateral symmetry, and the first linear structures extend to the front end along the rear end of the outer edge of the upper end surface of the lower rudder blade part; the first linear structure comprises a first rear section linear structure from the rear end of the lower rudder blade part to the widest position of the lower rudder blade part;

the outer edge of the lower end surface of the upper part of the rudder blade comprises two second linear structures which are arranged in bilateral symmetry, and the second linear structures extend to the front end along the rear end of the outer edge of the lower end surface of the upper part of the rudder blade; the second linear structure comprises a second rear section linear structure from the rear end of the upper rudder blade part to the widest position of the upper rudder blade part; the lower end of the upper rudder blade part comprises a stepped structure, the stepped structure comprises a first stepped surface connected with the lower rudder blade part and a second stepped surface with a gap with the lower rudder blade part, and a combined graph of projections of the outer edge of the first stepped surface and the outer edge of the second stepped surface on a horizontal plane encloses the outer edge of the lower end face of the upper rudder blade part;

the outer edge of the upper end surface of the upper part of the rudder blade comprises a third line-shaped structure which is bilaterally symmetrical, and the third line-shaped structure extends to the front end along the rear end of the outer edge of the upper end surface of the upper part of the rudder blade; the third linear structure comprises a third rear section linear structure from the rear end of the upper part of the rudder blade to the widest position of the upper part of the rudder blade;

and along the height direction of the semi-suspension rudder blade, the projections of the third rear-section linear structure and the second rear-section linear structure on the upper end face of the lower part of the rudder blade are coincided with the first rear-section linear structure.

In a second aspect, the semi-suspension rudder provided by the embodiment of the present invention includes the above semi-suspension rudder blade;

the semi-suspension rudder further comprises a rudder horn, and the rudder horn is connected with the ladder structure on the upper part of the rudder blade.

Further, the left side surface and the right side surface of the rudder horn are respectively aligned with the left side surface and the right side surface of the upper part of the rudder blade; the first linear structure further comprises a first front section linear structure from the widest position of the lower rudder blade part to the front end of the lower rudder blade part;

the area of the cross section of the arm part of the rudder horn is gradually increased from bottom to top, and the length of the upper end surface of the semi-suspension rudder is greater than that of the upper end surface of the lower part of the rudder blade along the front and back directions of the semi-suspension rudder;

the outer edge of the upper end face of the rudder horn comprises two fourth linear structures which are arranged in bilateral symmetry, each fourth linear structure comprises a fourth rear-section linear structure which extends from the front end of the outer edge of the upper end face of the rudder horn to the rear end of the rudder horn, the fourth rear-section linear structure is consistent with the first front-section linear structure, each fourth linear structure further comprises a straight line section which extends from the tail end of the fourth rear-section linear structure to the direction of the rudder blade, the straight line sections are parallel to the front and rear directions of the rudder blade, the interval distance between the straight line sections on the left side and the right side is equal to the maximum width value of the rudder blade, and the straight line sections are aligned with the end part of the third rear-section linear structure on the outer edge of the upper part of the rudder blade;

the outer edge of the lower end face of the rudder horn comprises two fifth linear structures which are arranged in bilateral symmetry, each fifth linear structure comprises a fifth front-section linear structure which extends to the maximum width of the semi-suspension rudder along the front end of the rudder horn, the fifth front-section linear structure is in butt joint with the end part of a second rear-section linear structure at the outer edge of the lower end face of the upper part of the rudder blade in the height direction, and the outer edge of the lower end face formed by the hanging of the rudder horn and the upper part of the rudder blade is consistent with the outer edge of the upper end face of the lower part of the rudder blade.

Furthermore, two first line structures which are symmetrical left and right enclose a NACA type structure.

Furthermore, two first line-shaped structures which are symmetrical left and right enclose an HSVA type structure.

Further, the two first line structures which are symmetrical left and right surround an JfS type structure.

Furthermore, the rear end surface of the arm of the rudder horn is a curved surface which is curved in a direction away from the rudder blade, and the rear end surface of the rudder blade is a curved surface which is curved in a direction toward the rudder horn.

In a third aspect, the embodiment of the invention provides a ship hull, which comprises the semi-suspended rudder.

The semi-suspension rudder blade provided by the embodiment of the invention comprises: the upper rudder blade part and the lower rudder blade part; the lower end of the upper part of the rudder blade is connected with the upper end of the lower part of the rudder blade; the outer edge of the upper end surface of the lower rudder blade part comprises two first linear structures which are arranged in bilateral symmetry, and the first linear structures extend to the front end along the rear end of the outer edge of the upper end surface of the lower rudder blade part; the first linear structure comprises a first rear section linear structure from the rear end of the lower rudder blade part to the widest position of the lower rudder blade part; the outer edge of the lower end surface of the upper part of the rudder blade comprises two second linear structures which are arranged in bilateral symmetry, and the second linear structures extend to the front end along the rear end of the outer edge of the lower end surface of the upper part of the rudder blade; the second linear structure comprises a second rear section linear structure from the rear end of the upper rudder blade part to the widest position of the upper rudder blade part; the lower end of the upper rudder blade part comprises a stepped structure, the stepped structure comprises a first stepped surface connected with the lower rudder blade part and a second stepped surface with a gap with the lower rudder blade part, and a combined graph of projections of the outer edge of the first stepped surface and the outer edge of the second stepped surface on a horizontal plane encloses the outer edge of the lower end face of the upper rudder blade part; the outer edge of the upper end surface of the upper part of the rudder blade comprises a third line-shaped structure which is bilaterally symmetrical, and the third line-shaped structure extends to the front end along the rear end of the outer edge of the upper end surface of the upper part of the rudder blade; the third linear structure comprises a third rear section linear structure from the rear end of the upper part of the rudder blade to the widest position of the upper part of the rudder blade; and along the height direction of the semi-suspension rudder blade, the projections of the third rear-section linear structure and the second rear-section linear structure on the upper end face of the lower part of the rudder blade are coincided with the first rear-section linear structure. Because the line type of the outer edge of the upper end surface and the outer edge of the lower end surface of the upper part of the rudder blade and the line type of the outer edge of the upper end surface of the lower part of the rudder blade can be correspondingly superposed, the vertical section of the rudder blade is rectangular, and the outer plate of the rudder blade has no folding point, so that the outer plate is easy to process.

According to the semi-suspension rudder and the ship body provided by the embodiment of the invention, because the semi-suspension rudder and the ship body provided by the embodiment of the invention use the semi-suspension rudder blade, the semi-suspension rudder and the ship body provided by the embodiment of the invention also have the advantages of the semi-suspension rudder blade.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic line drawing of a semi-mounted rudder according to the prior art;

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1;

fig. 3 is a line-type schematic view of the upper part of the rudder blade of the semi-suspended rudder blade according to the embodiment of the present invention;

fig. 4 is a schematic line diagram of a lower rudder blade portion of a semi-suspended rudder blade according to an embodiment of the present invention;

FIG. 5 is a cross-sectional view of a semi-suspended rudder blade according to an embodiment of the present invention;

fig. 6 is a schematic line diagram of a semi-suspension rudder according to an embodiment of the present invention.

Icon: 100-upper rudder blade part; 111-a second posterior segment linear structure; 121-a third back end linear structure; 200-lower rudder blade part; 211-a first back end of line configuration; 212-a first anterior segment linear structure;

300-rudder horn; 311-fourth back end linear configuration; 312-straight line segment; 320-fifth anterior segment linear structure; 400-break point.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 3 to 5, a semi-suspended rudder blade according to an embodiment of the present invention includes: an upper rudder blade part 100 and a lower rudder blade part 200; the lower end of the rudder blade upper part 100 is connected with the upper end of the rudder blade lower part 200; the upper rudder blade part 100 includes a left side plate and a right side plate, the lower rudder blade part 200 includes a left side plate and a right side plate, the left side plate of the upper rudder blade part 100 is welded to the left side plate of the lower rudder blade part 200, and the right side plate of the upper rudder blade part 100 is welded to the right side plate of the lower rudder blade part 200.

The outer edge of the upper end surface of the lower rudder blade portion 200 includes two first linear structures arranged in bilateral symmetry, and the first linear structures extend to the front end along the rear end of the outer edge of the upper end surface of the lower rudder blade portion 200; the first linear structure includes a first rear-stage linear structure 211 from the rear end of the lower rudder blade portion 200 to the widest position of the lower rudder blade portion 200. The two first linear structures enclose a closed figure similar to a drop shape, and the outer edge of the upper end face of the rudder blade lower part 200 and the outer edge of the lower end face can be overlapped in the height direction, that is, the vertical section of the rudder blade lower part 200 is rectangular.

The outer edge of the lower end surface of the rudder blade upper part 100 includes two second linear structures arranged in bilateral symmetry, and the second linear structures extend to the front end along the rear end of the outer edge of the lower end surface of the rudder blade upper part 100; the second linear structure comprises a second rear section linear structure 111 from the rear end of the upper rudder blade part 100 to the widest position of the upper rudder blade part 100.

The circumferential outer edge of the rudder blade and rudder horn 300 may be in a linear shape, such as NACA, HSVA, JfS, etc., which is easy to pass through. While the rudder blade in this embodiment is in the widest position in the rudder horn 300 butt joint. The lower end of the upper rudder blade part 100 comprises a stepped structure, the stepped structure comprises a first stepped surface connected with the lower rudder blade part 200 and a second stepped surface with a gap with the lower rudder blade part 200, and a combined graph of projections of the outer edge of the first stepped surface and the outer edge of the second stepped surface on a horizontal plane is enclosed to form an outer edge of the lower end face of the upper rudder blade part 100.

That is, the outer edge of the lower end surface of the rudder blade upper part 100 mentioned in this embodiment is not formed by a pattern on one horizontal plane, but is formed by combining two patterns on two planes having different heights by translation.

The outer edge of the upper end surface of the rudder blade upper part 100 includes a third line-shaped structure which is bilaterally symmetrical, and the third line-shaped structure extends to the front end along the rear end of the outer edge of the upper end surface of the rudder blade upper part 100; the third linear structure includes a third rear linear structure 121 from the rear end of the rudder blade upper part 100 to the widest position of the rudder blade upper part 100. And along the height direction of the semi-suspended rudder blade, the projections of the third rear linear structure 121 and the second rear linear structure 111 on the upper end surface of the lower rudder blade part 200 are both overlapped with the first rear linear structure 211. Because the line type of the outer edge of the upper end surface and the outer edge of the lower end surface of the upper rudder blade part 100 and the line type of the outer edge of the upper end surface of the lower rudder blade part 200 can be correspondingly superposed, the vertical section of the rudder blade is rectangular, and the outer plate of the rudder blade has no folding point 400, so that the outer plate is easy to process. After the break point 400 is eliminated, the outer plate of the rudder blade can be smooth, and the hydrodynamic performance of the rudder blade is improved.

As shown in fig. 6, the half-suspension rudder provided by the embodiment of the present invention includes the half-suspension rudder blade described above; the semi-suspension rudder further comprises a rudder horn 300, and the rudder horn 300 is connected with the ladder structure of the rudder blade upper part 100.

After the rudder blade is combined with the rudder horn 300, the left and right sides of the rudder horn 300 are aligned with the left and right sides of the upper rudder blade portion 100, respectively, and the pattern of the circumferential outer edge enclosed by the combination of the rudder blade and the rudder horn 300 may be a line shape easy for water flow, such as NACA, HSVA, JfS, and the like. The first linear structure further includes a first anterior linear structure 212 from the widest position of the lower rudder blade portion 200 to the front end of the lower rudder blade portion 200.

In order to ensure the strength of the rudder horn 300, the cross-sectional area of the arm of the rudder horn 300 gradually increases from bottom to top, that is, the arm of the rudder horn 300 becomes thicker from bottom to top, and the length of the upper end surface of the half-suspension rudder is greater than the length of the upper end surface of the lower rudder blade portion 200 along the front-rear direction of the half-suspension rudder. Therefore, the length of the upper end surface of the half-suspension rudder formed by combining the rudder blade and the rudder horn 300 is longer than the length of the upper end surface of the lower rudder blade portion 200.

The outer edge of the upper end surface of the rudder horn 300 includes two fourth linear structures symmetrically arranged in the left-right direction. The fourth linear structure includes a fourth rear linear structure 311 extending from the front end of the outer edge of the upper end surface of the rudder horn 300 to the rear end of the rudder horn 300, and the fourth rear linear structure 311 is identical to the first front linear structure 212, that is, they may be overlapped. The fourth linear structure further comprises a straight line segment 312 extending from the tail end of the fourth rear linear structure 311 to the direction of the rudder blade, the straight line segment 312 is parallel to the front-back direction of the rudder blade, the interval distance between the straight line segments 312 on the left and right sides is equal to the maximum width value of the rudder blade, and the straight line segment 312 is aligned with the end of the third rear linear structure 121 on the outer edge of the upper part 100 of the rudder blade; the introduction of the straight line section 312 plays a transition role, and ensures that the line shape of the outer edge of the upper end surface of the semi-suspension rudder is consistent with the line shape of the upper end surface of the lower rudder blade part 200.

The outer edge of the lower end surface of the rudder horn 300 includes two fifth linear structures which are arranged in bilateral symmetry, the fifth linear structures include a fifth front-section linear structure 320 which extends to the maximum width of the semi-suspension rudder along the front end of the rudder horn 300, the fifth front-section linear structure 320 is butted with the end part of the second rear-section linear structure 111 at the outer edge of the lower end surface of the upper rudder blade part 100 in the height direction, and the outer edge of the lower end surface formed by the hanging rudder horn 300 and the upper rudder blade part 100 is consistent with the outer edge of the upper end surface of the lower rudder blade part 200. The rudder horn 300 is complementarily inserted with the stepped structure of the lower end of the rudder blade upper part 100, and the side of the semi-suspension rudder forms a complete structure.

The rear end surface of the arm part of the rudder horn 300 is a curved surface which is curved in a direction away from the rudder blade, the rear end surface of the rudder blade is a curved surface which is curved in a direction toward the rudder horn 300, and the curved surface can better disperse the force acting on the semi-suspension rudder to each position of the semi-suspension rudder. The two curved surfaces are opposite and do not form the outer edge of the semi-suspension rudder.

In fig. 6, the hatched portion is a right triangle, one right-angle edge of the right triangle extends in the height direction, the other right-angle edge is a straight line segment 312, and the hatched portion is located in the area of the rudder horn 300 and at the joint between the rudder horn 300 and the rudder blade, so that the line shape of the rudder blade is not affected.

According to the ship hull provided by the embodiment of the invention, the semi-suspension rudder is introduced into the ship hull provided by the embodiment of the invention, so that the ship hull provided by the embodiment of the invention also has the advantages of the semi-suspension rudder.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.