Design load determination method for ship stern ramp

Abstract

The invention belongs to the field of ship structure design, and particularly relates to a method for determining design load of a ship stern ramp, which comprises the following steps of: calculating a wave shear N1 of a calculation section where a hinge is located if no stern ramp and cargo exist on a ship; the ship is provided with a stern ramp and goods and is in a lowering working condition, and calculating a wave shearing force N2 of a calculation section where a hinge is located; calculating a hinge design load FJ; calculating a design pressure head HW of the wave load of the stern ramp; calculating the design load FY of the oil cylinder; calculating structural stress sigma; judging whether sigma < lt > is met; sigma s. The method has the advantages of being simple in process and short in calculation time, economical efficiency is guaranteed, and meanwhile the design load of the stern ramp can be rapidly determined.

Description

Technical Field

[0001] The invention relates to a method for determining the design load of a ship stern ramp, and belongs to the field of ship structure design. Background Art

[0002] In the field of ship design, the stern ramp is an important component of the cargo loading and unloading system of a certain type of ship. The hinge and the cylinder are important equipment components to ensure the flexible lowering, recovery and position fixation of the stern ramp. In addition to the initially assumed weight of the stern ramp and the fixed cargo weight, the unknown loads that the stern ramp is subjected to during the lowering operation include the cylinder load, the hinge load and the wave load. The cylinder load and the hinge load are closely related to the selection of fastening devices such as the cylinder and the hinge, respectively, while the wave load is directly related to whether the assumed value of the stern ramp weight is appropriate.

[0003] It is usually not easy to calculate these three external forces. There are generally two ways to deal with them. One way is to estimate them through immature semi-empirical methods, which often makes the stern springboard body and fastening equipment bulky, which goes against the original intention of the lightweight design of the stern springboard; the other way is to use the water tank model test method to obtain them accurately, but this method has the obvious disadvantages of being time-consuming and poorly economical. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of non-lightweight design, long time consumption and poor economy in the existing determination of the design load of the ship stern ramp, and to provide an efficient and economical method for determining the design load of the ship stern ramp.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for determining the design load of a ship stern ramp comprises the following steps:

[0007] Step S1: Assuming that there is no stern ramp and cargo on board, determine the longitudinal weight distribution and corresponding buoyancy of the entire ship, and calculate the wave shear force N1 of the calculation section where the hinge is located according to the wave load analysis method;

[0008] Step S2: Assuming that there are stern ramps and cargo on board and they are in the lowering operation condition, the longitudinal weight distribution and corresponding buoyancy of the entire ship are re-determined, and the wave shear force N2 of the calculation section where the hinge is located is calculated according to the wave load analysis method;

[0009] Step S3: Based on the two states of step S1 and S2 with and without the stern ramp, the difference in wave shear force of the calculated section is the hinge design load F J :

[0010] F J =N1-N2

[0011] Step S4: Calculate the wave design load F perpendicular to the stern ramp plane W :

[0012]

[0013] Among them, G T is the initial assumed weight of the stern ramp; G H is the known and fixed weight of the cargo; h J h is the horizontal distance between the hinge and the cylinder; G h is the horizontal distance between the center of gravity and the cylinder; W is the horizontal distance between the wave force and the oil cylinder; θ is the angle between the lowered stern springboard plane and the horizontal plane; F f is the buoyancy; h f is the horizontal distance between the center of buoyancy and the cylinder;

[0014] Step S5: Calculate the design pressure head H of the stern ramp wave load W :

[0015]

[0016] Among them, μ is the conversion coefficient of the water pressure head of the stern springboard; S is the water contact area of ​​the stern springboard; ρ is the density of water; g is the acceleration of gravity;

[0017] Step S6: Calculate the cylinder design load F Y :

[0018] F Y =G T +G H -F J +F W ×cosθ-F f

[0019] Step S7: taking the design pressure head of the wave load as the action load, using the finite element method to calculate the structural stress σ of the stern ramp body assumed in the initial stage;

[0020] If σ<σ s If the requirements are met, the design load of the stern ramp determined in steps S2 to S6 is the final value;

[0021] If σ<σ is not satisfied s If the requirement is met, the weight of the stern ramp is increased and the structural stress is calculated again until σ<σ s The design load of the stern ramp is re-determined according to the requirements and the increased weight of the stern ramp body is taken as the initial assumed weight according to steps S2 to S6;

[0022] Among them, σ sIt is a structural stress criterion.

[0023] The following is a technical solution further defined by the present invention: the wave load analysis method is a linear frequency domain wave load method based on potential flow theory.

[0024] The following is a technical solution further limited by the present invention, wherein the wave shear force of the calculated section is the vertical wave shear force of the calculated section.

[0025] The following is a technical solution further defined by the present invention, in which the value range of the stern ramp water pressure head conversion coefficient μ is 0.5 to 1.0.

[0026] The following is a technical solution further defined by the present invention, in which the stern ramp water pressure head conversion coefficient μ is 0.7.

[0027] The following is a technical solution further defined in the present invention, in which the finite element method is a linear elastic finite element method.

[0028] The following is a technical solution further defined by the present invention, wherein the method is applied to determine the design load of a hull having a stern ramp.

[0029] The following is a technical solution further defined by the present invention, in which the hull and the stern ramp are connected via a hinge and an oil cylinder.

[0030] The following is a technical solution further defined by the present invention: one end of the hull and one end of the stern ramp are connected through a hinge, and the other end of the hull and the other end of the stern ramp are connected through an oil cylinder.

[0031] The following is a technical solution further defined by the present invention: the cylinder body of the oil cylinder is hingedly mounted on the hull, and the end of the movable end of the oil cylinder is hingedly connected to the stern ramp.

[0032] Compared with the prior art, the present invention has the following technical effects:

[0033] The method of the invention has the advantages of simple process and short calculation time, and can quickly determine the design load of the stern ramp while ensuring economy.

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1is a flow chart of the method of the present invention;

[0037] Figure 2 It is a simplified structural schematic diagram of the connection between the hull and the stern ramp of the present invention;

[0038] Figure 3 It is a schematic diagram of the design load of the stern ramp of the present invention.

[0039] Figure numerals: 1. hull; 2. stern ramp; 3. floating waterline; 4. calculated section where the hinge is located; 5. oil cylinder; 6. hinge. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0041] like Figure 2 As shown, when the stern ramp 2 is lowered, the hull 1 and the stern ramp 2 are connected through the hinge 6 and the cylinder 5; in the floating state corresponding to the loading floating waterline 3, the vertical wave shear forces N1 and N2 of the calculation section 4 where the hinge 6 is located can be calculated.

[0042] like Figure 3 As shown, F J is the hinge design load to be determined, F Y is the design load of the cylinder to be determined, F W Design loads for waves to be determined.

[0043] like Figure 1 As shown, a method for determining the design load of a ship stern ramp mainly includes the following steps:

[0044] 1. Assuming that there is no stern ramp and cargo on board, determine the longitudinal weight distribution and corresponding buoyancy of the entire ship. According to the linear frequency domain wave load method based on potential flow theory, the vertical wave shear force N1 of the calculation section where the hinge is located is quickly calculated to be 900 kN.

[0045] 2. Assuming that there is a stern ramp on the ship and it is in the lowering operation condition, the longitudinal weight distribution and corresponding buoyancy of the entire ship are re-determined. According to the linear frequency domain wave load method based on potential flow theory, the vertical wave shear force N2 of the calculation section where the hinge is located is quickly calculated to be 1400 kN.

[0046] 3. The difference in the vertical wave shear force of the calculated section obtained with and without the stern ramp is the hinge design load F J :

[0047] F J =N1-N2

[0048] The hinge design load F is obtained from this J 500 kN.

[0049] 4. Calculate the wave design load F perpendicular to the plane of the stern ramp according to the following formula: W :

[0050]

[0051] The initial assumed weight of the stern ramp is G T is 300 kN; the fixed weight of the cargo G is known H is 350 kN; the horizontal distance between the hinge and the cylinder is h J 12.5 meters; the horizontal distance between the center of gravity and the cylinder is h G is 4.5 meters; the horizontal distance between the wave force and the oil cylinder is h W is 5.5 meters; the angle θ between the lowered stern springboard plane and the horizontal plane is 10°; the buoyancy F f is 180 kN; the horizontal distance between the center of buoyancy and the cylinder is h f is 4.0 meters.

[0052] From this we can get the wave design load F W It is 746.8 kN.

[0053] 5. The design pressure head H of the stern ramp wave load is calculated according to the following formula: W :

[0054]

[0055] The conversion coefficient μ of the stern ramp water pressure head is 0.7; the stern ramp water contact area S is 62 meters 2 ; The density of water is ρ1 ton / m 3 ; Gravitational acceleration g is 9.8 m / s 2 .

[0056] The design pressure head H is obtained from this W is 1.75 meters.

[0057] 6. Calculate the cylinder design load F according to the following formula: Y :

[0058] F Y =(G T +G H )-F J +F W ×cosθ-F f

[0059] From this, we can get the design load F of the cylinder Y It is 705 kN.

[0060] 7. Taking the design pressure head H of the wave load as the acting load, the structural stress σ of the stern ramp body assumed in the initial calculation by the linear elastic finite element method is 160MPa, satisfying σ<σ s If the requirements are met, the design load of the stern ramp determined in steps 3 to 6 is considered to be the final value.

[0061] If the structural stress σ is 350Mpa, σ<σ s If the requirement is met, the weight of the stern ramp body G needs to be increased. T to 35 kN, and the structural stress σ is calculated again to be 252 MPa, satisfying σ<σ s The requirement is that the weight of the increased stern ramp body G T Assuming the initial weight to be 35, re-determine the design load of the stern ramp according to steps 2 to 6, and obtain the hinge design load F J The wave design load F is 530 kN. W The design pressure head H of the wave load is 774 kN. W is 1.82 meters, and the cylinder design load F Y It is 753 kN.

[0062] Among them, the structural stress criterion σ s It is 284Mpa.

[0063] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, all equivalent changes made according to the shape, structure and principle of the present invention without departing from the content of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the design load of a ship stern ramp, characterized in that: The following steps are involved: Step S1: Assuming that there is no stern ramp and cargo on board, determine the longitudinal weight distribution and corresponding buoyancy of the entire ship, and calculate the wave shear force N1 of the calculation section where the hinge is located according to the wave load analysis method; Step S2: Assuming that there are stern ramps and cargo on board and they are in the lowering operation condition, the longitudinal weight distribution and corresponding buoyancy of the entire ship are re-determined, and the wave shear force N2 of the calculation section where the hinge is located is calculated according to the wave load analysis method; Step S3: Based on the two states of step S1 and S2 with and without the stern ramp, the difference in wave shear force of the calculated section is the hinge design load F J : F J =N1-N2 Step S4: Calculate the wave design load F perpendicular to the stern ramp plane W : Among them, G T is the initial assumed weight of the stern ramp; G H is the known and fixed weight of the cargo; h J h is the horizontal distance between the hinge and the cylinder; G h is the horizontal distance between the center of gravity and the cylinder; W is the horizontal distance between the wave force and the oil cylinder; θ is the angle between the lowered stern springboard plane and the horizontal plane; F f is the buoyancy; h f is the horizontal distance between the center of buoyancy and the cylinder; Step S5: Calculate the design pressure head H of the stern ramp wave load W : Among them, μ is the conversion coefficient of the water pressure head of the stern springboard; S is the water contact area of ​​the stern springboard; ρ is the density of water; g is the acceleration of gravity; Step S6: Calculate the cylinder design load F Y : F Y =G T +G H -F J +F W ×cosθ-F f Step S7: taking the design pressure head of the wave load as the action load, using the finite element method to calculate the structural stress σ of the stern ramp body assumed in the initial stage; If σ<σ s If the requirements are met, the design load of the stern ramp determined in steps S2 to S6 is the final value; If σ<σ is not satisfied s If the requirement is met, the weight of the stern ramp is increased and the structural stress is calculated again until σ<σ s The design load of the stern ramp is re-determined according to the requirements and the increased weight of the stern ramp body is taken as the initial assumed weight according to steps S2 to S6; Among them, σ s It is a structural stress criterion.

2. A method for determining the design load of a ship stern ramp according to claim 1, characterized in that: The wave load analysis method is a linear frequency domain wave load method based on potential flow theory.

3. A method for determining the design load of a ship stern ramp according to claim 1, characterized in that: The wave shear force of the calculated section is the vertical wave shear force of the calculated section.

4. A method for determining the design load of a ship stern ramp according to claim 1, characterized in that: The value range of the stern ramp water pressure head conversion coefficient μ is 0.5 to 1.

0.

5. A method for determining the design load of a ship stern ramp according to claim 4, characterized in that: The conversion factor μ of the stern ramp water pressure head is 0.

7.

6. A method for determining the design load of a ship stern ramp according to claim 1, characterized in that: The finite element method is a linear elastic finite element method.

7. A method for determining the design load of a ship stern ramp according to claim 1, characterized in that: The method is applied to the determination of design loads for a ship hull having a stern ramp.

8. A method for determining the design load of a ship stern ramp according to claim 7, characterized in that: The hull and the stern ramp are connected by hinges and cylinders.

9. A method for determining the design load of a ship stern ramp according to claim 8, characterized in that: One end of the hull is connected to one end of the stern ramp through a hinge, and the other end of the hull is connected to the other end of the stern ramp through an oil cylinder.

10. A method for determining the design load of a ship stern ramp according to claim 9, characterized in that: The cylinder body of the oil cylinder is hingedly installed on the hull, and the end of the movable end of the oil cylinder is hingedly connected to the stern ramp.

Images