Structural Strength Analysis Method for a Catamaran Crane Ship without a Connecting Bridge

Abstract

Structural strength analysis method for a catamaran crane vessel without a connecting bridge, including: S1, using a three-dimensional model of the entire ship; S2, under the dispatching condition and the operation condition, according to the general transverse bending and torsion strength calculation method of the catamaran, calculating the stresses of the hulls and the connecting bridge, and checking the general transverse strength and torsion strength of the hulls; S3, using a truss model, considering the combination of unilateral loading, full load, no wind and windy conditions, calculating the stresses and binding forces of the lifting truss under the action of the lifting load and the wind load; S4, superimposing the stresses of the lifting truss under the action of the lifting load and the wind load on the truss stresses of the operation condition under the action of the overall load, and checking the strength of the truss according to the strength standard of the crane; the truss after stress superposition should not only meet the strength requirements for the connecting bridge in Appendix I.5 of Chapter 9, Part 1 of the "Inland River Code", but also meet the strength requirements for the lifting components in 3.2.16 of the "Lifting Code".

Description

Technical Field

[0001] The present invention belongs to the field of ship structure design. Based on relevant specifications, a method for structural strength analysis of a catamaran crane ship without a connecting bridge is proposed. Technical Background

[0002] With the continuous increase in the tonnage of sunken ship salvage in inland waterways and the frequent demand for ship maintenance and repair, there is a need to design a novel catamaran crane ship, as Figure 1 shown. There is no connecting bridge structure between the two hulls of this ship type, and the lifting truss also serves as the connecting bridge. Compared with ordinary crane ships, the distance between the hulls of this catamaran crane ship is large, which is more practical for actual operations such as salvaging sunken ships of larger sizes, hoisting goods, and hull maintenance. It has the advantages of large lifting capacity, stable lifting, and convenient lifting construction operations. The connecting bridge is an important component of a catamaran ship, and there are clear requirements for its structural form and size specifications. The "Steel Inland Shipbuilding Code (2021)" (hereinafter referred to as the "Inland Code") requires that a catamaran ship must be equipped with a connecting bridge greater than 80% of the ship's length between the two hulls, while this ship type only has a few connecting trusses, and this truss also serves as the lifting truss, bearing complex lifting loads. For such a ship with complex forces and novel structure, there is no corresponding specification that can be applied. However, there is currently no technology on how to check the strength of such non-standard ships, especially for the truss that also serves as the connecting bridge, and this is the key to the design of this ship type.

[0003] Since there are only regulations for catamaran ships and engineering ships in the "Inland Code", there is no checking criterion for catamaran crane ships. The catamaran ship part of the code mainly considers the action of wave loads and does not consider the action of lifting loads; the engineering ship part only targets single-hull ships, has no content on catamaran ships, and no requirements for lifting structures. And this ship is a catamaran crane ship, and the lifting truss also serves as the connecting bridge. Therefore, this ship type needs to meet the strength requirements of both catamaran ships and engineering ships, and at the same time needs to meet the relevant regulations of the "Code for Lifting Appliances on Ships and Marine Installations (2016)" (hereinafter referred to as the "Lifting Code").

[0004] In view of the catamaran crane ship without a connecting bridge, with complex forces and many combinations of lifting and hydrodynamic load conditions, if various wave loads and lifting loads are directly applied to the catamaran ship at the same time, the boundary conditions of the finite element model cannot be established, and it is an impossible task to carry out structural strength checking. Summary of the Invention

[0005] The present invention aims to overcome the above-mentioned drawbacks of the prior art and provides a method for structural strength analysis of a catamaran crane ship without a connecting bridge.

[0006] Therefore, the idea of the present invention is based on the individual action of various loads, and the combination of various load effects (i.e., stresses) is carried out while meeting the requirements of the "Inland River Code" and the "Lifting Code".

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0008] A method for analyzing the structural strength of a twin-hull lifting ship without a connecting bridge, comprising the following steps:

[0009] Step S1, a three-dimensional model of the whole ship is adopted, including all ship outer plates, bulkheads, decks and main supporting members, as well as the lifting rigid frame structure, etc. The boundary conditions for calculating the longitudinal bending strength of the hull are: (1) The first sealing plates of the side floating tanks on both sides of the slotted area: Apply transverse and vertical linear displacement constraints, that is, u y = u z = 0. (2) The nodes of the tail sealing plate corresponding to the nodes of the left side of the bow in (1): Apply longitudinal, transverse and vertical linear displacement constraints, that is, u x = u y = u z = 0; (3) The nodes of the tail sealing plate corresponding to the nodes of the right side of the bow in (1): Apply transverse and vertical linear displacement constraints, that is, u y = u z = 0. The boundary conditions for calculating the local strength of the hull are: Apply full displacement constraints to each node of the transverse strong frame plane adjacent to the slotted transverse end wall at the tail, that is, u x = u y = u z = 0, θ x = θ y = θ z = 0. Divide into dispatching and operating conditions, and according to the longitudinal and local strength calculation methods of engineering ships, check the longitudinal and local strength of the pontoons.

[0010] Step S2, a three-dimensional model of the whole ship is adopted, including all ship outer plates, bulkheads, decks and main supporting members, as well as the lifting rigid frame structure, etc. For the finite element model of the whole ship in a balanced state, points A and B are taken at the head and tail of the longitudinal middle section of the connecting bridge, and point C is taken at the side of the transverse middle section of any pontoon for constraint. Divide into dispatching conditions and operating conditions, and according to the total transverse bending and torsional strength calculation methods of twin-hull ships, calculate the stresses of the pontoons and the connecting bridge, and check the total transverse strength and torsional strength of the pontoons.

[0011] Step S3, adopt a truss model, constrain the root of the truss, u x = u y = u z = 0. Considering the combination of unilateral loading, full load and no wind, and windy conditions, calculate the stresses and binding forces of the lifting truss under lifting loads and wind loads.

[0012] In step S4, the stresses of the lifting truss under the action of lifting load and wind load are superimposed on the truss stresses under the operating conditions of the overall loads (longitudinal, transverse, and torsion), and the strength of the truss (the connecting bridge also serves as the lifting structure) is checked according to the strength standard of the crane. The truss after stress superposition should not only meet the strength requirements for the connecting bridge in Appendix I.5 of Chapter 9, Part 1 of the "Inland River Code", but also meet the strength requirements for the lifting components in Clause 3.2.16 of the "Lifting Code".

[0013] In the said step S1, a three-dimensional full-ship model is adopted, and the longitudinal and local strength checks of the sheet are carried out according to the longitudinal and local strength calculation methods of the engineering ship.

[0014] In the said step S2, a three-dimensional full-ship model is adopted, and the stress calculations of the sheet and the truss, as well as the transverse strength and torsion strength checks of the sheet, are carried out according to the transverse bending and torsion strength calculation methods of the catamaran.

[0015] In the said step S3, a truss model is adopted, and the root of the truss is constrained, u x = u y = u z = 0. Considering the combination of unilateral loading, full load, no wind, and windy conditions, the stress and binding force calculations of the lifting truss under the action of lifting load and wind load are carried out.

[0016] In the said step S4, the stresses of the lifting truss under the action of lifting load and wind load are superimposed on the truss stresses under the operating conditions of the overall loads (longitudinal, transverse, and torsion), and the strength of the truss (the connecting bridge also serves as the lifting structure) is checked according to the strength standard of the crane. The truss after stress superposition should not only meet the strength requirements for the connecting bridge in Appendix I.5 of Chapter 9, Part 1 of the "Inland River Code", but also meet the strength requirements for the lifting components in Clause 3.2.16 of the "Lifting Code".

[0017] The beneficial effects of the present invention are as follows: The strength analysis method proposed for this new ship type not only solves the analysis problems of complex forces, multiple working conditions, and diverse combination forms of the catamaran lifting ship, but also comprehensively checks the longitudinal and local strength, transverse and torsion strength, lifting truss strength, and support structure strength, ensuring the safety of the hull structure and providing effective technical support for ship inspection and certification. In addition, the calculation ideas and methods of this patent have reference value for the design and verification of ships of the same type. Description of the Drawings

[0018] Figure 1 is the point cloud diagram of the full-ship finite element model of the catamaran lifting ship to which the method of the present invention is applicable. In the figure, the full-ship finite element model adopts a right-handed coordinate system, with the x-axis positive towards the bow of the ship, the y-axis positive towards the port side, and the z-axis positive upwards.

[0019] Figure 2 It is the point cloud diagram of the maximum combined stress (LC03) of the longitudinal and local strength of the catamaran crane ship to which the method of the present invention is applicable. In the figure, the maximum combined stress of the longitudinal and local strength of the hull is 94.2 MPa, which is located at 45#, outer side of the hull, and the deck. The position is represented by three-dimensional coordinates X, Y, and Z, where X is the position along the ship length direction, generally represented by frame number; Y is the position in the ship width direction; Z is the vertical position. The same applies hereinafter.

[0020] Figure 3 It is the point cloud diagram of the overall constraint model of the catamaran crane ship to which the method of the present invention is applicable.

[0021] Figure 4 It is the point cloud diagram of the maximum combined stress (LC06) of the transverse and torsional strength of the catamaran crane ship to which the method of the present invention is applicable.

[0022] Figure 5 It is the point cloud diagram of the maximum combined stress (LC15) of the lifting truss of the catamaran crane ship to which the method of the present invention is applicable. In the figure, the maximum combined stress of the lifting truss is 144.0 MPa, which is located at 88#, inner column, and column bottom.

[0023] Figure 6 It is the flow chart of the method of the present invention. Detailed implementation manners

[0024] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0025] In this embodiment, MSC.Patran / Nastran is used to directly calculate the finite element of the longitudinal bending strength, local strength, transverse bending strength, torsional strength, rigid frame strength, and lifting strength of a 700 deadweight ton catamaran crane ship without a connecting bridge.

[0026] The main parameters of the ship are as follows: total length 48.15 m, width of each hull (left / right) 7.50 m / 7.50 m, molded width 28.00 m, molded depth 2.30 m, designed draft 1.05 m, and full load displacement 700 t.

[0027] The method for analyzing the structural strength of the catamaran crane ship without a connecting bridge in this embodiment includes the following steps:

[0028] Step S1, according to the calculation methods of the longitudinal and local strength of engineering ships, check the longitudinal and local strength of the hulls.

[0029] An overall model is adopted, such as Figure 1As shown in the figure. The wave load is applied to the bottom body plate in the form of a cosine wave. Considering the actual environment of the salvage operation on the Qiantang River, the wave load is conservatively taken as the migration condition. That is, when calculating the longitudinal bending strength, the design wave height is taken as 1.5 m and the wave length is the ship length. When calculating the local strength, the design wave height is taken as 1.5 m and the wave length is two ship lengths.

[0030] When calculating the longitudinal bending strength of the hull, the boundary conditions shall meet the following requirements: (1) For the first sealing plates of the side floating tanks on both sides of the grooved area: Apply transverse and vertical linear displacement constraints, that is, u y = u z = 0. (2) For the node on the tail sealing plate corresponding to the node on the left side of the bow in (1): Apply longitudinal, transverse and vertical linear displacement constraints, that is, u x = u y = u z = 0; (3) For the node on the tail sealing plate corresponding to the node on the right side of the bow in (1): Apply transverse and vertical linear displacement constraints, that is, u y = u z = 0. According to the requirements of Appendix II.4.1 of Chapter 10, Part 1 of the "Inland River Code", when calculating the local strength of the hull, the boundary conditions shall meet the following requirements: Apply full displacement constraints to each node on the plane of the transverse strong frame adjacent to the grooved transverse end wall at the tail, that is, u x = u y = u z = 0, θ x = θ y = θ z = 0.

[0031] The calculation results of the longitudinal and local strength are shown in Table 1. Figure 2 It is the maximum combined stress diagram. It can be seen from the results that the longitudinal and local strength of the hull meet the corresponding allowable standards in Sections 1.9.5.13 and 1.9.7.7 of Part 1 of the "Inland River Code", and there is a large margin for each stress.

[0032] Step S2, according to the calculation methods of the total transverse bending and torsional strength of the catamaran, calculate the stresses of the pontoons and the connecting bridge, and check the total transverse strength and torsional strength of the pontoons.

[0033] For the whole ship finite element model in the equilibrium state, it includes all the outer plates, bulkheads, decks and main support members of the ship, as well as the lifting rigid frame structure, etc. Use Figure 3 and Table 2 to set the boundary conditions. According to the requirements of Appendix I.4.1 of Chapter 9, Part 1 of the "Inland River Code", in the analysis of the total transverse and torsional strength, the load combination conditions are shown in Table 3. According to the requirements of Appendix I.4.2 of Chapter 9, Part 1 of the "Inland River Code", the total transverse bending moment of the hull can be equivalent by applying the transverse split forces f y along a series of nodes on the inner bilge of the pontoon.

[0034] fy = M bx / nz

[0035] In the formula:

[0036] M bx —Total transverse bending moment, M bx = 9.81Δb c / s, kN·m;

[0037] z—Vertical distance from the application point of the transverse split force to the neutral axis of the mid-longitudinal section, m;

[0038] n—Total number of nodes applying the transverse split force on a single sheet;

[0039] Δ—Displacement of the catamaran, taking the full load displacement, t;

[0040] b C —Distance from the center line of any sheet to the calculated section of the connecting bridge, m;

[0041] s—Navigation area coefficient.

[0042] According to the requirements of Appendix I.4.3 in Chapter 9 of Part 1 of the "Inland River Code", the total transverse torque of the hull can be equivalently applied by the vertical uniformly distributed force p x distributed antisymmetrically in the mid-longitudinal section of the sheet.

[0043] p x = 4M ty / L 2

[0044] In the formula:

[0045] L—Length of the catamaran, m;

[0046] M ty —Torque of the connecting bridge, kN·m, M ty = 9.81k 0 kΔL;

[0047] k 0 —Coefficient, k 0 = (1871 - 69.71L + 1.056L 2 - 0.00542L 3 ) × 10 -4 ;

[0048] k—Coefficient related to the navigation area.

[0049] The calculation results of the total transverse bending and torsion strength are shown in Table 4, Figure 4 which is the maximum combined stress diagram. It can be seen from the results that the total transverse bending and torsion strength of the hull meets the corresponding allowable standards in Appendix I.5 of Chapter 9 of Part 1 of the "Inland River Code", and there is a large margin for each stress.

[0050] Step S3: Adopt a truss model to superimpose the stresses under each working condition, and perform strength check on the truss (the connecting bridge also serves as the lifting structure) according to the strength standard of the crane.

[0051] In the overall structural analysis, consider the combinations of unilateral loading, full load, no wind, and windy working conditions. Calculate the following load combination working conditions as shown in Table 5. Then superimpose the calculation results with the hull's longitudinal bending stress, local bending stress, transverse bending stress, and torsional stress respectively. According to the "Lifting Specification", restrain the root of the truss, u x = u y = u z = 0.

[0052] Step S4: Superimpose the stresses of the lifting truss under the action of lifting load and wind load with the truss stresses under the working conditions of the overall loads (longitudinal, transverse, and torsional), and perform strength check on the truss (the connecting bridge also serves as the lifting structure) according to the strength standard of the crane.

[0053] The following takes LC10 as an example to illustrate the stress superposition. As shown in Table 6, in this way, obtain the maximum values of the rigid frame stress and internal force under the combination of lifting load and 9 kinds of wave loads.

[0054] The strength calculation results of the lifting truss are shown in Table 7, Figure 5 which is the maximum combined stress diagram. It can be seen from the results that except for the shear stress, the other stresses are relatively close to the allowable values. The lifting truss undertakes the connecting role in the working state, but still can meet the corresponding allowable criteria in the specification.

[0055] Table 1 Longitudinal and local strength calculation results (MPa)

[0056]

[0057] Table 2 Boundary conditions for transverse and torsional strength analysis

[0058]

[0059] Table 3 Working conditions for transverse and torsional strength calculation

[0060] Condition Number Load Combination LC04 <![CDATA[M bx (mid-vertical)]]> LC05 <![CDATA[M bx (Center arch)]]> LC06 <![CDATA[0.8M bx (Vertical midpoint) + 0.6M ty > LC07 <![CDATA[0.8M bx (Middle arch) + 0.6M ty > LC08 <![CDATA[0.6M bx (Vertical midpoint) + 0.8M ty > LC09 <![CDATA[0.6M bx (Center arch) + 0.8M ty >

[0061] Table 4 Transverse and torsional strength calculation results (MPa)

[0062]

[0063] Table 5 Working conditions for lifting truss strength calculation

[0064] Condition Number Load Combination Condition Number Load Combination <![CDATA[LC10 * > Unilateral Loading without Wind LC10 <![CDATA[Max: LC10 * +LC01~LC09]]> <![CDATA[LC11 * > Bilateral Loading without Wind LC11 <![CDATA[Max: LC11 * +LC01~LC09]]> <![CDATA[LC12 * > Unilateral Loading with Wind in x - direction LC12 <![CDATA[Max: LC12 * +LC01~LC09]]> <![CDATA[LC13 * > Bilateral Loading with Wind in x - direction LC13 <![CDATA[Max: LC13 * +LC01 to LC09]]> <![CDATA[LC14 * > Unilateral Loading with Wind in y - direction LC14 <![CDATA[Max: LC14 * +LC01~LC09]]> <![CDATA[LC15 * > Bilateral Loading with Wind in y - direction LC15 <![CDATA[Max: LC15 * +LC01~LC09]]>

[0065] Note: LC10*~LC15* in Table 5 are the working conditions considering only the lifting load, and LC10~LC15 are the most unfavorable working conditions under the combined action of the lifting load and the wave load.

[0066] Table 6 LC10 Combined Working Conditions (MPa)

[0067] Combined Condition <![CDATA[Total stress σ e > <![CDATA[Maximum principal stress σ l / w > Maximum Shear Stress τ <![CDATA[Axial stress σ of beam element z > LC10* + LC01 72.7 72.2 32.0 22.0 LC10* + LC02 74.0 76.0 32.2 25.4 LC10* + LC03 77.1 68.1 35.9 63.2 LC10* + LC04 105.0 57.8 33.3 72.1 LC10* + LC05 125.0 130.0 39.3 74.8 LC10* + LC06 107.0 70.9 30.1 73.5 LC10* + LC07 108.0 96.2 25.8 71.8 LC10* + LC08 97.6 70.6 28.2 71.8 LC10* + LC09 98.8 89.1 21.0 70.3 MAX 125.0 130.0 39.3 74.8

[0068] Table 7 Strength Calculation Results of the Lifting Truss (MPa)

[0069]

[0070] Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for analyzing the structural strength of a catamaran crane ship without a connecting bridge, comprising the following steps: Step S1: Use the three-dimensional model of the whole ship, including all the outer hull plates, bulkheads, decks and main supporting members, as well as the lifting steel frame structure; the boundary conditions for the longitudinal bending strength calculation of the hull are as follows: (1) The first sealing plates of the side floating tanks on both sides of the grooved area: Apply lateral and vertical linear displacement constraints, that is, u y = u z = 0; (2) The nodes of the tail sealing plate corresponding to the left bow nodes in (1): Apply longitudinal, lateral and vertical linear displacement constraints, that is, u x = u y = u z = 0; (3) The nodes of the tail sealing plate corresponding to the right bow nodes in (1): Apply lateral and vertical linear displacement constraints, that is, u y = u z = 0; The boundary conditions for the local strength calculation of the hull are as follows: Apply full displacement constraints to all the nodes on the transverse strong frame plane adjacent to the grooved transverse end wall at the tail, that is, u x = u y = u z = 0, θ x = θ y = θ z = 0; Divide into the dispatching and operation conditions, and according to the longitudinal and local strength calculation methods of the engineering ship, conduct the longitudinal and local strength checks of the pontoons; Step S2: Adopt a three-dimensional model of the whole ship, including all the outer hull plates, bulkheads, decks and main supporting members, as well as the lifting rigid frame structure; for the finite element model of the whole ship in a balanced state, take points A and B at the head and tail of the longitudinal middle section of the connecting bridge, and take point C at the side of the transverse middle section of any one hull for constraint; divide into the dispatching condition and the operating condition, and calculate the stresses of the hull and the connecting bridge and check the overall transverse strength and torsional strength of the hull according to the calculation methods of the overall transverse bending and torsional strength of the catamaran. Step S3: Using a truss model, constrain the root of the truss, where u x = u y = u z = 0; Considering the combinations of single-sided loading, full loading, no wind, and windy conditions, calculate the stresses and binding forces of the lifting truss under the action of lifting loads and wind loads; Step S4: Superimpose the stresses of the lifting truss under the action of the lifting load and the wind load on the stresses of the truss in the operating condition under the action of the overall loads (longitudinal, transverse, torsional), and check the strength of the truss (the connecting bridge also serves as the lifting structure) according to the strength standard of the crane; the truss after stress superposition should meet both the strength requirements for the connecting bridge in Appendix I.5 of Chapter 9 of Part 1 of the "Code for the Construction of Steel Inland Ships (2021)" and the strength requirements for the lifting members in 3.2.16 of the "Code for Lifting Appliances on Ships and Offshore Installations (2016)".

2. The method for analyzing the structural strength of a catamaran crane ship without a connecting bridge as described in claim 1, characterized in that, in the said step S1, a three-dimensional model of the whole ship is adopted, and the longitudinal and local strength of the hull is checked according to the calculation methods of the longitudinal and local strength of the engineering ship.

3. The method for analyzing the structural strength of a catamaran crane ship without a connecting bridge as described in claim 1, characterized in that, in the said step S2, a three-dimensional model of the whole ship is adopted, and the stresses of the hull and the truss are calculated and the overall transverse strength and torsional strength of the hull are checked according to the calculation methods of the overall transverse bending and torsional strength of the catamaran.

4. The method for analyzing the structural strength of a catamaran crane ship without a connecting bridge as described in claim 1, characterized in that, In the step S3, a truss model is adopted to constrain the root of the truss, and u x = u y = u z = 0; Considering the combinations of unilateral loading, full load, no wind, and windy conditions, calculate the stresses and binding forces of the lifting truss under the action of lifting loads and wind loads.

5. The method for analyzing the structural strength of a catamaran crane ship without a connecting bridge as described in claim 1, characterized in that, in the said step S4, the stresses of the lifting truss under the action of the lifting load and the wind load are superimposed on the stresses of the truss in the operating condition under the action of the overall loads (longitudinal, transverse, torsional), and the strength of the truss (the connecting bridge also serves as the lifting structure) is checked according to the strength standard of the crane; the truss after stress superposition should meet both the strength requirements for the connecting bridge in Appendix I.5 of Chapter 9 of Part 1 of the "Code for the Construction of Steel Inland Ships (2021)" and the strength requirements for the lifting members in 3.2.16 of the "Code for Lifting Appliances on Ships and Offshore Installations (2016)".

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