Design method for improving fatigue strength of ship superstructure

Abstract

The present invention provides a design method for improving the fatigue strength of a ship superstructure, the steps of the method include: determining the fatigue point position of a vertical support member on the side peripheral wall structure of the ship superstructure; establishing a finite element fatigue strength model, inputting each fatigue point into the model calculation, loading the wave load under the whole ship working condition into the model, and obtaining the structural stress of the fatigue point; calculating the fatigue life of the fatigue point based on the plate thickness, material and SN curve at the fatigue point; dividing the fatigue life into intervals, determining the interval corresponding to the fatigue life of each fatigue point, and optimizing the fatigue point based on the interval corresponding to the fatigue life. The above method can effectively improve the fatigue strength of the vertical support member, increase the fatigue life, and achieve the purpose of ensuring the structural strength of the ship and safe navigation.

Description

Technical Field

[0001] The invention relates to the field of shipbuilding, and in particular to a design method for improving the fatigue strength of a ship superstructure. Background Art

[0002] Since ships are continuously impacted by wave loads while sailing at sea, they are subjected to periodic external forces of uncertain magnitude, which affects the overall structural strength of the ship. Therefore, it is necessary to analyze, evaluate and calculate the fatigue strength of the ship structure.

[0003] The superstructure of a container ship is generally arranged above the main deck of the hull structure, slightly closer to the bow of the hull centerline, and the fuel tank structure is arranged under the main deck. The superstructure structure of a container ship is mostly a wide-narrow structure, with a small span along the length of the ship. The transverse outer wall is aligned with the fuel tank structure under the main deck, but the width of the superstructure spans the entire width of the ship, making the entire superstructure a flat outward floating structure, such as Figure 1 , Figure 2 As shown in Figure 2, under the action of wind load and wave load, the outer wall of the container ship superstructure is prone to structural tension and torsion.

[0004] like Figure 3 As shown, usually the structural stress will be transmitted to the vertical supporting members arranged on the side peripheral wall structure through the longitudinal side peripheral wall structure of the superstructure, so it is necessary to calculate the fatigue strength of the vertical supporting members and design the vertical supporting members. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the related art, an object of the present invention is to provide a design method for improving the fatigue strength of a ship superstructure, which is used for optimizing the design of vertical supporting components.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a design method for improving fatigue strength of a ship superstructure, the method comprising the following steps:

[0007] Determine the fatigue point position of the vertical support members on the side peripheral wall structure of the ship superstructure;

[0008] Establish a finite element fatigue strength model, input each fatigue point into the model calculation, load the wave load under the whole ship working condition into the model, and obtain the structural stress of the fatigue point;

[0009] Calculate the fatigue life of the fatigue point based on the plate thickness, material and SN curve at the fatigue point;

[0010] The fatigue life is divided into intervals, the interval corresponding to the fatigue life of each fatigue point is determined, and the fatigue point is optimized based on the interval corresponding to the fatigue life.

[0011] Optionally, the fatigue points are divided into fatigue welding points and fatigue free edges based on the positions of the fatigue points.

[0012] Optionally, the step of dividing the fatigue life into intervals, determining the intervals corresponding to the fatigue life of each fatigue point, and optimizing the fatigue points based on the intervals corresponding to the fatigue life includes: if the fatigue life of the fatigue point is greater than or equal to 25 years, the fatigue strength requirement is met, otherwise the fatigue point needs to be optimized.

[0013] Optionally, the fatigue life period of 0-25 years is divided into three intervals: the period greater than or equal to 20 years and less than 25 years is divided into the first interval, the period greater than or equal to 10 years and less than 20 years is divided into the second interval, and the period less than 10 years is divided into the third interval, and the fatigue point is optimized based on the interval corresponding to the fatigue life of the fatigue point.

[0014] Optionally, if the fatigue age of the fatigue point corresponds to the first interval, the fatigue point is polished.

[0015] Optionally, if the fatigue life of the fatigue point corresponds to the second interval, optimization is performed by changing the thickness and material of the component.

[0016] Optionally, if the fatigue life of the fatigue point corresponds to the third interval, the factors affecting the fatigue life of each fatigue point are first determined, and then the structure of the vertical supporting member is optimized based on each factor.

[0017] Optionally, factors affecting the fatigue life of the fatigue point include the through-weld hole form, bottom end length and toe end arc angle of the vertical supporting member. The fatigue life can be improved by changing the through-weld hole form, increasing the bottom end length and reducing the toe end arc angle.

[0018] Optionally, the size of the through-welding hole needs to be smaller than one quarter of the height of the vertical support member.

[0019] Optionally, when establishing the finite element fatigue strength model, fine grid division is performed on the position around the fatigue point, and the size of the fine grid is t·t, where t is the plate thickness in the fatigue point area.

[0020] As described above, the design method for improving fatigue strength of ship superstructure of the present invention has the following beneficial effects: the method of this embodiment first calculates the fatigue life of the fatigue point, and then analyzes the factors affecting the fatigue strength of the fatigue point according to the interval corresponding to the fatigue life, and then optimizes the factors according to the situation. Thus, the fatigue strength of the vertical support components on the side peripheral wall structure of the superstructure is effectively improved, the fatigue life is increased, and the purpose of ensuring the structural strength of the ship and safe navigation is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Shown is a schematic side view of a superstructure of a ship according to an embodiment of the present invention.

[0022] Figure 2 Shown is a schematic front view of a superstructure according to an embodiment of the present invention.

[0023] Figure 3 It is a schematic diagram showing the arrangement of vertical support members on the side panels of the superstructure before optimization in an embodiment of the present invention.

[0024] Figure 4 Shown is a flow chart of a design method for improving fatigue strength of a ship superstructure according to an embodiment of the present invention.

[0025] Figure 5 It is a schematic diagram showing the arrangement of the vertical support members on the side panels of the superstructure after optimization in an embodiment of the present invention.

[0026] Component number description

[0027] 1. Superstructure; 2. Fuel tank structure; 3. Main hull structure; 4. Side outer wall structure; 5. Vertical supporting members. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0029] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0030] For ease of description, spatial relational terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatial relational terms are intended to include other directions of the device in use or operation in addition to the directions depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can be one or more intervening layers. As used herein, "between..." means including the end point values.

[0031] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0032] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0033] like Figure 3 and Figure 4 As shown, this embodiment provides a design method for improving fatigue strength of a ship superstructure 1, the method comprising the steps of:

[0034] S1. Determine the fatigue point position of the vertical support member 5 on the side peripheral wall structure 4 of the ship superstructure 1.

[0035] The ship of this embodiment is a container ship. The fatigue point inspection types on container ships are mainly divided into two categories: fatigue welding points and fatigue free edges. Different fatigue point types have different fatigue calculation methods, and correspondingly different optimization schemes for improving fatigue life are also different. The fatigue point positions of this embodiment are shown in the figure, where ABC is a fatigue welding point and DE is a fatigue free edge. Among them, point A is the welding point between the through-welding hole of the vertical support member 5 and the main deck, point B is the welding point between the through-welding hole of the vertical support member 5 and the side outer plate, and point C is the welding point between the bottom toe end of the vertical support member 5 and the main deck. The three points ABC are affected by the stress of the side outer plate and the deck structure, and part of the stress will be transmitted to the vertical support member 5 through the three points ABC, so avoid generating structural hard points during structural design. Free edge D is the edge of the through-welding hole on the vertical support member 5, and free edge E is the edge of the vertical support member 5. Free edge D and free edge E are mainly affected by the structural strength of the vertical support member 5 itself.

[0036] S2. Establish a finite element fatigue strength model, input each fatigue point into the model calculation, load the wave load under the whole ship working condition into the fine grid model, and obtain the structural stress of the fatigue point.

[0037] In the process of establishing the finite element model, the hull model must be imported into the software first, and then the hull model is coarsely meshed, which can be understood as a larger mesh size. Then the area around the fatigue point is finely meshed, and the size of the fine mesh is t·t, where t is the plate thickness in the fatigue point area. By refining the mesh size around the fatigue point, the structural stress at the fatigue point can be calculated more precisely.

[0038] S3. Calculate the fatigue life of the fatigue point based on the plate thickness, material and SN curve at the fatigue point.

[0039] S4. Divide the fatigue life into intervals, determine the interval corresponding to the fatigue life of each fatigue point, and optimize the fatigue point based on the interval corresponding to the fatigue life.

[0040] If the fatigue life of the fatigue point is greater than or equal to 25 years, that is, it corresponds to the first interval, then the fatigue strength requirements are met. The period greater than or equal to 20 years and less than 25 years is divided into the first interval, the period greater than or equal to 10 years and less than 20 years is divided into the second interval, and the period less than 10 years is divided into the third interval. If the fatigue life of the fatigue point in the calculation result is greater than or equal to 20 years and less than 25 years, that is, it corresponds to the first interval, the fatigue welding point and the fatigue free edge are polished; if the fatigue life of the fatigue point in the calculation result is greater than or equal to 10 years and less than 20 years, that is, it corresponds to the second interval, then the thickness of the component is increased or high-strength steel is replaced, such as increasing the thickness of the vertical support member, the increase is 2-5mm, and the material can be changed from Grade A steel to AH32 steel, and AH32 steel to AH36 steel; if the fatigue life of the fatigue welding point and the fatigue free edge in the calculation result is less than 10 years, that is, it corresponds to the third interval, then simply increasing the plate thickness material is no longer sufficient, and the structural form of the vertical support member 5 needs to be changed.

[0041] If it is necessary to optimize by changing the structural form of the vertical support member 5, the factors affecting the fatigue life of each fatigue point are first determined before optimization, and then the structure of the vertical support member is optimized based on each factor.

[0042] The fatigue life of fatigue welding point A and fatigue welding point B is mainly affected by the through-weld hole form of vertical support member 5 (shown as a in the figure). Generally, the through-weld hole forms include waist round hole, key hole and omega hole (general terms are used here and will not be described in detail). The size of the through-weld hole must be less than one-fourth of the height of the vertical support member. In terms of fatigue strength, omega hole>key hole>waist round hole. If the fatigue life of fatigue welding point A and fatigue welding point B is less than 10 years, the waist round hole is changed to a key hole and recalculated. If the fatigue life does not improve significantly, it is changed to an omega hole, which can effectively reduce stress and increase life.

[0043] The fatigue life of the fatigue welding point C is mainly affected by the bottom length (shown as h in the figure) and the toe arc angle (shown as α in the figure) of the vertical support member 5. For example, the original bottom length is 375mm, and the length can be appropriately increased by 1 times. If the fatigue life after recalculation is greater than 25 years, it meets the requirements. If the fatigue life after recalculation still does not meet the requirements, increase the plate thickness and replace the material. If neither is applicable, increase the bottom length by 1.5 times. In addition, the fatigue strength of the fatigue point can be improved by adjusting the toe angle. The smaller the toe angle, the better the fatigue strength. For example, the toe angle is set to 15° and the fatigue life calculation is performed. If it does not meet the strength requirements, the toe angle is adjusted to 8°, which is the minimum limit angle for structural production design. In addition, the beveled rib elbow plate 6 on the back of the vertical support member can be replaced with a ribbed elbow plate 7 (such as Figure 5 ).

[0044] The fatigue life of the fatigue free edge D is affected by the thickness and material of the vertical support, and can be optimized by increasing the thickness of the vertical support and replacing it with high-strength steel.

[0045] The fatigue life of the fatigue free edge E is affected by its own arc radius, thickness and material. When the radius of the fatigue free edge E is larger, the fatigue free edge E is more relaxed. At this time, the fatigue strength of the fatigue free edge E is greater and the fatigue life is higher.

[0046] In the above steps, the fatigue strength of the fatigue point needs to be recalculated every time the optimization work is completed. If the fatigue life does not meet the requirements, the optimization is continued until the fatigue strength of the fatigue point meets the design requirements. The optimized vertical support member 5 is as follows: Figure 5 shown.

[0047] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A design method for improving fatigue strength of ship superstructure, characterized in that: The steps of the method include: Determine the fatigue point position of the vertical support members on the side peripheral wall structure of the ship superstructure; Establish a finite element fatigue strength model, input each fatigue point into the model calculation, load the wave load under the whole ship working condition into the model, and obtain the structural stress of the fatigue point; Calculate the fatigue life of the fatigue point based on the plate thickness, material and SN curve at the fatigue point; The fatigue life is divided into intervals, the interval corresponding to the fatigue life of each fatigue point is determined, and the fatigue point is optimized based on the interval corresponding to the fatigue life.

2. The design method for improving fatigue strength of ship superstructure according to claim 1, characterized in that: The fatigue points are divided into fatigue welding points and fatigue free edges based on their locations.

3. The design method for improving fatigue strength of ship superstructure according to claim 1, characterized in that: The steps of dividing the fatigue life into intervals, determining the intervals corresponding to the fatigue life of each fatigue point, and optimizing the fatigue points based on the intervals corresponding to the fatigue life include: if the fatigue life of the fatigue point is greater than or equal to 25 years, the fatigue strength requirement is met, otherwise the fatigue point needs to be optimized.

4. The design method for improving fatigue strength of ship superstructure according to claim 3, characterized in that: The period of fatigue years between 0 and 25 years is divided into three intervals: the period greater than or equal to 20 years and less than 25 years is divided into the first interval, the period greater than or equal to 10 years and less than 20 years is divided into the second interval, and the period less than 10 years is divided into the third interval. The fatigue points are optimized based on the intervals corresponding to the fatigue years of the fatigue points.

5. The design method for improving fatigue strength of ship superstructure according to claim 4, characterized in that: If the fatigue age of the fatigue point corresponds to the first interval, the fatigue point is polished.

6. The design method for improving fatigue strength of ship superstructure according to claim 4, characterized in that: If the fatigue life of the fatigue point corresponds to the second interval, optimization is performed by changing the thickness and material of the component.

7. The design method for improving fatigue strength of ship superstructure according to claim 4, characterized in that: If the fatigue life of the fatigue point corresponds to the third interval, the factors affecting the fatigue life of each fatigue point are first determined, and then the structure of the vertical supporting member is optimized based on each factor.

8. The design method for improving fatigue strength of ship superstructure according to claim 7, characterized in that: Factors affecting the fatigue life of fatigue points include the through-weld hole form, bottom end length and toe end arc angle of the vertical support member. The fatigue life can be improved by changing the through-weld hole form, increasing the bottom end length and reducing the toe end arc angle.

9. The design method for improving fatigue strength of ship superstructure according to claim 8, characterized in that: The size of the through-weld hole must be less than one-quarter of the height of the vertical support.

10. The design method for improving fatigue strength of ship superstructure according to claim 1, characterized in that: When establishing the finite element fatigue strength model, fine mesh division is performed around the fatigue point. The size of the fine mesh is t·t, where t is the plate thickness in the fatigue point area.

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