Fatigue point finite element mesh processing method

Abstract

The invention provides a fatigue point finite element mesh processing method. The method comprises the following steps: determining the position of a fatigue point in a high stress area; performing initial grid division on the ship body model; based on the plate thickness at the fatigue point, selecting a value which is multiple times of the plate thickness as a reference to further refine grid parameters in the area around the fatigue point; optimizing the shape of the grid; classifying the types of the fatigue points, and selecting a plate unit or a rod unit as a calculation model according to the type of each fatigue point. The method can accurately calculate the fatigue strength of the fatigue point, and ensures the structural design strength of the ship.

Description

Technical Field

[0001] The invention relates to the field of ship fatigue strength calculation, and in particular to a fatigue point finite element mesh processing method. Background Art

[0002] During the voyage of a ship, when the ship experiences pitching, heaving, torsion, etc., stress is easily concentrated at the connection parts of the components in the high stress areas of the hull structure, causing fatigue damage to the hull structure.

[0003] Therefore, when designing the hull structure, it is necessary to check the fatigue strength and improve the node design of the structure to ensure that the hull structure has sufficient fatigue life during the ship's shipping process. At present, when checking the fatigue strength of fatigue points in high stress areas, a finite element mesh model of the fatigue point is usually established, and the fatigue load is loaded according to the calculation conditions to perform fatigue spectrum analysis to calculate the fatigue life. Among them, the mesh quality and accuracy of the fatigue point finite element mesh model directly affect the calculation results, so the meshing method greatly affects the calculation of fatigue life. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the related art, an object of the present invention is to provide a fatigue point finite element mesh processing method for accurately calculating the fatigue life of ship structural parts.

[0005] To achieve the above-mentioned and other related purposes, the present invention provides a fatigue point finite element mesh processing method, the method comprising the following steps:

[0006] Determine the location of fatigue points within high stress areas;

[0007] Perform initial meshing of the hull model;

[0008] Based on the plate thickness at the fatigue point, a value several times the plate thickness is selected as a reference to further refine the mesh parameters in the area around the fatigue point;

[0009] Optimize mesh shape;

[0010] The types of fatigue points are classified, and plate elements or rod elements are selected as the calculation model according to the types of each fatigue point.

[0011] Optionally, the locations of the fatigue points include fuel tanks, engine rooms, cargo holds, superstructures, cabin sheds and hatch coaming areas.

[0012] Optionally, the refined grid parameters include grid size, shape and grid refinement range.

[0013] Optionally, based on the plate thickness at the fatigue point, a grid size of t×t is selected, where t is the plate thickness at the fatigue point.

[0014] Optionally, based on the plate thickness at the fatigue point, the mesh refinement range is 10t, t is the plate thickness at the fatigue point, and the mesh refinement directions are six directions around the fatigue point: up, down, front, back, left, and right.

[0015] Optionally, the number of refined grids is controlled within 80,000.

[0016] Optionally, the step of trimming the mesh shape is: no triangular mesh can appear within the mesh refinement range, and if a triangular mesh appears, the mesh shape is optimized.

[0017] Optionally, the step of trimming the mesh shape further comprises: using a quadrilateral mesh transition in a transition region between the initial mesh and the refined mesh.

[0018] Optionally, the types of the fatigue points are fatigue welding points and fatigue free edges.

[0019] Optionally, the step of selecting plate elements or rod elements as the calculation model according to the type of each fatigue point is: if the type of the fatigue point is a fatigue welding point, the plate element is used as the model for calculating the fatigue strength; if the type of the fatigue point is a fatigue free edge, the plate element is used as the model for calculating the fatigue strength, and the rod element is used to check the axial bending stress of the fatigue free edge.

[0020] As described above, the fatigue point finite element mesh processing method of the present invention has the following beneficial effects: determining the fatigue area to be investigated and classifying the fatigue position into types, and when establishing the finite element mesh model, firstly performing initial mesh division on the entire hull model, and then refining the mesh of the fatigue area to accurately analyze the structural stress in the fatigue area. Finally, selecting a suitable calculation model for calculation according to each type of fatigue area. The above method can realize accurate calculation of fatigue strength, thereby ensuring the design strength of the ship structure and safe navigation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Shown is a schematic flow chart of a fatigue point finite element mesh processing method according to an embodiment of the present invention.

[0022] Figure 2 It is a schematic diagram showing fatigue points of brackets at both ends of the superstructure and the cabin hangar enclosure wall in an embodiment of the present invention.

[0023] Figure 3 It is a schematic diagram showing fatigue points in the negative corner area of ​​the main deck of the cabin in an embodiment of the present invention.

[0024] Figure 4 It is a schematic diagram showing fatigue points of the cross-structure of the superstructure perimeter wall, transverse bulkhead and cofferdam top plate in an embodiment of the present invention.

[0025] Figure 5It is a schematic diagram showing the fatigue point at the toe of the hatch coaming structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] like Figure 1 As shown, this embodiment provides a fatigue point finite element mesh processing method, which can achieve the purpose of accurately calculating fatigue life, ensuring the structural strength of the ship, and safe navigation.

[0032] The steps of the fatigue point finite element mesh processing method include:

[0033] S1. Determine the location of fatigue points in high stress areas.

[0034] Based on the structural characteristics and load conditions of container ships, and according to calculation experience, the high stress areas of the whole ship are sorted out. For example, high stress areas generally appear in the fuel tank, engine room, cargo hold, superstructure, cabin shed and hatch coaming area. The fatigue analysis points are generally located in the large opening of the upper continuous deck of the engine room, the negative corner of the engine room, the bulkhead door hole, the brackets at both ends of the superstructure and the cabin shed wall, the cross intersection of the bulkhead, and the hatch coaming top plate and the toe end of the longitudinal plate in each area.

[0035] S2. Perform initial meshing on the hull model. Based on the plate thickness at the fatigue point, select a value several times the plate thickness as a reference to further refine the mesh size in the area around the fatigue point.

[0036] First, import the hull model into the software, and then the hull model can be initially meshed manually or automatically generated by the software. At this time, the size of the mesh is set to be relatively large, for example, the size of each mesh can be 800mm×800mm. For the convenience of description, the initially divided mesh is called a coarse mesh, and the size of the coarse mesh is not limited in this embodiment. For the convenience of calculation, structures such as holes that are smaller than the coarse mesh size and are non-fatigue points can be omitted in the hull model for simplification.

[0037] For the location of the fatigue point, the hull model needs to be displayed in the original scale to ensure the accuracy of the calculation results. When the coarse grid division work is completed, the coarse grid in the area around the fatigue point is further refined, and a smaller fine grid is further extracted from the coarse grid. In this embodiment, the parameters of the refined grid include the grid size and the grid refinement range. The grid size is the fine grid size, and the grid refinement range is the fine grid range. The purpose of extracting the fine grid from the coarse grid can be achieved according to the fine grid size and the fine grid range. In this embodiment, the fine grid size and the fine grid range are based on the plate thickness at the fatigue point. If the plate thickness at the fatigue point is t, the size of the fine grid is t×t, and the fine grid refinement range is 10t. Here, the refinement range refers to the distance of ten plate thicknesses extending in six directions of up, down, front, back, left and right with the fatigue point as the center. It should be noted that the boundary of the fine grid needs to be selected to the whole structure on the hull (such as the deck, longitudinal continuous bulkhead and transverse bulkhead). If the boundary of the fine grid is not directly selected to the whole structure, that is, the boundary of the fine grid is still a certain distance away from the whole structure, the area between the whole structure and the fine grid boundary is meshed to achieve transition. The transitional grid size here is between the coarse grid and the fine grid size, and the division method can be manual or automatic by software.

[0038] S3. Optimize the mesh shape. No triangular mesh should appear within the mesh refinement range. If a triangular mesh appears, it should be adjusted to a quadrilateral mesh. In addition, quadrilateral mesh transition should be used as much as possible in the transition area between coarse mesh and fine mesh.

[0039] To facilitate calculation, the refinement range of the fine grid should not be too large, and the number of grids should be controlled within 80,000 grids.

[0040] For example, the fatigue inspection points of the brackets at both ends of the enclosure are generally more in the superstructure and cabin shed areas. The enclosure is subjected to torsion and compression, so the brackets at both ends of the enclosure need to be inspected in detail, such as Figure 2 As shown in P and Q.

[0041] The thickness of the wall plate is 8mm, while the thickness of the bracket plate itself is 15mm. The fatigue point here examines the fatigue strength of the bracket plate itself, so the mesh size is the thickness of the bracket plate 15mm×15mm, and the mesh refinement range is the bracket plate itself and the range of 150mm outside the two bracket toes;

[0042] For superstructures, engine rooms or other areas, door holes are usually opened on the bulkhead according to the layout of the cabins. The form of the door holes will be different for different cabin types. When subjected to hull loads, the four corners of the door will be deformed due to twisting and squeezing with the structure, so the four corners of the door need to be inspected. In order to avoid stress concentration at the four corners, the four corners of the door should be made into arcs as much as possible.

[0043] When establishing the finite element mesh for the door frame, the plate thickness of the bulkhead where the door hole is located is 7mm, and the plate thickness around the door hole is 10mm. The mesh size is 10mm×10mm of the bulkhead plate thickness around the door hole. The mesh refinement range is within 100mm outside the door hole. It is also possible to refine only the four arc corners of the door.

[0044] Usually, the negative corners of the main deck and second deck of the engine room are subject to great structural stress. In order to resist the structural torsion strength, the plates in the negative corners are set very thick, basically more than 50mm and made of high-strength steel, such as Figure 3 As shown by the middle point T, negative corner areas generally need to be inspected in depth.

[0045] When establishing finite element meshes for negative corners, it should be noted that the shape of the negative corners is not a simple arc, and the arc form needs to be accurately established according to the structural diagram. Figure 3 The plate thickness of the negative corner is 70mm, the plate thickness of the deck is 35mm, and the grid size is 70×70mm, which is the thickness of the deck plate at the negative corner. The grid refinement range is within 700mm outside the arc of the negative corner.

[0046] Since ventilation equipment and boiler equipment need to be installed in the main deck and second deck areas of the engine room, it is necessary to open multiple large openings continuously on the main deck and second deck. These openings have an impact on the fatigue strength of the main deck and second deck areas and need to be examined in detail, especially when several large openings are opened continuously in one area.

[0047] When establishing the finite element mesh for the large opening, similar to the method of handling the negative corners of the cabin, the mesh size is the thickness of the deck where the opening is located.

[0048] For the cross-intersection structure of transverse and longitudinal bulkheads, it is easy to cause structural stress concentration, such as Figure 4 The S in the figure is the intersection of the superstructure wall, transverse bulkhead and cofferdam top plate, which needs to be examined in detail.

[0049] For the structural cross intersection, the fatigue point mesh size is generally selected from the minimum plate thickness of the cross intersection structure, and the mesh refinement range is 10 plate thicknesses above, below, front, back, left, and right of the cross intersection.

[0050] The hatch coaming structure is located at the top of the main hull deck opening and is usually made of thick high-strength steel. Stress concentration is likely to occur at the toe of the longitudinal hatch coaming, such as Figure 5 The V point in the middle needs to be inspected. The inspection point at the toe end is similar to the inspection point at the bracket.

[0051] S4. Classify the types of fatigue points and select a calculation model according to the type of each fatigue point.

[0052] The types of fatigue points are fatigue welding points and fatigue free edges. If the type of fatigue point is fatigue welding point, plate element is used as the model for calculating fatigue strength. If the type of fatigue point is fatigue free edge, plate element is used as the model for calculating fatigue strength, and rod element is used to check the axial bending stress of fatigue free edge.

[0053] For fatigue points on the bracket, there are both fatigue welding points and fatigue free edges; for fatigue points at door holes, the fatigue point type is fatigue free edge; for negative corner type, fatigue inspection points are mainly free edges around the negative corner; for large opening area type on deck, fatigue inspection points are mainly free edges around the opening; for cross structure type, fatigue inspection points are mainly cross welding points, and the front, back, top, bottom, left and right of the cross points need to be listed as the welding point inspection range; for the toe type of longitudinal hatch coaming, fatigue inspection points are similar to the bracket type, mainly the free edge of the longitudinal hatch coaming and the toe welding point.

[0054] After the above mesh modeling is completed, the wave load under the whole ship working condition is loaded into the calculation model to calculate the structural stress of the fatigue point.

[0055] 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 fatigue point finite element mesh processing method, characterized in that: The steps of the method include: Determine the location of fatigue points within high stress areas; Perform initial meshing of the hull model; Based on the plate thickness at the fatigue point, a value several times the plate thickness is selected as a reference to further refine the mesh parameters in the area around the fatigue point; Optimize mesh shape; The types of fatigue points are classified, and plate elements or rod elements are selected as the calculation model according to the types of each fatigue point.

2. The fatigue point finite element mesh processing method according to claim 1, characterized in that: The locations of the fatigue points include the fuel tank, engine room, cargo hold, superstructure, engine room shed and hatch coaming area.

3. The fatigue point finite element mesh processing method according to claim 1, characterized in that: The mesh refinement parameters include mesh size and mesh refinement range.

4. The fatigue point finite element mesh processing method according to claim 3 is characterized in that: Based on the plate thickness at the fatigue point, the grid size is selected as t×t, where t is the plate thickness at the fatigue point.

5. The fatigue point finite element mesh processing method according to claim 3 is characterized in that: Based on the plate thickness at the fatigue point, the mesh refinement range is 10t, t is the plate thickness at the fatigue point, and the mesh refinement directions are six directions around the fatigue point: up, down, front, back, left, and right.

6. The fatigue point finite element mesh processing method according to claim 1, characterized in that: The number of refined grids is controlled within 80,000.

7. The fatigue point finite element mesh processing method according to claim 1, characterized in that: The step of trimming the mesh shape is as follows: no triangular mesh should appear within the mesh refinement range, and if a triangular mesh appears, the mesh shape is optimized.

8. The fatigue point finite element mesh processing method according to claim 7, characterized in that: The step of modifying the mesh shape further includes: using a quadrilateral mesh transition in a transition area between the initial mesh and the refined mesh.

9. The fatigue point finite element mesh processing method according to claim 1, characterized in that: The types of the fatigue points are fatigue welding points and fatigue free edges.

10. The fatigue point finite element mesh processing method according to claim 9, characterized in that: The step of selecting plate elements or rod elements as the calculation model according to the type of each fatigue point is: if the type of the fatigue point is a fatigue welding point, the plate element is used as the model for calculating the fatigue strength; if the type of the fatigue point is a fatigue free edge, the plate element is used as the model for calculating the fatigue strength, and the rod element is used to check the axial bending stress of the fatigue free edge.

Images