Virtual shell method for ship vibration forecast attached water calculation

Abstract

The invention discloses a virtual shell method for ship vibration forecast attached water calculation, which comprises the following steps of: establishing a virtual ship hull shell unit on a node of an original ship hull shell unit based on a whole ship finite element model; the grid size of the virtual hull shell unit is larger than that of the original hull shell unit; the virtual hull shell unit is used for a grid unit for carrying out attached water mass calculation. According to the method, the workload of attached water mass calculation can be greatly reduced, the calculation time is greatly shortened, calculation resources are saved, and the vibration forecasting precision is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding technology, and in particular to a virtual hull method for calculating attached water for ship vibration prediction. Background Technology

[0002] When a ship is in motion, the water surrounding the hull is also in motion. Therefore, the water outside the hull has a significant impact on the ship's vibration, which can be categorized into three aspects: the effect of gravity, the effect of damping, and the effect of inertia. The effect of inertia is reflected in the change in the equivalent mass participating in the hull's vibration. It's as if a portion of the water outside the hull vibrates along with the hull; the mass of this water outside the hull is called the attached water mass. It has a mass of the same order as or even greater than the mass of the hull, and can significantly reduce the free vibration frequency of the hull.

[0003] With the improvement of computer computing power, ship vibration prediction generally adopts a full-ship finite element model. The model mesh size is generally the longitudinal girder spacing × rib spacing, usually around 800mm. However, for some larger ships, the vibration prediction mesh will be larger.

[0004] In vibration calculation and prediction, the influence of water surrounding the hull on vibration modes needs to be considered. Currently, the mainstream method for calculating attached water mass is the virtual mass method, which typically uses the finite element mesh of the hull shell to calculate the attached water mass based on the actual waterline under full load or ballast conditions. If the shell elements are directly selected as the elements for calculating the attached water mass using the virtual mass method, the number of meshes will be large.

[0005] like Figure 1 As shown, Figure 1 This is a full-ship model for vibration calculation of a certain type of ship. The vibration calculation model uses a finite element mesh with a longitudinal girder spacing × rib spacing. In vibration calculation and prediction, the influence of water surrounding the hull on the vibration modes needs to be considered. Currently, the mainstream method for calculating the attached water mass is the virtual mass method, which usually uses the finite element mesh elements of the hull shell to calculate the attached water mass according to the actual waterline under actual full load or ballast conditions. Figure 2 This is a shell model built using a finite element mesh with longitudinal rib spacing × rib spacing. For example... Figure 2 As shown, if the shell element is directly selected as the element for calculating the mass of attached water using the virtual mass method, the number of grids will be large.

[0006] It is evident that when the ship is large and there are many computational grids, if the computing power is limited, it is difficult to calculate the mass of the adjacent water, which will lead to excessively long vibration prediction time, or even situations where the computing power is unable to calculate the vibration results. Summary of the Invention

[0007] To overcome the aforementioned deficiencies in the existing technology, the present invention provides a virtual shell method for calculating attached water for ship vibration prediction.

[0008] The present invention solves the above-mentioned technical problems through the following technical solution:

[0009] A virtual hull shell method for calculating attached water mass in ship vibration prediction includes: establishing virtual hull shell elements on the nodes of the original hull shell elements based on the full ship finite element model; the mesh size of the virtual hull shell elements is larger than the mesh size of the original hull shell elements; the virtual hull shell elements are used as mesh elements for calculating attached water mass.

[0010] Furthermore, all nodes of the virtual hull shell unit are nodes of the original hull shell unit.

[0011] Furthermore, the density of the virtual hull shell unit is less than the density of the original hull shell unit.

[0012] Furthermore, the density of the virtual hull shell unit is less than one-tenth the density of the original hull shell unit.

[0013] Furthermore, the stiffness of the virtual hull shell unit is less than that of the original hull shell unit.

[0014] Furthermore, the stiffness of the virtual hull shell unit is less than one-tenth of the stiffness of the original hull shell unit.

[0015] Furthermore, the elastic modulus of the material of the virtual hull shell unit is less than that of the material of the original hull shell unit.

[0016] Furthermore, the elastic modulus of the material of the virtual hull shell unit is less than one-tenth of the elastic modulus of the material of the original hull shell unit.

[0017] Furthermore, the number of meshes in the virtual hull shell unit is less than the number of meshes in the original hull shell unit.

[0018] Furthermore, virtual hull shell units are used as grid units for calculating attached water mass to predict ship vibration.

[0019] The beneficial effects of the present invention are as follows: the method of the present invention can greatly reduce the workload of calculating the quality of attached water, greatly reduce the calculation time, save computing resources, and ensure the accuracy of vibration prediction. Attached Figure Description

[0020] Figure 1 A full-ship model for vibration calculation of a certain type of ship using existing technology.

[0021] Figure 2 In order to adopt existing technology Figure 1 Finite element mesh of the hull shell of the ship is established.

[0022] Figure 3 In order to be in Figure 2 A finite element mesh for calculating the quality of attached water is established using the method of this invention. Detailed Implementation

[0023] The present invention will be described more clearly and completely below with reference to a preferred embodiment and the accompanying drawings.

[0024] A virtual hull shell method for calculating attached water mass in ship vibration prediction includes: establishing virtual hull shell elements on the nodes of the original hull shell elements based on the full ship finite element model; the mesh size of the virtual hull shell elements is larger than the mesh size of the original hull shell elements; the virtual hull shell elements are used as mesh elements for calculating attached water mass.

[0025] All nodes of the virtual hull shell unit are nodes of the original hull shell unit.

[0026] The density of the virtual hull shell unit is less than the density of the original hull shell unit. Furthermore, the density of the virtual hull shell unit is less than one-tenth of the density of the original hull shell unit.

[0027] The stiffness of the virtual hull shell unit is less than that of the original hull shell unit. Furthermore, the stiffness of the virtual hull shell unit is less than one-tenth of the stiffness of the original hull shell unit.

[0028] The elastic modulus of the material of the virtual hull shell unit is less than that of the material of the original hull shell unit. Furthermore, the elastic modulus of the material of the virtual hull shell unit is less than one-tenth of that of the original hull shell unit.

[0029] The number of meshes in a virtual hull shell unit is less than the number of meshes in a raw hull shell unit.

[0030] Using virtual hull shell elements as grid cells for calculating attached water mass, ship vibration prediction is performed.

[0031] Take the calculation of the adjacent water for vibration prediction of a certain ship as an example. Figure 2 This is the finite element mesh of the ship's hull. Figure 3 In order to be in Figure 2 A finite element mesh for calculating the quality of attached water is established using the method of this invention.

[0032] like Figure 2 As shown, the original hull shell unit was approximately 800mm × 800mm in size. Figure 3As shown, according to the method of the present invention, a 2400mm × 2400mm grid was used, reducing the number of outer shell grids from approximately 53,000 to approximately 7,650. The elastic modulus of the original hull outer shell unit material was 206,000 N / mm². 2 Its density is 7.85 × 10⁻⁶. -9 t / mm 3 According to the method of the present invention, the elastic modulus of the material of the virtual hull shell unit is 1 N / mm². 2 Its density is 1×10 -12 t / mm 3 To make the distinction clear in the description, the method of the present invention will be referred to as the "method using a virtual shell" in the following text, while the prior art method for calculating attached water will be referred to as the "method without using a virtual shell".

[0033] Wet modal calculations of a ship were performed on the server using the same computing configuration, with and without the virtual shell method. Using the virtual shell method significantly reduced computational costs and time, completing the calculation in approximately 62% of the time required without it.

[0034] Meanwhile, the main modes were compared, as shown in Table 1 below.

[0035] Table 1 Comparison of natural frequencies using the virtual shell method and the method without using the virtual shell method

[0036]

[0037] As can be seen from the comparison results in Table 1, the modal frequencies calculated using the virtual shell method are very similar to those calculated without the virtual shell method, and the accuracy requirements for calculation are met.

[0038] The method of the present invention can greatly reduce the workload of calculating the quality of adjacent water, greatly reduce the calculation time, save computing resources, and ensure the accuracy of vibration prediction.

[0039] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A virtual shell method for calculating attached water in ship vibration prediction, characterized in that, It includes: Based on the full ship finite element model, virtual hull shell elements are established on the nodes of the original hull shell elements. The mesh size of the virtual hull shell element is larger than that of the original hull shell element; this virtual hull shell element is used as the mesh element for calculating the attached water mass.

2. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 1, characterized in that, All nodes of the virtual hull shell unit are nodes of the original hull shell unit.

3. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 1, characterized in that, The density of the virtual hull shell unit is less than that of the original hull shell unit.

4. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 3, characterized in that, The density of the virtual hull shell unit is less than one-tenth the density of the original hull shell unit.

5. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 1, characterized in that, The stiffness of the virtual hull shell unit is less than that of the original hull shell unit.

6. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 5, characterized in that, The stiffness of the virtual hull shell unit is less than one-tenth of the stiffness of the original hull shell unit.

7. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 1, characterized in that, The elastic modulus of the material of the virtual hull shell unit is less than that of the material of the original hull shell unit.

8. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 7, characterized in that, The elastic modulus of the material of the virtual hull shell unit is less than one-tenth of that of the material of the original hull shell unit.

9. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 1, characterized in that, The number of meshes in a virtual hull shell unit is less than the number of meshes in a raw hull shell unit.

10. The virtual hull method for calculating attached water for ship vibration prediction as described in claim 1, characterized in that, Using virtual hull shell elements as grid cells for calculating attached water mass, ship vibration prediction is performed.

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