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The calculation model of hull local strength based on ANSYS software

Abstract: the strength of hull structure is a problem that must be considered first in the process of hull design and construction. In the traditional design and calculation, meeting the requirements of specifications is taken as the design premise, and it is considered to meet the strength requirements at the same time. However, many factors in the actual navigation of ships cannot be estimated in advance, so the problem of strength safety has always been a focus of attention. With the introduction of views from all industries of finite element, various finite element software have been introduced to calculate and check the hull strength. Taking the strength analysis of a ship as an example, this paper analyzes the structural characteristics and stress conditions of the ship in detail. Aiming at the strength calculation of the front wall of the cab and the strong components of the superstructure, a finite element model processing method of segmented split modeling is proposed. It is proved that such a treatment method can meet the requirements of strength calculation and the calculation model is simple, which has a certain practical significance for the treatment of related problems of hull superstructure strength calculation

Introductionfinite element method is a numerical method to solve engineering and mathematical physics problems, also known as finite element method. It is the application and development of matrix method in the fields of structural mechanics and elastic mechanics. Because of its versatility and effectiveness, the finite element method has been widely used in engineering analysis, and has become an important part of computer-aided design and computer-aided manufacturing

ansys finite element analysis software has extremely powerful pre and post-processing and calculation and analysis capabilities, can simulate the coupling effect between various physical fields such as structures, and can realize the "whole process simulation" and "whole process analysis" of structures. Therefore, it provides convenience for static calculation and dynamic calculation in ship structure. Taking the strength analysis of a ship as an example, this paper proposes a finite element model processing method of segmented split modeling for the strength calculation of the front wall of the cab and the strong components of the superstructure

II. Determination of allowable stress

the front end wall and superstructure of the ship's cab are made of aluminum alloy, with a yield strength of 215n/mm2 and a tensile strength of σ B=300n/mm2, the allowable stress standard is 175/k. The material coefficient K is calculated according to the provisions of the sea Code: k=235/σ 0.2, and the non proportional elongation stress in the annealed state is 124n/mm2, then[ σ]= 1. According to the structure and principle, it is divided into mechanical type and electronic type; The mechanical type is the traditional product 75/k=175/(235/125) =93n/mm2

III. model processing and strength analysis

no matter from the perspective of performance 1 Simplified analysis of front end wall calculation model

for the front end wall of the cab, because most of the alloy plate has been excavated to install glass, the structural strength has been greatly weakened. Therefore, when checking the front wall strength, the space plate beam structure is used for simulation, and the shell plate element and beaml88 solid element are used to simulate the plate and skeleton structure of the structure respectively. The partial load of the glass is taken as the same distributed load as that of other parts, acting on the window stiffener and horizontal truss equivalently, and the calculated load of other parts is taken as the calculated water head, which is uniformly distributed in the plane. Because the whole structure is relatively weak compared with the enclosure and the upper and lower deck structures, the constraints around the model are safe to take the free support. The corresponding components and section elements of the front wall are shown in Table 1. Table 1 profile elements of end wall components

2 Simplified analysis of calculation model of superstructure strong members

for the direct calculation of superstructure and deck strong members of each layer, layered and segmented modeling is adopted. In order to correctly check the bearing capacity of the superstructure deck and the bearing capacity of the side wall, the calculation model is simplified to a spatial beam system structure. The beam system is composed of deck longitudinal girders, strong beams and side wall vertical girders, which can reduce the emissions of CO2 and SO2 by more than 64 million tons in China. Various profiles together with their strip plates are considered as beam elements, and beam element beaml88 is used in the structural model for simulation

take the compass deck area as an example. The calculation range of the compass deck area is from 57 rib to 80+400 rib. The calculated load: 4.5kn/m2 for the deck and 15.5kn/m2 for the side wall (as calculated, see Table 3). Because its profile is aluminum alloy, and its connection with the lower deck and transverse bulkhead is relatively weak, and its two ends of the column are approximately twisted, so the deck longitudinal truss at #80+400 rib, the connection between the side wall, rear end wall, vertical truss and the lower deck, and the boundary conditions at the connection between the column and the lower deck are all relatively safe to take free support. The deck load is equivalent to the linearly uniformly distributed cutting load acting on the deck girder, and the strong beam is used as the supporting member of the girder

the selection of relevant calculation components and their profile elements are shown in Table 2. Table 2 component section elements

3 Calculation of external force of structure

calculation of water head h according to h= αδ ( βλ-γ) M hmin=0.005l+1.25. The calculation of external force head of each layer of this fishery administration law enforcement ship is shown in Table 3. Table 3 Calculation of external force head on each deck of fishery administration law enforcement ship

IV. conclusion

with the gradual improvement of numerical analysis methods, especially the rapid development of computer computing speed, the whole computing system has less and less time for solving operations. ANSYS software developed by American ANSYS company, as one of the most famous finite element analysis software in CAE field, has been widely used in industrial field. Practice has proved that for the calculation of the superstructure of the hull, such a split modeling method can not only meet the requirements of strength calculation, but also reduce the time of model establishment and calculation. Compared with the treatment method of spatial plate girder structure modeled by the whole ship's local cabin, the calculation result is slightly deviated, but for the superstructure, this treatment method is feasible. (end)

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