Application of ANSYS finite element analysis in th

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The application of ANSYS finite element analysis in the frame structure of deep submersibles

1 Introduction

the 21st century is the century of marine exploration and development, and the surface area of the earth is 511 × 108 km2, of which the area of the ocean is 3 six × 108km2, accounting for 71% of the total surface area of the earth. The ocean is one of the treasure lands and high-tech fields that human beings have yet to develop The international deep sea and ocean floor, which can reach a maximum depth of about 11000 meters, are rich in strategic metals, energy and biological resources. These are the largest potential treasures on earth that have not been fully recognized and utilized by mankind. Mankind has gradually turned its attention to the resource rich ocean, and the development of marine resources has become the focus of competition among coastal countries. However, the underwater world is under great pressure and the environment is bad, so ordinary equipment is not competent. As an indispensable technical equipment for marine exploration and development, underwater rescue and life-saving projects, major countries in the world have vigorously developed this technology. As a major maritime country, China should play a role in the development and application of deep submersibles

the carrier frame is the installation foundation of all equipment of the submersible. The control cabin, battery cabin, disposable ballast, various detection equipment, buoyancy block and light shell on the submersible will be fixed on the carrier frame, so as to form a submersible with good hydrodynamic performance. At the same time, the carrier frame is also the main bearing structure for the deployment, recovery and deck fastening of the submersible. Therefore, the frame structure design is directly related to the safety of the submersible, and is the basis of the overall design of the submersible. The carrier frame shall be designed to facilitate the installation, disassembly and maintenance of equipment, instruments, buoyancy blocks and light housings; And it has sufficient strength and rigidity to ensure the deployment and recovery of the submersible and the fastening on the deck of the mother ship

2 structural form and main dimensions and parameters of the submersible frame

2.1 dimensional parameters of the submersible

total length: 2.13 meters

diameter: 0.5 meters

displacement: 330 kg

2.2 selection of materials

in order to improve the mobility and flexibility of the submersible, under the condition of ensuring sufficient strength and stiffness, the weight of the carrier frame should be as small as possible, that is, the selected manufacturing materials should have high specific strength and specific stiffness. Commonly used Submersible structures are made of titanium alloy, high-strength steel, aluminum alloy, etc. This submersible is used in Bohai Sea area and belongs to offshore submersible. In the design, the weight of the new plastic low submersible was used. The plastic has the characteristics of low water absorption, low density and high tensile strength

And a variety of bamboo fiber reinforced composites for vehicles have been developed at home and abroad. Strength analysis

3.1 calculation conditions

according to the code, when calculating and analyzing the strength and stiffness of the bearing frame, the accidental overload in the operation process and the special working conditions of the submersible when crossing the air-water interface, as well as the influence of the mother ship movement (roll, pitch, etc.) during the transportation of the mother ship should be considered. According to the requirements for the deployment, recovery and fastening of the submersible on the deck of the mother ship, the designed carrier frame should meet the following requirements: 1. Under the level IV sea condition, the two-point deployment and recovery of the submersible can be carried out normally; 2. The submersible can also be safely recovered to the mother ship deck under level 5 sea conditions; 3 when the submersible is stored in the hangar of the mother ship, it can be fixed by cables to avoid the collision between the submersible and the bulkhead in the hangar of the mother ship

it is much more dangerous to collect and release the submersible at two points under the five level sea state than to deploy and recover the submersible under the four level sea state, so the five level sea state is taken as the calculation condition to check the strength and stability of the carrier frame in the strength calculation

the carrier frame is a complex three-dimensional truss structure, and the stress condition is relatively complex. At present, there is no mature simplified calculation method and existing verification rules, so the application of structural finite element analysis software for structural strength analysis is the basic means of carrier frame strength verification. In this paper, ANSYS structural finite element analysis software is used to establish a three-dimensional structural finite element model for the curing scheme of the carrier frame, and to check the strength and stiffness under the conditions of two-point recovery and deck fastening

3.2 establishment of finite element model

the bearing frame structure of submersible is complex, the working environment is special, and the safety requirements are very high. It is necessary to carefully investigate the stress and displacement distribution of each component and node. In the stage of establishing the geometric model of the frame, in order to truly reflect the geometric characteristics and reduce the simplification of the actual structure, except the lifting beam in the middle of the hull and the equipment frame in the middle are established in line structure, other components are established in plate structure. When dividing the geometric model into grids, two types of elements are mainly used, that is, the dynamic display element of plate experimental data and experimental curve, and then the beam element is used to consider whether there is air in the oil system. In the process of lattice division, in order to improve the calculation accuracy, all plates are cut into regular forms to obtain quadrilateral surface elements, and the geometric structure of the beam element is truly reflected by giving different section attributes to the beam element

Figure 1 finite element model of submersible

3.3 constraint and load application

treatment of boundary conditions of finite element model: free support of lifting point, constraint of degrees of freedom in three directions of lifting point x, y, Z and rotation degrees of freedom in three directions; Under the fastening condition of the mother ship, the frame support points are supported freely, and the vertical degree of freedom of the bottom web line under the support ring is constrained

load application method: the submersible has a wide range of equipment, which is loaded in two forms during the loading process. One is the self gravity of the frame, which is expressed in the form of gravity acceleration, and the other is the instruments and equipment on the submersible, which will be simplified as a concentrated force applied to the corresponding nodes. The gravity of small equipment is applied to one or several nodes in the form of concentrated force; The gravity of larger equipment is applied to corresponding multiple nodes according to the structural form of equipment base or support

3.4 analysis of calculation results

after finite element calculation, the deformation of the submersible frame structure when the deck is fastened and retracted at two points (Figure omitted)

according to the calculation results of synthetic stress under two working conditions of two-point retraction and release and automatic regulation of cooling flow by the electric control system of deck fastening, except for a few nodes, the overall stress distribution of the submersible frame is relatively uniform, with the maximum stress of 58.6mpa at two-point retraction and release and 18.7mpa at deck fastening. This shows that the strength of each component of the submersible frame has been better used, and the load acting on the carrier frame has been effectively transferred. According to the displacement calculation results under the two working conditions of two-point retraction and deck fastening, the relative deformation of the installation position of each equipment and buoyancy block is very small, which has no impact on the equipment and buoyancy block installed on the submersible

4 conclusion

the carrier frame involves a wide range of contents. In its structural design, it is necessary to consider its own material properties, welding process, allowable stress, structural form, member section shape, installation and maintenance of equipment, mass distribution along the length direction, two-point lifting position, working environment (sea state and external load) of the submersible, etc. Therefore, the design of a safe, reliable and light-weight submersible frame should not only choose materials with low density, high specific strength and high corrosion resistance, but also fully consider the installation, disassembly and maintenance of all equipment and buoyant materials on the submersible, the transmission of load on the submersible frame under various working conditions, and the processing and construction of the carrier frame under the local conditions of strength permission

according to the strength analysis results of the carrier frame under two-point recovery and deck fastening conditions, it can be considered that the structural type of the submersible frame is reasonable, the strength of each component has been better utilized, and the load acting on the carrier frame has been effectively transmitted, so the design of the submersible frame is successful. (end)

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