In recent years, many companies have also proposed a certain pre-production issue for large marine valves (such as those with a diameter of Φ5350mm). However, based on the existing pre-production manuals for marine valves and corresponding standards, there is a significant lack of statistical data on the design of large-diameter marine valves, as well as a lack of pre-production experience for large marine valves. Therefore, a thorough and accurate calculation analysis needs to be carried out, and a transformation and force analysis calculation needs to be performed. Then, the final results should be implemented for the pre-production. Thus, it is ensured that it has satisfactory tightness and sufficient strength. However, due to the particularity of the structure of marine valves, it is difficult to perform analysis and calculation using classical mechanical methods. Only when it is considered appropriate can the finite element method be used for analysis and calculation. For the valve body and butterfly plate of the marine butterfly valve with a diameter of Φ5350mm, the analysis calculation is performed using the finite element method to provide theoretical basis for the reasonable structure and pre-production optimization, and to prevent unnecessary material consumption. 

The essence of the finite element analysis method is to approximate twice, transforming an elastic continuum with infinitely many degrees of freedom into a unit assembly with only a finite number of degrees of freedom, thereby simplifying the problem into a structural issue suitable for numerical solution. The first approximation is the division of the elements, and the very accurate boundaries are dispersed into simple boundaries. The continuous object is dispersed into a series of units only connected by nodes, and the dispersion is also called meshing clarification. The dispersed unit assembly will replace the original elastic continuum; the second approximation is that the real and complex displacement distribution is approximately expressed in the final result of the analysis, allowing one to visually see the final result of the analysis calculation. 

This requirement clearly states that up to now, the development and practical application of the finite element analysis method have relied on a crucial tool: the use of computers in actual calculations. By employing systematic software on computers to perform analysis calculations, the analysis speed has been significantly increased, and it has achieved a very crucial effect in practical applications. 

1. The structure of marine valves 

For this vessel, the valve is designed with a positive structure. The valve body is of a double-flange and ring-ribbed type. The butterfly plate is of an irregular plate type, with different types of ribs and plates reasonably arranged on it. The structure is quite complex. It was chosen for this purpose because it is considered suitable. Manual calculation was used to determine the working volume, which was quite labor-intensive. Therefore, a three-dimensional finite element analysis software was employed for the calculation. 

Finite element analysis of the valve body 

Structural disintegration is the foundation of the finite element method. The so-called structural disintegration refers to the division of the elastic assembly into a finite number of element bodies according to certain rules, so that adjacent elements are connected at the nodes, and the loads between elements are only transferred through the nodes. Structural disintegration is also called clear grid division, and the aggregated body of the disintegrated elements will replace the original elastic assembly. All the calculation analyses will be carried out on this calculation plate. 

First, establish a finite element plate model with a simple and concise structure for the valve body. 

2.1 Boundary Condition Confirmation 

The variations of the valve body are mainly influenced by the self-weight of the valve body itself and the weights of other components of the marine valves (such as the valve plate, power unit). Since this needs to fully consider the weights of other components when calculating, we choose to calculate the variations of the valve body when the marine valve is placed vertically, with a loading group of 3g gravitational acceleration in the Y direction. The bottom of the valve body is also loaded with constraints in the Y and X directions. At the same time, considering that the diameter of the marine valve is large, the end face effect of the pipeline will be revealed. Because this requires loading the Z direction constraints of the marine valve on the two flanges. 

2.2 Analysis of Load Conditions 

Because the valves used in ships have a large front diameter, it is commonly believed that a steel plate welding structure is suitable and is adopted. The main consideration here is the impact of the overall weight of the ship valve on the valve body, to prevent the valve body from deforming due to excessive self-weight, which would affect the normal operation of the ship valve. The gravitational acceleration is g, but from a safety perspective, we calculate it as 3g. By loading Y = 3g and through finite element analysis, it can be determined the deformation situation of the valve body under three times the gravitational acceleration. The following is the deformation situation of the valve body. As can be seen, the largest deformation amount is 0.6mm. 

Finite element calculation analysis of the valve plate 

Based on the past experience in designing marine valves, a size is first assigned to the main board and its ribs on the valve plate, because it belongs to the special-shaped plate. This is necessary to accurately establish the group stiffness matrix for the group finite element analysis. This also requires group modeling, which can ensure the continuity and force-related characteristics of the entire butterfly plate shape, and guarantee the correctness of the final calculation results. 

3.1 Boundary Condition Confirmation 

During operation, the motor rotates the valve shaft and the valve plate together by reducing its speed. The valve shaft transmits the torque to the valve plate through the connecting piece on the valve plate. When the valve plate is subjected to the force of the fluid medium, the force is also transmitted to the valve body through the connecting piece. Because the constraint conditions at the connecting piece on the valve plate should be: the three translational coordinates (X, Y, Z) should be restricted, and the three rotational coordinates should also be restricted. Therefore, the inner surface of the connecting piece should be compared to be more favorable than the corresponding node of the unit element, and its displacement and rotation angle should be zero. 

3.2 Analysis of Load Conditions 

First, consider the effect of the fluid medium. In this assumption, the office pressure is set at 0.1 MPa (1.0 kg/cm²), but from a safety perspective, we calculate it as Pressure = 0.3 MPa (3 kg/cm²). 

The situation of changes before and after the valve plate deformation is described. The major deformation occurs at the outermost point on the core surface perpendicular to the rotation axis of the valve plate. In this case, the maximum deformation is Zmax = 0.21mm. 

4 Analysis of the Final Results 

Analysis of valve variations in marine applications involves the fact that the main components of marine valves will undergo changes when subjected to force. The final results can be conveniently used to closely examine and analyze the post-variation conditions, and to conduct comparative analyses of the states of the components before and after the variations. This can also determine the volume of the variation in the original design intent of the component. Through calculation and analysis, if the variation of the component after being subjected to force exceeds the allowable range or is extremely small, corrections will be made to the structure (such as thickness), thus obtaining a reasonable structure. 

The stress analysis of marine valves is conducted after the force analysis of marine valves. Stress will be generated during this process, and the final result can be easily understood. The larger stresses on the components can be identified. From the perspective of force, the rationality of the component structure is analyzed and optimized. At the positions with high stress, measures such as installing reinforcing ribs can be reasonably adopted to enhance the marine valves. 

From the above analysis, by conducting stress analysis of the main components of marine valves and deformation analysis after the application of force, the positions with higher stress and greater deformation in the structure can be identified. These two aspects are combined to correct the structure of the marine valve, resulting in a reasonable design that ensures sufficient strength and rigidity, avoids heavy structure, reduces material, resource and energy consumption, and lowers production costs. 

5 Conclusion 

After conducting simulation analysis and calculation on marine valves, the following conclusions can be drawn: 

(1) It is possible to calculate the stress distribution on the marine valve components and display the stress values. Thus, the positions with higher stress can be identified and optimized. During the pre-design stage of the product, latent problems can be detected, thereby reducing the number of trial attempts and the associated costs. 

(2) The deformation of the valve plate after being subjected to force can be observed, and the corresponding deformation value can also be obtained. In this case, the position where the valve plate undergoes the greatest deformation is the outermost point on the core surface perpendicular to the rotation axis of the valve plate. This can be targeted for strengthening to prevent the waste of raw materials. 

(3) Through calculation and analysis, the structural assumptions are rationalized and optimized, ensuring that the assumed objects have sufficient strength and stiffness, while also saving resources and reducing costs. 

(4) The reliability of the products and the engineering design has been ensured; the time for launching the products onto the market has been shortened. 

(5) Conduct an accident analysis on the exposed problems of the marine valves to identify the root cause of the issues. 

The application of finite element analysis technology in the presetting of marine valves has led to a qualitative leap in the presetting level of marine valves. After conducting stress calculations and analyses on the key structures of marine valves, guiding suggestions for the presetting of marine valves were provided.