Analysis on the junction point's stress located at considering fluid-solid coupling effects for support arm under different wall thickness
Abstract
Fluid-structure interaction has a significant effect on stresses in the hinge point because of the impact of ocean currents to the pipeline. Aimed to support arms for deep-sea mining, numerical analysis method and the finite element software ADINA were adopted to analyze the pipeline structure - external fluid mutual coupling effect on stress at the hinge point. The results were shown that: (1) In the case of different wall thickness, the stress changes of the entire pipeline is relatively small, stress located mainly these places close to the junction in the pipelines, the maximum stress exists at the upper connection; (2) With wall thickness of the support pipe increasing, the maximum stress decreases, and when wall thicknesses changed from 9.5mm to 28.7mm interval 2.4mm ,the maximum stress value decreased 19.3%, 15.9%, 13.5%, 11.7%, 10.3%, 9.2%, 8.3%, 7.6% ;(3) With wall thickness increasing, the minimum stress value also reduced, and a minimum stress values decreased 19.9%, 14.0%, 5%, 14.6%, 28.7%, 15.9%, 8.6%, 2.7%,respectively.
Keywords
Download Options
Introduction
Fluid-structure interaction problems and general multi-physics problems are often too complex and difficult to analyze and solve, so they would be completed by experimental or numerical simulation method. Because of the Computational Fluid Dynamics and computational structural dynamics field study obtain great progress, these achievements make the fluidstructure interaction numerical simulation is completed.
At the same time, the way of Newton-Raphson and Fixed point iteration can be used to solve the problem which is involve in Fluid-structure interaction. In view of Newton-Raphson iteration method the monolithic [1] [2] [3] and partition [4] [5] method has been widely used. We can use the Newton-Raphson method to solve the nonlinear fluid equations and structural equation. The problem of the system lacking the knowledge of Jacobi matrix iteration method can be solved by the iterative linear equations within the Newton- Raphson. Besides it can use the product finite difference of vector Jacobi to approximate.
As we all know, Newton-Raphson method can not only work out the state flow and structural problems in the whole liquid and solid domain, but also may be applied to the FSI device problem of multi-degree freedom system on the situation of interface location unknown. This domain decomposes and condenses into subspace FSI problem error [6] . Therefore, the FSI problem with the unknown location of the interface can be transformed into the problem of finding roots or fixed point.
Using the Newton-Raphson iterative interface Newton - Raphson method may be able to find the answers, such as the Jacobi approximation linear physical model [7] [8].In the coupling iteration process, using the least squares model coupling the black boxes and the Newton Falla comparable to reverse approach for solving the domain of fluid and structure [9].This technique is based on the interface of quasi Newton least square model, and re- expresses FSI problem as the Jacobian matrix approximation technique of an unknown equation which is in the condition of system interface location and interface stress distribution. The system solves the Gauss - Seidel type and the fluid and structure solving the Jacobian matrix block quasiNewton iterative approximation least squares model [10] .The fixed point problem can be solved by fixed point iteration which is also known as the Gauss - Seidel iteration [6].It means that the fluid and structural issues have been resolved, until the change is less than the convergence criterion. However, the convergence speed is slow, especially in times of the interaction between the fluid and structural strong, such as High density fluid, Structure proportion or incompressible fluid. It adapt to the fixed point iteration convergence based on previously iteration, which can be stabilized and accelerated by the fastest descent relaxation factors and Aitken relaxation.
Conclusion
By studying mining institutions with the bracket connected , the pipeline was impacted by the external flow velocity of 1.8m / s, the internal conveying speed is 2 m / s, We obtained the law of effects such as stress and some meaningful conclusions as the follows.
(1) In the case of different thickness, the stress changes of the entire pipeline is relatively small, it is mainly in the pipes close to the junction, the maximum stress occurs at the upper end of the pipe connection.
(2)With the Support pipe wall thickness increases, the maximum stress decreases. From the diagram, we can calculate each increases the thickness of 2.4mm, the maximum stress value decreased 19.3%, 15.9%, 13.5%, 11.7%, 10.3%, 9.2%, 8.3%, 7.6%, and the thickness of 28.7mm reduced 64.2% than 9.5mm.From these data, the stress reducing effect can be found by increasing the wall thickness so that increasingly smaller.
(3)With the support pipe wall thickness increases, the minimum stress value decreases。From the diagram ，we can calculate each increases the thickness of 2.4mm, the minimum stress value decreased 19.9%, 14.0%, 5%, 14.6%, 28.7%, 15.9%, 8.6%, 2.7%, and the thickness of 28.7mm reduced 64.2% than 9.5mm. From these data, the stress reducing effect can be found by increasing the wall thickness so that increasingly smaller.