Finite Element Modeling for Transient Thermal- Structural Coupled Field Analysis of a Pipe Joint

Transcription

1 International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 88 Finite Element Modeling for Transient Thermal- Structural Coupled Field Analysis of a Pipe Joint C.G. Veeresh, Narasimhe Gowda and H.V. Lakshminarayana Abstract--- The focus of this paper is on the use of ANSYS software for thermal-structural analysis of a complex bolted-flanged connection between two pipes as shown in the accompany sketch. Traditionally, transient thermal stress analysis problems are solved first as heat transfer analysis problems, followed by stress analysis. However, it is logical to formulate and solve the problems using coupled thermal-structural analysis. Recently, ANSYS software has offered this coupled field analysis capability. The objective of this paper is to demonstrate the accuracy and versatility of this capability on a complex pipe joint. The development and validation of FEmodelling for Transient coupled thermal-structural analysis using ANSYS software is presented using a benchmark [1]. Significant results for a parametric study are graphically presented and discussed. Keywords--- Thermal Stress Analysis, Coupled Field Analysis, 1D Heat Conduction and Thermal Shock Loading I. INTRODUCTION HERMAL simulations play an important role in the design of many engineering applications, including internal T combustion engines, turbines, heat exchangers, piping systems, and electronic components. In many cases, engineers follow a thermal analysis with a stress analysis to calculate thermal stresses (that is, stresses caused by thermal expansions or contractions). The study of thermal stress is important aspect in design as they may results in mechanical failure of components. Thermal stresses are developed in body whenever any part is prevented from assuming the size and shape that it would freely assume under a change in temperature or two materials with differing thermal coefficients of expansion are used in design. Flanged pipe joints are common in pressure vessel and piping systems and are considered for case study. Transient thermal analysis determines temperature. And other thermal quantities that vary over time. Engineers commonly use temperatures that a transient thermal analysis calculates as input to structural analyses for thermal stress evaluations. Many heat transfer applications - heat treatment problems, nozzles, engine blocks, piping systems, pressure vessels, etc. - involve transient thermal analyses. A transient thermal analysis follows basically the same procedures as a steady-state thermal analysis. The main difference is that most Applied loads in a Transient analysis are functions of time Test Problem II. BENCHMARK A thick walled cylinder is shown in fig 1. Is at constant initial temperature i when its inner surface subjected to constant temperature input. The outer surface is maintained at the temperature i. fig 2 provides a schematic representation of thermal shock loading. The one dimensional solution of the governing equation gives the temperature distribution schematically shown in fig 3. The fig also shows the penetration depth. C.G. Veeresh, PG Student, Department of Design Engineering, Dayananda Sagar College of Engineering. PAPER ID: MED16

2 International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 89 Figure 1: Cylindrical Pipe Figure 2: Schematic representation of Thermal Shock Loading Figure 3: Schematic Representation Temperature Distribution and Depth of Penetration (1) Where, is the thermal diffusivity (2) At the distance (3) The finite element mesh and the time step are chosen as guided by the value. III. FE MODEL A typical FE model using axisymmetric solid element created using ANSYS is shown in fig 4. The coupled field element used is plane 13. With the Nodal DOF ux, uy, Temperature. The material properties used in the computation are given in table1. Table 1: Material Property Material Density Young's Yield stress Thermal Specific heat Mean thermal Name ( ) kg/ /m 3 modulus (E) ) pa conductivity (C) J/kg K pa. (K)W/m K expansion( 0) AISI304 Stainlesss E E E-05 Steel Grade Z5CN18.10 ISBN Bonfring

3 International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 90 Initial temperature of the body is 385 o C and a sudden thermal shock loading is applied to the inner surface. The FE model is constrained against rigid body motion in the axial direction. Component Element Total Element Total Nodes Cylindrical pipe Coupled field Plane IV. Figure 4: FE Model TARGET SOLUTION The predicted transient temperature distribution using a time step 1 sec presented in Fig 5. The thermal shock response is graphically presented in fig 6. The typical distribution of the von mises stress indused in the cylinder at T=15 is given in fig 7. Figure 5: Temperature Distribution at = 1sec and at T= 1sec, 30s The thermal shock response is presented in Fig 6. Figure 7: Stress Distribution in the Pipe

4 International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 91 Temperature Temperature vs Distance sec 3sec 7sec 10sec 15sec 20sec 25sec 30sec Distance(m) Figure 6: Thermal Shock Response V. CASE STUDY A flanged pipe joint with gasket in between shown in fig 8, is at constant initial temperature i = 385 o C and its inner surface AB is subjected to constant temperature input o = 427 o, the outer surface is maintained at the temperature i. Figure 7: A Flanged Pipe Joint Figure 8: Identification of Surfaces Between the welds, along KL and MN in fig 8, pipe and flange touch at random and at isolated points, if at all. Conductivity across this cylindrical interface is very low as compared with solid metal and is modeled as an insulator FE Model A typical finite element model using axisymmetric solid elements created using ANSYS is shown in fig 9. The coupled field element used is plane13 with the nodal DOF ux, uy, temperature, The material properties used in the computation are given in Table3. Table 3: Material Properties Thermal conductivity (K)W/m K Density ( ) kg/m 3 Specific heat (Cp) J/kg K Young's modulus (E) pa. Poisson's ratio Pipe 1.94E E E E-5 Flange 1.21E E E E-5 Weld 1.96E E E E-5 Gasket 2E E E5.49 3E-6 Mean thermal expansion( 0 ) Initial temperature of the body is 385 o C and a sudden thermal shock loading is applied to the inner surface AB.

5 International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 92 The FE model is constrained against rigid body motion in the axial direction.fe model of a flanged pipe joint with gasket in between is shown in the figure 8. And the mesh model data are shown in Table 4. Figure 9: FE Model Table 4: Mesh Model Data Component Element Total Element Total Nodes Cylindrical pipe Coupled field Plane VI. RESULT PRESENTATION The predicted transient temperature distribution is presented in fig 10. Figure 10: Temperature Distribution at T=1sec, 25sec, 60 sec The thermal shock response is presented in Fig 11. Temperature Temperature vs Distance Distance(m) 1sec 15sec 25sec 35sec 50sec 60sec Figure 11: Thermal Shock Response

6 International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 93 The typical distribution of the von misses stress induced in the cylinder at t= 15T is given in fig 12. Figure 12: Stress Distribution VII. CONCLUSION Finite Element Modeling and solution procedures are demonstrated for Transient Thermal Structural coupled field Analysis using ANSYS software. Target solutions are presented for a benchmark problem and the results are believed to be accurate.numerical results for thermal shock response of a pipe joint are presented graphically Using a highly refined FE model and a small enough time step. REFERENCES [1] Radu V, Taylor N, Paffumi E, Development of new analytical solutions for elastic thermal stress components in a hollow cylinder under sinusoidal transient thermal loading, International Journal of Pressure Vessels and Piping, Volume 85, April 2008, Pages [2] Mohammad A. Irfan, Walter Chapman, Thermal stresses in radiant tubes due to axial, circumferential and radial temperature distributions, Applied Thermal Engineering, Volume 29, September 2008, page [3] Cook R.D, Finite Element Modeling for Stress Analysis, John Wiley, New York, 1995.