Thermal Fatigue Analysis at a Mixing Tee by a Fluid-Structural Simulation

2011 ◽  
Author(s):  
Masayuki Kamaya ◽  
Yoichi Utanohara ◽  
Akira Nakamura
Keyword(s):  
Thermal Stress ◽  
Fatigue Damage ◽  
Cold Water ◽  
Axial Stress ◽  
Branch Pipe ◽  
Three Dimensional ◽  
Dynamics Simulation ◽  
Cold Spot ◽  
Current Case ◽  
Main Pipe

In this study, the thermal stress at a mixing tee was calculated by the finite element method using temperature transients obtained by a fluid dynamics simulation. The simulation target was an experiment for a mixing tee, in which cold water flowed into the main pipe from a branch pipe. The cold water flowed along the main pipe wall and caused a cold spot, at which the membrane stress was relatively large. Based on the evaluated thermal stress, the magnitude of the fatigue damage was assessed according to the linear damage accumulation rule and the rain-flow procedure. Precise distributions of the thermal stress and fatigue damage could be identified. Relatively large axial stress occurred downstream from the branch pipe due to the cold spot. The position of the cold spot changed slowly in the circumferential direction, and this was the main cause of the fatigue damage. In the thermal stress analysis for fatigue damage assessment, it was concluded that the detailed three-dimensional structural analysis was not required. Namely, for the current case, a one-dimensional simplified analysis could be used for evaluating the fatigue damage without adopting the stress enhancement factor Kt quoted in the JSME guideline.

Root Cause Analysis of SI Nozzle Thermal Sleeve Breakaway Failures Occurring at PWR Plants

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Jong Chull Jo ◽  
Myung Jo Jhung ◽  
Seon Oh Yu ◽  
Hho Jung Kim ◽  
Young Gill Yune
Keyword(s):  
Cold Water ◽  
Operation Mode ◽  
Branch Pipe ◽  
Thin Wall ◽  
Reactor Operation ◽  
Support Condition ◽  
Primary Coolant ◽  
Root Cause ◽  
Main Pipe ◽  
Flow Situation

At conventional pressurized water reactors (PWRs), cold water stored in the refueling water tank of emergency core cooling system is injected into the primary coolant system through a safety injection (SI) line, which is connected to each cold leg pipe between the main coolant pump and the reactor vessel during the SI operation, which begins on the receipt of a loss of coolant accident signal. In normal reactor power operation mode, the wall of SI line nozzle maintains at high temperature because it is the junction part connected to the cold leg pipe through which the hot main coolant flows. To prevent and relieve excessive transient thermal stress in the nozzle wall, which may be caused by the direct contact of cold water in the SI operation mode, a thermal sleeve in the shape of thin wall cylinder is set in the nozzle part of each SI line. Recently, mechanical failures that the sleeves are separated from the SI branch pipe and fall into the connected cold leg main pipe occurred in sequence at some typical PWR plants in Korea. To find out the root cause of thermal sleeve breakaway failures, the flow situation in the junction of primary coolant main pipe-SI branch pipe and the vibration modal characteristics of the thermal sleeve are investigated in detail by using both computational fluid dynamics code and structure analysis finite element code. As a result, the transient response in fluid pressure exerting on the local part of thermal sleeve wall surface to the primary coolant flow through the pipe junction area during the normal reactor operation mode shows oscillatory characteristics with the frequencies ranging from 15Hzto18Hz. These frequencies coincide with the lower mode natural frequencies of thermal sleeve, which has a pinned support condition on the outer surface with the circumferential prominence set into the circumferential groove on the inner surface of SI nozzle at the midheight of thermal sleeve. In addition, the variation of pressure on the thermal sleeve surface yields alternating forces and torques in the directions of two rectangular axes perpendicular to the longitudinal axis of cylindrical thermal sleeve, which causes both rolling and pitching motions of the thermal sleeve. Consequently, it is seen that this flow situation surrounding the thermal sleeve during the normal reactor operation can induce resonant vibrations accompanying the shaking motion of the thermal sleeve at the pinned support condition, which finally leads to the failures of thermal sleeve breakaway from the SI nozzle.

Numerical Estimation of Flow Penetrating Depth Into Stagnant Branch Pipes for Thermal Fatigue Prediction

2014 ◽  
Author(s):  
Yoshihiro Ishikawa ◽  
Yukihiko Okuda ◽  
Naoto Kasahara
Keyword(s):  
Thermal Stress ◽  
High Temperature ◽  
Temperature Fluctuation ◽  
Thermal Stratification ◽  
Branch Pipe ◽  
Large Temperature ◽  
Bend Pipe ◽  
Main Pipe ◽  
High Temperature Water ◽  
Temperature Water

In the nuclear power plants, there are many branch pipes with closed-end which are attached vertically to the main pipe. We consider a situation in which the high temperature water is transported in the main pipe, the branch pipe is filled with stagnant water which has lower temperature than the main flow, and the end of the branch pipe is closed. At the branch connection part, it is known that a cavity flow is induced by the shear force of the boundary layer which separates from the leading edge of the branch pipe along the main pipe wall. In cases where the high temperature water penetrates into the branch pipe, there is a possibility that a steep and large temperature gradient field, called “thermal stratification layer” is formed at the boundary between high and low temperature water in the branch pipe. If the thermal stratification layer is formed in a bend pipe, which is used for connecting the vertical branch pipe and to a horizontal pipe, at the same time, the temperature fluctuation by the thermal stratification layer motion occurs, there may cause the thermal stress in the piping material. Furthermore, keeping the piping material under the thermal stress, there might be a possibility of a crack on the surface of the bend pipe. For this reason, the evaluation of the position where the thermal stratification layer reaches is very important during early piping design process. And, deeply understanding regarding the phenomena, is also important. However, because of the complexities of the phenomena, it is difficult to immediately clarify the whole mechanisms of the thermal stress arising due to the temperature fluctuation by the thermal stratification layer change. The complete prediction method for the position of the thermal stratification layer based on the mechanisms that is able to be applied to any piping system, any temperature and any velocity conditions, is also difficult. Therefore, a practical approach is required. The authors attempt to develop the practical estimation method for the thermal stratification layer position using the three-dimensional Navier-Stokes simulation which was based on the Reynolds-average in order to reduce the computational costs. In this paper, three different configurations of the piping were simulated and the simulation results were compared with the experimental results obtained by the other research group.

A Comparative Study of Fatigue Damage Assessment Methods to a Rigid Planar Jumper

2018 ◽  
Author(s):  
Laila Aarstad Igeh ◽  
Zhenhui Liu ◽  
Jie Wu ◽  
Muk Chen Ong
Keyword(s):  
Fatigue Damage ◽  
Dimensional Space ◽  
Axial Stress ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Design Guidelines ◽  
Torsional Stress ◽  
Assessment Practice ◽  
Flexural Stress ◽  
Fatigue Assessment

A rigid jumper is an important part of the subsea production system, it may experience significant vortex induced vibrations (VIV) if subjected to current. It has normally non-straight geometry shape in three-dimensional space. Consequently, the response of a rigid jumper under VIV is much more complicated compared to straight pipeline structures. Currently, there are very limited studies and design guidelines including methods on how to assess the fatigue damage of rigid jumpers under VIV. The methodology used for straight pipelines is often applied by ignoring the non-straight geometry characteristics and the multi-axial stress states (coexisting of flexural and torsional stress). However, both experimental and numerical results show that the torsional stress does exist besides the flexural stress for rigid jumpers under VIV. On the other side, the response of the rigid jumper under VIV is also challenging. The objective of this study is to do a fatigue assessment practice based on state-of-the-art calculation methods to a rigid jumper on model scale. The VIV response is inherited from experimental tests and numerical calculations by either force or response model methods. The influence of torsional stress on fatigue assessment is demonstrated. Two approaches have been investigated. In the first method, the flexural and torsional stresses are evaluated separately. The second method uses the 1st principle stress to calculate the fatigue damage, thus the flexural and torsional stresses are evaluated together. It is shown that the use of the 1st principle stress gives higher fatigue damage if the torsional stress contribution is significant. Further, the principle stress method is also less time-consuming on processing the results. Detailed discussions based on results have been performed, which could be also applied to general real scale rigid jumpers.

Numerical Simulation on Internal Flows of Reducing Cross

2014 ◽  
Vol 945-949 ◽  
pp. 980-986
Author(s):  
Jian Ping Yuan ◽  
Wen Ting Sun ◽  
Yin Luo ◽  
Bang Lun Zhou
Keyword(s):  
Numerical Simulation ◽  
Flow Rate ◽  
Branch Pipe ◽  
Three Dimensional ◽  
Uniform Flow ◽  
Hydraulic Loss ◽  
Steady Flows ◽  
Internal Flows ◽  
Inlet Velocity ◽  
Main Pipe

In order to study the internal flows and hydraulic loss of reducing cross, numerical simulation was carried out on a horizontally installed reducing cross. Three schemes of pipe diameters were studied. The time-averaged N-S equations of three-dimensional steady flows in the reducing pipe were calculated by CFX 14.5 based on the standard - two equation turbulence model together with standard wall function. The results show that the higher the inlet velocity, the hydraulic loss become larger when the split ratios are same for the reducing cross. With the uniform inlet velocities the higher the inlet velocity, the quicker the increasing rate of the hydraulic loss in main pipe, as well as the branch pipe. The integral change rules of hydraulic loss are similar with the condition of uniform flow rate inflow when the flow patterns at inlet are uniform. But with the same spilt ratio, the hydraulic loss of uniform velocity inflow is markedly less than that of uniform flow rate inflow in both main pipe and branch pipe. The bigger the differences of the diameters between the main pipe and the branch pipe, the larger the hydraulic loss of the branch pipe.

Integrating 3D Stress Analysis With Flexible Multibody Dynamics Simulation

2017 ◽  
Author(s):  
Olivier A. Bauchau ◽  
Shilei Han
Keyword(s):  
Multibody Dynamics ◽  
Axial Stress ◽  
Three Dimensional ◽  
Flexible Multibody Dynamics ◽  
Beam Theory ◽  
Torsional Stiffness ◽  
Dynamics Simulation ◽  
Numerical Examples ◽  
Axial Forces ◽  
Flexible Multibody

This paper presents an approach toward the integration of 3D stress computation with the tools used for the simulation of flexible multibody dynamics. Due to the low accuracy of the floating frame of reference approach, the the multibody dynamics community has turned its attention to comprehensive analysis tools based on beam theory. These tools evaluate sectional stress resultants, not 3D stress fields. The proposed approach decomposes the 3D problem into two simpler problems: a linear 2D analysis of the cross-section of the beam and a nonlinear, 1D of the beam. This procedure is described in details. For static problems, the proposed approach provides exact solutions of three-dimensional elasticity for uniform beams of arbitrary geometric configuration and made of anisotropic composite materials. While this strategy has been applied to dynamic problems, little attention has been devoted to inertial effects. This paper assesses the range of validity of the proposed beam theory when applied to dynamics problems. When beams are subjected to large axial forces, the induced axial stress components become inclined, generating a net torque that opposes further rotation of the section and leading to an increased effective torsional stiffness. This behavior, referred to as the Wagner or trapeze effect, cannot be captured by beam formulations that assume strain components to remain small, although arbitrarily large motions are taken into account properly. A formulation of beam theory that includes higher-order strain effects in an approximate manner is developed and numerical examples are presented. The “Saint-Venant problem” refers to a three-dimensional beam loaded at its end sections only. The “Almansi-Michell problem” refers to a three-dimensional beam loaded by distributed body forces, lateral surface tractions, and forces and moments at its end sections. Numerical examples of beams subjected to distributed loads will be presented and compared with 3D finite element solutions.

Optimize Design on the Key Parts of Ring Die Fuel Pellet Machine

2013 ◽  
Vol 860-863 ◽  
pp. 2707-2711
Author(s):  
Wei Gao ◽  
Qing Yu Liu ◽  
Rong Fei Zhao ◽  
Shi Yang Gu
Keyword(s):  
Fatigue Damage ◽  
Production Efficiency ◽  
Three Dimensional ◽  
Dynamics Simulation ◽  
Fuel Pellet ◽  
Design Parameters ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Unit Output ◽  
Die Service Life

This paper analyzes the problems existing in the design and operation of ring die fuel pellet machine, and proposed to optimize the key parts. Determine the reasonable number of roller on the theory of fatigue damage after drawing up the related design parameters of ring die and the roller, a three-dimensional model of the link mold pellet machine is established using Pro/E soft-ware, and transferred the model into ADAMS software through Mech/Pro which dedicated interface software, then used ADAMS to make a dynamics simulation. Through calculation, the stress amplitude impact on the ring die and the Energy consumption per unit output are smallest when roller number is four. So, ring die service life and equipment production efficiency can be improved effectively through setting up reasonable roller number. Keywords-fuel pellet machine; roller; ring die; fatigue damage; three-dimensional model; dynamics simulation

Molecular Dynamics Simulations of High Energy Cascades in Iron

1994 ◽  
Vol 373 ◽  
Author(s):  
Roger E. Stoller
Keyword(s):  
Molecular Dynamics ◽  
Three Dimensional ◽  
High Energy ◽  
Dynamics Simulation ◽  
Method Of Molecular Dynamics ◽  
Energy Cascades ◽  
Iron Based ◽  
The Many ◽  
Property Changes ◽  
Dynamics Simulations

AbstractA series of high-energy, up to 20 keV, displacement cascades in iron have been investigated for times up to 200 ps at 100 K using the method of molecular dynamics simulation. Thesimulations were carried out using the MOLDY code and a modified version of the many-bodyinteratomic potential developed by Finnis and Sinclair. The paper focuses on those results obtained at the highest energies, 10 and 20 keV. The results indicate that the fraction of the Frenkel pairs surviving in-cascade recombination remains fairly high in iron and that the fraction of the surviving point defects that cluster is lower than in materials such as copper. In particular, vacancy clustering appears to be inhibited in iron. Some of the interstitial clusters were observed to exhibit an unexpectedly complex, three-dimensional morphology. The observations are discussed in terms of their relevance to microstructural evolution and mechanical property changes in irradiated iron-based alloys.

Design and operation of a tripod walking robot via dynamics simulation

Robotica ◽  
2010 ◽  
Vol 29 (5) ◽  
pp. 733-743 ◽  
Author(s):  
Conghui Liang ◽  
Hao Gu ◽  
Marco Ceccarelli ◽  
Giuseppe Carbone
Keyword(s):  
Mechanical Design ◽  
Low Cost ◽  
Three Dimensional ◽  
The Body ◽  
Dynamics Simulation ◽  
Walking Ability ◽  
Walking Robot ◽  
Three Dimensional Model ◽  
Software Environment ◽  
Leg Mechanisms

SUMMARYA mechanical design and dynamics walking simulation of a novel tripod walking robot are presented in this paper. The tripod walking robot consists of three 1-degree-of-freedom (DOF) Chebyshev–Pantograph leg mechanisms with linkage architecture. A balancing mechanism is mounted on the body of the tripod walking robot to adjust its center of gravity (COG) during walking for balancing purpose. A statically stable tripod walking gait is performed by synchronizing the motions of the three leg mechanisms and the balancing mechanism. A three-dimensional model has been elaborated in SolidWorks® engineering software environment for a characterization of a feasible mechanical design. Dynamics simulation has been carried out in the MSC.ADAMS® environment with the aim to characterize and to evaluate the dynamic walking performances of the proposed design with low-cost easy-operation features. Simulation results show that the proposed tripod walking robot with proper input torques, gives limited reaction forces at the linkage joints, and a practical feasible walking ability on a flatten ground.

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