Results 1 - 9 of 9
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[en] Incremental forming is a cold working process in which a small part of the material is being deformed and the area of local deformation is moving over the entire material. In this paper, we study description schemes to perform finite element analysis for the incremental forming. The selected description schemes to examine are the Lagrangian description and the arbitrary Lagrangian Eulerian (ALE) description. The sliding boundary scheme coupled with ALE is also examined to overcome the distortion problems of elements on the contact surface. Results show that the ALE description with the sliding boundary scheme is most favorable in overcoming the distortion of elements. This description leads to make the simulation continued to the final stage of the incremental forming. On the other hand, the Lagrangian description as well as the original ALE description makes the elements much distorted and the analysis is stopped long before arriving at the final shape of deformation
[en] The purpose of this study is to show the utility of ultrasonic guided waves in 439 stainless steel heat exchanger and Inconel steam generator tubing inspection. Phase velocity and group velocity dispersion curves for the longitudinal and flexural modes of a sample Inconel steam generator tube were presented. In experimental studies, ultrasonic guided wave applications were demonstrated for man made flaws. For the detection of EDM wears under a tube support plate in the heater exchanger tubing, a bore probe generated axisymmetric longitudinal guided wave modes in the tubing. For the detection and sizing of circumferential Laser notches in Inconel steam generator tubes, a variable angle beam transducer set up was used. Excellent detection results were demonstrated for EDM wears and Laser Notches with various modes and L(0,1) modes, respectively. Circumferential sizing of Laser notches was achieved with L(0,1) mode at 3.5 MHz.
[en] A finite element model was developed for the thermal analysis of a stud-to-plate laser brazing joint, and the transient temperature fields were analysed by using a three-dimensional model. The finite element program ABAQUS, together with a few user subroutines, was employed to perform the numerical approximation. Temperature-dependent thermal properties, effect of latent heat, and the convection and radiative heat losses were considered. The brazing parts used were AISI 304 stainless steel stud and aluminium A1 5052 plate, and the brazing alloy 88 A1-12 Si was used as filler metal. A pseudo-TM01 mode of the cw CO2 laser beam was used as heat source, for which TM00 mode generated by beam oscillator was optically modulated using axicon lens. Re-location of the filler metal during the brazing process including its wetting and spreading was examined by using a high speed motion analyser, and the results were incorporated inn the FEM modelling for defining the solution domain and boundary conditions. The numerical results were obtained for typical process parameters, and were compared with experimental ones determined by using the infrared and thermocouple measurements. 11 figs., 30 refs. (Author)
[en] In this study, detection of flaws in bent feeder pipes using ultrasonic guided wave was investigated using 3-D FEM, and 2-D FFT were specifically 1) the transient responses of the bent pipe were calculated by using a general-purpose finite element program, 2) the displacements were extracted at a series of sequential points as a function of spatial position and time, u(x,t), 3) and then 2-D FFT of u(x,t) was performed to determine U(k,w). From this relationship between the wave number(k) and angular frequency(w), the phase velocity and group velocity were calculated. In addition, accuracy of this method was verified by comparison of predicted modes for straight pipe with theoretical solution. Furthermore, verification of the result is made by the mode identification using wavelet transform. The modes invoked by both methods agree very well. In addition, the ultrasonic guide wave inspection of bent pipes was also investigated. In case of the longitudinal modes analysis for the bent pipe without crack, generated modes were similar with straight pipe. However, in case of the bent pipe with a crack, the received signals were changed at the end of the pipe due to the flaw presence. Thus, we could determine whether flaw exist in the feeder pipe or not by using torsional mode guide wave
[en] The steam generator tubes represent an integral part of major barrier against the fission product release to the environment. So, the rupture of these tubes could permit flow of reactor coolant into the secondary system and injure the safety of reactor coolant system. Therefore, if the crack was detected during In-Service Inspection of tubes the cracked tube should be evaluated by the plugging criteria and plugged or not. In this study, the fracture mechanics evaluation is carried out on the thru-wall axial crack due to Primary Water Stress Corrosion Cracking in the roll transition zone of steam generator tube to help the assurance the integrity of tubes and establish the plugging criteria. Due to the Inconel which is used to calculate the critical and allowable crack length. Based on Leak Before Break concept the leak rate for the critical crack length and the allowable leak rate are compared and the safety of tubes was given. (author)
[en] Lugs, brackets, stiffeners and other attachments may be welded, bolted and studded to the outside or inside of piping and the local stresses arise because of the radial thermal expansion of the piping, the dilatation of the piping due to its internal pressure, the circumferential contraction of the pipe as a results of an axial tensile force, etc., constrained by those. So the evaluation of the local stress for the piping constrained by the attachment in accordance with the ASME Section III, NB-3651.3, NC-3645 and ND-3645 are required for the Class 1, 2, and 3 piping. In this report, the formula for the local stress analysis for the piping welded to the seal plate was developed and the results from the theoretical analysis were compared with the results from the theoretical analysis were compared with the results analyzed by the ANSYS. The results from the theoretical analysis agree well to the results analyzed by the ANSYS with a conservatism. The conservatism in the theoretical analysis can be considered as a safety factor in the design stage. So, the formula developed in this report can be used very effectively for the design of the seal plate and the local stress analysis of the nuclear class 2 and 3 piping welded to the seal plate. 2 tabs., 7 figs., 5 refs. (Author) .new
[en] Advanced Power Reactor 1400 (APR 1400) which is to achieve the improvement of the safety and economical efficiency has been developed by Korea Hydro and Nuclear Power Co., Ltd. (KHNP) with the support from industries and research institutes. The steam generator for APR 1400 is an evolutionary type from System 80+, which is the recirculating U-tube heat exchanger with integral economizer. Compared to the System 80+ steam generator, it is focused on the improved design features, operating and design conditions of APR 1400 steam generator. Especially, from the operation experience of Korean Standard Nuclear Power Plant (KSNP) steam generator, the lessons-learned measures are incorporated to prevent the tube wear caused by flow-induced vibration (FIV). The concepts for the preventive design features against FIV are categorized to two fields; flow distribution and dynamic response characteristics. From the standpoint of flow distribution characteristics, the egg-crate flow distribution plate (EFDP) is installed to prevent the local excessive flow loaded on the most susceptible tube to wear. The parametric study is performed to select the optimum design with the efficient mitigation of local excessive flow. ATHOS3 Mod-01 is used and partly modified to analyze the flow field of the APR 1400 steam generator. In addition, the upper tube bundle support is designed to eliminate the presence of tube with a low natural frequency. Based on the improved upper tube bundle support, the modal analysis is performed and compared with that of System 80+. Using the results of flow distribution and modal analysis, the two mechanisms of flow-induced vibration are investigated; fluid-elastic instability (FEI) and random turbulence excitation (RTE). (authors)
[en] A turbine rotor bore ultrasonic testing inspection is critical to the safety and reliability of a power plant. However, UT inspection is a difficult process due to the limited accessibility to the inspection area and the time required for a complete UT inspection. To get rid of such a barrier, Doosan has developed an automated UT inspection system for turbine rotor bores. The system is consist of two major components: 1) an automated mechanical scanner and drive system and 2) a data acquisition and control system. The automated mechanical scanner and drive system is designed to rotate the scanner head at a constant speed as it traverses the length of the rotor bore. The data acquisition system has three channel transducers for straight beam and angle beam UT inspections and acquires the UT signals and constructs real time A-san, B-scan and C-scan and also has the capability of storing the captured ultrasonic signals for post processing. This paper describes the developed system together with the initial experimental verification of accuracy.
[en] Carbon capture and storage (CCS) technologies are a cornerstone for reducing CO_2 emissions from energy and energy-intensive industries. Among the various CCS technologies, solid sorbent looping systems are considered to be potentially promising solutions for reducing CO_2 capture energy penalty. We present an evaluation module for a carbonator with sorbent looping cycle to calculate the carbonation efficiency. The module incorporates a simple sorbent activity model, and the solid/gas balances are constructed by assuming simple reactor mixing quality. By conducting simulations, we examine the variation in the carbonation efficiencies as a function of the sorbent looping operation factors and discuss an optimum operating strategy