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Few studies on social welfare in South Korea have examined the effects of climate change, especially heat waves on vulnerable populations. The present study aims to investigate how heat waves affect vulnerable populations. This study utilized a cross-sectional study design, using the daily heat index and heat-related mortality data for Seoul, South Korea, in summer 2018. The research used micro-raw data of deaths caused by hypertensive, ischemic heart, and cerebrovascular diseases, as well as heat index data. An effect was observed for the heat index on mortality for individuals over 65 years of age, men, people with spouses, and those ages 75–79 years. [ABSTRACT FROM AUTHOR]

This study proposes a methodology to estimate time-varying in situ wear coefficient between steam generator tubes in nuclear power plants and their supporting structures. Actual wear depth measurement data of steam generator tubes of OPR1000 (Optimized Power Reactor 1000 MW) plants in Korea were collected and analyzed to investigate the behavior of fretting wear. To determine the in situ wear coefficient, a mathematical expression was developed as a function of various parameters such as measured wear depth time history, work rate, contact geometry of the tube, and its support. These calculated in situ wear coefficients were then used to obtain wear depth history curves. Results obtained were then compared with actual field measurement data to show the validity of the proposed method. Many researchers have obtained wear coefficients under laboratory conditions. However, those coefficients cannot be considered as realistic factors for operating steam generators. The in situ wear coefficient proposed in this study is based on wear measurement data obtained from real operating steam generator tubes. Therefore, they can be used to precisely predict the wear depth of steam generator tubes, thus allowing safe and economical management of steam generators. [ABSTRACT FROM PUBLISHER]

Abstract: Flow induced vibration of steam generator tubes potentially causes excessive fretting wear at the supports such as anti-vibration bars and tube support plates. For a reliable design of tubes against the flow-induced vibration related failure, the prediction of vibration and wear of tubes should be performed through complicated steps including the thermal-hydraulic analysis, dynamic modal analysis, evaluation of fluid-elastic instability, prediction of turbulence-induced vibration and wear depth for thousands of tubes. However, entire tubes cannot be evaluated within a limited time of design engineering by the conventional analysis methodology. In this paper, we describe an efficient computer program to assess the structural integrity of steam generator tubes against the flow-induced vibration related failure in a very systematic way. The program contains all the necessary thermal-hydraulic database of typical steam generators. It has a very special function to perform modal analysis for all thousands of tubes of a steam generator much faster than the conventional method. The program also performs fluid-elastic instability analysis and calculates the vibrational response to the turbulent flow excitation, and then can predict the wear depth for all tubes of a steam generator. Finally, we can generate the wear prediction map for whole tubes so that an efficient and practical steam generator maintenance management program is feasible. The utilization of the developed computer program for the design and maintenance of steam generators can significantly increase the structural integrity of steam generator tubes of a nuclear power plant. [Copyright &y& Elsevier]

A numerical study of casing treatments on a centrifugal compressor to improve stability and stall margin is presented. High efficiency, high pressure ratio, and a wide operating range are required for a high-performance centrifugal compressor. A ring groove casing treatment is effective for flow range enhancement in centrifugal compressors. Compressor performance was analyzed according to the ring groove location, and the results were compared with the case without a ring groove. The effect of guide vanes in the ring groove was also investigated. Four variants of grooves were modeled and simulated using computational fluid dynamics to optimize the groove location. Numerical analysis was performed using a commercial code ANSYS-CFX program. The simulation results showed that the ring groove increased the operating range of the compressor. The ring groove with guide vanes improved both performance of the compressor at low flow rates and the stall margin of the compressor. [ABSTRACT FROM AUTHOR]

Abstract: The present study performed full-scale pipe tests using 100A Schedule 80 pipe specimens with simulated notched and circular wall thinning to investigate the failure behavior of notched wall-thinned pipes. The tests were conducted under both monotonic and cyclic bending moments at a constant internal pressure of 10MPa at room temperature. The failure pattern, load carrying capacity, deformation ability, and fatigue strength of the notched wall-thinned pipes were evaluated by comparing results to those of circular wall-thinned pipes. The investigation showed that the effect of the type of thinning on the failure behavior was more sensitive under cyclic loading conditions than under monotonic loading conditions. The load carrying capacity of pipes with notched wall thinning was approximately the same or slightly less than that of pipes with circular wall thinning when the thinning area was subjected to tensile stress. However, when the thinning area was subjected to compressive stress, the load carrying capacity of pipes with notched wall thinning was greater than that of pipes containing circular wall thinning. The deformation ability and fatigue strength increased proportionally with the axial length of the thinning defect, and thus these properties were significantly reduced in notched wall-thinned pipes. [Copyright &y& Elsevier]

The present study performed pipe failure tests using 102 mm-Sch. 80 carbon steel pipe with various simulated wall thinning defects, to investigate the effect of axial length of wall thinning and internal pressure on the failure behavior of pipe thinned by flow accelerated corrosion (FAC). The tests were conducted under loading conditions of four-point bending with and without internal pressure. The results showed that a failure mode of pipe with a defect depended on the magnitude of internal pressure and axial thinning length as well as stress type and thinning depth and circumferential angle. Both load carrying capability (LCC) and deformation capability (DC) were depended on stress type in the thinning area and dimensions of thinning defect. For applying tensile stress to the thinned area, the dependence of LCC on the axial length of wall thinning was determined by circumferential thinning angle, and the DC was proportionally increased with increase in axial length of wall thinning regardless of the circumferential angle. For applying compressive stress to thinned area, however, the LCC was decreased with increase in axial length of the thinned area. Also, the effect of internal pressure on failure behavior was characterized by failure mode of thinned pipe, and it promoted crack occurrence and mitigated a local buckling of the thinned area. [Copyright &y& Elsevier]

• We demonstrate how the early warning system for nuclear power plants is configured and operated. • The analysis of the operation result is introduced and confirmed that the early warning system is operating properly. • Three cases prove the validity and effectiveness of the early warning system. This paper presents the validity and usefulness of early warning in online monitoring system for nuclear power plants. Early warning is one of the core functions of the online monitoring system, which uses pattern recognition to predict and alert potential problems in the equipment or system. This function was developed by using the AAKR technique and has been operated since 2016. We show that the early warning system is operating properly through an analysis of the operation result of the system, and present three cases that represent the functions and roles of the system. In the first two cases, the system detected a failure of equipment and measuring instrument, respectively. In the third case, the system went through pattern re-learning to overcome environmental changes. [ABSTRACT FROM AUTHOR]

Abstract Internet gaming addiction is a serious problem for some adolescents in South Korea, although it has not yet been fully explored. The present study aims to explore adolescents' motivations for internet games, how their lives are affected, how they perceive internet games, what they gained and lost, and how they made sense of internet gaming addiction. Interviews, focus groups, and photovoice with a sample of ten adolescents at risk of internet addiction were conducted. The participants reported serious symptoms of internet game addiction, which negatively affected their psychological health and self-identity. They also reported that they were aware of how internet games negatively affected their daily lives, academic performance, and family relationships worsened once they became addicted to internet games. However, they also perceived internet games as avenues for entertainment, stress relief, and peer bonding. Understanding adolescents' perceptions and meaning of internet gaming addiction can facilitate the development of effective psychosocial intervention programs, which can subsequently contribute to healthy coping strategies and positive adolescent development and identity. Highlights • Internet gaming addiction is a serious problem for adolescents. • However, the problem of adolescents' internet game addiction has not yet been fully explored. • The aim of the present study is to explore internet gaming addiction among South Korean adolescents. • Methods used for the study included interviews, focus groups and photovoice. [ABSTRACT FROM AUTHOR]

Highlights: [•] We evaluated bending load effect on the failure pressure of wall-thinned pipe elbows. [•] Burst tests were conducted on real-scale elbow specimens with local wall thinning. [•] The tests were performed under combined pressure and load-controlled bending. [•] Load-controlled bending reduced the failure pressure of wall-thinned elbows. [•] Bending load effect was significant for opening-mode and intrados wall-thinning case. [Copyright &y& Elsevier]

Abstract: A typical pressurized water reactor (PWR) steam generator has approximately 10,000 tubes. These tubes have different geometries, supporting conditions, and different material properties due to the non-uniform temperature distribution throughout the steam generator. Even though some tubes may have the same geometry and boundary conditions, the non-uniform distribution of coolant densities adjacent to the tubes causes them to have different added mass effects and dynamic characteristics. Therefore, for a reliable design of the steam generator, a separate modal analysis for each tube is necessary to perform the FIV (flow-induced vibration) analysis. However, the modal analysis of a tube including the finite element modeling is cumbersome and takes lots of time. And when a commercial finite element code is used, interfacing the modal analysis result, such as natural frequencies and mode shapes, with the FIV analysis procedure requires an additional significant amount of time and can possibly incur inadvertent error due to the complexity of data processing. It is therefore impossible to perform the complete FIV analysis for ten thousands of tubes when designing or maintaining a steam generator although it is necessary. Rather, to verify the safe design against the FIV, only a couple of tubes are chosen based on engineering judgment or past experience. In this paper, a computer program, PIAT-MODE, was developed which is able to perform modal analysis of all tubes of a PWR steam generator in a very efficient way. The geometries and boundary conditions of every tube were incorporated into PIAT-MODE using appropriate mathematical formulae. Material property data including the added mass effect was also included in the program. Once a specific tube is selected, the program automatically constructs the finite element model and generates the modal data very quickly. Therefore, modal analysis can be performed for every single tube in a straight way. When PIAT-MODE is coupled with the FIV analysis program, it gives an amazing benefit, which makes the FIV analysis of all tubes possible within a limited time during the design or maintenance period. Using the developed program, the stability ratio regarding the fluid-elastic instability and the amplitude of vibration resulting from the turbulence flow excitation can be calculated for all tubes according the standard ASME Code, therefore, much more reliable design of the steam generator against the FIV related failures can be achieved. For an operating plant, there is a requirement that every single tube must be quantitatively checked whether wear would be more than 40% in thickness during the next operation period. If yes, the tube must be plugged to prevent severe failure including the tube wall penetration. In order to decide the tube plugging, which leads the plant performance degradation, the wear prediction is required. The wear prediction analysis needs wear data by ultrasonic testing and modal property data of tubes. PIAT-MODE will be a power tool enabling the wear prediction in a limited maintenance period by supplying modal data for all tubes. [Copyright &y& Elsevier]

Abstract: This study performed a series of burst tests using real-scale elbow specimens containing simulated local wall thinning to evaluate the effects of wall-thinning defects on the failure pressure of pipe bends and elbows. The tests were conducted under simple internal pressure at ambient temperature. The experiments included various wall-thinning geometries with different thinning depths, lengths, and circumferential angles, as well as various thinning locations such as extrados, intrados, and full-circumference. The failure pressure decreased exponentially with increasing axial thinning length and decreased almost linearly with increasing thinning depth. These tendencies are similar to those observed for wall-thinned straight pipe. The failure pressure also decreased and gradually saturated with increasing circumferential thinning angle, unlike the results of wall-thinned straight pipe. All specimens failed by bulging, followed by cracking. The axial crack always occurred at the center of the wall-thinned area in the extrados and intrados wall-thinning cases. For the full-circumference wall-thinning case, however, the crack location and pattern were dependent on the axial thinning length. A comparison of the failure pressure with the results of existing models showed that the existing models were excessively conservative in all cases and could not properly predict the dependence of failure pressure on the wall-thinning geometry. [Copyright &y& Elsevier]

Abstract: This paper provides plastic limit loads of pipes with local wall thinning under combined pressure and bending, by quantifying effects of the axial extent and the shape of local wall thinning. The effect of the axial extent on plastic limit loads is not so significant for bending but could be more significant for internal pressure. It is also found that the effect of the shape of local wall thinning on limit loads could be significant. Thus idealization of local wall thinning as a rectangular shape rather than a circular one could lead to significantly conservative estimates of maximum loads, which is also supported by comparison with published full-scale pipe test data. [Copyright &y& Elsevier]

Abstract: The wall-thinning problem has become a hot issue in the assessment of the structural integrity of pipes and pipe items. A criterion is necessary to determine the possibility of continuing use for the wall-thinned pipes detected by non-destructive inspection. The American Society of Mechanical Engineers (ASME) Boiler & Pressure (B&PV) Vessel Section XI, Div. 1, Code Case N-597-2 [Requirements for analytical evaluation of pipe wall thinning, 2003] provides the criterion. But the code case has several limitations and difficulties for application and sometimes gives non-consistent allowable local thickness values. So works are in progress to modify and extend the code. For that purpose, it is also necessary to understand fully the technical bases of the code case. In Code Case N-597-2, the allowable local thickness of a thinned straight pipe is given through three different methods. Because of different technical bases, each method gives different thickness values and sometimes gives contradictory values. So, in this paper, attempts were made in order to propose a unified rule for the allowable local thickness and in order to remove or relax the restrictions on the application of the code case. For this purpose, elastic stress analyses were made using the finite element method and the stress results were examined. Based on the obtained bending stress results, a very simple procedure was proposed to obtain the consistent allowable local thickness for the thinned straight pipes. [Copyright &y& Elsevier]

Abstract: This paper presents elastic, shakedown and plastic limit loads for 90° elbows under constant internal pressure and cyclic in-plane bending, via finite element (FE) analysis. Effects of the elbow geometry (the bend radius to mean radius ratio and the mean radius-to-thickness ratio) and of the large geometry change are systematically investigated. By normalizing the in-plane bending moment by the plastic limit load solution of Calladine, the shakedown diagram is found to be close to unity up to a certain value of normalized pressure (normalized with respect to the limit pressure) and then to decrease almost linearly with increasing normalized pressure. The value up to which shakedown limit loads remain constant depends on the elbow geometry and the large geometry change effect. Effects of the elbow geometry and the large geometry change on shakedown diagrams are discussed. [Copyright &y& Elsevier]

Abstract: The authors have previously proposed plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on finite element (FE) limit loads resulting from three-dimensional (3-D) FE limit analyses using elastic–perfectly plastic materials [Kim YJ, Lee KH, Park CY. Limit loads for thin-walled piping branch junctions under internal pressure and in-plane bending. Int J Press Vessels Piping 2006;83:645–53]. The solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and for the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0. Moreover, the solutions considered the case of in-plane bending only on the branch pipe. This paper extends the previous solutions in two aspects. Firstly, plastic limit load solutions are given also for in-plane bending on the run pipe. Secondly, the validity of the proposed solutions is extended to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparisons with FE results show good agreement. [Copyright &y& Elsevier]

Abstract: The objective of this study was to investigate the effect of local wall thinning on the collapse behavior of pipe elbows subjected to a combined internal pressure and in-plane bending load. This study evaluated the global deformation behavior and collapse moment of the elbows, which contained various types of local wall-thinning defects at their intrados or extrados, using three-dimensional elastic–plastic finite element analysis. The analysis results showed that the global deformation behavior of locally wall-thinned elbows was largely governed by the mode of the bending and the elbow geometry rather than the wall-thinning parameters, except for elbows with considerably large and deep wall thinning that showed plastic instabilities induced by local buckling and plastic collapsing in the thinned area. The reduction in the collapse moment with wall-thinning depth was considerable when local buckling occurred in the thinned areas, whereas the effect of the thinning depth was small when ovalization occurred. The effects of the circumferential thinning angle and thinning length on the collapse moment of elbows were not major for shallow wall-thinning cases. For deeper wall-thinning cases, however, their effects were significant and the dependence of collapse moment on the axial thinning length was governed by the stress type applied to the wall-thinned area. Typically, the reduction in the collapse moment due to local wall thinning was clearer when the thinning defect was located at the intrados rather than the extrados, and it was apparent for elbows with larger bend radius. [Copyright &y& Elsevier]

Based on systematic three-dimensional (3-D), large strain FE limit analyses using elastic- perfectly plastic materials, this paper quantifies the effect of local wall thinning on plastic behavior and TES (twice-elastic-slope) plastic loads for 90° elbows under in-plane bending. The thinning geometry is assumed to be rectangular rather than circular, but the nonlinear geometry effect is fully considered. Results from systematic analyses lead to simple approximations for TES plastic loads, covering a wide range of elbow and thinning geometries. Although the proposed approximations are developed for the case when wall thinning locates in the center of the elbow, it is also shown that they can be equally applied to the case when thinning exists anywhere within the elbow. Brief discussion is made on application of the proposed approximations to estimate maximum load-carrying capacities of elbows with local wall thinning. [ABSTRACT FROM AUTHOR]

Abstract: The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic–perfectly plastic materials. To assure reliability of the FE limit loads, modelling issues are addressed first, such as the effect of kinematic boundary conditions and branch junction geometries on the FE limit loads. Then the FE limit loads for branch junctions under internal pressure and in-plane bending are compared with existing limit load solutions, and new limit load solutions, improving the accuracy, are proposed based on the FE results. The proposed solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0. [Copyright &y& Elsevier]

Abstract: The net-section limit load approach is typically used in assessment of pipes with local wall thinning, based on which a maximum load carrying capacity is easily estimated from one equation that includes two terms associated with the effect of the defect geometry and the material''s resistance (strength). To better understand the applicability of the net-section limit load approach to pipes with local wall thinning, four different limit load expressions for pipes with local wall thinning under pure bending are considered, together with two different definitions of the material''s resistance. Estimated failure moments are then compared with full-scale pipe test data. It is found that the use of an appropriate limit load solution reduces not only the degree of conservatism but also the dependence of the assessment results on the wall thinning geometry, and thus gives the best results. Therefore, finding such solutions for pipes with local wall thinning is an important issue. [Copyright &y& Elsevier]

Abstract: Inconel 690 is used for steam generator tube in nuclear power plants. In this study, microstructural effects on fretting wear of Inconel 690 were investigated. To change the microstructure of test specimens, heat treatments were performed in two steps; solution annealing (at a high temperature) and thermal treatment (at a low temperature). Observations of microstructure indicated that the temperature and duration of solution annealing affect the grain size of Inconel 690. The carbide morphology along grain boundaries was affected mainly by duration and temperature of thermal treatment. The results of the wear test show that specimens with larger grain and coarse carbides along the grain boundaries have greater resistance to wear. Cracks were found in specimens with carbides along the grain boundary whereas few cracks were found in carbide-free specimens. The carbide along the grain boundary seemed to help form and propagate cracks in the specimens with carbides. On the other hand, the microhardness of specimens had no major role in fretting wear. [Copyright &y& Elsevier]

Abstract: This paper investigates effects of variables related to 3-D finite element welding residual stress analyses of penetration nozzles on residual stresses. Five variables are considered; (i) number of elements in the circumferential direction, (ii) number of beads in the circumferential direction, (iii) kinematic boundary conditions, (iv) circumferential modelling angle in 3-D finite element models and (v) detailed weld shape. Based on sensitivity analysis results, guidelines for 3-D finite element welding residual stress analyses of penetration nozzles are provided. [Copyright &y& Elsevier]

A variety of centrifugal compressors are used in various fields of industry such as aircraft, home appliances, and vehicles. Comfort and quietness are important in these uses. As a result, noise has become an important consideration in compressor design besides the conventional performance parameters such as efficiency and pressure ratio. However, compressor noise has been difficult to understand because of the lack of information. The aim of this paper is to investigate the aero-acoustic characteristics of a centrifugal compressor for the fuelcell vehicle by experiments. The existing compressor system is modified to measure the internal pressure fluctuation at the impeller inlet, the impeller outlet and the diffuser outlet. Four microphone probes are also installed to determine the external noise levels and spectra of the compressor in an airtight room according to the RPM and mass flow rate. The test results show the possibility to tell the relative noise level of a centrifugal compressor with the internal pressure data. The external microphone signals have relation to the internal pressure signals. They have similar patterns and spectra. It is a noteworthy phenomenon because it is easier and inexpensive to predict pressure behaviors than noise characteristics of centrifugal compressors. The dominant noise source is the tonal noise during normal operation. But the broadband noise component due to the turbulent flow in the compressor increases during low flow rate operation. Computational simulations are carried out to describe these phenomena and to identify noise indicators. The turbulence kinetic energy and the pressure distribution obtained from CFD results may be indicative of the relative noise intensity of the compressor. The experimental facility, instrumentation and simulation conditions are described, and the results are presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract: The effects of safe-end length and kinematic boundary conditions during welding on weld residual stresses in dissimilar metal welds are systematically investigated using finite element analyses for typical pressurized water reactor surge nozzle configurations. The study is generalized by idealizing complex nozzle geometries as straight pipes with two welds. The impact of these variables on axial residual stresses at inner surface is examined, since these are of most concern for primary water stress corrosion cracking. Possible mechanisms controlling the development of welding residual stresses are used to qualitatively explain the predicted behavior. [Copyright &y& Elsevier]

Abstract: This paper provides closed-form plastic limit load solutions for elbows under in-plane bending and internal pressure, via three-dimensional (3D), geometrically linear FE limit analyses using elastic-perfectly plastic materials. Wide ranges of elbow and thinning geometries are considered. To investigate the effect of the axial thinning length on limit loads systematically, two limiting cases are considered; a sufficiently long thinning, and the circumferential part-through surface crack. Closed-form plastic limit load solutions for wall thinning with intermediate longitudinal extents are then obtained from these two limiting cases. The effect of the axial extent of wall thinning on plastic limit loads for elbows is highlighted by comparing that for straight pipes. Although the proposed solutions are developed for the case when wall thinning exists in the center of elbows, it is also shown that they can be applied to the case when thinning exists anywhere within the elbow. [Copyright &y& Elsevier]

Abstract: This paper quantifies the effect of a bend angle of a pipe bend on plastic loads, via small strain and large strain finite element (FE) limit analyses using elastic–perfectly plastic materials. To consider the effect of the attached straight pipe, two limiting cases are considered. One case corresponds to the pipe bend without the attached straight pipe, and the other to that with a sufficiently long attached straight pipe. For the former case, the FE results suggest that the limit load is not affected by the bend angle for both in-plane bending and internal pressure. For the latter case, however, the bend angle affects plastic loads. An interesting finding is that the plastic load smoothly changes from the limit load of the straight pipe when the bend angle approaches zero to the plastic load of the pipe bend when the bend angle approaches . Based on such observations, closed-form plastic load solutions are proposed for the pipe bend with an arbitrary bend angle under in-plane bending and internal pressure. [Copyright &y& Elsevier]

Fretting wear tests were performed to evaluate wear properties of steam generator (SG) tubes in room temperature water. In this study, wear experiments have been conducted at various loads and sliding amplitudes using five material conditions; the combination of SG tubes (Inconel 600HTMA, 690TT and Alloy 800) and their supports (405, 409 ferritic and 410 martensitic stainless steels) are being operated at Korean nuclear power plants. Experimental results show that wear coefficient of a work-rate model in Alloy 800 against 410 stainless steel is the highest (67×10−15 Pa−1), whereas that in Inconel 690TT against 409 stainless steel is the lowest (18×10−15 Pa−1). Based on the observation of the deformation layer using SEM, both Inconel 600HTMA and 690TT show very similar wear mechanisms. However, the wear mechanism of Alloy 800 is somewhat different. In the case of Inconel 600HTMA and 690TT, almost wear particles were released in the form of thin plate from deformation layers. However, wear particles in Alloy 800 were released both from plastic flow generated by severe deformation and from third body abrasion during fretting wear, which related to a lower wear-resistance compared to the Inconel 600HTMA and 690TT. The details of microstructural investigation show that Inconel 690TT has more resistance to fretting wear because its small cell structure could easily accommodate large strain on worn surface. In addition, the relationship between the wear coefficients of the work-rate model and the mechanical properties of deformation layers is suggested. [Copyright &y& Elsevier]