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This study presented experimental and numerical research to investigate the effect of cryogenic leakage on a plate structure of AH36-grade steel containing welded joints. To simulate the cryogenic leakage conditions, the welded plate was exposed to a temperature of −196 °C by supplying liquid nitrogen (LN2) to the center of the steel plate. The time-dependent temperature history and strain variation were measured by using thermocouples and strain gauges attached to the plate surface. Additionally, the residual stress of the middle surface section before and after the cryogenic leakage process was measured by X-ray diffraction analysis (XRD). A three-dimensional finite element model was created with the use of a commercial finite element analysis (FEA) program to simulate the flux-cored arc welding process and cryogenic leakage process. The steel surface temperature dropped sharply and reached approximately −196 °C at 160 s after LN2 supplement. After the first 650 s of the LN2 leakage experiment, the outside of the trough reached approximately −75 °C and −25 °C, depending on the location of the thermal couples. Although there was a relative difference in the results, the experiment and numerical simulation results for temperature and stress distribution showed good agreement. The results could be utilized in the ship design stage adopting welded structures as a basic database.

A critical issue that needs to be addressed for wider utilization of hydrogen as fuel is protection against hydrogen embrittlement during cryogenic storage as it weakens the microstructure bonding force of metals through hydrogen penetration. Austenitic stainless steel, which is usually used in cryogenic vessels and is well known for its high hydrogen resistance at room temperature, has also been reported to be vulnerable to hydrogen embrittlement under cryogenic temperatures. In addition, because large storage vessels are operated over a wide range of temperatures, material behavior at various temperature conditions should also be considered. Therefore, in the present study, hydrogen charging of austenitic stainless steel was performed under various temperature conditions for carrying out prestrain and tensile tests. A decrease in the tensile strength and elongation and an increase in the yield strength were observed in all cases. In particular, the case of 20% prestrain at cryogenic temperature followed by tensile test at room temperature after hydrogen charging showed fracture in the elastic region. The hydrogen index was evaluated from the perspective of elongation and reduction in area, which are factors that indicate the degree of ductility. The aforementioned case showed the most severe results, while non-prestraining followed by tensile tests at room temperature was the least effected by hydrogen. In addition, the effect of strain-induced martensite on hydrogen embrittlement was analyzed using electron backscattered diffraction (EBSD). It was observed that the higher is the prestrain at cryogenic temperatures, the greater is the volume fraction of α’ martensite, which leads to hydrogen embrittlement. The edges and center of the fracture surface were analyzed using scanning electron microscopy (SEM). The hydrogen-charged specimens exhibited brittle fractures at the edges and ductile fractures at the center. The more severe the embrittlement, the more were the number of intergranular fractures and microdimples observed at the edges.

Austenitic stainless steel is useful for storing and transporting liquefied natural gas (LNG) at temperatures below −163 °C due to its superior low-temperature applications. This study develops a computational method for the failure prediction of 304L stainless steel sheet to utilize its usability as a design code for industrial purposes. To consider material degradation in a phenomenological way during the numerical calculation, the combined Swift–Voce equation was adopted to describe the nonlinear constitutive behavior beyond ultimate tensile strength. Due to the stress state-dependent fracture characteristics of ductile metal, a modified Mohr–Coulomb fracture criterion was adopted using stress triaxiality and Lode angle parameter. The numerical formulation of the elastoplastic-damage coupled constitutive model with fracture locus was implemented in the ABAQUS user-defined subroutine UMAT. To identify the material and damage parameters of constitutive models, a series of material tests were conducted considering various stress states. It has been verified that the numerical simulation results obtained by the proposed failure prediction methodology show good agreement with the experimental results for plastic behavior and fractured configuration.

Besides genetic characteristics, people also undergo a process of skin aging under the influence of diverse factors such as sun exposure, food intake, sleeping patterns, and drinking habits, which are closely related to their personal lifestyle. So far, many studies have been conducted to analyze skin conditions quantitatively. However, to describe the current skin condition or predict future skin aging effectively, we need to understand the correlation between skin aging and lifestyle. In this study, we first demonstrate how to trace people’s skin condition accurately using scale-invariant feature transform and the color histogram intersection method. Then, we show how to estimate skin texture aging depending on the lifestyle by considering various features from face, neck, and hand dermoscopy images. Lastly, we describe how to predict future skin conditions in terms of skin texture features. Based on the Pearson correlation, we describe the correlation between skin aging and lifestyle, and estimate skin aging according to lifestyle using the polynomial regression and support vector regression models. We evaluate the performance of our proposed scheme through various experiments.

Leakage is one of the abnormal conditions in water distribution systems (WDSs). Real-time monitoring can be used to prevent or recover quickly from leakage. However, this is not enough: for improved leakage detection, a status diagnosis of the WDS must be performed together with this real-time monitoring, and numerous studies have been conducted on this. Furthermore, the existing proposed methodology only provides optimal sensor location and fast recognition. This paper proposes a technique that can quantitatively evaluate the volume of leakage along with leakage detection using deep learning technology. The hydraulic data (e.g., pressure, velocity, and flow) from the calibrated hydraulic model were used as training data and deep learning techniques were applied to conduct a simultaneous detection of leakage volume and location. We examined various scenarios regarding leakage volume and location for the data configuration of a simulated leakage accident. Furthermore, for optimal leakage detection performance, the detection performance according to the size of the network, the meter types of meters, the number of meters, and the locations of the meters were analyzed. This study is expected to be helpful in various aspects such as recovery and restoration decision making after leakage, because it simultaneously identifies the amount and location of the leakage.

Recently, due to extreme climate change, damage from flooding has been increasing; however, water shortages are being announced simultaneously. Moreover, the water distribution system’s ability to supply consumers is being overwhelmed because of urbanization, population concentration, and increases in water consumption. For this reason, to solve the water shortage problem, water reuse technologies are developing and improving that perform simple chemical treatment processes to reuse water for flushing toilets, washing, gardening, etc. but not as drinking water. However, most water reuse systems are designed and operated as independent systems, such as reusing water used in individual buildings or using rainwater. Therefore, this study develops an optimal design for the combined water systems, which is modeling and designing water distribution systems, urban drainage systems, and water reuse systems simultaneously to solve the water shortage and reduce flooding damage. To consider the combined water systems design, the existing water distribution system (WDS) demand is divided into drinking water and other uses, and the resource of other water is assumed by the rainwater storage tank for covering the amount of exceeding precipitation. To derive optimal design solutions for the combined three water systems, single- and multi-objective optimization techniques are applied considering various design criteria (i.e., construction cost, system resilience, and flooding volume on the exceeding design rainfall intensity). The developed combining water system design techniques could be used to create designs that solve the problems of medium and long-term water shortages and sustainable water systems development.

Water distribution systems (WDSs) are designed for supplying safe water under abnormal conditions. Therefore, the optimal design of WDSs should present a plan that satisfies the hydraulic constraint, pressure at the node, and flow rate of the pipe. The water quality constraint, that is, the residual chlorine standard, should be also satisfied. However, there is a problem of insufficient pressure or absence of water for the rapid increase in demand and abnormal situations caused by the destruction of pipes resulting from growing urbanization. This problem differs in node pressure and residence time, depending on the type of WDSs (i.e., loop, hybrid, and branch). Therefore, in this study, the optimal design of WDSs was determined by considering the form of the WDS and the residual chlorine concentration. To construct the layout of WDSs, the type was constructed and classified using the branch index, classification index, and hydraulic water-quality characteristics, which were analyzed accordingly. In addition, the objectives of the WDSs in terms of hydraulic (i.e., nodal pressure) and water-quality (i.e., reference values of residual chlorine concentrations) constraints were established to derive optimal designs that simultaneously stabilize and satisfy water. To stably supply water to the customer even in abnormal situations, an optimal multipurpose design was carried out by setting the sum of the surplus head and design cost as an objective function. These analyses can improve the water quality by simultaneously considering the residual chlorine concentration. They improved the hydraulic characteristics by considering only pressure in the existing design stage. In addition, by deriving an optimal design plan in terms of hydraulic quality according to topological features, we can derive an optimal design that assists the designer in decision making while improving the economic aspect and usability for the consumer.

The hydraulic analysis of water distribution systems (WDSs) is divided into two approaches, namely, a demand-driven analysis (DDA) and a pressure-driven analysis (PDA). In DDA, the basic assumption is that the nodal demand is fully supplied irrespective of the nodal pressure, which is mainly suitable for normal operating conditions. However, in abnormal conditions, such as pipe failures or unexpected increases in demand, the DDA approach may cause unrealistic results, such as negative pressure. However, despite these realistic hydraulic analysis approaches for WDSs being emphasized in the design process, this consideration was lacking in the design aspect. Therefore, in this study, the designs by the DDA-based design model and PDA-based design model are compared, and their design characteristics are analyzed to identify the efficiency of the WDSs design under abnormal system conditions. The developed PDA model was applied to three networks (a well-known benchmark system and a real-life WDN), and the results showed that the proposed model is superior to other reported models when dealing with negative pressure under abnormal conditions. In addition, the optimal design of WDN considered PDA is presented, and the optimal construction cost is decreased to increase the percentage of PDA.