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•Three novel machine learning models were developed to generate radon potential map.•Soil properties and local geology significantly affected the distribution of radon.•The results ...indicated that the GMDH-COA model outperformed the other models.
Prolonged inhalation of indoor radon and its progenies lead to severe health problems for housing occupants; therefore, housing developments in radon-prone areas are of great concern to local municipalities. Areas with high potential for radon exposure must be identified to implement cost-effective radon mitigation plans successfully or to prevent the construction of unsafe buildings. In this study, an indoor radon potential map of Chungcheongnam-do, South Korea, was generated using a group method of data handling (GMDH) algorithm based on local soil properties, geogenic, geochemical, as well as topographic factors. To optimally tune the hyper-parameters of GMDH and enhance the prediction accuracy of modelling radon distribution, the GMDH model was integrated with two metaheuristic optimization algorithms, namely the bat (BA) and cuckoo optimization (COA) algorithms. The goodness-of-fit and predictive performance of the models was quantified using the area under the receiver operating characteristic (ROC) curve (AUC), mean squared error (MSE), root mean square error (RMSE), and standard deviation (StD). The results indicated that the GMDH-COA model outperformed the other models in the training (AUC = 0.852, MSE = 0.058, RMSE = 0.242, StD = 0.242) and testing (AUC = 0.844, MSE = 0.060, RMSE = 0.246, StD = 0.0242) phases. Additionally, using metaheuristic optimization algorithms improved the predictive ability of the GMDH. The GMDH-COA model showed that approximately 7 % of the total area of Chungcheongnam-do consists of very high radon-prone areas. The information gain ratio method was used to assess the predictive ability of considered factors. As expected, soil properties and local geology significantly affected the spatial distribution of radon potential levels. The radon potential map produced in this study represents the first stage of identifying areas where large proportions of residential buildings are expected to experience significant radon levels due to high concentrations of natural radioisotopes in rocks and derived soils beneath building foundations. The generated map assists local authorities to develop urban plans more wisely towards region with less radon concentrations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To enhance the operational stability of submarines, this study conducts a comparative analysis of three pitch limit protection systems based on the reference model, potential function, and dynamic ...trim algorithm. The proposed depth limit protection system adjusts the depth command by comparing the desired depth, calculated by the outer-loop controller, against a predefined depth limit. Similarly, the pitch limit protection systems modify the command pitch calculated by the inner-loop controller to ensure it does not exceed the pitch limit. Submarine maneuvering simulations were conducted to verify the performance of the envelope protection system, which comprises depth and pitch limit protection systems. Simulation results confirmed the effectiveness of these methods, with the dynamic trim algorithm demonstrating superior control efficiency. This study advances submarine safety and stability by developing and validating advanced pitch limit protection systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We have performed integrated dynamics modeling for a supercavitating vehicle. A 6-DOF equation of motion was constructed by defining the forces and moments acting on the supercavitating body surface ...that contacted water. The wetted area was obtained by calculating the cavity size and axis. Cavity dynamics were determined to obtain the cavity profile for calculating the wetted area. Subsequently, the forces and moments acting on each wetted part-the cavitator, fins, and vehicle body-were obtained by physical modeling. The planing force-the interaction force between the vehicle transom and cavity wall-was calculated using the apparent mass of the immersed vehicle transom. We in-tegrated each model and constructed an equation of motion for the supercavitating system. We performed numerical simulations using the integrated dynamics model to analyze the characteristics of the supercavitating system and vali-date the modeling completeness. Our research enables the design of high-quality controllers and optimal supercavita-ting systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A lack of ventilation in multi-unit dwellings can affect human health adversely owing to accumulated radon gases; therefore, developing immediate and effective methods to reduce radon gas in indoor ...living environments is urgently needed. Therefore, this study conducted a basic research study to develop ventilation guidelines for radon through assessments of various ventilation strategies on indoor radon concentration in multiple-unit dwellings, a typical residential type in Korea. Radon measurement was conducted in November 2020 using RAD 7 Radon Detector (Durridge Co., Billerica, MA, USA) for living rooms and rooms of an apartment located in Uijeongbu, Gyeonggi-do, Korea. The radon reduction effect according to the ventilation conditions per hour was compared and evaluated by performing seven natural ventilation scenarios through opening and closing windows leading to the outside and three types of mechanical ventilation with high, middle, and low operating intensity. The concentration ratio (Cr) was estimated to present the indoor radon increase/decrease ratio. Among the natural ventilation scenarios, Case 3 had the highest radon reduction rate in the living room and Case 1 in the room, and Case 2 using natural ventilation equipment showed the lowest reduction rate in both the room and the living room. When ventilated by mechanical ventilation conditions, the radon reduction rate (Pr) was 70% or less under all conditions. Under the natural ventilation measurement condition, when every doors and windows was opened, it showed an effective ventilation in a short time. With high mechanical ventilation, the radon reduction effect in a relatively large space was better. Additionally, with middle and low mechanical ventilation, the reduction effect seems to be good in a relatively narrow space.
The hydrodynamic derivatives are necessary for assessing the dynamic characteristics, such as dynamic stability and maneuverability which are crucial in evaluating navigation safety and operational ...efficiency. Hence, it is required to compute the hydrodynamic derivatives precisely. This study nominates the new empirical formulae for predicting the hydrodynamic derivatives of a submarine. The proposed empirical formulae are derived from hydrodynamic forces and moments which are measured using Computational Fluid Dynamic (CFD) approach. Because the BB2 generic submarine is designed with an appropriate geometry and outstanding features, especially directionally stability, so, it is designated to establish the empirical formulae. The design parameters that have a significant impact on the maneuverability of the BB2 submarine, such as the length-to-diameter ratio, sail position, and sail height, are altered to fit different types of submarines for various purposes. Then, hydrodynamic derivatives of each change factor of the design parameter are taken using the least square method and assessed in relationship with the design parameters through correlation analysis. The high correlation values determine the independent variables which are the design parameters to form the empirical formulae for each hydrodynamic derivative based on multiple regression analysis. The applicability of the established empirical formulae is confirmed by applying them to calculate the hydrodynamic derivatives of BB2 and 2000 tons submarines, and comparing the calculation with the available data. The high precision implies that the established empirical formulae can be used to predict the hydrodynamic derivatives of similar profile submarines to the BB2 and 2000 ton submarines, and they can be extended to submarines in general at the designing phase.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Continuous generation of radon gas by soil and rocks rich in components of the uranium chain, along with prolonged inhalation of radon progeny in enclosed spaces, can lead to severe respiratory ...diseases. Detection of radon-prone areas and acquisition of detailed knowledge regarding relationships between indoor radon variations and geogenic factors can facilitate the implementation of more appropriate radon mitigation strategies in high-risk residential zones. In the present study, 10 factors (i.e., lithology; fault density; mean soil calcium oxide CaO, copper Cu, lead Pb, and ferric oxide Fe
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concentrations; elevation; slope; valley depth; and the topographic wetness index TWI) were selected to map radon potential areas based on measurements of indoor radon levels in 1,452 dwellings. Mapping was performed using three machine learning methods: long short-term memory (LSTM), extreme learning machine (ELM), and random vector functional link (RVFL). The results were validated in terms of the area under the receiver operating characteristic curve (AUROC), root mean square error (RMSE), and standard deviation (StD). The prediction abilities of all models were satisfactory; however, the ELM model had the best performance, with AUROC, RMSE, and StD values of 0.824, 0.209, and 0.207, respectively. Moreover, approximately 40% of the study area was covered by very high and high-risk radon potential zones that mainly included populated areas in Danyang-gun, South Korea. Therefore, the map can be used to establish more appropriate construction regulations in radon-priority areas, and identify more cost-effective remedial actions for existing buildings, thus reducing indoor radon levels and, by extension, radon exposure-associated effects on human health.
In this paper, we focus on planing avoidance control for a supercavitating underwater vehicle based on the potential function method. The planing margin can be calculated using the relative position ...between the cavity center and vehicle center at the end of the vehicle. The planing margin was transformed into a limit variable such as the pitch angle and yaw angle limit. To prevent the vehicle attitude from exceeding the limit variable, a potential function based planing envelope protection method was proposed. The planing envelope protection system overrides commands from the tracking controller, and the vehicle attitude converges to a desired angle, in which the potential function is minimized. Numerical simulations were performed to analyze the physical feasibility and performance of the proposed method. The results showed that the proposed methods eliminated the planing, allowing the vehicle to follow tracking commands.
A supercavitation is a modern technology that can reduce the frictional resistance of an underwater vehicle. To reach supercavity, which is when the cavity envelops the entire vehicle body, a vehicle ...passes through the transition phase from fully wetted to supercavitating operation where unsteady hydrodynamic forces and moments are created by partial cavity. This paper presents analytical and numerical investigations into the dynamics of a supercavitating vehicle in the transition phase as well as a neural network-based adaptive control method that guarantees a stable control performance with modeling uncertainty. The ventilated cavity model is used for the rapid supercavity condition, which is when the cavitation number is relatively high. The cavity profile decides the immersion depths of the fins and body to calculate the hydrodynamical effects on the body. The supercavitating system in the transition phase is replaced by linearized pitch motion dynamics to verify the performance of the design controller. In addition, a numerical simulation shows how the proposed control method can compensate for modeling uncertainty.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The adverse health effects associated with the inhalation and ingestion of naturally occurring radon gas produced during the uranium decay chain mean that there is a need to identify high-risk areas. ...This study detected radon-prone areas using a geographic information system (GIS)-based probabilistic and machine learning methods, including the frequency ratio (FR) model and a convolutional neural network (CNN). Ten influencing factors, namely elevation, slope, the topographic wetness index (TWI), valley depth, fault density, lithology, and the average soil copper (Cu), calcium oxide (Cao), ferric oxide (Fe2O3), and lead (Pb) concentrations, were analyzed. In total, 27 rock samples with high activity concentration index values were divided randomly into training and validation datasets (70:30 ratio) to train the models. Areas were categorized as very high, high, moderate, low, and very low radon areas. According to the models, approximately 40% of the study area was classified as very high or high risk. Finally, the radon potential maps were validated using the area under the receiver operating characteristic curve (AUC) analysis. This showed that the CNN algorithm was superior to the FR method; for the former, AUC values of 0.844 and 0.840 were obtained using the training and validation datasets, respectively. However, both algorithms had high predictive power. Slope, lithology, and TWI were the best predictors of radon-affected areas. These results provide new information regarding the spatial distribution of radon, and could inform the development of new residential areas. Radon screening is important to reduce public exposure to high levels of naturally occurring radiation.
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•Geogenic radon potential maps are generated using FR and CNN methods.•Slope, lithology, and TWI have significant influence on modelling radon level.•Approximately 20% of the study area is classified as very high risk for radon gas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study presents a corrected short-term model using the slope correction factor based on existing short-term models for estimating radon exhalation rates of building materials using the ...closed-chamber method. Based on the adequate performance range of statistical measurement on estimation fit for indoor air quality models presented in ASTM D5157, the accuracy was assessed under different test durations, and an appropriate test duration was obtained. The compatibility of the corrected short-term model was determined by comparing its estimation of the radon exhalation rate with that of the existing model. Then, the corrected short-term model was applied to 14 stone finishes. The results showed that the statistical measure on estimations by the corrected short-term model under a 48 h time duration was adequate for indoor air quality models. Compared with the long-term model, which requires >20 days for testing, the relative error for the radon exhalation rate was <10.4%. Furthermore, the radon exhalation rate estimated using the existing short-term model was over the range for adequate model performance. The range of radon exhalation rates for the 14 stone finishes was 0.01–0.13 Bq h−1, with a mean of 0.03 (±0.03) Bq h−1, which is similar to or slightly lower than those observed in previous studies. The proposed method can improve the accuracy of radon exhalation rate tests for building materials and shorten the test duration, thereby reducing costs. Moreover, the proposed method can be applied to estimate the indoor radon concentration originating from building materials.
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•A corrected short-term model for estimating radon exhalation rate was proposed.•The model under a 48 h test time period was adequate for the accuracy performance.•Compared to the long-term model, the relative error was less than 10.4%.•Our method can be applied to field tests, reducing time and improving accuracy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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