• Journal of the Society of Naval Architects of Korea
• /
• v.28 no.2
• /
• pp.52-68
• /
• 1991

A new propeller series is developed using the newly developed blade section(KH18 section) which behaves better cavitation characteristics and higher lift-drag ratio at wide range of angle-of-attack. The pitch and camber distributions are disigned in order to have the same radial and chordwise loading distribution with the selected circumferentially averaged wake input. Since the geometries of the series propeller, such as chord length, thickness, skew and rate distribations, are selected by regression of the recent full scale propeller geometric data, the performance prediction of a propeller at preliminary design stage can be mure realistic. Number of blades of the series propellers is 4 and the expanded blade area ratios are 0.3, 0.45, 0.6 and 0.75. Mean pitch ratios are selected as 0.5, 0.65, 0.8, 0.75 and 1.1 for each expanded area ratio. The new propeller series is composed of 20 propellers and is named as KD(KRISO-DAEWOO) propeller series. Propeller open water tests are performed at the experimental towing tank, and the cavitation observation tests and fluctuating pressure measurements are carried out at the cavitation tunnel of KRISO. $B_{P}-\delta$ curves, which can be used to select the optimum propeller diameter at the preliminary design stage, are derived from a regression analysis of the propeller often water test results. The KD-cavitation chart is derived from the cavitation observation test results by choosing the local maximum lift coefficient and the local cavitation number as parameters. The caviy extent of a propeller can be predicted more accurately by using the KD-cavitation chart at a preliminary design stage, since it is derived from the results of the cavitation observation tests in the selected ship's wake, whereas the existing cavitation charts, such as the Burrill's cavitation chart, are derived from the test results in uniform flow.

• Journal of Wetlands Research
• /
• v.25 no.2
• /
• pp.145-158
• /
• 2023

Constructed wetlands (CWs) are effective technologies for urban wastewater management, utilizing natural physico-chemical and biological processes to remove pollutants. This study employed a bibliometric analysis approach to investigate the progress and future research trends in the field of CWs. A comprehensive review of 100 most-recently published and open-access articles was performed to analyze the performance of CWs in treating wastewater. Spain, China, Italy, and the United States were among the most productive countries in terms of the number of published papers. The most frequently used keywords in publications include water quality (n=19), phytoremediation (n=13), stormwater (n=11), and phosphorus (n=11), suggesting that the efficiency of CWs in improving water quality and removal of nutrients were widely investigated. Among the different types of CWs reviewed, hybrid CWs exhibited the highest removal efficiencies for BOD (88.67%) and TSS (95.67%), whereas VSSF, and HSSF systems also showed high TSS removal efficiencies (83.25%, and 78.83% respectively). VSSF wetland displayed the highest COD removal efficiency (71.82%). Generally, physical processes (e.g., sedimentation, filtration, adsorption) and biological mechanisms (i.e., biodegradation) contributed to the high removal efficiency of TSS, BOD, and COD in CW systems. The hybrid CW system demonstrated highest TN removal efficiency (60.78%) by integrating multiple treatment processes, including aerobic and anaerobic conditions, various vegetation types, and different media configurations, which enhanced microbial activity and allowed for comprehensive nitrogen compound removal. The FWS system showed the highest TP removal efficiency (54.50%) due to combined process of settling sediment-bound phosphorus and plant uptake. Phragmites, Cyperus, Iris, and Typha were commonly used in CWs due to their superior phytoremediation capabilities. The study emphasized the potential of CWs as sustainable alternatives for wastewater management, particularly in urban areas.

• Korean Journal of Environment and Ecology
• /
• v.37 no.4
• /
• pp.273-288
• /
• 2023

Although many studies have been conducted on techniques and effects that can be applied to forest meditation in domestic forest healing meditation research, there has been little research on the space where forest meditation takes place. Nevertheless, a meditation space is not just a place concept but a forest environment element responsible for the healing function of a forest, i.e., a place containing healing factors, and can be an essential clue to the healing mechanism. Therefore, to determine whether a healing forest meditation space is suitable for meditation, this study selected the attribute items of the meditation space using the Delphi expert survey and then surveyed the user satisfaction of the healing forest meditation space using the IPA (Importance Performance Analysis) technique. The survey was conducted from August to November 2022, targeting 315 adults who used the forest meditation space at the National Center for Forest Therapy, the Saneum Healing Forest, and the Jathyanggi Pureunsup Arboretum in Gyeonggi Province. The result of the IPA analysis showed the average satisfaction with the forest meditation space was relatively high at 4.33 points on a 5-point Likert scale (4.33 points for the National Center for Forest Therapy, 4.34 points for the Saneum Healing Forest, and 4.37 points for the Jathyanggi Pureunsup Arboretum), indicating that the three healing forest meditation spaces were suitable for forest meditation. Satisfaction with the "Sounds of nature" was high in all three forests. On the other hand, all three forests showed a relatively low satisfaction with "Quietness," indicating it to be a priority problem to be addressed. Also, an open-ended questionnaire survey showed that the mediation space's natural elements, such as natural sounds, scenery, air, forest spaces, and scents, had a higher positive impact on meditation satisfaction than artificial elements, such as facilities. Therefore, it is essential to secure sound resources such as the sound of water and birds around the meditation space, and it is also necessary to consider ways to create a meditation forest in an independent area to avoid encounters with visitors and allow only participants in the forest healing meditation program to enter to increase satisfaction with forest meditation.

• Geophysics and Geophysical Exploration
• /
• v.25 no.4
• /
• pp.167-176
• /
• 2022

We designed a borehole deviation survey tool applicable for steel-cased holes, K-DEV, and developed a prototype for a depth of 500 m aiming to development of own equipment required to secure deep subsurface characterization technologies. K-DEV is equipped with sensors that provide digital output with verified high performance; moreover, it is also compatible with logging winch systems used in Korea. The K-DEV prototype has a nonmagnetic stainless steel housing with an outer diameter of 48.3 mm, which has been tested in the laboratory for water resistance up to 20 MPa and for durability by running into a 1-km deep borehole. We confirmed the operational stability and data repeatability of the prototype by constantly logging up and down to the depth of 600 m. A high-precision micro-electro-mechanical system (MEMS) gyroscope was used for the K-DEV prototype as the gyro sensor, which is crucial for azimuth determination in cased holes. Additionally, we devised an accurate trajectory survey algorithm by employing Unscented Kalman filtering and data fusion for optimization. The borehole test with K-DEV and a commercial logging tool produced sufficiently similar results. Furthermore, the issue of error accumulation due to drift over time of the MEMS gyro was successfully overcome by compensating with stationary measurements for the same attitude at the wellhead before and after logging, as demonstrated by the nearly identical result to the open hole. We believe that the methodology of K-DEV development and operational stability, as well as the data reliability of the prototype, were confirmed through these test applications.