• The Journal of the Acoustical Society of Korea
• /
• v.38 no.2
• /
• pp.214-221
• /
• 2019

In this paper, a temperature dependent acoustic receiving characteristics of underwater acoustic sensor is studied by theoretical and experimental investigations. Two different types (low mid frequency sensor and high frequency sensor) of underwater acoustic sensors are designed with different configuration of baffle and conditioning plate. The temperature dependent characteristics of the acoustic sensors are investigated within the temperature range from $-2^{\circ}C$ to $35^{\circ}C$. The material properties of the piezoelectric ceramics, molding and baffle, which are the primary materials of the acoustic sensors, are measured with temperature change. The temperature dependent RVS (Receiving Voltage Sensitivity) characteristics of the acoustic sensors are simulated by using the measured material properties. The RVS changes of the acoustic sensors are measured by changing temperature in the watertank where the acoustic sensors are installed. The measured and the simulated data show that the temperature dependent characteristics of the acoustic sensors are mainly dependent for the sound speed changes of the molding material.

• The Korean Journal of Archival Studies
• /
• no.48
• /
• pp.45-92
• /
• 2016

Corporations report their economical, environmental, social influences and achievements through sustainability reports. Apart from the financial reports, which are subject to legal restrictions, sustainability reports inform non financial achievements of a corporation, thus the reliability of the information is solely dependent on the corporation itself. The current sustainability reports are of types that cannot include proof or source of the index data, thus they are tended to be regarded as means of publicity. The reliability of the reports is often questioned. This research applied the concept of Evidence-Based Accountability, which will allow the confirmation of accountability through records including contents and context of the tasks. Evidence-Based Accountability means producing and accumulating witness records of actions, then managing the records as usable information and use them as accountability information. Index data from sustainability reports of domestic corporations and web based reports of Vodafone was reviewed. Measures to link task records as proof of index data was studied. To make this possible, record production and acquisition system was redesigned in order to secure required records as evidence. Linked build-up of SR system and RMS was proposed. The proposed system will allow collection and management of records as SR accountability information, and provide the data when necessary. Also, corporate infrastructure was proposed. This infrastructure will build a professional records management system in stages, through organizational system and regulations. Cooperation of staff in this infrastructure will support reliable corporate accountability.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.1
• /
• pp.127-136
• /
• 2019

Tunnel construction by TBMs should be supported by the performance of a screw conveyor in order to obtain the optimum penetration rate, so studies related to the screw conveyor performance have been being conducted. Compared to the study on the performance of the screw conveyor for the soil, however, the research on the performance of the screw conveyor for the rock is insufficient. Considering the domestic tunnel sites with more rock layers than soil layers, simulation of discharge of 6 types of rock chips by the screw conveyor was conducted using DEM. Regardless of the shape and volume of the rock chips, the discharge rates of the rock chips by the parallel placed screw conveyor at a speed of 10 RPM in the same rock mass were about 20% (standard deviation: 1.3%) of the maximum volume of discharge rate by the screw conveyor. It is expected that this study can be used as a reference material for screw conveyor design and operation in TBM excavations in rock masses.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.5
• /
• pp.36-46
• /
• 2019

The number of hosts connected to the Internet has increased dramatically, introducing the Domain Name System(DNS) in 1984. DNS is now an important key point for all users of the Internet by allowing them to use a convenient character address without memorizing a series of numbers of complex IP address. However, relative to the importance of DNS, there still exist many problems such as the authorization allocation issue, the disputes over public registration, security vulnerability such as DNS cache poisoning, DNS spoofing, man-in-the-middle attack, DNS amplification attack, and the need for many domain names in the age of hyper-connected networks. In this paper, to effectively improve these problems of existing DNS, we proposed a method of implementing DNS using distributed ledger technology, blockchain, and implemented using a Ethereum-based platform. In addition, the qualitative analysis performance comparative evaluation of the existing domain name registration and domain name server was conducted, and conducted security assessments on the proposed system to improve security problem of existing DNS. In conclusion, it was shown that DNS services could be provided high security and high efficiently using blockchain.

• Journal of Korean Society of Archives and Records Management
• /
• v.21 no.3
• /
• pp.187-215
• /
• 2021

Archives should provide a web-based archival information service with good usability based on the understanding of users' needs. Thus, this study analyzed the usability of the National Archives of Korea (NAK) website's search service through expert and usability evaluations for various users and suggested improvement plans. A literature review, heuristic evaluation, one of the usability expert evaluation methods, and usability evaluation for users were performed. As a result of expert evaluation, the severity rating for the usability problem was highest regarding a match between the system and real world and the lowest in error prevention. In the usability evaluation, it was assumed that the user's background and whether the website's help was provided is associated with usability. Usability evaluation was conducted for 22 participants, including those majoring in records management, web/application developers, and people without such backgrounds. Furthermore, a presurvey, a five-second test, and search tasks were conducted in a row. The analysis based on usability components in ISO 9241-11: 2018, i.e., effectiveness, efficiency, and satisfaction, showed that web/application developers had the highest search effectiveness, and those majoring in records management showed high effectiveness only in the search for archival content services. Background factors did not affect efficiency, and the more familiar with the finding aids, the better the efficiency. Moreover, providing the website's help was found to be positively associated with effectiveness and satisfaction. This study suggests that the NAK website will offer a user-friendly interface and search function, expand help support, and display a consistent web interface.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.3
• /
• pp.303-310
• /
• 2021

Cracks in bridges are important factors that indicate the condition of bridges and should be monitored periodically. However, a visual inspection conducted by a human expert has problems in cost, time, and reliability. Therefore, in recent years, researches to apply a deep learning model are started to be conducted. Deep learning requires sufficient data on the situations to be predicted, but bridge crack data is relatively difficult to obtain. In particular, it is difficult to collect a large amount of crack data in a specific situation because the shape of bridge cracks may vary depending on the bridge's design, location, and construction method. This study developed a crack detection model that generates and trains insufficient crack data through a Generative Adversarial Network. GAN successfully generated data statistically similar to the given crack data, and accordingly, crack detection was possible with about 3% higher accuracy when using the generated image than when the generated image was not used. This approach is expected to effectively improve the performance of the detection model as it is applied when crack detection on bridges is required, though there is not enough data, also when there is relatively little or much data f or one class.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.33 no.3
• /
• pp.122-130
• /
• 2021

A wind-speed estimation at the arbitrary elevations is key component for the design of the offshore wind energy structures and the computation of the wind-wave generation. However, the wind-speed estimation of the target elevation has been carried out by using the typical functions and their typical parameters, e.g., power and logarithmic functions because the available wind speed data is limited to the specific elevation, such as 2~3m, 10 m, and so on. In this study, the parameters of the vertical profile functions are estimated with optimal and analyzed the parameter ranges using the HeMOSU-1 platform wind data monitored at the eight different locations. The results show that the mean value of the exponent of the power function is 0.1, which is significantly lower than the typically recommended value, 0.14. The values of the exponent, the friction velocity, and the roughness parameters are in the ranges 0.0~0.3, 0~10 (m/s), and 0.0~1.0 (m), respectively. The parameter ranges differ from the typical ranges because the atmospheric stability condition is assumed as the neutral condition. To improve the estimation accuracy, the atmospheric condition should be considered, and a more general (non-linear) vertical profile functions should be introduced to fit the diverse profile patterns and parameters.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
• /
• 2014.10a
• /
• pp.25-48
• /
• 2014

Increased frequency of climate extremes is another face of climate change confronted by humans, resulting in catastrophic losses in agriculture. While climate extremes take place on many scales, impacts are experienced locally and mitigation tools are a function of local conditions. To address this, agrometeorological early warning systems must be place and location based, incorporating the climate, crop and land attributes at the appropriate scale. Existing services often lack site-specific information on adverse weather and countermeasures relevant to farming activities. Warnings on chronic long term effects of adverse weather or combined effects of two or more weather elements are seldom provided, either. This lecture discusses a field-specific early warning system implemented on a catchment scale agrometeorological service, by which volunteer farmers are provided with face-to-face disaster warnings along with relevant countermeasures. The products are based on core techniques such as scaling down of weather information to a field level and the crop specific risk assessment. Likelihood of a disaster is evaluated by the relative position of current risk on the standardized normal distribution from climatological normal year prepared for 840 catchments in South Korea. A validation study has begun with a 4-year plan for implementing an operational service in Seomjin River Basin, which accommodates over 60,000 farms and orchards. Diverse experiences obtained through this study will certainly be useful in planning and developing the nation-wide disaster early warning system for agricultural sector.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.6
• /
• pp.575-586
• /
• 2020

In this study, a two-dimensional hydraulic model test was conducted to examine the hydraulic phenomena that occur around the seawall when wave and wind coexist. Based on recent seawall repair and reinforcement examples, the experimental section was constructed under the condition of installing wave dissipation blocks on the safety surface of four different representative seawalls. Water level fluctuation, reflection, overtopping and wave pressure characteristics according to external force change were reviewed. It was confirmed that the top concrete shape of the seawall is the most important factor of the hydraulic characteristics that appear in front of the seawall, and the tendency is more pronounced when wind acts. Even in the case of vertical type seawall, when wind of 3 m/s~5 m/s occurs, the amount of overtopping increases to about 5%~12%. In the case of wave pressure, it was confirmed from the experimental results that the value increased from about 1.5 to 2.2 times in front of the top of concrete block. In addition, it was confirmed that when the shape of the seawall was different, the range of change in the hydraulic characteristics appeared larger. Therefore, when designing a seawall of a new shape, a more detailed review of the hydraulic characteristics should be accompanied based on these experimental results.

• Journal of the Korean GEO-environmental Society
• /
• v.12 no.5
• /
• pp.59-63
• /
• 2011

Ground dynamic parameter such as shear elastic modulus and damping ratio is a very important variable in design of ground-structure with repeated load and dynamic load. Shear elastic modulus and damping ratio on small strain below linear limit strain is constant regardless of strain. Shear elastic modulus as the maximum shear elastic modulus and damping ratio as the minimum damping ratio were considered. As a lot of experiment related to the maximum shear elastic modulus, which is in dynamic deformation characteristics, have been conducted, many factors including voiding ratio, over consolidation ratio(OCR), confining pressure, geology time, PI, and the number of load cycle affect to dynamic soil characteristic. However, the research of ground dynamic characteristic improved with grout is absent such as underground continuous wall construction, deep mixing method, umbrella arch method. In order to investigate the dynamic soil characteristics improved with grout, in this study, resonant column tests were performed with changing water content(20%, 25%, 30%) and injection ratio of grout(5%, 10%, 15%), cure time(7th day, 28th day) As a result, shear elastic modulus and damping ratio, which are ground dynamic parameter, are affected by the injection ratio of milk grout, cure time and water content.