• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.14-22
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• 2001

This paper presents the results of hull form design and powering performance for a 2.500 ton class trimaran frigate. A series of resistance tests and numerical calculations have been conducted to figure out the influences of side-hull form and position on the resistance characteristics of the trimaran. And the propulsion test was conducted to investigate the propulsion efficiency of the trimaran, and the powering performance of the trimaran was compared with that of the similar mono-hull ships in full scale. From the research it was found that the longitudinal position of side-hull had a large influence on the resistance characteristics of the trimaran while the side-hull form and transverse position had a small influence on it. The trimaran showed favorable resistance performance when the side-hull was located near the stern of trimaran, which was resulted from the fact that the side-hull stem was located near the primary wave hollow generated by the main hul1. The powering performance of the trimaran was superior to that of the similar mono-hull ships above the middle speed range.

• Journal of the Korea Society of Computer and Information
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• v.25 no.6
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• pp.65-72
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• 2020

Today, the Internet of Things is used in many places, including homes, industrial sites, and hospitals, to give us convenience. Many services generate new value through real-time data collection, storage and analysis as devices are connected to the network. Many of these fields are creating services and applications that utilize sensors and communication functions within IoT devices. However, since everything can be hacked, it causes a huge privacy threat to users who provide data. For example, a variety of sensitive information, such as personal information, lifestyle patters and the existence of diseases, will be leaked if data generated by smarwatches are abused. Development of IoT must be accompanied by the development of security. Recently, Differential Privacy(DP) was adopted to privacy-preserving data processing. So we propose the method that can aggregate health data safely on smartwatch platform, based on DP.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.6
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• pp.1401-1414
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• 2018

The k-means clustering algorithm groups input data with the number of groups represented by variable k. In fact, this algorithm is particularly useful in market segmentation and medical research, suggesting its wide applicability. In this paper, we propose a privacy-preserving clustering algorithm that is appropriate for outsourced encrypted data, while exposing no information about the input data itself. Notably, our proposed model facilitates encryption of all data, which is a large advantage over existing privacy-preserving clustering algorithms which rely on multi-party computation over plaintext data stored on several servers. Our approach compares homomorphically encrypted ciphertexts to measure the distance between input data. Finally, we theoretically prove that our scheme guarantees the security of input data during computation, and also evaluate our communication and computation complexity in detail.

• Journal of Digital Convergence
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• v.17 no.7
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• pp.285-292
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• 2019

With the popularization of PC, SNS and IoT, a lot of data is generated and the amount is increasing exponentially. Artificial neural network learning is a topic that attracts attention in many fields in recent years by using huge amounts of data. Artificial neural network learning has shown tremendous potential in speech recognition and image recognition, and is widely applied to a variety of complex areas such as medical diagnosis, artificial intelligence games, and face recognition. The results of artificial neural networks are accurate enough to surpass real human beings. Despite these many advantages, privacy problems still exist in artificial neural network learning. Learning data for artificial neural network learning includes various information including personal sensitive information, so that privacy can be exposed due to malicious attackers. There is a privacy risk that occurs when an attacker interferes with learning and degrades learning or attacks a model that has completed learning. In this paper, we analyze the attack method of the recently proposed neural network model and its privacy protection method.

• Journal of the Korean Orthopaedic Association
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• v.53 no.6
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• pp.459-465
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• 2018

Of the many factors that affect the clinical outcomes of orthopedic surgery, the surgical procedure is the most important. Robotics have been developed to perform the surgical procedures more accurately and consistently. Robotic surgical procedures in the orthopedic field were developed 20 years ago. Some designs of surgical robots have disappeared due to practical problems and complications, and an another design of surgical robots is emerging. To date, the use of robot surgery in arthroplasty is still controversial in terms of the clinical outcomes, practicality, and cost-effectiveness, even though it has been reported to be effective in the alignment and positioning of components in the field of artificial joints. Early robotic surgery was based mainly on active robot surgery according to the scheduled operation without the intervention of the operator. Recently the semi-active system of robotic surgery has been introduced. In a semi-active system, the robot constrains the surgeon to a haptic boundary defined by the computer based on the 3-dimensional imaging preoperative plan, and the operator can change the preoperative plan through real-time feedback during operation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.923-929
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• 2018

In this study, we analyzed the resistance performance and running attitude of a catamaran by numerical analysis with a conventional bow, which is generally applied, and a reverse, protruding bow. The shape of the reverse bow was compared through numerical analysis and model tests. The reverse bow shape showed an improved wave pattern by shifting the generation position of the forward divergent wave to the aft in comparison with a conventional bow shape. This effect was found to be effective in determining resistance and stable running attitude. The hull resistance improved by about 2.95 %. The comparative numerical analysis and model test for the reverse bow shape completed in this study should be useful for future hull design application.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.5
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• pp.601-608
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• 2019

In this study, the effect of hull appendages on the high-speed catamarans with reverse bow shapes is compared and analyzed by numerical analysis and circulating water tank model test. The reverse bow shape showed an improved wave shape by shifting the generation position of forward divergent wave to the stern direction and was effective in resistance and stable running posture (Kim et al., 2019). In the model test results of the running performance as the wave patterns and the change of the running posture due to the fin fitted with the inner side of the inverted bow and the interceptor, 1) Trim characteristics of the inverted bow 2) Improvement of superposition of inner wave by Fin 3) The trim control by the fin and the interceptor is considered to be effective in reducing the impact of the two hull connection decks (wetdeck).

• Journal of Aerospace System Engineering
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• v.15 no.1
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• pp.7-18
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• 2021

A semi-active MR damper landing gear is a damper that generates a fluid damping force and a magnetic field control damping force when the MR fluid passes through annular flow paths. In the case of MR fluid passing through annular flow paths, an incompletely developed flow inevitably occurs, causing an error in calculating damper inner forces including the fluid damping force. This error results in an inaccurate design of damper structural parameters and control gain selection, resulting in deterioration of dynamic characteristics and shock absorption performance of the landing gear. In this paper, we derived a mathematical model of an MR damper landing gear considering additional damping force generated in the entrance region of annular flow paths of the MR damper. If the mathematical modeling derived from this paper is applied to the design and optimization process of an MR damper landing gear, excellent performance of the MR damper landing gear is expected.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.2
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• pp.111-118
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• 2022

An electro-mechanical actuator (EMA) is an actuator that combines an electric motor with a mechanical power transmission elements, and it is suitable for urban air mobility (UAM) in terms of design freedom and maintenance. In this paper, the author presents the research results of the EMA that controls the rotor blade pitch angle of UAM. The actuator is based on an inverted roller screw and controls the blade pitch angle through a two-bar linkage. The dynamic equations for the actuator alone and the blade pitching motion with actuator were derived. For the latter, the equivalent moment of inertia is variable depending on the link angle due to the two-bar linkage. The variations of the equivalent moments of inertia are analyzed and compared in terms of the nut motion and the blade pitch motion. For an example model, the variation of the equivalent moment of inertia of the former is smaller than the latter, so it is judged that the dynamic equations derived from the point of view of the nut motion is suitable for the controller design.

• Journal of the Society of Disaster Information
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• v.18 no.3
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• pp.495-506
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• 2022

Purpose: When a serious disaster occurred in East Japan on March 11, 2011, some evacuees in shock failed to avoid danger to the best of their ability. Why did they hesitate and waste their time? And why didn't they choose correct escaping routes? This study attempts to classify human behavior through psychological point of view and cognitive science and to interpret behavioral patterns based on animal behaviors from the field of biology. Method: This study first conceptually categorized walking behavior into intellectualization, automaticity and instinct based on the existing literature and matched these with empirical data. Result: The actual walking patterns observed failed to be compatible with these categories and consequently, this study suggests the following five categories: normal, busy, fast & straight, freezing and tizzy. This new classification of walking behavior is based on speed, variation of speed and change of direction. Conclusion: The method used in this study and the results can be applied to simulations of walking behavior and analysis of behavior in emergency situations.