• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.18-31
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• 2018

Rotorcrafts have more severe crashworthiness conditions than fixed wing aircraft owing to VTOL and hovering. Recently, with the increasing demand for highly efficient transportation system, application of composite materials to aircraft structures is increasing. However, due to the characteristics of composite materials that are susceptible to impact and crash, demand to prove the crashworthiness of composite structures is also increasing. The purpose of present study is to derive the structural concept of composite subfloor for rotorcrafts and verify it. In order to design a crashworthy composite subfloor, the conceptual design of the testbed helicopter for the demonstration and the derivation of energy absorbing requirement were carried out, and the composite energy absorber was designed and verified. Finally, the testbed for the demonstration of a crashworthy composite structure was fabricated, and performed free drop test. It was confirmed that the test results meet the criteria for ensuring occupant survivability.

• Journal of Korean Society of Steel Construction
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• v.18 no.4
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• pp.503-514
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• 2006

FBG sensors are capable of measuring the strain of structures easily and more durably than electric resistance gauges. Thus, many researches are dedicated to the application for the response monitoring or non-destructive evaluation of structures using FBG sensors. Additionally, the measured strains at the top and bottom of a cross-section can be transformed into the curvature of the section, which can be used to calculate its vertical displacement. Hence, this study aims to measure the dynamic strain signals of a steel section simply supported beam and to estimate the dynamic displacement from the strain signals, after which the estimated displacement is com pared with the measured displacement. The dynamic characteristics (natural frequency, damping ratio and mode shape) of the beam are predicted from both the estimated and measured displacement signals, and from the strain time history of the FBG sensors. The predicted properties are compared with those of an analytical model of the beam. The estimated displacement. However, the predicted dynamic properties from both the estimated displacements and the measured strains are well-correlated with those from the measured displacement. It is therefore appreciated that the estimation of the dynamic properties of FBG sensor signals is reasonable. Especially, the strain signal of the FBG sensor was amplified at a higher-frequency region in comparison with the displacement estimation with higher-mode properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.106-111
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• 2017

In this study, the stiffness of an LMU (Leg Mating Unit), which is a device required for installing the top side part of an offshore structure, was examined through structural analysis. This unit is mounted on the supporting point of the structure and is used to absorb the shock at installation. It is a cylindrical structure with an empty center. To support the vertical load, elastomeric bearings (EBs) and iron plates are laminated in layers. The stiffness of the EBs is basically influenced by the size of the bearings, but it varies with the number of laminated sheets inside the same sized structure. The relationship between the stiffener and the compressive stiffness is investigated, and its design is suggested. The stiffness of the EBs is analyzed by calculating the reaction force, while controlling the displacement. First, the relationship between the size of the reinforcing plate and the compressive stiffness is considered. Next, the relationship between the number of stacked reinforcing plates and the compression stiffness is considered. Different loads are required for each installed point. The goal is to design the compression stiffness in such a way that the same deformation occurs at each point in the analysis. In this study, ANSYS is used to perform the FE analysis.

• Journal of Korean Orthopaedic Sports Medicine
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• v.3 no.1
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• pp.66-72
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• 2004

Purpose: To evaluate the compensatory mechanism in vivo and develop the treatment guide by performing the comprehensive functional tests of the posterior cruciate ligament (PCL) deficient subjects. Material and Methods: 10 PCL deficient subjects and 10 healthy control group were evaluated. Performed functional tests were range of motion, posterior drawer test, Telos, 30$^{\circ}$ flexion wt-bearing view, KT-1000 arthrometer, gait analysis, EMG test and isokinetic tests. Results: Physical, KT-1000, Telos posterior tests showed significant differences, but 300 full weight bearing lateral view, muscle strength test revealed no difference between two groups. Less knee flexion at initial contact and reduced maximum valgus moment were observed in PCL deficient group. In vertical drop landing, PCL group had increased plantar flexion angle at initial contact. Conclusion: Compensatory mechanisms such as reduced unstable components and absorbing the maximal load of the joint were occurred after PCL insufficiency, which result in good clinical and functional outcomes. Further investigations would be needed to understand the functional adaptations of PCL deficient subjects.

• Journal of IKEEE
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• v.24 no.1
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• pp.33-39
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• 2020

In this paper, we propose the design technique of the vehicle's load weight measuring system using tire pressure, which is one of the physical elements of tires. The proposed technique consists of four processes: noise correction by load and vibration, gas flow correction, data mixer and weight conversion. Noise correction by load and vibration eliminates noise that increases the tire's internal pressure due to external shocks and vibrations produced by the vehicle while it is in motion. In the gas flow correction process, the noise of the internal pressure of the tire is increased due to the temperature rise of the ground with respect to the data obtained through the noise correction process due to the load and vibration. In the data mixer process, the load and pressure on the tolerances the empty, median and the full load are classified according to the change in pressure of the tire that is delivered perpendicular to the tire in the event of cargo. In the weight conversion process, weight is expressed by weight through weight conversion algorithms using noise correction results by load and vibration and gas flow correction. The weight conversion algorithm calculates the weight conversion factor, which is the slope of the linear function with respect to the load and pressure change, and converts the weight. In order to evaluate the accuracy of the loading weight measurement system of the vehicle using the tire pneumatic system technique proposed in this paper, we propose the design technique of the vehicle's load weight measuring system using tire pressure, which is one of the physical elements of tires.. Noise correction results by load and vibration and gas flow data correction results showed reliable results. In addition, repeated weight precision test showed better weight accuracy than the standard value of 90% of domestic companies.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.243-254
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• 2019

In this study, problems of the waterproofing methods in which water leakage occurs in the upper slab of the underground parking lot of apartment houses and the requirements considering the characteristics of the upper slab, and selected the appropriate performance(proposal) for the composite polyurea process are reviewed. As a result of the study, it is necessary to review performance such as responsiveness to upper slab of the multi-unit underground parking lot that is comprised of (1) crack and behavior responsiveness, (2) surface integrity, (3) vertical watertight stability, (4) pressure layer construction, (5) impact and pressure response and (6) vehicle moving load. As a result of evaluating 5 items corresponding to the requirements for the soft and hard complex polyurea, all of them were found to meet the conditions, and each materials were improved by compounding the materials that had problems when applying a single-ply method, thereby clarifying the advantages and disadvantages of the material property. However, in order to apply to the actual site, additional evaluation on site applicability such as mock-up evaluation should be conducted, and subsequent studies on the applicability of the market through review of economic feasibility and maintenance is required.

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.33-42
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• 2021

Modern aircraft fighters improve the maneuverability and performance with the RSS (Relaxed Static Stability) concept and therefore these aircrafts are susceptible to abrupt pitch-up in the transonic and moderate Angle-of-Attack (AoA) flight region where the shock wave is formed and the mean aerodynamic center is moved forward during deceleration. Also, the modeling of the aircraft flying in this flight region is very difficult due to complex flow filed and unpredictable dynamic characteristics and the model-based control design technique does not fully cover this problem. In this paper, we analyzed the performance of the TPMC (Transonic Pitching Moment Compensation) control based on the model-based IDI (Incremental Dynamic Inversion) and the Hybrid IDI based on the model and sensor based IDI during the SDT (Slow Down Turn) in transonic region. As the result, the Hybrid IDI had quicker response and the same maximum g suppression performance and provided the predictable flying qualities compared to the TPMC control. The Hybrid IDI improved the performance of the Over-G protection controller in the transonic and moderate AoA region

• The Journal of Korean Institute of Information Technology
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• v.16 no.11
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• pp.51-59
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• 2018

The Multi-Mission Unmanned Surface Vehicle(MMUSV), which is manufactured using glass Fiber Reinforced Plastic(FRP) material, is designed to perform a surveillance and reconnaissance on the sea. Various navigation sensors, such as RADAR, RIDAR, camera, are mounted on a mast to perform an autonomous navigation. And a dummy gun is mounted on the deck of the MMUSV for a target tracking and disposal. It is necessary to analyze a strength for structures mounted on the deck because the MMUSV performs missions under a severe sea state. In this paper, a strength analysis of the mast structure is performed on static loads and lateral external loads to verify an adequacy of the designed mast through a series of simulations. Based on the results of captive model tests, a strength analysis for a heave motion of the mast structure is conducted using a simulation tool. Also a simulation and fatigue test for a mounting part between the MMUSV and the dummy gun are performed using a specimen. The simulation and test results are represented that a structure of the mast and mounting part of the dummy gun are appropriately designed.he impact amount are performed through simulation and experiments.

• Composites Research
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• v.20 no.5
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• pp.13-19
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• 2007

Fiber-reinforced thermoplastic composites not only approach almost near to the strength of thermosetting composite but also has excellent productivity, recycling property, and impact resistance, which are pointed as weaknesses of thermosetting composites. The study for strength calculation of one direction fiber-reinforced thermoplastic composites and the study measuring precisely fiber orientation distribution were presented. Need the systematic study for the data base that can predict mechanical properties of composite material and fiber orientation distribution by the fiber content ratio was not constructed. Therefore, this study was investigated what affect the fiber content ratio and fiber orientation distribution have on the strength of composites. Fiber-reinforced thermoplastic composites by changing fiber orientation distribution and the fiber content ratio were made. Tensile strength ratio of $0^{\circ}$ direction of fiber-reinforced composites increased being proportional the fiber content and fiber orientation function as change from isotropy(J=0) to anisotropy(J=1). But, tensile strength ratio of $90^{\circ}$ direction by separation of fiber filament decreased when tensile load is imposed fur width direction of reinforcement fiber length direction.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.513-523
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• 2017

We evaluated the viability of phytoplankton along the salinity gradient in the flood and ebb tides of spring tide of February and the ebb tide of neap tide of March 2017 in the Seomjin River Estuary. Additional laboratory experiments were also conducted to determine the reason of the pH changes along the salinity gradient using the field natural sample in February. In field, saltwater was well mixed at downstream vertically and the salinity gradient was horizontally appeared toward upstream of freshwater zone. There were strong negative correlations between salinity and nutrient (nitrate + nitrite R=0.99, p<0.001, and silicate R=0.98, p<0.001), implying that those two nutrients of freshwater origin were gradually diluted with mixing the saltwater. On the other hands, relatively high phosphate concentration was kept in the stations of saltwater over 15 psu, indicating that it was caused by resuspended sediments of Gwangyang Bay and downstream by tidal water mixing.Among phytoplankton community structure in winter, Eucampia zodiacus have occupied to be c.a. 70 % in the most stations. Based on the field survey results for survivability of phytoplankton by phytoPAM instrument, there was positive correlations between salinity and chlorophyll a (R=0.82, p<0.001) and, salinity and active chlorophyll a (R=0.80, p<0.001), implying that the dominant marine diatom species may have significantly damaged in low salinity conditions of upstream. Also, maximum mortality rate of phytoplankton caused by low salinity shock was appered to be 75% in the upstream station. In particular, the pH in spring tides of February had tended to increase with high phytoplankton accmulated stations, suggesting that it was related with absorption of $CO_2$ by the photosynthesis of dominant diatom. In laboratory experiments, phytoplankton mass-mortality caused by low salinity shock was also occurred, which is confirmed with reducing the photosynthetic electron transport activity. Following the phytoplankton mass-mortality, bacteria abundance was significantly increased in 24 hours. As a result, the mass-proliferating bacteria can produce the $CO_2$ in the process of biodegradation of diatoms, which can lead to pH decrease. Therefore, marine phytoplankton species was greatly damaged in freshwater mixing area, depending on along the salinity gradient that was considered to be an important role in elevating and reducing of pH in Seomjin River Estuary.