• Smart Structures and Systems
• /
• v.6 no.5_6
• /
• pp.481-504
• /
• 2010

Wireless smart sensor networks (WSSNs) have been proposed by a number of researchers to evaluate the current condition of civil infrastructure, offering improved understanding of dynamic response through dense instrumentation. As focus moves from laboratory testing to full-scale implementation, the need for multi-hop communication to address issues associated with the large size of civil infrastructure and their limited radio power has become apparent. Multi-hop communication protocols allow sensors to cooperate to reliably deliver data between nodes outside of direct communication range. However, application specific requirements, such as high sampling rates, vast amounts of data to be collected, precise internodal synchronization, and reliable communication, are quite challenging to achieve with generic multi-hop communication protocols. This paper proposes two complementary reliable multi-hop communication solutions for monitoring of civil infrastructure. In the first approach, termed herein General Purpose Multi-hop (GPMH), the wide variety of communication patterns involved in structural health monitoring, particularly in decentralized implementations, are acknowledged to develop a flexible and adaptable any-to-any communication protocol. In the second approach, termed herein Single-Sink Multi-hop (SSMH), an efficient many-to-one protocol utilizing all available RF channels is designed to minimize the time required to collect the large amounts of data generated by dense arrays of sensor nodes. Both protocols adopt the Ad-hoc On-demand Distance Vector (AODV) routing protocol, which provides any-to-any routing and multi-cast capability, and supports a broad range of communication patterns. The proposed implementations refine the routing metric by considering the stability of links, exclude functionality unnecessary in mostly-static WSSNs, and integrate a reliable communication layer with the AODV protocol. These customizations have resulted in robust realizations of multi-hop reliable communication that meet the demands of structural health monitoring.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.11
• /
• pp.57-70
• /
• 2018

In this study, verification of the nonlinear effective stress analysis is performed for introducing performance based earthquake resistance design of port and harbor structures. Seismic response of gravitational caisson quay wall in numerical analysis is compared directly with dynamic centrifuge test results in prototype scale. Inside of the rigid box, model of the gravitational quay wall is placed above the saturated sand layer which can show the increase of excess pore water pressure. The model represents caisson quay wall with a height of 10 m, width of 6 m under centrifugal acceleration of 60 g. The numerical model is made in the same dimension with the prototype scale of the test in two dimensional plane strain condition. Byrne's liquefaction model is adopted together with a nonlinear constitutive model. Interface element is used for sliding and tensional separation between quay wall and the adjacent soils. Verification results show good agreement for permanent displacement of the quay wall, horizontal acceleration at quay wall and soil layer, and excess pore water pressure increment beneath the quay wall foundation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.1
• /
• pp.94-101
• /
• 2019

Most of the existing rail structures have undergone a lot of aging since a considerable period of time has passed from completion. In particular, among existing railway bridges, many of the plate girder bridges are older bridges that have lived 40 to 60 years or more. Since the treadmill is directly connected to the girder without the ballast, the running load of the vehicle is directly transmitted to the bridge. Therefore, the shock and noise applied to the bridge are larger than those of the ballast bridge, and the dynamic shock and vibration are also relatively large. Therefore, it is very urgent to develop appropriate maintenance, repair and reinforcement technology for existing steel plate bridge. In this study, the authors introduced the characteristics of embedded rail (ERS) developed for improving the performance of the existing plate girder bridge and the techniques solving the vibration and noise problems. In order to evaluate the vibration and noise reduction performance of ERS, a non-ballast plate girder bridge with 5m length of sleepers installed and a plate girder bridge with ERS were fabricated. And, then, the vibration response generated under the same excitation condition was measured and analyzed. Also, the radiated noise analysis was performed using the vibration response data obtained from the experiment as the input data of the acoustic analysis model. As a result of experiments and analyses, it was confirmed that the plate girder bridge's vibration using ERS was reduced by 15.0~18.8dB and the average noise was reduced by 7.7dB(A) more than the non-ballast bridge.

• Journal of agricultural medicine and community health
• /
• v.44 no.3
• /
• pp.115-123
• /
• 2019

Objective: This study was conducted to examine the effects of a health promotion program on the health condition of rural elderly women implemented at primary health care posts using Korean Frailty Index. Methods: The research was designed a nonequivalent control group pretest-posttest setting. The participants in this study were 50 residents (intervention group: 25, control group: 25) selected from 4 villages 2 primary health care posts in J city Gyeongsangnam-do. The health promotion program was conducted at the primary health care posts twice a week for 12 weeks. This program consisted of basic exercises(Gukseondo + Theraband muscle strength training) and additional activities(including modified Theraband activity, rubber ball exercise, ball massage, nutrition class, singing class). Collected data were analyzed by descriptive statistics, paired t-test, and repeated measures ANOVA with SPSS 21.0. Results: Results of the health promotion program showed that the health conditions(measured by perceived health status, frailty score, upper/lower flexibility, maximum grip strength, dynamic balance test Timed Up and Go) of the experimental group(25) all statistical significantly improved. Conclusion: Study findings indicate that the health promotion program implemented at primary health care posts on rural elderly women is effective and can contribute to a developed health promotion program for local residents in the future.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.4
• /
• pp.601-609
• /
• 2022

Jack-up drilling rigs are mobile offshore platforms widely used in the offshore oil and gas exploration industry. These are independent, three-legged, self-elevating units with a cantilevered drilling facility for drilling and production. A typical jack-up rig includes a triangular hull, a tower derrick, a cantilever, a jackcase, living quarters and legs which comprise three-chord, open-truss, X-braced structure with a spudcan. Generally, jack-up rigs can only operate in water depths ranging from 130m to 170m. Recently, there has been an increasing demand for jack-up rigs for operating at deeper water levels and harsher environmental conditions such as waves, currents and wind loads. All static and dynamic loads are supported through legs in the jack-up mode. The most important issue by society is to secure the safety of the leg structure against collision that causes large instantaneous impact energy. In this study, nonlinear FE -analysis and verification of the requirement against collision for 35MJ recommended by DNV was performed using LS-Dyna software. The colliding ship used a 7,500ton of shore supply vessel, and five scenarios of collisions were selected. From the results, all conditions do not satisfy the class requirement of 35MJ. The loading conditions associated with chord collision are reasonable collision energy of 15M and brace collisions are 6MJ. Therefore, it can be confirmed that the identical collision criteria by DNV need to be modified based on collision scenarios and colliding members.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.50-59
• /
• 2021

Currently, the response correction factor is calculated by comparing the response measured by the load test on a bridge with the response analyzed in the initial analytical model. Then the load rating and the load carrying capacity are evaluated. However, the response correction factor gives a value that fluctuates depending on the measurement location and load condition. In particular, when the initial analytical model is not suitable for representing the behavior of a bridge, the range of variation is large and the analysis response by the calibrated model may give a result that is different from the measured response. In this study, a pseudo-static load test was applied to obtain static response with dynamic components removed under various load conditions of a vehicle moving at a low speed. Static response was measured on two similar PSC-I girder bridges, and the response correction factors for displacement and strain were calculated for each of the two bridges. When the initial analysis model was not properly set up, it is verified that the response of the analytical model corrected by the average response correction factor does not fall within the margin of error with the measured response.

• Journal of Aerospace System Engineering
• /
• v.16 no.4
• /
• pp.88-94
• /
• 2022

The vibration mode measurement test measures the natural vibration characteristics of the target specimen. The measured natural mode characteristics are compared with the numerical analysis result to verify the reliability of the numerical analysis. If necessary, it is used to supplement the numerical analysis model of the specimen used for the dynamic characteristic analysis. In this paper, the natural frequency and natural mode of the external fuel tank are respectively obtained through the vibration mode measurement test and the numerical analysis, using the finite element model. The results are compared to verify the reliability of the numerical analysis model of the external fuel tank to apply to the entire aircraft model. To measure the vibration mode of the test specimen, a bungee cord was used, to simulate the free boundary condition for the test specimen. And, 3-axis accelerometers were installed on the test specimen. The response characteristics of the test specimen were measured, by excitation with an impact hammer. As a result of the test, after performing the frequency response analysis on the response acceleration, the natural frequency of the test specimen and its vibration mode were confirmed. The reliability of the numerical analysis model was verified by comparing the frequency and vibration mode, obtained through the test and the numerical analysis.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.26 no.4
• /
• pp.81-93
• /
• 1989

The present study attempts to develop the theoretical model for the damage estimation of offshore tubular members which are subjected to the accidental impact loads due to collision, falling objects and so on. For the reasons of the simplicity of the problem being considered, however, this paper postulates that the accidental load can be approximated to be the quasi-static one, in which dynamic effects are negelcted. Based upon the theoretical and experimental results which are obtained from the present study as well as the existing literature, the load-displacement relations taking the interaction effect between the local denting and the global bending deformation into account are presented in the explicit form when the concentrated lateral load acts on the tubular member whose end condition is supposed to be rotation ally free and axially restrained, in which membrane forces develop. Thus, the practical estimation of damage deformation for the local denting and the global bending damage of tubular members against the accidental loads is possible and also the collision absorption capability of the member can be calculated by performing the integration of the area below the given load-displacement curves, provided that all the energy is dissipated to the deforming the member itself.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.1
• /
• pp.67-75
• /
• 2023

In this study, the dynamic characteristics of an offshore platform being installed and physical phenomena are analyzed from the perspective of interaction between operation and maneuvering simulation using a real-time Maneuvering & Operation simulator of Shipbuilding & Marine Simulation Center at Tongmyong University. It was simulated to install the semi-submersible drilling rig moored by 8 mooring lines according to a scenario that is similar to it on the real sea, and 4 tug boats for position keeping of the rig and an offshore support vessel for hook-up of the mooring lines were operated. During the simulation, the motion, trajectory, tension of the objects were output in real time, and they were analyzed at each work procedure. This study about the simultaneous simulation of operation and maneuvering showed the detailed motion of the offshore platform and ships on the operation procedure and the interaction between operation and maneuvering in specific environment condition. Also, it confirmed that the simulation can be utilized to determine the possibility of offshore platform installation in specific situations.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.1C
• /
• pp.63-74
• /
• 2008

Site response analyses were performed based on equivalent linear technique using the local geologic and dynamic site characteristics, which include soil profiles, shear wave velocity profiles and depth to bedrock for 125 sites collected in Korean Peninsula. From the results of site response analyses, 2-parameters site classification system based on the combination of mean shear wave velocity of soil and depth to bedrock was newly recommended for regions of shallow bedrock depth in Korea. First, as the borders of bedrock depth (H) for site classification were determined as 10m and 20m, the soil sites were divided into 3 classes as $H_1$, $H_2$ and $H_3$ sites. And then, the 3 site classes were subdivided into 7 classes based on the mean shear wave velocity of soil ($V_{s,soil}$). The feasibility of new site classification system was verified and the representative site coefficients ($F_a$ and $F_v$) and design response spectrum were suggested by analyzing uniform trend and dispersion of site coefficients for each site class. The suggested site coefficients and the regression curves present the nonlinear characteristics of soils according to the change of rock outcrop acceleration with uniform trend effectively. From the comparison between the mean values of response spectrum which was acquired from the site response analysis and the suggested design response spectrum, there was a little difference in some of site classes and it was verified to adjust the integration interval to make it more suitable for the site condition in Korea.