• Journal of Yeungnam Medical Science
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• v.20 no.2
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• pp.160-168
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• 2003

Background: Confirm the stability of intervertebral disc sustaining each fused lumbar spine cases, comparing vertical compression, A-P shear force and rotational moment on intervertebral disc of instrumented lumbar spine with simple vertical compression load and follower load using finite element analysis. Materials and Methods: We analyze the stability of intervertebral disc L4-5 supporting fused lumbar spine segments. After performing finite element modelling about L1-L5 lumbar vertebral column and L1-L4 each fusion level pedicle screw system for fused lumbar spine fine element model. Intervertebral discs with complex structure and mechanical properties was modeled using spring element that compensate stiffness and tube-to-tube contact element was employed to give follower load. Performing geometrical non-linear analysis. Results: The differences of intervertebral disc L4-5 behavior under the follower compression load in comparision with vertical compression load are as follows. Conclusion: As a result of finite element interpretation of instrumented lumbar spine, the stability of L4-5 sustaining fused lumbar segment, the long level fused lumbar spine observed hing stability under follower load. This research method can be the basis tool of effects prediction for instrumentation, a invention of a more precious finite element interpretation model which consider the role of muscle around the spine is loaded.

• Journal of the Korean Geosynthetics Society
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• v.14 no.1
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• pp.1-10
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• 2015

Recently, several researches on the development of new economical anchor systems have been performed to support floating structures. This study focused on the group suction piles, which connect mid-sized suction piles instead of a single suction pile with large-diameter. The group suction pile shows the complex bearing behavior with translation and rotation, so it is difficult to apply conventional design methods. Therefore, the numerical modeling technique was developed to evaluate the horizontal bearing capacity of the group suction piles in clay. The technique models suction piles as beam elements and soil reaction as non-linear springs. To analyze the applicability of the modeling, the horizontal load-movement curves of the proposed modeling were compared with those of three-dimensional finite element analyses. The comparison showed that the modeling underestimates the capacity and overestimate the displacement corresponding to the maximum capacity. Therefore, the correction factors for the horizontal soil resistance was proposed to match the bearing capacity from the three-dimensional finite element analyses.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.202-208
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• 2017

The recently developed marine engines for propulsion of ships have higher torsional exciting force than previous engines to improve the propulsion efficiency and to reduce specific fuel oil consumption. As a result, a viscous damper or viscous-spring damper is installed in front of marine engine to control the torsional vibration. In the case of viscous damper, it is supposed that there is no elastic connection in the silicon oil, which is filled between the damper housing and inertia ring. However, In reality, the silicon oil with high viscosity possesses torsional stiffness and has non-linear dynamic characteristics according to the operating temperature and frequency of the viscous damper. In this study, the damping characteristics of a viscous damper used to control the torsional vibration of the shafting system have been reviewed and the characteristics of torsional vibration of the shafting system equipped with a corresponding viscous damper have been examined. In addition, it is examined how to interpret the theoretically optimal dynamic characteristics of a viscous damper for this purpose, and the optimum design for the propulsion shafting system has been suggested considering the operating temperature and aging. when the torsional vibration of the shafting system is controlled by a viscous damper filled with highly viscous silicon oil.

• Journal of Wetlands Research
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• v.21 no.2
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• pp.102-113
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• 2019

Slack-tide sampling was carried out at 6 stations at high and low tide for a tidal cycle during spring tide of the early summer (June) and summer (July, August) of 2016 to determine the difference of water quality according to tide in Masan Bay, Korea. The mixing regime of all the water quality components investigated was well explained through the correlation with SAL. In the early summer and summer, TURB, DSi and NNN which mainly flow into the bay from the streams and SS, COD, AMN and $H_2S$ which mainly indicate the internal sink and source materials have a property of conservative mixing and non-conservative mixing, respectively. The conservative mixing showed a good linear relationship of the water quality between high and low tide, and the non-conservative mixing showed a variation of different pattern each other. Factor analysis performed on the concentration difference data sets between high and low tide helped in identifying the principal latent variables for them. In early summer, multiple effects (tidal action, natural influx and internal sinks and sources etc.) acted in combination for the differences to be distributed evenly in four factors (VF1~4), since there were few allochthonous inputs as a low-water season. On the contrary, in summer, the parameters showing large concentration difference at ST-1 affected by stream water were concentrated in one factor (VF1) and clearly distinguished from the parameters affected by the internal sinks and sources. In fact, there is no estuary (bay) that always maintains steady state flow conditions. The mixing regime of an estuary might be changed at any time due to the change of flushing time, and furthermore the change of end-member conditions due to the internal sinks and sources makes the occurrence of concentration difference inevitable. Therefore, when investigating the water quality of the estuary, it is necessary to take a sampling method considering the tide to obtain average water quality data.

• Journal of Biosystems Engineering
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• v.2 no.1
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• pp.7-24
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• 1977

This paper is the forth and fifth one of the study on balanced type oscillating mole drainer. In the light of the results from previous reports about the model tests, some design criteria were established and a prototype machine was set up for experimental purpose. Motion characteristics and functionof the each parts of the machine were checked and analyzed. After that, performance tests of the prototype machine were carried out in thefield. Obtained results are summarized as follows ; 1. Ten centimeter of the bullet diameter was determined so as to be able to attach it to the tractors with capacity of 30 PS to 40 PS. 2. To maintain the balance between the moments of the front shank and rear shank, the oscillating amplitude of the rear bullet was determined to be larger than that of the front bullet. At the same time , the oscillating direction of the rear bullet was designed with the inclines of ten to thirty degrees. 3. An octagonal dynamo transduced was developed for measuring the compressive force of the upper link is measuring the draft force of the machine. Acceptable linear relationship between forces and strain responses from O.D.T. was obtained. 4. Analysing the balancing mechanism of the acting part of the machine , it was found that the total draft force of the machine was equal to the difference between the sum of the draft force produced from the right and left side bending moments of the lower drawber and the compressive force on the upper link. 5. There are acceptable linear relationship between the strain and twisting moment by driving shaft, and between strain and shank moment. Above results enable us to carry out the field experiment with prototype machine. 6. When the test machine was used in the field, it was possible to reduce the oscillating acceleration by forty percent in average as compared it with the single bullet mole drainer. 7. When the test machine was used under the oscillating condition, the dratt torce was reduced by 27 percent to 59 percent as compared it with the test machine under non-oscillating condition, while the draft force was increased by 7 percent to 20 percent as compared it with the mole drainer having oscillating single bullet. The reasoning behind this fact was considered as the resistance force due to the rear shank and bullet. 8. As the amplitude and frequency of the bullet were increased, the torque was increased accordingly. This tendency could be varied with the various characteristics of the given soils. And the larger frequency and amplitute, the more increasing oscil\ulcornerlating power but decreasing draft brce were needed, and draft force was increased as the velocity was increased.9. When the amplitude of the rear bullet was designed to be larger than that of the front bullet, the minimum value of the moment was lowered and oscillating acceleration was reduced. And when the oscillating direction of the rear bullet was declined back\ulcornerwards, oscillating acceleration was increased along with the increasing angle of decli\ulcornernation. When the test machine was operated in high speed, the difference between maximum moments and minimum ones became narrow. This varying magnitude of moments appeared on the moment oscillogram seems to be correlated to the oscillating acceleration and draft force. 10. From the analysis of variance, it was found that those factors such as frequency, amplitude, and operating velocity significantly affected in the oscillating acceleration, the draft resistance, the torque, the moment, and the total power required. And interaction between frequency and amplitude affected in the oscillating acceleration. 11. Within the given situation of this study, the most preferable operating conditions of the test machine were 7 Hz in oscillating frequency, 0.54 m/sec in operating velocity, and 39.1 mm in oscillating amplitude of front and rear bullets. However, it is necessary to select the proper frequency and magnitude of oscillation depending on the soil properties of the field in which the mole drainer is practiced by use of a bal1nced type oscillating mole drainer. 12. It is recommended that a comparative study of the mole drainers would be performed in the near future using two separate balanced oscillating bullet with the one which is operated by oscillating the movable bullet in a single cylinder or other balanced type which may be single oscillating bullet with spring, damper or balancing weight, and that of thing. To expand the applicability of the balanced type oscillating mole drainer in practical use, it is suggested to develop a new mechanism which perform mole drain with vinyl pipe or filling material such as rice hull.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.1 no.1
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• pp.53-68
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• 1981

Most clays under sustained load exhibit time-dependent deformation because of creep movement of soil particles and many investigators have attempted to relate their findings to the creep behavior of natural ground and to the long-term stability of slopes. Since the creep behavior of clays may assume a variety of forms depending on such factors as soil plasticity, activity and water content, it is difficult and complicated to analyse the creep behavior of clays. Rheological models composed of linear springs in combination with linear or nonlinear dashpots and sliders, are generally used for the mathematical description of the time-dependent behavior of soils. Most rheological models, however, have been proposed to simulate the behavior of secondary compression for saturated clays and few definitive data exist that can evaluate the behavior of non-saturated clays under the action of sustained stress. The clays change gradually from a solid state through plastic state to a liquid state with increasing water content, therefore, the rheological models also change. On the other hand, creep is time-dependent, and also the effect of thixotropy is time-function. Consequently, there may be certain correlations between creep behavior and the effects of thixotropy in compacted clays. In addition, the states of clay depend on water content and hence the height of the specimen under drained conditions. Futhermore, based on present and past studies, because immediate elastic deformation occurs instantly after the pressure increment without time-delayed behavior, the factor representing immediate elastic deformations in the rheological model is necessary. The investigation described in this paper, based on rheological model, is designed to identify the immediate elastic deformations and the effects of thixotropy and height of clay specimens with varing water content and stress level on creep deformations. For these purposes, the uniaxial drain-type creep tests were performed. Test results and data for three compacted clays have shown that a linear top spring is needed to account for immediate elastic deformations in the rheological model, and at lower water content below the visco-plastic limit, the effects of thixotropy and height of clay specimens can be represented by the proposed rheological model not considering the effects. Therefore, the rheological model does not necessitate the other factors representing these effects. On the other hand, at water content higher than the visco-plastic limit, although the state behavior of clays is visco-plastic or viscous flow at the beginning of the test, the state behavior, in the case of the lower height sample, does not represent the same behavior during the process of the test, because of rapid drainage. In these cases, the rheological model does not coincide with the model in the case of the higher specimens.

• Journal of the Korean Institute of Landscape Architecture
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• v.41 no.6
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• pp.107-116
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• 2013

This study was undertaken to investigate the characteristics of retention and evapotranspiration in the extensive greening module of sloped and flat rooftops for stormwater management and urban heat island mitigation. A series of 100mm depth's weighing lysimeters planted with Sedum kamtschaticum. were constructed on a 50% slope facing four orientations(north, east, south and west) and a flat rooftop. Thereafter the retention and evapotranspiration from the greening module and the surface temperature of nongreening and greening rooftop were recorded beginning in September 2012 for a period of 1 year. The characteristics of retention and evapotranspiration in the greening module were as follows. The water storage of the sloped and flat greening modules increased to 8.7~28.4mm and 10.6~31.8mm after rainfall except in the winter season, in which it decreased to 3.3mm and 3.9mm in the longer dry period. The maximum stormwater retention of the sloped and flat greening modules was 22.2mm and 23.1mm except in the winter season. Fitted stormwater retention function was [Stormwater Retention Ratio(%)=-18.42 ln(Precipitation)+107.9, $R^2$=0.80] for sloped greening modules, and that was [Stormwater Retention Ratio(%)=-22.64 ln(X)+130.8, $R^2$=0.81] for flat greening modules. The daily evapotranspiration(mm/day) from the greening modules after rainfall decreased rapidly with a power function type in summer, and with a log function type in spring and autumn. The daily evapotranspiration(mm/day) from the greening modules after rainfall was greater in summer > spring > autumn > winter by season. This may be due to the differences in water storage, solar radiation and air temperature. The daily evapotranspiration from the greening modules decreased rapidly from 2~7mm/day to less than 1mm/day for 3~5 days after rainfall, and that decreased slowly after 3~5 days. This indicates that Sedum kamtschaticum used water rapidly when it was available and conserved water when it was not. The albedo of the concrete rooftop and greening rooftop was 0.151 and 0.137 in summer, and 0.165 and 0.165 in winter respectively. The albedo of the concrete rooftop and greening rooftop was similar. The effect of the daily mean and highest surface temperature decrease by greening during the summer season showed $1.6{\sim}13.8^{\circ}C$(mean $9.7^{\circ}C$) and $6.2{\sim}17.6^{\circ}C$(mean $11.2^{\circ}C$). The difference of the daily mean and highest surface temperature between the greening rooftop and concrete rooftop during the winter season were small, measuring $-2.4{\sim}1.3^{\circ}C$(mean $-0.4^{\circ}C$) and $-4.2{\sim}2.6^{\circ}C$(mean $0.0^{\circ}C$). The difference in the highest daily surface temperature between the greening rooftop and concrete rooftop during the summer season increased with an evapotranspiration rate increase by a linear function type. The fitted function of the highest daily surface temperature decrease was [Temperature Decrease($^{\circ}C$)=$1.4361{\times}$(Evapotranspiration rate(mm/day))+8.83, $R^2$=0.59]. The decrease of the surface temperature by greening in the longer dry period was due to sun protection by the sedum canopy. The results of this study indicate that the extensive rooftop greening will assist in managing stormwater runoff and urban heat island through retention and evapotranspiration. Sedum kamtschaticum would be the ideal plant for a non-irrigated extensive green roof. The shading effects of Sedum kamtschaticum would be important as well as the evapotranspiration effects of that for the long-term mitigation effects of an urban heat island.

• Journal of Korean Society of Forest Science
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• v.99 no.6
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• pp.922-928
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• 2010

There is a little information on the effect of calcium cloride ($CaCl_2$) which is used as deicing salt in Korea on the physiological responses of the street trees. Prunus sargentii is one of the most widespread tree species of street vegetation in Korea. In this study, the effect of $CaCl_2$ on photosynthetic apparatus such as chlorophyll fluorescence image and light response curve of P. sargentii in relation to their leaf and root collar growth responses were investigated. To study the effect of $CaCl_2$ treatment in the early spring, we irrigated twice in rhizosphere of P. sargentii (3-year-old) planted plastic pots with solution of 0.5%, 1.0%, 3.0% $CaCl_2$ concentration before leaf expansion. Results after treatments, total chlorophyll contents and the chlorophyll a/b, photosynthetic rate, quantum yield, dark respiration decreased with increasing $CaCl_2$ concentration. On the contrary, light compensation point increased with increasing $CaCl_2$ concentration. Through the linear regressions of correlation of photosynthetic rate with photosynthetic parameters (quantum yield, dark respiration and light compensation point), we found a significant relationship (p<0.05) between photosynthetic rate and quantum yield and light compensation point except dark respiration. Calcium cloride ($CaCl_2$) induced inhibition of photochemical efficiency ($F_v/F_M$) and non-photochemical quenching (NPQ) were found in treatments of $CaCl_2$, and these reduction rates between control and CaCl2 treatments were drastically showed at 80 days. We suggest that physiological activities are limited from treatment of $CaCl_2$. These reductions of photosynthetic apparatus ability caused eventually the reduction of leaf and diameter at root collar growth.

• Korean Journal of Ecology and Environment
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• v.46 no.4
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• pp.499-506
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• 2013

To estimate the effect of algae to particulate organic matter in the upper regions of brackish Lake Sihwa, temporal and spatial variations of particulate organic carbon (POC) and phytoplankton pigments (chlorophyll a; Chl-a, pheophytin-a; Pheo-a), and their relationships were studied at seven sites of the brackish regions from March to October 2005 and 2006. POC concentration varied from 1.0 to $76.6mgL^{-1}$ (mean $7.4mgL^{-1}$), with maximal concentrations occurring in the middle parts of the study area in spring of 2005 and 2006. Concentrations of Chl-a and Pheo-a varied from 1.3 to $942.9{\mu}gL^{-1}$ (mean $71.0{\mu}gL^{-1}$) and $1.4{\sim}1,545.5{\mu}gL^{-1}$ (mean $59.9{\mu}gL^{-1}$), respectively, and corresponded closely with variation in POC. During the study period Pheo-a concentration was 44.2% of total Chl-a, implying that non-living or inactive phytoplankton is also the important part of phytoplankton-derived POC in brackish regions of Lake Sihwa. From the positive linear relationships between POC and phytoplankton pigments (POC with Chl-a (r=0.93), total Chl-a (r=0.88), and Pheo-a (r=0.81)), it is suggested that phytoplankton was a significant component of POC in the upper regions of brackish Lake Sihwa. On the other hand, the ratios of POC/Chl-a and POC/total Chl-a (Chl-a+Pheo-a) were 82.9 and 35.9, respectively. The ratio of POC/total Chl-a is similar to those reported in previous studies, including 40~60 in estuaries. This study suggests that Pheo-a concentration is considered in estimation of POC concentration from phytoplankton pigments in aquatic systems with high content of Pheo-a, like an upper region of blackish Lake Sihwa.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.434-449
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• 2019

In this study, we develop a new cross-shore sediment module which takes the effect of infra-gravity waves of bound mode, and boundary layer streaming on the sediment transport into account besides the well-known asymmetry and under-tow. In doing so, the effect of individual random waves occurring during the unit observation period of 1 hr on sediment transport is also fully taken into account. To demonstrate how the individual random waves would affect the sediment transport, we numerically simulate the non-linear shoaling process of random wavers over the beach of uniform slope. Numerical results show that with the consistent frequency Boussinesq Eq. the application of which is lately extended to surf zone, we could simulate the saw-tooth profile observed without exception over the surf zone, infra-gravity waves of bound mode, and boundary-layer streaming accurately enough. It is also shown that when yearly highest random waves are modeled by the equivalent nonlinear uniform waves, the maximum cross-shore transport rate well exceeds the one where the randomness is fully taken into account as much as three times. Besides, in order to optimize the free parameter K involved in the long-shore sediment module, we carry out the numerical simulation to trace the yearly shoreline change of Mang-Bang beach from 2017.4.26 to 2018.4.20 as well, and proceeds to optimize the K by comparing the traced shoreline change with the measured one. Numerical results show that the optimized K for Mang-Bang beach would be 0.17. With K = 0.17, via yearly grand circulation process comprising severe erosion by consecutively occurring yearly highest waves at the end of October, and gradual recovery over the winter and spring by swell, the advance of shore-line at the northern and southern ends of Mang-Bang beach by 18 m, and the retreat of shore-line by 2.4 m at the middle of Mang-Bang beach can be successfully duplicated in the numerical simulation.