• Journal of Institute of Convergence Technology
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• v.3 no.2
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• pp.23-29
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• 2013

When a human operator interacts with a virtual wall that is modeled as a virtual spring model, the lager the stiffness of the virtual spring is, the more realistic the operator feels that the virtual wall is. In the previous studies, it is shown that the maximum available stiffness of a virtual spring to guarantee the stability can be increased when the first-order-hold method is applied, however the effects of a human impedance on the stability are not considered. This paper presents the effects of a human impedance on stability of haptic system with a virtual spring and a first-order-hold (FOH) method. The human impedance model is modeled as a linear second-order system model. The relations between the maximum available stiffness of a virtual spring and the human impedance such as a mass, a damping and a stiffness are analyzed through the MATLAB simulation. It is shown that the maximum available stiffness is proportional to the square root of the human mass or damping respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.1
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• pp.55-66
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• 1996

One-hour average concentrations of ground-level ozone from around 80 monitoring stations in Korea during 1991 to 1993 were analyzed to examine characteristics of the ozone concentration variations. Two types of variations were observed: one was for the Capital area typified by Kwanghwmun, and the other was for the south and east seashore region typified by Tongkwangyang. In the Capital area including Seoul, Inchon, Kyonggi-do and Chunchon, mean daily 1-hout maximum was the highest in June following high monthly averages in spring. But frequent precipitation prevented further rise of daily maximum in July and August even though there were frequent episodes of high concentration exceeding 100ppb. In the south and east seashore region, average concentration was the highest throughout the year, and daily maximum and minimum simultaneously changed owing to small contributions from photochemical reactions. The typical annual variation was spring peak, summer down, and fall rise. Spring peak accompanied an usual observations of background variations at remote sites in the Northern Hemisphere. Riess of average and daily maximum with lower daily minimum in fall were attributable to photochemical reactions.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.3
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• pp.357-362
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• 2011

Air springs are prevalently used as suspension in train. However, air springs are seldom used in automobiles where they improve stability and comfort by enhancing the impact-relief, breaking, and cornering performance. Thus, this study proposed a new method to analyze air springs and obtained some reliable design parameter which can be utilized in vehicle suspension system in contrast to conventional method. Among air spring types of suspension, this study focused on sleeve type of air spring as an analysis model since it has potential for ameliorating the quality of automobiles, specifically in its stability and comfort improvement by decreasing the shock through rubber sleeve. As a methodology, this study used MARC, as a nonlinear finite element analysis program, in order to find out maximum stress and maximum strain depending on reinforcement cord's angle variation in sleeves. The properties were found through uniaxial tension and pure shear test, and they were developed using Ogden Foam which is an input program of MARC. As a result, the internal maximum stresses and deformation according to the changes of cord angle are obtained. Also, the results showed that the Young's modulus becomes smaller, then maximum stresses decrease. It is believed that these studies can be contributed in automobile suspension system.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.6
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• pp.36-42
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• 2010

In this study, the deformation and stress are analyzed through modal and harmonic response analysis at resonance on leaf spring. The displacement range of 7 to 14 mm is shown at natural frequencies as 6 kinds of resonance modes. The maximum deformation is shown as 8.8781mm at Mode 2. The maximum displacement and stress at leaf spring are shown as 0.0458 mm and 72.533 MPa respectively on 1200 Hz. The comfortability of passenger becomes better on leaf spring at suspension system by use of this design model.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.3
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• pp.142-149
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• 1994

In order to investigate the environmental properties of set net grounds located in the coastal waters of Yeosu. The current in the vicinity of set net grounds was observed by drogue and current meter in 1990 and 1992. The results obtained are summarized as follows: The direction of tidal current at the north enterance of Yeosu bay was southerly in ebb and northwesterly in flood without the distiction of the neap tide and the spring tide. In spring tide the maximum Velocity of the tidal current was 68 cm/sec in ebb and 66 cm/sec in flood. In neap tide the maximum velocity of the tidal current was 37 cm/sec in ebb and 35 cm/sec in flood. And so the direction of residual current was the south ward mainly and 21 cm/sec. The direction of tidal current at set net fishing grounds was southwesterly in ebb and westerly or northwesterly in flood. Regardless of the distinction of neap and spring. The maximum velocity of the current in spring tide was 50 cm/sec in ebb and 40 cm/sec in flood and that in neap was 28 cm/sec in ebb and 25 cm/sec in flood. In spring tide the speed vector along the major axis of semidiurnal tide component was three times as large as diurnal tide. In neap tide, however, the speed vector was about 50% less then that in spring tide, and the semidiurnal tide and diurnal tide were equal in the size of current ellipse and the direction of major axis. The sea area had a southwesterly residual current. 11 cm/sec in spring tide and 7 cm/sec in neap tide. According to the result of drogue tracking, the vicinity of set net fishing ground had a southerly residual current which formed in Yeosu Bay and a weak westerly residual current toward Dolsando from Namhedo. Therefore, set net fishing ground in coastal water of Yeosu was distributed in boundary of inner water which formed from Seamjin river and offshore water supplied from the vicinity of Sorido and Yochido.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.2
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• pp.117-124
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• 2011

Valve springs with non-circular cross-section are widely used in automotive engines. Because of the reduced height, the oval cross-section provides some merits in its install height and stress distribution. This paper introduces a new method to generate optimal shape of the non-circular cross-section. For given width and height, arbitrary shape of the cross-section are described using the Hermite spline curves. Cross-section area and maximum stress level are chosen as performance indices, and nonlinear optimization problems are formulated with inequality constraints. Compared to a production spring wire, cross-section area can be reduced about 2.4 [%] without increasing maximum stress level. In addition, the other approach gives an optimum cross-section which reduces maximum stress level of 2.0 [%] without increasing cross-section area.

• Journal of Plant Biology
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• v.29 no.2
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• pp.117-127
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• 1986

Phytoplankton community was investigated at the Paldang Dam Reservoir in the Mid-Han River by it's depth, in spring and summer known as the period of phytoplankton's blooming. It was only in summer that phytoplankton bloomed at the investigated area. 128 kinds of phytoplankton were identified and of them, diatoms were abundunt in spring but cyanophyta and chlorophyta were in summer. Because some species with high pollution index were observed in summer, it could be proved that the investigated area was polluted especially in summer. In spring shown the circulation period by vertical distribution pattern of chlorophyll-a and isothermal distribution pattern of water temperature, maximum value of phytoplankton standing crops appeared at the upper layer, except for surface layer. In summer shown the circulation period after the stagnation period by vertical distribution pattern of chlorophyll-a and immediate destruction after stratification of water temperature, maximum value of phytoplankton standing crops appeared at the lower layer. the layer at which the maximum value of chlorophyll-a appeared also accorded with that of phytoplankton standing crops. So, it could be approved that there existed a close relationship among phytoplankton standing crops, chlorophyll-a, and water temperature.

• Transactions of Materials Processing
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• v.5 no.2
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• pp.145-155
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• 1996

The conventional five-stage forming processes of the valve-spring retainer are simulated using the rigid-plstiv finite element method. As a design criterion the improved process should satisfy the maximum forging load during processes within the loading limit of the available press and should not induce any geometrical defects. hollow bars are recommended as initial billets to skip the heading and piercing processes. Through various simulations it is found out that the one stage process results in less forging loads and better strain distributions.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.1
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• pp.50-56
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• 2015

This research was performed to test the hypothesis that the optimal fertilization rate for lettuce is various with soil moisture conditions. The experiment was conducted under a rainfall-intercepted facility in Suwon, South Korea from 2002 to 2003. Soil was irrigated at 30, 50, or 80 kPa of soil moisture tension at 15 cm soil depth in 2002 spring and fall and 20, 30, 50, or 80 kPa in 2003 spring. Fertilization was performed with four levels in spring for both years: none, 0.5, 1.0, and 1.5 times of the recommended N, P, and K fertilization rate. The irrigation amount increased with decreased irrigation starting point as soil moisture tension. The maximum yield was found at the lowest soil moisture tension in spring while irrigation at 50 kPa resulted in the greatest yield in fall. The yield responses of lettuce to fertilization rates were various with soil moisture condition. In spring, maximum yield was found at 1.0 or 1.5 times of the recommended fertilization rate at 20, 30, and 50 kPa irrigation while 0.5 or 1.0 times of fertilization rate resulted in the maximum yield in fall. Especially for 80 kPa irrigation in 2003 spring, yield was decreased by fertilization. It suggested that the optimum fertilization rate for lettuce is affected by soil moisture condition and that lower fertilization rate should be suggested when soil is managed in drier condition.

• 한국해양학회지
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• v.16 no.1
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• pp.31-37
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• 1981

Saline water movements in relation to tidal condition and river discharge in the estuary of the Nakdong River are discussed on the basis of the observation data. The difference of salinity between the surface and the bottom layer was 1∼3 at spring tide forming a vertically homogeneous estuary, while at neap tide, it ranges up to 7∼15 indicating a sharp salt wedge. The maximum salinity appeared approximately at an hour after the high water, that is, three hours after the landward velocity maximum, while the salinity maximum at around an hour after the low water, that is, three hours after the seaward velocity maximum. The density current speed at a section located 10km landward from the river mouth was observed approximately to be 45cm sec$\^$-1/ at 8m layer.The relations between the salinity at Gupo and the river discharge at Jindong are estimated by means of the least square method. The maximum length of the salt wedge is calculated approximately to be 22km at neap tide and 16km at spring tide, which is in accordance with the observed data. The salinity influence area is deduced to be 45km at spring tide and 35km at neap tide. The diffusion coefficient of salinity was estimated approximately to be 1.5 10$\^$8/$\textrm{cm}^2$ sec$\^$-1/ at Samrak and 8 10$\^$5/$\textrm{cm}^2$ sec$\^$-1/ at Gupo at neap tide, while it was 1.4 10$\^$7/$\textrm{cm}^2$ sec$\^$-1/ at Dongwon at spring tide.