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Herein, we analyzed the spatial and temporal variation of DO (dissolved oxygen), BOD (biochemical oxygen demand), and COD (Chemical Oxygen Demand) with the monthly mean observed data for 10 years (2008~2017) in the main stream of the Nakdong River. The water quality of the stations declined in a downstream direction, with the BOD and COD showing their highest values at the ST5 station. From the analysis of the correlation of water quality components at 10 stations, the correlation coefficient between the DO and water temperature was more than -0.90, and that between BOD and Chl-a was 0.48~0.85, and that between COD and TOC was more than 0.65 except for the ST5 and ST10 stations. From the regression analysis using data collected from all stations, the water temperature and DO decreased linearly with a coefficient of determination of 0.90, and the Chl-a and BOD could be described by increasing power functions with a coefficient of determination of 0.83. The TOC and COD followed increasing logarithm functions with a coefficient of determination of 0.58. The TOC efficiency at the 10 stations was estimated and the average efficiencies of BOD and COD were 15.5~36.3% and 57.4~89.6%, respectively.

In this paper, the applicability and usefulness of windprofiler input data were investigated to generate three dimensional wind field. A logical diagnostic model CALMET with windprofiler data at ten sites and with weather forecasting model WRF output was evaluated by statistically comparing with the radiosonde data at eight sites. The horizontal wind speed from CALMET simulated with hourly windprofiler data is in good agreement with radiosonde observations within 1.5 m/s of the root mean square error, especially local circulation of wind such as sea breeze over the coastal region. The root mean square error of wind direction ranged is due to the wind direction error from the windprofiler polluted by ground clutters. Since the exact wind can be produced quickly and accurately in most of the altitude with windprofiler data on CALMET, we expect the method presented in this study to be useful for the monitoring of safe environment as well as weather in the coastal zone.

Wind profiler provides vertical profiles of three-dimensional wind vectors with high spatiotemporal resolution. The wind vectors is useful to analyze severe weather phenomena and to validate the various products from numerical weather prediction model. However, the wind measurements are not immune to ground clutter, bird, insect, and aircraft. Therefore, quality of wind vectors from wind profiler must be quantitatively evaluated prior to its application. In this study, wind vectors from UHF wind profiler at Ganwon Regional Meteorological Administration was quantitatively evaluated using 27 radiosonde measurements that were launched every two or three hours according to rainfall intensity during Intensive Observation Period (IOP) from June to July 2013. In comparison between two measurements, wind vectors from wind profiler was relatively underestimated. In addition, the accuracy and quality of wind vectors from wind profiler decrease with increasing beam height. The accuracy and quality of the wind vectors for rainy periods during IOP were higher than for the clear-air measurements. The moderate rainfall intensity lead to multi-peaks in Doppler spectrum. It results in overestimation of vertical air motion, whereas wind vectors from wind profilers shows good agreement with those from radiosonde measurements for light rainfall intensity.

The momentum flux and the sensible heat flux were measured with the scintillometers and ultrasonic anemometers at 6 sites of which surface characteristics like roughness length and zero-displacement are different each other. We estimated the momentum flux and the sensible heat flux based on the bulk transfer method with the drag coefficient and the heat transfer coefficient calculated from the temperature and wind speed at two heights. The variation of bulk transfer coefficients showed a remarkable difference depending on the atmospheric stability which is less influenced by the zero-displacement than the roughness length. The estimated sensible heat fluxes were in good agreement with those measured at 3 m, showing 23.7 Wm -2 of the root mean square error that is less than 10% of its maximum. Since the estimated momentum flux is not only effected by drag coefficient but also by wind speed square, the determination of wind speed in the bulk transfer method is critical. Key words

In this study, before and after sunset carbon dioxide concentration and air temperature were observed in two points of atmosphere (lower observation point of the GL + 0.1 m, the upper observation point of GL + 1.0 m) on the foreshore at located in Suncheon Bay and their variations were analyzed. Observation was performed on the foreshore on 2~4 August 2010. Instrument (VAISALA, GMP343) was set two hours before sunset and then observation was made continuously for six hours. In three days, observed carbon dioxide concentration was 375~419 ppm, and the air temperature was in the range of 28.7~32.5 . The average concentration of carbon dioxide was 388~399 ppm in the upper observation point and 386~396 ppm in the lower observation point. It was higher in the upper observation point and its fluctuations were similar in two observation points. Correlation coefficients between carbon dioxide concentration and air temperature in the upper observation point were in the range of 0.64~ 0.88, and were calculated 0.65 to -0.90 in the lower observation point. For the carbon dioxide concentration, correlation coefficients between the upper part and the lower part were very high as 0.98 in three times. For th e air temperature, correlation coefficients between the upper part and the lower part were very high as 0.97 and 0.99. In the sam e observation time, the slope of the linear regression function as carbon dioxide concentration in the lower observation point fo r the upper observation point was in the range of 0.97~1.01. Carbon dioxide concentration Gwas slightly higher in the upper observation point. Because carbon dioxide in the lower observation point was closer on the surface of the foreshore and absorbed from atmosphere to the foreshore. In this study, it was showed that the vertical variation of carbon dioxide concentration was insignificant in the several meter scale of atmosphere on the surface of the foreshore.Key words : Foreshore, Sunset, Carbon dioxide, Air temperature

Quantitative precipitation estimation (QPE) is one of the most important elements in meteorological and hydrological applications. In this study, we adjusted the QPE from an S-band weather radar based on co-kriging method using the geostatistical structure function of error distribution of radar rainrate. In order to estimate the accurate quantitative precipitation, the error of radar rainrate which is a primary variable of co-kriging was determined by the difference of rain rates from rain gauge and radar. Also, the gauge rainfield, a secondary variable of co-kriging is derived from the ordinary kriging based on raingauge network. The error distribution of radar rain rate was produced by co-kriging with the derived theoretical variogram determined by experimental variogram. The error of radar rain rate was then applied to the radar estimated precipitation field. Locally heavy rainfall case during 6-7 July 2009 is chosen to verify this study. Correlation between adjusted one-hour radar rainfall accumulation and rain gauge rainfall accumulation improved from 0.55 to 0.84 when compared to prior adjustment of radar error with the adjustment of root mean square error from 7.45 to 3.93 mm.

Corrosion fatigue behaviors of high-performance steel, HSB800, and its heat-affected zones (HAZs) were investigated in air and seawater environments through uniaxial tension-compression fatigue tests. Three types of material including the as-received base metal (BM), coarse-grained (CG) HAZ, and inter-critically reheated coarse-grained (ICCG) HAZ of HSB800 were used. A 3.5% sodium chloride solution was used as a seawater environment. A 600–940 MPa maximum stress was applied during the fatigue load cycles, and the minimum stress was set to zero. The test results show that the ICCG HAZ had much less fatigue resistance than the BM and CG HAZ in both air and seawater environments. The deterioration mechanisms of the corrosion fatigue behaviors based on the microstructural aspects were also discussed. In addition, an empirical model for estimating corrosion fatigue life was developed by considering the stress sensitivity of loading conditions. Subsequently, material parameters in the power-law relationship between applied stress amplitude and cycles-to-failure were characterized. The ICCG HAZ exhibited more sensitivity on the stress level of the corrosion fatigue life than on those of the BM and CG HAZ. Meanwhile, the amount of environmental degradation of fatigue life of BM from in-air to in-seawater condition was greater than the others because of its microstructure with relatively adequate potential to corrode.

The densification behavior of titanium powder in the direct powder rolling process was investigated. An analytical model for the roll-backlash phenomenon during this process was proposed to conduct a realistic finite element analysis. Furthermore, the roll-backlash was quantitatively analyzed, and the relative densities of the greenstrip along the rolling direction were precisely estimated. Finally, the slip and nip phenomena were identified by calculating the contact pressure and shear stress between the titanium powder and the roller in order to understand the densification behavior of the powder during the rolling process.

Tensile tests were conducted on several cast aluminum specimens with different degrees of porosity. The effects of non-uniform void size and shape distributions, including spherical and non-spherical types, on stress-strain behavior resulting from different initiation mechanisms were investigated. A micro-mechanics-based statistical approach was employed, and the heterogeneous microstructures could therefore be modeled during the deformation process. The predicted changes of the distributions of void size and void shape gener- ally agreed with experimental results. Void spatial variation was also quantified, and its effects on the level of failure were analyzed. The void spatial variation facilitated development of inhomogeneous deformation, which results in failure.

This research investigated to reduce mass of heavy metals in AMD(acid mine drainage) by microbial mats formed on the channel bed. As, Cd, Cu, Fe, Mn and Zn components were monitored in water and microbial mats, at three points (AMD1, AMD2 and AMD3), in a total of six times. Average daily discharge mass of heavy metals was highest in July, Fe component contained more than 76% of total discharge mass. Discharge mass of heavy metals of AMD and heavy metal contents in microbial mats decreased with downstream at channel. Heavy metal components that average daily discharge mass is over 0.5 kg were Fe, Cu and Zn, and they were highest in July. Average removal efficiency of heavy metals in AMD was highest about 21% in Fe, this microbial mats were due to form from precipitation of Fe component in AMD by aerobic iron bacteria. Relative content for As component in microbial mats than AMD was over 16 times, this As components were due to absorb at iron oxide and iron hydroxide on the surface of microbial mats.

) Key Words : Fatigue Crack Propagation(피로균열전파), Fatigue Life Evaluation(피로수명평가), Crack Closure Phenomenon(균열 닫힘 현상) 초록: 응력확대계수비와 하중 주파수가 각각 ‘R=0.1, f=0.1 Hz’, ‘R=0.3, f=0.3 Hz’ 및 ‘R=0.5, f=0.5 Hz’인 세 가지 하중 조건에서 피로균열전파 실험을 하였으며 이를 바탕으로 고성능 강재의 피로균열전파거동 분석과 피로수명평가를 수행하였다. 하중 조건에 따른 피로균열전파거동을 모사하기 위해 수정된 Forman 모델을 제안하였으며 제안된 모델은 하한 응력확대계수폭과 균열 닫힘 현상에 의한 유효 응력확대계수폭을 고려함으로써 거동의 전 영역을 모사할 수 있었다. 응력확대계수비와 하중 주파수가 0.1인 경우, 균열이 약 5.0 mm 전파될 때 피로수명을 평가한 결과, Forman 모델은 8,814 cycles, 수정된 모델은 12,292 cycles의 계산결과를 얻었으며, 이를 12,774 cycles의 실제 실험결과와 비교할 때 수정된 Forman 모델이 실제 피로균열전파거동을 보다 효과적으로 모사하고 있음을 확인할 수 있었다. Abstract: Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of ‘R=0.1 and f=0.1 Hz’, ‘R=0.3 and f=0.3 Hz’, and ‘R=0.5 and f=0.5 Hz’ for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel.

Fatigue crack propagation in high-performance steel, HSB800, was investigated in air and seawater environments using three-point single-edge notched bending fatigue tests. Two types of heat affected zones (HAZ) resulting from welding processes, coarse grained and inter-critically reheated coarse grained zones, together with as-received metal were used to analyze the behavior. A 3.5% sodium chloride solution was used as the seawater, and several types of loading conditions, according to the stress ratio and loading frequency, were applied. The fatigue crack propagations were then assessed using the da/dN–Δ K curves. The results showed that the corrosion fatigue crack in seawater was more rapidly propagated than was that in the air environment. The third region of crack propagation was not observed in the da/dN–Δ K curve for the seawater environment, particularly in base metal. Generally, high stress ratio and load frequency shows a low threshold value in the stress intensity factor range. Furthermore, a different microstructural aspect of the crack propagation behavior in HAZs, as compared with that of the base metal, has been identified according to the crack propagation mechanisms.

The present study focuses on the fatigue properties in the weld heat-affected zone (HAZ) of 800 MPa grade high-performance steel, which is commonly used in bridges and buildings. Single- and multi-pass HAZs were simulated by the Gleeble system. Fatigue properties were estimated using a crack propagation test under a 0.3 stress ratio and 0.1 load frequencies. The microstructures and fracture surfaces were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results of the crack propagation test showed that the fatigue crack growth rate of coarse-grained HAZ (CGHAZ) was faster than fine-grained HAZ (FGHAZ), although both regions have identical fully martensite microstructures, because FGHAZ has smaller prior austenite grain and martensite packet sizes, which can act as effective barriers to crack propagation. The fatigue crack growth rate of intercritically reheated CGHAZ (ICCGHAZ) was the fastest among local zones in the HAZ, due to rapid crack initiation and propagation via the massive martensite–austenite (M–A) constituent.

Fatigue and corrosion fatigue crack propagation behaviors of high-strength steel, HSB800, were investigated in air and seawater environments. Three-point bending fatigue tests were conducted under various loading conditions at different levels of load frequency and ratio. A fracture model enabling mechanisms-based prediction of corrosion fatigue crack propagation is presented. The results obtained from the model follow the experimental data very well. Validation of the model was also conducted by comparison with other models that used in the analyses of corrosion fatigue crack propagation rates. As shown in results, the corrosion fatigue crack propagation rates ina seawater environmentwere higher than those in air condition underevery loadingconditions. These higher corrosion fatigue crack propagation rates were made possibly by the mechanisms of hydrogen embrittlement together with anodic dissolution.

Microstructures together with mechanical properties of commercially pure titanium (CP-Ti) developed by a newly designed multi-pass equal channel angular pressing (ECAP) process and cold extrusion were investigated. A T-type ECAP apparatus was developed to improve the efficiency of common ECAP and the performance of finished products. A much stronger CP-Ti billet was produced by using the proposed processes. As shown in the results, a severe plastic deformation occurred in the material by means of continuous shear deformation during the radical bending process through a repeated route. The resulting mechanical properties such as yield and tensile strength were improved according to the grain refinement that is connected with the Hall–Petch theory. Additively, cold extrusion was conducted to produce a cylindrical type bulk material by using the ECAP. Microstructural refinement with improvement of mechanical properties was attributed to this additional plastic forming process. Finished products developed by the T-type multi-pass ECAP and cold extrusion processes therefore have been shown to be remarkably hardened, such as the ultimate tensile strength of CP-Ti 292.5 initially to 791.9 MPa with significant refinement of the microstructure.

Actual evapotranspiration (AET) in the Suyeong-gu was estimated and correlations between AET and meteorological factors were analyzed. The study area was Suyeong-gu lay at the east longitude 05' 40" ~ 129 08' 08" and north latitude 07' 59" ~ 11' 01". The Kumryun mountain, the Bae mountain, the Suyeong river and the Suyeong bay are located on west, north, northeaster and south side in the study area, respectively. AET was estimated using precipitation (P), potential evapotranspiration (PET) and plant-available water coefficient. Meteorological factors to estimate PET were air temperature, dewpoint temperature, atmospheric pressure, duration of sunshine and mean wind speed (MWS). PET and AET were estimated by a method of Allen et al. (1998) and Zhang et al. (2001), respectively. PET was the highest value (564.45 mm/yr) in 2002 year, while it was the lowest value (449.95 mm/yr) in 2003 year. AET was estimated highest value (554.14 mm/yr) in 2002 year and lowest value (427.91 mm/yr) in 2003 year. Variations of PET and AET were similar. The linear regression function of AET as PET using monthly data was AET=0.87PET+3.52 and coefficient of determination was high, 0.75. In order to analyze relationship between the evapotranspiration and meteorological factors, correlation analysis using monthly data were accomplished. Correlation coefficient of AET-PET was 0.96 high, but they of AET-P and PET-P were very low. Correlation coefficients of AET-MWS and PET-MWS were 0.67 and 0.73, respectively. Thus, correlation between evapotranspiration and MWS was the highest among meteorological factors in Suyong-gu. This means that meteorological factor to powerfully effect for the variation of evapotranspiration was MWS. The linear regression function of AET as MWS was AET=84.73MWS+223.05 and coefficient of determination was 0.54. The linear regression function of PET as MWS was PET=83.83MWS+203.62 and coefficient of determination was 0.45.

This paper was studied respiration rate with physicochemical properties of soils at wetland, paddy field and forest in Nongju-ri, Haeryong-myeon, Suncheon city, Jeollanam-do. Soil temperature and respiration rate were measured at the field, and soil pH, moisture and soil organic carbon were analyzed in laboratory. Field monitoring was conducted at 6 points (W3, W7, W13, W17, W23, W27) for wetland, 3 points (P1, P2, P3) for paddy field and 3 points (F1, F2, F3) for forest in 10 January 2009. concentrations in chamber were measured 352~382 ppm for wetland, 364~382 ppm for paddy field and 379~390 ppm for forest, and the average values were 370 ppm, 370 ppm and 385 ppm, respectively. respiration rates of soils were measured for wetland, for paddy field and for forest, and the average values were , and . was uptake from air to soil in wetland and paddy field, but it was emission from soil to air in forest. respiration rate function in uptake condition increased exponential and linear as soil temperature and soil organic carbon. But, it in emission condition decreased linear as soil temperature and soil organic carbon. respiration rate function in wetland decreased linear as soil moisture, but its in paddy and forest increased linear as soil moisture. respiration rate function in all sites increased linear as soil pH, and increasing rate at forest was highest.

Shock absorption performances of various rubbers were investigated by using drop impact test. Several types of rubber such as NR, NBR, EPDM, SR and PUR with three respective levels of shore hardness were used for the test. As in the cases, the absorbed impact energies in rubbers were measured under seven different loads against impact energy between 5-80J. The impact absorption efficiencies of the rubbers then were evaluated by means of both single impact energy condition and summation of all impact energy applied condition. As shown in the results, PUR and EPDM have better shock absorption performances than other rubbers. Further analysis was extended to determine a shear modulus of SR through the finite element implementation with Blatz-Ko model. As can be seen, relatively higher level of absorption energy results in a decreasing shear modulus. 1. 서 론 고무재료는 우수한 충격흡수성능을 지님에 따라 다양한 산업에서 (1)그 활용도가 증가하고 있다. 그러나 고무재료의 충격흡수성능이 고무의 종류, 경도 및 사용환경 등에 의해 다르게 나타남에 따라 실질적인 충격흡수 구조에 적용함에 있어 적합한 고무를 선정하는 데는 상당한 어려움이 따른다. 따라서 충격흡수재의 설계 시 보다 효과적인 고무의 선정을 위해 종류, 경도, 사용환경에 따른 충격흡수성능의 체계적인 평가가 요구되고 있다. 또한 고무재료는 정적거동과 동적거동이 서로 다르게 나타나며 이는 충격거동 해석에서 요구되는 고무의 특성에도 영향을 미친다. 이에 따라 보다 정확한 고무의 충격해석을 위해 요구되는 고무의 동적 특성, 특히 동적 강성(dynamic modulus)의 평가를 위한 다양한 방법들이 제시되고 있다.

Hydraulic gradient of the landfill soils is estimated by Devlin (2003) method, and its variation characteristics from rainfall and permeability of the aquifer material are analyzed. The study site of 18 m 12 m is located in front of the Environment Research Center at the Pukyong National University, and core logging, slug/bail test and groundwater monitoring was performed. The sluglbail tests were performed in 9 wells (except BH9 well), and drawdown data with elapsed time for bail tests were analyzed using Bouwer-Rice and Hvorslev methods. The average hydraulic conductivity estimated in each of the test wells was ranged , and the average hydraulic conductivity in the study site was estimated for arithmetic average, for geometric average and for harmonic average. The permeability of landfill soils was higher at the east side of the study site than at the west side. Groundwater level in 10 wells was monitored 44 times from October 2 to November 7, 2007. The groundwater level was ranged 1.1871.610 m, and the average groundwater level range in each of the well showed 1.2561.407 m. The groundwater level was higher at the east side than at the west side of the study site, and this distribution is identify to it of hydraulic conductivity. The hydraulie gradient and the major flow direction for 10 wells were estimated 0.00720.0093 and , respectively. Also, the hydraulic gradient and the major flow direction for 9 wells were estimated 0.01020.0124 and , respectively. The hydraulic gradient of the study site increased from rainfall (83.5 mm) on October 7, causing by that the groundwater level of the site with high permeability was higher. The hydraulic gradient estimated on and after October 16 was stable, due to almost no rainfall. Thus, it was confirmed that the variation of the hydraulic gradient in the landfill soils was controlled by the rainfall.

Factors affecting non-uniform structures of cellular materials include wrinkled morphology, foam shape, and irregular solid structures. These factors result in different mechanical properties. The effect of different cell structure of aluminum foam on mechanical properties has been investigated in terms of several geometrical factors such as foam surface, foam volume, solid surface and solid volume. Uniaxial compression/tension tests have been performed by using a batch of various relative density foams. A 2-D micro-scan data of the foam structure with high spatial resolution was obtained by a Micro-CT through a digital processing technique of X-ray Tomography. The foam structures were then reconstructed as a set of flat cross-sections to interpret the 3-D morphological parameters. As shown by the results, the ratio of foam volume to solid volume has been substituted for the relative density well enough, and thus the higher of the relative density showed the greater of the total cell volume within the solid volume. The ratio of foam surface to solid volume also represented a degree of the total cell surface within a unit solid volume. Energy absorption has been changed with the ratio of foam surface to foam volume. The ratio of foam surface to foam volume in a specific morphology therefore can correctly characterize the complexity of the cell structures for the determination of mechanical properties of closed cell foams.

This paper presents a creep–fatigue-interacted lifetime prediction methodology based on continuum damage mechanics for the Ni-based superalloy under cyclic loading at high temperature. A unified life estimation model has been developed enabling stress–strain curves and cumulative damage to be predicted. Four types of low cycle fatigue tests were carried out at 650 °C. The effects of the levels of strain range and strain hold time together with frequency characteristics of fatigue behavior on the lifetime were investigated.

X-band marine radar was tested out the estimate of precipitation on the basis of rain gauge data and weather radar. This higher frequency radar is capable of measuring precipitation. The high resolution rainfall measurements will be used for run-off simulations and urban drainage applications.