• Nuclear Engineering and Technology
• /
• v.42 no.4
• /
• pp.382-393
• /
• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• Ocean and Polar Research
• /
• v.40 no.4
• /
• pp.213-222
• /
• 2018

We investigated seasonal variations in the abundance of the adults and the resting eggs of copepods to understand the role of copepod resting eggs for maintaining their population inhabiting the coastal area of Dadaepo, Korea. Adults and resting eggs of copepods were collected bi-monthly with a conical net (45 cm mouth diameter, $330{\mu}m$ mesh size) and van Veen grab ($0.1m^2$ area), respectively, from October 2016 to September 2017. The species of resting eggs were identified using mtCOI gene. The mean abundance of copepods was highest in October ($3686{\pm}1190inds{\cdot}m^{-3}$) and lowest in January ($176{\pm}60inds{\cdot}m^{-3}$) with the dominance of Paracalanus parvus s.l.. Among copepod producing resting eggs, Acartia omorii and Centropages abdominalis were dominant. The mean abundance of resting eggs was the highest in July ($9148{\pm}6787eggs{\cdot}m^{-2}$) and the lowest in October ($530{\pm}348eggs{\cdot}m^{-2}$). Most of the collected resting eggs were identified as A. omorii's. The mean abundances of A. omorii adults and resting eggs were highest in July, and both abundances fluctuated in a similar pattern except in September. In September, A. omorii adults were observed in a state of low abundance, while their resting eggs occurred in a state of high abundance. These results suggest that A. omorii maintain their population by producing a large quantity of resting eggs, particularly diapause eggs, before the seawater temperature rises. These eggs would hatch and be newly recruited to their population when the environmental condition becomes favorable.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.2
• /
• pp.220-228
• /
• 2019

To determine the horizontal and temporal distribution of common squid larvae, Todarodes pacificus (hereafter T. pacificus), we conducted surveys using an IKMT net (mesh size: $500{\mu}m$) with a Fisheries Research Vessel (FRV, TAMGU 21) in the southwestern part of the East Sea in summer (August and September) and autumn (November) 2015. A total of 228 larvae, ranging in mantle length (ML) from 1.4 mm to 21.9 mm, were collected at 35 stations over the research period. The monthly average mantle length of T. pacificus larvae did not differ significantly in August, September and November. (p > 0.05). Catch densities at positive stations ranged between 0.1 and $7.9inds./1,000m^3$ over the research period. Incidence rates of T. pacificus larvae were similar over three months, in the study area (62.9 % - 68.6 %). The 4 - 5 mm mantle length range had the highest frequency in size-frequency distributions for T. pacificus larvae. The larval survival temperature ($15-24^{\circ}C$) at positive stations for catch densities was located below a 20 m depth in August whereas it was located at the surface of the water in September and November. The survival temperature for larvae existed from the bottom to the surface of the water where larvae were sampled larvae in shallow sea areas. However, the larval survival temperature occurred in a shallower location than the upper layer of the thermocline in deep sea areas at a depth below 100 m.

• Nuclear Engineering and Technology
• /
• v.54 no.2
• /
• pp.479-485
• /
• 2022

At the Korea Institute of Radiological and Medical Sciences, physical human phantoms were developed to evaluate various radiation protection quantities, based on the mesh-type reference computational phantoms of the International Commission on Radiological Protection. The physical human phantoms were fabricated such that a radiophotoluminescent glass dosimeter (RPLGD) with a Tin filter, namely GD-352M, could be inserted into them. A Tin filter is used to eliminate the overestimated signals in low-energy photons below 100 keV. The measurement uncertainty of the RPLGD reader system based on GD-352M should be analyzed for obtaining reliable protection quantities before using it for practical applications. Generally, the measurement uncertainty of RPLGD systems without Tin filters is analyzed for quality assurance of radiotherapy units using a high-energy photon beam. However, in this study, the measurement uncertainty of GD-352M was analyzed for evaluating the protection quantities. The measurement uncertainty factors in the RPLGD include the reference irradiation, regression curve, reproducibility, uniformity, energy dependence, and angular dependence, as described by the International Organization for Standardization (ISO). These factors were calculated using the Guide to the Expression of Uncertainty in Measurement method, applying ISO/ASTM standards 51261(2013), 51707(2015), and SS-ISO 22127(2019). The measurement uncertainties of the RPLGD reader system with a coverage factor of k = 2 were calculated to be 9.26% from 0.005 to 1 Gy and 8.16% from 1 to 10 Gy. A blind test was conducted to validate the RPLGD reader system, which demonstrated that the readout doses included blind doses of 0.1, 1, 2, and 5 Gy. Overall, the E_n values were considered satisfactory.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.28 no.2
• /
• pp.183-193
• /
• 1995

Assuming that fishing nets are porous structures to suck water into their mouth and then filtrate water out of them, the flow resistance N of nets with wall area S under the velicity v was taken by $R=kSv^2$, and the coefficient k was derived as $$k=c\;Re^{-m}(\frac{S_n}{S_m})n(\frac{S_n}{S})$$ where $R_e$ is the Reynolds' number, $S_m$ the area of net mouth, $S_n$ the total area of net projected to the plane perpendicular to the water flow. Then, the propriety of the above equation and the values of c, m and n were investigated by the experimental results on plane nettings carried out hitherto. The value of c and m were fixed respectively by $240(kg\cdot sec^2/m^4)$ and 0.1 when the representative size on $R_e$ was taken by the ratio k of the volume of bars to the area of meshes, i. e., $$\lambda={\frac{\pi\;d^2}{21\;sin\;2\varphi}$$ where d is the diameter of bars, 21 the mesh size, and 2n the angle between two adjacent bars. The value of n was larger than 1.0 as 1.2 because the wakes occurring at the knots and bars increased the resistance by obstructing the filtration of water through the meshes. In case in which the influence of $R_e$ was negligible, the value of $cR_e\;^{-m}$ became a constant distinguished by the regions of the attack angle $ \theta$ of nettings to the water flow, i. e., 100$(kg\cdot sec^2/m^4)\;in\;45^{\circ}<\theta \leq90^{\circ}\;and\;100(S_m/S)^{0.6}\;(kg\cdot sec^2/m^4)\;in\;0^{\circ}<\theta \leq45^{\circ}$. Thus, the coefficient $k(kg\cdot sec^2/m^4)$ of plane nettings could be obtained by utilizing the above values with $S_m\;and\;S_n$ given respectively by $$S_m=S\;sin\theta$$ and $$S_n=\frac{d}{I}\;\cdot\;\frac{\sqrt{1-cos^2\varphi cos^2\theta}} {sin\varphi\;cos\varphi} \cdot S$$ But, on the occasion of $\theta=0^{\circ}$ k was decided by the roughness of netting surface and so expressed as $$k=9(\frac{d}{I\;cos\varphi})^{0.8}$$ In these results, however, the values of c and m were regarded to be not sufficiently exact because they were obtained from insufficient data and the actual nets had no use for k at $\theta=0^{\circ}$. Therefore, the exact expression of $k(kg\cdotsec^2/m^4)$, for actual nets could De made in the case of no influence of $R_e$ as follows; $$k=100(\frac{S_n}{S_m})^{1.2}\;(\frac{S_m}{S})\;.\;for\;45^{\circ}<\theta \leq90^{\circ}$$, $$k=100(\frac{S_n}{S_m})^{1.2}\;(\frac{S_m}{S})^{1.6}\;.\;for\;0^{\circ}<\theta \leq45^{\circ}$$

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.30 no.4
• /
• pp.543-549
• /
• 1997

The problems in the existing modeling rules for fishing nets, especially in the Tauti's rule which had been used most commonly, were investigated and it was found that the rules could not give a good similarity between the prototype and model nets because they din neither analyze the flow resistance of nets accurately nor decide the ratio of flow velocity between the two nets properly. Thus, the modeling rule was newly derived by regarding the nets as holey structures sucking water into their mouth and then filtering water through their meshes as in the previous paper. The similarity conditions obtained, between the two nets distinguished by subscript 1 and 2, are as follows; $$\frac{d_2}{d_1}=\sqrt{\frac{l_2}{l_1}},\;\frac{N_2}{N_1}=(\frac{d_1}{d_2})^{1.5}\frac{L_2}{L_1},\;\varphi_1=\varphi_2,\;\frac{d_{r2}}{d_{r1}}=\sqrt{\frac{L_2{(\rho_{r1}-\rho_{w1})}}{{L_1{(\rho_{r2}-\rho_{w2})}}$$ $$\frac{N_{a2}}{N_{a1}}=\frac{W_{a1}}{W_{a2}}(\frac{L_2}{L_1})^2,\;\nu_1=\nu_2\;and\;\frac{R_2}{R_1}=(\frac{L_2}{L_1})^2$$, where L is the length of nettings, d the diameter of netting twines, 2l the mesh size, $2\varphi$ the angle between two adjacent bars, N the number of meshes at the sides of nettings, $d_r$, the diameter of ropes, $\rho_r$, the specific gravity of ropes, $W_a$ the weight in water of one piece of float or sinker, $N_a$ the number of floats or sinkers, $\nu$ the flow velocity, and R the flow resistance of net. In the case where the model experiments aim at investigating the influence of weight in water of nettings on their shapes in nets subjected to the water flow of very low velocity, however, the following condition is added; $$\frac{\rho_2-\rho_{w2}}{\rho_1-\rho_{w1}}=\frac{d_1}{d_2}$$ where $\rho$ is the specific gravity of netting twines.

• Korean Journal of Environmental Biology
• /
• v.36 no.1
• /
• pp.11-20
• /
• 2018

In planktonic ecosystems, the microplastics are considered as a potential food source for the zooplankton. To study a relationship between the zooplankton and the neustonic microplastics, a research experiment was carried out during May in the surface layers of the Yeosu coastal areas including Yeoja Bay, Gamak Bay, Yeosuhae Bay, and Botdol Sea. A neustonic zooplankton net (mesh size $300{\mu}m$; mouth area $30cm{\times}18cm$) was towed from the side of the ship in the event that it would not be affected by waves crashing by the ship at a speed of ca. 2.5 knots. All of the microplastic particles were separated from the zooplankton. The zooplankton and microplastics were appearing in a range of 61 to $763indiv.m^{-3}$ and 0.0047 to $0.3471particle\;m^{-2}$, respectively. It was noted that the Acartia omorii, Paracalanus parvus s. l., Labidocera euchaeta, A. hongi, decapod larvae, and cirriped larvae were predominantly seen in the experiment. For verifying relationships between zooplankton and environmental factors in addition to microplastics, a model redundancy analysis (RDA) was performed. The zooplankton were divided into two groups on the basis of feeding types (i.e. particle feeders, and carnivores), and the associated zooplankton larvae were also separately considered. A review of the additional environmental factors such as water temperature, salinity, turbidity, chlorophyll-${\alpha}$ concentration, diatom density, and dinoflagellate density were also contained in the analysis. The results showed that a noted zooplankton abundance had no close relation with the occurring number of microplastic particles, but rather was significantly related with other noted environmental factors such as temperature, salinity, turbidity, and chlorophyll-${\alpha}$ concentration. This fact implies that most zooplankton can feed themselves as a unit, by selecting the most likely available nutritious foods, rather than microplastics under the circumstance of food-richness areas, such what food resources are available as in the location of coastal waters.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.30 no.5
• /
• pp.691-699
• /
• 1997

In order to find out the properties in flow resistance of trawlR=1.5R=1.5\;S\;v^{1.8}\;S\;v^{1.8} nets and the exact expression for the resistance R (kg) under the water flow of velocity v(m/sec), the experimental data on R obtained by other, investigators were pigeonholed into the form of $R=kSv^2$, where $k(kg{\cdot}sec^2/m^4)$ was the resistance coefficient and $S(m^2)$ the wall area of nets, and then k was analyzed by the resistance formular obtained in the previous paper. The analyzation produced the coefficient k expressed as $$k=4.5(\frac{S_n}{S_m})^{1.2}v^{-0.2}$$ in case of bottom trawl nets and as $$k=5.1\lambda^{-0.1}(\frac{S_n}{S_m})^{1.2}v^{-0.2}$$ in midwater trawl nets, where $S_m(m^2)$ was the cross-sectional area of net mouths, $S_n(m^2)$ the area of nets projected to the plane perpendicular to the water flow and $\lambda$ the representitive size of nettings given by ${\pi}d^2/2/sin2\varphi$ (d : twine diameter, 2l: mesh size, $2\varphi$ : angle between two adjacent bars). The value of $S_n/S_m$ could be calculated from the cone-shaped bag nets equal in S with the trawl nets. In the ordinary trawl nets generalized in the method of design, however, the flow resistance R (kg) could be expressed as $$R=1.5\;S\;v^{1.8}$$ in bottom trawl nets and $$R=0.7\;S\;v^{1.8}$$ in midwater trawl nets.

• Korean Journal of Weed Science
• /
• v.13 no.2
• /
• pp.104-113
• /
• 1993

The experiment was conducted in 1992 to find out the approach to the development of prediction model of weed population in paddy fields. The weed seeds of 88% over were separated from the soil by using $K_2CO_3$ 50% solution with specific gravity 1.34. The weed seeds which were floated on the solution due to the difference of specific gravity between soil particles and the seeds were effectively withdrawn by using a vaccum pump attached with an aspirator. The seeds withdrawn together with solution were taken by filtering with a nylon net of $0.31{\times}0.16mm$ mesh. The pressing method was more efficient and practical for the viability test of weed seeds separated from the soil compared with the germination test and the TTC test. For the prediction of weed population by the number of weed seedlings emerged at the sampled soil, the sampling method of 0-10cm deep at 5-6 sites per field was applicable. At the prediction method by the number of seedlings emerged, the smaller the seed sizes, the lower the prediction coefficients of weed species. It was considered that the prediction method by the number of seedlings emerged was more practical than the prediction method by the number of seeds separated from sampled soil, in relation to similarities to weed population, time and expenses required for examining, technical difficulties and applicability of weed species.

• Korean Journal of Environment and Ecology
• /
• v.26 no.1
• /
• pp.46-56
• /
• 2012

Benthic macroinvertebrates were investigated in Hoeongseong Lake region from March to October 2010, Korea. Macroinvertebrate communities, composition of the functional feeding groups, habitiat oriented groups and the biological water quality were assessed above and below Hoeongseong Dam in the lake region. Six sites, two (St.1~2) above the lake, two (St. 3~4) into the lake, and two (St. 5~6) below the dam, were selected for quantitative (Surber sampler $30cm{\times}30cm$, mesh size 0.2 mm) and qualitative (Hand net) samplings of benthic macroinvertebrates. As a result, a total of 83 species belonging to 43 families, 17 orders, 8 classes, and 5 phyla were recognized. The EPT-group (50 spp. : 60.24%) that is major taxa or EPT-group plus Diptera (61 spp. : 73.49%) occupied most of benthic macroinvertebrates community. Based on quantitative sampling, the number of benthic maroinvertebrates above the lake was 2,399 individuals including 54 species, 28 families, 11 orders, 4 classes, and 4 phyla, whereas 510 individuals including 16 species, 12 families, 7 orders, 4 classes, and 3 phyla in the lake and 626 individuals including 62 species, 33 families, 13 orders, 6 classes, and 4 phyla below the dam were collected respectively. Dominance index was the highest, with 0.82-0.93 ($0.87{\pm}0.05$) in Hoeongseong lake (St. 3-4), diversity index was 3.04-3.16 ($3.10{\pm}0.06$), evenness index was 0.79-0.85 ($0.82{\pm}0.03$), and richness index was 7.27-8.52 ($7.90{\pm}0.63$), which were relatively higher below the dam sites. In the functional feeding groups, collector-gatherers and collector-filterers were the highest in the whole sites, and predators (Micronecta sedula) was appeared highly in the lake. Moreover, swimmers, burrowers, and clingers were considerably occupied in all collecting sites. The result of the DCA, similarity analysis, and MRPP were well reflective of the composition of lake and stream macroinvertebrates. ESB indicate that the lake sites were evaluated heavily polluted under priority improvement waters. Also, Semisulcospira gottschei, Ecdyonurus kibunensis, Epeorus pellucidus, Rhoenanthus coreanus, Stenelmis sp., and Cheumatopsyche brevilineata are considered as an indicator species above and below Hoeongseong Lake, whereas Macrobrachium nipponense and Micronecta sedula are indicated in the lake.