• Magazine of the Korean Society of Agricultural Engineers
• /
• v.18 no.4
• /
• pp.4251-4258
• /
• 1976

In the construction of earth dam, embankment and highway by filling, a compaction contributes to increasing the density of soil by applying pressure. The effect of compaction depends on various factors such as soil type, moisture content, gradation, consistency, and compaction energy. In this study, the correlations amone maximum dry density, moisture content, dry density, and moisture content are analyzed. Some results obtained in this study are summarizep as follows. 1. The maximum dry density sinoreases with increased of optimum moisture content and the correlations of them can be represented by; ${\gamma}$dmx=a-b(W0) 2. Maximum dry density and liquid limit show negative linear correlation and can be represented by; ${\gamma}$dmx=a-b(LL). 3. Optimum moisture content and liquid limit, plastic limit show positive linear correlation and can be represented by the following equation, W0=a+b(LL) W0=a+b(PL). 4. Liquid limit and plastic limit show positive linear correlation, and can be represented by the following equation, LL=a+b(PL).

• Journal of Power Electronics
• /
• v.12 no.3
• /
• pp.487-494
• /
• 2012

A new low cost high power density photovoltaic power conditioning system (PV PCS) with an energy storage system is proposed in this paper. Its high power density and cost effectiveness can be achieved through the unification of the maximum power point tracker and the battery charger/discharger. Despite the reduced power stage, the proposed system can achieve the same performance in terms of maximum power point tracking and battery charging/discharging as the conventional system. When a utility power failure happens, the proposed system cannot perform maximum power point tracking at the UPS mode. However, the predetermined battery voltage near the maximum power point of the PV array can effectively generate a reasonable PV power even at the UPS mode. Therefore, it features a simpler structure, less mass, lower cost, and fewer devices. Finally, to confirm the operation, validity, and features of the proposed system, a theoretical analysis and experimental results from a single phase AC 220Vrms/1.5kW prototype are presented.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.3
• /
• pp.69-75
• /
• 2013

During the magnetic abrasive polishing of a curved surface, the improvement in surface roughness varies with the maximum value and distribution of magnetic flux density. Thus, in this study, the magnetic flux density on the curved surface was simulated according to curvature radii of magnetic tool. As a result of the simulation, the 14.5mm of the magnetic tool had a higher maximum magnetic flux density and it showed a large weighted magnetic flux density. The weighted magnetic flux density means the highest value for the magnetic flux density in the curvature of the magnetic tool. From the experimental verification, the better improvement in surface roughness was observed on wider area at the 14.5mm radius of the magnetic tool than other radii.

• Journal of the Korean GEO-environmental Society
• /
• v.14 no.3
• /
• pp.13-17
• /
• 2013

Determination of geotechnical characteristics of soil is either to use the field samples to measure the characteristics of soil through laboratory test or measuring the characteristics directly in the field. Field test can be derived similar value by considering characteristics of site and laboratory test can be confirmed the characteristic of soil by testing with field samples. This article describes relative density as the measure of compaction for cohesionless soils and presents several simple and mathematical relationships to help engineers estimate needed parameters for relative density calculations. The main purpose of this research is to investigate possible correlations between coefficient of uniformity, coefficient of curvature, maximum and minimum void ratio, mean grain size. Results show a linear relationship between the minimum and maximum void ratios and a power function relationship between coefficient of uniformity and the limiting void ratios. Void ratio range, which is the difference between the maximum and minimum void ratios, appeared to be log normally distributed but showed no simple mathematical fit to the data. these results were shown to help engineers estimate needed parameters for relative density calculations.

• Journal of Korean Society of Water and Wastewater
• /
• v.26 no.6
• /
• pp.883-888
• /
• 2012

Anode electrode is one of the most important factors in microbial fuel cell (MFC). This study was conducted to investigate the effects of mediator as methylene blue (MB) and electrode surface area on the power density of MFC with sponge and carbon nano tube (CNT) electrode (SC). The SC electrode with MB (MC) showed the maximum power density increased from 74.0 $mW/m^2$ to 143.1 $mW/m^2$. The grid shaped sponge and CNT (GSC) electrode showed the maximum power density of 209.2 $mW/m^2$ due to the increase of surface area from 88.0 to 152.0 $cm^2$. The GSC electrode with MB (GMC) revealed the maximum power density of 384.9 $mW/m^2$ which was 5.2 times higher than that obtained from the MFC with SC. Therefore MB and increase of surface area led to enhance the performance of microbial fuel cell such as power density.

• Journal of Korean Society of Water and Wastewater
• /
• v.27 no.4
• /
• pp.503-509
• /
• 2013

Electrochemical redox capacity of a microbial fuel cell (MFC) electrode is an important factor in the power density. This study was conducted to investigate the redox capacity of surface modified anode and cathode electrodes by measuring their conductivities. An anode electrode was modified with nitric acid and a cathode electrode was modified with heat treatment. The anode electrode modified with 20 % of the nitric acid concentration showed the highest conductivity of $6.2{\mu}S/cm/g$ and the maximum power density of $306.0mW/m^2$ when used in a MFC. The cathode electrode modified at $472^{\circ}C$ for 18 min showed the highest conductivity of $5.2{\mu}S/cm/g$ and the maximum power density of $276.20mW/m^2$ when used in a MFC. On the other hand, an MFC using both the electrodes showed the highest maximum power density of $408.2mW/m^2$. Meanwhile, a control MFC without modified electrodes generated very small voltage (0.014 mV), so the power density could not be measured.

• Korean Journal of Agricultural Science
• /
• v.3 no.2
• /
• pp.207-213
• /
• 1976

In order to obtain the prediction of the maximum dry density and the optimum moisture content of soil without soil moisture test, compaction test results from 157 different places either under construction or already completed were analyzed. The analyzed results were as follow The relationship between the maximum dry density and the optimum moisture content of the soil showing a correlation coefficient of 0.96 indicated that there was a high correlation between them. From the above relationship we obtained the equation, ${\gamma}_{dmax.}={\frac{1}{0.4193+0.00937W_{opt.}}$ Equation between the optimum moisture content and the maximum wet density of the soil was $W_{opt.}={\frac{0.4193{\gamma}_{tmax.}}{0.937_{\gamma}_{tmax.}-0.01}$, and the values of the optimum moisture content being predicted with the maximum wet density of the soil showed a little difference between those and tested values. The values of the maximum dry density being predicted with the moisture content estimated by the maximum wet density of the soil were within the range of ${\pm}5%$ of its tested values. The relationship between the dry density and the void ratio showed a high correlation between them (${\gamma}=0.9706$). From the above relationship, we obtained the equation, ${\gamma}_{dmax.}={\frac{1}{0.3938+0.3426e}}$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.12
• /
• pp.777-784
• /
• 2016

All-vanadium redox flow batteries (VRFBs) are used as energy storage systems for multiple intermittent power sources. The performance of the VRFBs depends on the materials and operating conditions. Hence, performance characterization is of great importance in the development of the VRFBs. This paper proposes a method for determining the maximum current density based on stoichiometric ratios. A laboratory-scaled VRFB with a projected electrode area of $25cm^2$ is electrically charged when the state of the charge has begun from 0.6. The operating conditions, such as current density and volumetric flow rate are important in the test, and the maximum current density is influenced by the mass transfer coefficient. The results show that increasing the electrolyte flow rate from 5 mL/min to 60 mL/min enhances the maximum current density up to $520mA/cm^2$.

• Journal of Korean Society of Forest Science
• /
• v.80 no.4
• /
• pp.351-359
• /
• 1991

Annual ring characteristics of pinus thunbergii grown in several air-polluted areas were investigated by soft X-ray densitometry. Ring width, maximum density and relative difference between maximum and minimum density(abbreviated to DD) were generally decreased after the beginning of operation of the factories at the vicinity of the pollution sources. Especially at the nearest areas of the industrial complex, those were distinctly decreased, and the changes, either increases or decreases, in percentage of latewood and minimum density could not be explained by the air pollution dosages. Ring width, maximum density and DD were being more apparently decreased after 5 years than those for 5 years after the beginning of operation, and also the rate of decrease was increased from after 5 years after the beginning of operation, and the rate of decrease of ring width was the highest of all. It was inferred that ring width, maximum density and DD of Pinus thunbergii could be used as indicators to detect the growth damage by air pollution.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.11 no.1
• /
• pp.71-83
• /
• 2007

The double diffusive convection of cold water in the vicinity of its density maximum in a rectangular partitioned enclosure of aspect ratio 5 with isothermal side walls and insulated top and bottom is studied numerically. A thin partition is attached to the hot wall. The species diffusivity of the fluid is assumed to vary linearly with concentration. The governing equations are solved by finite difference scheme. The effects of position and height of the partition, variable species diffusivity and enclosure width are analyzed for various hot wall temperatures. It has been found that adding partition on the hot wall reduces the heat transfer. The density inversion of the water has a great influence on the natural convection. When increasing species diffusivity parameter heat and mass transfer rate is decreased.