• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.6
• /
• pp.1150-1155
• /
• 1992

The cooling characteristics of a hot steel plate by a laminar impinging water bar were investigated experimentally. The dynamic parameters investigated were nozzle height L between nozzle and the hot plate, flow rate Q, and initial cooling temperature. Because the boiling phenomena on a hot steel plate are unsteady and change discontinuously, it is difficult to analyze the cooling characteristics directly. In this study the cooling efficiency was estimated by using the temperature decay rates and expansion speed of the water cooling zone. Temperature in the water cooling zone decreased rapidly and the radius of the water cooling zone expanded nearly in proportion to square root of the cooling time. With increasing initial temperature of a hot steel plate, the cooling efficiency became descendent. The cooling curve in the case of L/D = 30 showed the largest temperature decay rate and excellent cooling performance.

• Ocean Systems Engineering
• /
• v.4 no.3
• /
• pp.215-241
• /
• 2014

Steel catenary riser (SCR) is a popular/economical solution for the oil/gas production in deep and ultra-deep water. The behavioral characteristics of SCR have a high correlation with the motion of floating production facility at its survival and operational environments. When large motions of surface floaters occur, such as FPSO in 100-yr storm case, they can cause unacceptable negative tension on SCR near TDZ (touch down zone) and the corresponding elastic deflection can be large due to local dynamic buckling. The generation, propagation, and decay of the elastic wave are also affected by SCR and seabed soil interaction effects. The temporary local dynamic buckling vanishes with the recovery of tension on SCR with the upheaval motion of surface floater. Unlike larger-scale, an-order-of-magnitude longer period global buckling driven by heat and pressure variations in subsea pipelines, the sub-critical local dynamic buckling of SCR is motion-driven and short cycled, which, however, can lead to permanent structural damage when the resulting stress is greatly amplified beyond the elastic limit. The phenomenon is extensively investigated in this paper by using the vessel-mooring-riser coupled dynamic analysis program. It is found that the moment of large downward heave motion at the farthest-horizontal-offset position is the most dangerous for the local dynamic buckling.

• Environmental Engineering Research
• /
• v.22 no.1
• /
• pp.75-86
• /
• 2017

The aerosol content dynamics in a virtual system were investigated. The outcome was extended to monitor the mean concentration diffusion of aerosols in a predefined macro and micro scale. The data set used were wind data set from the automatic weather station; satellite data set from Total Ozone Mapping Spectrometer aerosol index and multi-angle imaging spectroradiometer; ground data set from Aerosol robotic network. The maximum speed of the macro scale (West Africa) was less than 4.4 m/s. This low speed enables the pollutants to acquire maximum range of about 15 km. The heterogeneous nature of aerosols layer in the West African atmosphere creates strange transport pattern caused by multiple refractivity. It is believed that the multiple refractive concepts inhibit aerosol optical depth data retrieval. It was also discovered that the build-up of the purported strange transport pattern with time has enormous potential to influence higher degrees of climatic change in the long term. Even when the African Easterly Jet drives the aerosols layer at about 10 m/s, the interacting layers of aerosols are compelled to mitigate its speed to about 4.2 m/s (macro scale level) and boost its speed to 30 m/s on the micro scale level. Mean concentration diffusion of aerosols was higher in the micro scale than the macro scale level. The minimum aerosol content dynamics for non-decaying, logarithmic decay and exponential decay particulates dispersion is given as 4, 1.4 and 0 respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.41 no.12
• /
• pp.1-6
• /
• 2004

In this study, heat and discharge treatments are arbitrary simulated for finding out the initiations and processes of surface degradation on the surface of polymer for using as a PCB substrate. Thermal-treatment changed the surface to the hydrophobic one with the increase of contact angle and surface potential decay, respectively. The XPS spectrum showed that the increased hydrophobicity in thermal treatment was originated from the continuous decrease of side-chains caused by secessions of oxygen groups and the increase of unsaturated double bond in carbon chains. Also, thermal-treatment caused the discoloration on the point of treated surface. These phenomena were attributed to the generation of ether group. In the chemical change by discharge treatment, a lot of side-chains occurred on the treated surface, and so the hydrophilicity increased as time elapsed.

• International Journal of Advanced Culture Technology
• /
• v.6 no.3
• /
• pp.151-162
• /
• 2018

In deriving the economic order quantity (EOQ) formula, it is tacitly assumed that the buyer has to pay product price while receiving the product from the supplier. However, as a marketing policy, some suppliers permit a delay in payments to the buyers to increase demand for the product they made. Credit transactions would have a positive effect on both suppliers and buyers. For a supplier who offers trade credit, it is an effective means of price differentiation to increase the demand for the product. Availability of opportunity to delay the payment in buyer effectively reduces the cost of holding stocks and therefore, the buyer has a lot of price options to choose his sales price for a customer. Since the buyer's order is affected by the customer's demand, the problems of determining the sales price and EOQ are interdependent and must be solved simultaneously. From this perspective, this paper evaluates the problem of determining the optimal sales price and EOQ for the buyer at the same time when the supplier allows a delay in payments for the product whose demand is represented as a function that decreases linearly with the sales price. For the analysis, it is also assumed that inventory is exhausted not only by customer's but also by decay.

• Fire Science and Engineering
• /
• v.15 no.2
• /
• pp.91-95
• /
• 2001

Decays of the ceiling jet front velocity under a circular ceiling are investigated. To simulate the ceiling jet in fires He and $N_2$gas were injected from a nozzle to the center of the ceiling. The jet fronts in the form of turbulent eddies were traced by a high-speed camera system. The instantaneous locations of the front were obtained from visual readings of visualized front, and the radial velocity was calculated from the information of the time and the location with respect to the front. The similarity and dimensional analysis were also carried out to reveal the relationship between the velocity decay and the radial distance. It was shown that the radial velocity of the front was inversely proportional to the radial distance in the fully developed region from the experimental results and the theoretical analysis.

• Journal of the Korea Concrete Institute
• /
• v.17 no.6 s.90
• /
• pp.1075-1084
• /
• 2005

The compressive strength of concrete is commonly used criterion in producing concrete. However, the tests on the compressive strength are complicated and time-consuming. More importantly, it is too late to make improvement even if the test result does not satisfy the required strength, since the test is usually performed at the 28th day after the placement of concrete at the construction site. Therefore, accurate and realistic strength estimation before the placement of concrete is being highly required. In this study, the estimation of the compressive strength of concrete was performed by probabilistic neural network(PNN) on the basis of concrete mix proportions. The estimation performance of PNN was improved by considering the correlation between input data and targeted output value. Improved probabilistic neural network was proposed to automatically calculate the smoothing parameter in the conventional PNN by using the scheme of dynamic decay adjustment (DDA) algorithm. The conventional PNN and the PNN with DDA algorithm(IPNN) were applied to predict the compressive strength of concrete using actual test data of two concrete companies. IPNN showed better results than the conventional PNN in predicting the compressive strength of concrete.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2004.11a
• /
• pp.160-165
• /
• 2004

Low-frequency damping characteristics of side-by-side moored LNG-FPSO and LNGC arc investigated through a series of free decay model tests in calm water and under wind load condition. It is shown that low frequency damping of LNGC changes dramatically, sway damping increases more than six times for 4m distance condition while it decreases by $30\%$ for 20m distance compared with a single LNGC case. Simulation using the experimental data enhances the results, which demonstrates the necessity of experimental low-frequency damping coefficients for simulation of side-by-side vessels motion behavior.

• Food Science and Preservation
• /
• v.5 no.2
• /
• pp.105-110
• /
• 1998

To find out suitable storage and marketing condition, northern type 'seosan' garlic was stored for 3 months at controlled atmosphere(CA), modified atmosphere(MA), low(0~1$^{\circ}C$) and room temperature(20$\pm$5$^{\circ}C$), and then marketed at low(2~3$^{\circ}C$) and room temperature (20$\pm$5$^{\circ}C$)after storage. The physiological properties of garlic were investigated among treatments. The garlic respiration increased after 2 months at room temperature storage, which seem to be dormancy break time. During storage of garlic by CA, MA condition, sprouting and weight loss were prevented effectively by suppress of respiration, and hardness was maintained higher then those of the others. Decay rate occurred 8.1% at room temperature storage, 2% at MA storage but didn't occurred at CA and low temperature storages. When marketed at room and low temperature after storage, increment of respiration and sprouting were delayed, and changes of weight and hardness were low in garlics stored at CA and MA. Decay rate occurred high in garlics stored at MA and room temperature.

• Tunnel and Underground Space
• /
• v.6 no.3
• /
• pp.209-222
• /
• 1996

Shut-in pressure, reopenting pressure and fracture orientation are very important parameters to be evaluated precisely in in-situ stress measurement by hydraulic fracturing. Graphical methods on pressure-time curves have been conventionally used, even though these are seriously dependent on subjectivity of interpreters. So there have been many demands on new method to objectivity in determining parameters. We have developed integrated hydrofracturing data processing program (HYDFRAC), based on nonlinear regression analysis and can be invoked under the Window graphical user interface. HYDFRAC consiste of three routines, that is shut-in pressure routine, reopening pressure routine, and fracture delineation routine. Each of routines include independent modules according to parameter determination methods. Its application to field tests ensured both objectivity and facility in determining of hydraulic fracturing parameters. Determining shut-in pressures at each pressurization cycles, we adopted the exponential pressure-decay method(EPD method), the bilinear pressure-decay-rate method (PDR method), and the tangent intersection method in order to find the pressurization-cyclic tendency of shut-in pressures. The estimated pressure by PDR method exists in the range of the upper and lower values by EPD method, and lies near to the upper value more than the lower. Being the pressurization cycle increased, the range of upper and lower limits come to be stabilized gradually. By graphical superposition method and bilinear pressure-accumulated volume method, reopening pressures were determined. Vertical and inclined fracture attitudes were determined by applying the directional statistics and sinusoidal curve fitting, respectively. The results of evaluation of hydrofracturing parameters showed that statistical methods could enhance the objectivity better than graphical methods.