• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.3
• /
• pp.551-558
• /
• 2004

Recently, fuel prices have been continually raised in diesel engine. Such a change in the fuel price influences enormously the development trend of marine diesel engines for slow speed, In other words, the focus was shifted from large diameter and high speed to low fuel consumption. Accordingly, more efforts are being made for engine manufacturing and development to develop highly efficient engines. In this study. a single cylinder 4 stroke cycle DI slow speed diesel engine was designed and manufactured, a 4 stroke cycle was configured and basic performances were evaluated. The results are as follows. The optimal fuel injection timing had the lowest value when specific fuel consumption was in BTDC 8~$10^{\circ}$, a little more delayed compared to high speed diesel engines. Cycle variation of engines showed about 5% difference at full loads. This is a significantly small value compared to the cycle variation in which stable operation is possible, showing the high stability of engine operation is good. The torque and brake thermal efficiency of engine increased with an increase of engine 250-450 rpm. but fuel consumption ratio increased from the 450 rpm zone and thermal efficiency abruptly decreased. Mechanical efficiency was maximally 70% at a 400 rpm that was lower than normal engines according to the increase of mechanical frictional loss for cross head part. The purpose of this study was to get more practical engines by comparing the above results with those of slow speed 2 stroke cycle diesel engines.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.10
• /
• pp.4754-4773
• /
• 2018

In sensor medium access control (SMAC) protocol, sensor nodes can only access the channel in the scheduling and listening period. However, this fixed working method may generate data latency and high conflict. To solve those problems, scheduling duty in the original SMAC protocol is divided into multiple small scheduling duties (micro duty MD). By applying different micro-dispersed contention channel, sensor nodes can reduce the collision probability of the data and thereby save energy. Based on the given micro-duty, this paper presents an adaptive duty cycle (DC) and back-off algorithm, aiming at detecting the fixed duty cycle in SMAC protocol. According to the given buffer queue length, sensor nodes dynamically change the duty cycle. In the context of low duty cycle and low flow, fair binary exponential back-off (F-BEB) algorithm is applied to reduce data latency. In the context of high duty cycle and high flow, capture avoidance binary exponential back-off (CA-BEB) algorithm is used to further reduce the conflict probability for saving energy consumption. Based on the above two contexts, we propose an improved SMAC protocol, micro duty adaptive SMAC protocol (MDA-SMAC). Comparing the performance between MDA-SMAC protocol and SMAC protocol on the NS-2 simulation platform, the results show that, MDA-SMAC protocol performs better in terms of energy consumption, latency and effective throughput than SMAC protocol, especially in the condition of more crowded network traffic and more sensor nodes.

• Tribology and Lubricants
• /
• v.20 no.5
• /
• pp.252-258
• /
• 2004

In this study, using high cycle fatigue (HCF) criteria, the simulation of rolling contact fatigue is conducted under elliptical contact. The HCF criteria fall into three categories: the critical plane approach, the stress invariant approach and the approach based on the mesoscopic scale. The accurate calculation of contact stresses and subsurface stresses is essential to the prediction of crack initiation life. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and the subsurface stress field is obtained using rectangular patch solutions. The simulation results show that the critical load is decreasing rapidly and the site of crack initiation also moves rapidly to the surface from the subsurface when the friction coefficient exceeds a specific value for all of three fatigue criteria.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2006.05a
• /
• pp.129-132
• /
• 2006

Recently, Society increasingly need the hish-rise building because of urban population concentration. and The hish-rise building need new systematic work-planning method. but it didn't use the construction project's work plan and management. his paper investigated efficient work-planning method. and the work-planning method in using domestic High-rise building's structure work. A investigated result is TACT, DOC LOB etc. and domestic using method is 3day and 4day-Cycle among the Tact. This paper is to compare and analysis two method. a purpose of paper is to analyse application through the case of using the work-planning method. also To find efficient method.

• Journal of Welding and Joining
• /
• v.31 no.4
• /
• pp.47-53
• /
• 2013

SCMH2 steel is widely used in the industrial members of car and tractor. This study focused on material properties and evaluation technology of the SCMH2 steel regarding the surface treatment followed by carburizing and nitriding, by means of impact test, hardness test. and fatigue test including HCF (high cycle fatigue) and VHCF (very high cycle fatigue). Drop weight impact tester (Instron, 9250 Hv) and Cantilever type rotating-bending fatigue tester (YRB200, 3150 rpm) were used to characterize the SCMH2 standard specimen before and after carburizing/nitriding. In order to understand those effects on fatigue characteristics and material properties, the fractured surfaces were carefully observed and analyzed by SEM (scanning electron microscope) and EDS (energy-dispersive X-ray spectroscopy).

• Journal of Korean Port Research
• /
• v.14 no.4
• /
• pp.395-406
• /
• 2000

In this paper, an improved high efficiency gantry crane for container transportation is designed. The basic concept of the designed crane can be used with modification of the classical gantry crane instead of changing lots of them. This crane can reduce the cycle time more than the classical gantry carne. The high efficiency gantry crane can improve the productivity of the container transportation job because of reducing cycle time. The loading and unloading capability are compared with classical crane. The result show that show that the proposed crane has better performances than classical type.

• Nuclear Engineering and Technology
• /
• v.39 no.1
• /
• pp.21-30
• /
• 2007

Current high-temperature gas-cooled reactors (HTGRs) are based on a closed Brayton cycle with helium gas as the working fluid. Thermodynamic performance of the axial-flow helium gas turbines is of critical concern as it considerably affects the overall cycle efficiency. Helium gas turbines pose some design challenges compared to steam or air turbomachinery because of the physical properties of helium and the uniqueness of the operating conditions at high pressure with low pressure ratio. This report present a review of the helium Brayton cycle experiences in Germany and in Japan. The design and availability of helium gas turbines for HTGR are also presented in this study. We have developed a new throughflow calculation code to calculate the design-point performance of helium gas turbines. Use of the method has been illustrated by applying it to the GTHTR300 reference.

• Nuclear Engineering and Technology
• /
• v.51 no.3
• /
• pp.867-876
• /
• 2019

Second harmonic generation using nonlinear ultrasonic waves have been shown to be an early indicator of possible fatigue damage in nuclear power plant components. This technique relies on measuring amplitudes, making it highly susceptible to variations in transducer coupling and instrumentation. This paper proposes an experimental procedure for in-situ surface wave nonlinear ultrasound measurements on specimen with permanently mounted transducers under high cycle fatigue loading without interrupting the experiment. It allows continuous monitoring and minimizes variation due to transducer coupling. Moreover, relations describing the effects of the measurement system nonlinearity including the effects of the material transfer function on the measured nonlinearity parameter are derived. An in-situ high cycle fatigue test was conducted using two 304 stainless steel specimens with two different excitation frequencies. A comprehensive analysis of the nonlinear sources, which result in variations in the measured nonlinearity parameters, was performed and the effects of the system nonlinearities are explained and identified. In both specimens, monotonic trend was observed in nonlinear parameter when the value of fundamental amplitude was not changing.

• Journal of Science Education
• /
• v.37 no.1
• /
• pp.157-169
• /
• 2013

The purpose of this study is to analyze carbon cycle concepts based on earth systems from the perspective of high school students. The subjects for this study were seven students who have completed Earth-science I curriculum. to analyze of carbon cycle concepts based on earth systems perspective, the methods of word association, casual map and drawing were used. The results of this study were as follows: first, 5 out of 7 students have suggested carbon cycle concepts less than three. Second, the carbon cycle concepts on the change of state were 2. Also, the carbon cycle concets on process were 8. Third, 2 out of 7 students present 2 feedback loops, 3 out of 7 students 1 feedback loops, but 2 out of 7 students couldn't present the feedback loops associated with carbon cycle. Finally, As for carbon cycle concepts through drawing, 1 out of 7 students drew 9 concepts, 3 out of 9 students drew 7 concepts and the rest of them drew 5, 4, 3 concepts respectively. These results suggest that concept and feedback loop thinking skills on carbon cycle are a low level. Therefore, It is suggested that more educational programs be developed on various topics in order for high school students to improve their system thinking skills as well as knowledge integration of earth systems.

• Korean Journal of Geomatics
• /
• v.3 no.2
• /
• pp.129-140
• /
• 2004

This paper addresses solutions th the challenges of carrier phase integer ambiguity resolution and cycle slip detection/identification, for maintaining high accuracy of an integrated GPS/Pseudolite/INS system. Such a hybrid positioning and navigation system is an augmentation of standard GPS/INS systems in localized areas. To achieve the goal of high accuracy, the carrier phase measurements with correctly estimated integer ambiguities must be utilized to update the system integration filter's states. The contribution presents an effective approach to increase the reliability and speed of integer ambiguity resolution through using pseudolite and INS measurements, with special emphasis on reducing the ambiguity search space. In addition, an algorithm which can effectively detect and correct the cycle slips is described as well. The algorithm utilizes additional position information provided by the INS, and applies a statistical technique known as th cumulative-sun (CUSUM) test that is very sensitive to abrupt changes of mean values. Results of simulation studies and field tests indicate that the algorithms are performed pretty well, so that the accuracy and performance of the integrated system can be maintained, even if cycle slips exist in the raw GPS measurements.