• Journal of Aerospace System Engineering
• /
• v.4 no.4
• /
• pp.28-36
• /
• 2010

Current tanks have been developed to increase mobility and firepower, and its maximum range and destructive power are improved. This great change causes remained vibration of a gun barrel after firing. For this reason, people are trying to control vibration of gun barrel effectively. This thesis presents a modeling method and analysis results for gun barrel by using a thermal shroud as an absorber mass. DTS(Dynamically Tuned Shroud) is a vibration damping system using a thermal shroud as an added mass for decreasing remained vibration. The model has an advantage that the gun barrel's vibration can be decreased by dissipating a kinetic energy of thermal shroud without install an additional dynamic absorber to tip of the gun barrel. For analyzing the damping performance of the DTS, We derived an equation of motion of the barrel after setting a mathematical modeling, and found out the frequency analysis and tendency according to stiffness ratio between barrel and shroud.

• International Journal of Aerospace System Engineering
• /
• v.3 no.1
• /
• pp.25-29
• /
• 2016

This paper highlights the performance of an impulse turbine which is a part of turbopump in a liquid rocket first stage engine. The turbopump, currently under development at Korea Aerospace Research Institute, has an impulse type turbine with 12 nozzles and a single rotor. The impulse turbine can archive high specific power with the low gas flow rates. The supersonic impulse turbine with a single rotor can make a simple structure. High-pressure gases are converted into the dynamic energy with flows through the 12 nozzles and drive the rotor to make the power for the pumps. The turbine test was performed in the high-pressured turbine test facility with air gas instead of burned gas. A hydraulic dynamometer was used to absorb the power from the turbine and control the rotational speed and torque. The test points were at several pressure ratios with 7 different rotational speeds. Results showed the efficiency was highest at the design pressure ratio. The efficiency was insensitive to the pressure ratio variation than the rotational speed. It was a typical characteristic in an impulse turbine.

• Proceedings of the KSR Conference
• /
• 2008.06a
• /
• pp.1032-1038
• /
• 2008

KTX train system is composed of TORNAD* network for transmitting information of train's internal equipments and OBCS which proceed information within train. OBCS of one trainset consisted of 28 equipments takes intelligent and dynamic composition according to equipment handling, train command and control flow. Each OBCS which is installed within trainset handle and supervise mutually action information about equipments, transmit it to driver to transmit information about train operation and preventive management. This mutual supervision and information transmission use KTX TORNAD* network system. TORNAD* network system is the one which is uniquely developped by GEC ALSTHOM, the KTX trainset manafacturing provider and this field is excluded from technical know-how transfer item. Through the research on analysis method of KTX TORNAD* system data structure which is operating on Seoul-Pusan Line, I hope that this thesis can contribute to train network system's standardization after applying it to improvement of train network system maintenance, enhancing quality of train service and applying it to future Korean rolling stock network system development.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.1
• /
• pp.132-141
• /
• 1995

The torque converter, an important component of automatic transmissions, is a hydrodynamic device which has a great influence on transient characteristics of vehicle during shift. To predict the accurate driving performance in extremely transient state such as shifting process, a detailed analysis of the torque converter is required. In this study, one dimensional performance model of the torque converter based on the concept of mean flow path, was used to analyze the shifting transients and the exact values of equivalent parameters were determined from the experimental results by using BOX program. The dynamic modelings of the components of power transmission systems such as engines, planetary gear systems, clutches and one-way clutches, were carried out. To analyze the shifting transients of tracked vehicle, a simulation program was developed. In the modeling of power transmission systems, the stiffness of shafts was neglected and shifting control logic(TCU) was included. Using the developed simulation program, the driving conditions were simulated and the results of simulation were verified through the experiments on the dynamometer.

• Journal of Drive and Control
• /
• v.14 no.1
• /
• pp.35-40
• /
• 2017

Whereas fuel economy of a vehicle is measured using a chassis dynamometer, that of construction machinery such as an excavator shall be presumably measured using simulated work cycle. In order to measure fuel consumption under a simulated work cycle, a measurement methodology, while excavator operates in dynamic(transient) motion, needs to be examined and developed. In this work, three methods (gravimetry, ECU CAN signal and mass flow meter) are studied and compared. This work reveals that when ECU CAN signal is properly calibrated and evaluated, compared to gravimetry or mass flowmeter, it could be used to measure fuel consumption with accuracy and thus for approval of the fuel economy of construction machinery.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.9 no.1
• /
• pp.100-113
• /
• 2017

Snap rolling during hard turning and instability during emergency rising are important features of submarine operation. Hydrodynamics modeling using a high incidence flow angle is required to predict these phenomena. In the present study, a quasi-steady dynamics model of a submarine suitable for high-incidence-angle maneuvering applications is developed. To determine the hydrodynamic coefficients of the model, static tests, dynamic tests, and control surface tests were conducted in a towing tank and wind tunnel. The towing tank test is conducted utilizing a Reynolds number of $3.12{\times}10^6$, and the wind tunnel test is performed utilizing a Reynolds number of $5.11{\times}10^6$. In addition, least squares, golden section search, and surface fitting using polynomial models were used to analyze the experimental results. The obtained coefficients are presented in tabular form and can be used for various purposes such as hard turning simulation, emergency rising simulation, and controller design.

• Journal of the Korean Society of Safety
• /
• v.31 no.3
• /
• pp.47-52
• /
• 2016

This paper describes the design and fabrication of high frequency ground impedance measuring system for assessment of grounding system for Lightning protection. The ground impedance measuring system has been designed and fabricated which makes it possible to assess the ground impedance by frequency ranges from 100 Hz to 1 MHz. The effective grounding systems having a very low impedance to electromagnetic disturbance such as lightning surges and noises in microelectronics and high-technology branches are strongly required. In order to analyze the dynamic characteristic of grounding system impedances in lightning and surge protection grounding systems, it is highly desirable to assess the ground impedances as a measure of performance of grounding system in which lightning and switching surge currents with fast rise time and high frequency flow. The measuring system is based on the variable frequency power supply and consists of signal circuit part, main control part, data acquisition and processing unit, and voltage and current probe system. The ground impedance measuring system can be used to assess grounding system during occurrence of lightning.

• The Journal of Industrial Distribution & Business
• /
• v.9 no.1
• /
• pp.25-38
• /
• 2018

Purpose - The purpose of this study is to empirically investigate the impact of donor's fiscal status on aid decisions before and after the 2008 global financial crisis. The effects on aid can change depending on the donor country's fiscal status and the period of financial crisis. Research design, data, and methodology - A fixed effect regression and dynamic panel GMM is conducted using a comprehensive dataset combining 31 donor and 167 recipient countries during 1996-2015. The key explanatory variable is central government debt-to-GDP ratio of donor country. Recipient countries' GNI per capita, population, governance indicators, and bilateral trade-to-GDP ratio between donor and recipient countries are included as control variables. Results - We can confirm the relationship between donor country's fiscal status and aid flow. The cyclical component of government debt is found to have a negative impact on grant decisions particularly after the 2008 global financial crisis. This effect becomes larger in the countries with high government debt-to-GDP ratio. ODA decisions from the countries with low financial constraint do not significantly affected by the recipient countries' factors such as GNI, population, and governance indicator. Conclusions - Based on the empirical results of this study, the source of aid should be diversified by incorporating private sector and innovative financing sources.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.16 no.8
• /
• pp.2801-2815
• /
• 2022

With the advent and realization of Software Defined Network (SDN) architecture, many organizations are now shifting towards this paradigm. SDN brings more control, higher scalability, and serene elasticity. The SDN spontaneously changes the network configuration according to the dynamic network requirements inside the constrained environments. Therefore, a monitoring system that can monitor the physical and virtual entities is needed to operate this type of network technology with high efficiency and proficiency. In this manuscript, we propose a real-time monitoring system for data collection and visualization that includes the Prometheus, node exporter, and Grafana. A node exporter is configured on the physical devices to collect the physical and virtual entities resources utilization logs. A real-time Prometheus database is configured to collect and store the data from all the exporters. Furthermore, the Grafana is affixed with Prometheus to visualize the current network status and device provisioning. A monitoring system is deployed on the physical infrastructure of the KOREN topology. Data collected by the monitoring system is further pre-processed and restructured into a dataset. A monitoring system is further enhanced by including machine learning techniques applied on the formatted datasets to identify the elephant flows. Additionally, a Random Forest is trained on our generated labeled datasets, and the classification models' performance are verified using accuracy metrics.

• Journal of Drive and Control
• /
• v.13 no.2
• /
• pp.10-18
• /
• 2016

A front-end loader (FEL) mounted on an agricultural tractor is one of the most commonly used implements to mechanize routine agricultural tasks. When the FEL is used with a loaded bucket, careful operation is required to maintain safety and avoid spillage when the tractor passes a bump because a change in the gravity center of the tractor due to varied loadings can affect the stability of the tractor. Use of a boom suspension system consisting of accumulators and orifice dampers can be instrumental in reducing pitching vibrations while increasing the handling performance of the FEL-mounted tractor. The objective of this research was to reduce bump shocks by adding an orifice and a flow control valve to the original hydraulic circuit composed solely of accumulators. A simulation study was performed using the SimulationX program to investigate the effects of an accumulator and an orifice-throttle damper on bump shocks. Results showed that the peak pressure on a boom cylinder and the vertical acceleration of a bucket were significantly affected by use of both an accumulator and an orifice damper. In a field test conducted with a 75-kW tractor, the peak pressure of the boom cylinder, and the root mean square (RMS) vertical acceleration of the bucket and seat were reduced by on average, 23.0, 42.2, and 44.9% respectively, as compared to those measured with the original accumulator system, showing that an improved design for the accumulator hydraulic circuit can reduce bump shocks. Further studies are needed to design a tractor suspension system that includes the effects of cabin suspension and tires as well as dynamic analysis.