• Journal of Advanced Navigation Technology
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• v.17 no.1
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• pp.107-114
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• 2013

In this paper, we propose controller to control the acceleration of unmanned aircraft turbojet engine. The high-gain observer to estimate the rotational speed of compressor is used, and the turbojet engine controller applying fuzzy heuristic techniques and PID control algorithm are designed. fuzzy PID controller produces the flow control input to prevent the surge and flame-out phenomena at the acceleration and deceleration of the turbojet engine. The standard acceleration is set and the fuel flow control is defined by the fuzzy heuristic. Computer simulations are performed using MATLAB in order to verify the performance of the proposed controller.

• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.165-171
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• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.2
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• pp.94-100
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• 2013

A convergent-divergent nozzle or venturi nozzle has been used to accelerate the wind speed at its throat. The wind speed at the throat is inversely proportional to its area according to the continuity equation. In this numerical study, an airflow phenomena in the venturi system placed at a vertical structure was investigated to understand the vortex effect occurred at the rear-side of the vertical structure on the air speed increment at the throat of the venturi system. For this study, a venturi system sized by $20(m){\times}20(m){\times}6(m)$ was modelled and the area ratio(AR) of the model venturi was 2.86. To see the vortex effect on the air flow acceleration in the venturi throat, two different boundary conditions was defined From the study, it was found that the pressure coefficient(CP) of the venturi system with the vortex formed at the exit of the venturi was about 2.5times of the CP of the venturi system without the vortex effect. The velocity increment rate of the venturi system with the vortex was 61% but 9.5% only at the venturi system without the vortex. Conclusively, it can be said that the venturi system installed in a vertical structure has very positive effect on the flow acceleration at its throat due to the vortex formed at the rear-side of the vertical structure.

• Wind and Structures
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• v.18 no.6
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• pp.599-618
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• 2014

In this study, a square rectangular tall building is considered to investigate the effects of turbulence integral length scale and turbulence intensity on the along-wind responses, across-wind responses and torsional responses of the tall building by Large Eddy Simulation (LES). A recently proposed inflow turbulence generator called the discretizing and synthesizing random flow generation (DSRFG) approach is applied to simulate turbulent flow fields. It has been proved that the approach is able to generate a fluctuating turbulent flow field satisfying any given spectrum, desired turbulence intensity and wind speed profiles. Five profiles of turbulence integral length scale and turbulence intensity are respectively generated for the inflow fields by the DSRFG approach for investigating the effects of turbulence integral length scale and turbulence intensity on the wind-induced responses of the tall building. The computational results indicate that turbulence integral length scale does not have significant effect on the along-wind (displacement, velocity and acceleration) responses, across-wind displacement and velocity responses, while the across-wind acceleration and torsional responses vary without a clear rule with the parameter. On the other hand, the along-wind, across-wind and torsional responses increase with the growth of turbulence intensity.

• Advances in aircraft and spacecraft science
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• v.6 no.6
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• pp.497-513
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• 2019

A wind tunnel test was conducted that measured surface fluctuating pressures aft of a ramp at transonic speeds. Dynamic pressure test data was used to perform a study to determine best locations for streamwise sensor pairs for shocked and unshocked runs based on minimizing the error in root-mean-square acceleration response of the panel. For unshocked conditions, the upstream sensor is best placed at least 6.5 ramp heights downstream of the ramp, and the downstream sensor should be within 2 ramp heights from the upstream sensor. For shocked conditions, the upstream sensor should be between 1 and 7 ramp heights downstream of the shock, with the downstream sensor 2 to 3 ramp heights of the upstream sensor. The shock was found to prevent the passage coherent flow structures; therefore, it may be desired to use the shock to define the boundary of subzones for the purpose of loads definition. These recommendations should be generally applicable to a range of expansion corner geometries in transonic flow provided similar flow structures exist. The recommendations for shocked runs is more limited, relying on data from a single dataset with the shock located near the forward end of the region of interest.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.3
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• pp.78-83
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• 2014

A special part such as a flow passage opening device is required to prevent the disconnection of fuel transfer in a pressurized fuel tank. To meet this requirement, the device utilizing an acceleration follow-up technique was invented. RecurDyn, a dynamic analysis tool, is introduced in this article to predict the device's performance and to determine parameters affecting it. In the analysis, it is shown that balancing weights can open the passage in accordance with fuel position.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.59 no.1
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• pp.65-73
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• 2023

This study analyzed the duct characteristics of hubless rim-driven propeller (RDP) used in underwater robots. In the previous study, flow visualization experiments were performed with an advancing ratio of 0.2 to 1. The vortex at the front of the duct increased in strength while maintaining its size as the advancing ratio decreased. Therefore, it is necessary to study the optimization of the duct shape. Conventional propeller thrusters use acceleration/deceleration ducts to increase their efficiency. However, unlike conventional propellers, it is impossible to apply to airfoil acceleration/deceleration ducts due to the RDP structure. In this study, duct wake flow characteristics, thrust force, and efficiency according to the duct shape of RDP were analyzed using numerical analysis techniques. Duct design is limited and six duct shapes were designed. As a result, an optimized duct shape was designed considering duct wake flow characteristics, thrust force, and efficiency. The shape that the outlet width of the RDP was kept constant until the end of the duct showed higher thrust force and efficiency.

• ETRI Journal
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• v.39 no.4
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• pp.525-534
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• 2017

A hardware-acceleration architecture that separates virtual network functions (VNFs) and network control (called HSN) is proposed to solve the mismatch between the simple flow steering requirements and strong packet processing abilities of software-defined networking (SDN) forwarding elements (FEs) in SDN/network function virtualization (NFV) architecture, while improving the efficiency of NFV infrastructure and the performance of network-intensive functions. HSN makes full use of FEs and accelerates VNFs through two mechanisms: (1) separation of traffic steering and packet processing in the FEs; (2) separation of SDN and NFV control in the FEs. Our HSN prototype, built on NetFPGA-10G, demonstrates that the processing performance can be greatly improved with only a small modification of the traditional SDN/NFV architecture.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.281-288
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• 2009

Numerical investigations have been conducted on the assessment of the performance of drug-eluting stent. Computational fluid dynamics is applied to investigate the flow disturbances and drug distributions released from the stent in the immediate vicinity of the given idealized stent in the protrusion into the flow domain. Our simulations have revealed the drug concentration in the flow field due to the presence of a drug-eluting stent within an arterial segment. Wall shear stress increases with Reynolds number for a given stent diameter, while it increases with stent diameter for a given Reynolds number. The drug concentration is dependent on both Reynolds number and stent geometry. In pulsatile flow, the minimum drug concentration in the zone of inter-wire spacing occurs at the maximum acceleration of the inlet flow while the maximum drug concentration gains at the maximum deceleration of the inlet flow. These results provide an understanding of the flow physics in the vicinity of drug-eluting stents and suggest strategies for optimal performance of drug-eluting stent to minimize flow disturbance.

• International Journal of Automotive Technology
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• v.7 no.2
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• pp.145-154
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• 2006

In the companion paper, the composition and structure of the MATDYMO (Multi-Agent for Traffic Simulation with Vehicle Dynamic Model) were proposed. MATDYMO consists of the road management system, the vehicle motion control system, the driver management system, and the integration control system. Among these systems, the road management system and the integration control system were discussed In the companion paper. In this paper, the vehicle motion control system and the driver management system are discussed. The driver management system constructs the driver agent capable of having different driving styles ranging from slow and careful driving to fast and aggressive driving through the yielding index and passing index. According to these indices, the agents pass or yield their lane for other vehicles; the driver management system constructs the vehicle agents capable of representing the physical vehicle itself. A vehicle agent shows its behavior according to its dynamic characteristics. The vehicle agent contains the nonlinear subcomponents of engine, torque converter, automatic transmission, and wheels. The simulation is conducted for an interrupted flow model and its results are verified by comparison with the results from a commercial software, TRANSYT-7F. The interrupted flow model simulation is implemented for three cases. The first case analyzes the agents' behaviors in the interrupted flow model and it confirms that the agent's behavior could characterize the diversity of human behavior and vehicle well through every rule and communication frameworks. The second case analyzes the traffic signals changed at different intervals and as the acceleration rate changed. The third case analyzes the effects of the traffic signals and traffic volume. The results of these analyses showed that the change of the traffic state was closely related with the vehicle acceleration rate, traffic volume, and the traffic signal interval between intersections. These simulations confirmed that MATDYMO can represent the real traffic condition of the interrupted flow model. At the current stage of development, MATDYMO shows great promise and has significant implications on future traffic state forecasting research.