• Korea-Australia Rheology Journal
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• v.17 no.1
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• pp.1-7
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• 2005

Acrylonitrile-Butadiene-Styrene (ABS), polycarbonate (PC) and their alloys are an important class of engineering thermoplastics that are widely used for automotive industry, computer and equipment housings. For the process of recycling mixtures of ABS and PC, it is desirable to know how sensitive the blend properties are to changes in compositions. It was for this reason that blends of virgin ABS and virgin PC at five different compositions, namely, $15\%,\;30\%,\;50\%,\;70%$ and $85\%$ by weight of ABS were prepared and characterised by rheological and mechanical measurements. Rheological properties of these blends in steady, oscillatory and transient step shear and mechanical properties, namely, tensile strength, elongation-at-break and Izod impact strength are reported. The results show that PC behaves in a relatively Newtonian manner, but ABS exhibits significant shear thinning. The ABS-rich blends show a trend that is similar to that of ABS, while PC-rich blends, namely $0\%$ and $15\%$, exhibit a nearly Newtonian behaviour. However, at a fixed shear rate or frequency, the steady shear or the dynamic viscosity varied respectively in a non-mono-tonic manner with composition. Except for $15\%$ blend, the viscosities of other blends fall into a narrow band indicating a wide-operation window of varying blend ratio. The blends exhibited a lower viscosity than either of the two pure components. The other noticeable feature was that the blends at $70\%$ and $85\%$ ABS content had a higher G' than pure ABS, indicating an enhancement of elastic effect. The tensile yield strength of the blends followed the 'rule of mixtures' showing a decreasing value with the increase of ABS content in PC. However, the elongation-at-break and the impact strength did not appear to obey this 'rule of mixtures,' which suggests that morphology of the blends also plays a significant role in determining the properties. Indeed, scanning electron micrographs of the fracture surfaces of the different blends validate this hypothesis, and the $15\%$ blend is seen to have the most distinct morphology and correspondingly different behaviour and properties.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.21-32
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• 2002

Small and full scale model tests were performed to obtain the transient responses of shafts subjected to elastic impact by impact-echo test. Four end conditions of drilled shafts were considered: (1) free, (2) fixed, (3) rock-socketed, and (4) soft bottom. In small scale model tests, mock-up shafts were fabricated to simulate these four drilled shafts using poly-urethane and plastic material. Additionally, skin frictions between shaft and rock were changed to find out the effect of side contact on dynamic responses. All impact responses were tested in the air. Subsequently, full scale model tests were also carried out on concrete shafts that were in free and rock-socketed condition. The end conditions of the drilled shafts could be identified with good reliability by the waveforms from both small and full scale model tests. The results obtained in this study will provide an improved understanding of the impact responses for end conditions, especially for rock-socketed drilled shafts that are frequently designed and built in Korea.

• Journal of the Korean Institute of Intelligent Systems
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• v.8 no.6
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• pp.37-47
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• 1998

This paper proposes a controller design method using the evolutionary computation algorithm and the fuzzy logic to control the wafer temperature in rapid thermal processing. First, we design the feedforward static controller to provide the control powers of the lamps for the given steady state temperature. Second, the feedforward dynamic controller is designed for the additional control powers to achieve a given transient response. These feedforward controllers are implemented by using the fuzzy logic to act as a global nonlinear controller over a wide range of operating points. The parameters of these controllers are optimized by using the evolutionary computation algorithm so that it can be used when the mathematical model is not available. In addition, the feedback error controller is introduced to compensate the feedforward controllers when there exist disturbances and modeling errors. The gain of feedback error controller is also obtained by the evolutionary computation algorithm. Through simulations, we verify the proposed control system can give a satisfactory performance.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.127-136
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• 2011

The settlement of a compaction plate resting on the surface of rubble-mound and subjected to a vibrating vertical load can be characterized by a transient amplitude and a plastic settlement. As long as the maximum imposed load does not exceed the bearing capacity of the rubble-mound, plastic settlement will approach an ultimate value and essentially steady-state vibration will ensue. For the settlement behavior by vibro-compaction, most laboratory experiments were conducted on laterally confined samples with loads over the full surface area or on samples placed on a vibrating table. In the field, the loads cover only a small fraction of the surface area. In this study, crushed stones are loaded with the same as field condition. According to the vibro-compaction experiments on crushed stone, it was found that approximately 90% of total settlement occur within 2 minutes and plastic settlement increases with increasing cyclic stress levels including static and dynamic stress. A compaction equation on which the number of load cycles, amplitude of plate, settlement, width of plate, and cyclic stress are related each other is proposed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.1
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• pp.92-99
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• 2009

Deeply-driven ground rod in the rainy season may contact with rainwater and ground water. When surge voltages are applied to the submerged ground rods, the ionization around the ground rods are occurred. Ionization in soil and/or water is affected in dynamic performance of ground rod systems. This work aims at studying the transient performance of ground rod system under impulse voltage using scale model in an electrolytic tank. The potential reduction and energy dispersion caused by ionization were treasured and quantitatively analyzed using the Matlab Program. As a result, the peak voltage at the terminal of ground rod was varied with water resistivity and charging voltage of Marx generator. The potential at the terminal of the ground rod was approximately reduced to a half of the applied voltage just below breakdown voltage. Also the energy more than half of the applied energy was dispersed through the ground rod due to ionization just below breakdown voltage.

• Journal of Mechanical Science and Technology
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• v.19 no.3
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• pp.778-791
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• 2005

A novel pneumatic artificial muscle actuator (PAM actuator), which has achieved increased popularity to provide the advantages such as high strength and high power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source, inherent safety and mobility assistance to humans performing tasks, has been regarded during the recent decades as an interesting alternative to hydraulic and electric actuators. However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. Then it is not easy to realize the performance of transient response of pneumatic artificial muscle manipulator (PAM manipulator) due to the changes in the external inertia load with high speed. In order to realize satisfactory control performance, a variable damper-Magneto­Rheological Brake (MRB), is equipped to the joint of the manipulator. Superb mixture of conventional PID controller and a phase plane switching control method brings us a novel controller. This proposed controller is appropriate for a kind of plants with nonlinearity, uncertainties and disturbances. The experiments were carried out in practical PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with phase plane switching control method and without regard for the changes of external inertia loads.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.92-102
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• 2012

The process of the wind noise analysis around an OSRVM is developed and is verified by simulating unsteady flow field past a generic OSRVM mounted on the flat plate at the Reynolds number of $Re_D=5.2{\times}10^5$ based on the mirror diameter. The transient flow field past a generic OSRVM is simulated with various turbulence models, namely DES-SA, LES Constant SGS, and LES Dynamic SGS. The sound radiation is predicted using the Ffowcs- Williams and Hawkings analogy. For the present simulation, the 6.35million cells are generated. Time averaged pressure coefficients at 34 locations on the surface of the generic OSRVM are compared with the available experimental data. Also, 12 Sound Pressure Levels located on the surrounding mirror are compared with the available experimental data. Both of them show good agreements with experimental data.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.3
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• pp.96-106
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• 2007

The terminal voltage of a synchronous generator is maintained by the field current control of excitation system. Generally AC/DC converter which is component of AVR(Automatic Voltage Regulator) system for excitation current control is connected to diode rectifier and DC/DC converter system. In the case of diode rectifier system of phase controlled converter as AC/DC converter have low power factor and harmonics of lower order in the line current. In this paper, two stage three phase PWM AC/DC converter is studied to solve these problems. The characteristics of a proposed converter reduces the harmonics and reactive power of the distribution line and has fast dynamic response in transient period using boost converter and current control mode buck converts. The proposed method is verified by the computer simulation and experimental results in prototype generation system.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.57-63
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• 2009

A modeling and simulation program for an environmental control system (ECS) of a pod installed under wings of an aircraft was developed in order to estimate the system‘s performance during a flight. First, through the system configuration analysis in the main operational condition of the aircraft system, an ECS configuration adopting an air cycle machine (ACM) was selected. Therefore the modeling program was developed to simulate the ECS with an ACM. Second, the sensitivity analyses on performance variation of main components were conducted to complete the conceptual design of the ECS. A design point for the system and its components was obtained through the analysis with the modeling and simulation program. The design point for the system and components was obtained through the analysis with the modeling and simulation program. Third, in order to study the feasibility of the ECS configuration, off-design performances of the ECS on various flight conditions, such as take off, maneuver, cruise and landing etc were estimated. Dynamic characteristics were analyzed by transient performance evaluations.

• Ocean Systems Engineering
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• v.7 no.3
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• pp.179-193
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• 2017

Dynamic response analysis of offshore triceratops with stiffened buoyant legs under impact and non-impact waves is presented. Triceratops is relatively new-generation complaint platform being explored in the recent past for its suitability in ultra-deep waters. Buoyant legs support the deck through ball joints, which partially isolate the deck by not transferring rotation from legs to the deck. Buoyant legs are interconnected using equally spaced stiffeners, inducing more integral action in dispersing the encountered wave loads. Two typical nonlinear waves under very high sea state are used to simulate impact and non-impact waves. Parameters of JONSWAP spectrum are chosen to produce waves with high vertical and horizontal asymmetries. Impact waves are simulated by steep, front asymmetric waves while non-impact waves are simulated using Stokes nonlinear irregular waves. Based on the numerical analyses presented, it is seen that the platform experiences both steady state (springing) and transient response (ringing) of high amplitudes. Response of the deck shows significant reduction in rotational degrees-of-freedom due to isolation offered by ball joints. Weak-asymmetric waves, resulting in non-impact waves cause steady state response. Beat phenomenon is noticed in almost all degrees-of-freedom but values in sway, roll and yaw are considerably low as angle of incidence is zero degrees. Impact waves cause response in higher frequencies; bursting nature of pitch response is a clear manifestation of the effect of impact waves on buoyant legs. Non-impact waves cause response similar to that of a beating phenomenon in all active degrees-of-freedom, which otherwise would not be present under normal loading. Power spectral density plots show energy content of response for a wide bandwidth of frequencies, indicating an alarming behaviour apart from being highly nonlinear. Heave, being one of the stiff degrees-of-freedom is triggered under non-impact waves, which resulted in tether tension variation under non-impact waves as well. Reduced deck response aids functional requirements of triceratops even under impact and non-impact waves. Stiffened group of buoyant legs enable a monolithic behaviour, enhancing stiffness in vertical plane.