• Wind and Structures
• /
• v.14 no.2
• /
• pp.133-151
• /
• 2011

For a detailed investigation of the dynamic behaviour of slender bridges under wind action especially the motion-induced fluid forces should be available not only for harmonic motions but also for more general ones. If linear transfer behaviour is assumed, the force-displacement relation for almost arbitrary motions can be handled in the frequency domain using aerodynamic transfer functions. In aerospace engineering as well as in bridge engineering, these functions are usually approximated by special kinds of complex-valued rational functions which depend on complex frequencies. The quality of this approximation is evaluated for several bridge cross sections in this article. It is shown that rational functions are for some sections scarcely suitable to realistically represent the transfer behaviour of motion-induced aerodynamic forces for arbitrarily complex frequencies.

• The Journal of the Acoustical Society of Korea
• /
• v.22 no.3E
• /
• pp.133-140
• /
• 2003

A time series simulation is presented by a ray approach for the simulating the received waveform of a broadband acoustical signals interacting with the ocean boundaries. The environment is assumed to be horizontally stratified, and the seafloor is described in terms of homogeneous fluid half-space. The ray approach includes the effects of reflection from the air-water, water-sediment interface and phase shifts due to boundaries interaction. To generate time series, we assume that the acoustic energy propagates from source to receiver along eigenrays and represent the action of the bottom on the incident wave by a linear filter and characterized in the frequency domain by the transfer function. As example application, the time series for an explosive source in a shallow water environment is calculated and analyzed in terms of acoustical process. good agreement with measured time series is demonstrated.

• Proceedings of the KIPE Conference
• /
• 2004.07a
• /
• pp.312-315
• /
• 2004

This paper presents a tuning-free conditional integration anti-windup strategy for induction machine with Proportional-Integral (PI) type speed controller. The on/off condition of integral action is determined by the frequency domain analysis of machine torque command without a prior knowledge of set-point changes. There are no tuning parameters to be selected by users for anti-windup scheme. In addition, the dynamic performance of the proposed scheme assures a desired tracking response curve with minimal oscillation and settling time even in the change of operating conditions. This algorithm is useful in many high performance induction machine applications not to allow the oscillation and overshoot of speed/torque responses. The main idea can be extended to general applications such as chemical processes and industrial robots.

• Korean Journal of Child Studies
• /
• v.19 no.2
• /
• pp.115-132
• /
• 1998

The present study investigated the construction of the moral concepts of 3-, 4-, and 5- year old Korean children. Instruments were the Maternal Behavior Research Instrument by Schaefer for mother and feather nurturing attitudes, and the Domain Distinctiveness Model for children's moral judgments. Maternal and teacher attitudes were categorized by the affection-rejection factor consisting of affection-affection, affection-rejection, rejection-affection, and rejection-rejection dimensions, and by the permissive, -control factor consisting of permissive-permissive, permissive-control, control-permissive, and control-control dimension. Children's data were collected with an individualized interview in which children were asked to judge moral and social conventional transgression events. 30 children were assigned to each of the maternal/teacher attitude dimensions; thus, there were 120 children for each factor. Results showed that (1) the affection-affection cohort was must strongly related to moral rules using both the seriousness criterion and deserved punishment criterion, and (2) the permissive-permissive cohort was most strongly related to reasoning and action. However, this cohort did not break out of children's structural limitation (limited responses to the intangible).

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1992.10a
• /
• pp.182-186
• /
• 1992

A self tuning technique is derived for PID controllers which are widely used in industries. The tuning algorithm is based upon a fuzzy indirect reasoning method and an iterative technique. The fuzzy technique is considered to obtain ease and simplicity of tuning process. The PID gains for the first tuning action are determined by a method which is modified from the Ziegler-Nichols step response method. The first PID gains are determined to obtain a control performance so close to a design performance that the followed tuning process can be made effectively. The design parameters are given as time-domain variables which human is familiar with. The results of simulation studies show that the proped tuning method can produce an effective tuning for arbitaray design performances.

• Korea-Australia Rheology Journal
• /
• v.14 no.3
• /
• pp.121-128
• /
• 2002

A series of thermoplastic polymers and their blends were melt-processed with high intensity ultrasonic wave in an intensive mixer. For the effective transfer of ultrasonic energy, an experimental apparatus was specially designed so that polymer melt can directly contact with ultrasonic horn. It was observed that significant variations in the rheological properties of polymers occur due to the unique action of ultrasonic wave without any aid of chemical additives. It was also found that the direct sonication on immiscible polymer blends in melt state reduces the domain sizes considerably and stabilizes the phase morphology of the blends. The degree of compatibilization was strongly affected by viscosity ratio of the components and the morphology was stable after annealing in properly compatibilized blends. It is suggested that ultrasound assisted melt mixing can lead to in-situ copolymer formation between the components and consequently provide an effective route to compatibilize immiscible polymer blends.

• Journal of the Korean Society for Precision Engineering
• /
• v.13 no.5
• /
• pp.74-83
• /
• 1996

An iterative tuning technique is derived for PID controllers which are widely used in industries. The tuning algorithm is based upon a fuzzy indirect reasoning method and an iterative technique. The PID gains for the first tuning action are determined by a method which is modified from the Ziegler-Nichols step response method. The first PID gains are determined to obtain a control performance so close to a design performance that the following tuning process can be made effectively. The design paramaters are given as time-domain variables which human is familiar with. The results of simulation studies show that the proposed tuning method can produce an effective tuning for arbitrary design performances.

• Journal of Advanced Marine Engineering and Technology
• /
• v.22 no.5
• /
• pp.693-701
• /
• 1998

This study presents result of comparison between two other numerical method method of char-acteristics(MOC) and Lax-Wendroff method(LWM) applied at wave action analysis of intake and exhaust pipe in terms of calculated pressure velocity and emitted noise in the time and the fre-quency domain by means of fast Fourier transform analysis. Particularly FCT(Flux Corrected Transport)scheme is appended to LWM to protest unaceptable overshoots occurring near discon-tinuity. The final conclusion of this study is that MOC should be replaced by a second order finite difference approach because of larger contributions due to high frequency components than the results from the method of characteristics. Clear benefits we can get by change are faster calcula-tion higher accuracy conservation of mass and consistent calculation method.

• Journal of Fisheries and Marine Sciences Education
• /
• v.20 no.3
• /
• pp.462-472
• /
• 2008

Education is a field that has tried to make use of the advantages of computers since they were introduced to the world. Intelligent Tutoring System and multimedia have become methods of teaching students of Computer Science, Education, Psychology, and Cognitive Science. Until now, they have been designed and produced only on the basis of a very specific domain and format. However, in the education field, most learners ask for integrated service that is practical, realizable, and sensitive to technological change. Therefore, in this study, we would like to present the technological and formal integration model as an ITS model which acknowledges changes in the fields of technology and education. As a technological integration model, the integration model of traditional Symbolic Artificial Intelligence and Artificial Neural Networks was presented. As a formal integration model, three integration models were presented according to (a) the process of learning diagnosis (b) learners' action behaviors (c) intelligence service respectively.

• Wind and Structures
• /
• v.7 no.6
• /
• pp.405-420
• /
• 2004

In common approaches, bridge dynamics under wind action is analyzed by modeling the interaction between fluid and structure by means of transient wind loads acting over the structure itself. Amid various possible manners to describe such types of loads, a representation based on families of 'indicial functions' is adopted here. The aim is to investigate its flexibility to capture the main features of wind-bridge interaction. A set of coefficients is involved in indicial functions. The values that one may attribute to them suffer uncertainties coming from experimental errors affecting data. Here, the sensitivity of a 2-DOF schematic model to the variations of these coefficients is investigated at fixed values of dynamic derivatives and for various types of indicial functions. It is shown how parameter variations influence phase portraits.