• Journal of the Society of Naval Architects of Korea
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• v.31 no.2
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• pp.65-77
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• 1994

This paper presents a derailed application procedure of the linear quadratic(LQ) theory for a SWATH heave and pitch control. A time domain model of coupled, linear time-invariant second order differential equations is derived from the frequency response model with the frequency dependent added mass and damping approximated as constant values at the heave natural frequency. Wave exciting forces are modeled as a sum of sinusoids. A systematic selection procedure of state and control weighting matrices is presented to obtain good transient behavior and acceptable fin movement. The validity of this controller design process is throughly investigated by simulations both in time domain and frequency domain and singular value plots of transfer function matrices. The finally designed control system shows good overall performances revealing that the applicability of the present study is proved successful.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.61-66
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• 2009

For a spread-moored FPSO (Floating Production, Storage, & Off-loading) subjected to environmental excitation from waves, current, and wind, a procedure to determine optimum length and stiffness of mooring lines is suggested using quasi-static frequency domain response analyses. Coupled relations between design parameters are closely examined. In consideration of this, optimized design parameters are proposed based on minimum weight condition. The initial design parameters for numerical analyses are calculated using the static catenary equation of mooring lines. It is demonstrated the line tension and vessel's offset are influenced by the mooring line length and stiffness. Accordingly it is suggested the optimum vessel's offset range should be determined considering line fatigue damage. The availability and limitation of the application of quasi-static analysis method for spread mooring system are explained by comparing the result of time domain analysis with one of frequency domain analysis.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.10
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• pp.435-442
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• 2006

One of the most important topics about the safety of electrical and electronic system is the reliability of the wiring system. The Time-Frequency Domain Reflectometry(TFDR) is a state-of-the-art system for detecting and estimating of the fault on a wiring. In this paper, We've considered the load resistance measurement on a coaxial cable using TFDR in a way of expanded application. The TFDR system was built using commercial Pci extensions for Instrumentation(PXI) and LabVIEW. The proposed real time TFDR system consisted of the reference signal design, signal generation, signal acquisition, algorithm execution and results display part. To implement real time system, all of the parts were programmed by the LabVIEW which is one of the graphical programming languages. Using the application software implemented by the LabVIEW, we were able to design a proper reference signal which is suitable for target cable and control not only the arbitrary waveform generator in the signal generation part but alto the digital storage oscilloscope in the signal acquisition part. By using the TFDR real time system with the terminal resistor on the target cable, we carried out load impedance measurement experiments. The experimental results showed that the proposed system are able not only to detect the location of impedance discontinuity on the cable but also to estimate the load resistance with high accuracy.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.968-980
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• 2023

The dynamic structural responses are sensitive to the time-frequency content of seismic waves, and seismic input motions in time-history analysis are usually required to be compatible with design response spectra according to nuclear codes. In order to generate spectra-compatible input motions while maintaining the intrinsic non-stationarity of seismic waves, an improved time-domain approach is proposed in this paper. To maintain the nonstationary characteristics of the given seismic waves, a new time-frequency envelope function is constructed using the Hilbert amplitude spectrum. Based on the intrinsic mode functions (IMFs) obtained from given seismic waves through variational mode decomposition, a new corrective time history is constructed to locally modify the given seismic waves. The proposed corrective time history and time-frequency envelope function are unique for each earthquake records as they are extracted from the given seismic waves. In addition, a dimension reduction iterative technique is presented herein to simultaneously superimpose corrective time histories of all the damping ratios at a specific frequency in the time domain according to optimal weights, which are found by the genetic algorithm (GA). Examples are presented to show the capability of the proposed approach in generating spectra-compatible time histories, especially in maintaining the nonstationary characteristics of seismic records. And numerical results reveal that the modified time histories generated by the proposed method can obtain similar dynamic behaviors of AP1000 nuclear power plant with the natural seismic records. Thus, the proposed method can be efficiently used in the design practices.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.13-18
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• 2003

This paper proposes a design method of PID controllers in the framework of a constrained optimization problem. Owing to the popularity for the controller's simplicity and robustness, a great deal of literature concerning PID control design has been published, which can be classified into frequency-based and time-based approaches. However, both approaches have to be considered together for a designed PID control to work well with a guaranteed closed-loop stability. For this purpose, a penalty function is formulated to satisfy both frequency- and time-domain specifications, and is minimized by a recet nonlinear optimization algorithm to attain optimal PID control gains. The proposed method is compared with Wang's and Ho's methods on a suite of example systems. Simulation results show that the PID control tuned by the proposed method improves time-domain performance without deteriorating closed-loop stability.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.10 no.16
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• pp.39-51
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• 1987

This paper deals with the case analysis of second order processes under sampled-data. Proportional Integral-Derivative(PID) control, and development of Decision Support Systems(DSS) for such processes. In this paper three techniques were described for identifying the dynamics of closed loop stable processes. The first, called pulse testing is a frequency-domain method, which yields the frequency response diagram of an open loop process. The second is a time-domain method which yields the gain and time constants of the process model. The third technique is based on step response and gives the parameters of PID controllers. The development of DSS design programs consisting of above three techniques will provide very powerful tools in the microcomputer based process control.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.623-625
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• 2013

Tire hydroplaning is one of the most important tire performances, especially for safety on wet road surface. And nowadays various methods such as FEM and FVM analysis are being applied to design and improve tire hydroplaning performance, along with on-vehicle test of tire hydroplaning. Conventional evaluation of tire hydroplaning has been done by comparing peak lateral acceleration and vehicle speed in time domain. But in this paper, frequency domain analysis of lateral acceleration when hydroplaning at high speed has been carried out to get the quantitative comparison between test tires. And it is concluded that the frequency spectrum analysis of lateral acceleration gives much better discrimination, as compared to the conventional time domain analysis of lateral acceleration and vehicle speed.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.771-776
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• 2010

Since the importance of seismic design is greater, dynamic analysis is more widely using than past. The input motion is one of the most important factors of dynamic analysis. However, in Korea input motions are selected from U.S. and Japan those are captured from large magnitude earthquakes without considering seismic environment or generated in frequency domain. In this research, the methodology for generating input motions those are considered seismic environment and design code is proposed. The seismic environment compatibility is considered by performing deaggregation and the design code compatibility is considered by time-domain artificial time history accelration generation method. The results shows that seismic environment and design code compatible input motions are successfully generated.

• Journal of Korea Society of Industrial Information Systems
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• v.13 no.2
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• pp.1-7
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• 2008

This paper presents a method to design a repetitive controller that is robust to variations in the system parameters. The uncertain parameters are specified probabilistically by their probability distribution functions. Instead of working with the distribution functions directly, the repetitive controller is designed from a set of models that are generated from the specified probability functions. With this multiple-model design approach, any number of uncertain parameters that follow any type of distribution functions can be treated. furthermore, the controller is derived by minimizing a frequency-domain based cost function that produces monotonic convergence of the tracking error as a function of repetition number. Numerical illustrations show how the proposed multiple-model design method produces a repetitive controller that is significantly more robust than an optimal repetitive controller designed from a single nominal model of the system.

• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.137-141
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• 1986

This paper presents optimal recursive digital filter design to meet simultaneous specifications of magnitude and linear phase characteristics. As is well known, the overshoot in the vicinity of discontinuity is hight. The technique using linear programming (the dual programming) is choosing more specification points in the vicinity of band limit frequency. The resulting filter can shown improved response and numerical accuracy with reduced nonuniform specification points in frequency domain.