• Proceedings of the KIPE Conference
• /
• 2001.10a
• /
• pp.160-168
• /
• 2001

The RPWM (Random· Pulse Width Modulation) is a switching technique to spread the voltage and current harmonics over a wide frequency area. By using randomly changing switching frequency of the inverter, the power spectrum of the electromagnetic acoustic noise can be spread to the wide-band area. The wide­band noise is much more comfortable and less annoying than the narrow-band one. So, the RPWM has been attracting interest as an excellent method for the reduction of acoustic noise on the inverter drive system. In this paper a new RPPWM (Random Position Space Vector PWM) is proposed and implemented. Each of three phase pulses is located randomly in each switching interval. Along with the randomization of PWM pulses, the space vector modulation is also executed in the C167 micro-controller. The experimental results show that the voltage and current harmonics are spread to a wide band area and that the audible switching noise is reduced by the proposed RPPWM method.

• International Journal of Aeronautical and Space Sciences
• /
• v.17 no.4
• /
• pp.551-564
• /
• 2016

High-speed flight vehicles (HSFVs) such as space launch vehicles and missiles undergo severe dynamic loads which are generated during the launch and in in-flight environments. A typical vehicle is composed of thin plate skin structures with high-performance electronic units sensitive to such vibratory loads. Such lightweight structures are then exposed to external dynamic loads which consist of random vibration, shock, and acoustic loads created under the operating environment. Three types of dynamic loads (acoustic loads, rocket motor self-induced excitation loads and aerodynamic fluctuating pressure loads) are considered as major components in this study. The estimation results are compared to the design specification (MIL-STD-810) to check the appropriateness. The objective of this paper is to study an estimation methodology which helps to establish design specification for the dynamic loads acting on both vehicle and electronic units at arbitrary locations inside the vehicle.

• International Journal of Aeronautical and Space Sciences
• /
• v.7 no.2
• /
• pp.26-32
• /
• 2006

This paper targets a direct and quantitative prediction of characteristics of unstable waves in a combustion chamber, which employs the governing equations derived in terms of amplification factors of flow variables. A freshly formulated nonlinear acoustic equation is obtained and the analysis of unsteady waves in a rocket engine is attempted. In the present formalism, perturbation method decomposes the variables into time-averaged part that can be obtained easily and accurately and time-varying part which is assumed to be harmonic. Excluding the use of conventional spatially sinusoidal eigenfunctions, a direct numerical solution of wave equation replaces the initial spatial distribution of standing waves and forms the nonlinear space-averaged terms. Amplification factor is also calculated independently by the time rate of changes of fluctuating variables, and is no longer an explicit function for compulsory representation. Employing only the numerical computation, major assumptions inevitably inherent, and in erroneous manner, in up to date analytical methods could be avoided. With two definitions of amplification factor, 1-D stable wave and 3-D unstable wave are examined, and clearly demonstrated the potentiality of a suggested theoretical-numerical method of combustion instability.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.8 no.3
• /
• pp.230-238
• /
• 2003

In this paper, Inverter drives adopting 2 phase space vector SRP-PWM (Separately Randomized Pulse Position PWM) with fixed switching frequency is proposed. The proposed 2 phase space vector SRP-PWM scheme is based on the 3 phase SRP-PWM. In the proposed SRP-PWM scheme, each of two phase pulses is located randomly in each switching interval. The experimental results show that the voltage and acoustic noise harmonics are spread to a wide band area. Also, the performance of the proposed 2 phase SRP-PWM and the conventional center aligned SVM are compared to each other. In result, the speed response is nearly similar to each other from the viewpoint of the v/f constant control.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.8
• /
• pp.790-797
• /
• 2010

Mode transition of the axi-symmetric screech tone in the low supersonic Mach number range from 1.0 to 1.20 is numerically analyzed. The axi-symmetric Navier-Stokes equations and the k-e turbulence model are solved in the cylindrical coordinate system. The dispersion-relation-preserving(DRP) scheme is applied for space discretization and the optimized four levels marching method are used for time integration. At low supersonic Mach numbers with an axi-symmetric A1 mode in the simulation, it is shown that acoustic propagation due to the nonlinear effects is seen in the lateral direction and the screech tone frequency is the same as the vortex passing frequency due to the generation of intense large-scale vortical motions.

• The Journal of Sustainable Design and Educational Environment Research
• /
• v.19 no.2
• /
• pp.21-31
• /
• 2020

The purpose of this study was to analyze the contents of the sound environment among the various environmental factors that directly or indirectly affect the quality of education through the remodeling of the small hall of the College of Humanities at W University. Before remodeling into a lecture room, the small hall of the College of Humanities at W University, which is the subject of this study, was designed to create an indoor sound environment suitable for a lecture room by recognizing differences in acoustic performance between the performance halls that require adequate sound quality and the lecture rooms where the clarity of voice is important. Therefore, this study aimed to present examples of improved acoustic performance in lecture rooms by remodeling through the stages of measuring acoustic performance before remodeling, presentation of a change in finishing materials through sound simulation, and measurement of sound performance after remodeling. It is expected that this process can be used as an example of securing indoor acoustic performance suitable for educational space, such as lecture rooms, by changing the finishing materials.

• Journal of Institute of Control, Robotics and Systems
• /
• v.11 no.9
• /
• pp.774-780
• /
• 2005

For the accurate inspection of the resources and space in the ocean, the method of locating the measurement equipments in the seafloor and retrieving these equipments later after a certain period of time. is generally used. In this method, the reliability of retrieving measurement equipments is very important. In our proposed remotely-controlled acoustic release system, an underwater ultrasonic wave recognition algorithm by which we can recognize the sound signal without the influence of disturbances due to underwater environment changes is developed, and a battery is used for the reduction of electric power consumption. we show the effectiveness of our proposed system through experimental results.

• Proceedings of the IEEK Conference
• /
• 2000.11d
• /
• pp.123-126
• /
• 2000

In this paper, the portable game machine called W"alking Beat" is designed and implemented not only to propose the new possibilities for the peripheral equipment market of portable acoustic machine but also to overcome the limitation of the acoustic simulation game machine such as the existing Beat Mania. The old game machine can be used only in a particular place, where it is installed. However, in order to get over the constraint on this space problem "Walking Beat Game Machine" is designed to facilitate the portability. In addition, the frequency analysis method using FFT algorithm is employed by regarding the music data for the portable digital acoustic machine as source so that the limitation that the existing game machine depends heavily on the previously registered game contents can be overcome. By making it possible to play games for all the music and putting an emphasis on multimedia trend only to listen to the music, it is speculated that it can contribute to the development of the new culture in the near future.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.53 no.8
• /
• pp.145-149
• /
• 2016

For obtaining high speed data rate, underwater acoustic communication has several problems by the different environmental problem. To achieve high speed data rate, a method of multiple antennas have been researched. V-BLAST Algorithm is a detection method applied to terrestrial wireless communications. In this paper, BER performance of VBLAST detection for MIMO system is analyzed in the paper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.33-36
• /
• 2007

Acoustic holography exhibits the spatial distribution of sound pressure in time or frequency domain. The obtained picture often contains far more than what we need in practice. For example, when we need to know only the locations and overall propagation pattern of sound sources, a method to show only what we need has to be introduced. One way of obtaining the necessary information is to use envelope in space. The spatial envelope is a spatially slowly-varying amplitude of acoustic waves which contains the information of sources' location. A spatial modulation method has been theoretically developed to get a spatial envelope. By applying the spatial envelope, not only the necessary information is obtained but also computation time is reduced during the process of holography. The spatial envelope is verified as an effective visualization scheme in time domain by being applied to complicated sound fields.