• Proceedings of the KSR Conference
• /
• 2009.05a
• /
• pp.1069-1077
• /
• 2009

For external noise prediction of railway vehicles, sophisticated individual source modelling as well as appropriate noise propagation model from the sources is necessary to ensure the accuracy of the predicted results and contributions of each equipment to the overall noise levels. Accurate and reasonable identification procedures of sound sources of equipment including source strength, directivity and positions installed in the train play an important role in a prediction model, since it is not easy to establish a simple model for the sources with a single rule due to the complexity of source characteristics of equipment in size and directivity pattern. This paper guidelines practical considerations for identification of noise sources in railway vehicles including typical source characteristics of several sub-systems that emits noise to the environment, particularly for electric multiple unit(EMU), and verify effectiveness of assumptions used in the modelling of equipment by measurement with a simple part. The predicted external noise level of a complete train using Exnoise, which was developed by Hyundai-Rotem and has been verified in the a lot of field-tests, incorporating source modelling considered in this paper shows close correlation with the measured ones.

• Journal of the Korean Home Economics Association
• /
• v.46 no.5
• /
• pp.87-96
• /
• 2008

The purpose of this study was to establish which factors were considered when fashion companies discussed the intention of employing the internet in various capacities. A total of 228 candidates were surveyed between 17-11-07 and 17-01-08. The collected data was used to conduct various descriptive and comparative analyses. Firstly, environmental factors considered important were internal pressure, external pressure and uncertainty of the market. Organizational factors considered important were support of the chief executive officer, capacity of the organization and future directivity. Profit factors considered important were elevation of the business, customer relationship management, advantage of the internet and reduction of expenses. Prohibitive factors considered important were miscellaneous expenses, secession of the customer, internal opposition of the organization and convertible expenses. Secondly, fashion companies regarded internal pressure, external pressure, support of the chief executive officer, capacity of the organization, future directivity, elevation of the business, customer relationship management, advantage of the internet and miscellaneous expenses as important when discussing the introduction of the internet.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.6 no.2
• /
• pp.55-64
• /
• 2003

Underwater acoustic noise measurement is an essential element for vulnerability assessment of modern naval platforms. But during the last few decades environmental conditions have drastically changed due to the gradually increasing sea ambient noise level and decreasing submarine radiated noise level. A real-time underwater acoustic measurement system with vertical line array is designed for the quiet submarine radiated noise assessment in challenging environment. This system has a constant directivity index in measurement frequency range and accurate tracking capability for the transmission loss compensation and navigation aids inside the submarine. This system has been validated at sea and used several times for the submarine noise measurement.

• Proceedings of the KIEE Conference
• /
• 2000.07c
• /
• pp.2213-2215
• /
• 2000

In this paper we implemented a novel re-entrant mode microstrip directional coupler for realizing the high directivity characteristic using finite element (FE) analysis. In microstrip configuration, the high directivity can be reached by matching the even- and odd-mode effective phase velocities. Through the values of capacitance obtained from 2-dimensional finite element(FE) analysis, the phase velocities for each mode and the design parameter were extracted for the proposed coupled-line configuration. Based on the extracted design parameter with phase matching condition we designed and fabricated 30dB directional coupler at 850MHz. Experimental results show good performance with excellent isolation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.703-706
• /
• 2000

The acoustic characteristics radiated from the acoustic transducer with metal-piezoceramic laminated circular plate were simulated. The Vibrational modes of metal-piezoceramic laminated circular plates were calculated by using the finite element method. After meshing the inside closed boundary of the acoustic transducer, the pressure gradients and the isotaric lines were calculated for the various frequencies. It has been observed that the characteristics of the sound pressure calculated for the various frequencies. Also, the directivity patterns and the sound pressure radiated from the acoustic transducer were calculated by 2-dimensional analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.545-550
• /
• 2005

A parametric loudspeaker is a device to generate highly directional sound using ultrasounds. The parametric loudspeaker could be used to focus sound in a limited space, so it is important to study the characteristics of the parametric loudspeaker in near-field. Mechanism of the audible sound generation in the parametric loudspeaker is explained by nonlinear interaction of the ultrasounds and is modeled as KZK equation, the nonlinear wave equation which contains attenuation, nonlinearity and diffraction. To measure the directional characteristics of the parametric loudspeaker precisely, a method to reduce the spurious signal which taints the measured signal was invented. With the method, directivity patterns of the parametric loudspeaker were measured and compared to the approximated solution and piston sources.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.240-243
• /
• 2005

A design procedure using spatial Fourier transform is presented for a structural-acoustic coupled radiator that can emit sound in the desired direction with high power and low side lobe level. The design procedure consists of three steps. Firstly, the structural-acoustic coupled radiator is chosen to obtain strong coupling between structural vibration and acoustic pressure. The radiator is composed by two spaces which are separated by a wall. Spaces can be categorized as reverberant finite space and unbounded semi-infinite space, and the wall are composed of two plates and an opening. The velocities on the wall are predicted. Secondly, directivity and energy distribution of radiator are predicted in wave number domain using spatial Fourier transform. Finally, optimal design variables are calculated using a dual optimal algorithm. Its computational example is presented including the directivity and resulting pressure distribution using proposed procedure.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.21 no.6
• /
• pp.790-798
• /
• 2018

Discrete noise signals from a small scale tactical unmanned aerial vehicle(UAV) propeller were predicted numerically using time domain approach. Two-bladed 29 inch propeller in diameter and 150 kgf in gross weight were used for main parameters of the UAV based on the actual size of the similar scale vehicle. Panel method and Farassat formula A1 were adopted for aerodynamic and aeroacoustic analysis respectively. Time domain signals of both thickness and loading noises were transformed into frequency domain to analyze the discrete noise characteristics. Directivity pattern in a plane perpendicular to the rotating disc plane and attenuation of noise intensity according to double distance were also presented.

• Proceedings of the KSME Conference
• /
• 2005.11a
• /
• pp.174.1-174.1
• /
• 2005

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.10a
• /
• pp.389-390
• /
• 2013