• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.759-769
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• 2013

Electronic equipment has been applied to virtually every area associated with commercial, industrial, and military applications. Specifically, electronics have been incorporated into avionics components installed in aircraft. This equipment is exposed to dynamic loads such as vibration, shock, and acceleration. Especially, avionics components installed in a helicopter are subjected to simultaneous sine and random base excitations. These are denoted as sine on random vibrations according to MIL-STD-810F, Method 514.5. In the past, isolators have been applied to avionics components to reduce vibration and shock. However, an isolator applied to an avionics component installed in a helicopter can amplify the vibration magnitude, and damage the chassis, circuit card assembly, and the isolator itself via resonance at low-frequency sinusoidal vibrations. The objective of this study is to investigate the dynamic characteristics of an avionics component installed in a helicopter and the structural dynamic modification of its tray plate without an isolator using both a finite element analysis and experiments. The structure is optimized by dynamic loads that are selected by comparing the vibration, shock, and acceleration loads using vibration and shock response spectra. A finite element model(FEM) was constructed using a simplified geometry and valid element types that reflect the dynamic characteristics. The FEM was verified by an experimental modal analysis. Design parameters were extracted and selected to modify the structural dynamics using topology optimization, and design of experiments(DOE). A prototype of a modified model was constructed and its feasibility was evaluated using an FEM and a performance test.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.131-140
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• 2022

Installing Continuous Welded Rail (CWR) is one of the economical ways to resolve the challenges of noise, vibration, and the open-deck steel railway bridge impact, and the SSF method using the interlocking sleeper fastener has recently been developed. In this study, the method employed for determining the optimum vertical stiffness of the sleeper pad installed under the bridge sleeper, which is utilized to adjust the rail height and absorb shock when the train passes when the interlocking sleeper fastener is applied, is presented. To determine the optimal vertical stiffness of the sleeper pad, related existing design codes are reviewed, and, running safety, ride comfort, track safety, and bridge vibration according to the change in the vertical stiffness of the sleeper pad are estimated via flexible multi-body dynamic analysis,. The flexible multi-body dynamic analysis is performed using commercial programs ABAQUS and VI-Rail. The numerical analysis is conducted using the bridge model for a 30m-long plate girder bridge, and the response is calculated when passing ITX Saemaeul and KTX vehicles and freight wagon when the vertical stiffness of the sleeper pad is altered from 7.5 kN/mm to 240 kN/mm. The optimum stiffness of the sleeper pad is calculated as 200 kN/mm under the conditions of the track components applied to the numerical analysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1166-1176
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• 2011

The prospect in opening the arctic trade transportation route on a year-round basis offers vast opportunity of exploring untapped resources and shortened navigational routes. In addition, the environment's remoteness and lack of technical experiences remains a big challenge for the maritime industry. With this, engine designers and makers are continually investigating, specifically optimizing propulsion shafting system design, to meet the environmental and technical challenges of the region. The International Association of Classification Society, specifically machinery requirements for polar class ships(IACS UR13), embodies the propulsion shafting design requirements for ice class vessels. However, the necessity to upgrade the various features of the unified rules in meeting current polar requirements is acknowledged by IACS and other classification societies. For the polar class propulsion shafting system, it is perceived that the main source of excitation will be the propeller - ice load interaction. The milling - and the impact load, in addition to the load cases interpreted by IACS, contribute greatly to the overall characteristic of the system and due considerations are given during the propulsion design stage. This paper will expound on the excitation load estimation factors affecting the dynamic response of the different propulsion shafting system design. It is anticipated that detailed understanding of these factors will have a significant role during propulsion shafting design in the future.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.2
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• pp.79-86
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• 2014

This paper describes an integrity evaluation method for emergency diesel generator(EDG) and rotor part of EDG. EDG is a very important equipment in the nuclear power plant(NPP). EDG supplies electricity to the safety-related equipments for the safety shut down of NPP in an emergency situation of earthquake. The safety of the rotor part of EDG is also important during seismic impact from earthquake. The finite element modelling of the EDG including rotor part was constructed. The modal analysis of EDG was firstly performed. The first natural frequency was calculated and revealed higher than the cutoff frequency of seismic spectrum. Then the stress analysis was done to compare with the allowable stress. The safety of the rotor part was investigated by the finite element analysis of the rotor and journal bearing interaction to find film thickness and critical speed. The seismic load was applied to rotor part in a manner that the load was a weighted static load. Analysis results showed that the maximum stress was within the range of allowable stress and the film thickness is larger than the permissible minimum thickness, and the critical speed was out of the operating speed. Hence, the structural and dynamic integrity of EDG could be confirmed by the numerical analysis method used in this paper. However, dynamic analysis of a rotating rotor and supporting bearing with the seismic impact needs to be investigated in a more rigorous method since the seismic load to the rotating part complicates the behavior of rotating system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.30-41
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• 2017

Types of noise barrier installed for noise attenuation are largely divided into noise-absorbing format and noise-proofing format. In these days, installation of transparent noise barrier is general trend to solve problems that hinder sunshine and landscape. Some kinds of transparent boards are used to one of components in noise barriers, but in some cases, less transparency and worse pollution due to yellowing phenomena, and severe material deformation are to harm the urban aesthetics Therefore laminated-tempered glass board in that yellowing phenomena does not occur can be replaced as a transparent one to secure those shortcomings. In this paper, the structural safety against train induced vibration and the resistibility to wind load are analyzed for laminated-tempered glass system as a component of noise barrier installed on Metro railway elevated bridges. Also the appropriateness is evaluated through flexural bending performance test, compressive strength test, modulus of elasticity tests, and impact test for the system or the glass material itself. All of these processes are intended to present the deployment of logic to evaluate the adequacy for the system.

• International Journal of Highway Engineering
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• v.13 no.2
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• pp.9-20
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• 2011

Most of domestic expansion joint system was applied by exposed expansion joint system. There are cases where it is damaged by driving. As the result noise and impact happened, and the social cost due to frequent repair works is increasing. So based on the Asphalt Plug Joint(APJ) system that applied in the United States and Europe, new buried expansion joint system was lately developed a system of Buried Folding Lattice Joint(BFLJ) that changed substructure. In this research, we have tested for durability and flexibility performance of buried expansion joint system that based on the type of asphalt mixture. Also we have evaluated for durability of BFLJ system against vehicle load using accelerated pavement testing. As a result of the experiment, the developed BFLJ system gives high flexibility performance and resolves transformation concentration along the joint section more than APJ system. Also it could be seen that the BFLJ system could overcome the disadvantages of APJ and prevent early damage. Because surface deflection of BFLJ system against vehicle load was measured low, and sub system in the buried expansion joint system was not damaged against vehicle load.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.12
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• pp.847-854
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• 2012

The demand for noise barriers and necessity for the installation are highly growing because residential areas have become diverse and locational priority is changed to consider how to approach highway easily. However, public annoyance to the noise generated from highway is continued despite lots of noise barrier are installed. Moreover, there are growing concerns to maintain noise barriers to be free from losing transparency, dust stack, and shock fracture. To resolve these issues, it is suggested to develop new polymer materials and conceptually new noise barrier. In this study, as a first step to develop a new noise barrier to overcome current technological challenges as well as economic issues, recent research trends have been analyzed and found the direction for the future research in terms of material, supplementary function, and patterning.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.309-316
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• 2018

Various studies have been conducted to improve the BSR (Buzz, Squeak, Rattle) noise generated irregularly while the vehicle is running. In vehicle, When an external force such as vibration or force flows into the contact surface, BSR noise is generated at the contact surfaces of nearby components. In this paper, BSR conceptually explain the kind of noise generation mechanisms and the basic principles of generation, which have been proven by observing and improving noise phenomena in automobiles over the last 10 years. Through this, it is expected that researchers who want to study BSR related improvement research not only in automobiles but also in other industries, It will be able to understand the BSR phenomenon and provide a framework for thinking out improvement ideas and to carry out further research.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.92-98
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• 2005

Screen can provide any disturbed resistance that affects the change in characteristics of turbulence, velocity and pressure distributions of the flow field, and thus it has been widely used to control the flow. Some previous related studies for compressible flows have limitations such as, considering relatively low-Mach-number flows in the range of 0.3 ∼ 0.7, and not observing the detailed shock structures of the flow fields. An experimental study on highly compressible axi-symmetric supersonic jet flow fields behind wire-gauze screen has thus been carried out. Continuous/instantaneous flow images by Schlieren flow- visualization technique and the information of Pitot pressure/flow-noise measurements of the flow field behind the screen for various jet expansion conditions have been obtained. Effects of various porosity and inclination angles of the screen at the nozzle exit have also been investigated, and the experimental results have been compared to the case with no screen installed.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.141-146
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• 2012

The rail surface defects which are generated on repeated rolling contact fatigue are getting increased according to high speed, high density, and minimum weight. In addition, Increasing noise and vibration are affected by these also impact load generated as well. Because of this phenomenon, more serious and critical damages were occurred. In fact, in order to control them, the rail grinding amount in Korea. This study evaluated how depth of hardening on rail surface is formed and suggested optimal rail grinding amount by RCF(rolling contact fatigue) test with generated contact pressure between KTX wheel and UIC60 rail by applying FEM analysis. Therefore, the amount was generated approximately 0.2mm/20MGT to maintain integrity of rail surface by getting rid of depth of hardening on rail according to rail accumulated passing tonnage.