• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.210-215
• /
• 2007

In this paper, excitation systems using an active tuned mass damper (ATMD) are presented in order to simulate the wind induced responses of a building structure. The actuator force for the excitation systems is calculated by using the inverse transfer function of a target structural response to the actuator. The analyses results from a 76-story benchmark building problem in which wind load obtained by wind tunnel test is given, indicate that the excitation system installed at a specific floor can approximately embody the structural responses induced by the wind load applied to each floor of the structure. The excitation system designed by the proposed method can be effectively used for evaluating the wind response characteristics of a practical building structure and for obtaining an accurate analytical model of the building under wind load.

• Tunnel and Underground Space
• /
• v.30 no.1
• /
• pp.1-14
• /
• 2020

Microseismic monitoring is utilized for the performance verification and safety management of the structure by detecting fine levels of damage. In order to construct a highly reliable microseismic monitoring system, the role of signal conditioner is critical. The signal conditioner helps with accurate data collection and precision control of the device, and performs additional functions such as signal conversion, linearization, and amplification. In this technical report, noise reduction signal conditioner suitable for mining sites was developed and reviewed for the purpose of implementing more precise monitoring by supplementing the previously developed microseismic monitoring system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.485-492
• /
• 2005

Since blast-induced vibration may cause serious problem to the rock mass as well as the nearby structures, the prediction of blast-induced vibration and the stability evaluation must be performed before blasting activities. Dynamic analysis has been Increased recently in order to analyze the effect of the blast-induced vibration. Most of the previous studies, however, were based on the continuum analysis unable to consider rock joints which significantly affect the wave propagation and attenuation characteristics. They also adopted pressure curves estimated by theoretical or empirical equations as input detonation load, thus there were very difficult to reflect the characteristics of propagating media. In this study, therefore, we suggested a discontinuum dynamic analysis technique which uses velocity waveform obtained from a test blast as an input detonation load. A distinct element program, UDEC was used to consider the effect of rock joints. In order to verify the validity of proposed method, the test blast was simulated. The predicted results from the proposed method showed a good agreement with the measured vibration data from the test blast Through the dynamic numerical modelling on the planned road tunnel and slope, we evaluated the effect of blast-induced vibration and the stability of rock slope.

• Journal of the Society of Naval Architects of Korea
• /
• v.58 no.2
• /
• pp.105-111
• /
• 2021

The main source of underwater radiated noise of ships is cavitation generated by propeller blades. After the Cavitation Inception Speed (CIS), noise level at all frequencies increases severely. In determining the CIS, it is based on the results observed with the naked eye during the model test, however accuracy and consistency of CIS values are becoming practical issues. This study was carried out with the aim of developing a technology that can automatically recognize cavitation images using deep learning technique based on a Convolutional Neural Network (CNN). Model tests on a three-dimensional hydrofoil were conducted at a cavitation tunnel, and tip vortex cavitation was strictly observed using a high-speed camera to obtain analysis data. The results show that this technique can be used to quantitatively evaluate not only the CIS, but also the amount and rate of cavitation from recorded images.

• Journal of the Korean Society of Visualization
• /
• v.19 no.3
• /
• pp.136-142
• /
• 2021

Submerged and semi-submerged vehicles expel cooling water through an outlet. In this process, induced noise and vibration by the flow around the outlet have been reported, and it may cause problems directly related to survivability of the navy vessels. The coolant outlet has a net-type structure and circular columns are mostly used. In this study, flow measurements using PIV and LDV were performed for different type outlets; conventional (flat plate with round bar) and improved (flat and flat plate) configurations. Experiments were conducted at a cavitation tunnel where pressure and steady flow rate conditions are ensured for sufficient time to measure the flow. The average velocity field of the outlets were measured and compared through LDV measurements, and instantaneous vorticities were evaluated through PIV measurements. The results show that the improved type of the outlet is advantageous in terms of flow stability compared to the conventional type of the outlet.

• Journal of the Korean Society of Visualization
• /
• v.20 no.3
• /
• pp.128-135
• /
• 2022

Cavitation occurs inevitably in marine propellers rotating at high speed in the water, which is a major cause of underwater radiated noise. Cavitation-induced noise from propellers rotating at a specific frequency not only reduces the sonar detection capability, but also exposes the ship's location, and it causes very fatal consequences for the survivability of the navy vessels. Therefore cavity inception speed (CIS) is one of the important factors determining the special performance of the ship. In this study, we present a method using computer vision that can detect and quantitatively estimate tip vortex cavitation on a propeller rotating at high speed. Based on the model test results performed in a large cavitation tunnel, the effectiveness of this method was verified.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.6
• /
• pp.757-764
• /
• 2019

Depressurization occurs around underwater objects moving at high speeds. This causes cavitation nuclei to expand, resulting in cavitation. Cavitation is accompanied by an increase in noise and vibration at the site, particularly in the case of thrusters, and this has a detrimental ef ect on propulsion performance. Therefore, predicting cavitation is necessary. In this study, an analytical method for cavitation noise is developed and applied to an elliptic wing. First, computational fluid dynamics are performed to obtain information about the flow fields around the wing. Then, through the cavitation nuclei density function, number of cavitation nuclei is calculated using the initial radius of the nuclei and nuclei are randomly placed in the upstream with large pressure drop around the wing tip. Bubble dynamics are then applied to each nucleus using a Lagrangian approach for noise analysis and to determine cavitation behavior. Cavitation noise is identified as having the characteristics of broadband noise. Verification of analytical method is performed by comparing experimental results derived from the large cavitation tunnel at the Korea Research Institute of Ships & Ocean Engineering.

• Tunnel and Underground Space
• /
• v.16 no.2 s.61
• /
• pp.179-188
• /
• 2006

The vibration or/and noise generated by blast operations might cause not only structural damage to properties but mentally also to humans and animals. For that reason, maximum permitted vibration and noise levels are set by sensitivities of structures and they are used for the management of blast vibration. It is known that the fish lived in water are more sensitive to vibration than land animals, and thus the adverse impact of the blasting on fish farms should be very concerned. This study investigated the vibration and noise levels at a large eel farm located some 840 meters of the blasting site through the large real-scale experiments of blastings, prior to conducting the actual blasting. As a result, it was found that the noise met the requirement to be within maximum permitted level, while the ground vibration exceeded the permitted vibration. Accordingly, the impact of the excess vibration was investigated by an existing empirical method and verified by a new three dimensional numerical analysis. In this study, such an inspection process was briefly described, and a method was suggested for the examination of possible adverse effects from blasting on vibration-sensitive structures like the eel farm. The study also introduced a design method that controls the blast effects - ground vibration and noise.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.05a
• /
• pp.157-164
• /
• 2005

Urban conditions such as underground facilities and ambient noises due to cultural activity restrict the application of conventional geophysical techniques in general. We used the refraction microtremor (REMI) technique as an alternative way to get the geotechnical information, in particular shear-wave (S-wave) velocity information, at a site along an existing rail road. The REMI method uses ambient noises recorded using standard refraction equipment to derived shear-wave velocity information at a site. It does a wavefield transformation on the recorded wavefield to produce Rayleigh wave dispersion curve, which are then picked and modeled to get the shear-wave velocity structure. At this site the vibrations from the running trains provided strong noise sources that allowed REMI to be very effective. REMI was performed along the planned new underground rail tunnel. In addition, Suspension PS logging (SPS) were carried out at selected boreholes along the profile in order to draw out the quantitative relation between the shear wave velocity from the PS logging and the rock mass rating (RMR) determined from the inspection of the cores recovered from the same boreholes, These correlations were then used to relate the shear-wave velocity derived from REMI to RMR along the entire profile. The correlation between shear wave velocity and RMR was very good and so it was possible to estimate the RMR of the total zone of interest for the design of underground tunnel,

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.25 no.5
• /
• pp.387-401
• /
• 2023

The Earth Pressure Balanced (EPB) Shield Tunnel Boring Machine (TBM) is widely employed for constructing urban underground spaces due to its minimal vibration and low noise levels. The injection of additives offers several advantages, including maintaining shield chamber pressure, reducing shear strength, minimizing cutter wear, and decreasing the permeability of the excavated soil. This technique is known as soil conditioning and involves the application of additives such as foam, polymer, and bentonite slurry. In this study, weathered granite soil commonly encountered at domestic tunnel sites was used as a soil specimen. Foam and polymer were applied as additives to assess the rheological properties of conditioned soils. The workability was evaluated through slump tests, while the rheological properties were assessed through laboratory pressurized vane shear tests conducted under the same conditions. Specially, the polymer was applied under specific conditions with low workability with high slump values, with the aim of evaluating the impact of polymer application. The test results revealed that with an increase in the Foam Injection Ratio (FIR), the slump value also increased, while the torque, peak strength, yield stress, apparent viscosity, and thixotropic area decreased. Conversely, an increase in the Polymer Injection Ratio (PIR) led to results opposite to those of FIR. Additionally, a correlation between the slump value and yield stress was proposed. When comparing conditions with only foam applied to those with both foam and polymer applied, even with similar slump values, the yield stress was found to be lower in the latter conditions.