• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.335-341
• /
• 2001

The bubble cavitation and cloud cavitation are the major sources of cavitation-induced sound and vibration. A numerical method which predicts the trajectory and volume change of a cavity is developed, to predict the cavitation noise of a body. It is shown, by using the numerical method, that the cavitation inception and events rate is strongly dependent on the screening effect caused by the pressure gradient around a body, which is confirmed experimentally. Additionally, the effectiveness of a cavitation control method utilizing air injection is investigated experimentally. It is demonstrated that the noise level of the cloud cavitation can be significantly reduced by the air-injection method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.1716-1720
• /
• 2000

To develop the code of predicting flow-field and aeroacoustic noise by a electrical cable, a combined CFD-acoustic analogy approach is selected. The two-dimensional, unsteady, incompressible Reynolds-Averaged Navier-Stokes solver with a ${\kappa}{\omega}$, ${\kappa}{\omega}$ SST turbulence modeling is used to calculate the near-field around electrical cable. Near-field results are then coupled with two-dimensional Curle's integral formulation based upon Lighthill's acoustic analogy with an assumption of acoustic compactness. To validate this code, numerical results are compared with experimental data for a circular cylinder. The simulation shows an overprediction on acoustic amplitudes, but overally speaking, the spectrum pattern of sound pressure agrees well with experiment in an acceptable amount of error. In addition, various cross sections of a cable were selected and compared with each other in terms of drag and radiated noise.

• Advances in aircraft and spacecraft science
• /
• v.9 no.4
• /
• pp.319-333
• /
• 2022

This work presents a numerical investigation of the aerodynamics and aero acoustics of the HVAB rotor in hover conditions. Two fully turbulent models are employed, the one-equation Spalart-Allmaras model and the two-equation k-ω SST model. Transition effects are investigated as well using the Langtry-Menter γ-Re θt transition transport model. The noise generation and propagation are being investigated using the Ffows-Williams Hawking model for far-field noise and the broadband model for near-field noise. Comparisons with other numerical solvers and with the PSP rotor test data are presented. The results are presented in terms of thrust and power coefficients, the figure of merit, surface pressure distribution, and Sound pressure level. Velocity, pressure, and vortex structures generated by the rotor are also shown in this work. In addition, this work investigates the contribution of different blade regions to the overall noise levels and emphasizes the importance of considering specific areas for future improvements.

• The Journal of the Acoustical Society of Korea
• /
• v.34 no.5
• /
• pp.343-350
• /
• 2015

In this paper, we perform a study on the directionality of broadband ship radiation noise, mainly resulting from propeller cavitation. By examining a few foreign studies for ship radiation noise and domestic data measured in Korean waters, it is reconfirmed that the asymmetric directionality of the ship radiation noise at bow and stern aspect is observed commonly. In order to explore the reason of this asymmetric directionality, a numerical analysis, based on the acoustic boundary element method, is applied into the geometric form equal to the commercial ship used in the domestic experiment. The numerical result demonstrates that the diffraction of the propeller cavitation noise by ship is a primary cause of the bow-stern asymmetry in the directionality of ship radiation noise.

• Smart Structures and Systems
• /
• v.12 no.6
• /
• pp.679-694
• /
• 2013

In this paper the application of the Interpolation Damage Detection Method to the numerical model of a suspension bridge instrumented with a network of Micro-Electro-Mechanical System sensors is presented. The method, which, in its present formulation, belongs to Level II damage identification method, can identify the presence and the location of damage from responses recorded on the structure before and after a seismic damaging event. The application of the method does not require knowledge of the modal properties of the structure nor a numerical model of it. Emphasis is placed herein on the influence of recorded signals noise on the reliability of the results given by the Interpolation Damage Detection Method. The response of a suspension bridge to seismic excitation is computed from a numerical model and artificially corrupted with random noise characteristic of two families of Micro-Electro-Mechanical System accelerometers. The reliability of the results is checked for different damage scenarios.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.2060-2065
• /
• 2003

Aeolian tone generation from a two dimensional circular cylinder is numerically investigated via direct numerical simulation and hydrodynamic-acoustic splitting method. All governing equation are spatially discretized with the sixth-order compact scheme and fourth-order Runge-Kutta method to avoid excessive numerical dissipations and dispersions of acoustic quantities. Comparisons of two results show that the previous splitting method can not accurately predict the aeroacoustic noise of wall bounded shear flow. In this study, a perturbation viscous term and a new energy equation have been developed. This modified splitting method accurately predicts aeroacoustic noise from wall-bounded shear flow. The present results agree very well with the direct numerical simulation solution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.797-803
• /
• 2000

Recently, the singing phenomenon was encountered during the sea trials of high speed catamaran and 46,000 TDW product carrier and remedied after various treatments, which were based on the reduction of vortex shedding strength and the avoidance of resonance, respectively. And, the numerical approach for structure-acoustical problem like singing phenomenon was established using MSC/NASTRAN and SYSNOISE. In this paper, the effectiveness of numerical approach was verified through the control of singing noise. And the results according to the modification were also discussed. Finally, the future works were described to enhance the numerical approach pattern for singing phenomenon.

• Ocean Systems Engineering
• /
• v.10 no.1
• /
• pp.49-65
• /
• 2020

In this study, the effects of inclined shaft angle on the hydro-acoustic performance of cavitating marine propellers are investigated by a numerical method developed before and Brown's empirical formula. The cavitating blades are represented by source and vortex elements. The cavity characteristics of the blades such as cavitation form, cavity volume, cavity length etc., are computed at a given cavitation number and at a set advance coefficient. A lifting surface method is applied for these calculations. The numerical lifting surface method is validated with experimental results of DTMB 4119 model benchmark propeller. After calculation of hydrodynamic characteristics of the cavitating propeller, noise spectrum and overall sound pressure level (OASPL) are computed by Brown's equation. This empirical equation is also validated with another numerical results found in the literature. The effects of inclined shaft angle on thrust coefficient, torque coefficient, efficiency and OASPL values are examined by a parametric study. By modifying the inclination angles of propeller, the thrust, torque, efficiency and OASPL are computed and compared with each other. The influence of the inclined shaft angle on cavity patterns on the blades are also discussed.

• Journal of Ship and Ocean Technology
• /
• v.7 no.3
• /
• pp.13-33
• /
• 2003

This paper presents a numerical study on tip vortex cavitation inception predictions based on non-spherical bubble dynamics including splitting and jet noise emission. A brief summary of the numerical method and its validation against a laboratory experiment are presented. The behavior of bubble nuclei is studied in a tip vortex flow field at two Reynolds numbers, provided by a viscous flow solver. The bubble behavior is simulated by an axisymmetric potential flow solver with the effect of surrounding viscous flow taken into account using one way coupling. The effects of bubble nucleus size and Reynolds number are studied. An effort to model the bubble splitting at lower cavitation numbers is also described.

• Journal of the Korean GEO-environmental Society
• /
• v.11 no.6
• /
• pp.21-29
• /
• 2010

In this study, a new noise & vibration-free screw concrete pile method that was expected environmentally friendly method was introduced, also the numerical analyses of a conventional PHC pile and a new screw concrete pile were done. As a result, the bearing capacity behavior and the settlement behavior of 2 kinds of concrete pile were analyzed and compared.