• Journal of the Society of Naval Architects of Korea
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• v.49 no.6
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• pp.484-490
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• 2012

Experiments of circulating water channel and two dimensional numerical simulations were performed to investigate the fluctuating characteristics of pressure in moonpool. Based on the quasi-two dimensional characteristics of pressure fluctuations disclosed by the spatial cross-correlations, the numerical results showed qualitatively good agreement with experimental data. Proper orthogonal decomposition was employed to the spatial distributions of pressure fluctuations in order to find the first and second modes of fluctuations. The first mode of pressure fluctuations showed that the fluctuating characteristics of pressure were related to the behaviors of vortical structures. The velocity fluctuations were conditionally averaged to make clear that the coherent structures were responsible for the pressure fluctuations in moonpool.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.177-178
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• 2014

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.244-245
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• 2012

• Journal of the Korean Society of Combustion
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• v.6 no.2
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• pp.29-35
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• 2001

Unsteady numerical study has been conducted on combustion dynamics of a lean-premixed swirl-stabilized gas turbine swirl injector. A three-dimensional computation method utilizing the message passing interface (MPI) parallel architecture, large eddy simulation(LES), and proper orthogonal decomposition (POD) technique was applied. The unsteady turbulent flame dynamics are simulated so that the turbulent flame structure can be characterized in detail. It was observed that some fuel lumps escape from the primary combustion zone, and move downstream and consequently produce hot spots. Those flame dynamics coincides with experimental data. In addition, basis modes of the unsteady turbulent flame are characterized using proper orthogonal decomposition (POD) analysis. The flame structure based on odd basis modes is apparently larger than that of even ones. The flame structure can be extracted from the summation of the basis modes and eigenvectors at any moment.

• Wind and Structures
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• v.30 no.6
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• pp.559-573
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• 2020

This paper presents a study on the effectiveness of the proper orthogonal decomposition (POD) technique for reconstruction of wind pressure field as applied to a cylindrical shell roof based on simultaneously measured wind pressure data. The influence of wind loading mode truncation on the statistics of dynamic pressures and wind load effects are investigated. The results showed that truncation of higher wind loading modes can have more noticeable influence on the maximum and minimum pressures that the standard derivation (STD) values. The truncation primarily affects the high-frequency content of the pressures. Estimation of background response using wind loading modes is more effective than the use of traditional structural modal analysis.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.1
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• pp.164-169
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• 2010

Proper Orthogonal Decomposition (POD) is applied to the analysis of 2-dimensional cylinder wake flow. Time histories of flow variables were obtained by the incompressible CFD analysis. By using the method of snapshots the correlation matrix was constructed, and then eigenvalues, POD modes and time coefficients were calculated. Finally the flow field was reconstructed by using a few of the lower POD modes, and compared to the original ones.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.5
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• pp.383-389
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• 2014

POD analysis has been done to investigate the internal flow characteristics using LES calculation results of hybrid rocket combustion chamber. The special emphasis was put on the change in the mode energy distribution caused by the installation of diaphragm compared to the baseline case. Also the comparison was made to investigate the effect of wall blowing on the changes in the mode energy between the regions near and far from the diaphragm. For baseline case, POD results clearly distinguish the primary mode containing most of flow energy from the rest of flow modes (2-9 mode) depicting small scale modes. Also, the increase in the energy of flow modes 2-5 is responsible for the formation of relatively large scale structures due to diaphragm. In addition, the comparison of mode energy distributions of flow fields with diaphragm shows similar patterns in both wall blowing and no blowing case. This implies that the local increase in regression rate just after the diaphragm is directly associated with the increase in energy distributions of 2-5 modes.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.1
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• pp.20-29
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• 2010

The complicated flow characteristics of upper propeller wake influenced by hull wake are investigated in detail in the present study. A two-frame PIV (particle image velocimetry) technique was employed to visualize the upper propeller wake region. As the upper hull wake affects strongly propeller inflow, upper propeller wake shows much unstable vortical behavior, especially in the tip vortices. Velocity field measurements were conducted in a cavitation tunnel with a simulated hull wake. Generally, the hull wake generated by the hull of a marine ship may cause different loading distributions on the propeller blade in both upper and lower propeller planes. The unstable upper propeller wake caused by the ship's hull is expressed in terms of turbulent kinetic energy (TKE) and is identified by using the proper orthogonal decomposition (POD) method to characterize the coherent flow structure in it. Instabilities appeared in the eigen functions higher than the second one, giving unsteadiness to the downstream flow characteristics. The first eigen mode would be useful to find out the tip vortex positions immersed in the unstable downstream region.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.10
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• pp.840-845
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• 2012

An ARX(Auto-Regressive eXogenous) modeling technique for vortex dynamics in the BFS(Backward Facing Step) flow field is proposed in this paper. In order for the modeling of the dynamics, the spatial and temporal modes are extracted through POD(Proper Orthogonal Decomposition) analysis. Determining the orders of the inputs and outputs for an ARX structure is carried out by the spectrum analysis and temporal mode analysis, respectively. The order of input delay terms is also determined by the flow velocity. Finally the coefficients of the ARX model are designed by using an artificial neural network.

• Smart Structures and Systems
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• v.14 no.4
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• pp.569-594
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• 2014

Damage detection methods based on modal analysis have been widely studied in recent years. However the calculation of mode shapes in real structures can be time consuming and often requires dedicated software programmes. In the present paper the combined application of proper orthogonal decomposition and gapped smoothing method to structural damage detection is presented. The first is used to calculate the dynamic shapes of a damaged structural element using only the time response of the system while the second is used to derive a reference baseline to which compare the data coming from the damaged structure. Experimental verification is provided for a beam case while numerical analyses are conducted on plates. The introduction of a stiffener on a plate is investigated and a method to distinguish its influence from that of a defect is presented. Results highlight that the derivatives of the proper orthogonal modes are more effective damage indices than the modes themselves and that they can be used in damage detection when only data from the damaged structure are available. Furthermore the stiffened plate case shows how the simple use of the curvature is not sufficient when analysing complex components. The combined application of the two techniques provides a possible improvement in damage detection of typical aeronautical structures.