POD Method Research Articles

Dynamics of the Tip Vortices in the Wake Behind a Circular Cylinder of Finite Length

The dynamics of the tip vortices in the wake behind a wall-mounted finite-length circular cylinder of the aspect ratio 2 was studied experimentally using time resolved stereo PIV technique. The cylinder was mounted normal to a ground plane and it was subjected to a cross-flow with thin boundary layer developed on the wall, the Reynolds number based on inflow velocity and cylinder diameter was 9.7 thousands. The dynamics of tip vortices were analysed using the POD method applied to the plane perpendicular to the flow close to the cylinder. Besides the decaying power spectrum, slower that the Kolmogorov-type one, the two distinct frequencies were detected on Strouhal numbers 0.09 and 0.15. These frequencies could be linked to the vortical structures dynamics in the wake. The frequency Sh = 0.15 corresponds to predominantly spanwise vortices dynamics with anti-symmetrical patterns with respect to the cylinder axis, while the frequency Sh = 0.09 corresponds to mainly streamwise vortical structures dynamics with symmetrical patterns respectively. Thus, the von Kármán vortex street was detected on Strouhal frequency 0.15.

Association of Diabetic Retinopathy and Lipid Profile in Diabetic Patients in Mathura District

Background: It is estimated that diabetes mellitus affects 4 percent of the world’s population, almost half of whom have some degree of diabetic retinopathy at any given time. Elevated serum lipid levels are associated with an increased risk of retinal hard exudate in persons with diabetic retinopathy. Therefore the current study was undertaken to determine the association of serum lipid profile with diabetic retinopathy and its severity. Subjects and Methods: One hundred fifty diabetic patients, out of these, 75 diabetic patients with retinopathy served as the study group I and 75 diabetic patients with no retinopathy formed group II (control group). Simultaneously, 75 age and sex matched healthy subjects were also studied as controls (group III). Serum total cholesterol, serum triglyceride, serum low density lipoprotein and serum high density lipoprotein were measured by using enzymatic method and autoanylyser. Fasting blood sugar and post prandial blood sugar were estimated by using GOD POD method. Results: Most of the patients in Group I had some degree of visual impairment. However there was no statistical significance with p >0.05. The mean value of total cholesterol was higher in both group I and group II with value being higher in group1 (229.09mg/dl) as compared to group II (215.32mg/dl). Triglyceride levels also followed the similar trend with group I having mean value of 238.95mg/dl and group II having 179.93 mg/dl. But only total cholesterol value had statistical significance p < 0.05. Conclusion: The present study demonstrated statistically significant correlation between diabetic retinopathy and hypercholesterolemia. Increased cholesterol level was significantly associated with the occurrence of all grades of retinopathy especially severe NPDR, very severe NPDR and PDR. No correlation was found between lipid profile and visual acuity. These data suggest that hyperlipidaemia should be promptly treated in diabetic patients.

Robust and Fast Registration of Infrared and Visible Images for Electro-Optical Pod

To deal with the registration of infrared and visible image with significant difference in contrast and large geometric distortion in electro-optical pod, a robust and fast registration method by using common structural features is proposed in this paper. First, to adjust the scales of input images, a geometric transformation model is built based on parameters of the cameras. Then, a global structural feature extraction strategy is developed by using phase congruency and significance ranking space. Those features are not only invariant to the scale and contrast but also embody the structural of the input images maximally and uniformly. Finally, to enhance the robustness to contrast, blurring, and incompleteness of structures, an adaptive feature matching method with kernelized correlation filter is presented. Experimental results demonstrate that the proposed method has better performance than several state-of-the-art methods in robustness and precision, and also confirm its validity in the real environment.

Using POD method in experiments with convection flow on the cube benchmark

Investigations of the flow structure on the benchmark “cube” under conditions of natural convection caused by a vertical temperature gradient are performed using a low cost PIV-measuring system with continuous laser. The obtained velocity fields were processed with POD method to obtain typical structures (modes) in the flow. It is shown that the steady flow can be described by combination of the first three modes. It is demonstrated that only starting with the third mode there is a significant change in the spectra of the amplitude coefficients of the modes, the peak shifts to the region of higher frequencies. Thus accounting for this mode is essential for describing turbulent processes in the system and verification of numerical calculations. Comparison with the results of the LES simulation performed using the Ansys CFX package (taking into account the results of processing the experimental data by the POD method) demonstrated good agreement both in the structure of the modes and in their frequency spectra.

Volumetric Proper Orthogonal Decomposition of an impinging jet using SPIV measurement

Impinging jets which interact with sharp edges like slotted plates can be found in ventilation and air conditioning systems. In some cases, these configurations can be a source of desirable sounds like in musical instruments. However, they can be a source of noise in other applications such as air conditioning systems. Thus in order to reduce the noise produced from such configurations a more profound study of the flow dynamics should be implemented. All previous studies of impinging jets on a slotted plate were done in 2D. Accordingly, the objective of the present study was to reconstruct the studied volume by combining stereoscopic PIV measurements and the POD method. Consequently, an experimental set up has been developed and implemented in order to generate a flow that hits a slotted plate. On the other side, the PIV technique was used in order to study the dynamics of such a flow. The kinematic fields of twenty two parallel planes are measured by means of stereoscopic PIV. Afterwards, the analysis of the most energetic modes was obtained by the application of the snapshot POD on the kinematic fields obtained by POD. The results showed that the reconstruction of each of the planes needed only three first three modes. The reconstructed volume is obtained by an interpolation of the reconstructed planes which were phased by a trigger signal. The analysis of the vortex structures were done by the application of several vortex detection criteria.

On the boundary layer structure on suction side of an airfoil

The structure of boundary layer on an airfoil suction side was studied using stereo time resolved PIV technique experimentally in low Reynolds number, about 33 thousands. The mean velocity field is close to the 2D case, however the instantaneous structure is highly dynamical and 3D. Dynamics of the vortices in the boundary layer has been analysed using POD method. The results show lag of coherence in the streamwise direction, oblique patterns are detected instead.

Fast solution methods of parameterized high-fidelity models

High-fidelity simulation based on solving partial differential equations has become an indispensable approach in innovative research of nuclear energy. However, due to the prohibitively high computation cost, it is yet unfeasible to run simulations on the whole reactor core level with all the physics resolved on fine meshes, especially in the analysis which need carry out many times of calculations. Model order reduction strategies are promising ways to achieve significant speedups by replacing the original large-scale model by a reduced order model of substantially smaller scale. Two effective model order reduction techniques, i.e., the reduced basis finite element method and the POD-Galerkin method, are studied and applied in the present study to solve the transient thermo-elastic problem and the fluid dynamics problem, respectively. For the former, the boundary conditions, the physical parameters and the body heat source are treated as parameters. The greedy-POD algorithm is applied to construct reduced basis space and the for the latter, the Reynolds number is treated as a parameter. The pure POD method is applied to construct the basis space. During on the online stage, three to five orders of computation speed up has been achieved by using the built reduced order models compared with that by the full order models while the accuracy of the results is well ensured. It is demonstrated that model order reduction techniques will be a practical way to deploy numerical reactors.

A Weighted POD Method for Elliptic PDEs with Random Inputs

In this work we propose and analyze a weighted proper orthogonal decomposition method to solve elliptic partial differential equations depending on random input data, for stochastic problems that can be transformed into parametric systems. The algorithm is introduced alongside the weighted greedy method. Our proposed method aims to minimize the error in a $$L^2$$ norm and, in contrast to the weighted greedy approach, it does not require the availability of an error bound. Moreover, we consider sparse discretization of the input space in the construction of the reduced model; for high-dimensional problems, provided the sampling is done accordingly to the parameters distribution, this enables a sensible reduction of computational costs, while keeping a very good accuracy with respect to high fidelity solutions. We provide many numerical tests to assess the performance of the proposed method compared to an equivalent reduced order model without weighting, as well as to the weighted greedy approach, in both low and high dimensional problems.

Evolution of vortical structures behind an inclined flat plate

2D3C TR-PIV technique was utilized to investigate streamwise-oriented vortical structures behind an inclined flat plate. The angle of attack was set to 7 deg, several fields of view in the wake were investigated. The instantaneous velocity vector fields were captured, dynamics of the flow was studied using POD method. The streamwise structures are determined by vorticity and low- and high-velocity streaks are defined. The acquired results are in a good agreement with the new hypothesis of a principle of flight.

Prediction of wind loads on high-rise building using a BP neural network combined with POD

According to the limited wind tunnel test results to obtain detailed data of surface wind pressure on buildings has important significance for the accurate calculation of cladding wind pressure and wind-induced response of structures. In this paper, a backpropagation neural network (BPNN) combined with proper orthogonal decomposition (POD-BPNN) is proposed for the prediction of the mean, root-mean-square (RMS) pressure coefficients and the time series of wind-induced pressures on a building surface, respectively. In this study, simultaneous pressure measurements are made on a high-rise building model in a boundary layer wind tunnel and parts of the model test data are used as the training input–output sets for BPNN and POD-BPNN models. Comparisons of the prediction results by the POD-BPNN approach and those from the wind tunnel test demonstrate that the BPNN combined with POD method can successfully and efficiently predict the time series of pressure data on all surfaces of a high-rise building on the basis of wind tunnel pressure measurements from a certain number of pressure taps.

Identification of coherent structures in the flow past a NACA0012 airfoil via proper orthogonal decomposition

Proper orthogonal decomposition, POD, is employed to identify coherent structures in the turbulent flow past a NACA0012 airfoil. An analysis of different POD techniques is presented including the standard snapshot method, the spectral POD (SPOD) method, and a Fourier-POD implementation combined with the SPOD. The latter technique is viable once the present turbulent flow has a homogeneous direction along the airfoil span. An assessment of different vector norms and filter functions employed in the POD reconstruction is presented. The evaluation of the several POD techniques allows the investigation of the physics of the current turbulent flow including the observation of coherent structures and their relation to the airfoil noise generation mechanisms. The SPOD technique is applied assuming periodic and non-periodic temporal signals in the construction of the covariance matrix. Although it slightly alters the spectrum of the POD singular values, the periodic SPOD considerably reduces the noise observed in the singular vectors. The application of the Gaussian filtering allows an enhanced control in the response of the SPOD when compared with a square-box filter. The present POD reconstructions employ norms based on kinetic energy and pressure. For both norms, two-dimensional coherent structures are observed along the turbulent boundary layer and wake regions for the first pair of modes. These structures have a spectral content at the same frequency of the tonal noise radiation by the airfoil. The POD analysis also allows the identification of further coherent structures in the present flow. The kinetic energy norm is able to reconstruct low-frequency structures in the flow field for higher POD modes, while the pressure norm reconstructs high-frequency structures. This behavior is related to the physics captured by each POD norm in the present turbulent flow.

توسعه الگوی رتبه کاسته برای بازسازی داده های مفقود شده میدان های جریان ناپایا با استفاده از یک روند تجزیه زمانی

In this paper, the proper orthogonal decomposition method has been used for gappy data reconstruction of the unsteady incompressible viscous flow and calculation of related forces (such as aerodynamics coefficients). The present approach is based on combination of POD method and solution of an optimization problem to get a reduced order model. This model reconstructs missed data or incomplete snapshots with relevant accuracy and fast speed. Two kinds of model have used in this manner. In the first approach, a simple iterative approach is used to reconstruct of the relative missed or incomplete basis functions of snapshots ensemble. The Second method, which is proposed recently by the author, used a time advancing and domain decomposition method along time direction, for reconstruction of incomplete ensemble members with high missing percentage. Essential trait of this method is about application of step by step reconstruction of primary ensemble to reduce number of unknown variables and obtaining an accurate model to recover the missed data. The outcome results of two approaches have compared with direct simulation CFD data which are shown appropriate ability and good agreement

METABOLIC SYNDROME IN FEMALE WORKERS FROM A TEXTILE MILL: EFFECT OF NOISE

Objective: Noise creates alteration in human health in both physical as well as psychological variations. Effect of noise on components of metabolic syndrome (MetS) has been discussed but not well established. The aim of this study was to investigate the MetS in female workers from textile mill.Methods: A total of 65 female workers were recruited for the study from the high noise (&gt;70 dB) area and low noise (&lt;40 dB) area of a textile mill. Body mass index (BMI), blood pressure (BP), blood sugar (BS), and lipid profile were investigated of the female workers. BP was estimated by auscultatory method. BS was investigated by glucose oxidase-peroxidase (POD) method. Total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were investigated by cholesterol oxidase (CHOD)-POD method, GPO- PAP method, CHOD-POD/phosphotungustate method, and friedewald formula, respectively.Results: Significant outcomes were obtained in this study. BMI was significantly (&lt;0.01) higher in workers working in high noise area compared to low noise (&lt;40 dB) area. Systolic BP and diastolic BP was also significantly (&lt;0.01) higher in high noise area. Fasting BS level was found to be significantly (&lt;0.01) lower in low noise area. In case of lipid profile significant (&lt;0.01) results were obtained except LDL-C. TC and TG were found to be related with noise since their concentration was higher in high noise area compared to low noise area. However, HDL-C was found to be lower in high noise area compared to low noise area.Conclusion: Continuous exposure to occupational noise might be reason for developing cardiovascular disease depending on the degree of MetS in industrial workers. BP and BS seems to be better predictor of MetS in assessing cardiovascular risk.Keywords: Occupational noise, Metabolic syndrome, Dyslipidemia.

On 3D flow-structures behind an inclined plate

Stereo PIV measurements has been performed behind the inclined plate, angle of attack 5 and 10 deg. Occurrence and dynamics of streamwise structures behind the plate trailing edge have been studied in details using POD method. The streamwise structures are represented by vortices and low- and highvelocity regions, probably streaks. The obtained results support the hypothesis of an airfoil-flow force interaction by Hoffman and Johnson [1,2].

POD and GUM Universal Methods for Making Safety Measurable

&lt;p&gt;Various non-destructive testing (NDT) methods such as ultrasounds (UT) or eddy current (ET) have been established for in-service inspections (ISI) or for condition assessment in different kind of industries such as in the nuclear or aerospace business. Another example for a common NDT inspection task is the detection of tendon ducts in the field of civil engineering (CE) using Ground Penetrating Radar (GPR) as well as the determination of its lateral and depth position. Therefore, the detection limits of the used inspection system, which depends on the depth position and the number of tendon ducts and distances between them, has to be well known. One approach to determine the limits of detection is the application of the POD method (probability of detection) as a universal procedure, which excludes the human factor and calculates the a&lt;sub&gt;90/95&lt;/sub&gt; value and other characteristic parameters. With this information, different inspection systems can be compared objectively to choose the most suitable NDT-system for each individual inspection task. To distinguish between a real variation in the tendon duct position and the accuracy of the inspection system, the knowledge about the uncertainty of measurement is required. To determine the accuracy of the selected NDT-system, the GUM procedure (guide to the expression of uncertainty in measurement) has been established and provides a statistical evaluated result in form of the measurement result and its expanded uncertainty. This article introduces a procedure using the example of tendon duct detection (POD) and depth position description (GUM) in concrete with Ground Penetrating Radar (GPR). Finally, the universal application of both methods (POD and GUM) in different fields of industries is illustrated by some examples.&lt;/p&gt;

Bifurcation analysis of reduced rotor model based on nonlinear transient POD method

The singularity theory is applied to study the bifurcation behaviors of a reduced rotor model obtained by nonlinear transient POD method in this paper. A six degrees of freedom (DOFs) rotor model with cubically nonlinear stiffness supporting at both ends is established by the Newton's second law. The nonlinear transient POD method is used to reduce a six-DOFs model to a one-DOF one. The reduced model reserves the dynamical characteristics and occupies most POM energy of the original one. The singularity of the reduced system is analyzed, which replaces the original system. The bifurcation equation of the reduced model indicates that it is a high co-dimension bifurcation problem with co-dimension 6, and the universal unfolding (UN) is provided. The transient sets of six unfolding parameters, the bifurcation diagrams between the bifurcation parameter and the state variable are plotted. The results obtained in this paper present a new kind of method to study the UN theory of multi-DOFs rotor system.

Structure-preserving Galerkin POD reduced-order modeling of Hamiltonian systems

The proper orthogonal decomposition reduced-order model (POD-ROM) has been widely used as a computationally efficient surrogate model in large-scale numerical simulations of complex systems. However, when it is applied to a Hamiltonian system, a naive application of the POD method can destroy the Hamiltonian structure in the reduced-order model. In this paper, we develop a new reduced-order modeling approach for Hamiltonian systems, which modifies the Galerkin projection-based POD-ROM so that the appropriate Hamiltonian structure is preserved. Since the POD truncation can degrade the approximation of the Hamiltonian function, we propose to use a POD basis from shifted snapshots to improve the approximation to the Hamiltonian function. We further derive a rigorous a priori error estimate for the structure-preserving ROM and demonstrate its effectiveness in several numerical examples. This approach can be readily extended to dissipative Hamiltonian systems, port-Hamiltonian systems, etc.

Application of the transient proper orthogonal decomposition method for order reduction of rotor systems with faults

The physical significance of the transient proper orthogonal decomposition (TPOD) method is proposed based on the energy of the proper orthogonal mode (POM). The POM energy can reveal the amount occupation of the dynamical characteristics of the reduced model relative to the original one. The TPOD method is compared with the traditional POD method; the bifurcation diagrams and the transition curves of POM energy are applied to verify the efficiency and accuracy of the TPOD method. On the basis of the POM energy analysis, the optimal order reduction model can be provided by the TPOD method. Two examples of the rotor-bearing systems are established by the Newton’s second law to study the physical significance of the TPOD method: One is the rotor system with pedestal looseness at one end and the other is looseness at both ends. The effects of the initial conditions (displacement and velocity) to the frequency components of the original systems and the order reduction efficiency are discussed. The variations of the frequency components can provide the guidance to the fault detections of the rotor systems.

Comparative numerical analysis using reduced-order modeling strategies for nonlinear large-scale systems

We perform a comparative analysis using three reduced-order strategies–Missing Point Estimation (MPE) method, Gappy POD method, and Discrete Empirical Interpolation Method (DEIM)–applied to a biological model describing the spatio-temporal dynamics of a predator–prey community. The comparative study is focused on the efficiency of the reduced-order approximations and the complexity reduction of the nonlinear terms. Different variants are discussed related to the projection-based model reduction framework combined with selective spatial sampling to efficiently perform the online computations. Numerical results are presented.

Nonlinear model reduction via a locally weighted POD method

SummaryIn this article, we propose a new approach for model reduction of parameterized partial differential equations (PDEs) by a locally weighted proper orthogonal decomposition (LWPOD) method. The presented approach is particularly suited for large‐scale nonlinear systems characterized by parameter variations. Instead of using a global basis to construct a global reduced model, LWPOD approximates the original system by multiple local reduced bases. Each local reduced basis is generated by the singular value decomposition of a weighted snapshot matrix. Compared with global model reduction methods, such as the classical proper orthogonal decomposition, LWPOD can yield more accurate solutions with a fixed subspace dimension. As another contribution, we combine LWPOD with the chord iteration to solve elliptic PDEs in a computationally efficient fashion. The potential of the method for achieving large speedups while maintaining good accuracy is demonstrated for both elliptic and parabolic PDEs in a few numerical examples. Copyright © 2016 John Wiley &amp; Sons, Ltd.