POD Method Research Articles

Optimization of indoor thermal environment for high-altitude sentry buildings with attached ventilation based on proper orthogonal decomposition

The low-oxygen and severe cold climate characteristics of high-altitude regions significantly impact individuals' physiological health and thermal comfort inside buildings, especially for sentry buildings where the enclosure is fully exposed to the outdoors. This study aimed to optimize the indoor environment for high-altitude sentry buildings with attached ventilation. Firstly, the optimal location of exhaust outlets and oxygen sources in the heating mode of high-altitude sentry buildings was studied, and it showed high performance in terms of thermal comfort and energy efficiency. Additionally, the POD method and interpolation methods were applied to expand the sample dataset and identify the optimal combination of attached ventilation parameters and oxygen supply concentration, creating a comfortable, oxygen-enriched environment within the sentry buildings while also considering energy efficiency. The results indicate that when the optimization objective is weighted towards thermal comfort, the percentage of dissatisfied (PD) and the draught rate (DR) values under the optimal scheme are reduced by 82 % and 46.6 %, respectively, compared to previous studies. However, when the emphasis is on energy efficiency in environmental optimization, the air supply energy under the optimal scheme has a 64.4 % reduction compared to previous research results. When considering both optimization objectives simultaneously, the PD and DR values under the optimal scheme are reduced by 35.9 % and 96.9 %, respectively, compared to previous research results. These results demonstrate significant improvements in both thermal comfort and energy efficiency relative to our previous study.

Research on Model Reduction of AUV Underwater Support Platform Based on Digital Twin

Digital twin technology, as a data-driven and model-driven innovation means, plays a crucial role in the process of digital transformation and intelligent upgrading of the marine industry, helping the industry to move towards a new stage of more intelligent and efficient development. In order to solve the defects of the Autonomous Underwater Vehicle (AUV) underwater support platform structure deformation field, digital twin technology and model reduction technology are applied to an AUV underwater support platform, and a five-dimensional digital twin model of the AUV underwater support platform is studied, including five dimensions: physical world, digital world, twin data center, service application, and data connection. The digital twin of the subsea support platform is established by using the digital twin modeling technology. The POD method is used to calculate the deformation field matrix of the support structure of the subsea support platform under the 0–5 sea state, and the corresponding eigenvalues and eigenvectors are obtained. By intercepting the eigenvectors corresponding to the eigenvalues of the high energy proportion, the low-order equation is constructed, and the reduced-order model under each sea state can be quickly solved. The experimental results show that the model reduction technology can greatly shorten the model solving time, and the calculated results are highly consistent with the simulation results of the finite element full-order model, which can realize the rapid analysis of the deformation response of the subsea support platform structure, and provide a theoretical basis and technical support for the subsequent simulation, state evaluation, visual monitoring, and predictive maintenance.

Order reduction of special valve models based on pod method

Abstract The opening size of the disc-type special regulating valve (referred to as the special valve) can be used to regulate the fluid pressure and flow inside the cabin, and is an important equipment in the intake system of the high-altitude simulation test bench (referred to as the high-altitude bench). Due to the high dimensionality and complex solution of the special valve model, the calculation time is relatively long. In this paper, the Proper Orthogonal Decomposition (POD) model reduction method is applied to the mathematical model of the special valve, and the POD basis matrix is constructed through snapshots, thus obtaining a low-dimensional model and improving computational efficiency. The research results indicate that, while ensuring sufficient accuracy, this method can reduce the dimensionality of the special valve model, improve the computational speed of the simulator in calculating this case, and verify the effectiveness of the POD method.

An evaluation of the commonly used portable medical sensors performance in comparison to clinical test results for telehealth systems

Background and ObjectiveOne of the primary challenges faced by telehealth systems is the accurate transmission of patient information to remote doctors. In this context, portable medical sensors deployed at the remote patients' end play a crucial role in measuring vital information. There are many sensors available in the market. However, the accuracy of the sensors has been always a concern. The objective of this study is to verify different sensors and create awareness for using accurate sensors to avoid misdiagnosis for the patients’ safety. MethodsThis study considered the test result of a Japanese clinical pathology laboratory as the reference gold standard. The clinical pathology laboratory uses 1) Hexokinase UV method for blood glucose, 2) Enzymatic Determination method for cholesterol, 3) Automatic Analyzer (EDTA-2 K) of Hemoglobin, and 4) Uricase POD method for uric acid. To assess the performance of a medical sensor, its test results were compared to the gold standard test results obtained from the laboratory using the same sample. A Normalized Root Mean Square Error (NRMSE) threshold of less than 0.2 was established as the criterion for determining whether the medical sensor's performance fell within an acceptable range. ResultsAmong the eight most commonly used blood glucose devices in the Asian market, only one device was deemed acceptable with NRMSE less than 0.2. However, all four devices found in the Japanese market showed their acceptability. In the case of cholesterol, hemoglobin, and uric acid devices, only a limited number of items were available in Asian markets. Some of the hemoglobin and uric acid devices were found to be somewhat acceptable, while all the cholesterol sensors were found erroneous. ConclusionsThis study has clearly shown the issues with the portable medical sensors and recommends the device approval authority of each country to approve sales of the quality sensors only for patients’ safety.

Complex gravity-acoustic impact on V-flame structure

Development of efficient and safe energy systems for space objects includes ensuring fire safety. This problem requires a deep understanding of influence of gravitational forces on combustion processes, which explains the importance of studying this issue. The paper analyzes the dynamics of inverted conical methane-air flame under conditions of normal and reverse gravitational force with external acoustic excitation. Applied frequencies of acoustic excitation could be parasitic or be produced during proper work of different technical systems of aircraft. High speed recording of flame chemiluminescence and PIV analysis were conducted. Decomposition of flow vector pictures into the modes was calculated using POD method. Energy contribution into the flow was analyzed for its separate elements at the different frequencies of excitation. At the high excitation frequencies vortex generation intensity in the shear layer with reverse gravity is about the same as it was observed in the experiments with normal gravity direction, that could indicate dominance of acoustic mechanism of the vortexes stimulation over the mechanism of shear instability. At external excitation frequency equals 240 Hz significant growth of shear vortex diameters and increasing of perpendicular oscillations amplitude of flame branches were obtained. Thereby in such experiment with 240 Hz external acoustic excitation the most intensive large scale instability of flow was observed.

Numerical Investigation into Characteristics of WIPCC and Distortion of S-shaped Intake

Water injection pre-compressor cooling technology can efficiently increase the engine thrust and expand the flight envelope of the aircraft. Changes in the curvature of the intake and the evaporative cooling of the spray medium naturally distort the total pressure, total temperature, and characteristics of the swirl of the flow before it enters the engine. This study conducts numerical research on the aerothermal process of the WIPCC in an S-shaped intake using the Eulerian-Lagrangian method. The spatial evolution of critical variables along the flow direction and specific cross-sections were obtained by analyzing the statistical time-averaged results of multiphase flow. The transient distortion descriptors were quantified and analyzed following the SAE standard, which revealed the characteristics of various distortions and their spatial-temporal changes. Furthermore, the variables reflecting the transient flow structure were decomposed using the POD method to obtain the coherent structure of each mode and its frequency and energy characteristics. The results showed that aerodynamic breakup was the main cause of droplet size reduction and led to a decrease of 74.4% and 63.8% in Sauter droplet size under two conditions, respectively. The downstream mixing of flows in the S-duct mitigated the distortions caused by the intake's changing curvature and droplet evaporation. After the mixing of flows under specific conditions, the total pressure distortion coefficient decreased from 0.30 to 0.12, the swirl intensity decreased from 4°-6° to 2°-4°, and the high total temperature extent decreased from 0.65 to 0.35. The POD mode of the variables exhibited broadband characteristics with multiple spikes and energy dispersion. The main modes of the drop coefficients in total pressure and temperature corresponded to large- and small-scale structures, respectively, with Strouhal number ranges of 0.079-0.394 and 0.362-1.260. These results reveal the effects of WIPCC on the aerothermal processes in the S-shaped intake and the mechanism of generation and evolution of distortions. Moreover, the results provide reasonable boundary conditions for numerical investigations of wet compression under intake distortions.

Data-Driven Balanced Truncation for Predictive Model Order Reduction of Aeroacoustic Response

Rapid prediction of the aeroacoustic response is a key component in the design of aircraft and turbomachinery. In this work, we propose a technique for highly accelerated prediction of aeroacoustic response using a data-driven model reduction approach based on the eigensystem realization algorithm (ERA). Specifically, we create and compare ERA reduced-order models (ROMs) based on the training data generated by solving the linearized and nonlinear Euler equations, and we use them to predict the aeroacoustic response of an airfoil in a purely predictive setting subject to different types of gust loading. Activating each input channel separately in the full-order model (FOM) to generate the Markov sequence for training makes it computationally challenging to use the ERA in aeroacoustics applications. We address this bottleneck by first proposing a multifidelity gappy POD method to reduce the computation cost on the FOM and ROM levels by querying the high-resolution FOM only for the input channels identified by gappy POD. Second, we use tangential interpolation at the ROM level to reduce the size of the Hankel matrix. The proposed methods enable application of the ERA for accurate online acoustic response prediction, and they reduce the offline computation cost of ROMs.

The interfacial modes and modal causality in a dispersed bubbly turbulent flow

While data-driven analysis has demonstrated significant success in single-phase flow systems, its application to multi-phase flows has been relatively limited with fewer examples. In this study, we present a modal analysis and modal causality analysis of dispersed bubbly turbulent flow, with the aim of providing new insights into the interfacial gas–liquid interaction. Our study employs an in-house coupled level-set volume-of-fluid solver, which is combined with a modified fast Fourier transforms algorithm to perform interface-resolved direct numerical simulations in a turbulent channel flow with 96 bubbles occupying 5.4% volume. In the downward flow orientation, we observe that bubbles are mainly clustered in the channel center, producing pseudo-turbulence with isotropic characteristics. We apply the proper orthogonal decomposition method to the phase-resolved, three-dimensional velocity field, radius of the bubble as well as the surface tension force in order to extract the dominant modes. Notably, our results reveal the presence of two energetic modes in both the gas and liquid phases, as well as the interface, namely, the vortex-ring mode and the quadrupolar mode. We further investigate the causal relationship across the gas–liquid interface using the modal information transfer entropy. Our findings demonstrate a strong causality between the gas phase and the surface tension, whereas the causality between the liquid phase and surface tension is comparatively weak due to the multi-scale characteristics of the turbulent fields. Overall, our novel approach to investigating the interfacial gas–liquid interaction in dispersed bubbly turbulent flow provides valuable insights that enhance physical understanding and could lead to improved flow control and efficiency in a range of industrial processes. The identification of previously unidentified energetic modes using the POD method has the potential to advance research in this field, with potential implications for future design of control strategies in complex systems.

Unsteady Simulation and Mode Analysis of Disturbed Cylinder Flow

The unsteady simulation of cylinder flow with inlet velocity disturbance is simulated and compared with that without disturbance. POD is adopted to analyze and capture the dominant modes of the vortex street in the cylinder wake. The results show that the POD method is efficient in reconstructing the flow field. When the inlet velocity disturbance exists, the number of modes required to reconstruct the flow field accurately is almost unchanged, but the energy proportion of each mode changes. The larger the disturbance frequency is, the smaller the shape and vorticity magnitude of the vortex street is, and the slower the generation speed is. If the frequency deviates too much from the original frequency of the flow field, the effect of inlet velocity disturbance will be shielded.

Numerical Analysis of Transient State Heat Transfer by Spectral Method Based on POD Reduced-Order Extrapolation Algorithm

In order to meet the requirements of high accuracy and fast algorithm for numerical heat transfer simulation, an iterative scheme of Proper Orthogonal Decomposition (for short, POD) dimension reduction based on the classical central difference Galerkin spectral method is proposed for solving two-dimensional transient heat conduction problems. The POD dimension reduction spectral method model is constructed by taking the calculation results of classical central difference Galerkin spectral method as sample data. The numerical algorithm characteristics of flow and heat transfer are studied by using a partial differential equation as a mathematical model, and the error estimation is given. Finally, different time intervals are used as parameters to simulate experiments. The results show that the POD method is applicable to transient nonlinear heat conduction problems, and the maximum average relative error of the reconstructed temperature field is 0.89675%. Moreover, the POD method not only has a high calculation accuracy, but also has an average calculation speed as high as 310.25 times that of the central difference Galerkin algorithm. It can be seen that under the condition that the error between the solution of POD dimension reduction extrapolation algorithm and the solution of classical central difference Galerkin spectrum method is small enough, the POD method can greatly reduce the calculation amount, shorten the running time, and ensure a high accuracy of the calculation results, thus verifying the effectiveness and feasibility of the algorithm.

Phase proper orthogonal decomposition of non-stationary turbulent flow

A phase proper orthogonal decomposition (phase POD) method is demonstrated utilizing phase averaging for the decomposition of spatiotemporal behavior of statistically non-stationary turbulent flows in an optimized manner. The proposed phase POD method is herein applied to a periodically forced statistically non-stationary lid-driven cavity flow, implemented using the snapshot proper orthogonal decomposition algorithm. Space-phase modes are extracted to describe the dynamics of the chaotic flow, in which four central flow patterns are identified for describing the evolution of the energetic structures as a function of phase. The modal building blocks of the energy transport equation are demonstrated as a function of the phase. The triadic interaction term can here be interpreted as the convective transport of bi-modal interactions. Non-local energy transfer is observed as a result of the non-stationarity of the dynamical processes inducing triadic interactions spanning across a wide range of mode numbers.

POD method for acceleration of blood flow reconstruction in a vessel with contrast enhanced X-ray CT

ABSTRACT The reconstruction of blood velocity in a vessel from contrast-enhanced X-ray CT projections is a complex inverse problem. In this work, we investigate an inversion approach based on the adjoint method with a partial differential equation as constraint. The proper orthogonal decomposition method is used to accelerate the reconstruction with reduced basis for the velocity, the density and the adjoint method. The effectiveness of the reconstruction method is shown with simulated realistic stationary and non-stationary blood flows in a vessel.

Post-excision drying of immature Phalaenopsis seeds improves germination and desiccation tolerance

• Immature P halaenopsis seeds cannot tolerate drying and germinate poorly. • Incubation of excised immature seeds without free water increased germination. • Drying excised seeds slowly induced desiccation tolerance. • Excision of seeds induced two LEA protein genes regardless of drying. • Some LEA proteins may increase germinability. Long-term storage of many commercially valuable orchid seeds is uniquely challenging because they can only be germinated in aseptic culture, a practice requiring that fruits be prematurely excised before they dehisce to facilitate sterilization. The seeds from these fruits cannot tolerate the desiccation required for long-term storage, resulting in potential loss of valuable germplasm. Our aim is to develop methods to increase germinability and desiccation tolerance in immature orchid seeds to prepare them for long-term storage and to explore underlying biochemical factors. We assessed germinability, desiccation tolerance and expression of two typical L ate E mbryogenesis A bundant ( LEA) genes in Phalaenopsis amabilis, P. aphrodite and their hybrid seeds as a function of moisture content both during natural development and during experimental treatments of excised immature seeds. Germinability increased whenever excised seeds were incubated in the absence of free water at moisture contents high enough to permit protein synthesis, a treatment which resulted in the rapid (within 24 h) upregulation of two typical LEA genes. Whereas incubating excised seeds without free water at high moisture contents for 4 days improved germination and induced LEA genes, only drying of excised seeds over the course of 4 days induced tolerance to eventual moisture contents less than 10% moisture. In conclusion, our results suggest that the germination of seeds from orchid capsules excised prior to dehiscence (as for the green pod method) is improved by maintaining them for several days following excision at high relative humidity in the absence of free water. Such seeds can also be induced to tolerate desiccation - and thus potentially long term dry storage - by slowly drying them over the course of several days. Our results also support the hypothesis that some of the typical LEA proteins improve germinability but are alone insufficient for the development of desiccation tolerance.

ASSOCIATION OF SERUM URIC ACID WITH ATHEROGENIC INDEX OF PLASMA AND FASTING BLOOD SUGAR IN METABOLIC SYNDROME AMONG DIABETIC AND NON DIABETICS

Background: Metabolic syndrome is a cluster of metabolic abnormities like hypertension central obesity, insulin resistance and atherogenic dylipidemia and is stongly assosciated with the atherosclerotic cardiovascular disease. To evaluate the association of serum uric acidObjective: with atherogenic index of plasma and fasting blood sugar in diabetes mellitus. A total of 50 individuals aged >35yrs were selected asMethods: cases based on predened enrollement criteria and 50 healthy individuals as controls. Serum uric acid and serum lipid prole were measured in all study subjects. SUA were done by uricase method and atherogenic index of plasma (AIP) was formulated by log TG-C/HDL and FBS by GOD- POD method. A total of 50 cases belongs to 35-50 yrs of age group. The study found that the mean levels of Serum Uric acid (SUA) higherResults : than controls ,mean levels of TG( 194.3±18.2 ) in DM patients were signicantly higher than those of controls were as mean levels of HDL-C ( 31.32±3.13 ) in DM patients were lower than those of controls. The mean AIP in DM patients was (0.7846±0.0677 ) signicantly higher than that of controls. The diabetic patients showed a positive signicant (r = 0.12569 P = <0.0001 ) correlation b/w AIP and SUA and PositiveConclusion: correlation b/w SUA and FBS (r=0.31176 P=<0.0001).

An Extreme Learning Machine Based Adaptive VISMA for Stability Enhancement of Renewable Rich Power Systems

Maintaining power system stability in renewable-rich power systems can be a challenging task. Generally, the renewable-rich power systems suffer from low and no inertia due to the integration of power electronics devices in renewable-based power plants. Power system oscillatory stability can also be affected due to the low and no inertia. To overcome this problem, additional devices that can emulate inertia without adding synchronous machines can be used. These devices are referred to as virtual synchronous machines (VISMA). In this paper, the enhancement of oscillatory stability of a realistic representative power system using VISMA is proposed. A battery energy storage system (BESS) is used as the VISMA by adding an additional controller to emulate the inertia. The VISMA is designed by using Fruit Fly Optimization. Moreover, to handle the uncertainty of renewable-based power plants, the VISMA parameters are designed to be adaptive using the extreme learning machine method. Java Indonesian Power Grid has been used as the test system to investigate the efficacy of the proposed method against the conventional POD method and VISMA tuning using other methods. The simulation results show that the proposed method can enhance the oscillatory stability of the power system under various operating conditions.

Research on reverse identification algorithm of indoor pollution source based on machine learning

Indoor sudden pollutant leakage brings environmental pollution and occupational exposure, so it is more and more important to obtain the location and identification of leakage sources. Through the forward method based on machine learning, this paper establishes a reverse traceability model for indoor multiple pollution sources. The POD method is used to obtain a large number of intermediate working condition data. The data pre-processing strategy of first normalization and then random forest feature screening can effectively improve the accuracy and generalization ability of the model. Based on a real environmental room case, model verification and sensor deployment optimization are carried out. The results show that the four sensors deployed in a specific location can achieve more than 95% positioning accuracy. In addition, the leakage possibility ranking component embedded in the model can effectively guide the staff to check the leakage points in turn, and the efficiency of three checks is as high as 99.91%.

Reduced Order Model based on SPOD for Aerothermoelastic Analysis of a Hypersonic Panel

This study has established a reduced order model (ROM) based on spectral proper orthogonal decomposition (SPOD) method in order to proceed an aerothermoelastic response analysis of a hypersonic panel. The two-way coupling between aerothermal and aeroelastic systems is applied [1]. Three aspects of POD-ROM are investigated: 1) the selection of snapshots for POD modes; 2) the comparison between classical POD [2] and SPOD [3]; 3) how to find global POD modes in a parameter space of flight altitude and Mach number. The snapshots are sampled from aerothermoelastic response data via the classical Galerkin method. The numerical results show that the dynamic response of the panel in time history is stable flat first, dynamically stable buckling, and subsequently flutter occurs with transient chaos and then limit cycle oscillation (LCO). Moreover, we find that: 1) the selection of the entire time response as the snapshots for production of POD modes reveals that the long-term buckling and LCO response will interfere the resulting POD modes. Therefore, taking the transient chaotic response as snapshots is a better choice; 2) compared with the classical POD method, the proposed SPOD method for the present aerothermoelastic system improves the accuracy and efficiency obviously; 3) the global POD modes here are essentially the natural modes of the aerothermoelastic panel and thus are related to the temperature of panel. This is of great significance to further understand the physical mechanism of the present aerothermoelastic system and develop fast calculation methods.

Effect of Nozzle Outlet Shape on Cavitation Behavior of Submerged High-Pressure Jet

A submerged high-pressure water jet is usually accompanied by severe cavitation phenomenon. An organ pipe nozzle can greatly improve the cavitation performance of the jet, making use of the self-excited oscillation of the flow. In order to study the effect of organ pipe nozzles of different nozzle outlet shapes on cavitation behavior of submerged high-pressure jet, in this paper we build a high-pressure cavitation jet experiment system and carried out a high-speed photography experiment to study cavitation cloud characteristics of a high-pressure submerged jet. Two organ pipe nozzles with and without a whistle were compared. The dynamic characteristics of the cavitation cloud was extracted through the POD method, it was found that the result effectively reflect the dynamic characteristics of the cavitation jet. The reconstruction coefficients of mode-1 obtained by the POD can better reflect the periodic time-frequency characteristics of cavitation development. The effect of the nozzle outlet shape on the cavitation behavior of organ pipe nozzle was analyzed based on unsteady numerical simulation, and it was found that the jet generated by the nozzle with a divergent whistle had a larger vorticity in the shear layer near the outlet. Further, stronger small-scale vortex and much severe cavitation occurred from the nozzle with a divergent whistle.

Influence of the different pod positions and screening methods on soybean pod shattering

Pod shattering is one of the major soybean constraints in the soybean production centers, particularly in the tropics. The screening for pod shattering resistance of 16 genotypes was carried out using detached and undetached pod methods on the three different pod positions on the stem. The field research was arranged in a randomized block design, during the dry season in Banyuwangi, Indonesia. The shattering evaluation was conducted in the laboratory using the ovendry method. The screening methods to investigate the pod shattering resistance of each genotype consisted of the detached pod (DP), undetached pod (UDP), and undetached whole-stem method (UWS). The result showed that the detached pod method (DP) resulted in a higher average podshattering percentage (15%) than the undetached pod methods (UDP and UWS, 13% and 11%, respectively). Nevertheless, the detached pod and undetached pod methods provide a consistent result for the evaluation of pod shattering resistance, showed by their correlation coefficients (DP and UDP, r = 0.98**; DP and UWS, r = 0.98**, UDP and UWS, r = 0.99**). The detached pod with the oven-dry method was suggested to be used for screening of pod shattering resistance. This method enables to screen genotypes in greater numbers, provides a homogeneous selection pressure and environmental condition. Pods at the upper part of the stem were more resistant to shattering than those pods in the middle part and lower part. The pod length, seed length, seed weight, pod wall weight to the pod weight ratio, and weight of 25 seeds appeared to be the significant indicators for pod shattering resistance. The shattering evaluation resulted in five soybean genotypes (Anj/G100H-28, Anj/G100H-44, Anj/Rjbs-304, Anj/Rjbs-30, and Detap 1) with consistent resistance to pod shattering based on the three methods. These genotypes can be used as donor parents in the breeding program for pod shattering resistance.

Effect of coherent structures on convective heat transfer in a swirling impinging jet

The present paper reports on the detailed investigation of the flow dynamics and unsteady heat transfer in an impinging jet in regimes with high swirl and vortex breakdown. A combination of the time-resolved stereoscopic PIV, time-resolved PLIF and high-speed IR-thermometry methods is used. Two cases of distances between the jet nozzle and impingement surface are considered, H = d and H = 2d. The Reynolds number is fixed as Re = 5000. The temperature distribution in the flow has a maximum on the jet axis near the surface in the region of the central recirculation zone. The data are processed using the POD method to extract coherent flow structures and quantify temperature fluctuations on the impact surface. The helical vortex structure in the case of H = d influences heat transfer between the swirling jet and the surface, the temperature fluctuations on the surface reach 0.05 degrees.