Space Increments Research Articles

Variation of wake patterns and force coefficients of the flow past square bodies aligned inline

In this numerical study, the variation of wake patterns and force coefficients of the flow past four square bodies aligned inline are investigated. A two-dimensional numerical code is developed using the Lattice Boltzmann method (LBM) for this study. The code is first validated for the flow past a single and two tandem square cylinders. The results are compared to those available in literature and found to be in good agreement. After validation the calculations are further performed to investigate the effect of gap spacing (g) for the flow past four inline square cylinders at two different Reynolds numbers (Re) 100 and 200. The gap spacing is chosen in the range 0.25 ≤ g ≤ 7. Six different flow patterns: Single slender body, alternate reattachment, quasi steady reattachment, intermittent shedding, chaotic flow and periodic flow are found in this study with successive increment in spacing. It is found that some flow patterns existing at Re = 100 do not exist at Re = 200. The generated vortices at Re = 200 are much stronger as compared to those at Re = 100. The spacing value g = 3 is found to be critical at Re = 100 while at Re = 200 the spacing value g = 2 is critical due to abrupt changes in flow characteristics. At some spacing values the downstream cylinders have higher values of average drag coefficients as compared to upstream ones. In general the upstream cylinder (c1) have higher drag forces at Re = 200 than at Re = 100. The root mean square values of lift coefficient are found to be greater than the corresponding root mean square values of drag coefficient.

Spectral simulation of vector random fields with stationary Gaussian increments in d-dimensional Euclidean spaces

This paper addresses the problem of simulating multivariate random fields with stationary Gaussian increments in a d-dimensional Euclidean space. To this end, one considers a spectral turning-bands algorithm, in which the simulated field is a mixture of basic random fields made of weighted cosine waves associated with random frequencies and random phases. The weights depend on the spectral density of the direct and cross variogram matrices of the desired random field for the specified frequencies. The algorithm is applied to synthetic examples corresponding to different spatial correlation models. The properties of these models and of the algorithm are discussed, highlighting its computational efficiency, accuracy and versatility.

A Brief Commentary on Space-Time-Height Relativity

This article contributes a mathematical visualization on the relativity among space-time-height accordingly with the A. Einstein’s special relativity theory. The variation of time with the increment and decrement of space and height is truly focused and elaborated inside. The Lorentz expression about the relativity interprets the relativity of mass correspondingly with the energy of matter. This proposed theory visualize the relativity among three dimensions at a time i.e. space, time and height. Space, time and height are taken as three individual dimensions and all 3D plots are sketched collaborating with these dimensions. To comprehend the theory several explanations are established and several expressions are derived and plotted manually. All the expressions conclude with a great satisfaction that the relativity of time also exists in the collaboration with space and height both instantaneously.

Wavelet synthetic method for turbulent flow.

Based on the idea of random cascades on wavelet dyadic trees and the energy cascade model known as the wavelet p model, a series of velocity increments in two-dimensional space are constructed in different levels of scale. The dynamics is imposed on the generated scales by solving the Euler equation in the Lagrangian framework. A dissipation model is used in order to cover the shortage of the p model, which only predicts in inertial range. Wavelet reconstruction as well as the multiresolution analysis are then performed on each scales. As a result, a type of isotropic velocity field is created. The statistical properties show that the constructed velocity fields share many important features with real turbulence. The pertinence of this approach in the prediction of flow intermittency is also discussed.

A general self-preservation analysis for decaying homogeneous isotropic turbulence

A general framework of self-preservation (SP) is established, based on the transport equation of the second-order longitudinal velocity structure function in decaying homogeneous isotropic turbulence (HIT). The analysis introduces the skewness of the longitudinal velocity increment, $S(r,t)$ ($r$ and $t$ are space increment and time), as an SP controlling parameter. The present SP framework allows a critical appraisal of the specific assumptions that have been made in previous SP analyses. It is shown that SP is achieved when $S(r,t)$ varies in a self-similar manner, i.e. $S=c(t){\it\phi}(r/l)$ where $l$ is a scaling length, and $c(t)$ and ${\it\phi}(r/l)$ are dimensionless functions of time and $(r/l)$, respectively. When $c(t)$ is constant, $l$ can be identified with the Kolmogorov length scale ${\it\eta}$, even when the Reynolds number is relatively small. On the other hand, the Taylor microscale ${\it\lambda}$ is a relevant SP length scale only when certain conditions are met. The decay law for the turbulent kinetic energy ($k$) ensuing from the present SP is a generalization of the existing laws and can be expressed as $k\sim (t-t_{0})^{n}+B$, where $B$ is a constant representing the energy of the motions whose scales are excluded from the SP range of scales. When $B=0$, SP is achieved at all scales of motion and ${\it\lambda}$ becomes a relevant scaling length together with ${\it\eta}$. The analysis underlines the relation between the initial conditions and the power-law exponent $n$ and also provides a link between them. In particular, an expression relating $n$ to the initial values of the scaling length and velocity is developed. Finally, the present SP analysis is consistent with both experimental grid turbulence data and the eddy-damped quasi-normal Markovian numerical simulation of decaying HIT by Meldi & Sagaut (J. Turbul., vol. 14, 2013, pp. 24–53).

The Effect of Plate Spacing in Plate Heat Exchanger Design as a Condenser in Organic Rankine cycle for Low Temperature Heat Source

Abstract Plate spacing is one of variable that influences plate heat exchanger (PHE) design as a condenser in Organic Rankine Cycle (ORC) system. The rises of plate spacing have effects to channel cross sectional area, channel velocity, equivalent diameter, and Reynold number at hot and cold fluid sides in PHE. Those parameters affect the total heat transfer area and total pressure drop that influence the PHE condenser performance. This paper investigated the detail effect of the plate spacing increments in the final total heat transfer area and total pressure drop design result. The plate spacing in design calculation method is varied and the other independent variables are assumed to be constant. The design was conducted by calculating condenser capacity at both sides and both zones, estimating overall heat transfer coefficient, and calculating heat transfer area and plate film coefficient. Analysis continued by calculating overall heat transfer coefficient that has small percent of error with the estimated overall heat transfer coefficient, calculating pressure drop, total plate number and total heat transfer area. The result of calculation shows that the rises of plate spacing increase the total heat transfer area and decrease the cold and hot fluid total pressure drop. The rises of plate spacing increase channel cross sectional area and equivalent diameter, and decrease channel velocity and Reynold number at zone 1 (without phase change) and zone 2 (with phase change). Therefore, the increment of heat transfer areas is unpreferable and the decrement of pressure drops is preferable.

Numerical investigation of wake modes for flow past three tandem cylinders using the multi-relaxation-time lattice Boltzmann method for different gap spacings

In this paper, the effect of gap spacing on the flow past three square cylinders in tandem arrangement is studied numerically using a 2-D multi-relaxation-time lattice Boltzmann method (MRT-LBM). The Reynolds number is fixed at 75 and variation of the gap spacing is from 0.5 to 17. The results are compared to some earlier published results and found to be in good agreement. Five different wake modes are observed by the increment in the gap spacing. To understand the effect of different gap spacings on the flow-induced forces; a detailed analysis of mean drag coefficient, time signal analysis of drag and lift coefficients, Strouhal number, root mean square values of drag and lift coefficients is presented in this article. In this study, it is observed that the critical gap spacing is 3, its existence and effects on the flow characteristics are also studied.

Simulation of Monsoon Depressions Using WRF-VAR: Impact of Different Background Error Statistics and Lateral Boundary Conditions

AbstractIn a variational data assimilation system, background error statistics (BES) spread the influence of the observations in space and filter analysis increments through dynamic balance or statistical relationships. In a data-sparse region such as the Bay of Bengal, BES play an important role in defining the location and structure of monsoon depressions (MDs). In this study, the Indian-region-specific BES have been computed for the Weather Research and Forecasting (WRF) three-dimensional variational data assimilation system. A comparative study using single observation tests is carried out using the computed BES and global BES within the WRF system. Both sets of BES are used in the assimilation cycles and forecast runs for simulating the meteorological features associated with the MDs. Numerical experiments have been conducted to assess the relative impact of various BES in the analysis and simulations of the MDs. The results show that use of regional BES in the assimilation cycle has a positive impact on the prediction of the location, propagation, and development of rainbands associated with the MDs. The track errors of MDs are smaller when domain-specific BES are used in the assimilation cycle. Additional experiments have been conducted using data from the Interim European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim) as initial and boundary conditions (IBCs) in the assimilation cycle. The results indicate that the use of domain-dependent BES and high-resolution ERA-I data as IBCs further improved the initial conditions for the model leading to better forecasts of the MDs.

Three-Dimensional Chemiluminescence Imaging of Unforced and Forced Swirl-Stabilized Flames in a Lean Premixed Multi-Nozzle Can Combustor

A tomographic image reconstruction technique has been developed to measure the 3D distribution of CH* chemiluminescence of unforced and forced turbulent premixed flames. Measurements are obtained in a lean premixed, swirl-stabilized multi-nozzle can combustor. Line-of-sight images are acquired at equally spaced angle increments using a single intensified charge-coupled device camera. 3D images of the flames are reconstructed by applying a filtered back projection algorithm to the acquired line-of-sight images. Methods of viewing 3D images to characterize the structure, dynamics, interaction and spatial differences of multi-nozzle flames are presented. Accuracy of the reconstruction technique is demonstrated by comparing reconstructed line-of-sight images to measured line-of-sight downstream-view images of unforced flames. The effect of the number of acquired projection images on the quality of the reconstruction is assessed. The reconstructed 3D images of the unforced multi-nozzle flames show the structure of individual flames as well as the interaction regions between flames. Forced flame images are obtained by phase-synchronizing the camera to the forcing cycle. The resulting 3D reconstructions of forced flames reveal the spatial and temporal response of the multi-nozzle flame structure to imposed velocity fluctuations, information which is essential to identifying the underlying mechanisms responsible for this behavior.

A quantitative simulation study of asymmetrical tectonic subsidence control on non-synchronous sequence stacking patterns of Eocene lacustrine sediments in Bohai Bay Basin, China

Compared with large-scale passive margin marine basins, continental basins are susceptive to local or regional tectonic, geomorphologic and climatic influences and can form complicated sequence stratigraphic architectures, configurations and sedimentary facies. We report herein a quantitative simulation study on the influences of asymmetrical tectonic subsidence on sequence stratigraphic stacking patterns in rift basins by varying tectonic subsidence, sediment supply, and intra-rift lake levels. It has been demonstrated that isochronous sequences within a rift basin can exhibit both synchronous and non-synchronous stacking patterns as a result of differential asymmetric tectonic subsidence. In sequence stratigraphy, synchronous stacking patterns refer to isochronous sequences at any parts of a basin, which are either all retrogradational or all progradational. We propose the concept of non-synchronous stacking patterns of isochronous sequence stratigraphy for rift basins. Non-synchronous stacking patterns refer to the fact that, within the same basin, some parts may concomitantly exhibit stacking patterns that are exactly opposite to that of other parts. Non-synchronous stacking patterns can form when the accommodation space increment (∆A) is less than that of sedimentary supply (∆S) in one area, but larger than or equal to that of ∆S in another. Moreover, the duration of non-synchronous stacking patterns is controlled by both ∆A and ∆S. Recognition of non-synchronous stacking patterns within isochronous sequence stratigraphy provides a conceptual model for correlation of sequence stratigraphic units in tectonically asymmetric rift basins in eastern China and similar basins around the world.

Fatigue crack propagation in turbine disks of EI698 superalloy

In-service fatigue cracking of turbine disks of EI698 superalloy is discussed based on crack growth analyses. In the bolt joint for disks to shaft connecting there is high level of stress-state, which directed to earlier in-disks fatigue crack origination in low-cycle-fatigue regime. Fracture surface pattern such as fatigue striations were used for their spacing measurement and crack growth duration estimating. Developed disk tests on a special bench by the equivalent program to in-service cyclic loads have allowed discovering one-to-one correlation between fatigue striation spacing and crack increment in one flight. Number of fatigue striations and beach-marks calculations permitted to estimate crack growth period for the different stages of in-service disks cracking. Equivalent stress level for in-service cracked disks was calculated and compared with stress-level intested disks under stress equivalent program to in-service operated cyclic loads. Based on this result nondestructive inspection intervals were discussed and recommended for in-service disks in dependence on number of their flights at the moment of developed inspection to exclude in-flight disks fast fracture.

FDTD Analysis with Overset Grid Generation Method for Rotating Body and Evaluation of Its Accuracy

This paper presents an alternative approach for the analysis of EM field by a rotating body with FDTD method and Overset Grid Generation method, considering Lorentz transformation for the higher velocity cases. This approach has been previously proposed for the case of linear and uniformly moving body against/to the incident wave. Here, the approach is expanded to a rotating body which includes the interpolation technique in the space and time increment along the cylindrical rotation at the fixed axis. First, the grid size ratios between the main mesh and the sub-mesh are studied. The appropriate choice of the grid size ratio is obtained. Then, the modulations of the EM field when the incident wave hits the rotating body in high velocity cases are analyzed. The relationship of the phase shift and the velocity is further observed. The observed EM fields are compared with the theoretical results and achieved good agreements in high relative velocities. The assessment of the numerical errors in a rotating environment is also highlighted. This numerical approach may have numerous situations to which it can be applied. This may be involved with the design of rotating devices such as microactuator, commutator and others.

추론 비용 감소를 위한 Jess 추론과 시멘틱 웹 RL기반의 모바일 클라우드 상황인식 시스템

The context aware service is the service to provide useful information to the users by recognizing surroundings around people who receive the service via computer based on computing and communication, and by conducting self-decision. But CAS(Context Awareness System) shows the weak point of small-scale context awareness processing capacity due to restricted mobile function under the current mobile environment, memory space, and inference cost increment. In this paper, we propose a mobile cloud context system with using Google App Engine based on PaaS(Platform as a Service) in order to get context service in various mobile devices without any subordination to any specific platform. Inference design method of the proposed system makes use of knowledge-based framework with semantic inference that is presented by SWRL rule and OWL ontology and Jess with rule-based inference engine. As well as, it is intended to shorten the context service reasoning time with mapping the regular reasoning of SWRL to Jess reasoning engine by connecting the values such as Class, Property and Individual which are regular information in the form of SWRL to Jess reasoning engine via JessTab plug-in in order to overcome the demerit of queries reasoning method of SparQL in semantic search which is a previous reasoning method.

An Experimental Investigation on Initial Plasma Characteristics of Triggered Vacuum Switch

The trigger characteristics of triggered vacuum switch are significantly influenced by initial plasma. An RC charge collector is designed based on the frequency spectrum characteristics of the initial plasma current, and the emission charge characteristics of the initial plasma are analyzed. The experimental results indicate the following: The RC charge collector is suitable to collect the charge of the initial plasma at R = 5 Ω and C = 300 nF, the charge of the initial plasma includes electrons and ions, the electrons are slightly more than the ions, the charge of the initial plasma increases linearly at the beginning with the increment of the charging voltage of the trigger circuit and the trigger current and then ascends gradually to a plateau under a gap space of 4 mm, and the charge of the initial plasma exponentially decreases with the increment of the gap space below 4 mm and then tardily drops to a stable value with the gap space continuingly increasing.

Assimilation of pCO2 data into a global coupled physical‐biogeochemical ocean model

As part of the CARBOOCEAN project, measurements of the partial pressure of carbon dioxide (pCO2) in the ocean have been collected since 2001. Our aim was to use these data in a data assimilation context to improve the representation of pCO2 and its associated prognostic variables in biogeochemical models. Based upon a sequential framework a new method for the assimilation of pCO2 data was developed. This method had to account for oceanic pCO2 being a derived quantity with a functional dependence on temperature, salinity, dissolved inorganic carbon (DIC), and alkalinity. Our method calculates pCO2 increments using an analysis correction technique and then converts these into increments in model variables. Temperature and salinity are assumed to be error free, and so only DIC and alkalinity are updated. Furthermore, in DIC and alkalinity space increments are taken to be perpendicular to the local line of constant pCO2. Our method was tested by assimilating pCO2 data from 2006 into the NEMO‐HadOCC biogeochemical model and then comparing the output from this model to a control with no pCO2 assimilation. While lack of data prevented the assimilation system from correcting a significant systematic error in the subpolar North Atlantic, results from this experiment showed that pCO2 assimilation, despite limited data, reduced RMS and mean errors and also brought the model closer to climatology in the subtropical North Atlantic.

Estudio experimental del empuje sobre estructuras de contención en suelos reforzados con geomallas

This article presents an experimental study on the variation with depth of the stresses due to lateral earth pressure on a wall retaining a soil reinforced with geogrids. To this end, an apparatus was designed and constructed especially tailored for performing lateral earth pressure tests under plain strain conditions. The experimental apparatus and the measurement instruments as well as the soil and the sample preparation and the geogrids used, are described. In a first stage of research, samples without reinforcing are tested and the results are compared with those from classic earth pressure theories. Subsequently, results from lateral earth pressure tests in soils reinforced with one, two, three and four geogrids are presented. It is concluded that the inclusion of geogrids as soil reinforcement reduces the earth pressure on the retaining structure. This lateral earth pressure reduction is approximately of 25% when one geogrid is used, 50% with two or three geogrids and 75% with four geogrids for the spacing, surcharges and displacement increments used. It was possible to identify that the lateral earth pressure distribution with depth not only does not follow a triangular variation, but it develops stress arching in the soil and between the geogrids.

Simulation of Trough Withering of Tea using One Dimensional Heat and Mass Transfer Finite Difference Model

One-dimensional heat and mass transfer mathematical model was developed to simulate moisture content of tea leaves during trough withering. Model solutions were approached using finite difference method with appropriate boundary conditions. A computer program written in QBASIC was used to calculate the real time moisture content of tea leaves and other psychometric parameters of conditioned air during withering. Four experiments were performed using commercial type of withering trough to validate the developed model. Leaf samples were drawn from top, middle and bottom layers of the leaf bed in the trough for one-hour time interval for 12 h of the test period. Simulated moisture data calculated by the program was compared with the experimental data. Time and space increments of the model were chosen minimizing the estimation error of moisture content. Results showed that the experimental and simulated moisture data were in close agreement for top, middle and bottom layers of the withering trough with standard errors in the range of 0.2940&ndash;1.2872, 0.7148&ndash;1.1025 and 0.7106&ndash;4.5478, respectively on percent wet basis. <strong>Keywords</strong>: Fresh tea leaves; one dimensional heat and mass transfer model; withering trough DOI: <a href="http://dx.doi.org/10.4038/tar.v22i3.3701">http://dx.doi.org/10.4038/tar.v22i3.3701</a> <em>Tropical Agricultural Research </em>22(3) (2011) 282-295

Row spacing effect on leaf area development, light interception, crop growth and grain yield of summer soybean crops in Northern China

We investigated the effect of row spacing on the structure and radiation utilization efficiency of summer soybean crops in Northern China during the 2006 and 2007 growing seasons. The experiment consisted of 5 planting patterns resulting in the same plant population density (3.09 × 105 plant/ha), where row spacing was 18, 27, 36, 45 and 54 cm. We observed a significant negative correlation between DM weight and row spacing in both years. Dry matter was mainly allocated to the middle-lower strata of the canopy. The LAI of all treatments decreased with row spacing increments. At podding stage, PAR interceptionratio showed a minimum at 12:00 and decreased with row spacing between 11:00 to 13:00. The RUE of row spacing 18 and 27 cm was significantly higher than those of other treatments. There was a significant positive correlation between seed number and plant growth rate. The yield of row spacing 18 and 27 cm were significantly higher than those of row spacing 45 and 54 cm. The results indicate that summer soybean population of relatively uniform distribution could improve population structure, increases the PAR interception and RUE under rainfed agriculture in Northern China. Key words: Glycine max, dry matter, radiation utilization efficiency, growth, development.

Turbulent phenomena in protein folding

Protein folding and hydrodynamic turbulence are two long-standing challenges, in molecular biophysics and fluid dynamics, respectively. The theories of these phenomena have been developed independently and used different formalisms. Here we show that the protein folding flows can be surprisingly similar to turbulent fluid flows. Studying a benchmark model protein (an SH3 domain), we have found that the flows for the slow folding trajectories of the protein, in which a partly formed N- and C-terminal β sheet hinders the RT loop from attaching to the protein core, have many properties of turbulent flows of a fluid. The flows are analyzed in a three-dimensional (3D) space of collective variables, which are the numbers of native contacts between the terminal β strands, between the RT loop and the protein core, and the rest of the native contacts. We have found that the flows have fractal nature and are filled with 3D eddies; the latter contain strange attractors, at which the tracer flow paths behave as saddle trajectories. Two regions of the space increment have been observed, in which the flux variations are self-similar with the scaling exponent h=1/3, in surprising agreement with the Kolmogorov inertial range theory of turbulence. In one region, the cascade of protein rearrangements is directed from larger to smaller scales (net folding), and in the other, it is oppositely directed (net unfolding). Folding flows for the fast trajectories are essentially "laminar" and do not have the property of self-similarity. Based on the results of our study, we infer, and support this inference by simulations, that the origin of the similarity between the protein folding and turbulent motion of a fluid is in a cascade mechanism of structural transformations in the systems that underlies these phenomena.

A Non-Gaussian Ensemble Filter Update for Data Assimilation

Abstract A deterministic square root ensemble Kalman filter and a stochastic perturbed observation ensemble Kalman filter are used for data assimilation in both linear and nonlinear single variable dynamical systems. For the linear system, the deterministic filter is simply a method for computing the Kalman filter and is optimal while the stochastic filter has suboptimal performance due to sampling error. For the nonlinear system, the deterministic filter has increasing error as ensemble size increases because all ensemble members but one become tightly clustered. In this case, the stochastic filter performs better for sufficiently large ensembles. A new method for computing ensemble increments in observation space is proposed that does not suffer from the pathological behavior of the deterministic filter while avoiding much of the sampling error of the stochastic filter. This filter uses the order statistics of the prior observation space ensemble to create an approximate continuous prior probability distribution in a fashion analogous to the use of rank histograms for ensemble forecast evaluation. This rank histogram filter can represent non-Gaussian observation space priors and posteriors and is shown to be competitive with existing filters for problems as large as global numerical weather prediction. The ability to represent non-Gaussian distributions is useful for a variety of applications such as convective-scale assimilation and assimilation of bounded quantities such as relative humidity.