Linear and Non Linear Models

Numerical modelling of turbulence plays a crucial role in providing accurate microscale wind fields which are necessary to predict transport and dispersion of pollutants in the vicinity of buildings reliably. Although more elaborate turbulence models have been developed, two-equation turbulence models are widely applied in atmospheric flow and dispersion models. The large CPU time required for direct numerical simulation (DNS) and large eddy simulation (LES) still prohibits their application to microscale wind flow simulations of practical interest. In this study, the results obtained by the microscale model MIMO for the three-dimensional flow around a surface mounted cubical obstacle, using different two-equation turbulence models, are discussed. The accuracy of the investigated turbulence models is assessed by comparing the numerical results with wind tunnel measurements.

Numerical modelling of turbulence plays a crucial role in providing accurate wind fields, which are necessary to predict transport and dispersion of pollutants in the vicinity of buildings reliably. Although the standard k-e has some well-known deficiencies and more elaborate turbulence models have been developed it is still by far the most widely applied in atmospheric flow and dispersion models. The large CPU time requirement of direct numerical simulation (DNS) and large eddy simulation (LES) still prohibits their application to wind engineering problems of practical interest. Many linear two-equation turbulence models have been proposed in recent years to overcome the deficiencies of the standard k-e turbulence model. However, comparison shows that none achieves much greater accuracy in all regions of typical wind engineering flow fields. In this paper, a new nonlinear turbulence model is proposed which leads to improved results compared to a conventional eddy-viscosity scheme. The flows considered for the validation of the new model range from simple shear and boundary layer flows, to flows around arrays of cubic obstacles. The accuracy of the proposed turbulence model is assessed by comparing the numerical results with wind-tunnel measurements.

Data centers are large-scale, energy-hungry infrastructure serving the increasing computational demands as the world is becoming more connected in smart cities. The emergence of advanced technologies such as cloud-based services, internet of things (IoT), and big data analytics has augmented the growth of global data centers, leading to high energy consumption. This upsurge in energy consumption of the data centers not only incurs the issue of surging high cost (operational and maintenance) but also has an adverse effect on the environment. Dynamic power management in a data center environment requires the cognizance of the correlation between the system and hardware-level performance counters and the power consumption. Power consumption modeling exhibits this correlation and is crucial in designing energy-efficient optimization strategies based on resource utilization. Several works in power modeling are proposed and used in the literature. However, these power models have been eva...

For semi-submersible units, the magnitude of air gap or local wave impact in the survival condition is a key design driver. Linear analyses are widely used in the industry to predict survival air gap for semi-subs. Large relative motions, leading to large changes in shape of the submerged hull and large changes in water plane area make this approach questionable.In this paper, the GG5000, a twin pontoon four legged semi-sub is considered. Both linear analyses and model tests had been performed, but the results were diverging. It was decided to investigate further, using non-linear hydrodynamic analyses.Initially, the model test setup is reproduced in the numerical model. The simulation model is verified for both response power spectra and extreme response distributions. In the non-linear simulations, the wetted surface of the hull is updated for each time step. Both excitation and restoring forces are based on the instantaneous wetted surface. This proves essential for the prediction of large motions. Later, the verified simulation model is run with realistic full scale setup including elastic catenary moorings with coupled cable dynamics, thruster assist, irregular waves and irregular wind.Highly non-linear effects proven to be vital to accurate air gap prediction are investigated and their representation in the non-linear analyses is validated against model tests.

Cities are complex, networked and continuously changing social ecosystems, shaped and transformed through the interaction of different interests and ambitions. They are linked to places, where various aspects of past events are projected and expressed by means of personal memories and narrations (urban memory), representing a promise for future: a vision of freedom, creativity, opportunity and prosperity. At the same time, technology is currently promoting unprecedented changes in urban areas, which are often marked as smart city developments. This paper studies the history of cultural and creative industries, bringing forward the dedicated digital storytelling strategies that promote active audience engagement in urban cultural heritage. A collaborative model is proposed and analyzed (in multiple perspectives), aiming at providing an integrated manner for heritage documentation, management and dissemination. The development deals with the Digital City of Thessaloniki, Greece, a big city, not a boundless one, rich in culture, but with rather poor heritage management mechanisms. The research focuses on theoretical and practical aspects for the citizens' collection and interpretation of "digital heritage" documents (artifacts, places, etc.), resulting in a model that fuels audience engagement and collaboration of cultural organizations. Model-design is validated through state-of-the-art review and formative evaluation processes (both qualitative and quantitative), with an associated SWOT analysis that points out strengths, weaknesses, opportunities and threats. Although the proposed methodology has been adapted to the needs of a particular (digital) city, the current paper goes beyond a case study, as it brings forward novel technological and methodological guidelines, which could be successfully deployed in districts with similar cultural, geographical, and technical features.

Universities are isomorphic not because of the effectiveness of their processes but because of the legitimacy assigned by institutional logic. However, sustainable development discourses invoke a novel mission for producing knowledge and innovation for sustainable development. Accordingly, this research collected data from five types of internal stakeholders' intellections of the four pillars of green university infrastructure. The analysis of data collected from 89 university stakeholders sufficient for a 90% confidence level with 5% relative tolerable error was organized as five groups in a contingency table for the chi-square test. The statistical analysis, that is, the chi-square value, indicates that all five stakeholders perceive in the same direction – that the four pillars of the green university soft infrastructure need to be reconfigured to produce green knowledge and innovation. Hence, the findings inspire the conventional universities and policymakers to transform th...

Cities are complex, networked and continuously changing social ecosystems, shaped and transformed through the interaction of different interests and ambitions. They are linked to places, where various aspects of past events are projected and expressed by means of personal memories and narrations (urban memory), representing a promise for future: a vision of freedom, creativity, opportunity and prosperity. At the same time, technology is currently promoting unprecedented changes in urban areas, which are often marked as smart city developments. This paper studies the history of cultural and creative industries, bringing forward the dedicated digital storytelling strategies that promote active audience engagement in urban cultural heritage. A collaborative model is proposed and analyzed (in multiple perspectives), aiming at providing an integrated manner for heritage documentation, management and dissemination. The development deals with the Digital City of Thessaloniki, Greece, a big city, not a boundless one, rich in culture, but with rather poor heritage management mechanisms. The research focuses on theoretical and practical aspects for the citizens' collection and interpretation of "digital heritage" documents (artifacts, places, etc.), resulting in a model that fuels audience engagement and collaboration of cultural organizations. Model-design is validated through state-of-the-art review and formative evaluation processes (both qualitative and quantitative), with an associated SWOT analysis that points out strengths, weaknesses, opportunities and threats. Although the proposed methodology has been adapted to the needs of a particular (digital) city, the current paper goes beyond a case study, as it brings forward novel technological and methodological guidelines, which could be successfully deployed in districts with similar cultural, geographical, and technical features.

This paper deals with the turbulence closure problem associated with the Reynolds-averaged Navier-Stokes equations for compressible flows. Due to the known limitations faced by the turbulent closure model based on the Boussinesq hypothesis, additional tensors are needed in order to capture the complete Reynolds stress tensor. Models such as this are in the group of the so-called nonlinear eddy viscosity models. The methodology here presented consists mainly in translating the coefficients obtained via orthogonal projection of the Reynolds stresses that are calculated from a large eddy simulation onto a given basis of tensors. In addition, these coefficients can be seen as turbulent parameters which have analogous interpretation in a class of non-Newtonian fluids. The proposed closure, expressed in terms of the mean strain-rate and its Gordon-Schowalter convected derivative, has a concise and clear physical interpretation. In addition to the turbulent viscosity, parameters associated with the Gordon-Schowalter convected derivative are incorporated to help the interpretation of the nonlinear turbulent model. The methodology is applied to a compressible flow through a narrow channel with a series of holes of cylindrical shape. This configuration is representative of what is generally found in a Hole-Pattern turbomachinery seal. Different number of holes are tested in order to evaluate the influence of neighborhood holes in the analysis. The comparison between the Boussinesq hypothesis and the extended model shows how the latter one outperforms the former. Even though the nonlinear model has shown some limitations, there are still tensorial subspaces of the Reynolds stress tensor obtained from the LES approach that the present nonlinear model could not reach. In addition, the physical coefficients did not present strong similarities for the different configurations tested, what can be a challenge for constructing a complete closure model.

Data centers are large-scale, energy-hungry infrastructure serving the increasing computational demands as the world is becoming more connected in smart cities. The emergence of advanced technologies such as cloud-based services, internet of things (IoT), and big data analytics has augmented the growth of global data centers, leading to high energy consumption. This upsurge in energy consumption of the data centers not only incurs the issue of surging high cost (operational and maintenance) but also has an adverse effect on the environment. Dynamic power management in a data center environment requires the cognizance of the correlation between the system and hardware-level performance counters and the power consumption. Power consumption modeling exhibits this correlation and is crucial in designing energy-efficient optimization strategies based on resource utilization. Several works in power modeling are proposed and used in the literature. However, these power models have been evaluated using different benchmarking applications, power-measurement techniques, and error-calculation formulas on different machines. In this work, we present a taxonomy and evaluation of 24 software-based power models using a unified environment, benchmarking applications, power-measurement techniques, and error formulas, with the aim of achieving an objective comparison. We use different server architectures to assess the impact of heterogeneity on the models’ comparison. The performance analysis of these models is elaborated in the article.

Universities are isomorphic not because of the effectiveness of their processes but because of the legitimacy assigned by institutional logic. However, sustainable development discourses invoke a novel mission for producing knowledge and innovation for sustainable development. Accordingly, this research collected data from five types of internal stakeholders' intellections of the four pillars of green university infrastructure. The analysis of data collected from 89 university stakeholders sufficient for a 90% confidence level with 5% relative tolerable error was organized as five groups in a contingency table for the chi-square test. The statistical analysis, that is, the chi-square value, indicates that all five stakeholders perceive in the same direction – that the four pillars of the green university soft infrastructure need to be reconfigured to produce green knowledge and innovation. Hence, the findings inspire the conventional universities and policymakers to transform th...

Efficient stock market plays important role in stimulating economic development through providing channel for mobilising domestic savings and facilitating the allocation of financial resources from dormant to more productive activities. This paper evaluates the Ugandan Securities Exchange (USE) for evidence of weak-form efficient market hypothesis in the context of random walk model, using both linear and non-linear models. Preliminary analysis from the USE daily returns, for the 01 September 2011 to 31 December 2016 period, show negative skewness, leptokurtosis, and non-normal distribution. Estimates from the linear models show evidence of weak-form efficiency. Conversely, estimates from non-linear models show evidence against weak-form efficiency of the USE. The study concludes that USE returns may only be predicted using non-linear models and fundamental analysis. In order words, linear models and technical analysis may be clueless for predicting future returns.

This paper uses a case based study-"product sales estimation" on real-time data to understand the applicability of linear and non-linear models. We use a systematic approach to address the given problem statement of sales estimation for a given product by applying both linear and non-linear techniques on a data set of selected features from the original data set. Feature selection is a process that reduces the dimensionality of the data set by eliminating those features which contribute minimal to the prediction of the dependent variable. The next step is training the model which is done using two techniques from linear & non-linear domains, one of the best ones in their respective areas. Data Re-modeling has then been done to extract new features from the data set by changing the structure of the dataset & the performance of the models is checked again. Data Remodeling often plays a crucial role in boosting classifier accuracies by changing the properties of the dataset. We then try to analyze the reasons due to which one model proves to be better than the other & hence try and develop an understanding about the applicability of linear & non-linear models. The target mentioned above being our primary goal, we also aim to find the classifier with the best possible accuracy for product sales estimation in the given scenario.

This document discusses the evaluation of a consolidated linear performance model of Texas State University's HPC LEAP Cluster, and the development of a non-linear model to represent the performance of the NVIDIA V100 Graphics Processing Unit (GPU). The consolidated model constructed for the LEAP Cluster was evaluated by using it to compute execution times for different sizes of processes and comparing those times to the actual processes run on LEAP. The model itself is found to effectively represent the performance trends of LEAP but fail to match the actual value. The GPU's performance analysis was done by first collecting performance data then using non-linear methods to model it. The number of floating-point operations required to perform a square matrix multiplication is readily known, so the performance data was gathered by running a simple square matrix multiplication program and measuring its execution time. The size of the matrices was then used to determine the num...

Understanding conservation needs relies on robust estimates of key population parameters, such as survival, abundance and somatic growth. We investigated the somatic growth and abundance dynamics of 2 aggregations of immature green turtles, at Tortuga Bay and Puerto Manglar (Culebra, Puerto Rico), throughout 15 yr of capture-mark-recaptures. We used nonlinear models to investigate the effects of carapace length, sampling year, growth interval and the presence of fibropapillomas on growth rates, and used the size-specific growth rate function to estimate how long turtles remain at each bay. Abundances were estimated and compared with timespecific growth rate functions, to infer density-dependency effects on somatic growth rates, and trends in abundance were evaluated by fitting generalized linear models. We found foraging site specific growth rates and report the highest mean somatic growth rate for green turtles in the wild (6.1 ± 1.7 cm yr −1 , at Puerto Manglar). The size-specific growth rate function was monotonic at both sites, with growth rates declining continuously with increasing carapace length. We inferred minimum ages at maturity of 14 and 22 yr, for Puerto Manglar and Tortuga Bay turtles, respectively. Throughout the 15 yr of this study there was a positive trend in aggregation size at Puerto Manglar (mean annual increase of 10.9%), which was not observed at Tortuga Bay. Our study highlights the influence of geography and habitat quality on somatic growth rates, and delivers robust demographic estimates valuable for local and regional assessments of the conservation status of the green turtle.

An increasing number of engineering applications require accurate predictions of the flow around buildings to guarantee performance and safety. This paper investigates the effects of variations in the turbulent inflow, as predicted in different numerical simulations, on the flow pattern prediction around buildings, compared to wind tunnel tests. Turbulence characteristics were assessed at several locations around a model square high-rise building, namely, above the roof region, at the pedestrian level, and in the wake. Both Reynolds-averaged Navier–Stokes (RANS, where turbulence is fully modelled) equations and large-eddy simulation (LES, where turbulence is partially resolved) were used to model an experimental setup providing validation for the roof region. The performances of both techniques were compared in ability to predict the flow features. It was found that RANS provides reliable results in regions of the flow heavily influenced by the building model, and it is unreliable w...

The present work is a numerical simulation of flow over buildings. The numerical simulation was carried out using an open source Computational Fluid Dynamics (CFD) tool called OpenFOAM®. The Reynolds Averaged Navier Stokes Equations (RANS) was solved along with a two-equation turbulent closure. The solutions from the numerical simulations are post-processed with open source software namely Paraview which is based on Visualisation Tool Kit (VTK). Effect of flow over buildings is described in terms of contours of velocity. Further, the same data is processed with Line Integral Convolution (LIC) to reveal three-dimensional flow properties on a plane parallel to the inlet flow. The streamlines are visualised in addition to the LIC and velocity contours. The post processed results reveal the real flow physics with just LIC alone or with the help of streamlines and contours.

This paper presents a study of the hydraulic behaviour of a gully under surcharge conditions using both numerical and experimental models. These results can be useful for the validation of the linking elements in Dual Drainage (DD) models, recently created. The final numerical results for the gully were obtained using the grid generator SALOME Platform and the Computational Fluid Dynamics (CFD) model OpenFOAM TM. Experiments were carried out in a 8 m long and 0.5 m wide channel, fitted with a 600 x 300 x 300 [mm] gully and a gully outlet with a 80 mm diameter pipe that works as inlet in this study. The selected solver, mesh size and contraction at the bottom inlet allowed for an adequate modelling of the gully under surcharge conditions. The experimental and numerical results are in good agreement.

This document discusses the evaluation of a consolidated linear performance model of Texas State University's HPC LEAP Cluster, and the development of a non-linear model to represent the performance of the NVIDIA V100 Graphics Processing Unit (GPU). The consolidated model constructed for the LEAP Cluster was evaluated by using it to compute execution times for different sizes of processes and comparing those times to the actual processes run on LEAP. The model itself is found to effectively represent the performance trends of LEAP but fail to match the actual value. The GPU's performance analysis was done by first collecting performance data then using non-linear methods to model it. The number of floating-point operations required to perform a square matrix multiplication is readily known, so the performance data was gathered by running a simple square matrix multiplication program and measuring its execution time. The size of the matrices was then used to determine the number of floating-point operations and divided by the execution time to calculate FLOPS. The final model for the GPU was generated by using a set of logarithmic functions that mapped the GPU performance to a semi-logarithmic scale of the number of floating-point operations.

Cities are complex, networked and continuously changing social ecosystems, shaped and transformed through the interaction of different interests and ambitions. They are linked to places, where various aspects of past events are projected and expressed by means of personal memories and narrations (urban memory), representing a promise for future: a vision of freedom, creativity, opportunity and prosperity. At the same time, technology is currently promoting unprecedented changes in urban areas, which are often marked as smart city developments. This paper studies the history of cultural and creative industries, bringing forward the dedicated digital storytelling strategies that promote active audience engagement in urban cultural heritage. A collaborative model is proposed and analyzed (in multiple perspectives), aiming at providing an integrated manner for heritage documentation, management and dissemination. The development deals with the Digital City of Thessaloniki, Greece, a big city, not a boundless one, rich in culture, but with rather poor heritage management mechanisms. The research focuses on theoretical and practical aspects for the citizens' collection and interpretation of "digital heritage" documents (artifacts, places, etc.), resulting in a model that fuels audience engagement and collaboration of cultural organizations. Model-design is validated through state-of-the-art review and formative evaluation processes (both qualitative and quantitative), with an associated SWOT analysis that points out strengths, weaknesses , opportunities and threats. Although the proposed methodology has been adapted to the needs of a particular (digital) city, the current paper goes beyond a case study, as it brings forward novel technological and methodological guidelines, which could be successfully deployed in districts with similar cultural, geographical, and technical features.

In the present paper, the analysis of concentration and flow fields around a model building was performed using two different approaches in turbulence modeling. In the first approach, the non-linear model of Ehrhard and Moussiopoulos was employed as one of the best cubic non-linear eddy viscosity models, and large eddy simulation was utilized in the second approach. The obtained results suggest that although the non-linear model has the ability to predict the anisotropic normal components of Reynolds stress tensor, due to time-averaged nature of its governing equations, it is incapable of estimating the correct values of Reynolds stress components and turbulent characteristics in the wake region of the model building. So the predicted turbulence kinetic energy values by the non-linear model are 45% smaller than those of large eddy simulation approach in the wake region behind the model building. Also different predictions of the wake region structure by the non-linear model and large eddy simulation approach revealed that elongation of iso-surface for K h i = 1.5 in non-linear model is 56% more than that of large eddy simulation approach. The large eddy simulation approach shows much consistent behavior to the physics governing the flow compared to the non-linear model. Also good agreement observed between the results obtained through this approach and the experimental data. However, the disadvantage of large eddy simulation approach is the high computational costs.

During the last decade, there has been an increased interest on cloud computing and especially on the adoption of public cloud services. The process of developing cloud-based public services or migrating existing ones to the Cloud is considered to be of particular interest—as it may require the selection of the most suitable applications as well as their transformation to fit in the new cloud environment. This paper aims at presenting the main findings of a migration process regarding Smart City applications to a cloud infrastructure. First, it summarises the methodology along with the main steps followed by the cities of Agueda (Portugal), Thessaloniki (Greece) and Valladolid (Spain) in order to implement this migration process within the framework of the STORM CLOUDS project. Furthermore, it illustrates some crucial results regarding monitoring and validation aspects during the empirical application that was conducted via these pilots. These findings should be received as a helpful experience for future efforts designed by cities or other organisations that are willing to move their applications to the Cloud.

Understanding conservation needs relies on robust estimates of key population parameters, such as survival, abundance and somatic growth. We investigated the somatic growth and abundance dynamics of 2 aggregations of immature green turtles, at Tortuga Bay and Puerto Manglar (Culebra, Puerto Rico), throughout 15 yr of capture-mark-recaptures. We used nonlinear models to investigate the effects of carapace length, sampling year, growth interval and the presence of fibropapillomas on growth rates, and used the size-specific growth rate function to estimate how long turtles remain at each bay. Abundances were estimated and compared with time-specific growth rate functions, to infer density-dependency effects on somatic growth rates, and trends in abundance were evaluated by fitting generalized linear models. We found foraging site specific growth rates and report the highest mean somatic growth rate for green turtles in the wild (6.1 ± 1.7 cm yr−1, at Puerto Manglar). The size-specific growth rate function was monotonic at both sites, with growth rates declining continuously with increasing carapace length. We inferred
minimum ages at maturity of 14 and 22 yr, for Puerto Manglar and Tortuga Bay turtles, respectively. Throughout the 15 yr of this study there was a positive trend in aggregation size at Puerto Manglar (mean annual increase of 10.9%), which was not observed at Tortuga Bay. Our study highlights the influence of geography and habitat quality on somatic growth rates, and delivers robust demographic estimates valuable for local and regional assessments of the conservation status of the green turtle.