Analytical Modeling Approach Research Articles

Experimental and numerical study of bond between masonry and near-surface mounted steel bars

This addresses the bond between masonry and near surface mounted steel bars through experimental and numerical investigation. In the experimental program, 12 masonry prisms were prepared from commercial clay bricks and were strengthened using NSM steel bars fixed by cement mortar or epoxy; the prisms were subjected to pull-out testing and the failure loads and modes were studied. Numerical modeling and nonlinear analysis were made for the tested prisms using commercial software ANSYS.V.15. Comparison between experimental and numerical results showed good agreement regarding failure loads and failure modes which validates the efficiency of the adopted numerical modeling and nonlinear analysis approach. The numerical analysis showed that the widespread assumption of perfect bond between the strengthening bars and masonry gives misleading results, and therefore the behavior and resistance of the interface between steel bars and mortar/epoxy or between the mortar/epoxy and masonry should be adequately included in the modeling. Moreover, a numerical study was conducted to investigate the influence of several variables, namely the bar diameter and the embedment length, on the bond between NSM steel bars and masonry elements. The numerical study revealed that the failure load obviously increases with increase of embedment length and slightly with increasing the steel bar diameter.

An approach to model manufacturing of an enhanced swing differential Colpitts oscillator based on heterostructures to increase density of their elements with account mismatch-induced stress: on optimization of annealing

In this the paper, we consider an approach for increasing of density of field-effect transistors, which comprised of an enhanced swing differential Colpitts oscillator. Based on this approach, we describe manufacture of this oscillator in a heterostructure with a specialized structure. Doping of some specific regions of the considered heterostructure should be done by using diffusion type of doping or by ion type of doping. After the doping, dopant and radiation defects will be annealed by the used optimized procedure. We also will consider an approach of decreasing of mismatch-induced stress value in this heterostructure. We introduce an analytical approach for modeling of mass and heat transport in multilayer structures during manufacturing of integrated circuits taking into account mismatch-induced stress.

Improved Frequency-Domain Steady-State Modeling of the Dual-Active-Bridge Converter Considering Finite ZVS Transition Time Effects

This article presents an improved analytical modeling (IAM) approach for the dual-active-bridge (DAB) converter in the frequency-domain. Specifically, finite transition times are incorporated into the improved modeling that are significant in DAB converters operated at high frequency. The IAM approach is first motivated by comparing traditional frequency-domain modeling against realistic simulation results in LTspice. Next, the IAM approach is mathematically developed in an iterative fashion, where the conventional frequency-domain approach is used as the initialization of the operational behavior of the converter. Subsequent iterations of the IAM algorithm incorporate finite rise- and fall-times of device output capacitances based on detailed switching behavior analyses, which may considerably perturb the desired modulation parameters (i.e., phase shift and zero states). While the initially proposed IAM approach demonstrates advantages over ideal modeling, it is still shown to exhibit errors when applied to device transitions with significant nonlinearity in parasitic output capacitance. To account for this, a three-slope approximation to the switching transition is then motivated and developed, which enables significantly improved steady-state prediction accuracy. Simulation and experimental results confirm unacceptable inaccuracies associated with the conventional frequency-domain modeling across a wide range of operating conditions, alongside enhanced accuracy provided by the proposed modeling approach.

Macro-Modelling Approach for the In-Plane Cyclic Response of Cold-Formed Steel Partition Walls

Past earthquakes demonstrate that non-structural elements could be vulnerable to a relatively low intensity ground shaking which induces negligible structural damage. The study aims to improve previously developed macro-models of cold-formed steel (CFS) partition walls to properly capture their in-plane cyclic response and damage states of important components in a CFS partition wall under imposed excitation. An effective analytical modelling approach is adopted for a simple modelling procedure and less computational effort. The proposed analysis model of partition walls consisting of several lumped spring elements is verified using direct comparison with two full scale CFS partition wall tests. The analytical and experimental results are compared in terms of force–displacement relations, dissipated energy, and an influential damage mechanism of components consisting of partition walls. The comparison shows that the analytical model well captures the experimental response such as the overall strength and stiffness degradation and pinching behavior. Moreover, the damage mechanism predicted by the analytical model is in good agreement with that observed during the tests.

Can Positive Affective Variables Mediate Intervention Effects on Physical Activity? A Systematic Review and Meta-Analysis

Well-developed theories are necessary to guide the public in increasing physical activity (PA) and promoting physical health. The role of positive affective variables (PAVs) in exercise is gaining more attention, but none of the literature has provided a systematic review and quantitative analysis of its mediating role. Therefore, the purposes of this study are (1) to systematically review studies of PA interventions, that use PAVs as the mediating variables, in order to evaluate and provide narrative summaries of these studies; (2) to statistically synthesize evidence for the mechanism of the effects of PAVs on PA outcomes. To conduct an extensive search, a PRISMA-compliant protocol was completed, and five electronic databases had been searched by 1 April 2020. We used a two-stage structural equation modeling (TSSEM) analysis approach to test how interventions trigger the critical PA change process to influence outcomes. The search strategy generated 1,732 papers potentially relevant to this study; forty of these studies met the data extraction criteria for meta-analytic mediation analysis. The path coefficient from intervention to PAV a = 0.26 (95% CI = 0.08 to 0.44), the path coefficient from PAV to PA b = 0.21 (95% CI = 0.13 to 0.28), and the direct effect from intervention to PA is also significant (c = 0.19, 95% CI = 0.12 to 0.26). In addition, the indirect effect of intervention on PA via PAV was statistically significant (c' = 0.05, 95% CI = 0.02 to 0.10). This reveals that PAVs partially mediate the relationship between interventions and PA. Our study is the first to systematically summarize the effects of experimental studies to increase PA through PAVs. It is highly recommended to make future interventions more innovative and to target the PAVs as mediators with higher fidelity.

Effect of Modeling Beam-Column Joints on Performance Assessment of Columns in Non-Ductile RC Frames

Seismic performance evaluation of non-seismically detailed reinforced concrete buildings requires proper analytical modeling approaches for beam-column joints which are most vulnerable parts. This study investigates the influence of beam column joint modeling assumptions on performance evaluation of non-ductile RC buildings. Numerical simulation model includes truss-based elements for beam-column connections and fiber-based elements for beams and columns. Two-dimensional four- and six- story reinforced concrete frames of an existing RC building are designed and analyzed by conducting incremental dynamic analyses. Column chord rotations and corresponding strains are compared with code provisions for performance assessment of non-ductile RC frames.

Incorporation of Stress Time Dependence into Failure Projection Modeling of Corroding Bridge Post-Tensioning Tendons

Post-tensioning (PT) has evolved to become an important technology for designing long span bridge structures. However, tendon failures resulting from wire/strand corrosion have been reported as early as 2 y post construction. In response to this, a recent study introduced and evaluated an analytical modeling approach that projects corrosion-induced wire and strand fractures and tendon failures, given statistics that characterize wire corrosion rate. This past modeling effort assumed that tensile stress in tendons was constant with time at 63% of the guaranteed ultimate tensile strength (GUTS); however, in actuality this stress decreases with time over an assumed 10,000 d (approximately 27 y) from an initial value of about 70% of GUTS to a long-term value in the range 60% to 63% of ultimate at mid-span for a simply supported beam as a consequence of long-term concrete creep and shrinkage and strand relaxation. The present study builds upon this model by incorporating this time dependence of tendon stress into the failure projection modeling. Results are discussed within the context of better understanding bridge tendon integrity issues and corrosion related failure concerns.

Properties relationship evaluation and plasticity analytical model approach for Brazilian tropical species

In anisotropic materials such as wood, different responses to bending induced stresses could be expected. This study evaluated the behavior of properties of modulus of rupture (MOR) in bending, the tension strength parallel to grain and the compression strength parallel to grain of Brazilian tropical hardwood species in accordance with Brazilian, European and International Standards, and an analytical equation considering plasticity in the compressed region. Experimental data were obtained using clear wood specimens and tests on ten species. An analysis of the mechanical behavior was conduced for three strength relationships: bending to compression, bending to tension and tension to compression. Linear regression models were determined using the 5th percentile and compared to the ones found by the standards cited. The experimental results were also evaluated to an analytical equation modified from the moment equilibrium of a cross-section. Of the equations evaluated in this study, the ones suggested by the European and International standards for tension strength from bending strength were the ones which best estimated the 5th percentile on experimental data. Other relationships did not show a good agreement with the equations. The analytical equation used had a mean model error 37.4% higher than the experimental values for the prediction of the ratio of tension to bending strength.

Explicit the urban waterlogging spatial variation and its driving factors: The stepwise cluster analysis model and hierarchical partitioning analysis approach

Urban waterlogging is a hydrological cycle problem that seriously affects people's life and property. Characterizing waterlogging variation and explicit its driving factors are conducive to prevent the damage of such disasters. Conventional methods, because of the high spatial heterogeneity and the non-stationary complex mechanism of urban waterlogging, are not able to fully capture the urban waterlogging spatial variation and identify the waterlogging susceptibility areas. A more robust method is recommended to quantify the variation trend of urban waterlogging. Previous studies have simulated the waterlogging variation in relatively small areas. However, the relationship between variables is often ignored, which cannot comprehensively reveal the dominant drivers affecting urban waterlogging. Therefore, a novel approach is proposed that combined stepwise cluster analysis model (SCAM) and hierarchical partitioning analysis (HPA) within a general framework and verifies the applicability through logistic regression, artificial neural network, and support vector machine. According to the dominant driving factors, different simulation scenarios are established to analyze waterlogging density variation. Results found that the SCAM provides accurate and detailed simulated results both in urban centers where waterlogging frequently occurs and urban fringe with few waterlogging events, which shows an excellent performance with a high classification accuracy and generalization capability. HPA detected that the impervious surface abundance (28.07%), vegetation abundance (20.80%), and cumulate precipitation (16.25%) are the dominant drivers of waterlogging. This result suggests that priority should be given to controlling these three factors to mitigate the risk of waterlogging. It is interesting to note that under different urbanization and rainfall scenarios, the urban waterlogging susceptibility has a considerable variation. The watershed spatial location and watershed characteristics are relevant aspects to be considered in identifying and assessing waterlogging susceptibility, which provides original insights that urban waterlogging mitigation strategies should be developed according to different local conditions and future scenarios.

On the Energy Efficiency of Heterogeneous Cellular Networks With Renewable Energy Sources—A Stochastic Geometry Framework

In this paper, we introduce an analytical approach for modeling and analyzing the performance of multi-tier cellular networks that are powered by the power grid and by renewable energy sources. The proposed approach relies on modeling the locations of the base stations, either powered by the power grid or by renewable energy sources, by using Poisson point processes. The availability of renewable energy is modeled by using a Poisson point process in the time domain. In addition, the temporal dynamics of the batteries of the base stations powered by renewable energy sources are modeled by using a discrete Markov chain with a number of states that is equal to the finite storage capacity of the batteries. In particular, the coverage probability, the spectral efficiency, and the energy efficiency of the considered network model are formulated in an analytical, closed-form, expression, which depends on the probability that the typical base station is available, i.e., it has sufficient power to serve at least one mobile terminal in its cell. This latter probability is shown to be the solution of the steady state equation of the Markov chain that models the temporal dynamics of the batteries of the base stations. Under the assumption that the batteries of the base stations can be either empty or fully charged, we formulate an optimization problem in order to maximize the energy efficiency as a function of the transmit power and the deployment density of the base stations, and identify sufficient conditions for which the problem admits a unique solution. The accuracy of the proposed approach and the performance trends inferred from it are substantiated with the aid of extensive Monte Carlo simulations.

Predicting the permeability and specific surface area of compressed and uncompressed fibrous media including the Klinkenberg effect

In this study a geometric anisotropic two-strut model is presented to predict the permeability of fibrous porous media subject to compression. A further novelty of this study is the inclusion of the Klinkenberg effect in the permeability prediction of the two-strut model and existing three-strut model. The specific surface area of the anisotropic models are predicted by making use of two approaches, i.e. a geometric approach and a combined kinematic-geometric approach. The Klinkenberg effect has also been introduced into the non-compressed models. The model predictions are compared to a variety of available experimental data for non-woven fibre media and metal foams from the literature and the correspondence proves to be satisfactory. The analytical modelling approach presented adds value to the empirical studies in the literature which comprises of curve fitting procedures together with the introduction of empirical coefficients into the Forchheimer or Ergun equations to obtain correlation with experimental data.

Large eddy simulation study of extended wind farms with large inter turbine spacing

We study the performance of extended wind farms with very large inter turbine spacings, i.e. with an inter turbine spacing of more than 10 turbine diameters, using large-eddy simulations (LES) for the special case of neutral conditions. We compare the results with predictions from different analytical modeling approaches and discuss in which parameter regimes the different model predictions agree with the LES predictions. We find in LES that the normalized power output variance increases further downstream in the wind farm. Besides, we analyze the power output correlation between the subsequent downstream turbines. We find that the correlations decrease with increasing turbine spacing due to the increased mixing induced by the wind turbine wakes. For all cases considered here, the power output correlation with downstream turbines becomes negligible after about 40 turbine diameters.

Evaluation of hybridized performance of amine scrubbing plant based on exergy, energy, environmental, and economic prospects: A gas sweetening plant case study

Gas sweetening is a key process in gas refineries. The equipment involved in gas sweetening generally consume a considerable amount of energy, leading to negative impacts in terms of economic and environmental prospects. This research work includes simulation, analytical, and numerical modeling approaches to evaluate exergy, energy, economic, and environmental analysis of a gas sweetening plant (GSP). Various compositions of methyl-di-ethanolamine (MDEA) and di-ethanolamine (DEA) blend are studied to mitigate exergy destruction, energy loss, and CO2 emissions in the sweetening process. According to the results, the absorber and stripper are responsible for 37% of the total exergy destruction and 29% of the total energy loss, respectively. DEA concentration plays an imperative role in exergy and energy management of the GSP. The optimum amine concentration of 40 wt% decreases the total exergy destruction from 6.6 MW to 4.8 MW and lowers the energy loss by 36.7%. This optimization strategy then results in a substantial reduction in CO2 emissions by 2893.6 tons per year (t/y), compared to the current operation state. The economic assessment confirms the profitability of the plant to be operated at the optimal amine concentration. This research study provides an efficient strategy to optimize a variety of industrial plants that include energy consuming sections.

2N-rule: Searching topological phases and robust edge modes in carbon nanotubes

We theoretically report an explicit and robust scheme, 2N-rule, for systematically searching topological phases in carbon nanotubes (CNTs) of all diameters. By investigating the topological Zak phase based on both analytical model and first-principles approaches, such a 2N-rule of insulating CNT(n,0) is generally established: when n=2N, where N is an integer (an even n), it is a topological insulator; otherwise, it is a normal insulator. For finite-length topological CNTs, topologically protected quantum modes naturally occur at the tube ends, which hold significant robustness against external environment perturbations, taking advantage over fragile edge states in conventional systems. The topological CNTs can provide a platform for potential applications in reliable carbon nanoelectronics as well as exploring fundamental science of one-dimensional topological materials.

A fast and accurate generalized analytical approach for PV arrays modeling under partial shading conditions

This paper proposes a generalized analytical approach to model the photovoltaic (PV) arrays under partial shading conditions (PSC). The proposed method is simple: it requires only the standard test condition (STC) parameters of the PV modules and the irradiance level imposed on each module. By using this information, the P-V and I-V curves of shaded PV arrays are obtained by simple steps. Firstly, the current-voltage (I-V) curves for all assembled submodules receiving the same level of irradiance are generated using the two-diode model. The parameters of the latter are computed using a fast parameter extraction method. Secondly, the I-V curve of each shaded string is computed using the computed I-V curves of its submodules. In the last step, the resulted I-V curve of the array is obtained by summation of all I-V strings curves. The proposed method is simple, fast, and can be coded in any development platform. Besides, the prediction accuracy is enhanced by incorporating the real effect of bypass and blocking diodes in the model. Furthermore, the proposed method could be generalized for any number of series/parallel connections in a shaded PV array. The method can be useful to generate critical shading patterns for maximum power point tracking (MPPT) algorithms evaluation. It can also be used as a tool to obtain instant shading patterns in PV array simulators.

Quantitative assessment of nonlinear macro-models for global behavior and design of planar RC walls

Performance-Based Seismic Design (PBSD) procedures require adequate estimation of the global cyclic force–displacement (F-D) behaviors of the primary lateral load-resisting elements. As reinforced concrete (RC) walls constitute one of the most widely used lateral load elements in building construction, several nonlinear analytical modeling approaches have been developed over the past several decades to numerically simulate the hysteretic behavior of these structures. However, comparisons between these models have often provided few details on the model input parameters, have not used consistent model discretization, and have assessed hysteretic predictions more qualitatively than quantitatively. Accordingly, the objectives of this paper are to: 1) provide detailed information on the modeling parameters used to simulate the cyclic lateral F-D behavior of a set of planar RC walls with flexure-dominant as well as shear-dominant behaviors, 2) evaluate the sensitivity of the F-D curves to different wall model discretizations applied consistently between different models, and 3) propose and use a new quantitative approach to assess the hysteretic behaviors predicted by the numerical models. The considered models are PERFORM 3D, MVLEM, SFI-MVLEM, and BTM. To represent the information that is typically known during the design of a structure, the nonlinear modeling parameters were limited to the wall geometry, reinforcing layout, concrete compression strength, and reinforcing steel yield strength, with no calibration of the material behaviors to the reported test results. A total of 2,300 analyses were performed to simulate four slender and four squat previously-tested RC walls. Results of the cyclic lateral F-D predictions were evaluated based on commonly used measures of effective stiffness, maximum strength, and ultimate displacement. Additionally, the hysteretic response of the numerical simulations was assessed by proposing, validating, and using the Modified Nash-Sutcliffe Efficiency (NSEm) metric. Comparisons between the computing times for the models were also made, as well as comparisons of the local nonlinear behavior of a slender wall. Results show that the discretization used in the PERFORM 3D, MVLEM, and SFI-MVLEM simulations did not significantly affect the predicted global response, whereas the discretization did affect the F-D curves from the BTM model. The values of NSEm agreed with qualitative evaluations of the F-D curves and were able to properly evaluate complex cyclic behaviors of RC walls including pinching and stiffness deterioration. The results of this investigation are expected to be used as modeling guidelines of RC walls when conducting PBSD.

Mass transfer during transient condensate vaporization: Experimental and modeling study

The gas condensate reservoirs, which are a major source of energy, usually experience an unwanted phenomenon called liquid drop-out. Gas injection as a proven effective remedy is generally employed to diminish the liquid loss. The condensate recovery by gas injection is typically estimated by assuming local equilibrium. This assumption is not valid in porous media when the limited contact area, high velocity, and low residence time are involved, particularly in near-wellbore region. In this study, we attempt to calculate mass transfer coefficient of the gas condensate systems in porous media at the transient state. Hence, a number of experiments are performed where the tests include three injection gases (CO2, N2, and CH4), three liquid types as condensate components (C5, C6, and C7), and three mean grain sizes (150–300 μm) within a wide range of gas velocity (0.00472–0.0283 cm/s). The experiments are modeled numerically and analytically based on the effluent concentrations. The obtained mass transfer coefficients are then employed to introduce new models such that Sherwood number (Sh) is correlated to Peclet (Pe) and Schmidt (Sc) numbers, and other physical/operational parameters. Based on a systematic sensitivity analysis as well as the modeling results, both analytical and numerical modeling approaches are promising and viable. The statistical parameters are calculated to be 97.13% (R2) and 0.0044 (mean squared error or MSE) for the analytical method, and 97.33% (R2) and 0.00303 (MSE) for the numerical solution, confirming the accuracy and reliability of the employed models. The mass transfer coefficients are then fitted well using three correlations with R2 values of 95.29%, 97.04%, and 96.73%, and absolute relative deviation or ARD magnitudes of 13.22%, 11.73%, and 11.44%. The new proposed correlations can be simply implemented in numerical/analytical modeling and commercial software packages to obtain the non-equilibrium mass transfer coefficients of components in the gas phase. The sensitivity analysis also reveals that condensate shrinkage has a significant effect on the amount of mass transfer and vaporization. Methane shows a relatively higher potential to strip the liquid condensate in comparison with other gases in the experiments. Among the liquid hydrocarbons, pentane has a higher tendency to evaporate into the flowing gas phase, followed by hexane and heptane. It is also found that porous system cases with larger mean grain size offer more suitable conditions for enhancement of mass transfer. The findings of this study can help to better understand the mass transfer during gas injection in gas condensate reserves under transient condition.

Analytical and Numerical Methods to Estimate the Effective Mechanical Properties of Rutherford Cables

Superconducting Nb3Sn Rutherford cables can be used in the accelerator magnets above 10 T regions that cannot be reached with NbTi. These cables are composed of superconducting multifilamentary strands, interstitial epoxy, and insulation materials. To properly design the magnets made from these cables, it is essential to analyze their mechanical behavior. The prerequisite for this is the knowledge of the mechanical performance of Rutherford cables. In large magnets, these cables cannot be modeled with all details but effective properties and homogenization are typically required. In this work, an analytical model and numerical approach for predicting the effective mechanical properties of Rutherford cables are developed. The analytical model is established on a two-step homogenization and mechanical analysis for composite. The effective mechanical properties of the filament area and the transverse Young's modulus of the strand are first determined by means of utilizing the mechanical theory of the unit cell approach. The composite effective mechanical properties of the strand and interstitial epoxy are homogenized in the first step. The second step homogenization derives the effective mechanical properties of the strands epoxy composite and insulation layers. The numerical approach to determine the effective mechanical properties is based on the finite-element analysis. The developed methodologies are used to obtain the effective mechanical properties of two Nb3Sn Rutherford cables. The influence of the insulation thickness and modulus, the strand's modulus, is studied.

Evaluating the potential for bird‐habitat models to support biodiversity‐friendly urban planning

Abstract Urban expansion poses a major threat to wildlife populations. Biodiversity‐friendly urban landscapes could deliver benefits for both wildlife and people, by incorporating conservation and ecosystem services objectives. Well‐designed urban developments could also soften the ecological impacts of urbanization. However, delivering urban landscapes that integrate biodiversity requirements effectively remains challenging. Ecological models, designed to predict wildlife population responses to alternative urban designs, could prove effective in supporting the creation of biodiversity‐friendly urban landscapes. Here, we combine national‐scale bird abundance data with high resolution, spatially explicit habitat data to characterize relationships between bird densities and urban landscape form in Britain. From these analyses and cross validation, we evaluate the potential for well‐parameterized, species‐specific models to be used to predict bird densities in novel or modified urban areas. Our analyses indicate that responses of bird abundance to urban habitat are species‐specific and complex, with few variables consistently affecting a large proportion of species. However, contiguous areas of greenspace within urban sites are preferential for accommodating breeding birds, compared to a more fragmented arrangement of multiple, small greenspace patches. In combination, the bird‐habitat relationships identified could successfully predict observed variation in abundance for most bird species considered. Further evaluation of habitat descriptor variables, spatial scales of species' habitat use and analytical modelling approaches may be needed to improve the predictive ability of bird‐habitat models for certain species, particularly waterbirds and those observed less frequently in urban areas. Synthesis and applications. We modelled breeding bird abundance in built‐up areas with respect to the characteristics and contexts of urban environments. While most variables were important for multiple species, responses overall were species‐specific, so simple assemblage metrics, like diversity, will not describe the variation in bird communities well. However, the results illustrate the potential of an evidence‐based, spatially explicit evaluation of urban development impacts on biodiversity, by predicting the consequences for bird numbers. Subject to verification of predictive ability, practitioners can apply the models to compare, for example, land‐sparing and sharing within developments, or to quantify the biodiversity requirements for effective offsetting. This would be facilitated by incorporation into an online tool allowing user‐determined input scenarios.

Incentives and contract design for knowledge sharing in construction joint ventures

Employing the differential game theory, this study proposes the dynamic incentive model for knowledge sharing in Design-Build joint ventures (DBJVs) under three types of contracts: no cost-sharing contract (NCSC), cost-sharing contract (CSC) and centralized decision-making contract (CDMC). The analytic model and numerical analysis approach are used to compare solutions in the three scenarios. The results indicate that the optimal amount of shared knowledge and the optimal payoff under the CDMC are both the highest. Besides, the leader will offer part of the knowledge sharing cost for the follower if the leader gets more than one-third payoff of the system. Compared with the NCSC, the system payoff under the CSC increases greatly, which is much larger than the payoff increment from the CSC to the CDMC. Furthermore, empirical evidence on major findings are provided. This research contributes to the literature on knowledge sharing in joint ventures.