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This paper presents a quasistatic problem of an elastic body in frictional contact with a moving foundation. The model takes into account wear of the contact surface of the body caused by the friction. We recall existence and uniqueness results obtained in Sofonea et al. (2017). The main aim of this paper is to present a fully discrete scheme for numerical approximation together with an error estimation of a solution to this problem. Finally, computational simulations are performed to illustrate the mathematical model. [ABSTRACT FROM AUTHOR]

Abstract The mathematical model of heating substation, which is an important part of district heating system, is presented in this paper. The main components of district heating substation system, from the automatic control perspective, that are observed in this paper are heat exchanger and three-way valve. Presented mathematical model is developed so it could operate in real-time, since the crucial aspect of development, deployment and testing of new control techniques and optimization algorithms is their accurate validation on the real system. However, the accessibility to a real system is often not possible. Corresponding to this, an alternative is the existence of the correct mathematical model of a process, with the ability to operate in real-time. First, the presented mathematical model of district heating substation is decomposed to the simpler models of its main elements, in order to provide the analysis of the various parameters on the model performance through numerical simulation. Second, a real-time model is developed in LabVIEW software package and deployed on the embedded controller with a real-time processor as a three-layer application which enables data acquisition and communication with a programmable controller. [ABSTRACT FROM AUTHOR]

Simulating multi-body dynamics with both rigid and flexible parts and with frictional contacts is a hard problem. We solve this by expressing the couplings between the bodies as position level constraints. The implicit treatment of the constraint directions gives us improved stability over velocity based methods. Then by employing regularization of nonlinear constraints and a convex minimization formulation, we bridge constraint-based methods to traditional force-based methods. In fact, the former are just a dual variables formulation of the latter. We solve this dual problem using position based dynamics (PBD). We show how PBD is a completely valid modeling technique and we extend it with an accurate contact and Coulomb friction model. We further show for the first time how the same solver can be used to simulate both rigid and deformable solids with two way coupling. For the soft bodies we introduce a novel form of linear finite elements expressed as constraints, that is more accurate than PBD mass-spring systems. More of our results include the energy conserving Newmark integrator and the accelerated Jacobi solver suitable for parallel architectures. Note that this paper is an extended and revised version of the conference paper published in [1]. [ABSTRACT FROM AUTHOR]

Preload relaxation, caused by elastic interaction between tightened bolts, is one of the major reasons for non-uniformity of pretension force. But how to accurately assess the residual tension of a bolt is still extremely difficult. This paper considers two types of multiple bolted joint and six kinds of tightening sequence. Based on the deformation compatibility equation and elastic interaction stiffness, the generalized mathematical model for evaluating residual preload of bolts is established. Certain model parameters are obtained through numerical simulation. To analyze the influence of initial tightening torque, spacing between bolt holes, bolt material and gasket material on the elastic interaction stiffness, experimental devices and test procedures are developed. Furtherly, preload relaxation models are validated by tests conducted on six types of multi-bolted joint with the same surface roughness. Results of the proposed mathematical model of pretension force show a good consistency with those of corresponding experiment. • A mathematical model for estimating preload relaxation of bolted joint subjected to elastic interaction was established. • The elastic interaction stiffness between bolts was analyzed based on developed Experimental devices and test procedures. • The proposed mathematical model of pretension force shows a good consistency with the corresponding experiment. [ABSTRACT FROM AUTHOR]

This paper presents a computational heat transfer model of a rotary kiln used for the production of rutile titanium dioxide by the calcination of paste-like hydrous titanium dioxide. The work details the modelling of several chemical reactions occurring in the solid bed region along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. Finite-difference techniques are used and the steady state thermal conditions are assumed. The kiln is divided into axial segments of equal length. The solution is of marching type and proceeds from the solid inlet to the solid outlet. The direction of gas flow is opposite to that of the solids. Mass balance of each species in the solid charge, and mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperatures, and species concentration at the exit of that segment. The kiln length predicted by the present model is 45.75 m as compared to 45 m of an actual kiln reported by Ginsberg and Modigell (2011). The steady-state axial gas and solid temperature profiles have been also satisfactorily validated with the numerical results of the aforementioned paper. The output data consist of refractory wall temperature distribution, the axial solids and gas temperature profiles, axial solids composition profile, the length required for drying of the solid charge and the total kiln length required to achieve 98% conversion of anatase TiO 2 to rutile TiO 2 . A detailed parametric study with respect to the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and kiln rotational speed lent a good physical insight into the rutile-TiO 2 production process in a rotary kiln. [ABSTRACT FROM AUTHOR]

The upstream offshore multi-phase well-pipeline-riser installations are facing huge challenges related to slugging flow: An unstable flow regime where the flow rates, pressures and temperatures oscillate in the multi-phase pipelines. One typical severe slug is induced by vertical wells or risers causing the pressure to build up and hence originates the oscillating pressure and flow. There exist many negative consequences related to the severe slugging flow and thus lots of investments and effort have been put into reducing or completely eliminating the severe slug. This paper reviews in details the state-of-the-art related to analysis, detection, dynamical modeling and elimination of the slug within the offshore oil & gas Exploration and Production (E&P) processes. Modeling of slugging flow has been used to investigate the slug characteristics and for design of anti-slug control as well, however most models require specific facility and operating data which, unfortunately, often is not available from most offshore installations. Anti-slug control have been investigated for several decades in oil & gas industry, but many of these existing methods suffer the consequent risk of simultaneously reducing the oil & gas production. This paper concludes that slug is a well defined phenomenon, but even though it has been investigated for several decades the current anti-slug control methods still have problems related to robustness. It is predicted that slug-induced challenges will be even more severe as a consequence of the longer vertical risers caused by deep-water E&P in the future. [ABSTRACT FROM AUTHOR]

State of charge (SOC) estimators with online identified battery model have proven to have high accuracy and better robustness due to the timely adaption of time varying model parameters. In this paper, we show that the common methods for model identification are intrinsically biased if both the current and voltage sensors are corrupted with noises. The uncertainties in battery model further degrade the accuracy and robustness of SOC estimate. To address this problem, this paper proposes a novel technique which integrates the Frisch scheme based bias compensating recursive least squares (FBCRLS) with a SOC observer for enhanced model identification and SOC estimate. The proposed method online estimates the noise statistics and compensates the noise effect so that the model parameters can be extracted without bias. The SOC is further estimated in real time with the online updated and unbiased battery model. Simulation and experimental studies show that the proposed FBCRLS based observer effectively attenuates the bias on model identification caused by noise contamination and as a consequence provides more reliable estimate on SOC. The proposed method is also compared with other existing methods to highlight its superiority in terms of accuracy and convergence speed. [ABSTRACT FROM AUTHOR]

• Normal mode stability analysis performed on counjugate heat transfer (CHT) 1D problem. • Stability analysis reveals existence of lower stability bound for coupling coefficient in Robin-Dirichlet interface boundary conditions. • Validity of stability analysis results is verified empirically. • Stability analysis is extended to more general CHT problems. This paper aims to evaluate and validate a mathematical coupling model, based on a normal mode stability analysis, for steady conjugate heat transfer problems. In order to achieve this goal, an aerothermal computational code was designed specifically ex novo to meet the needs of the current study. A large number of numerical simulations were carried out within the framework of the Dirichlet-Robin fluid-solid interface procedure and with conditions strictly identical to those adopted in the mathematical model. These coupled computations have been synthesized in five representative cases. The computed results show that the stability limit and the numerical Biot number derived from the coupling model are very reliable parameters. Many other physical and numerical aspects, such as the splitting of the coupling period are also considered in this work from which some interesting and promising results are obtained. At the end of this paper, we assess the general potential, limits and constraints of the mathematical model and its extension to multidimensional cases is discussed. [ABSTRACT FROM AUTHOR]

• Presenting a method for automatic generation of program code for process models. • Ontology captures model information and equations for the modelled domain. • Model generated in a graph-based model environment reflecting the ontology information. • Equations translated to output format using language templates for the mathematical operators. The implementation of coded mathematical process models is regarded as a cumbersome and challenging task, reasons being that the modeller needs to have expertise both in modelling and computer science. Our ProcessModellerSuite implements a staged approach to modelling starting with the formulation of a context-dependent ontology defining a structure against which the mathematical representation of the principal model components is defined. Process models are then generated by interactively constructing a graph of communicating principle components, which enables the generation of arbitrary complex process models and intermediate storage of customised unit models. This storage of unit models forms the equivalent of the traditional unit-operations libraries, by allowing for insertion of the unit models into other graphs. A task builder combines the information from the graph with the used model components to automatically generate executable program code of the process model, which will be the topic of this paper. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a model predictive control (MPC) is proposed for wind farms to minimize wake-induced power losses. A constrained optimization problem is formulated to maximize the total power production of a wind farm. The developed controller employs a two-dimensional dynamic wind farm model to predict wake interactions in advance. An adjoint approach as an efficient tool is utilized to compute the gradient of the performance index for such a large-scale system. The wind turbine axial induction factors are considered as the control inputs to influence the overall performance by taking the wake interactions into account. A layout of a 2 × 3 wind farm is considered in this study. The parameterization of the controller is discussed in detail for a practical optimal energy extraction. The performance of the adjoint-based model predictive control (AMPC) is investigated with time-varying changes in wind direction. The simulation results show the effectiveness of the proposed approach. The computational complexity of the developed AMPC is also outlined with respect to the real time control implementation. [ABSTRACT FROM AUTHOR]

Highlights • An electrical heating method to enhance shale gas production is proposed. • A mathematical model of shale gas production by electrical heating is developed. • The effects of parameters on gas production are investigated by numerical simulation. • Numerical simulation suggests that electrical heating method has a good performance to enhance shale gas recovery. Abstract Gas production from shale gas reservoirs can be enhanced by increasing the temperature of the reservoirs due to the increased desorption of the adsorbed gas. However, limited techniques are currently available for practically introducing heat into such low permeability reservoirs. This paper investigates the feasibility of an electrical resistance heating method to promote shale gas production by increasing the temperature of the reservoirs. To achieve our research goal, a mechanistic numerical model is developed to describe electrical field, temperature field, and pressure field. To capture gas flow in a shale gas reservoir, non-linear flow, diffusion and adsorption/desorption which are all dependent on temperature are incorporated into a dual continuum media model. In our study, the gas production enhancement by electrical heating with two parallel horizontal electrode wells is evaluated using this model. We then assess impacts of the thermal properties of the formation, electrode length, electrical power, Langmuir volume and starting time of heating on gas production. The results indicate that the electrical heating method using two parallel horizontal electrodes can be an efficient method to enhance shale gas production. The heat capacity and conductivity of the formation have significant impacts on gas production. Reservoirs with low conductivity and low heat capacity tend to produce more gas due to heating. Meanwhile, shale gas reservoirs with high Langmuir volume also tend to yield more gas due to heating for. To maximize gas production, electrical power should be optimized based on the properties of shale gas reservoir and heating equipment. Longer electrodes heat more formations of the reservoir and thus lead to higher gas production by using the electrical heating method. In order to efficiently enhance shale gas production, electrical heating should start later in gas production, instead of earlier. [ABSTRACT FROM AUTHOR]

Abstract To improve the effectiveness of national image study on the "Belt and Road" countries in Central Asia, a national image study method based on the multivariate linear is proposed in this paper. First, the national competitiveness database of International Institute for Management Development (IMD) and World Economic Forum is adopted to construct the evaluation index system of the "Belt and Road" countries; second, the multivariate linear regression analysis method is introduced to analyze the evaluation index system model of the "Belt and Road" countries mentioned above; third, the effectiveness of the proposed algorithm is verified through the simulation experiment. [ABSTRACT FROM AUTHOR]

Plant-wide oscillation detection is an important task in the maintenance of large-scale industrial control systems, owing to the fact that in an interactive multi-loop environment oscillation generated in one loop may propagate to the different parts of the plant. In such a scenario, it is required that different loops oscillating due to a common cause and hence similar frequency may be grouped together. In this paper an adaptive method for plant-wide oscillation detection based on multivariate empirical mode decomposition (MEMD) along with a grouping algorithm is proposed. The method can identify multiple oscillation groups among different variables as well as variables with random noise only. The proposed method is also applicable to both non-linear and non-stationary time series where the techniques based on the conventional Fourier analysis are prone to errors. Within each group that oscillate due to a common cause, the method can also indicate the location of the probable root cause of oscillations. The efficacy of the proposed method is established with the help of both simulation and industrial case studies. [ABSTRACT FROM AUTHOR]

Microalgae are used for the industrial production of high value compounds. The aim in continuous bioreactors is to obtain the highest biomass production. It is necessary to guarantee that the bioprocesses attain and maintain the optimal reference biomass C X * ( t ), despite endogenous and exogenous disturbances. This paper describes the numerical simulation of the application of active disturbance rejection control (ADRC) to control the dilution rate ( D(t) ) in a continuous culture of the microalga Chlorella vulgaris . To reduce the bioprocess to a “SISO” system, the authors chose the dilution rate, D(t), to be the only control signal. The control proposal was illustrated and evaluated through a numerical simulation using MATLAB/Simulink™ environment. The performance of the ADRC was tested by the application of external perturbations and variation of parameters over a nominal case. At nominal conditions, D(t) was always maintained within the physical limits imposed by the bioprocess. Step and smooth type signals, at 96.4%·| D max ( t )|, were imposed as external perturbation on the control signal input, D(t) . The controller response kept the output signal C X ( t ) within an insignificant 0.0043%·| C Xmax ( t )|. The algal culture had a strongly asymmetric response to variations of the ideal maximum growth rate, μ max ( t ) ± 30%·| μ max ( t )|, and of the nominal light intensity, I in ( t ) ± 30%·| I in ( t )|. Nonetheless, the controller promptly returned the output signal to its reference value, C X ( t )*. The numerical test of the control proposal, in summary, showed that the ADRC strategy ensures excellent reference tracking capability and robustness towards parametric uncertainties, un-modeled dynamics, and external disturbances. [ABSTRACT FROM AUTHOR]

Abstract This paper deals with applications of fault detection and diagnosis algorithms based on the Kalman filter and fault factor method for an open-cycle liquid propellant rocket engine in a steady state. In order to develop the algorithms, we designed the Kalman filter with a linearized model of a liquid propellant rocket engine and energy balance equations with fault factors. To confirm the fault detection and diagnosis algorithms, we developed a mathematical model of an open-cycle liquid propellant rocket engine and artificially injected various faults, such as decreasing turbine efficiency and a sensor fault. We then executed the fault detection and diagnosis algorithms and analyzed the results of each algorithm. These processes are numerically demonstrated for the open-cycle liquid propellant rocket engine at full thrust level by using the simulated measurement data of the liquid propellant rocket engine mathematical model. Highlights • A mathematical model of an open-cycle liquid propellant rocket engine (OCLPRE) is developed. • Kalman filter and fault factor methods are used for fault detection-diagnosis of the OCLPRE. • The pros and cons of each fault detection-diagnosis algorithms are analyzed. • The performances of the algorithms are demonstrated by numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, we establish a mathematical model, that is, an initial-boundary value problem of partial differential equations (PDE), to describe the three dimensional (3D) motion of a marine cable being laid onto the seabed of varying depth. Based on this PDE model, a numerical method for simulating dynamically the moving process of marine cable is developed, which can be used to determine the cable laying operations in practice such that the marine cable can be laid on the prescribed position on seabed. [ABSTRACT FROM AUTHOR]

The paper is mainly concerned with the oscillations of numerical solutions by the linear θ − methods for a kind of linear delay differential equations with positive and negative coefficients. Some conditions under which the numerical solutions are oscillatory are obtained and it is proved that oscillations of the analytical solutions are preserved by the numerical solutions under mild conditions. Numerical experiments are given to demonstrate our results. [ABSTRACT FROM AUTHOR]

Sensitivity Analysis (SA) investigates how the variation in the output of a numerical model can be attributed to variations of its input factors. SA is increasingly being used in environmental modelling for a variety of purposes, including uncertainty assessment, model calibration and diagnostic evaluation, dominant control analysis and robust decision-making. In this paper we review the SA literature with the goal of providing: (i) a comprehensive view of SA approaches also in relation to other methodologies for model identification and application; (ii) a systematic classification of the most commonly used SA methods; (iii) practical guidelines for the application of SA. The paper aims at delivering an introduction to SA for non-specialist readers, as well as practical advice with best practice examples from the literature; and at stimulating the discussion within the community of SA developers and users regarding the setting of good practices and on defining priorities for future research. [ABSTRACT FROM AUTHOR]

The goal of this paper is to identify the effects of in-pore transport of liquid water and water vapor as well as phase changes on the hygrothermal behavior of earthen buildings. Indeed, one of the main assets used to promote these constructions is their role in moisture buffering hence temperature and relative-humidity quality controlling. However, there is no clear consensus yet concerning the impact of these phenomena on the global energy performance of the buildings. A coupled model is therefore proposed in this paper, based on heat and mass balances inside the earthen walls, in order to clarify this question. This model considers separately the kinematics of each phase (e.g. liquid water, vapor, dry air and solid matrix), in interaction with each other. It also takes into account the impact of pore water confinement on the liquid-to-vapor phase change, in particular on the resulting latent heat released or absorbed. The model is successfully compared to experimental results on instrumented full-scale rammed earth wall subjected to temperature cycles. It eventually allows identifying the singular hygrothermal behavior of earth material by testing the range of applicability of the simplifying assumptions which are commonly made in function of the permeability of the tested material. [ABSTRACT FROM AUTHOR]

The paper addresses the single range observability analysis of a kinematics model of cooperating underactuated underwater vehicles. Teams of underwater vehicles that communicate with each other may be able to access and exchange their relative distances through, by example, acoustic signal time-of-flight measurements. Such relative distance measurements together with vehicle’s attitude and velocity information may be used onboard to implement a navigation filter to estimate the vehicle’s relative positions and orientations. A pre-requisite for successfully designing such navigation filters is to assess the systems observability properties. Contrary to the majority of existing studies on single range observability, the paper considers a more realistic underactuated kinematics model for slender body autonomous underwater vehicles rather than a simple point mass model. The paper extends previous results building on an augmented state technique allowing to reformulate the nonlinear observability problem in terms of a linear time varying one. As a result, all possible (globally) unobservable motions are characterized in terms of the systems’ initial conditions and velocity commands within the class of interest. The fundamental results reported are also illustrated by numerical simulations providing evidence of different motions generating the same output, namely lacking observability. [ABSTRACT FROM AUTHOR]

Segregation models often focus on private racial preference but overlook the institutional context. This paper represents an effort to move beyond the preference centricity. In this paper, an ideal Pigovian regulatory intervention is emulated and added into Schelling’s (1971) classic spatial proximity model of racial segregation, with an aim to preserve collective welfare against the negative externalities induced by the changing local racial compositions after individual relocations. A key discovery from a large number of cellular automata is that the Pigovian regulation tends to result in less segregated but also less efficient (in terms of aggregate utility) residential patterns than laissez faire . This finding, albeit from a highly stylized model, bears intellectual relations to an important practical question: What are the potential racial effects of Pigovian local planning interventions, such as financially motivated anti-density zoning or the collection of a development impact fee? On top of its modest policy implications, this paper demonstrates a bottom-up computational modelling approach to reconcile the preference-based and institution-orientated academic perspectives regarding racial residential segregation. [ABSTRACT FROM AUTHOR]

Diagrams are ubiquitous in software engineering and widely used for software modelling. The visual contract language (VCL) enables an approach to software design modelling that is entirely graphical and has a mathematical basis. VCL's main novelties lie in its capacity to describe predicates visually and in its graphical front-end to formal modelling. VCL is brought to life in the visual contract builder (VCB) tool presented in this paper. VCB provides diagram editors for the whole VCL suite, it type-checks diagrams and generates Z formal specifications from them; the Z specification enables formal verification and validation using Z theorem provers. The paper evaluates VCB based on the results of a survey carried out in the context of a controlled experiment. The work presented here is a contribution to the area of visual design modelling: the paper presents a state of the art tool supporting the novel VCL language and concrete empirical results on the usefulness and effectiveness of tool and language in particular, suggesting benefits of visual modelling in general. [ABSTRACT FROM AUTHOR]

Rotating bioreactor, such as the NASA bioreactor, which was designed by the National Aeronautics and Space Administration (NASA), USA, can be used to mimic micro-gravity conditions and simulate the effects of microgravity on cells growth. The cell growth in the bioreactor depends on the nutrient availability which in turn depends on the cell density and distribution within the bioreactor. In this work, we use a numerical model of suspended particle motion to simulate the cell motion and distribution in a specific variant of the NASA bioreactor, namely, the high aspect ratio vessel (HARV) bioreactor. The nutrient distribution in the bioreactor is simulated based on a convection–diffusion-reaction supplemented by laboratory experiments aimed at obtaining the required data. We present the modelling framework in this paper and discuss the most salient simulated results. For example, the simulation results show that the distributions of the cells in the bioreactor appear as concentric circles and that the cells density is higher in the middle of the HARV bioreactor. These cell distributions imply that they may accumulate in the middle of the bioreactor at sufficiently high cell density. The results also demonstrate that the concentration of nutrient is fairly uniform in the bioreactor but decreases slightly from the outer radius of the HARV bioreactor to the inner radius. This is possibly caused by the higher consumption of glucose due to the higher cell density in the middle of the radius. We expect that the modelling framework in this paper would help optimise the culture conditions for the cells in HARV bioreactors. [ABSTRACT FROM AUTHOR]

Simulation and experimental verification of a fuel calibration system based on hydraulic metering cylinder has been carried out in this paper. A novel hydraulic metering cylinder is designed for more accurate flow rate measurement. The calibration workbench with this cylinder is presented and mathematically modeled. Also, the calibration system is numerically simulated in AMESim. The simulation results show that the calibration system can work smoothly. In addition, the impact of given plunger speeds and calibration strokes on the accuracy of the calibration results is experimentally verified. It can be found that stroke of approximate 600 mm and a medium given speed are the most effective ways to reduce the measuring error under the experimental condition provided in this paper. Moreover, a calibration error less than 0.5% is achieved in the fuel calibration system. [ABSTRACT FROM AUTHOR]

A computational study treating cavitation phenomenon within a single bubble undergoing various controlled ultrasonic waveforms is presented in this paper. Numerical simulations using sinusoidal, square, triangular and sawtooth waves crossing an aqueous media, saturated with oxygen, are conducted upon various operational conditions of frequency and amplitude. Bubble radius, temperature and pressure were estimated over time for 64 combined cases. The obtained results show that at relatively low acoustic pressure, i.e. 1.5 and 2 atm, the square wave is proved to generate the highest temperature and pressure inside the bubble, while triangular and sawtooth ones remain the less interesting waveforms for sonochemical application within the same operational conditions. At higher amplitudes above 2.5 atm, this trend is changed, especially at low frequencies, i.e. 200 and 300 kHz, where square wave showed some limitations in attaining the optimal values of the strong collapse within one acoustic cycle. [ABSTRACT FROM AUTHOR]

The complexity of thermal management increases as integrated circuits evolved into 3D architectures. Because of the large variation that exists in the thermal conductivity of materials and the geometrical size of structures in the 3D-stacked IC (3D-SIC) network, the extensive computational costs typically render a full-chip-scale numerical simulation impossible. Thus, this paper proposes a fast and implementable full-chip-scale numerical simulation method for thermal management of 3D-SIC. A compact thermal resistance network, with both lateral and vertical heat dissipations considered, is analyzed to establish an accurate anisotropic equivalent thermal conductivity model. The key heat dissipation component, the high thermal conduction path (HTCP) constructed using through-silicon vias (TSVs), micro-bumps, and Cu wires in the redistribution layer (RDL), is fully analyzed by modeling a compact thermal resistance network. The equivalent thermal conductivity of each stacked layer is extracted in blocks from the network and then applied in a finite element calculation for full-chip-scale numerical simulation. Three partitioning strategies to block each stacked layer are tested. As compared to the results of direct finite element simulation of a small-scale 3D-SIC, the proposed method yields improved simulation accuracy (temperature difference <7.5%) and a considerable computational cost reduction (grid number reduced by >77%). As a demonstration, the temperature distribution of a large-scale 3D-SIC with 306 TSVs and 1647 hotspots is successfully simulated within 82 min by implementing this method using a personal computer (Intel Core i5 6300HQ, 60 GB memory). [ABSTRACT FROM AUTHOR]

This paper presents a fundamental study of ultra-lean flames stabilized behind a thin, highly conducting metallic rectangular bluff body acting as a flame holder. Using high fidelity numerical simulations, we reproduce a phenomenon observed experimentally, showing that in this configuration steady hydrogen–methane flames can exist at equivalence ratios below the flammability limit associated with planar unstrained flames with the same hydrogen–methane proportion. These ultra–lean hydrogen–enriched mixtures exhibit a distinct stabilization mechanism compared to pure methane flames: they stabilize in the form of inverted closed V or U flames farther away from the flame holder as the inflow reactants velocity is reduced, leading eventually to blow-off for sufficiently small velocities. Conversely, as the reactants flow rate is increased, the flames anchor closer to the flame holder, and surprisingly no blow-off is observed at high velocities. This response is shown to be linked to the presence of hydrogen in the fuel mixture and its large diffusivity, which results in locally richer mixtures in the strained, curved flame base. [ABSTRACT FROM AUTHOR]

The application of computer simulation models plays a significant role in the understanding of water dynamics in basins. The recent and explosive growth of the processing capabilities of General-Purpose Graphics Processing Units (GPGPUs) has resulted in widespread interest in parallel computing from the modelling community. In this paper, we present a GPGPU implementation of finite-differences solution of the equations of the 2D groundwater flow in unconfined aquifers for heterogeneous and anisotropic media. We show that the GPGPU-accelerated solution implemented using CUDA 1 C/C++ largely outperforms the corresponding serial solution in C/C++. The results show that the GPGPU-accelerated implementation is capable of providing up to a 56-fold speedup in the solution using an ordinary office computer equipped with an inexpensive GPU 2 card. The code developed for this research is available for download and use at http://modelagemambientaluffs.blogspot.com.br/ . [ABSTRACT FROM AUTHOR]

Plants are a food source for man and many species. They also are sources of medicines, fibers for clothes and are essential for a healthy environment. But plants are subject to diseases. Many of these are caused by viruses. In plants most of the virus propagation is done by a vector, usually insects that bite infected plants and the susceptible plants. Chemical insecticides are commonly used to control the insects, but unfortunately these chemicals have toxic effects on humans, animals and the environment in general. An alternative is to introduce a new species, or just increase the number of a naturally present one, to prey on the insects and thus control their number. The different steps in the virus propagation process take time. In this paper we add a predator to a plant-virus propagation model with delays. The model is based on delay differential equations. There are five populations: susceptible and infected plants, susceptible and infected vectors, and predators. The infected vectors have no ill effects from the virus so they do not fight the virus and therefore they do not recover. The predators do not get sick from the virus. The total number of plants is assumed to be constant since for crops the framers will replace the death plants and one of the plant populations can be determined using the total constant plant population. Therefore we have a system of five delay ordinary differential equations in five unknowns. We assume that predators are introduced at the initial time and after their growth rate has a Holling 2 type dependence on the number of vectors. We consider two delays: the time it takes from the moment a plant is bitten by an infected vector to the moment the plant is infected; and a second smaller delay for the time from the moment a vector bites an infected plant to the moment the vector becomes infected. We determine the non-negative steady state solutions of the system of delay differential equations. We analyze their stability by calculating the eigenvalues of the linearized system about each equilibrium point. We do numerical simulations for certain values of the parameters. Finally we search for bifurcation points numerically using the software package biftool. Conditions are presented for which the disease is controlled or even eliminated. From the practical side, the model can be used to determine the amount of introduced predators necessary to eliminate the epidemic under different conditions. [ABSTRACT FROM AUTHOR]

Abnormal traffic behaviors are common traffic phenomena. Existing traffic simulators focus on showing how traffic flow develops after an anomaly occurs; however, they cannot depict the anomaly itself. In this paper, we introduce the concept of shadow traffic for modeling traffic anomalies in a unified way in traffic simulations. We transform the properties of anomalies to the properties of shadow vehicles and then describe how these shadow vehicles participate in traffic simulations. Our model can be incorporated into most existing traffic simulators with little computational overhead. Moreover, experimental results demonstrate that our model is capable of simulating a variety of abnormal traffic behaviors realistically and efficiently. [ABSTRACT FROM AUTHOR]

A modeling approach to investigate the complex behavior of granular trench and reinforcement system is presented in this paper. For this purpose experimental and numerical investigations have been carried out on the behavior of pullout resistance of an embedded strip anchor with and without geogrid reinforcement layers at stabilized loose and dense sand using a granular. Different parameters have been considered, such as number of geogrid layers, embedment ratios, relative density of soil and height ratios of granular trench. For sand and granular trench the CANAsand constitutive model were utilized to investigate failure mechanism and the associated rupture surfaces in the analysis. The obtained results indicate that, when soil was improved with the granular-geogrid trench, the uplift force significantly increased. The ultimate uplift capacity of anchor plate and the variation of surface deformation for all the tests indicated a close agreement between the experimental and numerical models. Also, numerical results show that larger deformations at ultimate pullout load are associated with high void ratios whereas smaller deformations are related with low void ratios. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of the buoyancy and finite size particles on the heat transfer process in the turbulent thermal boundary layer, we have carried out three simulations in the present paper, a single-phase neutral boundary layer, an unstable boundary layer with buoyancy effect, and a multi-phase boundary layer with thousands of finite size particles. This is the first time that particle-resolved direct numerical simulation (PR-DNS) is used in the study of thermal boundary layer. The DNS results show the turbulent statistics as well as the thermal structures. It turns out that both the buoyancy and the finite size particles will dramatically affect the turbulent statistics of the boundary layer. Detailed comparisons between the three simulations reveal that the buoyancy effect reshapes the coherent structures in the boundary layer, while finite size particles mainly induce additional disturbance all over the computational domain. Specifically, the Reynolds shear stress and the wall normal turbulent heat flux are remarkably enhanced in the log region by the effect of buoyancy. On the other hand, the finite size particles cause remarkable increment of velocity fluctuations all over the boundary layer, while have the effect of stabilizing temperature fluctuation near the wall. [ABSTRACT FROM AUTHOR]

In this paper, a numerical study of heat and mass transfer in counter-flow indirect evaporative air coolers is presented using an approach proposed by previous work. The mathematical model equations of continuity, momentum, energy and concentration are solved by the finite volume method to obtain the value of primary outlet dimensionless temperature. This mathematical model developed is validated against published data acquired from literature. The key target of presented analysis is to develop a performance correlation based on five dimensionless factors: ratio of channel length to half width of secondary air channel, ratio of water to secondary air mass flow rate, primary air inlet Reynolds number, secondary air inlet dimensionless temperature and water film inlet dimensionless temperature. Numerical simulations are performed by changing the value of each dimensionless factor under a constant value for other parameters. The simulation results are regressed to obtain the empirical constants of the correlation. The value of outlet dimensionless temperature is varied from 0.47 to 0.92. The developed correlation can predict the performance of the counter-flow indirect evaporative air coolers within a discrepancy of 12.6%. The correlation would be helpful to provide a simpler equation to improve the calculation speed within the engineering allowable accuracy range. [ABSTRACT FROM AUTHOR]

The (abstract) Tile Assembly Model (aTAM), is a mathematical paradigm for the study and algorithmic design of DNA self-assembly systems. It employs the use of so-called DNA-tiles, which are abstractions of experimentally achievable DNA nanostructure complexes with similar inter-matching behaviours. To this day, there are about half-dozen different experimental implementations of DNA tiles and their sub-sequent algorithmic assembly into larger complexes, see e.g. Reif et al. (2012) [29] . In order to provide further insight into the assembly process, the aTAM model has been extended to a kinetic counterpart (kTAM). Although there is a wide abundance of different variants of the abstract model, e.g., stage, step, hierarchical, temperature-k, signal-passing, etc. (see e.g. Patitz (2012) [22] ), numerical simulations of the kinetic counterpart have been performed only for a few types of these systems. This might be due to the fact that the numerical models and simulations of kTAM were almost exclusively implemented using classical stochastic simulation algorithms frameworks, which are not designed for capturing models with theoretically un-bounded number of species. In this paper we introduce an agent- and rule-based modelling approach for kTAM, and its implementation on NFsim, one of the available platforms for such type of modelling. We show not only how the modelling of kTAM can be implemented, but we also explore the advantages of this modelling framework for kinetic simulations of kTAM and the easy way such models can be updated and modified. We present numerical comparisons both with classical numerical simulations of kTAM, as well as comparison in between four different kinetic variant of the TAM model, all implemented in NFsim as stand-alone rule-based models. [ABSTRACT FROM AUTHOR]

Objective: Dynamic ambulance redeployment policies tend to introduce much more flexibilities in improving ambulance resource allocation by capitalizing on the definite geospatial-temporal variations in ambulance demand patterns over the time-of-the-day and day-of-the-week effects. A novel modelling framework based on the Approximate Dynamic Programming (ADP) approach leveraging on a Discrete Events Simulation (DES) model for dynamic ambulance redeployment in Singapore is proposed in this paper.Methods: The study was based on the Singapore's national Emergency Medical Services (EMS) system. Based on a dataset comprising 216,973 valid incidents over a continuous two-years study period from 1 January 2011-31 December 2012, a DES model for the EMS system was developed. An ADP model based on linear value function approximations was then evaluated using the DES model via the temporal difference (TD) learning family of algorithms. The objective of the ADP model is to derive approximate optimal dynamic redeployment policies based on the primary outcome of ambulance coverage.Results: Considering an 8min response time threshold, an estimated 5% reduction in the proportion of calls that cannot be reached within the threshold (equivalent to approximately 8000 dispatches) was observed from the computational experiments. The study also revealed that the redeployment policies which are restricted within the same operational division could potentially result in a more promising response time performance. Furthermore, the best policy involved the combination of redeploying ambulances whenever they are released from service and that of relocating ambulances that are idle in bases.Conclusion: This study demonstrated the successful application of an approximate modelling framework based on ADP that leverages upon a detailed DES model of the Singapore's EMS system to generate approximate optimal dynamic redeployment plans. Various policies and scenarios relevant to the Singapore EMS system were evaluated. [ABSTRACT FROM AUTHOR]

This paper presents numerical studies of large-size and high-quality fused silica glass synthesis by SiCl 4 flame hydrolysis deposition method, specifically the correlation of uniformities of SiO 2 deposition and OH concentration with the optimal location of the substrate placement. A comprehensive computational model is developed to describe the complex turbulent reacting flow with the detailed SiCl 4 -H 2 -O 2 reaction mechanism. Numerical simulation is first conducted to obtain the characteristics of SiCl 4 hydrolysis flame without considering the substrate and the SiO 2 particle formation. The distribution of SiO 2 accumulation is then calculated. The potential region and location for placing substrate are initially determined based on the criterion of a uniform SiO 2 accumulation. Further, the effects of H 2 -O 2 equivalence ratio and the SiCl 4 flow rate on the distributions of the temperature, SiO 2 concentration and OH concentration are investigated. It is found that the H 2 -O 2 equivalence ratio is sensitive to the temperature and the OH concentration, and the flow rate of SiCl 4 mainly affects the temperature and SiO 2 concentration. This finding indicates that the H 2 -O 2 equivalence ratio and the flow rate of SiCl 4 have equally important roles in determining the optimal location for the deposition substrate placement. The presence of the substrate also changes the distributions of the temperature and compositions concentrations in the furnace. Adjusting the substrate location is an effective strategy to achieve optimal location with more uniform distributions of the SiO 2 accumulation and the OH concentration on the deposition surface. [ABSTRACT FROM AUTHOR]

The main market studies depict a future in which all one-aisle aeroplanes will mount engines composed of elements with complex surfaces. Among the new generation of tools, the barrel-shaped tools were released to the market for the machining of such types of surfaces. However, there are no evidences reported in the literature about how do these tools work. This work presents for the first time a mathematical model based on the numerical discretization of barrel cutters to predict the cutting forces. The effects of helix angle, runout and lead and tilt angles were included and the model was validated for a range of conditions in a 5-axis machine. In this line, this paper enables future mathematical developments including more details and aiming at other complex problems. [ABSTRACT FROM AUTHOR]

A numerical simulation of a basin type solar desalination still, improved by a Natural Circulation Loop (NCL), is presented in this paper. A transient thermal model was proposed for forecasting the still thermal-hydraulic behaviour under different operating conditions. The proposed mathematical model is derived from the energy balance equations of the different components of the still, as well as, momentum equation for the humid air flowing in the system. The main heat and mass transfer phenomena having a place in the system are considered by the simulation. An extensive validation of the model has been performed by comparing the simulation results against experimental data obtained during four typical summer days. The comparison shows a reasonable agreement between the simulation results and the experimental data. The results showed that the root mean square error is ranged from 2.7% to 26% and the coefficient of determination is close to 1.0. [ABSTRACT FROM AUTHOR]

Significant variance exists in the nominal capacity of lithium ion (Li-ion) pouch cells used for commercial electric vehicle battery packs. Accurate estimation of heat generation in such cells is critical for designing battery thermal management system. However, multi-physics models describing thermal behaviour of these cells are too complex whereas other numerical models discount the effect of cell capacity on heat generation. This paper proposes a new computational model based on artificial neural network (ANN) for estimating battery heat generation rate with cell nominal capacity as one of its key inputs along with ambient temperature, discharge rate and depth of discharge. A custom-designed calorimeter is utilised for experimentally generating the training dataset for the ANN. Problem of data scarcity is addressed analytically and virtual samples are produced via enthalpy formulation for battery heat generation. Subsequently, the model is trained using Levenberg–Marquardt algorithm. Results disclose that a three-layered feedforward ANN with one hidden layer having six neurons is optimum for this application. The architecture of the trained ANN for accurately simulating thermal behaviour of LiFePO 4 pouch cells of the nominal capacities from 8 to 20 Ah under varied conditions is exemplified. [ABSTRACT FROM AUTHOR]

Concentrations measurements are typically corrupted by noise. Data reconciliation techniques improve the accuracy of measurements by using redundancies in the material and energy balances expressed as relationships between measurements. Since in the absence of kinetic models these relationships cannot integrate information regarding past measurements, they are expressed in the form of algebraic constraints. This paper shows that, even in the absence of a kinetic model, one can use shape constraints to relate measurements at different time instants, thereby improving the accuracy of reconciled estimates. The construction of shape constraints depends on the operating mode of the reactor. Moreover, it is shown that the representation of the reaction system in terms of vessel extents helps identify additional shape constraints. A procedure for deriving shape constraints from measurements is also described. Data reconciliation using both numbers of moles and extents is illustrated via a simulated case study. [ABSTRACT FROM AUTHOR]

In this paper, a novel model is presented for predicting thermophysical properties of superheated steam (SHS) in offshore superheated steam injection wells (OSSIW). Firstly, a mathematical model comprised of mass, energy and momentum balance equations is proposed for OSSIW. Secondly, the distribution of temperature, pressure and superheat degree along the wellbores are obtained by finite difference method on space and solved by using the iteration technique. Then, model validation and sensitivity analysis are conducted. The results show that (1). The superheat degree increases at first but then turns to decrease with the increase of injection rate. (3). The superheat degree increases with the increase of injection temperature. (4). The superheat degree at well bottom increases at first but then turns to decrease with the increase of injection pressure. (5). The superheat degree in the wellbore has a drop when seawater starts to flow. [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-criteria approach in order to reduce the waiting time on the assignment of users to medico-social institutions. The main goal is to ascertain whether alternative assignment policies can improve global response to users’ demands, and to assess the performances of each alternative (scenario) compared to the current practice. We propose a mathematical model of user assignment to medico-social structures and professionals, under constraints of resource capacity, professionals’ skills and user requirements (formulated in an individual support project). With alternative assignment policies, users’ needs could be covered partially. They also authorize the involvement of several structures and several professionals in the response to the request. A mixed integer linear programming solver is used to solve this assignment problem, following a lexicographic approach in case of partial coverage policy. For some assignment policies that have long calculation times, we propose a simulated annealing approach in order to speed up the resolution. In order to validate simulated annealing approach, we compared it with a greedy randomized adaptive search procedure. The problem is solved for instances where we have real size data for a set of institutions for disabled children and teenagers. We present and compare computational results over several scenarios, highlighting the improvement provided by each alternative assignment policy. [ABSTRACT FROM AUTHOR]

A tethered-net is a promising method for space debris capturing. However, its deployment dynamics is complex because of the flexibility, and its dependency of the deployment parameters is insufficiently understood. To investigate the deployment dynamics of tethered-net, four critical deployment parameters, namely maximum net area, deployment time, traveling distance and effective period are identified in this paper, and the influence of initial deployment conditions on these four parameters is investigated. Besides, a comprehensive study on a model for the tethered-net based on absolute nodal coordinates formulation (ANCF) is provided. Simulations show that the results based on the ANCF modeling method present a good agreement with that based on the conventional mass–spring modeling method. Moreover, ANCF model is capable of describing the flexibility between two nodes on the net. However, it is more computationally expensive. [ABSTRACT FROM AUTHOR]

Precision in computations is a considerable challenge to adequately addressing many current scientific or engineering problems. The way in which the numbers are represented constitutes the first step to compute them and determines the validity of the results. The aim of this research is to provide a formal framework and a set of computational primitives to address high precision problems of mathematical calculation in engineering and numerical simulation. The main contribution of this research is a mathematical model to build an exact arithmetical unit able to represent without error rational numbers in positional notation system. The functions under consideration are addition and multiplication because they form an algebraic commutative ring which contains a multiplicative inverse for every non-zero element. This paper reviews other specialized arithmetic units based on existing formats to show ways to make high precision computing. It is proposed a formal framework of the whole arithmetic architecture in which the operators are based. Then, the design of the addition operation is detailed and its hardware implementation is described. Finally, extensive evaluation of this operator is performed to prove its ability for exact processing. [ABSTRACT FROM AUTHOR]

This paper presents a new one-fluid method for simulating formation and the collapse of cavitation regions in water during an isothermal process. In this method, the fluid phase changes are included into the wave pattern of an exact Riemann solver. The model behavior is assessed by comparing the numerical results with the other numerical models for several 1D Riemann problems. One-dimensional water hammer problems with vast creation and collapsing of cavitation zones are simulated as well—and the numerical results are compared to experimental results. The new model results are in very good agreement with accepted results reported in the literature. The presented results clearly show that the new model is able to capture the various behaviors of water during the phase change in the saturation dome and the vapor state, which was neglected in previous studies. Finally, the new model is adopted to an ALE method on an adaptive triangular grid to simulate an underwater explosion phenomenon inside a rigid cylinder—and the results are compared with other simulations. [ABSTRACT FROM AUTHOR]

Two-phase flows in pipelines occur in a variety of processes in the nuclear, petroleum and gas industries. Because of the practical importance of accurately predicting steady and unsteady flows along the line, two-fluid models have been extensively used in numerical simulations. These models are usually written as a system of non-linear partial-differential equations. A reliable prediction of such flows is a difficult task to accomplish due to the numerous sources of uncertainties, such as the basic two-phase flow model, the flow-pattern models, the initial and boundary conditions and the numerical method used to solve the initial-boundary-value problem. Several numerical methods, conservative or not, may be used to discretize the problem. In this paper we analyze the global performance of the numerical model, obtained when we couple a classical one-dimensional single-pressure four-equation two-fluid model to a numerical discretization based on the flux-corrected transport (FCT) method, to solve the stratified-pattern two-phase flow that occurs in typical gas-gathering offshore pipelines. The gas phase is considered to be compressible and the liquid phase is incompressible, whereas the flow is assumed to be isothermal. We show that the FCT method is second-order in space and that our numerical kernel produces accurate simulations for steady, as well as unsteady, simulations. We also analyze the hyperbolicity property of the two-fluid model and the adequate prescription of the boundary conditions. The results show that hyperbolicity is lost in part of the area of the stratified-pattern region of a classical flow-pattern diagram. Moreover, the eigenvalues alternate signs at the boundaries, which has implications on how to impose the boundary conditions. Numerical simulations of typical offshore gas pipeline flows show very good agreement when compared to a commercial software. [ABSTRACT FROM AUTHOR]