Fast Numerical Model Research Articles

Computational study of performance of cascaded multi-layered packed-bed thermal energy storage for high temperature applications

Continued effort towards decarbonizing the power sector has attracted enhanced research interest on the ideas revolving around different Coal-Concentrated Solar Power hybrid plant concepts. A few pre-feasibility studies indicate the importance of high-temperature (> 600 °C) latent heat packed-bed energy storage systems to ensure operational flexibility of the power plants, especially during the peak demand. In this study, a tractable and computationally fast numerical model comprising of two simplified non-equilibrium energy equations for the working fluid and the phase change material (PCM), respectively, is developed to account for the radiation effects at the high temperatures in the cascaded multi-layered packed bed latent heat thermal energy storage (PBLTS). The PBLTS is filled with spherical capsules of different diameters, containing PCMs having different melting temperatures, while air is chosen as the heat transfer fluid (HTF). The arrangement of different capsule diameters is found to affect the thermal performance of the storage significantly during the charging and discharging process. Equal bed heights with the capsule size arrangement of 10, 20, 30 mm from the inlet towards the oulet of the storage tank showed enhanced thermal performance during discharging operation. An aspect ratio between 4 and 4.5 leads to a better discharging performance of the storage, maintaining a stabilized high temperature at the storage outlet for a longer duration. It is found that the radiative heat transfer plays a significant role at high temperature (> 650 °C) in dictating the performance of the thermal energy storage system during the charging operation.

A Fast State-Based Peridynamic Numerical Model

A Fast State-Based Peridynamic Numerical Model

Van der Waals interlayer potential of graphitic structures: From Lennard–Jones to Kolmogorov–Crespy and Lebedeva models

The experimental knowledge on interlayer potential of graphitic materials is summarized and compared with the computational results based on phenomenological models. Besides Lennard–Jones approximation, the Mie potential is discussed, as well as the Kolmogorov–Crespy model and equation of Lebedeva et al. An agreement is found between a set of reported physical properties of graphite (layer binding energies, compressibility along c-axis in a broad pressure range, Raman frequencies for bulk shear and breathing modes under pressure), when a proper choice of model parameters is taken. It is argued that anisotropic potentials, Kolmogorov–Crespy and Lebedeva, are preferable for modeling, as they provide a better, self-consistent description. A method of fast numerical modeling, convenient for the accurate estimation of the discussed physical properties, is proposed. It may be useful in studies of other van der Waals homo/heterostructures as well.

Rapid Simulation of 3D Liquid Sloshing in the Lunar Soft-Landing Spacecraft

Sloshing of liquid fuel has significant implications in the accurate control of the spacecraft. Rapid simulation of the force and moment exerted by liquid against the spacecraft is rather important for the dynamics and control of the spacecraft. Fast numerical simulation models, especially those capable of dealing with violent liquid sloshing in the lunar soft-landing spacecraft with fluid merging and splitting, are required for real-time control algorithms. For this purpose, a modified smoothed particle hydrodynamics method, namely, noninertial smoothed particle hydrodynamics (NI-SPH), is proposed. In this method, noninertial coordinate system is used to derive transient external excitations to liquid. Meanwhile, the linear and angular momentum theorems of the particle system are adopted to calculate the force and moment exerted by liquid against the spacecraft, which avoids the accuracy loss of the integration of pressures. Furthermore, parallelization based on OpenMP is used to speed up the simulation. To show the accuracy and efficiency, results from the NI-SPH method are compared with those obtained by traditional computational fluid dynamics software, for several 3D liquid sloshing cases.

Three-dimensional numerical modeling of gravity and magnetic anomaly in a mixed space-wavenumber domain

Fast and accurate numerical modeling of gravity and magnetic anomalies is the basis of field-data inversion and quantitative interpretation. In gravity and magnetic prospecting, the computation and memory requirements of practical modeling is still a significant issue, which leads to the difficulty of using efficient and detailed inversions for large-scale complex models. A new 3D numerical modeling method for gravity and magnetic anomaly in a mixed space-wavenumber domain is proposed to mitigate the difficulties. By performing a 2D Fourier transform along two horizontal directions, 3D partial differential equations governing gravity and magnetic potentials in the spatial domain are transformed into a group of independent 1D differential equations wrapped with different wavenumbers. Importantly, the computation and memory requirements of modeling are greatly reduced by this method. A modeling example with 4,040,100 observations can be finished in approximately 28 s on a desktop using a single core, and the independent differential equations are highly parallel among different wavenumbers. The method preserves the vertical component in the space domain, and thus a mesh for modeling can be finer at a shallower depth and coarser at a deeper depth. In general, the new method takes into account the calculation accuracy and the efficiency. The finite-element algorithm combined with a chasing method is used to solve the transformed differential equations with different wavenumbers. In a synthetic test, a model with prism-shaped anomalies is used to verify the accuracy and efficiency of the proposed algorithm by comparing the analytical solution, our numerical solution, and a well-known numerical solution. Furthermore, we have studied the balance between computational accuracy and efficiency using a standard fast Fourier transform (FFT) method with grid expansion and the Gauss-FFT method. A model with topography is also used to explore the ability of modeling topography with our method. The results indicate that the proposed method using the Gauss-FFT method has characteristics of fast calculation speed and high accuracy.

Effective thrust bearing model for simulations of transient rotor dynamics

The paper introduces a new fast combined analytical and numerical computation model of thrust bearing, which can be applied to analyse the transient rotor dynamics of rotating machines. The bearing model is designed to allow an efficient solution to long-term processes while retaining its high-level capability to describe the bearing dynamics and tribology. The model includes the effects of lubricant inlet temperature and pressure and also effects of temperature, shear rate and inertia of the bearing lubricant layer. This bearing model used in the virtual turbocharger allows detailed analysis of both the design of the bearing itself and the vibration and noise issues of the turbocharger. The results obtained through the bearing model are verified using Computational Fluid Dynamics (CFD) and by technical experiments on real exhaust gas turbochargers.

Downwind flow behaviours of cuboid-shaped obstacles: modelling and experiments

Buildings or fence-like structures are frequently modelled as cuboids in simulations of environmental assessments. Understanding flows around and downwind of typical isolated buildings, in the form of cuboids, provide insightful building disposition strategies, which are particularly useful in the field of urban planning. Fast analytical models or computational numerical models are essential for sensitivity studies of various design parameters that require validation against field/experimental data. The aim of this study is to compare in detail the robustness of analytical perturbation models and the computational fluid dynamics (CFD) k − ε turbulence models for predicting the mean wake velocity defects along the centre line downwind of the cuboids, both in the near- and far-wake regions. Depending on aspect ratios of cuboids, the decay rate of maximum velocity defect behaves differently. Moreover, the CFD code over-predicts the magnitude of maximum defect in comparison with the perturbation models, whereas it over-predicts or under-predicts when compared to actual measurements. A physical explanation has been proposed in this paper. The steady CFD models, requiring less empirical input, are shown to provide satisfactory results for approximate computations of flows in the near- and far-wake regions of cuboid buildings with appropriate settings of inflow profiles and wall function.

Coupled thermo-electromagnetic model of a new robotic high-frequency local induction heat treatment system for large steel components

A new robotic high-frequency local induction heat treatment system is studied. The system is designed to perform on-site local heat treatment on large steel components such as hydropower turbine runner. A flat spiral coil is moved by a robot arm over the area to treat. A fast numerical model is developed to predict the temperature distribution and system settings. Several numerical strategies are proposed to minimize the computation time. The model combines an equivalent circuit with thermal finite elements and the electromagnetic mutual impedance method. A simple approach based on the concept of complex permeability is proposed to model hysteresis losses. The computed power losses in the RLC circuit and the temperature field in flat paramagnetic and ferromagnetic workpieces are compared with experimental measurements. Results confirm the accuracy of the coupled thermo-electromagnetic model.

Hydrodynamic Impedance Correction for Reduced‐Order Modeling of Spermatozoa‐Like Soft Micro‐Robots

AbstractHydrodynamic interactions play a key role in the swimming behavior and power consumption of bio‐inspired and biomimetic micro‐swimmers, cybernetic or artificial alike. Bio‐inspired robotic micro‐swimmers require fast and reliable numerical models for robust control in order to carry out demanding therapeutic tasks as envisaged for more than 60 years. The fastest known numerical model, the resistive force theory (RFT), incorporates local viscous force coefficients with the local velocity of slender bodies in order to find the resisting hydrodynamic forces, however, omitting the induced far‐field. As a result, the power requirement cannot be predicted accurately. The question of predicting and supplying the necessary power is one of the obstacles impeding the micro‐robotic efforts. In this study, a novel strategy is proposed to improve the RFT‐based analysis, particularly for spermatozoa and spermatozoa‐inspired micro‐swimmers with elastic slender tails, in order to present a practical solution to the problem. The postulated analytical improvement and the associated correction coefficients are based on hydrodynamic impedance analysis of the time‐dependent solution of three‐dimensional (3D) Navier–Stokes equations incorporated with deforming mesh and subject to conservation of mass.

In Situ Experiment and Numerical Model Validation of a Borehole Heat Exchanger in Shallow Hard Crystalline Rock

Accurate and fast numerical modelling of the borehole heat exchanger (BHE) is required for simulation of long-term thermal energy storage in rocks using boreholes. The goal of this study was to conduct an in situ experiment to validate the proposed numerical modelling approach. In the experiment, hot water was circulated for 21 days through a single U-tube BHE installed in an underground research tunnel located at a shallow depth in crystalline rock. The results of the simulations using the proposed model were validated against the measurements. The numerical model simulated the BHE’s behaviour accurately and compared well with two other modelling approaches from the literature. The model is capable of replicating the complex geometrical arrangement of the BHE and is considered to be more appropriate for simulations of BHE systems with complex geometries. The results of the sensitivity analysis of the proposed model have shown that low thermal conductivity, high density, and high heat capacity of rock are essential for maximising the storage efficiency of a borehole thermal energy storage system. Other characteristics of BHEs, such as a high thermal conductivity of the grout, a large radius of the pipe, and a large distance between the pipes, are also preferred for maximising efficiency.

A fast convolution based waveform model for conventional and unfocused SAR altimetry

In this paper we derive a closed-form solution to generate a backscatter power representation for both unfocused synthetic aperture radar altimetry and conventional altimetry signals in the frequency/slow-time domain. This new approach involves fast convolutions and leads to a fast numerical computational model which uses very few approximations. The transform back to the range-time/doppler frequency domain is then made numerically.Two retrackers based on this Signal Model Involving Numerical Convolution (SINC) are constructed for conventional and synthetic aperture radar altimetry and are named SINC2 and SINCS respectively. Output from retracking are the epoch t0 with respect to the tracking reference point, the significant wave height and the backscattering cross section at normal incidence σ0.Main benefits of the SINC model are its flexibility, the possibility to use the real point target response (PTR) or more complex representations of the height probability density function of scattering sea surface elements (PDF), and its fast computation speed to retrack the waveforms.The retrackers are applied to CryoSat-2 reduced SAR (RDSAR) and unfocused SAR waveforms. The RDSAR SINC2 retracker is only ten percent slower than the commonly used MLE3 retracker, which is a minor slowdown compared to the benefits of the SINC model. The SAR processing including the SINCS retracking procedure is three times slower than the RDSAR processing including retracking with SINC2.Model and algorithms are validated on both synthetic data generated by Monte-Carlo simulations and on real datasets. SAR SAMOSA+ results accessible through the ESA G-POD SARvatore service serve as a reference. Cross-validation shows higher agreement between SAR SAMOSA+ and SAR SINCS sea level anomaly and lower agreement between SAR SAMOSA+ and RDSAR SINC2, with accuracy of −0.1 cm for SAR SINCS and 1.7 cm for RDSAR SINC2. Instead, the accuracy of significant wave height, 4.9 cm and 3.9 cm for SAR and RDSAR and of backscatter coefficient, 0.16 and 0.12 dB in SAR and RDSAR, are comparable.Cross-validation results shows for sea level anomaly and significant wave height a higher precision of SAR SINCS and a lower precision of RDSAR SINC2, with precision of 0.92 cm and 6.6 cm for SAR SINCS and 1.96 cm and 12.6 cm for RDSAR SINC2 in sea level anomaly and significant wave height respectively. Instead, the precision of the backscatter coefficient is higher in RDSAR SINC2 than in SAR SINCS, and is 0.014 and 0.016 dB.In summary the new open ocean retrackers are a viable alternative recommended for both reduced and unfocused SAR processing in open ocean.

A new approach for nonlinear vibration analysis of thin and moderately thick rectangular plates under inplane compressive load

In this study, a hybrid method is proposed to investigate the nonlinear vibrations of pre- and post-buckled rectangular plates for the first time. This is an answer to an existing need to develope a fast and precise numerical model which can handle the nonlinear vibrations of buckled plates under different boundary conditions and plate shapes. The method uses the differential quadrature element, arc-length, harmonic balance and direct iterative methods. The governing differential equations of plate vibration have been extracted considering shear deformations and the initial geometric imperfection. The solution is assumed to be the sum of the static and dynamic parts which upon inserting them into the governing equations, convert them into two sets of nonlinear differential equations for static and dynamic behaviors of the plate. First, the static solution is calculated using a combination of the differential quadrature element method and an arc-length strategy. Then, putting the first step solutions into the dynamic nonlinear differential equations, the nonlinear frequencies and modal shapes of the plate are extracted using the harmonic balance and direct iterative methods. Comparing the obtained solutions with those published in the literature confirms the accuracy and the precision of the proposed method. The results show that an increase in the nonlinear vibration amplitude increases the nonlinear frequencies.

Implementation of different 2D finite element modelling approaches in axial flux permanent magnet disc machines

Three-dimensional (3D) finite element (FE) modelling of axial flux permanent magnet (AFPM) motors is one of the time-consuming tasks which must be completed before manufacturing the prototype motor. A simple, fast, accurate, and effective numerical modelling approach for such 3D problems would be particularly useful for researchers. This study presents simple and effective 2D FE modelling approaches for AFPM motors with good accuracy with less computational effort. The modelling approaches are based on a number of 2D models or planes with inner rotor, outer rotor, or linear motor topologies. All the 2D planes with either topology are superposed together to represent the real AFPM machine. These approaches are examined in detail with various types of experimentally verified AFPM motors. Results obtained from the proposed modelling approaches are verified with 3D FE analyses and experimental data. The results indicate that the proposed 2D modelling approaches can significantly reduce the computation time with good accuracy as opposed to conventional 3D FE modelling of AFPM motors.

Continuous monitoring of noise levels in the Gulf of Catania (Ionian Sea). Study of correlation with ship traffic

Acoustic noise levels were measured in the Gulf of Catania (Ionian Sea) from July 2012 to May 2013 by a low frequency (<1000Hz) hydrophone, installed on board the NEMO-SN1 multidisciplinary observatory. NEMO-SN1 is a cabled node of EMSO-ERIC, which was deployed at a water depth of 2100m, 25km off Catania. The study area is characterized by the proximity of mid-size harbors and shipping lanes. Measured noise levels were correlated with the passage of ships tracked with a dedicated AIS antenna. Noise power was measured in the frequency range between 10Hz and 1000Hz. Experimental data were compared with the results of a fast numerical model based on AIS data to evaluate the contribution of shipping noise in six consecutive 1/3 octave frequency bands, including the 1/3 octave frequency bands centered at 63Hz and 125Hz, indicated by the Marine Strategy Framework Directive (2008/56/EC).

Development of the curvilinear coordinate method for the computation of quasi‐static fields induced by an eddy current probe scanning a 3D conductor of complex shape characterized by an arbitrary 2D surface

SummaryThis paper deals with the development of a semi‐analytical model for the fast computation of the quasi‐static field induced by any eddy current probe in a 3D conductor of complex shape. The workpiece is considered as a planar half‐space mock‐up with an interface air conductor characterized by an arbitrary 2D surface a(x, y). The curvilinear coordinate method consists in introducing a change of coordinates to be able to write analytically and easily the boundary conditions at the interface air‐metal. Due to the novel generalized metric space, the covariant form of Maxwell equations must be considered. The curvilinear coordinate method is widely used in the optical community for the analysis the diffraction phenomenon on gratings. The method has been applied recently for eddy current calculations in the planar case for 2.5D configurations characterized by a 3D eddy current probe and a 2D layered stratified conducting media. By an extension to 3D problems, this work constitutes the preliminary task for the development of a complete numerical model, which has the capability to address very complex eddy current nondestructive testing configurations such as a stratified layered media constituted by a set rough interfaces. For that purpose, the modal formalism is described for the first time in the 3D case, and several numerical experiments show the validity and the efficiency of the fast numerical model in comparison to the finite element method.

Simulation of incremental sheet forming using partial sheet models

Abstract Academic and industrial interest in flexible forming has grown rapidly over the last two decades, leading to a large volume of research in this area. However, despite this interest, numerical modelling of the process is still challenging and the mechanics of the process is not yet fully understood. This paper presents fast numerical models for Incremental Sheet Forming. The models are shown to reduce computational time by up to 24 times, with a maximum shape error of 8%. The results suggest that the approach could be used to model process within acceptable time, and could be potentially used to explore the process in more detail using solid (brick) elements.

Predictability of the dispersion of Fukushima-derived radionuclides and their homogenization in the atmosphere

Long-range simulation of the dispersion of air pollutants in the atmosphere is one of the most challenging tasks in geosciences. Application of precise and fast numerical models in risk management and decision support can save human lives and can diminish consequences of an accidental release. Disaster at Fukushima Daiichi nuclear power plant has been the most serious event in the nuclear technology and industry in the recent years. We present and discuss the results of the numerical simulations on dispersion of Fukushima-derived particulate 131I and 137Cs using a global scale Lagrangian particle model. We compare concentrations and arrival times, using two emission scenarios, with the measured data obtained from 182 monitoring stations located all over the Northern Hemisphere. We also investigate the homogenization of isotopes in the atmosphere. Peak concentrations were predicted with typical accuracy of one order of magnitude showing a general underestimation in the case of 131I but not for 137Cs. Tropical and Arctic plumes, as well as the early detections in American and European midlatitudes were generally well predicted, however, the later regional-scale mixing could not be captured by the model. Our investigation highlights the importance of the parameterization of free atmospheric turbulence.

Matching curvilinear coordinates for the computation of the distribution of eddy currents in a cylindrical tube described by an arbitrary longitudinal internal/external profile

This paper addresses the problem of the development of a fast numerical model for the computation of the electromagnetic field in the quasi-static regime. A semi-analytical approach is achieved in order to obtain fast simulation tools dedicated to the simulation of complex configurations of eddy current (EC) inspection: an EC probe scans a conducting cylindrical tube of complex shape and with varying electromagnetic properties. In this paper, though the cylindrical tube to be inspected presents some angular symmetry, the complexity of the configuration lies in the arbitrary shape of the tube’s walls and the dependence of constitutive parameters of the material on the radial or axial coordinates. In this context, no modal approach can be used to expand the components of the fields. This problem is overcome by using a pseudospectral Fourier method. Maxwell’s equations are written in a covariant form in order to translate boundary conditions at each interface in an analytical form. Tangential components of the fields with respect to the boundary surface are expanded by using a high order Chebyshev polynomials. Spatial derivatives of the components of the fields with respect to the radial coordinate are thus approximated at some collocation points. Numerical validations are discussed in order to show the efficiency of the proposed numerical model.

Studying the limits of production rate and yield for the volume manufacturing of hollow core photonic band gap fibers.

Hollow core photonic band gap fibers have great potential in low latency data transmission and power delivery applications, but they are currently only fabricated in research scale fabrication facilities, with km-scale lengths. To drive cost reduction and volume manufacturing it is essential to be able to upscale the preform size, but before embarking on costly experimental attempts it is useful to apply fluid dynamics models to study how the fiber drawing dynamics would be affected by such a change. In this work we use a fluid dynamics model to virtually draw increasingly longer lengths of the same fiber from preforms of identical length but different diameters. Taking advantage of our fast numerical model we explore the physical dynamics of the draw process. We discover that the draw tension is the key thermodynamic parameter and that an upper length limit exists beyond which undesirable distortions in the microstructure become difficult to control. These mechanisms are identified and possible mitigation methods described which could allow the fabrication of over 200 km fiber from a single preform.

A fast response free-piston engine generator numerical model for control applications

This paper presents a linearization of the dynamic equation for a free-piston engine generator (FPEG), and simplifies it to a one-degree forced vibration system with viscous damping. The analogy between a mass-spring damper and a FPEG system is expressed, and the solution to the vibration system is solved. The model was successfully validated with respect to experimental data obtained from a prototype. The simulated piston displacement during steady operation showed similar trends with the test results and the error of the displacement amplitude was controlled within 3%. The state-space equations and the transfer function of the system are obtain using the fast response numerical model. An example of model application in the real FEPG control system was provided. Compared to the previous numerical model with differential approaches, the solving time of the proposed fast response model can be significantly reduced. The simplicity and flexibility of the proposed model make it feasible to be implemented to several computing software, i.e. Matlab, AMESim, Labview, Dymola et al. It can be easily implemented to real-time Hardware-in-the-Loop (HIL) simulation model for the future piston dynamic control system development. In addition, since it reveals how an FPEG operates in a resonant principle, the model is useful for parameter selection in the FPEG design process.