Two-dimensional Simulation Model Research Articles

Estimation of Acoustic Energy and Performance Characterization of Acoustic Concentrator

Among many methods of particle concentration in liquid, acoustic concentrator uses ultrasonic standing wave to concentrate microparticles in liquid. In order to determine its performance on particle concentration, estimation of acoustic energy density inside the concentrator is important since energy density is the main contributing factor in calculating the primary acoustic radiation force acting on the particles. The balance between the primary radiation force and hydrodynamic force acting on the particles inside the acoustic concentrator determine the performance of the acoustic concentrator. Therefore, this study focuses on the measurement of acoustic energy density inside the h-shaped acoustic concentrator and characterization of performance of the concentrator. First, energy density is estimated by curve-fitting the experimental particle position in the ultrasonic field with one-dimensional theoretical position. Second, two-dimensional acoustic and hydrodynamic fields are determined using two-dimensional simulation model in COMSOL Multiphysics. Integrating the governing equation for particle motion in the balance of acoustic and hydrodynamic forces result in the particle trajectory and it is compared with the experimental observation. The results would provide deeper insight into the operation of acoustic concentrator and the detailed phenomenon of particle motions inside the concentrator.

Dynamic Fracture Properties of Rocks Subjected to Static Pre-load Using Notched Semi-circular Bend Method

A dynamic load superposed on a static pre-load is a key problem in deep underground rock engineering projects. Based on a modified split Hopkinson pressure bar test system, the notched semi-circular bend (NSCB) method is selected to investigate the fracture initiation toughness of rocks subjected to pre-load. In this study, a two-dimensional ANSYS finite element simulation model is developed to calculate the dimensionless stress intensity factor. Three groups of NSCB specimen are tested under a pre-load of 0, 37 and 74 % of the maximum static load and with the loading rate ranging from 0 to 60 GPa m1/2 s−1. The results show that under a given pre-load, the fracture initiation toughness of rock increases with the loading rate, resembling the typical rate dependence of materials. Furthermore, the dynamic rock fracture toughness decreases with the static pre-load at a given loading rate. The total fracture toughness, defined as the sum of the dynamic fracture toughness and initial stress intensity factor calculated from the pre-load, increases with the pre-load at a given loading rate. An empirical equation is used to represent the effect of loading rate and pre-load force, and the results show that this equation can depict the trend of the experimental data.

Radiation Heat Transfer and Vapor Shielding in a Two-Dimensional Model of an Electrothermal Plasma Source

Electrothermal (ET) plasma discharges are emerging as valuable mechanisms for pellet injection in magnetic confinement fusion reactors. They have been shown to be capable of achieving the required pellet velocities and pellet launch frequencies required for edge localized mode control. Another advantage of ET plasma discharges is their ability to simulate fusion disruption events by depositing large heat fluxes on exposed materials. A deeper understanding of the heat transfer processes occurring in ET plasma discharges will aid in this particular application. ET plasma discharges involve the passage of high currents (order of tens of kA) along the axis of a narrow, cylindrical channel. As the current passes through the channel, radiant heat is transferred from the plasma core to the capillary wall. Ablated particles eventually fill the plasma channel and the partially ionized plasma is ejected. It is well known that the ablated material separating the plasma core from the ablating surface can act as a vapor shield and limit the radiation heat flux reaching the ablating surface. In this work, the results from a two-dimensional simulation model for ET plasma discharges are presented. The simulation of the plasma in a two-dimensional domain combined with the diffusion approximation for radiation heat transfer is shown to successfully simulate the effects of the vapor shield layer that develops inside these devices.

Modeling the Effects of Focal Adhesion Size Restriction on Cell Shape during Spreading

Focal adhesions (FAs) are known to exhibit mechanosensitive properties. Changes in FA size, distribution, and dynamics is leveraged in controlling various signaling networks that enable a cell to demonstrate mechanochemical sensitivity to its environment. Here, we present a two-dimensional model and finite element simulations of a cell interacting with a deformable substrate through FA complexes. The cell is treated as a hypoelastic material that is allowed to undergo active deformation representative of spreading and localized actomyosin contractions, and the substrate is modeled as linearly elastic. FA complexes are modeled by collections of linear springs that can form and break dynamically. Our aim is to understand how controlling the size of FAs, either via disassembly by microtubules or by ligand patterning, affects cellular responses. We model microtubule induced FA disassembly by systematically removing FA springs from regions closest to the cell nucleus. Alternately we also examine control of FA size by ligand patterning using reaction-diffusion equations describing the interchange between bound and unbound integrins, which accounts for the conservation of the total number of integrins within the cell. We verify our model of the coupling between integrin activation and actomyosin contractions by demonstrating that stress fibers form between adhesive patches as reported in the experimental work of Thery et al [1]. In addition, we compare the effects of the proposed two models for controlling FA evolution on intracellular stresses, substrate displacement patterns, FA distribution, and cell shape for different substrate stiffnesses and ligand patterns.[1] M. Thery, A. Pepin, E. Dressaire,Y. Chen, and M. Bornens (2006). Cell Distribution of Stress Fibers in Response to the Geometry of the Adhesive Geometry, Cell Motility and the Cytoskeleton, 63, pp. 341-355.

Proposal of Two-dimensional Local Curvature Multi-vertex Model for Grain Growth Simulation

Proposal of Two-dimensional Local Curvature Multi-vertex Model for Grain Growth Simulation

Simulation of solidification process for billet with ϕ350mm section, continuous casted

The quality of continuous casting product depends both on the quality of the steel, and on technological parameters adopted during the casting and how solidification of billets is conducted. A simulation of the solidifying process is very useful in the industrial casting practice, providing specialists with information about the phenomena during the process and the manner in which certain parameters may vary in order to obtain the desired effects. This paper presents a two-dimensional simulation model that can be used in the continuous casting process, when micro-coolers are used in order to control thermal regime during solidification.

Modelling of Gas Tungsten Arc Welding Pool under Marangoni Convection

Due to lack of comprehensive experimental studies on welding processes, and to better understand the mechanisms behind these processes, especially the weld pool shape variations suspected due to Marangoni Effect or surface tension shear stress, a two-dimensional simulation model was developed to study the physics of gas tungsten arc welding (GTAW). Experimental spot-welds on Ti-5Al-5Mo-5V-3Cr was carried out to compare to the model for crucial clues such as, the magnitude of Marangoni convectional stress that is difficult to determine experimentally; and to estimate the Enhancement Factor, an artificial parameter incorporated into the model proven to account for any discrepancies between simulated results and experimental weld pool shapes, due to lack of viscosity temperature dependent data as well as flow instabilities. The model confirmed that Marangoni Convection is indeed the most dominant force in shaping the weld pool, followed by thermal buoyancy force and electromagnetic force. As the investigation went on, the validity of past welding simulations assuming a constant flow scheme was examined, concluding with the recommendation of applying a laminar flow regime at the initial welding times and turbulent flow with elapsing welding time to effectively eliminate simulation inaccuracies.

A two-dimensional simulation model for the molded underfill process in flip chip packaging

The flip chip process involves the deposition of solder bumps on the chip surface and their subsequent direct attachment and connection to a substrate. Underfilling traditional flip chip packaging is typically performed following a two-step approach. The first step uses capillary force to fill the gap between the chip and the substrate, and the second step uses epoxy molding compound (EMC) to overmold the package. Unlike traditional flip chip packaging, the molded underfill (MUF) concept uses a single-step approach to simultaneously achieve both underfill and overmold. MUF is a simpler and faster process. In this study, a 2D numerical model is developed to simulate the front movement of EMC flow and the void formation for different geometric parameters. The 2D model simplifies the procedures of geometric modeling and reduces the modeling time for the MUF simulation. Experiments are conducted to verify the prediction results of the model. The effect on void formation for different geometric parameters is investigated using a 2D model.

An extended two-dimensional borehole heat exchanger model for simulation of short and medium timescale thermal response

Common approaches to the simulation of Borehole Heat Exchangers (BHEs) assume heat transfer in circulating fluid and grout to be in a quasi-steady state and ignore fluctuations in fluid temperature due to transport of the fluid around the U-tube loop. Such effects have been shown to have an impact on peak temperatures and hence operation of heat pumps systems when short time scales are considered. A model has been developed that combines a two-dimensional numerical model and models of the pipe loop components. A novel heat exchanger analogy is employed to calculate the heat exchanger outlet temperatures such that iterative procedures can be avoided and numerical stability is unconditional. These approaches result in a model that is computationally efficient and captures much of the short timescale dynamic effects represented in fully three-dimensional models. This is demonstrated by comparison with experimental data and by comparing two and three-dimensional model behaviour in the frequency domain. Predicted monthly outlet temperatures and heat transfer rates are furthermore shown to be in close agreement with experimental values and in good agreement with existing borehole heat exchanger models. The model is computationally efficient enough to allow use in routine analysis and design tasks.

Numerical simulation for the production of chemically active species in primary and secondary streamers in atmospheric-pressure dry air

Production of chemically active species in primary and secondary streamers is investigated using a two-dimensional axisymmetric numerical simulation model. The production processes of N2(v = 1), O(3P) and N(4S), which each have different threshold energies, are simulated using experimentally obtained pulsed voltages with peak values, Vpeak, of 18, 24 and 30 kV in dry air at atmospheric pressure. As Vpeak increases, the simulated length of the secondary streamer increases, although there is little change in the primary streamer characteristics. This means that the ratio of the secondary streamer phase to the primary streamer phase increases for increasing Vpeak. The simulated results show that as Vpeak increases, the energy efficiency of O(3P) production increases and that of N2(v = 1) production decreases. On the other hand, the energy efficiency of N(4S) production has reduced dependence on Vpeak. These characteristics can be explained by the spatiotemporal variations of the reduced electric field in the primary and secondary streamer.

A Comparison of learning gains when using a 2D simulation tool versus a 3D virtual world: An experiment to find the right representation involving the Marginal Value Theorem

The use of three-dimensional Virtual Worlds in the classroom offers the promise of engaging and authentic learning experiences. Given the effort and investment involved in the creation of these worlds, more studies are needed which measure the learning gains. In particular, greater understanding is needed concerning what aspects of the technology are beneficial for learning what sort of content and in what context. We conducted two experimental studies involving 129 biology students over a two-year period that sought to make a contribution towards this understanding. Our study compared the knowledge of students after a traditional classroom lecture about a biological theorem known as Marginal Value Theorem, with their knowledge after they were exposed to simulations of two-dimensional models developed in NetLogo and three-dimensional models developed in Unity3D. Perhaps due to cognitive overload and distractors in the virtual world, it appears that the two-dimensional NetLogo model delivered better learning outcomes.

유인수로의 운영에 따른 달성보 인공하도식 어도의 유인효율 평가

In this study, the attraction efficiency of the by-pass fishway installed at Dalseong Weir in Nakdong River was assessed according to operation of the attraction waterway by using River2D which is a two-dimensional physical habitat simulation model. The model was calibrated and validated through the measured water elevation. The attraction efficiency of the fishway was evaluated at the low flow condition because the target fish, Zacco platypus (Z. platypus), have moved frequently up and downstream at the spawning season from April to June. From simulation results, it can be deduced that the attraction efficiency at situation of open attraction waterway is superior to that of close attraction waterway. Also it is shown that velocity field at inner region of the fishway is suitable for migration of the fish.

Ferrogels cross-linked by magnetic nanoparticles—Deformation mechanisms in two and three dimensions studied by means of computer simulations

Ferrogels, i.e., magnetic nanoparticles immersed into a swollen polymer gel, are materials which combine the magnetic properties of a ferrofluid with the elastic properties of a hydrogel. This makes it possible to control their shape and elasticity by means of external magnetic fields. Magnetic gels are therefore considered for medical and technical applications such as actuation and drug delivery systems. In this paper, we focus on a special class of magnetic gels in which the magnetic nanoparticles act as the cross-linkers of the polymer network. Experimentally this is achieved by functionalizing the nanoparticles' surface such that the polymers can covalently bind to it. In this way, a coupling between the orientation of the nanoparticles and the polymer matrix is created. When an external magnetic field is applied to such a system, the magnetic particles align to the field, and due to the coupling between the nanoparticles' orientation and the gel matrix, a strain is exerted on the polymers. This leads to a shrinking of the gel as a whole. In this paper, we explain how to extend a two-dimensional simulation model for such a system (Soft Matter 8 (2012) 9923 [18]) to three dimensions. We will show that, while an isotropic deformation was observed in the two-dimensional case, in three dimensions the gel shrinks anisotropically. This is due to the fact that orientational fluctuations of the nanoparticles are hindered in the direction perpendicular to an external magnetic field.

Event Based Flood Inundation Mapping Under the Impact of Climate Change: A Case Study in Lower Kelani River Basin, Sri Lanka

The downstream low lying region of the Kelani River including the Colombo suburbs, experience severe inundation due to localized heavy rainfall events and high precipitation in the upper basin. Under the impact of climate change it is very likely that more frequent heavy rainfalls in tropics [1] will occur. Therefore it is extremely important to have a better understanding about future rainfall patterns and intensities in the basin and inundation extents of the low lying regions characterized by high population concentration and economic activities that form the suburbs of the commercial capital. This paper presents the extreme rainfalls occurrence potential and resulting flood inundation along the lower reach of Kelani River. Coarse grid atmospheric parameters provided by GCM models for A2 and B2 scenarios of IPCC [1] are downscaled to catchment scale by the application of Statistical Downscaling Model (SDSM). Flood discharge and inundation along the Kelani River reach below Hanwella was analyzed by the application of two-dimensional flood simulation model (FLO-2D). Inflow to the model at Hanwella, is estimated by the HEC- HMS model under future extreme rainfall events. Areas vulnerable for inundation under the above climate change scenarios are presented.

Finite Element Simulation and Experiment of Mechanical Expanding for Longitudinal Welded Pipe

A two-dimensional finite element simulation model of longitudinal welded pipe is established by the nonlinear finite element software ABAQUS. Testing enlargement mould is used for the expanding experiments for the welded pipe under the laboratory condition. The expanding force, ovality and the shape are simulated and measured. Comparing the experimental and the simulated results, the values are fitted well.

Understanding the Role of Substrate Elasticity on Intracellular Stresses during Cell Spreading

We present a two-dimensional mathematical model and finite element simulations of a cell interacting with a deformable substrate to better understand how substrate mechanical properties affect cellular mechanical response and spread areas. The cell is treated as an actively deforming hypoelastic material and the substrate is linearly elastic. The model predicts stress and displacement fields in both the cell and the substrate. This model of cell and substrate mechanics is coupled to models describing active cellular deformation due to stress fiber contraction and evolution of focal adhesions. In this work we compare cellular stresses and substrate displacements predicted by the model on substrates of increasing stiffness against two experimental works i) Hersh et. al. 20131 with cardiomyocytes and (ii) Marinkovic et. al. 20122 with hMSc's. The model predicts an increase in compressive stresses within the cell for the two cell types with increasing substrate stiffness between 1kPa-90kPa, which is in agreement with experimental results. Further model predictions of increase in substrate displacements with substrate stiffness are in good quantitative agreement with the experimental results. In addition on softer substrates we predict that increased stress fiber contraction due to a greater compliance of the substrate at the sites of attachment results in smaller spread areas.

Investigating parametric effects on performance of a high-temperature URSOFC

Summary The aim of this paper is to investigate the effects of variable parameters on the performance of a unitized regenerative solid oxide fuel cell (URSOFC) using a two-dimensional axisymmetric simulation model. This model was validated using the performance curves of an in-house button-type URSOFC. The parameters studied include the operating temperature and the porosity, tortuosity, and grain diameter of the electrodes while the URSOFC is operated in the solid oxide fuel cell mode and the solid oxide electrolyzer cell (SOEC) mode. The predicted results show that the temperature and the electrode porosity have a beneficial effect on the performance of the URSOFC because of an enhancement of the electrochemical reactions and the species mass transfer, respectively. However, when the URSOFC is operated in the SOEC mode, the cell performance decreases as the electrode porosity increases. This indicates that the decreasing reaction active sites as a result of the higher porosity have a dominant effect on the performance in the SOEC mode. The cell performance also decreases as the tortuosity and grain diameter of the electrodes increase. In addition, the effect of the electrode grain diameter on the cell performance is predicted to be insignificant for the URSOFC operated in the SOEC mode. The results of investigations presented in this paper can assist in the optimal design and management of a URSOFC. Copyright © 2014 John Wiley & Sons, Ltd.

Numerical investigation of the nonlinear flow characteristics in an ultra-supercritical utility boiler furnace

The temperature deviation is an inherent issue in large-scale tangentially fired pulverized-coal boilers. This article investigates numerically the forming mechanism of gas velocity and temperature deviations from the perspective of nonlinear flow characteristics in an ultra-supercritical utility boiler. Firstly, the cold state simulations of two-dimensional and three-dimensional models of furnace are performed. With the increase of Reynolds number from burner nozzles, the temperature and velocity distributions in furnace show the trend of symmetrical, slightly asymmetrical, and completely asymmetrical. The generated tangential radius of flow becomes larger and declining. It is concluded that the nonlinear flow characteristics is the key issue for the velocity and temperature deviations in the tangentially fired pulverized-coal boiler furnace. Secondly, the full combustion simulation is carried out under BMCR (Boiler Maximum Continuous Rating) conditions and validated by experimental measurement. It is also found that the centre of tangent circle becomes larger along the height of the boiler furnace and deflects though the burner structure and boundary conditions are absolutely symmetrical. The temperature and velocity distributions are asymmetrical under BMCR conditions. Due to the nonlinear flow, it inevitably brings the residual swirling flow at the upper furnace zone which is one origin of temperature deviation of the gas after the furnace exit.

Steady seepage simulation of underground oil storage caverns based on Signorini type variational inequality formulation

To analyze the seepage characteristics of water-sealed underground oil storage caverns, a calculation software was programmed based on the Signorini type variational inequality formulation. The storage region and boundary condition of oil-groundwater contact surface were generalized, and a two-dimensional numerical simulation model of finite-element method was built. The seepage characteristics and the water inflow of oil storage caverns were analyzed, while the conditions of different oil levels in caverns with water curtain system were taken into account. The effect of a water curtain system was assessed, and the design parameters of water curtain system such as width, water pressure, borehole space, and elevation were evaluated. The seepage simulation model was applied to estimate the seepage field and water inflow of the Huangdao underground oil storage caverns during the future operation period.

Parallel continuous simulated tempering and its applications in large-scale molecular simulations

In this paper, we introduce a parallel continuous simulated tempering (PCST) method for enhanced sampling in studying large complex systems. It mainly inherits the continuous simulated tempering (CST) method in our previous studies [C. Zhang and J. Ma, J. Chem. Phys. 130, 194112 (2009); C. Zhang and J. Ma, J. Chem. Phys. 132, 244101 (2010)], while adopts the spirit of parallel tempering (PT), or replica exchange method, by employing multiple copies with different temperature distributions. Differing from conventional PT methods, despite the large stride of total temperature range, the PCST method requires very few copies of simulations, typically 2-3 copies, yet it is still capable of maintaining a high rate of exchange between neighboring copies. Furthermore, in PCST method, the size of the system does not dramatically affect the number of copy needed because the exchange rate is independent of total potential energy, thus providing an enormous advantage over conventional PT methods in studying very large systems. The sampling efficiency of PCST was tested in two-dimensional Ising model, Lennard-Jones liquid and all-atom folding simulation of a small globular protein trp-cage in explicit solvent. The results demonstrate that the PCST method significantly improves sampling efficiency compared with other methods and it is particularly effective in simulating systems with long relaxation time or correlation time. We expect the PCST method to be a good alternative to parallel tempering methods in simulating large systems such as phase transition and dynamics of macromolecules in explicit solvent.