Study of the conservation properties in two-way coupled dispersed multiphase flows using finite volume methods

In order to simulate dispersed multiphase flows, the coupling level must be determined according to the volume fraction in the system. The volume fraction is the ratio of the total volume of the dispersed phases over the total volume of the flow. In dilute flows, with volume fractions smaller than 10-6, only the influence of carrier phase over the dispersed phase is considered which is known as one-way coupling. Nonetheless, in dispersed flows with higher volume fractions, the effect of the dispersed phase over the continuous one should be taken into consideration, known as two-way coupling. This effect normally is applied as a source term in the conservation equations of the carrier phase. Depending on the numerical method and the discrete operators employed, these source terms can lead to some issues when aiming to preserve physical properties like mass, momentum and energy. Moreover, in order to validate the two-way coupling method, a particle-laden turbulent flow benchmark case with a mass loading of 22% is simulated by means of large eddy numerical simulation (LES). The aim of this work is to study the conservation properties of dispersed multiphase flows like momentum, kinetic energy and thermal energy through two-way coupling between dispersed and continuous phases.

On the modeling of ultrasound wave propagation in the frame of inverse problem solution

In this paper we consider the inverse problem of detecting the inclusions inside the human tissue by using the acoustic sounding wave. The problem is considered in the form of coefficient inverse problem for first-order system of PDE and we use the gradient descent approach to recover the coefficients of that system. The important part of the sceme is the solution of the direct and adjoint problem on each iteration of the descent. We consider two finite-volume methods of solving the direct problem and study their Influence on the performance of recovering the coefficients.

Three-Dimensional Numerical Modeling of a Coastal Highway Bridge under Stokes Waves

This article investigated the effect of structural flexibility on a coastal highway bridge subjected to Stokes waves through a three-dimensional numerical model. Wave-bridge interaction modeling was performed by an FSI model with the coupling of finite element and finite volume methods. An experimental model validated the FSI numerical analysis. Eventually, the overall results of hydrodynamic and structural analyses are presented and discussed. The results illustrate that the structural flexibility significantly increases the initial shock of the wave force on the flexible bridge. In contrast, the fixed bridge tolerates the least forces in the initial shock of the wave force. Then, by adding a wedge-shaped part to the bridge structure, an attempt was made to reduce the initial shock of the wave force to the structure. The results showed the wedge-shaped part with an angle of 30° reduces the initial shock of wave forces down to 50% for horizontal force and 43% for vertical force on the flexible structure.

Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. IV. Application to Solar Observations

In this ISSI-supported series of studies on magnetic helicity in the Sun, we systematically implement different magnetic helicity calculation methods on high-quality solar magnetogram observations. We apply finite-volume, discrete flux tube (in particular, connectivity-based) and flux-integration methods to data from Hinode’s Solar Optical Telescope. The target is NOAA Active Region 10930 during a 1.5-day interval in 2006 December that included a major eruptive flare (SOL2006-12-13T02:14X3.4). Finite-volume and connectivity-based methods yield instantaneous budgets of the coronal magnetic helicity, while the flux-integration methods allow an estimate of the accumulated helicity injected through the photosphere. The objectives of our work are twofold: a cross-validation of methods, as well as an interpretation of the complex events leading to the eruption. To the first objective, we find (i) strong agreement among the finite-volume methods, (ii) a moderate agreement between the connectivity-based and finite-volume methods, (iii) an excellent agreement between the flux-integration methods, and (iv) an overall agreement between finite-volume- and flux-integration-based estimates regarding the predominant sign and magnitude of the helicity. To the second objective, we are confident that the photospheric helicity flux significantly contributed to the coronal helicity budget and that a right-handed structure erupted from a predominantly left-handed corona during the X-class flare. Overall, we find that the use of different methods to estimate the (accumulated) coronal helicity may be necessary in order to draw a complete picture of an active region corona, given the careful handling of identified data (preparation) issues, which otherwise would mislead the event analysis and interpretation.

Metamodels’ Development for High Pressure Die Casting of Aluminum Alloy

Simulation is a very useful tool in the design of the part and process conditions of high-pressure die casting (HPDC), due to the intrinsic complexity of this manufacturing process. Usually, physics-based models solved by finite element or finite volume methods are used, but their main drawback is the long calculation time. In order to apply optimization strategies in the design process or to implement online predictive systems, faster models are required. One solution is the use of surrogate models, also called metamodels or grey-box models. The novelty of the work presented here lies in the development of several metamodels for the HPDC process. These metamodels are based on a gradient boosting regressor technique and derived from a physics-based finite element model. The results show that the developed metamodels are able to predict with high accuracy the secondary dendrite arm spacing (SDAS) of the cast parts and, with good accuracy, the misrun risk and the shrinkage level. Results obtained in the predictions of microporosity and macroporosity, eutectic percentage, and grain density were less accurate. The metamodels were very fast (less than 1 s); therefore, they can be used for optimization activities or be integrated into online prediction systems for the HPDC industry. The case study corresponds to several parts of aluminum cast alloys, used in the automotive industry, manufactured by high-pressure die casting in a multicavity mold.