Parameterizing the Effects of Tumor Shape in Magnetic Nanoparticle Thermotherapy Through a Computational Approach

In this work effects of tumor shape on magnetic nanoparticle hyperthermia (MNPH) are investigated and evaluated using four categories (spherical, oblate, prolate, and egg-shape) of tumor models having different morphologies. These tumors have equal volume; however, due to the differences in their shapes, they have different surface areas. The shape of tumors is quantified in terms of shape factor (ζ). Simulations for MNPH are done on the physical model constituting tumor tissue enclosed within the healthy tissue. Magnetic hyperthermia is applied (frequency 150 kHz, and magnetic field amplitude 20.5 kA/m) to all tumor models, for 1 hour, after injection of magnetic nanoparticles (MNPs) at the respective tumor centroids. The distribution of MNPs after injection is considered Gaussian. The governing model (Pennes' bioheat model) of heat transfer in biological media is solved with the finite volume-immersed boundary (FV-IB) method to simulate MNPH. Therapeutic effects are calculated using the Arrhenius tissue damage model, cumulative equivalent minutes at 43°C (CEM 43), and heterogeneity in temperature profiles of the tumors. Results show that the therapeutic effects due to MNPH depend significantly on the shape of a tumor. Tumors with higher shape factors receive less therapeutic effects in comparison to the tumors having lower shape factors. An empirical thermal damage model is also developed to assess the MNPH efficacy in real complex-shaped tumors.

Studying the deployment of high-lift devices by using dynamic immersed boundaries

Purpose This paper aims to describe a research effort towards the comprehension of the unsteady phenomena due to the deployment of high-lift devices at approach/landing conditions. Design/methodology/approach The work starts from a preexisting platform based on an immersed boundary (IB) method whose capabilities are extended to study compressible and viscous flows around moving/deforming objects. A hybrid Lagrangian-Eulerian approach is designed to consider the motion of multiple bodies through a fixed Cartesian mesh. That is, the cells’ volumes do not move in space but rather they observe the solid walls crossing themselves. A dynamic discrete forcing makes use of a moving least-square procedure which has been validated by simulating well-known benchmarks available for rigid body motions. Partitioned fluid-structure interactions (FSI) strategies are explored to consider aeroelastic phenomena. A shared platform, between the aerodynamic and the structural solvers, fulfils the loads’ transfer and drives the sequence of the operating steps. Findings The first part of the results is devoted to a basic two-dimensional study aiming at evaluating the accuracy of the method when simple rigid motions are prescribed. Afterwards, the paper discusses the solution obtained when applying the dynamic IB method to the rigid deployment of a Krueger-flap. The final section discusses the aeroelastic behaviour of a three-element airfoil during its deployment phase. A loose FSI coupling is applied for estimating the possible loads’ downgrade. Research limitations/implications The IB surfaces are allowed to move less than one IB-cell size at each time-step de-facto restricting the Courant-Friedrichs-Lewy (CFL) based on the wall velocity to be smaller than unity. The violation of this constraint would impair the explicit character of the method. Practical implications The proposed method improves automation in FSI numerical analysis and relaxes the human expertise/effort for meshing the computational domain around complex three-dimensional geometries. The logical consequence is an overall speed-up of the simulation process. Originality/value The value of the paper consists in demonstrating the applicability of dynamic IB techniques for studying high-lift devices. In particular, the proposed Cartesian method does not want to compete with body-conforming ones whose accuracy remains generally superior. Rather, the merit of this research is to propose a fast and automatic simulation system as a viable alternative to classic multi-block structured, chimaera or unstructured tools.

Immersed boundary method for multiphase transport phenomena

Multiphase flows with momentum, heat, and mass transfer exist widely in a variety of industrial applications. With the rapid development of numerical algorithms and computer capacity, advanced numerical simulation has become a promising tool in investigating multiphase transport problems. Immersed boundary (IB) method has recently emerged as such a popular interface capturing method for efficient simulations of multiphase flows, and significant achievements have been obtained. In this review, we attempt to give an overview of recent progresses on IB method for multiphase transport phenomena. Firstly, the governing equations, the basic ideas, and different boundary conditions for the IB methods are introduced. This is followed by numerical strategies, from which the IB methods are classified into two types, namely the artificial boundary method and the authentic boundary method. Discussions on the implementation of various boundary conditions at the interphase surface with momentum, heat, and mass transfer for different IB methods are then presented, together with a summary. Then, the state-of-the-art applications of IB methods to multiphase flows, including the isothermal flows, the heat transfer flows, and the mass transfer problems are outlined, with particular emphasis on the latter two topics. Finally, the conclusions and future challenges are identified.

Morphometry of Male Reproductive Organ and Sperm Evaluation of Belgian Blue Crossbreed Cattle as a Candidate of Superior Bull

The purpose of this study was to observe the size of reproductive organ and to evaluate the sperm quality of Belgian Blue (BB) crossbreed cattle. This cattle are the crossbreeding result between a female Brahman Cross (BX) cattle inseminated with frozen semen from pure male BB cattle, by Artificial Insemination (IB) method, as a candidate of superior bull. The samples of this study were 2.5 years old (BB1), (BB2), and (BB3) crossbreed cattle. Its process involved general physical examination, genital organ inspection, sperm production, and quality assessment. The data obtained were analyzed through descriptive analysis. The results of this study were the three BB crossbred cattle showed the good appearance of normal reproductive organs with scrotum circumferences of each bull were 40.2 cm, 38.6 cm, and 39.8 cm respectively, and sperm quality of the good and the normal motility values of each bull were 82%, 81% and 80%, viability 84%, 83%, and 86%, and the sperm concentrations of each bull were 2.218 million/ml, 1.986 million/ml and 2.120 million/ml respectively. As a result, it could be concluded that those three BB crossbreed cattle are suitable for being used as a superior bull.

Immersed Boundary Method for Simulating Interfacial Problems

We review the immersed boundary (IB) method in order to investigate the fluid-structure interaction problems governed by the Navier–Stokes equation. The configuration is described by the Lagrangian variables, and the velocity and pressure of the fluid are defined in Cartesian coordinates. The interaction between two different coordinates is involved in a discrete Dirac-delta function. We describe the IB method and its numerical implementation. Standard numerical simulations are performed in order to show the effect of the parameters and discrete Dirac-delta functions. Simulations of flow around a cylinder and movement of Caenorhabditis elegans are introduced as rigid and flexible boundary problems, respectively. Furthermore, we provide the MATLAB codes for our simulation.

Large eddy simulation coupled with immersed boundary method for turbulent flows over a backward facing step

In the present work, large eddy simulation coupled with immersed boundary (LES-IB) method is applied to simulate a backward facing step (BFS) flow, which is a canonical fluid dynamics problem involving flow separation, recirculation and reattachment that are common in many practical applications. The computed reattachment length, a primary parameter to evaluate the overall performance of the numerical method, shows promising accuracy in the present work compared to the alternative numerical simulations. Based on the mean velocity profiles at four representative locations, there is fairly well quantitative agreement among the present LES-IB, DNS and the experiment. The results reveal that the reverse flow in the reattachment region leads to little over-prediction of the reattachment length compared to the DNS result. Furthermore, second-order statistics are in good agreement with the reference data in spite of discrepancies in the recirculation and reattachment region owing to complex flow structure, verifying the accuracy of the present method. In addition, the instantaneous flow fields are also analyzed to show the capability of the present LES-IB method in vortex-capture, and one may see the transient process of flow separation based on the analysis of Lagrangian coherent structure (LCS).

Evaluating Implementations of the Immersed Boundary Method in the Weather Research and Forecasting Model

The terrain-following coordinate system used by many atmospheric models can cause numerical instabilities due to discretization errors as resolved terrain slopes increase and the grid becomes highly skewed. The immersed boundary (IB) method, which does not require the grid to conform to the terrain, has been shown to alleviate these errors, and has been used successfully for high-resolution atmospheric simulations over steep terrain, including vertical building surfaces. Since many previous applications of IB methods to atmospheric models have used very fine grid resolution (5 m or less), the present study seeks to evaluate IB method performance over a range of grid resolutions and aspect ratios. Two classes of IB algorithms, velocity reconstruction and shear stress reconstruction, are tested within the common framework of the Weather Research and Forecasting (WRF) Model. Performance is evaluated in two test cases, one with flat terrain and the other with the topography of Askervein Hill, both under neutrally stratified conditions. WRF-IB results are compared to similarity theory, observations, and native WRF results. Despite sensitivity to the location at which the IB intersects the model grid, the velocity reconstruction IB method shows consistent performance when used with a hybrid RANS/LES surface scheme. The shear stress reconstruction IB method is not sensitive to the grid intersection, but is less consistent and near-surface velocity errors can occur at coarse resolutions. This study represents an initial investigation of IB method variability across grid resolutions in WRF. Future work will focus on improving IB method performance at intermediate to coarse resolutions.

Locomotion of a self-propulsive pitching plate in a quiescent viscous fluid

The locomotion of a flexible plate pitching in a quiescent viscous fluid is numerically studied by using the lattice Boltzmann method (LBM) for the fluid and a finite element method (FEM) for the plate, with an immersed boundary (IB) method for the fluid–structure interaction (FSI). In the simulation, the leading edge of the plate undergoes a prescribed pitching motion, and the entire plate moves freely due to the fluid–plate interaction. The effects of the pitching amplitude, bending rigidity, plate-to-fluid mass ratio and Reynolds number on the propulsive performance of the flexible plate are examined in a range of parameters. The numerical results show that a certain flexibility can remarkably improve the propulsive speed and efficiency. The optimal parameters for the pitching plate are obtained, i.e. [Formula: see text] ([Formula: see text] is a non-dimensional frequency, with [Formula: see text] means rigid plate and larger [Formula: see text] means more flexible) and 20° ≤ α0 ≤ 25° ( α0 is the pitching amplitude). The comparisons of three plate-to-fluid mass ratios (1.0, 2.5 and 5.0) show that the mass of the plate decreases the propulsive speed, but contrarily increases the efficiency. The results obtained in the present study provide an insight into the understanding of the performance of self-propulsive plate in pitching motion and can further guide the engineering design of micro aerial vehicles.