Full Three-dimensional Simulations Research Articles

An Analysis of Microwave Ablation Parameters for Treatment of Liver Tumors from the 3D-IRCADb-01 Database.

Simulation techniques are powerful tools for determining the optimal conditions necessary for microwave ablation to be efficient and safe for treating liver tumors. Owing to the complexity and computational resource consumption, most of the existing numerical models are two-dimensional axisymmetric models that emulate actual three-dimensional cancers and the surrounding tissue, which is often far from reality. Different tumor shapes and sizes require different input powers and ablation times to ensure the preservation of healthy tissues that can be determined only by the full three-dimensional simulations. This study aimed to tailor microwave ablation therapeutic conditions for complete tumor ablation with an adequate safety margin, while avoiding injury to the surrounding healthy tissue. Three-dimensional simulations were performed for a multi-slot microwave antenna immersed in two tumors obtained from the 3D-IRCADb-01 liver tumors database. The temperature dependence of the dielectric and thermal properties of healthy and tumoral liver tissues, blood perfusion, and water content are crucial for calculating the correct ablation time and, thereby, the correct ablation process. The developed three-dimensional simulation model may help practitioners in planning patient-individual procedures by determining the optimal input power and duration of the ablation process for the actual shape of the tumor. With proper input power, necrotic tissue is placed mainly in the tumor, and only a small amount of surrounding tissue is damaged.

Vortex breakdown in time-dependent electromagnetically driven flow between concentric spheres

The electromagnetically driven flow in the wide gap of a concentric sphere system is studied experimentally and numerically in the laminar regime (Re≤1540). The azimuthal driving Lorentz force is primarily promoted by the interaction of a direct current and a dipolar magnetic field. The current is injected through two ring-shaped copper electrodes located at the equatorial zone of each sphere, and the magnetic field is produced by a permanent magnet located inside the inner sphere. Velocity profiles for the azimuthal component in the equatorial plane were obtained with particle image velocimetry, and the radial velocity component of the flow was recorded using ultrasonic Doppler velocimetry. Laser-fluorescein technique was used for flow visualization. It was found that for a critical electric current (Re = 1140), an instability occurs and the flow becomes time-dependent. We found, theoretically and experimentally, a vortex breakdown structure at each of the polar zones of the spherical gap, and to the best knowledge of the authors, this is the first time it is reported with electromagnetic forcing. A full three-dimensional numerical simulation reproduces the experimental observations qualitatively and quantitatively.

Polarization-independent multimode interference coupler with anisotropy-engineered bricked metamaterial

Many applications, including optical multiplexing, switching, and detection, call for low-cost and broadband photonic devices with polarization-independent operation. While the silicon-on-insulator platform is well positioned to fulfill most of these requirements, its strong birefringence hinders the development of polarization-agnostic devices. Here we leverage the recently proposed bricked metamaterial topology to design, for the first time, to our knowledge, a polarization-independent 2 × 2 multimode interference coupler using standard 220 nm silicon thickness. Our device can be fabricated with a single etch step and is optimized for the O-band, covering a wavelength range of 160 nm with excess loss, polarization-dependent loss, and imbalance below 1 dB and phase errors of less than 5°, as demonstrated with full three-dimensional finite-difference time-domain simulations.

Dynamic response mechanism of borehole breathing in fractured formations

The borehole breathing observed when drilling into natural fractured formations is often erroneously identified as leakage or kick. The main reason for this phenomenon is that the fractures around the well have opened and closed after being affected by the wellbore pressure fluctuations. In this paper, a three-dimensional geological model is established for simulating fractured borehole breathing based on the Cohesive unit method, and the full three-dimensional simulation of fractured borehole breathing is realized for the first time. Based on this model, this paper studies the dynamic response characteristics of the fractured borehole breathing mechanism in detail, and analyzes a variety of parameters that may affect borehole breathing. The research results show that: increasing the viscosity of drilling fluid can effectively inhibit the occurrence of borehole breathing and extend its duration; formation elastic modulus is inversely correlated with borehole breathing; borehole breathing is not sensitive to changes in formation Poisson’s ratio and porosity; horizontal geostress affects the severity of borehole breathing by determining the reopening pressure of the fracture; changes in the original width of the fracture will not affect the total volume of backflow, but will affect the amount of mud lost in the early stage.

Research on steam flow excited vibration of nuclear power condenser based on full three-dimensional numerical simulation technology

Numerical calculation is regarded as the most effective research method for studying problems about a condenser due to the experimental difficulty caused by the huge size. However, almost all numerical research studies about condensers are two-dimensional, which severely reduce the reliability of the research about a three-dimensional problem. In this case, a full three-dimensional computational fluid dynamics (CFD) method based on a porous medium model was first used to study the seawater leakage event in a condenser. The steam flow field of the condenser under a series of operation conditions was obtained. The distribution of a risk coefficient of steam flow excited vibration (SFEV) was obtained as well. The results show that the sweep velocity of steam across a titanium tube was the primary factor determining the risk coefficient of SFEV. The risk of SFEV of the outer layer in the upper finger joint region is relatively high. It is necessary to install anti-abrasive strips or implement preventive tube plugging. According to the calculated results, the recommended values of electric power limits for a nuclear power unit were given, which was 840 MW under half-side condenser operation conditions in summer. Through comparing the simulated flow field before and after tube plugging, it is found that local tube plugging in the high-risk area will transfer the position of the high-risk point of SFEV.

Three-Dimensional Numerical Simulation and Experimental Investigations of Benchmark Experiment of Sn-10 wt. %Pb Alloy Solidification Under Thermosolutal Convection

Abstract A full three-dimensional (3D) numerical simulation of solidification was carried out for a benchmark experiment on a binary Sn-10 wt. %Pb alloy. The experiment process involves a melting stage, a first holding stage at constant temperature with electromagnetic stirring, setting a mean horizontal temperature difference (second holding stage), and finally solidification stage by decreasing the temperature under a imposed horizontal temperature gradient. The numerical model is applied only to investigate the solidification stage and compared with the measured temperature fields and macrosegregation obtained from the postmortem analysis. A columnar numerical model based on a two-phase volume-averaged approach is used for the numerical simulation, accounting for thermosolutal convection and assuming perfect microscopic mixing (lever rule) in the mushy zone. It demonstrates that such a model is able to predict stratification in the solute from the liquid phase and mushy zone during the solidification. The effect of the sedimentation on macrosegregations and channel segregation or freckles which develop during the solidification stage is also predicted by the model and compared with experimental data. Emphasis is given to the main factors that have a direct effect on the development and morphology of segregated channels, namely, the remelting phenomenon, dendrite fragmentation, and the solidification front instabilities.

Charge migration and attosecond solitons in conjugated organic molecules

Charge migration is the electronic response that immediately follows localized ionization or excitation in a molecule, before the nuclei have time to move. It typically unfolds on sub-femtosecond time scales and most often corresponds to dynamics far from equilibrium, involving multi-electron interactions in a complex chemical environment. While charge migration has been documented experimentally and theoretically in multiple organic and inorganic compounds, the general mechanism that regulates it remains unsettled. In this work we use tools from nonlinear dynamics to analyze charge migration that takes place along the backbone of conjugated hydrocarbons, which we simulate using time-dependent density functional theory. In this electron-density framework we show that charge migration modes emerge as attosecond solitons and demonstrate the same type of solitary-wave dynamics in both simplified model systems and full three-dimensional molecular simulations. We show that these attosecond-soliton modes result from a balance between dispersion and nonlinear effects tied to time-dependent multi-electron interactions.%Our soliton-mode mechanism, and the nonlinear tools we use to analyze it, pave the way for understanding migration dynamics in a broad range of organic molecules.%For instance, we demonstrate the opportunities for chemically steering charge migration via molecular functionalization, which can alter both the initially localized electron perturbation and its subsequent time evolution.

Optimal design of radial inflow turbine for ocean thermal energy conversion based on the installation angle of nozzle blade

Ocean Thermal Energy Conversion (OTEC), as a new type of renewable energy, has huge development potential. Turbine is the most critical component in the ocean thermal energy conversion system, which directly determines the performance and energy conversion efficiency of the system. Therefore, the optimal design of turbines is very important to improve the efficiency of ocean thermal energy conversion. Based on the full consideration of the small temperature difference application characteristics of ocean thermal energy conversion and the special thermophysical properties of organic working fluids, this paper designs an ammonia working centripetal turbine with a power of 100 kW for OTEC applications, and then analyzes the effect of different geometric parameters on turbine performance. At the same time, the key parameters of the turbine are optimized based on full three-dimensional CFD numerical simulation analysis. It's shown that the nozzle blade installation angle has a very important impact on the performance of the turbine. Through optimization, when the nozzle blade installation angle reaches 30.5°, the efficiency is 91.77%, which is 6.25% points higher than the design value. The internal flow field performance is the best without obvious shock wave and reverse vortex phenomenon, which further improves the efficiency of the turbine and improves the internal flow.

Study of the spherical Couette flow with electromagnetic stirring

The flow driven by electromagnetic forcing of an electrolytic fluid in a concentric sphere system with differential rotation is studied experimentally and theoretically in the laminar regime. The electromagnetic force is generated by the interaction of a direct current injected radially through electrodes located at the equatorial zone of the spheres and a dipolar magnetic field produced by a permanent magnet inside the inner sphere. Even though the flows are fully three-dimensional, under some assumptions, they can be mathematically modeled with a general one-dimensional solution from the incompressible Navier–Stokes equations. Additionally, in order to deepen the flow dynamics, a full three-dimensional numerical simulation is also obtained. Experimentally, velocity profiles in the equatorial plane between spheres were obtained with particle image velocimetry. The analytical solution reproduces qualitatively the experimental profiles, whereas the numerical solution reproduces quantitatively the experimental measurements.

Simulation of the Schiaparelli Entry and Comparison to Aerosciences Flight Data

The European Space Agency flew an entry, descent, and landing demonstrator module called Schiaparelli that entered the atmosphere of Mars on 19 October 2016. The entry and descent instrumentation suite had sensors on both the heat shield and backshell and included forebody pressure transducers and thermocouples (Atmospheric Mars Entry and Landing Investigations and Analysis, or AMELIA), along with aftbody pressure transducers and heat flux (COMbined Aerothermal and Radiometer Sensors instrument package, or COMARS) and narrowband radiative heatflux sensors (Infrared CO Two Measurement, or ICOTOM). Because of the failed landing attempt, only a subset of the flight data was transmitted before and after plasma blackout. The goal of this paper is to present comparisons of the flight data with calculations using NASA’s aerodynamic and aeroheating simulation tools. Simulations were conducted at various angles of attack to compare against forebody pressure data and to infer the angle of attack used in full three-dimensional simulations to calculate the total heat flux at the sensor locations. Comparisons with the COMARS total heat flux data and backshell pressure data are presented. Furthermore, due to the sparse dataset, results are also compared with the reconstructed heat flux, which was calculated from an inverse analysis of the AMELIA thermocouple data. The simulations agree within 16% for both the total heat flux measured in flight and the heat flux reconstructed from the thermocouple data. A potential link between the Schiaparelli high spin rate observed during entry as documented in the anomaly report and the unexpected stagnation point pressure measurement is also discussed.

Cloud Microphysical Implications for Marine Cloud Brightening: The Importance of the Seeded Particle Size Distribution

AbstractMarine cloud brightening (MCB) has been proposed as a viable way to counteract global warming by artificially increasing the albedo and lifetime of clouds via deliberate seeding of aerosol particles. Stratocumulus decks, which cover wide swaths of Earth’s surface, are considered the primary target for this geoengineering approach. The macroscale properties of this cloud type exhibit a high sensitivity to cloud microphysics, exposing the potential for undesired changes in cloud optical properties in response to MCB. In this study, we apply a highly detailed Lagrangian cloud model, coupled to an idealized parcel model as well as a full three-dimensional large-eddy simulation model, to show that the choice of seeded particle size distribution is crucial to the success of MCB, and that its efficacy can be significantly reduced by undesirable microphysical processes. The presence of even a small number of large particles in the seeded size spectrum may trigger significant precipitation, which will reduce cloud water and may even break up the cloud deck, reducing the scene albedo and hence counteracting MCB. On the other hand, a seeded spectrum comprising a large number of small particles reduces the fraction of activated cloud droplets and increases entrainment and evaporation of cloud water, which also reduces the efficiency of MCB. In between, there may exist an aerosol size distribution that minimizes undesirable microphysical processes and enables optimal MCB. This optimal size distribution is expected to be case dependent.

Hydrodynamic dispersion in Hele-Shaw flows with inhomogeneous wall boundary conditions

Single-phase flow inside a Hele-Shaw cell can exhibit inhomogeneous flow fields, for example when actuated by electroosmosis with varying wall mobilities, leading to internal pressure gradients. We derive a two-dimensional dispersion model for a dissolved species in such a non-uniform flow field, utilizing a multiple-scale perturbation approach. The resulting two-dimensional transport equation is an advection–diffusion equation containing an effective dispersion tensor field and additional advection-correction terms. It can be viewed as a generalization of the well-known Taylor–Aris dispersion model. The dispersion model allows for flow fields with both stationary and oscillatory components. For the special case of non-uniform flow induced by both pressure gradients and electroosmosis, we derive expressions for the flow field in the long-wavelength limit. These include arbitrary, time-dependent functions for both the driving field as well as the wall mobilities. We discuss the general characteristics of the model using a sinusoidally varying wall mobility, and derive analytical expressions for the dispersion tensor. Then, in order to validate the model, we compare three-dimensional Lagrangian particle tracing simulations with the dispersion model for several test cases, including stationary and oscillatory shear flow as well as a recirculating flow field. For each test case, a good agreement between the full three-dimensional simulations and the results of the two-dimensional dispersion model is obtained. The presented model has the potential to significantly simplify computations of mass transport in Hele-Shaw flows.

Role of surfactant-induced Marangoni stresses in drop-interface coalescence

We study the effect of surfactants on the dynamics of a drop-interface coalescence using full three-dimensional direct numerical simulations. We employ a hybrid interface-tracking/level-set method, which takes into account Marangoni stresses that arise from surface-tension gradients, interfacial and bulk diffusion and sorption kinetic effects. We validate our predictions against the experimental data of Blanchette and Bigioni (Nat. Phys., vol. 2, issue 4, 2006, pp. 254–257) and perform a parametric study that demonstrates the delicate interplay between the flow fields and those associated with the surfactant bulk and interfacial concentrations. The results of this work unravel the crucial role of the Marangoni stresses in the flow physics of coalescence, with particular attention paid to their influence on the neck reopening dynamics in terms of stagnation-point inhibition, and near-neck vorticity generation. We demonstrate that surfactant-laden cases feature a rigidifying effect on the interface compared with the surfactant-free case, a mechanism that underpins the observed surfactant-induced phenomena.

A fast algebraic approach for noninvasive prediction of fractional flow reserve in coronary arteries

The fractional flow reserve (FFR) index is an important clinical indicator for characterizing coronary artery disease (CAD) functional significance, allowing cardiologists to decide whether intervention is required or not. Noninvasive techniques for calculating FFR are still incompletely resolved and rely heavily on time consuming numerical methods, which may hinder their clinical translation. This paper reports on the development of two fast and noninvasive methods for predicting FFR in diseased coronary arteries. The new methods are derived from physical principles and account for patient-specific physiological parameters that can be noninvasively measured. The developed algebraic equations calculate FFR without performing any tedious numerical simulations, making them attractive for clinical applications. The performance of the methods is assessed by comparing their predictions with measurements and with results obtained by full three-dimensional numerical simulations on healthy and diseased idealized coronary arteries and actual anatomical branches. Results generated by the new methodology are within 5% of measurements and in very good agreement with values obtained numerically.

Generation and effects of electromotive force in turbulent stochastic reconnection

Reconnection is an important process that rules dissipation and diffusion of magnetic energy in plasmas. It is already clear that its rate is enhanced by turbulence and that reconnection itself may increase its stochasticity, but the main mechanism that connects these two effects is still not completely understood. The aim of this work is to identify, from the terms of the electromotive force, the dominant physical process responsible for enhancing the reconnection rate in turbulent plasmas. We employ full three-dimensional numerical simulations of turbulence driven by stochastic reconnection and estimate the production and dissipation of turbulent energy and cross-helicity, the amount of produced residual helicity, and determine the relation between these quantities and the reconnection rate. We observe the development of the electromotive force in the studied models with plasma-β=0.1−2 and the Lundquist number S=10−5−10−4. The turbulent energy and residual helicity develop in the large-scale current sheet, with the latter decreasing the effects of turbulent magnetic diffusion. We demonstrate that the stochastic reconnection, apart from the turbulence, can produce a finite value of cross-helicity (the magnitude of the turbulent cross-helicity to energy of the order of 10−5−10−3). Under this situation, the cross-helicity to turbulent energy ratio, however, has no correlation with the reconnection rate. We show that in this range of magnitude, the cross-helicity is not a necessary condition for fast reconnection to occur. The results suggest that cross-helicity is inherent to turbulent fields, but the reconnection rate enhancement is possibly caused by the effects of magnetic turbulent diffusion and controlled by the residual helicity.

Colliding-Wind Binaries as a Source of TeV Cosmic Rays

In addition to gamma-ray binaries which contain a compact object, high-energy and very high–energy gamma rays have also been detected from colliding-wind binaries. The collision of the winds produces two strong shock fronts, one for each wind, both surrounding a shock region of compressed and heated plasma, where particles are accelerated to very high energies. Magnetic field is also amplified in the shocked region on which the acceleration of particles greatly depends. In this work, we performed full three-dimensional magnetohydrodynamic simulations of colliding winds coupled to a code that evolves the kinematics of passive charged test particles subject to the plasma fluctuations. After the run of a large ensemble of test particles with initial thermal distributions, we show that such shocks produce a nonthermal population (nearly 1% of total particles) of few tens of GeVs up to few TeVs, depending on the initial magnetization level of the stellar winds. We were able to determine the loci of fastest acceleration, in the range of MeV/s to GeV/s, to be related to the turbulent plasma with amplified magnetic field of the shock. These results show that colliding-wind binaries are indeed able to produce a significant population of high-energy particles, in relatively short timescales, compared to the dynamical and diffusion timescales.

High-Performance On-Chip Silicon Beamsplitter Based on Subwavelength Metamaterials for Enhanced Fabrication Tolerance.

Efficient power splitting is a fundamental functionality in silicon photonic integrated circuits, but state-of-the-art power-division architectures are hampered by limited operational bandwidth, high sensitivity to fabrication errors or large footprints. In particular, traditional Y-junction power splitters suffer from fundamental mode losses due to limited fabrication resolution near the junction tip. In order to circumvent this limitation, we propose a new type of high-performance Y-junction power splitter that incorporates subwavelength metamaterials. Full three-dimensional simulations show a fundamental mode excess loss below 0.1 dB in an ultra-broad bandwidth of 300 nm (1400–1700 nm) when optimized for a fabrication resolution of 50 nm, and under 0.3 dB in a 350 nm extended bandwidth (1350–1700 nm) for a 100 nm resolution. Moreover, analysis of fabrication tolerances shows robust operation for the fundamental mode to etching errors up to ±20 nm. A proof-of-concept device provides an initial validation of its operation principle, showing experimental excess losses lower than 0.2 dB in a 195 nm bandwidth for the best-case resolution scenario (i.e., 50 nm).

Probabilistic Bearing Capacity Prediction of Square Footings on 3D Spatially Varying Cohesive Soils

The bearing capacity of square and/or rectangular footings in geotechnical foundation designs traditionally is determined based on experimental observations and/or deterministic analysis assuming uniform soil profiles. However, soils are spatially varying, and this spatial variability can significantly affect the bearing capacity of the foundation soils. Probability-based design methods can address this problem explicitly. However, a full three-dimensional (3D) probabilistic simulation, such as that involving the random finite-element method, generally is prohibitive, because it involves numerous Monte Carlo runs of a complicated nonlinear elastoplastic algorithm. This paper developed and validated an approximate analytical method based on local averaging theory and geometric averages of soil properties directly under the footing. It was found that the theoretical prediction of the first two moments of a square footing bearing capacity agrees very well with crude Monte Carlo simulation. The analytical prediction of the probability of a design failure was validated through simulation and can be used directly in reliability-based designs against bearing failure.

Coupled electro-chemo-elasticity: Application to modeling the actuation response of ionic polymer–metal composites

We have formulated a large deformation thermodynamically-consistent electro-chemo-elasticity theory for modeling the actuation response of ionic polymer–metal composites. Our theory accounts for the simultaneous evolution of the electric potential, the concentration of the mobile hydrated cations, and the deformation of the host ionic polymer matrix. We have numerically implemented our theory in an implicit finite element program. We use this simulation capability to first calibrate the material parameters in the theory for a Nafion-based ionic polymer–metal composite, and then validate our theory by comparing predictions from the theory against other experimental data available in the literature. We also demonstrate the utility of our simulation capability by conducting full three-dimensional simulations of two soft-robotics applications with some geometric complexity: (i) a biomimetic fin, and (ii) a micro-gripper.

Simulation of shock-body interactions using the Runge–Kutta discontinuous Galerkin method with adaptive mesh refinement implemented on graphic accelerators

In this paper, a numerical scheme for solving the equations of the dynamics of a compressible fluid, based on the Runge–Kutta discontinuous Galerkin (RKDG) method and an adaptively refined cubic mesh (AMR), is applied to the problems of shock interaction with solid and liquid obstacles. Features of effective implementation algorithm for the graphic processors (GPU) are described. Several well-known validation test problems are considered. Results of full detailed three-dimensional simulations of the shock with the gas or fluid bubble using the developed GPU–RKDG–AMR solver are presented.