Arbitrary Surface Geometry Research Articles

Coupled material point and level set methods for simulating soils interacting with rigid objects with complex geometry

The material point method (MPM) is often used to simulate soils that interact with (nearly) rigid objects, such as structures, machines, or rocks. Yet MPM simulations of such problems are quite challenging when the objects have complex shapes. In this paper, we propose an efficient approach for incorporating geometrically complex rigid objects into MPM modeling. The proposed approach leverages the level set method, which can efficiently delineate arbitrary surface geometry, to represent the boundary of a discrete object. For coupling the level set object with the MPM domain, a robust algorithm is developed on the basis of contact mechanics. Through numerical examples of varied complexity, we verify the proposed approach and demonstrate its ability to efficiently simulate challenging problems wherein soils interact with complex rigid objects such as debris-resisting baffles, a vehicle wheel, and basal terrain.

Complex geometry three-dimensional curvilinear grids construction for numerical flow calculations

The urgency of constructing spatial curvilinear grids in areas with complex geometry is formulated. An overview of the construction of two-dimensional curvilinear computational grids is given. The article describes the rationale for the fact that the methods described in the review cannot fully calculate the flow parameters in regions with complex geometry. A method for constructing three-dimensional grids for bodies with arbitrary surface geometry is described. The results of constructing a three-dimensional grid are presented using a hemisphere as an example. An estimate of the measures of non-orthogonality for the test case is given.

Modeling of interference microscopy beyond the linear regime

Coherence scanning interferometry (CSI), a type of interference microscopy, has found broad applications in the advanced manufacturing industry, providing high-accuracy surface topography measurement. Enhancement of the metrological capability of CSI for complex surfaces, such as those featuring high slopes and spatial frequencies and high aspect-ratio structures, requires advances in modeling of CSI. However, current linear CSI models relying on approximate surface scattering models cannot accurately predict the instrument response for surfaces with complex geometries that cause multiple scattering. A boundary elements method is used as a rigorous scattering model to calculate the scattered field at a distant boundary. Then, the CSI signal is calculated by considering the holographic recording and reconstruction of the scattered field. Through this approach, the optical response of a CSI system can be predicted for almost any arbitrary surface geometry.

A GPU-accelerated package for simulation of flow in nanoporous source rocks with many-body dissipative particle dynamics

Mesoscopic simulations of hydrocarbon flow in source shales are challenging, in part due to the heterogeneous shale pores with sizes ranging from a few nanometers to a few micrometers. Additionally, the sub-continuum fluid–fluid and fluid–solid interactions in nano- to micro-scale shale pores, which are physically and chemically sophisticated, must be captured. To address those challenges, we present a GPU-accelerated package for simulation of flow in nano- to micro-pore networks with a many-body dissipative particle dynamics (mDPD) mesoscale model. Based on a fully distributed parallel paradigm, the code offloads all intensive workloads on GPUs. Other advancements, such as smart particle packing and no-slip boundary condition in complex pore geometries, are also implemented for the construction and the simulation of the realistic shale pores from 3D nanometer-resolution stack images. Our code is validated for accuracy and compared against the CPU counterpart for speedup. In our benchmark tests, the code delivers nearly perfect strong scaling and weak scaling (with up to 512 million particles) on up to 512 K20X GPUs on Oak Ridge National Laboratory’s (ORNL) Titan supercomputer. Moreover, a single-GPU benchmark on ORNL’s SummitDev and IBM’s AC922 suggests that the host-to-device NVLink can boost performance over PCIe by a remarkable 40%. Lastly, we demonstrate, through a flow simulation in realistic shale pores, that the CPU counterpart requires 840 Power9 cores to rival the performance delivered by our package with four V100 GPUs on ORNL’s Summit architecture. This simulation package enables quick-turnaround and high-throughput mesoscopic numerical simulations for investigating complex flow phenomena in nano- to micro-porous rocks with realistic pore geometries. Program summaryProgram title:USERMESO 2.5Program files doi:http://dx.doi.org/10.17632/zzpv74bz9m.1Licensing provisions: GNU General Public License 3Programming language: CUDA C/C++ with MPI and OpenMPNature of problem: Particle-based simulation of multiphase flow and fluid–solid interaction in nano- to micro-scale pore networks of arbitrary pore geometries.Solution method: Fluid particles and solid wall particles are modeled with a many-body dissipative particle dynamics (mDPD) model – a mesoscopic model for coarse-grained fluid and solid molecules. The pore surface wall boundary for arbitrary surface geometries is modeled with a no-slip boundary condition for fluid particles that prevents fluid particles from indefinitely penetrating in the walls. The time evolution of the system is integrated using the Velocity-Verlet algorithm.Restrictions: The code is compatible with NVIDIA GPUs with compute capability 3.0 and above.Unusual features: The code is implemented on GPGPUs with significantly improved speed.

Universal inverse design of surfaces with thin nematic elastomer sheets

Programmable shape-shifting materials can take different physical forms to achieve multifunctionality in a dynamic and controllable manner. Although morphing a shape from 2D to 3D via programmed inhomogeneous local deformations has been demonstrated in various ways, the inverse problem-finding how to program a sheet in order for it to take an arbitrary desired 3D shape-is much harder yet critical to realize specific functions. Here, we address this inverse problem in thin liquid crystal elastomer (LCE) sheets, where the shape is preprogrammed by precise and local control of the molecular orientation of the liquid crystal monomers. We show how blueprints for arbitrary surface geometries can be generated using approximate numerical methods and how local extrinsic curvatures can be generated to assist in properly converting these geometries into shapes. Backed by faithfully alignable and rapidly lockable LCE chemistry, we precisely embed our designs in LCE sheets using advanced top-down microfabrication techniques. We thus successfully produce flat sheets that, upon thermal activation, take an arbitrary desired shape, such as a face. The general design principles presented here for creating an arbitrary 3D shape will allow for exploration of unmet needs in flexible electronics, metamaterials, aerospace and medical devices, and more.

Spin-hall-active platinum thin films grown via atomic layer deposition

We study the magnetoresistance of yttrium iron garnet/Pt heterostructures in which the Pt layer was grown via atomic layer deposition (ALD). Magnetotransport experiments in three orthogonal rotation planes reveal the hallmark features of spin Hall magnetoresistance. To estimate the spin transport parameters, we compare the magnitude of the magnetoresistance in samples with different Pt thicknesses. We check the spin Hall angle and the spin diffusion length of the ALD Pt layers against the values reported for high-quality sputter-deposited Pt films. The spin diffusion length of 1.5 nm agrees well with that of platinum thin films reported in the literature, whereas the spin Hall magnetoresistance Δρ/ρ=2.2×10−5 is approximately a factor of 20 smaller compared to that of our sputter-deposited films. Our results demonstrate that ALD allows fabricating spin-Hall-active Pt films of suitable quality for use in spin transport structures. This work provides the basis to establish conformal ALD coatings for arbitrary surface geometries with spin-Hall-active metals and could lead to 3D spintronic devices in the future.

Collective diffusion of dense adsorbate at surfaces of arbitrary geometry

A convenient variational formula for collective diffusion of many particles adsorbed at lattices of arbitrary geometry is formulated. The approach allows us to find the expressions for the diffusion coefficient for any value of the system’s coverage. It is assumed that particles interact via on-site repulsion excluding double site occupancy. It is shown that the method can be applied to various systems of different geometry. Examples of real systems such as GaAs with specific energetic landscapes are also presented. Diffusion of Ga adatoms on GaAs(0 0 1) surface reconstructed in two different symmetries is studied. It is shown how increasing Ga coverage changes the character of diffusion from isotropic 2D into highly anisotropic, almost 1D. It is shown how important the role of the inter-particle correlations is, which influences the value of the collective diffusion coefficient at higher coverages.

Numerical implementation of a cold-ion, Boltzmann-electron model for nonplanar plasma-surface interactions

Plasma-surface interactions are ubiquitous in the field of plasma science and technology. Much of the physics of these interactions can be captured with a simple model comprising a cold ion fluid and electrons which satisfy the Boltzmann relation. However, this model permits analytical solutions in a very limited number of cases. This paper presents a versatile and robust numerical implementation of the model for arbitrary surface geometries in cartesian and axisymmetric cylindrical coordinates. Specific examples of surfaces with sinusoidal corrugations, trenches, and hemi-ellipsoidal protrusions verify this numerical implementation. The application of the code to problems involving plasma-liquid interactions, plasma etching, and electron emission from the surface is discussed.

Experimental Validation of a Boundary Layer Convective Heat Flux Measurement Technique

If a steady thermal boundary layer is sufficiently thick, wall heat fluxes and associated convective heat transfer coefficients can be directly calculated from measured temperature distributions taken within it using a traversing thermocouple probe. The boundary layer can be laminar, turbulent, or transitional and on a surface of arbitrary surface temperature distribution and geometry. Herein, this technique is presented and validated in a steady, turbulent, two-dimensional boundary layer on a flat, uniform-heat-flux wall. Care is taken to properly account for radiation from the wall and conduction within the thermocouple wire. In the same setting, heat flux measurements are made for verification purposes using an energy balance on a segment of the test wall carefully designed to minimize and include radiation and conduction effects. Heat flux values measured by the boundary layer measurement technique and by the energy balance measurement agree to within 4.4% and the difference between the two lie completely within their respective measurement uncertainties of 5.74% and 0.6%.

Optimization Methods for the Design of Sensitive Surface ESR Resonators

Electron spin resonance (ESR) is a powerful spectroscopic technique that has many applications in a wide variety of scientific fields, including chemistry, biology, materials science, and physics. One significant drawback of conventional ESR, however, is its relatively low sensitivity compared to other spectroscopic techniques. Arguably, the most dominant element affecting ESR sensitivity is the microwave resonator used to pick up the ESR signal of the spins. Traditionally, ESR mostly employs a limited set of resonator configurations (e.g., rectangular cavity, dielectric, or loop-gap resonator) that are suboptimal with respect to a wide range of samples. In principle, a smart resonator design can be used to optimize spin sensitivity for a given sample’s properties. In this work, we make use of an efficient Genetic Algorithm (GA) approach to numerically solve, analyze, and optimize a unique class of surface microresonators. The GA is based on a method of moments code, customized directly to render the complexity of a particular resonator’s geometries in our search. The main purposes of the algorithm are to routinely generate more sensitive microresonators, optimized for a predefined sample’s dimensions, and to study the functional relations between the devices’ resonance frequency, quality, and filling factors and their topology, in order to reach a rational optimal design. Preliminary results associated with new, unique, and sensitive surface microresonators are shown and analyzed. Such resonators are cheap and easy to produce on a mass scale with an arbitrary surface geometry.

An analytically based numerical method for computing view factors in real urban environments

A view factor is an important morphological parameter used in parameterizing in-canyon radiative energy exchange process as well as in characterizing local climate over urban environments. For realistic representation of the in-canyon radiative processes, a complete set of view factors at the horizontal and vertical surfaces of urban facets is required. Various analytical and numerical methods have been suggested to determine the view factors for urban environments, but most of the methods provide only sky-view factor at the ground level of a specific location or assume simplified morphology of complex urban environments. In this study, a numerical method that can determine the sky-view factors (ψ ga and ψ wa ) and wall-view factors (ψ gw and ψ ww ) at the horizontal and vertical surfaces is presented for application to real urban morphology, which are derived from an analytical formulation of the view factor between two blackbody surfaces of arbitrary geometry. The established numerical method is validated against the analytical sky-view factor estimation for ideal street canyon geometries, showing a consolidate confidence in accuracy with errors of less than 0.2 %. Using a three-dimensional building database, the numerical method is also demonstrated to be applicable in determining the sky-view factors at the horizontal (roofs and roads) and vertical (walls) surfaces in real urban environments. The results suggest that the analytically based numerical method can be used for the radiative process parameterization of urban numerical models as well as for the characterization of local urban climate.

Poloidal tilting symmetry of high order tokamak flux surface shaping in gyrokinetics

A poloidal tilting symmetry of the local nonlinear gyrokinetic model is demonstrated analytically and verified numerically. This symmetry shows that poloidally rotating all the flux surface shaping effects with large poloidal mode number by a single tilt angle has an exponentially small effect on the transport properties of a tokamak. This is shown using a generalization of the Miller local equilibrium model to specify an arbitrary flux surface geometry. With this geometry specification we find that, when performing an expansion in large flux surface shaping mode number, the governing equations of gyrokinetics are symmetric in the poloidal tilt of the high order shaping effects. This allows us to take the fluxes from a single configuration and calculate the fluxes in any configuration that can be produced by tilting the large mode number shaping effects. This creates a distinction between tokamaks with mirror symmetric flux surfaces and tokamaks without mirror symmetry, which is expected to have important consequences for generating toroidal rotation using up–down asymmetry.

Geometric Effects of an Inhomogeneous Sea Ice Cover on the under Ice Light Field

Light measurements in the ocean provide crucial information about the energy fluxes in the climate and ecosystem. Currently radiative transfer problems are usually considered in horizontally homogeneous layers although it is known to be a crude assumption in many cases. In this paper, we examine the effects of a horizontally inhomogeneous sea ice layer on the light field in the water underneath. We implemented a three dimensional model, capable to simulate the light field underneath arbitrary surface geometries using ray optics. The results show clear effects of the measurement geometry on measured fluxes obtained with different sensor types, which need to be taken into account for the correct interpretation of the data. Radiance sensors are able to better sense the spatial variability of ice optical properties as compared to irradiance sensors. Furthermore we show that the determination of the light extinction coefficient of water from vertical profiles is complicated under a horizontally inhomogeneous ice cover. This uncertainty in optical properties of the water, as well as the measurement geometry also limits the possibility to correct light measurements taken at depth for the influence of water in between the sea ice and the sensor.

Fast image–charge calculations for multi-particle simulations in FT-ICR analyzer cells of arbitrary geometry

As improvements in Fourier transform ion cyclotron resonance (FT-ICR) mass analyzers continue to provide higher resolving power and better mass accuracy, it becomes important to consider small perturbations to the observed frequency such as those resulting from the interaction between an ion and its image–charge. Multi-particle simulations can help in understanding these forces. Previously, particle-in-cell simulations have used a basic implementation of the image–charge force on the flat edges of the workspace. In the case of cylindrical cells, however, this does not provide an accurate representation of these forces. Until recently, the calculation of image–charge on curved electrodes has been impractical due to the high computational cost, but this cost can be mitigated by parallelizing the calculations on general purpose graphic processing units (GPUs). In this paper, a new parallelizable charge collocation based method for including high resolution image–charge effects on surfaces of arbitrary geometry is presented. This method is then used to explore the effects of image–charge interactions on observed cyclotron frequency in cylindrical ICR analyzer cells by simulating the trajectories of populations of Cs+ ranging from 20,000 ions to 1,000,000 ions.

Simulation of ion energy and angular distribution functions using Monte Carlo method coupled with multidimensional radio frequency sheath model developed utilizing COMSOL Multiphysics

We have developed a numerical tool to precisely predict the ion energy and angular distribution functions (IEDF and IADF) for an rf sheath formed around an arbitrary surface geometry in a single- or dual-frequency capacitively coupled plasma (CCP). A Monte Carlo method is utilized to simulate ion trajectories and collisions with neutrals in an oscillating sheath calculated with our multidimensional rf sheath model based on a finite element method. The IEDF calculated for a one-dimensional sheath in a dual-frequency CCP agreed very well with the measured data. The comparison proved the validity of the present model. We also present the IEDF and IADF obtained for a two-dimensional sheath around a wafer edge and an adjacent focus ring in another dual-frequency CCP to demonstrate a multidimensional capability of the present model.

Determination of bottom pressure in river flow over an obstacle

Free-surface flow in natural watercourses was investigated using two-dimensional incompressible fluid equations written for a longitudinal vertical plane. Within the framework of similarity theory, expanding the unknown variables in power series of given structure reduces the problem to a sequence of ordinary differential equations for which an analytical solution is obtained. The solution reproduces the spatial pattern of the flow over the bottom surface of arbitrary geometry. The results of calculation of the pressure field near an underwater pipeline are presented which can be used in the stability analysis of pipeline-bottom soil systems in the case of scouring.

Shielded resistive electromagnets of arbitrary surface geometry using the boundary element method and a minimum energy constraint

Eddy currents are generated in MR by the use of rapidly switched electromagnets, resulting in time varying and spatially varying magnetic fields that must be either minimized or corrected. This problem is further complicated when non-cylindrical insert magnets are used for specialized applications. Interruption of the coupling between an insert coil and the MR system is typically accomplished using active magnetic shielding. A new method of actively shielding insert gradient and shim coils of any surface geometry by use of the boundary element method for coil design with a minimum energy constraint is presented. This method was applied to shield x- and z-gradient coils for two separate cases: a traditional cylindrical primary gradient with cylindrical shield and, to demonstrate its versatility in surface geometry, the same cylindrical primary gradients with a rectangular box-shaped shield. For the cylindrical case this method produced shields that agreed with analytic solutions. For the second case, the rectangular box-shaped shields demonstrated very good shielding characteristics despite having a different geometry than the primary coils.

Semianalytical Finite Element Method Model for Radio Frequency Sheaths in Single- and Dual-Frequency Capacitively Coupled Plasmas

We propose a semianalytical rf sheath model for single- and dual-frequency capacitively coupled plasmas (CCPs) based on the finite element method (FEM). The one-dimensional nonlinear rf sheath theory and its extension to dual-frequency CCPs are incorporated into the commercial FEM software COMSOL Multiphysics and coupled with the Poisson solver in it. The model enables a time-dependent but rapid simulation of the nonlinear motion of an rf sheath formed around an arbitrary surface geometry of a local region in a single- or dual-frequency CCP. Some application results obtained using the model are demonstrated and validated.

Three dimensional imaging with randomly distributed sensors

As a promising three dimensional passive imaging modality, Integral Imaging (II) has been investigated widely within the research community. In virtually all of such investigations, there is an implicit assumption that the collection of elemental images lie on a simple geometric surface (e.g. flat, concave, etc), also known as pickup surface. In this paper, we present a generalized framework for 3D II with arbitrary pickup surface geometry and randomly distributed sensor configuration. In particular, we will study the case of Synthetic Aperture Integral Imaging (SAII) with random location of cameras in space, while all cameras have parallel optical axes but different distances from the 3D scene. We assume that the sensors are randomly distributed in 3D volume of pick up space. For 3D reconstruction, a finite number of sensors with known coordinates are randomly selected from within this volume. The mathematical framework for 3D scene reconstruction is developed based on an affine transform representation of imaging under geometrical optics regime. We demonstrate the feasibility of the methods proposed here by experimental results. To the best of our knowledge, this is the first report on 3D imaging using randomly distributed sensors.

Inspiration, simulation and design for smart robot manipulators from the sucker actuation mechanism of cephalopods

Octopus arms house 200–300 independently controlled suckers that can alternately afford an octopus fine manipulation of small objects and produce high adhesion forces on virtually any non-porous surface. Octopuses use their suckers to grasp, rotate and reposition soft objects (e.g., octopus eggs) without damaging them and to provide strong, reversible adhesion forces to anchor the octopus to hard substrates (e.g., rock) during wave surge. The biological ‘design’ of the sucker system is understood to be divided anatomically into three functional groups: the infundibulum that produces a surface seal that conforms to arbitrary surface geometry; the acetabulum that generates negative pressures for adhesion; and the extrinsic muscles that allow adhered surfaces to be rotated relative to the arm. The effector underlying these abilities is the muscular hydrostat. Guided by sensory input, the thousands of muscle fibers within the muscular hydrostats of the sucker act in coordination to provide stiffness or force when and where needed. The mechanical malleability of octopus suckers, the interdigitated arrangement of their muscle fibers and the flexible interconnections of its parts make direct studies of their control challenging. We developed a dynamic simulator (ABSAMS) that models the general functioning of muscular hydrostat systems built from assemblies of biologically constrained muscular hydrostat models. We report here on simulation studies of octopus-inspired and artificial suckers implemented in this system. These simulations reproduce aspects of octopus sucker performance and squid tentacle extension. Simulations run with these models using parameters from man-made actuators and materials can serve as tools for designing soft robotic implementations of man-made artificial suckers and soft manipulators.