Complicated Geometry Research Articles

Fabrication of carbon nanotube components using 3D printing: Review

One of the most recognizable innovations in nanotechnology is the Carbon Nanotube (CNT). Due to their promising applications, CNTs have been the focus of many studies during the last two decades. CNTs are nano-sized, very flexible, resistant to corrosion, electrically and thermally conductive, biocompatible, and can be customized and functionalized. By building up materials layer by layer, Additive Manufacturing (AM) is a useful method for fabricating nanocomposites in complicated geometries. It has recently come to light that AM techniques are promising contenders for synthesizing CNT applications with varied functions. Extrusion-based 3D printing techniques (such as Fused Deposition Modeling (FDM), inkjet printing, and Direct Ink Writing (DIW)) show great potential for fabricating CNT applications such as sensors, batteries, electrodes, supercapacitors, and scaffolds. This article provides an overview of the latest literature on 3D-printed CNT applications using various AM processes.

Non-uniform Compact Schemes for Parallel Computing

Here, the performance of a sixth order accurate Non-Uniform Compact Scheme (NUCS6) in a parallel framework using the domain decomposition method is analyzed. Traditional compact schemes are used for uniform grids. However, study of flows involving complicated geometries requires transformation of computational domain onto a uniform grid. Compact schemes developed for physical plane computations eliminate the need for such grid transformations. The first successful implementation of uniform compact schemes on a parallelized framework with Schwartz domain decomposition demonstrated the effect of overlap points in eliminating spurious signals at inter-processor boundaries Sengupta et al. [Jour. Comp. Phy. 220 (2007)]. This paper presents the performance of a high order non-uniform compact scheme (NUCS6) in parallel computations with the domain decomposition method. The results of the benchmark problem of flow in a 2D square lid-driven cavity at post-Hopf bifurcation Reynolds number of 10000 is presented to show how the width of overlap region affects the growth and evolution of gyrating polygonal vortex at the centre of the cavity.

Polarization- and angle-insensitive broadband long wavelength infrared absorber based on coplanar four-sized resonators.

In many potential applications, there is a high demand for long wavelength infrared (LWIR) absorbers characterized by a compact configuration, broad operational bandwidth, high absorption efficiency, and polarization- and angle-insensitive characteristics. In this study, we design and demonstrate a high-performance broadband LWIR absorber based on coplanar four-sized resonators, consisting of arrays of titanium (Ti) disks with different diameters supported by a continuous zinc selenide (ZnSe) layer and by a Ti film acting as a back-reflector. Particle swarm optimization (PSO) is employed to optimize the complicated geometry parameters, and the final optimized device exhibits near-unity absorption (∼96.7%) across the entire operational bandwidth (8 µm∼14 µm) under unpolarized normal incidence, benefiting from the impedance-matching condition and the multiple surface plasmon resonances of this configuration. Furthermore, the proposed absorber is insensitive to the angle of incidence due to the localized surface plasmon resonances supported by these four-sized resonators, and is insensitive to the state of polarization thanks to the highly symmetric feature of the circular pattern. The measured absorption of the fabricated sample exhibits a relatively high coincidence with the simulation, with an average absorption of 88.9% ranging from 8 µm to 14 µm. The proposed absorber, which can be easily integrated into a standardized micro/nano manufacture process for cost-effective large-scale production, provides a feasible solution for improving optical performance in thermal emitter, infrared detection, and imaging applications. Furthermore, the generalized design principle employing the optimized method opens up new avenues for realizing target absorption, reflection, and transmission based on more complicated structure configurations.

Electrical Circuit Modeling of Nanofluidic Systems

AbstractNanofluidic systems exhibit transport characteristics that have made technological marvels such as desalination and energy harvesting possible by virtue of their ability to influence small currents due to selective ion transport. Traditionally, these applications have relied on nanoporous membranes whose complicated geometry impedes a comprehensive understanding of the underlying physics. To bypass the associated difficulties, we consider the simpler nanochannel array and elucidate the effects of interchannel interactions on the Ohmic response. It is demonstrated that a nanochannel array is equivalent to an array of mutually independent but identical unit‐cells whereby the array can be represented by an equivalent electrical circuit of resistances connected in a parallel configuration. The model is validated using numerical simulations and experiments. The approach to modeling nanofluidic systems by their equivalent electrical circuit provides an invaluable tool for analyzing and interpreting experimental measurements.

GEOMETRIC ANALYSIS AND DESIGN OF FLAT FORM TOOLS

Form tool means a cutting tool which is appropriate manufacturing of workpieces having more complicated geometry. The contour of manufactured workpiece is manufactured by the tool profile. This cutting tool can be used in case of serial and quantity production. The advantageous of their usage are the lower turning time and the lower standard deviation of the workpiece sizes. The reached accuracy on the workpiece is independent from the qualification of the worker. The aim of this publication is the explanation of the geometric analysis and the design by analytical and constructional way. This type of tool is advantageously usable for manufacturing on CNC machine or conventional machine.

A Relationship for Effective Thermal Conductivity of Reinforced Concrete Structures

Thermal conductivity is an important parameter in predicting the temperature distribution of large reinforced concrete structures. To accurately predict the temperature gradients, the effect of the steel rebar must be considered. An overall effective thermal conductivity was proposed to account for the steel reinforcement to eliminate the need to consider the complicated geometry of the rebar. In this study, the thermal conductivity of concrete cylinders embedded with 4% and 8% steel reinforcement was measured following industry standards. The effective thermal conductivity was calculated and shown to increase with the reinforcement ratio. Finite-element analysis (FEA) was conducted to model the experimental tests, and an equation was proposed to estimate the effective thermal conductivity. Additionally, FEA was used to model a concrete pier cap using the effective thermal conductivity. It was concluded that the simple effective thermal conductivity could be used to simulate the complicated steel reinforcement in the concrete.

Different build strategies and computer-aided process planning for fabricating a functional component through hybrid-friction stir additive manufacturing

ABSTRACT Hybrid Additive Manufacturing (HAM) technologies leverage the strength of Additive Manufacturing (AM) and Subtractive Manufacturing (SM) in fabricating complex geometries with precision. Friction Stir Welding (FSW) has been acknowledged for joining sheets of similar or dissimilar materials with improved mechanical/metallurgical properties. However, due to the inherent pinhole defect and complicated toolpath planning, this process has not been explored much for fabricating the objects in a layer-by-layer manner. Therefore, this work investigates Computer Aided Process Planning (CAPP) for realizing fully functional metallic parts through a HAM system. This HAM system uses a Sheet Lamination (SL) process, i.e. Friction Stir Additive Manufacturing (FSAM), synergistically coupled with an SM process, i.e. machining. To realize complicated geometries through the proposed HAM system, three different build strategies are developed viz. Near-net block fabrication, Near-net shape fabrication via ‘form-then-bond approach’ and ‘bond-then-form approach.’ Each build strategy consists of a detailed CAPP that includes toolpath planning, tooling aspects, simulated outcome and so on. Further, these build strategies are discussed for realizing the parts with Functionally Graded Materials (FGM) & embedded structures. Finally, a monolithic object of aluminium has been fabricated as a case study to demonstrate one of the aforementioned build strategies.

Enhancing multi-physics modelling with deep learning: Predicting permeability through structural discontinuities

Numerical modelling of complex structural discontinuities such as fractures poses a computational challenge, as it involves solving multi-scale and multi-physics phenomena and simulating various processes, including solid, fluid, thermal and chemical interactions. To overcome the limitations of long computation times, simplifications or conceptualizations are often required. However, in multi-physics modelling, it is desirable to obtain predictions of certain parameters without making simplifications. In this study, a data-driven deep learning approach is presented that predicts physical permeability parameters through discontinuities with complicated geometries based on digital images. Images of fractures were generated from a digitalized rough fracture surface of subsurface rock. Permeability was calculated using the Stokes equation and Finite Volume discretization for training and testing purposes. Two cases were analyzed: when the fluid velocity field of the fracture was provided to the CNN for training, and a more challenging case when it was not. Results show that deep learning can accurately predict permeability without fluid velocity information. Besides, the model generalizes well, providing accurate predictions of permeability for fractures with significantly different roughness parameters. In conclusion, this approach can reduce computation time during multi-physics modelling and can be used to predict continuous physical permeability values from an image of a fracture with a complex surface.

Combined loading effect on high cycle fatigue fracture behaviors of a stainless steel welded structure of elbow and socket

In welded structures with complicated geometries and combined loading state, it is crucial to establish the criteria for fatigue failure. High cycle fatigue tests under combined loading states were performed using stainless steel sheets and welded specimens of elbow pipe and socket in this work. The cyclic stress–strain curve of the parent sheet were applied to the characteristics analysis of the welded specimens. Mode I or Mode I + III fatigue fracture occurred at the stress concentration part of the weld, and the crack starting point was different depending on the loading mode. The applied load was divided into bending and torsion for analysis, and the crack initiation was found on the side with the higher equivalent stress converted according to the Gough-Pollard failure criterion. The crack grew almost perpendicularly to the surface of the elbow pipe, and exhibited the appearance of a transgranular fracture. The fatigue limit based on the stress intensity factor (SIF) amplitude calculated by the proposed method using the strain energy release rate remained nearly constant even though the measured surface strain differed greatly. It is possible to predict the fatigue limit and life of similar structures by simplified models.

Concurrent reaction-bonded joining and densification of additively manufactured silicon carbide by liquid silicon infiltration

In this study, additive-manufactured silicon carbide preforms were joined and densified by reaction bonding via liquid silicon infiltration. The silicon carbide preforms were first printed by binder jetting additive manufacturing. To demonstrate concurrent joining and densification, two preforms with carbon or parchment papers at the interface were concurrently joined and infiltrated by liquid silicon. Results showed a robust interface with thicknesses ranging from 150 to 500 µm, depending on the paper type and the number of paper layers. High-energy synchrotron X-ray revealed that β-phase silicon carbide was formed inside the interface. Finally, two additively manufactured samples with complicated channel geometry were successfully joined. Energy dispersive spectroscopy of the interface of the channeled samples showed a consistent and robust joining. This concurrent approach of joining and densification enables efficiency improvement of fabricating silicon carbide parts with complicated geometries and widens geometry freedom for additive manufacturing of silicon carbide.

Unraveling Twisty Linear Polarization Morphologies in Black Hole Images

We investigate general relativistic magnetohydrodynamic simulations to determine the physical origin of the twisty patterns of linear polarization seen in spatially resolved black hole images and explain their morphological dependence on black hole spin. By characterizing the observed emission with a simple analytic ring model, we find that the twisty morphology is determined by the magnetic field structure in the emitting region. Moreover, the dependence of this twisty pattern on spin can be attributed to changes in the magnetic field geometry that occur due to the frame dragging. By studying an analytic ring model, we find that the roles of Doppler boosting and lensing are subdominant. Faraday rotation may cause a systematic shift in the linear polarization pattern, but we find that its impact is subdominant for models with strong magnetic fields and modest ion-to-electron temperature ratios. Models with weaker magnetic fields are much more strongly affected by Faraday rotation and have more complicated emission geometries than can be captured by a ring model. However, these models are currently disfavoured by the recent EHT observations of M87*. Our results suggest that linear polarization maps can provide a probe of the underlying magnetic field structure around a black hole, which may then be usable to indirectly infer black hole spins. The generality of these results should be tested with alternative codes, initial conditions, and plasma physics prescriptions.

A Wideband Millimeter-Wave Corrugated Horn at 30–50 GHz Taking Advantage of All-Metal 3-D Printing Fabrication

The development of commercial all-metal 3D-printing technology provides a new fabrication method for wideband millimeter-wave corrugated horns up to 50 GHz. Compared with conventional fabrication techniques, such as direct machining, electroforming or recently developed methods relying on the assembly of platelets, all-metal 3D-printing has advantages of low cost, fast delivery, possibility of mass production, flexibility in fabrication of complicated geometries and good mechanical robustness. In this letter, we report the development of a wideband millimeter-wave corrugated horn at 30-50 GHz (50% fractional bandwidth) based on commercial all-metal 3D-printing technology. Measurement results reported in this letter show good performance in terms of both return loss and cross-polarization.

Nuclear engineering for monitoring the thinning of the pipe wall of the Angra 1 power plant

Large thermoelectric generation systems based on the Rankine cycle require monitoring of the thinning of the pipe wall caused by steam flow due to aging processes such as erosion and accelerated corrosion processes. Inspection difficulties are related to hostile environments (50 oC and 100% relative humidity) and spaces with complicated geometry, such as pipeline curves and their support structures. This work presents a monitoring program that integrates wall thickness inspections performed with a robotic system and Industry 4.0 technology to process the collected data and disseminate information throughout the organization. The robotic system is developed using “Digital Twin” technology, a very realistic virtual modeling scheme that allows interaction with the real world environment. They include equipment and all the steps to carry out the inspection process. The tube wall thickness monitoring system will be used at the Angra 1 nuclear power plant (Brazil).

Meshless generalized finite difference method for two- and three-dimensional transient elastodynamic analysis

In this paper, a meshless collocation method is introduced for two-dimensional (2D) and three-dimensional (3D) transient elastodynamic problems by applying the generalized finite difference method (GFDM) in conjunction with the Houbolt scheme. Coupled equilibrium equations with a time-dependent loading are transformed into the static equations at time nodes by adopting the Houbolt method. After then, the solution of the static equations is achieved with the GFDM with second-order and fourth-order expansions. Several numerical examples involving complicated geometries and different initial and boundary conditions are simulated to validate the performance of the present approach.

A High-Order-Accurate 3D Surface Integral Equation Solver for Uniaxial Anisotropic Media

This paper introduces a high-order accurate surface integral equation method for solving 3D electromagnetic scattering for dielectric objects with uniaxially anisotropic permittivity tensors. The N-Müller formulation is leveraged resulting in a second-kind integral formulation, and a finite-difference-based approach is used to deal with the strongly singular terms resulting from the dyadic Green’s functions for uniaxially anisotropic media while maintaining the high-order accuracy of the discretization strategy. The integral operators are discretized via a Nyström-collocation approach, which represents the unknown surface densities in terms of Chebyshev polynomials on curvilinear quadrilateral surface patches. The convergence is investigated for various geometries, including a sphere, cube, a complicated NURBS geometry imported from a 3D CAD modeler software, and a nanophotonic silicon waveguide, and results are compared against a commercial finite element solver. To the best of our knowledge, this is the first demonstration of high-order accuracy for objects with uniaxially anisotropic materials using surface integral equations.

Stability of drawing of microstructured optical fibres

We consider the stability of the drawing of a long and thin viscous thread with an arbitrary number of internal holes of arbitrary shape that evolves due to axial drawing, inertia and surface tension effects. Despite the complicated geometry of the boundaries, we use asymptotic techniques to determine a particularly convenient formulation of the equations of motion that is well-suited to stability calculations. We will determine an explicit asymptotic solution for steady states with (a) large surface tension and negligible inertia, and (b) large inertia. In both cases, we will show that complicated boundary layer structures can occur. We will use linear stability analysis to show that the presence of an axisymmetric hole destabilises the flow for finite capillary number and which answers a question raised in the literature. However, our formulation allows us to go much further and consider arbitrary hole structures or non-axisymmetric shapes, and show that any structure with holes will be less stable than the case of a solid axisymmetric thread. For a solid axisymmetric thread, we will also determine a closed-form expression that delineates the unconditional instability boundary in which case the thread is unstable for all draw ratios. We will determine how the detailed effects of the microstructure affect the stability, and show that they manifest themselves only via a single function that occurs in the stability problem and hence have a surprisingly limited effect on the stability.

Modelling and analysis of metal flowing behaviors in constraining ring rolling of tapered ring with thin wall and three high ribs

Tapered ring with thin wall and three high ribs (TRTWTHR), showing complicated geometry (wall thickness is less than 4 mm and rib height exceeds 20 mm), is extensively utilized to fabricate the critical structural parts of aerospace equipment such as spacecraft cabin, rocket body and fuel tank because of light weight and high carrying capacity. How to fabricate TRTWTHR with high performance is a critical problem that aerospace area needs to solve. In this work, constraining ring rolling (CRR) technique is first adopted to form TRTWTHR. However, unreasonable metal streamlines (UMS) and uncoordinated growth of three ribs easily occur in CRR of TRTWTHR, which makes the forming quality of TRTWTHR difficult to be controlled. Faced with this difficulty, an analytical model that can predict UMS and the height of three ribs in CRR of TRTWTHR is established so as to guide the process design of CRR. Subsequently, the reliability of the established analytical model and the feasibility of CRR of TRTWTHR are confirmed by FE simulation and experiment. Then, using the established analytical model, the window of UMS occurring relevant to the tapered angle of TRTWTHR and the location of the rib of middle end is developed. Finally, three uncoordinated growth modes among three ribs are found when the width of three ribs is identical and UMS do not occur, and the mechanisms of three uncoordinated growth modes are revealed.

Biocompatibility enhancement via post-processing of microporous scaffolds made by optical 3D printer.

Providing a 3D environment that mimics the native extracellular matrix is becoming increasingly important for various applications such as cell function studies, regenerative medicine, and drug discovery. Among the most critical parameters to consider are the scaffold's complicated micro-scale geometry and material properties. Therefore, stereolithography based on photopolymerization is an emerging technique because of its ability to selectively form volumetric structures from liquid resin through localized polymerization reactions. However, one of the most important parameters of the scaffold is biocompatibility, which depends not only on the material but also on the exposure conditions and post-processing, which is currently underestimated. To investigate this systematically, microporous scaffolds with pore sizes of 0.05mm3 corresponding to a porosity of 16,4% were fabricated using the stereolithography printer Asiga PICO2 39 UV from the widely used resins FormLabs Clear and Flexible. The use of various polymers is usually limited for cells because, after wet chemical development, the non-negligible amount of remaining monomers intertwined in the photopolymerized structures is significantly toxic to cells. Therefore, the aim of this research was to find the best method to remove monomers from the 3D scaffold by additional UV exposure. For this purpose, a Soxhlet extractor was used for the first time, and the monomers were immersed in different alcohols. A Raman microspectroscopy was also used to investigate whether different post-processing methods affect DC (cross-linking) to find out if this specifically affects the biocompatibility of the scaffolds. Finally, mesenchymal stem cells from rat dental pulp were examined to confirm the increased biocompatibility of the scaffolds and their ability to support cell differentiation into bone tissue cells.

Exotic marginally outer trapped surfaces in rotating spacetimes of any dimension

The recently developed MOTSodesic method for locating marginally outer trapped surfaces (MOTSs) was effectively restricted to non-rotating spacetimes. In this paper we extend the method to include (multi-)axisymmetric time slices of (multi-)axisymmetric spacetimes of any dimension. We then apply this method to study MOTSs in the BTZ, Kerr and Myers–Perry black holes. While there are many similarities between the MOTSs observed in these spacetimes and those seen in Schwarzschild and Reissner-Nordström, details of the more complicated geometries also introduce some new, previously unseen, behaviours.

A Typical Workflow to Simulate Cytoskeletal Systems.

Many cytoskeletal systems are now sufficiently well known to permit their precise quantitative modeling. Microtubule and actin filaments are well characterized, and the associated proteins are often known, as well as their abundance and the interactions between these elements. Thus, computer simulations can be used to investigate the collective behavior of the system precisely, in a way that is complementary to experiments. Cytosim is an Open Source cytoskeleton simulation suite designed to handle large systems of flexible filaments with associated proteins such as molecular motors. It also offers the possibility to simulate passive crosslinkers, diffusible crosslinkers, nucleators, cutters, and discrete versions of the motors that only step on unoccupied lattice sites on a filament. Other objects complement the filaments by offering spherical or more complicated geometry that can be used to represent chromosomes, the nucleus, or vesicles in the cell. Cytosim offers simple command-line tools for running a simulation and displaying its results, which are versatile and do not require programming skills. In this workflow, step-by-step instructions are given to i) install the necessary environment on a new computer, ii) configure Cytosim to simulate the contraction of a 2D actomyosin network, and iii) produce a visual representation of the system. Next, the system is probed by systematically varying a key parameter: the number of crosslinkers. Finally, the visual representation of the system is complemented by the numerical quantification of contractility to view, in a graph, how contractility depends on the composition of the system. Overall, these different steps constitute a typical workflow that can be applied with few modifications to tackle many other problems in the cytoskeletal field.