Concave Geometry Research Articles

Study on influence of concave geometry shoulder tool in Friction Stir Welding (FSW) by using Image Processing and Acoustic Emission Techniques

In the present study, the influence of concave geometry shoulder tool of FSW on weld quality was analysed by using Acoustic Emission and Image processing techniques has been done. The interaction of tool shoulder with base material in the arrangement of friction stir weld is studied by contemplated the banded texture of weld bead surface using image processing techniques. Experiments are carried out by capturing the images of weld bead surface of friction stir welded specimens produced using different process parameters. The images are digitally processed and analysed by characterizing locale of interest along good and defect weld region based on X-Ray radiography and AE results of friction stir welded specimens to determine first order and second order measurable statistical textural parameters of weld bead surface using MATLAB

Edge-Guided Mode Performance and Applications in Nonreciprocal Millimeter-Wave Gyroelectric Components

The analogies between the behavior of gyromagnetic and gyroelectric nonreciprocal structures, the use of the simple transfer matrix approach, and the edge-guided (EG) wave property, supported in a parallel plate model for integrated magnetized semiconductor waveguide, are investigated in those frequency regions, where the effective permittivity is negative or positive. As with their ferrite counterparts, the leakage of the EG waves along the curvilinear semiconductor-metal edge is observed for those frequencies where the effective permittivity is positive. This induces spurious resonances in the semiconductor junctions having a convex–concave geometry. Furthermore, the very small reflection from the open semiconductor edge is observed for those frequencies where the effective permittivity is negative. This provides the unidirectional wave propagation in the parallel plate semiconductor (PPS) guide where one edge is open as well as in the PPS guide inserted into a dc magnetic antiparallel field. Hence, as a practical application, new EG mode nonreciprocal semiconductor devices are proposed as complementary to the already known ferrite versions. The simulated characteristics of the ideal junction and their implementation in finline technology clearly illustrate their broadband, nonreciprocal operation in the millimeter-wave regions (25–250 GHz), something which is difficult to achieve with ferrite devices.

Macro-voxel algorithm for adaptive grid generation to accelerate grid traversal in the radiative heat transfer analysis via Monte Carlo method

In the thermal radiation analysis via Monte Carlo method, the ray tracing algorithm often consumes a significant fraction of CPU time. As such, an efficient grid traversal algorithm can considerably affect the performance of the Monte Carlo method. This paper presents a new grid traversal acceleration algorithm by merging adjacent small empty voxels in a preprocessing step due to the fact that larger empty space, named “macro-voxel”, allows for traversing a ray over a large distance at a smaller cost. The proposed algorithm is validated theoretically, and the results are examined for a gray box with diffuse surfaces. Timing results of the new algorithm are compared with the USD method in a typical 3D radiation furnace with concave geometry and the speedup ratio of both the macro-voxel algorithm and the USD method with respect to direct method are calculated for an optimal grid of voxels. For the considered geometry, the macro-voxel algorithm is found to be clearly superior to the USD even if the size of the problem is large and the geometry is not convex.

Combined Pulse-Echo Ultrasound and Multispectral Optoacoustic Tomography With a Multi-Segment Detector Array.

The high complementarity of ultrasonography and optoacoustic tomography has prompted the development of combined approaches that utilize the same transducer array for detecting both optoacoustic and pulse-echo ultrasound responses from tissues. Yet, due to the fundamentally different physical contrast and image formation mechanisms, the development of detection technology optimally suited for image acquisition in both modalities remains a major challenge. Herein, we introduce a multi-segment detector array approach incorporating array segments of linear and concave geometry to optimally support both ultrasound and optoacoustic image acquisition. The various image rendering strategies are tested and optimized in numerical simulations and calibrated tissue-mimicking phantom experiments. We subsequently demonstrate real-time hybrid optoacoustic ultrasound image acquisition in a healthy volunteer. The new approach enables the acquisition of high-quality anatomical data by both modalities complemented by functional information on blood oxygenation status provided by the multispectral optoacoustic tomography.

My personal head related transfer function: High quality individualized computer models

In this paper, we present a method to obtain individual 3D CAD-models of the head and pinna. The method is a hybrid method: A photogrammetric technique for the head is combined with a molding process for the pinna. For the 3D reconstruction of the head, a set of pictures from different perspectives of the person is taken. Therefore the person is stepwise rotated while seated and pictures are taken using semi-professional photographic equipment. Four different orbits are used: top level, upper level, eye level, and low level. These pictures, about 120, are then combined using a commercial photogrammetric software. Due to the complex and concave geometry of the pinna, an additional step has to be taken. An alginate mold is made for each pinna which then is molded again to obtain a positive plaster replica of the pinna. This replica is then converted to a CAD model. For this last step, two methods were compared: the same photogrammetric process as before and using a 3D scanner. Both CAD models, head and pinn...

An optimized and accurate Monte Carlo method to simulate 3D complex radiative enclosures

The modeling of radiative heat transfer in complex radiant enclosures is a particularly challenging subject. This simulation is often best treated by calculating distribution factors through the Monte Carlo method. In order to enhance performance of the Monte Carlo method, efficient algorithms to find location of emission and direction of emission in the original Monte Carlo method are implemented. Next, the best ray tracing algorithm is introduced by comparing timing results of the USD, the BSP, the Simplex and the VVA acceleration ray tracing algorithms to make it numerically efficient as possible. Also, the constrained maximum likelihood estimation is used to enhance accuracy of the Monte Carlo by smoothing inherent random errors in the estimated distribution factors to simultaneously satisfy both of the reciprocity and summation rules. Accuracy of the Monte Carlo method is tested for a classical problem, namely a 3D box, with diffuse gray walls. For efficiency study, the optimized Monte Carlo method is then tested for two real radiative enclosures with convex and concave geometries. All ray tracing algorithms are found to result in computational gains, with respect to direct calculations that do not employ any acceleration technique. In the considered test cases, the VVA and the USD algorithms are found to be clearly superior to the BSP and the Simplex algorithms, particularly for concave geometries that have some obstructions within the computational domain.

Three-dimensional piezoelectric MEMS actuator by using sputtering deposition of Pb(Zr,Ti)O3 on microstructure sidewalls

For the realization of piezoelectric microelectromechanical systems (MEMS) with multiple degrees-of-freedom, lead zirconate titanate thin films were deposited and micropatterned on the sidewalls of a pre-etched substrate with a feature depth of several hundred micrometers. The piezoelectric test structures, consisting of concave geometries and cantilevers with vertical and sloped sidewalls were successfully fabricated onto a 4 inch full sized wafer. Characterization of the fundamental properties of the lead zirconate titanate thin films indicated values comparable to those deposited on flat substrates. Actuation tests demonstrated that the triangular column cantilevers can be driven both in-plane and out-of-plane. The deposition of lead zironate titanate thin films onto a vertical sidewall created bimorph cantilevers composed of piezo/non-piezo/piezo structures in the horizontal direction. The use of microfabrication techniques to deposit lead zironate titanate thin films on pre-etched substrates gives MEMS actuators with multiple degrees-of-freedom and batch process compatibility.

Characteristics and formation mechanism of the July 25, 2013, Tianshui group-occurring geohazards

A field investigation was conducted for the group-occurring mountain torrent geohazards that took place on July 25, 2013, in Tianshui City, China. The formation causes, range, development characteristics, and distribution laws of these geohazards were systematically revealed. In addition, a three-dimensional dynamic numerical continuum model was established to simulate the motion characteristics of the typical landslides in Tianshui City. The field investigation and simulation results show that the mountain torrent geohazards that occurred on July 25, 2013, had five major characteristics: universality and evident group occurrence, local outbreak, strong concealment, considerable potential damage, and a significant hazard chain mode. The hazards’ intensity was aggravated by the superposition effects of intense rainfall and earthquakes. Most of the landslide-prone slopes in these geohazards had a concave geometry. The landslides occurred mainly within a slope gradient range of 35°–45°; the most common slope angle was 40°. The loess landslides had a narrow-strip shape and ranged in width from several meters to 10 m and in length from 10 s of meters to 100 s of meters. These landslides were relatively small scale, with volumes from 10 to 100 s of cubic meters. The mean velocity, frontal velocity, total kinetic energy, and total potential energy of the typical landslide masses all increased sharply during the downslope motion and decreased gradually in the deposition zone. Entrainment was a very important factor in these landslide events, as it caused the mass of the hazard bodies to increase; the increased mass, together with a high motion velocity (30 m/s), enhanced the destructiveness of the hazard bodies.

Heat transfer enhancement via Görtler flow with spatial numerical simulation

PurposeThe centrifugal instability mechanism of boundary layers over concave surfaces is responsible for the development of quasi-periodic, counter-rotating vortices aligned in a streamwise direction known as Görtler vortices. By distorting the boundary layer structure in both the spanwise and the wall-normal directions, Görtler vortices may modify heat transfer rates. The purpose of this study is to conduct spatial numerical simulation experiments based on a vorticity–velocity formulation of the incompressible Navier–Stokes system of equations to quantify the role of the transition in the heat transfer process.Design/methodology/approachExperiments are conducted using an in-house, parallel, message-passing code. Compact finite difference approximations and a spectral method are used to approximate spatial derivatives. A fourth-order Runge–Kutta method is adopted for time integration. The Poisson equation is solved using a geometric multigrid method.FindingsResults show that the numerical method can capture the physics of transitional flows over concave geometries. They also show that the heat transfer rates in the late stages of the transition may be greater than those for either laminar or turbulent ones.Originality/valueThe numerical method can be considered as a robust alternative to investigate heat transfer properties in transitional boundary layer flows over concave surfaces.

Annular 1-3 piezocomposite high intensity focused ultrasound transducer of a concave geometry

For medical therapeutic applications, we have developed a concave annular high intensity focused ultrasound (HIFU) transducer that is made of a 1-3 piezocomposite plate and operates at 3 MHz. The transducer has 16 annular channels, and the annuli have been designed to focus at the geometrical center of the sphere. The focal point can be controlled to scan a three dimensional volume by electronic and mechanical means. The focal point is moved along the normal axis of the transducer by electronically steering the sixteen annular channels. The focal point is also rotated back and forth by mechanically wobbling the piezocomposite plate with a kinematic linkage. The kinematic linkage is driven by an electric motor installed inside the transducer. The optimal combination of the number of channels, the width of the kerf between channels, and the width of each channel were determined by means of the OpQuest-Nonlinear programming algorithm and the finite element method. The objective of the optimization was to minimize the side lobe levels while focusing the ultrasound beam to a prescribed position. Based on the design, an experimental prototype of the transducer was fabricated and its performance was measured, which showed excellent agreement with the design.

Auto-recognition and generation of material removal volume for regular form surface and its volumetric features using volume decomposition method

Computer-aided process planning (CAPP) plays a vital role in manufacturing of a product by computer-aided techniques. Auto-recognition of a surface’s volumetric features and segregation of auto-generated material removal volume into feature volumes is necessary to achieve successful downstream manufacturing activities like automated process planning and scheduling. Only few studies generated material removal volume for a product but resulted in drawbacks such as material removal volume discontinuity between two adjacent material removal volumes generated from two adjacent faces that form convex geometry, and material removal volume overlap between two adjacent material removal volumes generated from two adjacent faces that form concave geometry. An effort has been made to newly classify the regular form surface features and develop an algorithm that automatically recognizes regular form computer-aided design (CAD) model’s surface and their volumetric features, and also auto-generate material removal volume for the recognized features. The surface and volumetric features of a CAD model are successfully recognized by the developed algorithm, and estimated material removal volume of these features is obtained from stock model. The material removal volume discontinuity and overlap limitation that occurred in few studies are eliminated. The percentage difference in overall delta volume (ODV) obtained by algorithm and by manual calculations is less than 0.01 %. Exploded view of auto-generated material removal volumes is obtained for subsequent process planning applications.

Influence of squeeze-film damping on the dynamic behavior of a curved micro-beam

A fixed–fixed curved micro-beam resonator under the influence of harmonic electrostatic field is considered. Due to the presence of incompressible fluid between the micro-beams and the electrode, a squeeze-film damping affects the dynamic behavior of the resonator. The combined effect of curved geometry and fluid squeeze-film damping is investigated for micro-beams with concave and convex geometries. A reduced-order model is obtained through the application of Galerkin discretization on a coupled fluid–structure system composed of the nonlinear Euler–Bernoulli beam equation and Burgdorfer’s model for the neighboring fluid. The dynamic behavior is assessed by investigating the influence of squeeze-film damping on the linear and nonlinear frequency response and the maximum resonant deflection of curved up and curved down micro-beams.

On the kinetics of dendritic sidebranching: A three dimensional phase field study

The underlying mechanism for dendritic sidebranching was studied using 3-D phase field modeling. Results showed that in 3-D the requirement of applying the random thermal noise to induce dendritic sidebranching (i.e., normally the case for 2-D phase field simulations) was fully relaxed. The stretching of the secondary or higher order arms occurred spontaneously and symmetrically as the growth of the dendrite. With periodic external perturbation and if the stimulating frequency was lower than a critical value, both tip velocity and sidebranching would get completely synchronized with the perturbation. Whereas if the perturbation frequency was higher than the critical value, rather than increasing, the sidebranching frequency would become stable and maintain at the same magnitude as that of the natural sidebranching, i.e., when no external perturbation was applied. It was shown that the underlying mechanism for sidebranching was deterministic rather than stochastic, and anisotropy tendency and curvature effect were shown to be the most important influence factors. Moreover, the difference of the anisotropy tendency would lead to an uneven distribution of curvature on the solid/liquid interface, i.e., formation of concave and convex geometries. The growth of these geometries would subsequently break the initial spherical structure of solid seed and lead to further sidebranching.

Matematyczny model obróbki kształtowej uzębień o kołowo-łukowym zarysie zębów typu Nowikowa

Article presents mathematical model of form machining of cylindrical convexo-concave Novikov gear teeth by means of disk-type tools. Example of these king of tools is disk-type milling cutter or grinding wheel. Moreover based on the given convex and concave tooth geometry the tool profile has been established.

Magnetic force-assisted self-locking metallic bead array for fabrication of diverse concave microwell geometries.

Spheroid cell culture is very useful for further understanding cellular behavior including motility and biochemical reaction since it mimics three-dimensional (3D) in vivo organ tissue. Among previously proposed various methods for spheroid production, such as hanging drop and spinner flask, microwell is a recently developed method harnessing microtechnology to produce uniform-sized spheroids. Although soft-lithography has been popular for creating microwell arrays, a 3D spherical geometry has been regarded as difficult to fabricate using conventional methods, or often requires complex fabrication processes and expensive equipment. Here, we propose a new method for fabricating concave microwells for cell spheroid production and culture. To demonstrate this method, we fabricated a 30 × 30 microwell array in 3 × 3 cm plates, utilizing metal beads, a through-hole array, and an assembly of small magnets. The spherical metal beads were used as a mold for the microwell, naturally creating the desired 3D concave microwell geometry. One of the key ideas was to place and hold each metal bead in the designated through-hole using the small magnet array. We also performed computational simulation of the magnetostatic force to design and observe the magnetic force field in detail. In addition, to provide a practical demonstration of the proposed system in cell biology, we created and cultured adipose-derived stem cell spheroids for 14 days for chondrogenic differentiation. This method allows further variations in microwell geometry that will enhance the method's applicability as a helpful tool for various studies in cell biology, cancer research, and tissue engineering.

CFD simulation of wind-driven upward cross ventilation and its enhancement in long buildings: Impact of single-span versus double-span leeward sawtooth roof and opening ratio

A leeward sawtooth roof building has an inlet opening in the lower level of the windward facade and an upper-level outlet opening near the roof top, in the leeward facade. Leeward sawtooth roof buildings can be applied to efficiently ventilate low-rise buildings. Previous studies of the authors showed that the ventilation potential strongly depends on the roof inclination angle and roof geometry. The current study focuses on the ventilation flow in single-zone elongated low-rise buildings with a single-span versus double-span leeward sawtooth roof and different opening ratios. Straight, concave and convex roof geometries are evaluated. The analysis is performed using 3D steady Reynolds-averaged Navier–Stokes Computational Fluid Dynamics (CFD) simulations with the SST k-ω turbulence model. The computational grid is based on a grid-sensitivity analysis and the simulation results are validated based on Particle Image Velocimetry (PIV) measurements from literature. For the single-span cases, the convex roof results in the highest volume flow rate, which is about 8.8% higher than for the concave roof, and 3.5% higher than the straight roof. A double-span roof performs slightly better than a single-span roof with respect to ventilation flow rates (below 4.2%) in case of a straight or concave roof, but worse in case of a convex roof (−12%). The internal roof geometry near the outlet opening plays an important role in the ventilation of the building. Finally, the inlet-to-outlet opening ratio has an important effect on the volume flow rates, with significantly higher ventilation flow rates for a lower opening ratio.

Present-day stress field in subduction zones: Insights from 3D viscoelastic models and data

3D viscoelastic FE models were performed to investigate the impact of geometry and kinematics on the lithospheric stress in convergent margins. Generic geometries were designed in order to resemble natural subduction. Our model predictions mirror the results of previous 2D models concerning the effects of lithosphere-mantle relative flow on stress regimes, and allow a better understanding of the lateral variability of the stress field. In particular, in both upper and lower plates, stress axes orientations depend on the adopted geometry and axes rotations occur following the trench shape. Generally stress axes are oriented perpendicular or parallel to the trench, with the exception of the slab lateral tips where rotations occur. Overall compression results in the upper plate when convergence rate is faster than mantle flow rate, suggesting a major role for convergence. In the slab, along-strike tension occurs at intermediate and deeper depths (>100km) in case of mantle flow sustaining the sinking lithosphere and slab convex geometry facing mantle flow or in case of opposing mantle flow and slab concave geometry facing mantle flow. Along-strike compression is predicted in case of sustaining mantle flow and concave slabs or in case of opposing mantle flow and convex slabs. The slab stress field is thus controlled by the direction of impact of mantle flow onto the slab and by slab longitudinal curvature. Slab pull produces not only tension in the bending region of subducted plate but also compression where upper and lower plates are coupled. A qualitative comparison between results and data in selected subductions indicates good match for South America, Mariana and Tonga–Kermadec subductions. Discrepancies, as for Sumatra–Java, emerge due to missing geometric (e.g., occurrence of fault systems and local changes in the orientation of plate boundaries) and rheological (e.g., plasticity associated with slab bending, anisotropy) complexities in the models.

Extremely Stable Current Emission of P-Doped SiC Flexible Field Emitters.

Novel P-doped SiC flexible field emitters are developed on carbon fabric substrates, having both low Eto of 1.03-0.73 Vμm-1 up to high temperatures of 673 K, and extremely high current emission stability when subjected to different bending states, bending circle times as well as high temperatures (current emission fluctuations are typically in the range ±2.1%-3.4%).

Effect of geometric curvature on vitrification behavior for polymer nanotubes confined in anodic aluminum oxide templates.

The glass transition behavior of polystyrene (PS) nanotubes confined in cylindrical alumina nanopores was studied as a function of pore diameter (d) and polymer tube thickness (δ). Both the calorimetric glass transition temperature and the microstructure measured by a nonradiative energy transfer method indicated that the polymer nanotube, or concave polymer thin film, exhibited significant differences in vitrification behavior compared to the planar one. A closer interchain proximity and an increased T_{g} were observed for polymer nanotubes with respect to the bulk polymer. T_{g} for polymer nanotubes was primarily dependent on the curvature radius d of the template, while it was less dependent on the thickness δ of the PS tube wall in the range of 11-23 nm. For small nanotubes (d=55nm), the T_{g} increased as high as 18°C above the bulk value. This vitrified property reverted back to the bulk value when the substrate was chemically removed, which indicated the crucial importance of the interfacial effect imposed by the hard wall with a concave geometry.

Hybrid optoacoustic tomography and pulse-echo ultrasonography using concave arrays.

Implementation of hybrid imaging using optoacoustic tomography (OAT) and ultrasound (US) brings together the important advantages and complementary features of both methods. However, the fundamentally different physical contrast mechanisms of the two modalities may impose significant difficulties in the optimal tomographic data acquisition and image formation strategies. We investigate the applicability of the commonly applied imaging geometries for acquisition and reconstruction of hybrid optoacoustic tomography and pulse-echo ultrasound (OPUS) images. Optimization of the ultrasound image formation strategy using concave array geometry was implemented using a synthetic aperture method combined with spatial compounding. Experimental validation was performed using a custom-made multiplexer unit executing switching between the two modalities employing the same transducer array. A variety of array probes with different angular coverages were subsequently tested, including arrays for clinical hand-held imaging as well as stationary arrays for tomographic small animal imaging. The results demonstrate that acquisition of OAT data by mere addition of an illumination source to the common US linear array geometry may result in significant limited-view artifacts and overall loss of image quality. On the other hand, unsatisfactory US image quality is achieved with tomographic arrays solely optimized for OAT image acquisition without considering the optimal transmit-receive beamforming parameters. Optimal selection of the array pitch size, tomographic coverage and spatial compounding parameters has achieved here an accurate hybrid imaging performance, which was experimentally showcased in tissuemimicking phantoms, post-mortem mice, and hand-held imaging of a healthy volunteer. The efficient combination of the two modalities in a single imaging device reveals the true power of functional and molecular imaging capacities of OAT in addition to the morphological and functional imaging capabilities of US.