Effect Of Geometric Variations Research Articles

Stress Load and Ascending Aortic Aneurysms: An Observational, Longitudinal, Single-Center Study Using Computational Fluid Dynamics.

Ascending aortic aneurysm (AAoA) is a silent disease with high mortality; however, the factors associated with a worse prognosis are not completely understood. The objective of this observational, longitudinal, single-center study was to identify the hemodynamic patterns and their influence on AAoA growth using computational fluid dynamics (CFD), focusing on the effects of geometrical variations on aortic hemodynamics. Personalized anatomic models were obtained from angiotomography scans of 30 patients in two different years (with intervals of one to three years between them), of which 16 (53%) showed aneurysm growth (defined as an increase in the ascending aorta volume by 5% or more). Numerically determined velocity and pressure fields were compared with the outcome of aneurysm growth. Through a statistical analysis, hemodynamic characteristics were found to be associated with aneurysm growth: average and maximum high pressure (superior to 100 Pa); average and maximum high wall shear stress (superior to 7 Pa) combined with high pressure (>100 Pa); and stress load over time (maximum pressure multiplied by the time interval between the exams). This study provides insights into a worse prognosis of this serious disease and may collaborate for the expansion of knowledge about mechanobiology in the progression of AAoA.

DESIGN AND ANALYSIS OF ELECTRICAL CHARACTERISTICS OF INVERTED-T JUNCTIONLESS (JL) FET THROUGH GEOMETRIC AND PROCESS VARIATIONS FOR HIGH FREQUENCY APPLICATIONS

An inverted-T structure is implemented with the Junctionless (JL) topology at nanoscale dimensions. The Inverted-T Junctionless (ITJL) FET features a multi-fin architecture that utilizes the unused space within the fins and combines it with the junctionless topology, maintaining the same doping concentration from source to drain. In order to mitigate the short channel effects and overcome the fabrication challenges, an inverted-T FET has been designed. The crucial performance parameters of device are explored by varying the geometric dimensions and process parameters. The performance of ITJLFET is measured by varying different parameters namely temperature (T), doping concentration (Nd), work function 𝒎 ), and dielectric constant (K) at 30-nm technology node and effect of geometric variations are measured by altering the gate length (Lg) and oxide thickness (Tox). Inverted-T junctionless field effect transistor (ITJLFET) is designed with different gate lengths in the range of 14 nm to 30 nm and shows the improvement in ION by 64% as compared to the conventional JLFET. The parametric analysis like transfer characteristics (Id-Vgs), Ion/IOFF ratio, subthreshold swing (SS), drain induced barrier lowering (DIBL) and gate capacitance (Cgg) are investigated for 250 K to 350 K. From the results, it is perceived that temperature has less effect on the Inverted-T junctionless transistor performance. The cut-off frequency for the designed device is calculated and observed to be in the range of 0.3 to 1.5 THz. Hence, device can be used for high-frequency applications at the submicron regime.

Effect of geometric variation and solar flux distribution on performance enhancement of absorber tube thermal characteristics for compound parabolic collectors

A compound parabolic collector (CPC) is a concentrated solar thermal technology widely used for thermal energy storage and electricity generation. Usage of proficient absorber tube configuration improves its thermal efficiency and the present study is an attempt to numerically evaluate the feasibility of employing elliptical absorber tube design in CPCs. Initially, the thermal characteristics of the conventional circular and proposed elliptical absorber tube configurations were evaluated for an ideal condition, taking into account the solar radiation effect from Monte-Carlo ray-tracing analysis. The effect of governing factors that include fluid flow rate (0.015–0.05 kg/min), heat flux (1175–1200 W/m2), and inclination angle (3°) were analyzed for optimum condition identification delivering maximum efficiency. Further analysis was focused on evaluating the thermal loss influence with face-split and top-wall insulation conditions. Results indicated that the elliptical configuration outperformed the circular tube with an increment in the maximum temperature rise by 42.2%, 33.4%, and 27.7% for simple, face-split, and face-split top-wall insulated conditions along with better stability over the local hydrodynamic changes. Face-split analysis contributed to better realistic results over constant heat flux and it was inferred that the inclined face-split elliptical configuration exhibited maximum thermal efficiency with higher temperature rise and nominal pressure drop characteristics.

In Vitro and In Silico Investigations on Drug Delivery in the Mouth-Throat Models with Handihaler®.

This work aimed to evaluate the relative inhalation parameters that affect the deposition of inhaled aerosols, including mouth-throat morphology, airflow rate, and initial condition of emitted particles. In vitro experiments were conducted using the US Pharmacopeia (USP) throat and a realistic mouth-throat (RMT) with Handihaler®. Then, in silico study of the gas-solid flow was performed by computational fluid dynamics and discrete phase method. Results indicated that aerosol deposition in RMT was higher compared to that in USP throat at an airflow rate of 30 L/min, with 33.16 ± 7.84% and 21.11 ± 7.1% lung deposition in USP throat and RMT models, respectively, which showed a better correlation with in vivo data from the literature. Increasing airflow rate resulted in better drug aerosolization, while the fine particle dose trend ascended before declining, with the peak value obtained at a flow rate of 40 L/min. Overall, the effect of geometrical variation was more significant. Additionally, in silico results demonstrated clearly that the initial conditions of the emitted particles from inhalers affected the subsequent deposition. Larger momentum possessed by the central aerosol jet entering the mouth directly led to stronger impaction, which resulted in the deposition in the front region of mouth-throat models. This study is beneficial to develop an in silico method to understand the underlying mechanisms of in vivo mouth-throat deposition.

Geometry-Driven Criterion Function for Predicting Shrinkage Porosity in Stainless Steel Castings with T-Junction

Metal castings with the presence of shrinkage porosity are often recycled or rejected and in turn reduce productivity of the process as well as increase energy cost involved in the process. This can be overcome by prevention of its occurrence using a suitable prediction technique. A detailed study of literature reveals that several Criterion Functions (an empirical model that connects solidification phenomena with formation of shrinkage porosity) have been employed to predict the location of shrinkage porosity in castings manufactured using particular process-alloy combination by values of process parameters (mostly thermal gradient, cooling rate, and velocity of molten metal). However, criterion function considering the effect of geometric variation in stainless steel castings on an extent of shrinkage porosity need to be established. In the present work, a benchmark casting, a combination of three T junctions, has been cast and used for the development of geometry-driven criterion function for stainless steel castings. Real experimental results with the presence of shrinkage porosity were used for superimposing on virtual experimental results (simulated results) for establishment of local simulation conditions. These conditions are further used in extrapolating results using casting simulation. The developed geometry-driven criterion function was further validated and found to be effective in prediction of shrinkage porosity.

Analysis and simulation of asymmetrical nanoscale self-switching transistor

ABSTRACT In this paper, we present a computational study on the electrical behaviour of self-switching transistors (SSTs) based on InGaAs/InP heterojunction. Our simulation is based on the solution of Poisson and Schrodinger equations self-consistently by using Finite Element Method (FEM). By using this method, electrical characteristics of device, such as ratio, subthreshold swing, and intrinsic gate-delay time are investigated. Also, the effects of geometrical variations on the electrical parameters of SSTs are simulated. We show that appropriate design of the device allows current modulation exceeding at room temperature.

A novel compliant assembly variation analysis with consideration of initial deviation and welding shrinkage

Welding, as the most common joining technique, causes welding deformations that reduce the geometrical accuracy of hull structures. In conventional variation analysis, welding distortion is not taken into account. In this paper, a compliant assembly variation modeling and analysis method is presented to investigate the impact of local weld-induced shrinkage on the propagation relation from the initial deviation to the final assembly deviation in thin plate assembly. First, welding deformations in the form of inherent strains are incorporated into variation analysis model based on Kirchhoff plate model. Additionally, part deviations are also introduced via equivalent forces in order to consider the effects of geometrical variation on compliant assembly. Then, other variation sources, such as fixture locating errors, are modeled as equality constraints of the mechanical variation model, which are then transformed into boundary conditions with Lagrange multiplier method. With an additional stiffness matrix, we describe concisely the coupling relationship between initial deviations and welding deformations caused by gaps and misalignments. In order to validate the effectiveness of the proposed method, numerical simulations and experimental verifications are carried out for two assembly cases, and the results show that the present method has high prediction accuracy and efficiency. This study provides a potential application for improving assembly dimensions considering the inevitable manufacturing deviations and welding deformations.

Geometrically induced wall shear stress variability in CFD-MRI coupled simulations of blood flow in the thoracic aortas

Aortic aneurysm is associated with aberrant blood flow and wall shear stress (WSS). This can be studied by coupling magnetic resonance imaging (MRI) with computational fluid dynamics (CFD). For patient-specific simulations, extra attention should be given to the variation in segmentation of the MRI data-set and its effect on WSS.We performed CFD simulations of blood flow in the aorta for ten different volunteers and provided corresponding WSS distributions. The aorta of each volunteer was segmented four times. The same inlet and outlet boundary conditions were applied for all segmentation variations of each volunteer. Steady-state CFD simulations were performed with inlet flow based on phase-contrast MRI during peak systole.We show that the commonly used comparison of mean and maximal values of WSS, based on CFD in the different segments of the thoracic aorta, yields good to excellent correlation (0.78–0.95) for rescan and moderate to excellent correlation (0.64–1.00) for intra- and interobserver reproducibility. However, the effect of geometrical variations is higher for the voxel-to-voxel comparison of WSS. With this analysis method, the correlation for different segments of the whole aorta is poor to moderate (0.43–0.66) for rescan and poor to good (0.48–0.73) for intra- and interobserver reproducibility.Therefore, we advise being critical about the CFD results based on the MRI segmentations to avoid possible misinterpretation. While the global values of WSS are similar for different modalities, the variation of results is high when considering the local distributions.

A new equilibrium solution for masonry spiral stairs

This paper considers stone or brick staircases that appear to cantilever from an exterior wall as they spiral upward. A new equilibrium solution is proposed that does not rely on cantilevering from the wall. Unlike previously proposed membrane solutions, the proposed new analytical solution, called Linear Arch Static Analysis (LASA), is based on a 1D no-tension filament, or a set of such 1D filaments (that -by following Rankine’s definition- we call space linear arches), and is therefore particularly efficient. Each space linear arch represents a compressive element that spirals down the staircase, simulating a compressive force that is transferred through and between each stair. In addition, the equilibrium of each filament requires the contribution of horizontal uniaxial compressive forces which are provided by the exterior wall support and transmitted horizontally through each stair. The lines of action of such uniaxial compressive stresses are entirely contained inside the masonry. The new solution is applied to both circular and elliptical stairs to demonstrate the new equilibrium solutions, but also to quantify and highlight the magnitude of resulting forces and the efficiency of the solution. The effect of geometric variations on internal forces are also explored to evaluate the efficiency and feasibility of various potential stair geometries.

Glue modelling in variation management of compliant assemblies: critical issues and possible solutions

ABSTRACT Variation management aims to reduce the effects of geometric variations of parts to assemble. Industry is facing a digital revolution in being able to manage geometrical deviation data along the entire lifecycle of a product. This requires the development of new assembly simulation models and tools. New design trends are orienting towards more and more lighter products. They are constituted by thin metal sheets or in composite material. Lighter products in composite materials are always joined through structural adhesive. This work presents different ways to model the adhesive inside a simulation that allows to predict the geometrical variations of an assembly constituted by compliant parts. Three different ways to model adhesive, i.e. glue contact, beam and shell elements, were taken into account. Different thickness values, different component constraints and application points of part variations were also considered. Two lighter assemblies were considered: one constituted by two metal plane sheets that are partially overlapped; the second is formed by three thin sheets in composite material, one plane and two L-shaped. The critical issues connected with the three different solutions to model adhesives in a simulation to manage geometric variations from component to assembly were underlined to guide a possible choice.

Effect of geometrical variations on the structural performance of shipping container panels: A parametric study towards a new alternative design

Abstract In the field of logistics, containers are indispensable for shipments of large quantities of goods, particularly for exports and imports distributed by land, sea, or air. Therefore, a container must be able to withstand external loads so that goods can safely reach their destination. In this study, seven different models of container skins were developed: general honeycomb, cross honeycomb, square honeycomb, corrugated wall, flat, flat with a single stiffener, and flat with a cross stiffener. Testing was performed using the finite element method. In the static simulation, the best results were obtained by the model with corrugated walls. As the main element and the content of the sandwich panel structure, the core plays a role in increasing the ability of the structure to absorb force, thereby increasing the strength of the material. In the thermal simulation, the best results were obtained by the general honeycomb walls. Vibration simulations also showed that the square honeycomb design was better at absorbing vibration than the other models. Finally, the corrugated model had the best critical load value in the buckling simulation.

Effect of geometrical variations on the failure mechanisms of perforated steel plate shear Walls—a parametric study towards a new design

As an effective lateral resisting system, a steel plate shear wall (SPSW) should provide adequate ductility and dissipate energy while protecting its boundary elements (BEs). Herein, the failure modes of a recently-introduced design for SPSWs (a perforated panel with a web-reduced beam section) was investigated. The aim was to control the failure mechanism of this arrangement by various geometrical modifications. To obtain a high-performing design, the interaction of the structural components was studied in terms of plastic strain distribution, ductility, strength, and stiffness. To this end, a finite element prototype was populated for a range of geometrical parameters. The analyses were carried out by varying the panel and beam perforation sizes; then, one excelling combination was further challenged by altering its panel thickness and the frame aspect ratio. The model successfully distinguished between three common failure modes and provided an interesting insight into the causality of the failure mechanisms. It was found that the size of the perforations in the panel and the beam, and the size of the horizontal boundary elements could be manipulated to obtain the desired mechanism. Therein, the tensile failure of the panel was dominant where a plastic band formed across the panel and protected the vertical BEs and their connections. Moreover, the model outperformed its imperforate counterpart in terms of hysteresis ductility and absorbed energy (by about 250%) due to the increased engagement of the structural members. Finally, the findings were summarised into some practical recommendations for improving the design of the proposed arrangement.

Effect of dome size on flow dynamics in saccular aneurysms – A numerical study

Image-based Computational Fluid Dynamic (CFD) simulations of anatomical models of human arteries are gaining clinical relevance in present days. In this study, CFD is used to study flow behaviour and hemodynamic parameters in aneurysms, with a focus on the effect of geometric variations in the aneurysm models on the flow dynamics. A computational phantom was created using a 3D modelling software to mimic a spherical aneurysm. Hemodynamic parameters were obtained and compared with the available literature to validate. Further, flow dynamics is studied by varying the dome size of the aneurysm from 3.75 mm to 6.25 mm with an increment of 0.625 mm keeping the neck size constant. The aneurysm is assumed to be located at a bend in the arterial system. Computational analysis of the flow field is performed by using Navier – Stokes equation for laminar flow of incompressible, Newtonian fluid. Parameters such as velocity, pressure, wall shear stress (WSS), vortex structure are studied. It was observed that the location of the flow separation and WSS vary significantly with the geometry of the aneurysm. The reduction of WSS inside the aneurysm is higher at the larger dome sizes for constant neck size.

Effects of geometric variations on buckling properties of carbon nanostructures: A finite element analysis

Critical Bucking Load (CBL) is one of the essential parameters to describe the mechanic stabilities of materials, e.g. the low-dimensional carbon nanostructures. While the CBL of pristine carbon nanotubes have been previously investigated using the quantum mechanics-based calculations, the effect of geometrical variation on the CBL of carbon nanomaterials is rarely reported since it need considerably large atomic models, which needs high computational cost. In this study, both the analytical and Finite Element (FE) methods were employed to systematically explore the impact of atomic vacancies, shapes and heterostructures on the CBLs of carbon nanomaterials with the acceptable computational cost. Our studies on the pristine CNTs first demonstrate the validity of the method we used. After that, the systems with mono-/bi-/tri-/pinole-vacancies either on nanocones, nanotube, linearly-joined nanotubes or angle-adjoined were simulated and analyzed. Our results reveal that the CBL values decrease with the increase of the aspect ratio of all considered nanomaterials. Based on the obtained results, the CBL of nanocone with the aspect ratio of 1, reduces significantly, from 50 nN to 10 nN when the aspect ratio is 3. The CBL of homogeneous, capped, and joint CNTs reduces to below 2 nN when the aspect ratio is above 14. The introduction of geometric variations can greatly affect the CBL values. The larger atomic vacancy has more serious impact on the CBLs. The most highlighted impact is for the pinhole vacancy where the CBL reduces to up to 70% of the original value. Our studies on linearly-joint and angle-joint carbon hybrids further demonstrate that the CBL can also be affected by the boundary conditions and joint structures of the hybrids.

A comparative computational study of tunneling transistors based on vertical graphene–hBCN heterostructures

In this paper, the electrical characteristics of tunneling transistors based on vertical graphene and a hexagonal boron-carbon-nitrogen (hBCN) heterostructure are studied and compared theoretically. We have considered three different types of hBCN, i.e., BC2N, BC2N′, and BC6N as a tunneling barrier. Our simulation is based on the nonequilibrium Green’s function formalism along with an atomistic tight-binding (TB) model. The TB parameters are obtained by fitting the band structure to first-principles results. By using this method, electrical characteristics of the device, such as the ION/IOFF ratio, subthreshold swing, and intrinsic gate-delay time, are investigated. For a fair comparison, the effects of geometrical variations and number of tunneling barrier layers on the electrical parameters of the device are simulated and investigated. We show that, by an appropriate design, the device can be used for low-power or high-performance applications. The device allows current modulation exceeding 106 at room temperature for a 0.6 V bias voltage.

Full-Quantum Simulation of Graphene Self-Switching Diodes

We present a quantum study on the electrical behavior of the self-switching diode (SSD). Our simulation is based on non-equilibrium Green’s function formalism along with an atomistic tight-binding model. Using this method, electrical characteristics of devices, such as turn-on voltage, rectification ratio, and differential resistance, are investigated. Also, the effects of geometrical variations on the electrical parameters of SSDs are simulated. The carrier distribution inside the nano-channel is successfully simulated in a two-dimensional model under zero, reverse, and forward bias conditions. The results indicate that the turn-on voltage, rectification ratio, and differential resistance can be optimized by choosing appropriate geometrical parameters.

Effect of geometric variations on tibiofemoral surface and post-cam design of normal knee kinematics restoration

BackgroundRestoration of natural knee kinematics for a designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty (TKA). In different posterior-stabilized TKAs, there are wide variations in tibiofemoral surfaces and post-cam design. However, it is not known whether these design variations preserve natural knee kinematics. The purpose of this study was to determine the most appropriate tibiofemoral surface and post-cam designs to restore natural knee kinematics of the TKA.MethodsA subject-specific finite element knee modal was used to evaluate tibiofemoral surface and post-cam design. Three different posts in convex, straight, and concave geometries were considered with a fixed circular cam design in this study. In addition, this post-cam design was applied to three different surface conformities for conforming, medial pivot, and subject anatomy mimetic tibiofemoral surfaces. We evaluated the femoral rollback, internal-external rotation, and quadriceps muscle force under a deep-knee-bend condition.ResultsThe three different tibiofemoral conformities showed that the convex post provided the most natural-knee-like femoral rollback. This was also observed in internal rotation. In surface conformity, subject anatomy mimetic tibiofemoral surfaces showed the most natural -knee-like kinematics and quadriceps force.ConclusionsThis study confirmed that convex post design and subject anatomy mimetic tibiofemoral surfaces provided the most natural-knee-like kinematics. This study suggested that post-cam design and tibiofemoral surface conformity should be considered in conventional and customized TKA.

Assessment of Stress-Strain Behavior of Corroded Steel Reinforcement Using Digital Image Correlation (DIC)

Abstract Understanding the stress-strain behavior of corroded rebars is essential for understanding the structural behavior of corroding reinforced concrete structures. However, conventional methods of testing have several drawbacks, which have led to differences in opinion among researchers regarding the mechanical behavior of corroded rebars. This article proposes an improved method using Digital Image Correlation (DIC) to assess the stress-strain behavior of corroded rebars. The study is conducted in two phases: (a) development of the testing and evaluation method and (b) determination of the mechanical properties (i.e., yield strength, ultimate strength, and ultimate strain) of naturally corroded cold-twisted deformed (CTD) steel rebars using the developed method. The stress-strain behavior of one pristine plain mild (PM) steel and 13 naturally corroded steel rebars collected from a 15-year-old building are investigated in this study. The experimental results show that the proposed method can provide more accurate estimates of mechanical properties than the conventional methods. The developed method facilitates a better understanding of the stress-strain behavior at the fracture location (FL) and other local points of interest on corroded steel rebars. Because DIC measures local strains, the proposed method is able to measure local strain heterogeneity and therefore distinguish between the effects of geometrical variations from those due to true material degradation. This is in contrast to the conventional methods wherein deformation is measured over a finite gauge length, which results in a measurement of average deformation rather than true local deformation. This study emphasizes the need for measurement of full-field deformation to assess the stress-strain behavior of the corroded rebars with highly uneven cross-sectional area.

Evaluating How Functional Performance in Aerospace Components Is Affected by Geometric Variation

Geometric variation stemming from manufacturing can be a limiting factor for the quality and reliability of products. Therefore, manufacturing assessments are increasingly being performed during the early stages of product development. In the aerospace industry, products are complex engineering systems, the development of which require multidisciplinary expertise. In such contexts, there are significant barriers against assessing the effects of geometric variation on the functionality of products. To overcome these barriers, this article introduces a new methodology consisting of a modelling approach linked to a multidisciplinary simulation environment. The modelling approach is based on the parametric point method, which allows point-scanned data to be transferred to parameterised CAD models. In a case study, the methodology is implemented in an industrial setting. The capability of the methodology is demonstrated through a few applications, in which the effects of geometric variation on the aerodynamic, thermal, and structural performance of a load-bearing turbofan component are analysed. The proposed methodology overcomes many of the current barriers, making it more feasible to assess the effects of geometric variation during the early design phases. Despite some limitations, the methodology contributes to an academic understanding of how to evaluate geometric variation in multidisciplinary simulations and provides a tool for industry.

Single-Phase Cryogenic Flow and Heat Transfer Through Microscale Pin Fin Heat Sinks

Single-phase heat transfer and pressure drop of liquid nitrogen in microscale heat sinks are studied experimentally in this paper. Effects of geometrical variations are characterized on the thermofluidic performance of staggered microscale pin fin heat sinks. Pitch-to-diameter ratio and aspect ratio of the micro pin fins are varied. The pin fins have square shape with 200 or 400 μm width and are oriented at 45 degrees to the flow direction. Thermal performance of the heat sinks is evaluated for Reynolds numbers (based on pin fin hydraulic diameter) from 108 to 570. Results are presented in a nondimensional form in terms of friction factor, Nusselt number, and Reynolds number and are compared with the predictions of existing correlations in the literature for micro pin fin heat sinks. Comparison of flow and heat transfer performance of the micro pin fin heat sinks reveals that at a particular critical Reynolds number of ∼250, pin fin heat sinks with the same aspect ratio but larger pitch ratio show a transition in both friction factor and Nusselt number. In order to better characterize this transition, visualization experiments were performed with the Fluorinert PF5060 using an infrared camera. At the critical Reynolds number, for the larger pitch ratio pin fin heat sink, surface thermal intensity profiles suggest periodic flapping of the flow behind the pin fins at a Strouhal number of 0.227.