Geometry Factors Research Articles

Estimation of CMAS infiltration depth in EB-PVD TBCs: A new constraint model supported with experimental approach

Two standard 7YSZ coatings were deposited by EB-PVD techniques and tested against CMAS infiltration at short time intervals (up to 8 min.) at 1250 °C in air. They exhibited different microstructures, i.e. porosities and microstructural features. Two species of CMAS with different compositions were used and their viscosities were determined using the concentric cylinder method and their contact angles were measured using high temperature heating microscopy. The theoretical viscosities, which were calculated using a statistical model based on the chemical composition of the melts, differed from the measured values of the viscosities by one order of magnitude. A large variation in the contact angles within a very short range of temperature (1243–1266 °C) was observed as well. The porosity and surface area measurements were performed on both EB-PVD microstructures using the nitrogen physisorption method. Additionally, the produced coatings exhibited porosities of 14.5 and 29.5 percent and the infiltration experiments have shown that the more porous coating provides higher infiltration resistance. The effect of porosity on CMAS infiltration kinetics was investigated and the results elucidate that the porosity network plays a more preeminent role than the amount of porosity. The experimental infiltration results have been compared with calculated infiltration data using a novel mathematical approach proposed in previous studies in which the permeability of the coatings is assessed with two contrasting methods termed “concentric pipe” and “open pipe” models. The infiltration was calculated by incorporating the experimentally determined properties such as contact angle, viscosity and porosity. A fitting parameter has been derived from the equations for the geometry factor for both microstructures. The calculated and experimental results are in good agreement with the concentric pipe model supporting the validity of this CMAS infiltration model.

In situ X-ray tomography investigation of the crack formation in an intermetallic beta-stabilized TiAl-alloy during a stepwise tensile loading

The impact of high temperature exposure on the mechanical damage behavior of the intermetallic TiAl alloy TNM has been investigated by means of high resolution laboratory computer tomography (CT). An in situ testing device was adapted allowing the study of cracking behavior during tensile testing of unnotched samples by CT. Accordingly, failure of exposed and unexposed samples is controlled by the fracture toughness. Unexposed samples reveal crack formation in the interior at only about 1/3 of their plastic elongation to failure. These internal cracks grow gradually with increasing nominal stress and are subjected to significant crack deflection by the microstructure until the crack growth accelerates and the samples fail. After exposure for 1 h at 800 °C cracks originate in the surface region of the samples at almost the same nominal stresses at which internal cracks first appear. However, due to higher fracture mechanical geometry factor, surface cracks become critical almost instantly after their formation resulting in a reduced ductility, which is known as environmental embrittlement in literature. It is supposed that crack formation at the surface after exposure is the result of stress concentrations which are built-up during plastic deformation due to interstitials in the surface layer.

Pore-network extraction algorithm for shale accounting for geometry-effect

Extracted pore-network modeling is an efficient and reliable way to provide a platform for mathematical simulation of fluid flow in porous media and predicting the transport properties. However, the existing algorithms for pore-network extraction have deficiencies in capturing the unique features of shales, including the geometry information and the complex connections between adjacent pore bodies. The newly developed method, based on the maximal-ball algorithm, proposes a novel and enhanced algorithm for the classification of pore bodies and throats. The extremely small pores, composed by only several voxels, can be captured by the new method. We capture the pore-throat geometry by characterizing the cross section of each maximum inscribed sphere connecting the two adjacent pore bodies; the pore-body geometry is characterized using the locally largest maximum inscribed sphere and the overlapping ones. The novel algorithm takes into account the complex connection between the adjacent pore bodies in determining the pore-throat size, where the flow capacity is maintained. A Marcellus shale core sample is used to validate our new method. The core sample is scanned using scanning electron microscope with the resolution of 4 nm, and the three-dimensional reconstruction of the porous media is built. We extract the pore-network model based on the three-dimensional reconstruction and analyze the statistic of the properties, like the distribution of pore size and geometry factor. The pore structures are quantitatively compared with the structures extracted by the previous maximal-ball method. The results show that our new method can capture more extremely small pores than the previous method and the classification of pore throats and bodies is more reasonable. So, the newly developed method is more reliable to extract physically realistic pore networks.

Three-Dimensional Simulation of Aggregate and Asphalt Mixture Using Parameterized Shape and Size Gradation

Aggregate occupies at least three-quarters of the volume of asphalt mixture and can significantly affect the performance of pavement. The geometrical morphology influences the slippage and interlock among aggregates for resisting and distributing applied loads. In recent years, the discrete-element method (DEM) has been employed for simulation of asphalt mixture structure. This paper introduces an approach for simulation of aggregate and asphalt mixtures using parameterized shape and size gradation. Both the plane geometry factor (PGF) and the section aspect ratio (SAR) were employed to describe the three-dimensional (3D) geometric characteristics of aggregates. A numerical technique of aggregate models was implemented with probabilistic parameters depending on statistical results of PGFs and SARs. The 3D numerical model of asphalt mixtures was assembled with three different components, and was validated by uniaxial compression tests via comparison with the laboratory result. It was found that the PGF and SAR are appropriate to describe the three-dimensional features of aggregate shapes, because a simplified space object can be described by a two-dimensional (2D) graphical projection and a vector scalar corresponding to the space vector. Probability distribution curves of PGFs and SARs between coarse aggregates were in concordance with the Gauss-type function, because their correlation coefficients were all greater than 95%. It was verified that the developed clumping algorithm of aggregates was reasonable in terms of the shape and size gradation. Based on the parallel-bond model and Burger's model, the results of virtual tests were in good agreement with those of laboratory uniaxial tests. The angularity (PGF) of aggregates has a beneficial effect on the strength and stability of asphalt mixtures, whereas the flat-elongated feature (SAR) has a negative effect on the strength and stability of asphalt mixtures.

Estimation of geometry factor of header pipe by CFD

Estimation of geometry factor of header pipe by CFD

Development of Computer-Based Model for Design and Analyses of Worm Gearing Mechanism

Current computer software for designing gear systems have limited flexibility and few offer multiple gearing design options. The objective of this study was to develop an interactive package for the design and analyses of worm gearing mechanisms. The worm gears were designed based on full-depth involute teeth. Mathematical models were developed to compute geometry factors for surface durability of single-enveloping worm gearing cases which were extracted from established American Gear Manufacturers Association (AGMA) standards. Maximum percentage errors from the geometry features, bending loads and wear loads are 0.97%, 3.27% and 1.77% respectively and insignificant. A software capable of computing geometry parameters, bending and wear loads, and selecting appropriate materials for worm mechanisms with good accuracy has been developed.

Development of Computer-Based Model for Design and Analyses of Worm Gearing Mechanism

Current computer software for designing gear systems have limited flexibility and few offer multiple gearing design options. The objective of this study was to develop an interactive package for the design and analyses of worm gearing mechanisms. The worm gears were designed based on full-depth involute teeth. Mathematical models were developed to compute geometry factors for surface durability of single-enveloping worm gearing cases which were extracted from established American Gear Manufacturers Association (AGMA) standards. Maximum percentage errors from the geometry features, bending loads and wear loads are 0.97%, 3.27% and 1.77% respectively and insignificant. A software capable of computing geometry parameters, bending and wear loads, and selecting appropriate materials for worm mechanisms with good accuracy has been developed.

Early-stage design strategies: Early-stage design considerations for the energy-efficiency of high-rise office buildings

Decisions made at early stages of the design are of the utmost importance for the energy-efficiency of buildings. Wrong decisions and design failures related to a building’s general layout, shape, facade transparency or orientation can increase the operational energy tremendously. These failures can be avoided in advance through simple changes in the design. Using extensive parametric energy simulations by DesignBuilder, this paper investigates the impact of geometric factors for the energy-efficiency of high-rise office buildings in three climates contexts: Amsterdam (Temperate), Sydney (Sub-tropical) and Singapore (Tropical). The investigation is carried out on 12 plan shapes, 7 plan depths, 4 building orientations and discrete values for window-to-wall ratio. Among selected options, each sub-section determines the most efficient solution for different design measures and climates. The optimal design solution is the one that minimizes, on an annual basis, the sum of the energy use for heating, cooling, electric lighting and fans. The results indicate that, the general building design is an important issue to consider for high-rise buildings: they can influence the energy use up to 32%. For most of the geometric factors, the greatest difference between the optimal and the worst solution occurs in the sub-tropical climate, while the tropical climate is the one that shows the smallest difference. In case of the plan depth, special attention should be paid in a temperate climate, as the total energy use can increase more than other climates. Regarding energy performance, the following building geometry factors have the highest to lowest influence: building orientation, plan shape, plan depth, and window-to-wall ratio.

롤러-랙 피니언 시스템의 이뿌리 굽힘응력

A tooth root bending stress equation for a roller-rack and pinion (RRP) system is presented in this paper as a solution to the problem of tooth root breakage in a pinion jacking system based on an involute tooth profile. The bending strength geometry factor for the RRP system was determined by the same procedure as that for the involute tooth profile. The tooth root bending stress of the RRP system was found to be lower than that of the involute teeth with the same design specification. It can also be lowered by increasing the profile shift coefficient and the number of teeth of the pinion, and by decreasing the roller diameter coefficient. Finally, it was confirmed that the RRP system could provide a new solution to the bending strength problem of a conventional rack and pinion system.

Colloidal Pixel‐Based Micropatterning Using Uniform Janus Microparticles with Tunable Anisotropic Particle Geometry

AbstractA new platform for designing 2D colloidal arrays by using Janus microparticles (JMPs) with tunable anisotropic particle geometry is introduced. The JMPs are synthesized by the photopolymerization of biphasic emulsion droplets produced by capillary‐based microfluidics while adjusting the spreading coefficient between −4.4 and −7.2 mN m−1. The unidirectional rubbing of JMPs leads to their exact positioning in the stencil holes. The ratio of the hole diameter to the bigger bulb diameter of JMPs, ranging from 1.05–1.16, is critical for maximizing the positioning rate. When the anisotropic geometry factor is near zero, a standing particle configuration with a protrusion in the stencil hole is obtained more efficiently due mainly to the enhanced steric constraint. Finally, it is demonstrated that different types of JMPs with controlled sizes and geometries can be arrayed at specific hole sites of the stencil, thus enabling development of a colloidal pixel‐based micropatterning technology.

The effects of initial crack length on fracture characterization of rubbers using the J-Integral approach

The effects of initial crack length on the mode I fracture properties of crosslinked elastomers were investigated. A J-integral approach was implemented using single-specimen test procedures. Quasi-static fracture tests were carried out on filled and unfilled acrylonitrile-butadiene rubbers with various pre-cut (initial) crack lengths, a0, at a fixed rate of extension, using single edge notch rectangular bar specimens. Data from these experiments were analyzed and crack resistance curves (R curves) were obtained. A detailed analysis of the single-specimen method was carried out to establish correlation with the fracture properties derived from the more involved multi-specimen method. The weak dependence of geometry factor on rubber composition and displacement (in the neighborhood of crack initiation displacement) was verified. The crack initiation resistance and tearing modulus of the materials were calculated based on the R curve for each initial crack length. Fracture properties of lightly cracked specimens (a0/W<0.4, where W is the specimen width), including crack initiation resistance, strain at crack initiation, tearing modulus and maximum load and extension before fracture, were found to show significant variations with a0. These variations are characterized and discussed for the filled and unfilled rubber materials.

Driver behavior analysis on rural 2-lane, 2-way highways using SHRP 2 NDS data

Objective: Rural 2-lane, 2-way (RTLTW) highways comprise a large portion of the rural road network in the United States. Crashes on RTLTW roads have been a major concern for traffic safety and may impact traffic significantly. Driver behavior on RTLTW roads has not been analyzed thoroughly. This article analyzed the role of driver behavior fault in crashes/near-crashes on RTLTW roads.Methods: A total of 467 crash/near-crash records and 160 baseline events (normal driving) were extracted from the Strategic Highway Research Program 2 Naturalistic Driving Study (NDS) database. The contribution of driver behavior to crash risk compared to roadway geometry and environmental factors was ranked using random forest. The influence of different factors on driver behavior fault in a crash/near-crash was further examined using a probit model. The reliability of the model was evaluated using 3 different parameters.Results: It was found that driver behavior fault was the most important factor in crashes that occurred on RTLTW roads. Driver age, traffic density, alignment, presence of an intersection, and hands on wheel were found to be highly related to driver behavior fault.Conclusions: Young drivers (16–19 years old) were more likely to have driving behavior fault compared to other age groups. The presence of an intersection may also slightly increase the probability of driver behavior fault. The curve on the road can increase the risk of driver behavior fault. Drivers were more likely to have driver behavior fault when no hands were on the wheel. Sites with curves near intersections are locations where drivers are more likely to have behavior fault.

Comparison of Proximal Femoral Geometry and Risk Factors between Femoral Neck Fractures and Femoral Intertrochanteric Fractures in an Elderly Chinese Population.

Background:Few studies have investigated the differences in proximal femoral geometry and risk factors between patients with different types of hip fracture, especially in elderly Chinese. This study aimed to assess the differences in proximal femoral geometry parameters between patients with femoral neck fractures and patients with intertrochanteric fractures to provide guidance for individualized customized prosthesis and accurate reconstruction of proximal femurs in elderly Chinese patients.Methods:We retrospectively studied the electronic medical records of 198 elderly patients over 65 years of age who were admitted to the orthopedic department with hip fractures between January 2017 and December 2017 in The Third Hospital, Hebei Medical University. Age, fracture site, gender, and proximal femoral geometry parameters (neck shaft angle [NSA], center edge angle [CEA], femoral head diameter [FHD], femoral neck diameter [FND], femoral neck axial length [FNAL], hip axial length [HAL], and femoral shaft diameter [FSD]) were recorded. Student's t-test was used to compare the continuous variables, Chi-square test was used to analyze categorical variables, and multiple logistic stepwise regression analysis was used to evaluate the influencing factors of hip fracture type.Results:Statistically significant differences in NSA (137.63 ± 4.56° vs. 132.07 ± 4.17°, t = 1.598, P < 0.001), CEA (37.62 ± 6.77° vs. 43.11 ± 7.09°, t = 5.597, P < 0.001), FND (35.21 ± 3.25 mm vs. 34.09 ± 3.82 mm, t = 2.233, P = 0.027), and FNAL (99.30 ± 7.91 mm vs. 103.58 ± 8.39 mm, t = 3.715, P < 0.001) were found between the femoral neck fracture group and femoral intertrochanteric fracture group. FHD, FND, FSD, HAL, and FNAL were different between sexes (all P < 0.001). The greater NSA was the risk factor for femoral neck fractures (odds ratio [OR]: 0.70, P < 0.001), greater CEA and longer FNAL were risk factors for femoral intertrochanteric fractures (OR: 1.15, 1.17, all P < 0.001), and greater FND was a protective factor for femoral intertrochanteric fractures (OR: 0.74, P < 0.001).Conclusions:We demonstrate differences in geometric morphological parameters of the proximal femur in different hip fracture types, as well as an effect of sex. These differences should be considered in the selection of prostheses for fracture internal fixation and hip replacements. These data could help guide the design of individualized customized prostheses and improve the accurate reconstruction of the proximal femur for elderly Chinese hip fracture patients.

Numerical simulation on fracture resistance and factors affecting toughness for welded joint of low-alloy steel

Crack propagation resistance for welded joint was numerically simulated by ABAQUS software, where compact tensile (CT) specimens with different thickness and depth of side groove were taken to discuss the variation and reliability of results. It is found that the critical fracture toughness Jc increases with the thickness and then decreases gradually to the plane strain fracture toughness. The equivalent thickness Beq was put forward by numerical simulation. Strain energy density and the volume of plastic deformation zone were calculated to explain the effect of thickness on Jc based on the theory of energy dissipation. The simulated results revealed that another critical geometry factor like the depth of side groove up to 25% of total thickness contributed to a smaller J integral distribution gradient. The CT specimen with suitable geometry size was obtained according to the numerical results, which helps in guiding the experimental test of fracture toughness. The simulation results of fracture resistance demonstrate a good consistency with experiments, showing that numerical model is of high reliability, and stable Jc could be achieved at suitable specimen size.

Estimating the Permeability of Naturally Structured Soil From Percolation Theory and Pore Space Characteristics Imaged by X‐Ray

AbstractThe saturated hydraulic conductivity of soil, Ks, is a critical parameter in hydrological models that remains notoriously difficult to predict. In this study, we test the capability of a model based on percolation theory and critical path analysis to estimate Ks measured on 95 undisturbed soil cores collected from contrasting soil types. One parameter (the pore geometry factor) was derived by model fitting, while the remaining two parameters (the critical pore diameter, dc, and the effective porosity) were derived from X‐ray computed tomography measurements. The model gave a highly significant fit to the Ks measurements (p &lt; 0.0001) although only ~47% of the variation was explained and the fitted pore geometry factor was approximately 1 to 2 orders of magnitude larger than various theoretical values obtained for idealized porous media and pore network models. Apart from assumptions in the model that might not hold in reality, this could also be attributed to experimental error induced by, for example, air entrapment and changes in the soil pore structure occurring during sample presaturation and the measurement of Ks. Variation in the critical pore diameter, dc, was the dominant source of variation in Ks, which suggests that dc is a suitable length scale for predicting soil permeability. Thus, from the point of view of pedotransfer functions, it could be worthwhile to direct future research toward exploring the correlations of dc with basic soil properties and site attributes.

The roles of interfaces and other microstructural features in Cu/Nb nanolayers as revealed by in situ beam bending experiments inside an scanning electron microscope (SEM)

Interfaces and their interactions with other microstructural features, such as grain boundaries or twin structures, have been widely viewed as parameters for designing metallic nanolayers. These interfaces could play a role in hindering cracks from propagating across the nanolayers while in operation. To date, many studies have focused on the roles of interfaces in affecting the plasticity mechanisms and thus the deformability of nanolayers. However, no studies have investigated on the subsequent mechanisms of fracture leading to the final failure. In this study, in situ microfracture bending tests inside a scanning electron microscope (SEM) were performed on the notched clamped beams of Cu/Nb nanolayers with a similar layer thickness using two different fabrication processes: physical vapor deposition (PVD) and accumulative roll bonding (ARB). Due to the columnar grains of the Cu/Nb PVD beams, a sudden catastrophic linear elastic, brittle fracture phenomenon was observed; in the Cu/Nb ARB beams, fracture events of notch widening phase and crack initiation and fracture along the shear instability were observed. Detailed examinations showed the presence of competing mechanisms between the multilayered interface, columnar grain boundary, and experimental factors of beam geometry and the position of the tip. With this newfound knowledge, new types of metallic nanolayers can be designed with enhanced strength and fracture resistant properties.

Optimization of geometry parameters with separation efficiency and flow split ratio for downhole oil-water hydrocyclone

High water cut of crude oil has already become a serious problem for earlier oil well, and downhole oil-water hydrocyclone is thought as one of the solutions to solve this problem. But high separation efficiency usually accompanies with big flow split ratio which still costs large efforts to treat it. In this work, research was carried out to detect the effects of geometry factors on separation efficiency and flow split ratio to optimize the geometry. The oil-water two-phase flow in two-cone hydrocyclone was seriously analyzed and a mathematic model was built to describe it. Results show that backflow generates in upper cone and lower cone, therefore the evaluation and optimization are focused on upper cone, lower cone and lower cylinder. First, cases were designed using orthogonal analysis to overcome the interaction of different factors with constant length of lower cone. The angle of lower cone should be bigger than 0.5° and smaller than 3.0° to obtained a high efficiency with suitable flow split ratio. The change of angle of lower cone alters the critical diameter and affects the velocity and backflow in upper cone. Then, simulations were carried out with constant critical diameter to eliminate this influence to further detect their effects on separation and optimize the geometry. The differences of separation efficiencies are all within 1% with same critical diameter, but effects on flow split ratio are much obvious. The optimization of geometry should be focused on flow split ratio, and the promotion of separation efficiency should be focused on determine the relationship between critical diameter and flow rate. The optimal values are recommended for angle of upper cone, angle of lower cone and length of lower cylinder with critical diameter 28 mm.

Experimental and DEM studies on the distribution of voidage in the random filling bed of ellipsoidal particles

ABSTRACT The average voidage, radial voidage and axial voidage distribution in ellipsoidal pellets bed layer were studied by experiments and Discrete Element Method (DEM) Simulation. A series of experiments were used to determine the collision parameters of DEM model. The influence of the bed geometry factor on the average voidage and the radial voidage of the bed layer were investigated, the distribution of axial voidage in the bed was observed under different bed height conditions. The results show that the pellet diameter and cylinder diameter are the critical factor affecting the bed voidage distribution. With the bed geometry factor increasing, the average voidage of the bed gradually decreased. When D/dp > 50, the average voidage of the bed approaches to a constant (0.292). The damped oscillation of the radial voidage distributes from the wall toward the center of bed, and there is a maximum value near the wall. When the total height of the bed is constant, ignoring the influence of edge effect, the axial voidage increased gradually and eventually tends to be constant. With the gradual increase of the bed height, the change rate of the voidage and the axial voidage at the same height gradually decreased.

Effects of the geometry factor on the reflection loss characteristics of the modified lanthanum manganite

The synthesis and characterization of modified lanthanum manganite materials by using mechanical milling technique have been performed. This magnetic material is prepared by oxides, namely lanthanum oxide, barium carbonate, iron oxide, titanium dioxide, and manganese carbonate. The mixture was milled for 10h, compacted at 5000 psi into pellets with three kinds of different thickness (d = 1.5, 2.0 and 4.0 mm, respectively) and then sintered at temperature of 1000 °C for 10h. The refinement results of x-ray diffraction pattern showed that the sample is single phase. The sample had composition in accordance to stochiometry composition. The geometry factor consists of the particle morphology observed using scanning electron microscope and thickness measured millimeter device. The microstructure analyses shows that the particle shapes was aggregates with the particle sizes distributed homogeneously on the surface of the sample. The results of the microwave absorption indicated that there were three of absorption peak frequency at 9.9 GHz, 12.0 GHz, and 14.1 GHz. The microwave absorption of the sample increases with increasing thickness of absorption area. We concluded that the increasing thickness of absorption region resulted new resonance frequencies, and the new resonance frequencies are joined to each other to form a wider resonance frequency and it is known as a broadband absorber. The first section in your paper.

Evaluation of geometric factors influencing thermal performance of horizontal spiral-coil ground heat exchangers

This study aims to estimate the thermal performance of a horizontal spiral-coil ground heat exchanger (GHE), focusing on the geometry factor of the spiral-coil. Prior to the thermal performance evaluation, an indoor thermal response test (TRT) was conducted with a 5 m x 1 m x 1 m steel box filled with dry Joomunjin sand and TRT equipment was used to validate the numerical analysis using the commercial program COMSOL Multiphysics 5.2a, which is based on computational fluid dynamics (CFD). Next, the number of analysis cases was set by selecting the key factors affecting the thermal performance of a horizontal GHE: installation depth, fluid velocity, thermal conductivity of the ground, and numerical studies were conducted on the 16 cases. As a result of the analysis, it was observed that the pitch does not affect thermal performance if the pitch exceeds 0.6 m. These same results were derived even when additional changes in the key factors were taken into consideration. In addition, it was revealed that the spiral diameter does not affect the thermal performance of the horizontal spiral-coil GHE. Therefore, we concluded that the geometric factor that determines the optimal thermal performance of the horizontal spiral-coil GHE is not the spiral diameter but the pitch, and the 0.6 m pitch of the horizontal spiral-coil GHE can provide a compromise between the thermal performance and installation land space.