Search Results (13)

The theta projection method has been used to predict uniaxial creep curve shapes for a wide range of materials. However, one of the criticisms of the existing method is that the multilinear approach, commonly used to correlate theta parameters to applied test conditions, does not extrapolate well over a full range of creep conditions, due to not accounting for changes in creep mechanisms. This is particularly important for evaluating the creep behaviour of structural engineering components that operate in an environment in which a wide range of stress and/or temperatures exist during their service life. This study uses the theta projection method to evaluate creep curves for the nickel-based superalloy, Waspaloy, over a range of test conditions, considering changes in observed dominant creep mechanisms. A clear break in the trend of ${\theta }_3$ and ${\theta }_4$ with respect to stress is observed, indicating that a change in mechanism is important for tertiary creep. Using a power law approach along with optimisation algorithms, the residual error between predicted and experimentally observed creep curves is reduced. With more accurate prediction of creep curves, creep rates throughout the duration of creep can be more accurately calculated, providing the basis of more accurate computational creep models. Full article

This paper verified the possibility of applying chitosan and/or ferulic acid or polycaprolactone (PCL)-based coatings to polydimethylsiloxane/neodymium–iron–boron (PDMS/NdFeB) composites using the spin-coating method. The surface modification of magnetic composites by biofunctional layers allows for the preparation of materials for biomedical applications. Biofunctional layered magnetic composites were obtained in three steps. The spin-coating method with various parameters (time and spin speed) was used to apply different substances to the surface of the composites. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to analyze the thickness and surface topography. The contact angle of the obtained surfaces was tested. Increasing spin speed and increasing process time for the same speed resulted in decreasing the composite’s thickness. The linear and surface roughness for the prepared coatings were approximately 0.2 μm and 0.01 μm, respectively, which are desirable values in the context of biocompatibility. The contact angle test results showed that both the addition of chitosan and PCL to PDMS have reduced the contact angle θ from 105° for non-coated composite to θ~59–88° depending on the coating. The performed modifications gave promising results mainly due to making the surface hydrophilic, which is a desirable feature of projected biomaterials. Full article

Study Design: Retrospective analysis at a tertiary care center. Objective: This study describes a method of analyzing postoperative results using lateral view clinical photographs to create normalized projection ratios of the glabella and radix. Methods: We reviewed preoperative and postoperative photographs of 15 patients. All photographs were in the lateral view Frankfort horizontal plane. We calculated the distances between the (a) tragus and cornea, (b) cornea and radix, (c) cornea and glabella, and the (θ) nasofrontal angle. Results: Fifteen sets of patient photographs were analyzed and found that there was a favorable 14% reduction at the radix and an even greater reduction (78.9%) at the glabella. The nasofrontal angle was improved to a more feminine range from 131.84° preoperatively to 145.86° postoperatively. Conclusions: Normalized projection ratios of the glabella and radix, along with the nasofrontal angle, can be used to objectively measure outcomes of frontal feminizing cranioplasty. Full article

Creep deformation is one of the main failure forms for superalloys during service and predicting their creep life and curves is important to evaluate their safety. In this paper, we proposed a back propagation neural networks (BPNN) model to predict the creep curves of MarM247LC superalloy under different conditions. It was found that the prediction errors for the creep curves were within ±20% after using six creep curves for training. Compared with the θ projection model, the maximum error was reduced by 30%. In addition, it is validated that this method is applicable to the prediction of creep curves for other superalloys such as DZ125 and CMSX-4, indicating that the model has a wide range of applicability. Full article

The use of 3D printing in modular building connections is a novel and promising technique. However, the performance of 3D printed steel modular building connections has not been investigated adequately to date. Therefore, this paper presents a three-dimensional finite element model (FEM), using the multi-purpose software Abaqus, to study the effect of different geometrical and material parameters on the ultimate behaviour of modular building connections (herein named 3DMBC) using a wire and arc additive manufacturing (WAAM) method, as part of the UK’s 3DMBC (3D Modular Building Connections) project. The proposed model considers material and geometrical non-linearities, initial imperfections, and the contact between adjacent surfaces. The finite element results are compared with the currently available experimental results and validated to ensure developed FEM can be used to analyse the behaviour of 3DMBC with some adjustments. Case studies were investigated using the validated model to analyse the ultimate behaviour with different nominal and WAAM-produced materials under various loading arrangements. Based on the results, it is recommended to conservatively use the treated or untreated WAAM material properties obtained in θ = 90° print orientation in the finite element modelling of 3DMBCs considering the complex component arrangements and multi-directional loading in the modular connections. It is also noted that the thickness of beams and columns of fully 3D printed connections can be increased to achieve the same level of performance as traditional modular connections. For the 3DMBCs printed using untreated WAAM, the thickness increment was found to be 50% in this study. Full article

Using random projection, a method to speed up both kernel k-means and centroid initialization with k-means++ is proposed. We approximate the kernel matrix and distances in a lower-dimensional space ${\mathbb{R}}^d$ before the kernel k-means clustering motivated by upper error bounds. With random projections, previous work on bounds for dot products and an improved bound for kernel methods are considered for kernel k-means. The complexities for both kernel k-means with Lloyd’s algorithm and centroid initialization with k-means++ are known to be $O\left(nkD\right)$ and $\Theta \left(nkD\right)$, respectively, with n being the number of data points, the dimensionality of input feature vectors D and the number of clusters k. The proposed method reduces the computational complexity for the kernel computation of kernel k-means from $O\left(n^{2}D\right)$ to $O\left(n^{2}d\right)$ and the subsequent computation for k-means with Lloyd’s algorithm and centroid initialization from $O\left(nkD\right)$ to $O\left(nkd\right)$. Our experiments demonstrate that the speed-up of the clustering method with reduced dimensionality $d=200$ is 2 to 26 times with very little performance degradation (less than one percent) in general. Full article

In the present work, a comparative study of two major non-intrusive polynomial chaos methods, Point-Collocation Non-Intrusive Polynomial Chaos (NIPC) and Non-Intrusive Spectral Projection (NISP), was conducted for the transitional $\gamma -R_{\theta }$ transitional model. Three multiple model coefficients, C_a2, C_e1, and C_e2 were considered with multiple random inputs with the assumption of uniform distributions with ±10% deviation. The target transitional flows were one around a flat plate and Aerospatiale A-airfoil. Deterministic solutions were obtained by employing the open source software OpenFOAM. The results of two methods were compared to the results of Monte Carlo simulation with 500 runs. The order convergence of the mean value and the standard deviation (STD) were compared in terms of the quantities of interest, drag and lift coefficients. Further, the most effective model coefficient for each transitional flow could be found through the calculation of the Sobol index. Full article

The orientation of fibers with elliptical cross-sections cannot be estimated using standard optical microscopy analysis methods in which the ratio of the minor-axis to the major-axis and orientation of the major-axis are directly used to determine the fiber spherical coordinates, $\theta$ and $\varphi$ . A new method for estimating the orientation of fibers with elliptical cross-sections is presented and validated using both simulations and experiments. Fibers with elliptical cross-sections rather than circular possess a roll degree of freedom, which significantly affects the dimensions of projected cross-sections in viewing planes. The equations of the projected ellipse of an elliptic cylinder onto a viewing plane are determined in terms of typical spherical coordinate system angles, $\theta$ and $\varphi$ , the roll angle, $\alpha$ , and the fiber semi-major and semi-minor diameters. Fiber angles are determined by numerical fitting of the developed equations to measured ellipses. An ambiguity in the determined angles is identified, and, in the special case of fiber bundles, a scheme is presented by which the ambiguity can be resolved. Validation experiments showed that the method is quite effective at estimating fiber orientation from micrographs when fiber cross-section dimensions are measured beforehand, and the additional ambiguity is resolved easily in the case of fiber bundles. Full article

The high temperature creep behaviors of a Zr-based bulk metallic glass (BMG) are studied by uniaxial tensile creep experiments under applied stresses of 50–180 MPa at temperatures of 660–700 K. The microstructural observations of the BMG samples after creep tests show that crystalline phases can be detected under high temperature or high applied stress. Constitutive models for predicting the high temperature creep behaviors of the studied Zr-based BMG are established based on the θ projection method. The creep activation energy and stress exponent are also calculated to establish the creep model. The parameters of the established models are found to be closely associated with the applied stress and temperature. The results show an excellent agreement between the measured and predicted results, confirming the validity of the established model to accurately estimate the high temperature creep curves for the Zr-based BMG. Moreover, based on the classical diffusion creep theory, a schematic model is proposed to describe the creep behaviors of BMGs from the framework of free volume theory. Full article

The construction of a substation will undoubtedly change the properties of any surrounding native soil. In order to study the influence of backfill material on grounding grid performance and in turn optimize that performance, current distribution, electromagnetic fields, ground, and soil structure analysis (CDEGS) was undertaken to simulate the secondary peak of the step voltage generated by a large backfill soil area. As for the various parameters of the finite soil volume, the influence of the soil length L, the edge gradient tan θ, and the resistivity ρ on the secondary peak of step voltage was researched. Then, a grounding test system was established, the selection process of the protection resistors was clarified, and the usage method of agar gel was improved. The feasibility of simulating backfill material with agar gel was verified, and the influence of resistivity and soil scale on the secondary peak of the step voltage was tested. The results show that the larger the backfill material length is, the larger the resistivity is, and the lower the peak voltage is. The effect of soil resistivity on the secondary peak will be greater when the range of backfill material is larger, which means that reducing soil resistivity can effectively reduce the secondary peak. Therefore, a smaller slope can be formed at the edge of the earthwork in the actual substation to reduce the project amount and save investment, which has a certain degree of engineering significance. Full article

Vortex generators (VGs) are increasingly used in the wind turbine manufacture industry as flow control devices to improve rotor blade aerodynamic performance. Nevertheless, VGs may produce excess residual drag in some applications. The so-called sub-boundary layer VGs can provide an effective flow-separation control with lower drag than the conventional VGs. The main objective of this study is to investigate how well the simulations can reproduce the physics of the flow of the primary vortex generated by rectangular sub-boundary layer VGs mounted on a flat plate with a negligible pressure gradient with an angle of attack of the vane to the oncoming flow of β = 18°. Three devices with aspect ratio values of 2, 2.5 and 3 are qualitatively and quantitatively compared. To that end, computational simulations have been carried out using the RANS (Reynolds averaged Navier–Stokes) method and at Reynolds number Re = 2600 based on the boundary layer momentum thickness θ at the VG position. The computational results show good agreement with the experimental data provided by the Advanced Aerodynamic Tools of Large Rotors (AVATAR) European project for the development and validation of aerodynamic models. Finally, the results indicate that the highest VG seems to be more suitable for separation control applications. Full article

The mutation parameter θ is fundamental and ubiquitous in the analysis of population samples of DNA sequences. This paper presents a new highly efficient estimator of θ by utilizing the phylogenetic information among distinct alleles in a sample of DNA sequences. The new estimator, called Allelic BLUE, is derived from a generalized linear model about the mutations in the allelic genealogy. This estimator is not only highly accurate, but also computational efficient, which makes it particularly useful for estimating θ for large samples, as well as for a large number of cases, such as the situation of analyzing sequence data from a large genome project, such as the 1000 Genomes Project. Simulation shows that Allelic BLUE is nearly unbiased, with variance nearly as small as the minimum achievable variance, and in many situations, it can be hundreds- or thousands-fold more efficient than a previous method, which was already quite efficient compared to other approaches. One useful feature of the new estimator is its applicability to collections of distinct alleles without detailed frequencies. The utility of the new estimator is demonstrated by analyzing the pattern of θ in the data from the 1000 Genomes Project. Full article

Gamma titanium aluminides (γ-TiAl) display significantly improved high temperature mechanical properties over conventional titanium alloys. Due to their low densities, these alloys are increasingly becoming strong candidates to replace nickel-base superalloys in future gas turbine aeroengine components. To determine the safe operating life of such components, a good understanding of their creep properties is essential. Of particular importance to gas turbine component design is the ability to accurately predict the rate of accumulation of creep strain to ensure that excessive deformation does not occur during the component’s service life and to quantify the effects of creep on fatigue life. The theta (θ) projection technique is an illustrative example of a creep curve method which has, in this paper, been utilised to accurately represent the creep behaviour of the γ-TiAl alloy Ti -45Al-2Mn-2Nb. Furthermore, a continuum damage approach based on the θ-projection method has also been used to represent tertiary creep damage and accurately predict creep rupture. Full article