113 research outputs found
Investigation of possible half-metallic antiferromagnets on double perovskites LaABBO (A= Ca, Sr, Ba; B, B= transition elements)
No full textFirst-principle calculation on nearly half-metallic antiferromagnetic behavior of double perovskites La2VReO6
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Methylammonium-free, high-efficiency, and stable all-perovskite tandem solar cells enabled by multifunctional rubidium acetate
No full text202505 bcchVersion of RecordOthersThe National Natural Science Foundation of China (52202293 and 52330004, J.T.); the Fundamental Research Funds for the Central Universities (WUT: 2023IVA075 and 2023IVB009, J.T.); National Natural Science Foundation of China (52302327, C.X.); RISE project Grant (Q-CDBK, Z.R.); Start-up Fund for RAPs under the Strategic Hiring Scheme (PoluU) (1-BD1H, Z.R.); PRl Strategic Grant (1-CD7X, Z.R.); RI-iWEAR Strategic Supporting Scheme (1-CD94, Z.R.); the National Natural Science Foundation of China (No. 52302333, Y.B.); Guangdong Basic and Applied Basic Research Foundation (2023A1515012788, Y.B.); Shenzhen Science and Technology Program (KQTD20221101093647058, Y.B.)PublishedC
Assessment of Cavitation Erosion with a Multiphase Reynolds-Averaged Navier-Stokes Method
No full textCavitation erosion is one of the remarkable catastrophic consequences of cavitation. Predicting the cavitation aggressiveness quantitatively and predicting the most probable location of cavitation erosion are complex problems that currently still motivate an important amount of basic and applied research in the fields of hydrodynamics, physics and metallurgy. The work addresses two main issues: Numerical simulations of cavitating flows over hydrofoils; and an assessment of the risk of cavitation erosion on the surface of hydrofoils. The capability of the multiphase RANS method to predict the relevant and critical unsteady cavitation dynamics in the flow over hydrofoils has been investigated on two NACA hydrofoils (NACA0015 hydrofoil and NACA0018-45 hydrofoil) in the 2D and 3D domain, respectively. It was found that the large-scale structures and the typical unsteady cavitation dynamics predicted by the RANS method implemented in FLUENT were in fair agreement with the observations from experiments. To find the best criteria for an assessment of the risk of cavitation erosion, current erosion risk assessment models and methodologies that use computational fluid dynamic tools or experimental results as input were reviewed and evaluated. An erosion intensity function was proposed based on the mean value of those values of the time derivative of the local pressure that exceeds a certain threshold, and was evaluated for the NACA0015 hydrofoil and NACA0018-45 hydrofoil. A good correlation was found between the locations with the high erosion risk obtained from the computations and the damage area observed from paint tests.Marine & Transport TechnologyMechanical, Maritime and Materials Engineerin
Processing real time road traffic data from probe vehicles using a hybrid micro-macro road traffic model
No full textThe utilisation of probe vehicles is an advancing technique for real time road traffic monitoring. A hybrid stochastic road traffic model has been developed based on micro and macro traffic theories to process received probe vehicle data and extract relevant information for DTM purposes. With Bayes' rule for conditional probabilities, the hybrid micro-macro model is analysed. The pdfs for individual as well as the mean speed is used, together with the qvdiagram. With different estimators the actual road link speed is estimated, based on N probe messages for the distinct applications of ATIS and ATMS.Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
Numerical methods for the implementation of the Cahn-Hilliard equation in one dimension and dynamic boundary condition in two dimensions
No full textThis project can be divided into two parts. The goal of the first part is to numerically implement the Cahn-Hilliard equation in one dimension both explicitly and implicitly. This will be done using Matlab. The goal of the second part is to validate the coupled Cahn-Hilliard-Navier-Stokes equation and the dynamic boundary condition for moving contact lines of (Carlson et al, 2011, p.9) by considering a two-dimensional spreading droplet case. This will be done using the CFD software OpenFOAM. In Chapter 1, the theory of positive and negative diffusion, including the normal diffusion equation and the Cahn-Hilliard equation, are discussed. Some background is given regarding the thermodynamics of the Cahn-Hilliard equation and its steady-state solution. After that, the theory of the coupled Cahn-Hilliard-Navier-Stokes equation, the dynamic boundary condition for moving contact lines and the case which is implemented in OpenFOAM, are discussed. In Chapters 2 and 3, the diffusion equation and the Cahn-Hilliard equation are implemented in one dimension, using the Euler Forward scheme. In implementing the Cahn-Hilliard equation, two different discretizations are used, of which only one gives the desired results. Next, an extensive stability analysis is done, using a linearization of the Cahn-Hilliard equation as well as numerical experiments. The stability condition is increasingly severe with increasing interface width. Regarding the results of the evolving interface, a qualitative analysis is done which discusses three subjects: the deviation of the solutions with the steady-state solution, the interface width for different parameters and grid sizes and the interface overshoot, which is an unphysical appearence. In Chapter 4, two semi-implicit methods and one implicit iterative method, are discussed. The implementations of the two semi-implicit methods, Implicit-Explicit (ImEx) and Modified Furihata, are succesful and their stability conditions are better than the stability condition of the Euler Forward scheme, for most interface widths. The results regarding the evolving interface are nearly identical to the results of the Euler Forward scheme, therefore the qualitative analysis is also similar. The implicit iterative method, which involves the use of the G\^ateaux derivative, has not been succesfully implemented, eventhough two different discretizations are used. The results regarding the evolving interface are behaving in a positive diffusive way, which results in a flattening interface with time. In Chapter 5, the coupled Cahn-Hilliard-Navier-Stokes equation and a dynamic boundary condition for moving contact lines are used to model a spreading droplet on a flat surface. The implemented model is validated using different cases in which the steady-state contact angle and the friction factor of the surface varies. Next, parametric studies are done regarding the interface width, the surface tension and the ratio of the surface tension and the friction factor. The conclusions are that the modeled system differs too much from the system in literature to make an absolute comparison but, qualitatively, the model behaves as expected.Transport PhenomenaChemical EngineeringApplied Science
A new analytical model for settlement analysis of a single pile in multi-layered soil
No full textIn this study, an extension of the variational model proposed by Vallabhan and Mustafa (1996) for the settlement analysis of an axially loaded pile embedded in a multi-layered soil profile is presented. In this model, the soil profile and the embedded pile are divided into a number of sub-layers according to the actual number of soil layers observed in the field. The displacement shape function of each soil layer is given as the product of an exponential equation along the pile depth and Bessel's solution in the radial direction. The displacement relationship in each layer can be derived through transformation matrices. One of the major features of this method is that the total number of pile elements is the same as the total number of soil sub-layers. All the field components, such as displacements, stresses, and strains in the soil, can be calculated by closed-form solutions except the only unknown variable, β, which is a variable as expressed by the modified Bessel's functions of the second kind, and which can be determined by iteration techniques. Comparisons were made with the results of finite element analysis and field pile-loaded tests. Reasonable results were obtained for all cases
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