Mathematics

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18 pages, 173050 KiB

Open AccessArticle

LLE-NET: A Low-Light Image Enhancement Algorithm Based on Curve Estimation

by Xiujie Cao and Jingjun Yu

Mathematics 2024, 12(8), 1228; https://doi.org/10.3390/math12081228 - 19 Apr 2024

Viewed by 414

Low-light image enhancement is very significant for vision tasks. We introduce Low-light Image Enhancement via Deep Learning Network (LLE-NET), which employs a deep network to estimate curve parameters. Cubic curves and gamma correction are employed for enhancing low-light images. Our research trains a [...] Read more.

Low-light image enhancement is very significant for vision tasks. We introduce Low-light Image Enhancement via Deep Learning Network (LLE-NET), which employs a deep network to estimate curve parameters. Cubic curves and gamma correction are employed for enhancing low-light images. Our research trains a lightweight network to estimate the parameters that determine the correction curve. By the results of the deep learning network, accurate correction curves are confirmed, which are used for the per-pixel correction of RGB channels. The image enhanced by our models closely resembles the input image. To further accelerate the inferring speed of the low-light enhancement model, a low-light enhancement model based on gamma correction is proposed with one iteration. LLE-NET exhibits remarkable inference speed, achieving 400 fps on a single GPU for images sized

640 \times 480 \times 3

while maintaining pleasing enhancement quality. The enhancement model based on gamma correction attains an impressive inference speed of 800 fps for images sized

640 \times 480 \times 3

on a single GPU. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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15 pages, 4779 KiB

Open AccessArticle

A Novel Monte Carlo Method to Calculate the Thermal Conductivity in Nanoscale Thermoelectric Phononic Crystals Based on Universal Effective Medium Theory

by Zhizhong Yan and Ercong Cheng

Mathematics 2023, 11(5), 1208; https://doi.org/10.3390/math11051208 - 1 Mar 2023

Viewed by 1404

Abstract

Thermal reduction by enhancing heat-generation phonon scattering can improve thermoelectric performance. In this paper, the phonon transport subjected to internal heat generation in two-dimensional nanoscale thermoelectric phononic crystals is investigated by a novel Monte Carlo method based on the universal effective medium theory, [...] Read more.

Thermal reduction by enhancing heat-generation phonon scattering can improve thermoelectric performance. In this paper, the phonon transport subjected to internal heat generation in two-dimensional nanoscale thermoelectric phononic crystals is investigated by a novel Monte Carlo method based on the universal effective medium theory, called the MCBU method. The present approach is validated. Compared with the universal effective medium theory method, the MCBU method is easier to implement. More importantly, the deviation of the computation time between the two methods can be ignored. With almost the same time cost, the present method can accurately calculate the effective thermal conductivity of complex geometric structures that cannot be calculated by the effective medium theory. The influences of porosity, temperature, pore shape and material parameters on thermal conductivity are discussed in detail. This study offers useful methods and suggestions for fabricating these materials with heat isolation and reduction. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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28 pages, 4975 KiB

Open AccessArticle

Magnetohydrodynamic Bioconvective Flow of Williamson Nanofluid over a Moving Inclined Plate Embedded in a Porous Medium

by Amir Abbas, Radhika Khandelwal, Hafeez Ahmad, Asifa Ilyas, Liaqat Ali, Kaouther Ghachem, Walid Hassen and Lioua Kolsi

Mathematics 2023, 11(4), 1043; https://doi.org/10.3390/math11041043 - 18 Feb 2023

Cited by 8 | Viewed by 1429

Abstract

Research interest in nanotechnology is growing due to its diversified engineering and medical applications. Due to the importance of bioconvection in biotechnology and various biological systems, scientists have made significant contributions in the last ten years. The present study is focusing on the [...] Read more.

Research interest in nanotechnology is growing due to its diversified engineering and medical applications. Due to the importance of bioconvection in biotechnology and various biological systems, scientists have made significant contributions in the last ten years. The present study is focusing on the investigation of the magnetohydrodynamics (MHD) bioconvective heat transfer of a Williamson nanofluid past an inclined moving plate embedded in a porous medium. The partial differential equations governing the considered configuration are established, then transformed into ordinary differential equations using suitable similarity transformations. The variables corresponding to the velocity, temperature, nanoparticle volume fraction, and density of motile micro-organisms along with their gradients, are computed using the bvp4c-MATLAB built-in numerical solver. Results showed the rising of the buoyancy ration parameter leads to an increase in the flow velocity. It has been also observed that the flow intensity becomes more important with an increase in the Weissenberg number, and the opposite occurs with an increase in the bioconvective Rayleigh number. As an effect of the Brownian motion, a random fluid particle’s motion is encountered. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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17 pages, 7400 KiB

Open AccessArticle

Enhancing the Heat Transfer Due to Hybrid Nanofluid Flow Induced by a Porous Rotary Disk with Hall and Heat Generation Effects

by Naif Abdulaziz M. Alkuhayli

Mathematics 2023, 11(4), 909; https://doi.org/10.3390/math11040909 - 10 Feb 2023

Cited by 6 | Viewed by 1388

Abstract

A study of hybrid-nanofluid flow induced by the uniform rotation of a circular porous disk is presented for the purpose of facilitating the heat transfer rate. The Hall and Ohmic heating effects resulting from an applied magnetic field and the source of heat [...] Read more.

A study of hybrid-nanofluid flow induced by the uniform rotation of a circular porous disk is presented for the purpose of facilitating the heat transfer rate. The Hall and Ohmic heating effects resulting from an applied magnetic field and the source of heat generation/absorption are also considered to see their impact on flow behavior and enhancing the heat transfer rate. The physical problem under the given configuration is reduced to a set of nonlinear partial differential equations using the conservation laws. Similarity transformations are adopted to obtain a system of ordinary differential equations which are further solved using the Shooting Method. Results are presented via graphs and tables thereby analyzing the heat transfer mechanism against different variations of physical parameters. Outcomes indicate that the wall suction plays a vital role in determining the behavior of different parameters on the velocity components. It is notable that the wall suction results in a considerable reduction in all the velocity components. The enhanced Hartman number yields a growth in the radial velocity and a decay in the axial velocity. Moreover, consequences of all parametric effects on the temperature largely depend upon the heat generation/absorption. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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29 pages, 14571 KiB

Open AccessArticle

Weighted Radial Basis Collocation Method for the Nonlinear Inverse Helmholtz Problems

by Minghao Hu, Lihua Wang, Fan Yang and Yueting Zhou

Mathematics 2023, 11(3), 662; https://doi.org/10.3390/math11030662 - 28 Jan 2023

Cited by 4 | Viewed by 1117

Abstract

In this paper, a meshfree weighted radial basis collocation method associated with the Newton’s iteration method is introduced to solve the nonlinear inverse Helmholtz problems for identifying the parameter. All the measurement data can be included in the least-squares solution, which can avoid [...] Read more.

In this paper, a meshfree weighted radial basis collocation method associated with the Newton’s iteration method is introduced to solve the nonlinear inverse Helmholtz problems for identifying the parameter. All the measurement data can be included in the least-squares solution, which can avoid the iteration calculations for comparing the solutions with part of the measurement data in the Galerkin-based methods. Appropriate weights are imposed on the boundary conditions and measurement conditions to balance the errors, which leads to the high accuracy and optimal convergence for solving the inverse problems. Moreover, it is quite easy to extend the solution process of the one-dimensional inverse problem to high-dimensional inverse problem. Nonlinear numerical examples include one-, two- and three-dimensional inverse Helmholtz problems of constant and varying parameter identification in regular and irregular domains and show the high accuracy and exponential convergence of the presented method. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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15 pages, 4004 KiB

Open AccessArticle

A Collapse Strength Model for a 7” Crescent-Worn Casing Connection Considering Sealing Integrity

by Xing Zhou, Qinfeng Di, Xiaoliang Wang, Dakun Luo, Feng Chen and Wenchang Wang

Mathematics 2023, 11(2), 489; https://doi.org/10.3390/math11020489 - 16 Jan 2023

Viewed by 1253

Abstract

Collapse failure under external pressure is one of the common failure forms of casing. Much research has been performed on the casing body, but few on the threaded connection, in view of the general belief that the threaded connection has a thicker wall [...] Read more.

Collapse failure under external pressure is one of the common failure forms of casing. Much research has been performed on the casing body, but few on the threaded connection, in view of the general belief that the threaded connection has a thicker wall and larger collapse strength than the casing body. However, under external pressure, the sealing capacity of a worn casing connection will decrease due to deformation of the sealing structure, so the influence of sealing ability should be considered to determine the collapse strength of casing. In this paper, we established a three-dimensional finite element model of a 7” crescent-worn casing connection and calculated the collapse strength of the connection under different wear depths. Meanwhile, the stress distribution characteristics on the sealing surface were obtained and the influence of wear on the sealing performance of the casing connection under external pressure was analyzed. The results showed that when the wear rate exceeds a certain value, the collapse strength of the connection based on sealing integrity was lower than that of the casing body. Based on these, a collapse strength model for a 7” crescent-worn casing connection considering sealing integrity was developed and a safety evaluation method of the collapse strength of the worn casing string was proposed. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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50 pages, 12714 KiB

Open AccessArticle

The Effect of Adhesion on Indentation Behavior of Various Smart Materials

by Qinghui Luo, Yueting Zhou, Lihua Wang and Shenghu Ding

Mathematics 2022, 10(23), 4511; https://doi.org/10.3390/math10234511 - 29 Nov 2022

Cited by 4 | Viewed by 1818

Abstract

The nanoindentation technique plays a significant role in characterizing the mechanical properties of materials at nanoscale, where the adhesion effect becomes very prominent due to the high surface-to-volume ratio. For this paper, the classical adhesion theories were generalized to study the contact behaviors [...] Read more.

The nanoindentation technique plays a significant role in characterizing the mechanical properties of materials at nanoscale, where the adhesion effect becomes very prominent due to the high surface-to-volume ratio. For this paper, the classical adhesion theories were generalized to study the contact behaviors of various piezoelectric materials indented by conical punches with different electric properties. With the use of the Hankel integral transform, dual integral equations, and superposing principle, the closed-form solutions of the physical fields for the Johnson-Kendall-Roberts (JKR) and Maugis-Dugdale (M-D) models were obtained, respectively. The contribution of the electrical energy to the energy release rate under the conducting punch was taken into consideration. The relationships between the contact radius, the indentation load, and the indentation depth were set up using the total energy method for the JKR model and the Griffith energy balance for the M-D model, respectively. Numerical results indicate that increasing the half cone angle of the conical punch enhances the adhesion effect, which can significantly affect the accuracy of the results of characterization in nanoindentation tests. It was found that the effect of electric potential on adhesion behaviors is sensitive to different material properties, which are not revealed in the existing studies of axisymmetric adhesive contact of piezoelectric materials and multiferroic composite materials. The load-displacement curves under conical punches with different half cone angles have very different slopes. These results indicate that the half cone angle has a prominent effect on the characterization of mechanical properties of piezoelectric solids in nanoindentation tests. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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25 pages, 11227 KiB

Open AccessArticle

Simulations of Hypersonic Boundary-Layer Transition over a Flat Plate with the Spalart-Allmaras One-Equation BCM Transitional Model

by Yu Chen and Nick Gibbons

Mathematics 2022, 10(19), 3431; https://doi.org/10.3390/math10193431 - 21 Sep 2022

Viewed by 1592

Abstract

Transitional flow has a significant impact on vehicles operating at supersonic and hypersonic speeds. An economic way to simulate this problem is to use computational fluid dynamics (CFD) codes. However, not all CFD codes can solve transitional flows. This paper examines the ability [...] Read more.

Transitional flow has a significant impact on vehicles operating at supersonic and hypersonic speeds. An economic way to simulate this problem is to use computational fluid dynamics (CFD) codes. However, not all CFD codes can solve transitional flows. This paper examines the ability of the Spalart–Allmaras one-equation BCM (SA-BCM) transitional model to solve hypersonic transitional flow, implemented in the open-source CFD code Eilmer. Its performance is validated via existing wind tunnel data. Eight different hypersonic flow conditions are applied. A flat plate model is built for the numerical tests. The results indicate that the existing SA-BCM model is sensitive to the freestream turbulence intensity and the grid size. It is not accurate in all the test cases, though the transitional length can be matched by tuning the freestream intensity. This is likely due to the intermittency term of the SA-BCM model not being appropriately calibrated for high-velocity flow, though if the model can be recalibrated it may be able to solve the general high-velocity flows. Although the current SA-BCM model is only accurate under certain flow conditions after one calibration process, it remains attractive to CFD applications. As a one-equation model, the SA-BCM model runs much faster than multiple-equation flow models. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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14 pages, 2462 KiB

Open AccessArticle

The Adaptive Composite Block-Structured Grid Calculation of the Gas-Dynamic Characteristics of an Aircraft Moving in a Gas Environment

by Victor V. Kuzenov, Sergei V. Ryzhkov and Aleksey Yu. Varaksin

Mathematics 2022, 10(12), 2130; https://doi.org/10.3390/math10122130 - 19 Jun 2022

Cited by 18 | Viewed by 1446

Abstract

This paper considers the problem associated with the numerical simulation of the interaction between the cocurrent stream occurring near a monoblock moving in the gas medium and solid fuel combustion products flowing from a solid fuel rocket engine (SFRE). The peculiarity of the [...] Read more.

This paper considers the problem associated with the numerical simulation of the interaction between the cocurrent stream occurring near a monoblock moving in the gas medium and solid fuel combustion products flowing from a solid fuel rocket engine (SFRE). The peculiarity of the approach used is the description of gas-dynamic processes inside the combustion chamber, in the nozzle block, and the down jet based on a single calculation methodology. In the formulated numerical methodology, the calculation of gas-dynamic parameters is based on the solution of unsteady Navier–Stokes equations and the application of a hybrid computational grid. A hybrid block-structured computational grid makes it possible to calculate gas flow near bodies of complex geometric shapes. The simulation of the main phase of interaction, corresponding to the stationary mode of rocket flight in the Earth’s atmosphere, has been carried out. A conjugated simulation of the internal ballistics of SFRE and interaction of combustion products jets is conducted. Full article

(This article belongs to the Special Issue Advanced Numerical and Computational Methods for Engineering and Applied Mathematical Problems)

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