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This paper is concerned with optimal design problems for two-material thermal conductors via level set methods based on (doubly) nonlinear diffusion equations. In level set methods with material representations via characteristic functions, gradient descent methods cannot be applied directly in terms of the differentiability of objective functionals with respect to level set functions, and therefore, appropriate sensitivities need to be constructed. This paper proposes a formulation via the positive parts of level set functions to avoid heuristic derivation of sensitivities and to apply (generalized gradient) descent methods. In particular, some perturbation term, such as a perimeter constraint, is involved in the formulation, and then an existence theorem for minimizers will be proved. Furthermore, convergence of objective functionals for minimizers with respect to a parameter of the perturbation term will also be discussed. In this paper, by deriving so-called weighted sensitivities, two-phase domains are numerically constructed as candidates for optimal configurations to approximate minimum values for classical design problems in two-dimensional cases. [ABSTRACT FROM AUTHOR]

Convolutional neural networks (CNN) have been extensively utilized for image segmentation tasks, with the U-Net architecture emerging as a classical model in medical imaging due to its simple structure and high scalability. However, for complex medical images, particularly those with blurred lesion boundaries, the U-Net model often loses significant edge information during feature extraction. Each layer in the encoder section is convolved with a simple stack of equal design, which is clearly not able to obtain sufficient feature information from an otherwise low-quality image. In order to solve this problem, the DRLSU-Net model is proposed which combines an enhanced U-Net architecture with distance regularized level set evolution (DRLSE). The DRLSU-Net model takes the results of U-Net pre-segmentation as an intermediate medium, combines the U-Net model with the level set method. Indirectly represent the target contour through the zero level set to obtain a more intuitive target edge location. Specifically, the Parallel Dilated Convolutional Sequence (PDCS) is introduced in the U-Net encoder to minimize information loss during down-sampling, and preserve more edge details. Secondly, the Mixed Attention Mechanism (MAM) is introduced into the decoder, aiding the network in recovering important information during image reconstruction, thus generating a more accurate output sequence. Finally, the pre-segmentation label mapping is converted into a level set function representation, which serves as a priori information for the level set method. A new energy functional is constructed to guide the evolution of the level set curves, helping to obtain a clear contour boundary. The performance of the DRLSU-Net model is evaluated on the ISIC2017, ISIC2018, CVC-ClinicDB, and Lung datasets. Extensive experiment results show better performance than other state-of-the-art (SOTA) methods in terms of mIoU and F1-socre, and the results indicate that the DRLSU-Net model performs competitively in medical image segmentation tasks. [ABSTRACT FROM AUTHOR]

A level set-based method using a reaction diffusion equation is applied for optimization problems of two dimensional (2D) sound barriers. The level set method is employed to implicitly represent the sound barrier structure, which distinguishes the material and void domains by the value of the level set function. The boundary element method is employed to solve acoustic problems governed by Helmholtz equation. Topological derivatives are computed by the boundary integral equation combined with the adjoint variable method. The distribution of level set function is iteratively updated based on the reaction diffusion equation to find the optimal structure. For the existent floating scatterers in the optimization process and the sharp and narrow parts on the surface of the sound barrier, we propose a filtering algorithm to remove floating scatterers and develop a method to achieve a smooth surface of the sound barrier. The shape optimization of sound barriers is achieved using these techniques, integrating the level set-based topology optimization method. Numerical tests are provided to demonstrate the validity and effectiveness of the proposed methods. • An efficient LSM optimization method is developed herein. • Filtering algorithm is developed to remove floating scatterers. • We improve the surface smoothness by removing the sharp and narrow edges. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to study the mechanism of efficient sputum excretion from the distal lung by using a tessellationally distal lung model with alveolar pores. Design/methodology/approach: First, a two-dimensional tessellational composite structure of the bronchus, alveoli and alveolar pores (Kohn pore) is constructed with the tessellational splitting and fusion of regular hexagonal elements. Then, the level set method is used to study the effects of alveolar pores and their sizes, expiratory cycles and respiratory intensity. Findings: The existence of alveolar pores is the prerequisite for sputum excretion, and there is an optimal size of alveolar pores for sputum excretion. Strong asymmetric respiration can break the reversibility of the flow at a low Reynolds number and causes significant net displacement of sputum. The expiratory cycle is negatively correlated with the net displacement of sputum. The respiratory intensity is positively correlated with the net displacement of sputum. Originality/value: This research is helpful for understanding the complex sputum excretion process in diseases, such as pneumonia, and developing corresponding adjuvant therapy. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to further improve the efficiency of multi-objective optimization design of synchronous reluctance motors (SynRMs) using the level set (LS) method, which has the advantage of obtaining a practical shape. The solutions obtained by gradient methods tend to be local ones due to the multi-modality of the objective function, especially when multiple objective functions. A huge number of trial calculations are required to obtain a high-quality and broadly distributed Pareto front. Therefore, it is indispensable to effectively get out of the local solutions in the optimization process with the LS method. Design/methodology/approach: The authors propose a novel method appropriately switching multiple objective functions with high independence of sensitivity information. The authors adopt highly independent mathematical expressions for the objective functions of the average torque and torque ripple. In addition, the authors repeatedly perform the optimization while appropriately selecting the sensitivity information of one objective function from multiple ones, which enables the authors to effectively break out of local solutions in the optimization process. Findings: The proposed method was applied to the shape optimization of SynRM flux barriers and successfully searched a more extensive and advanced Pareto front in comparison with the conventional method. Originality/value: The proposed method adopts search spaces with mathematical high independence for average torque and torque ripple. In the optimization process, when the solution search is judged to get stuck by several criteria, the search space is alternately switched to effectively get out of local solutions. [ABSTRACT FROM AUTHOR]

The University of Connecticut has published new findings in mechanical science, focusing on the computational design of curvilinear scaffolds for bone repair using direct ink writing technology. The research introduces a method to optimize ceramic scaffolds for maximum bone growth, considering factors such as defect shape, applied loading, and bone density. The study demonstrates the methodology on a scaffold implanted in a pig mandible, showcasing the effectiveness of the design in promoting bone ingrowth while adhering to manufacturing constraints. This research contributes to advancements in bone research and mechanical science, offering insights into innovative approaches for bone repair. [Extracted from the article]

Researchers at the University of Pittsburgh have developed a computational method for estimating the mechanical properties of tissues using clinical imaging data. The method involves comparing the shape of a target tissue structure with an estimated shape using a level-set-based objective functional. The researchers found that the proposed method consistently and effectively minimized the shape difference to estimate material parameters. This approach has the potential to provide estimates of in vivo mechanical properties of tissues directly from imaging data. [Extracted from the article]

Intensity inhomogeneity and high noise are two common but challenging issues in image segmentation and is particularly pronounced when the two issues simultaneously appear in one image. As a result, most existing level set methods yield poor performance when applied to these images. To address this issue, this paper proposes a robust variational level set method (RVLSM) based on adaptive diffusion mechanism and local cluster criterion, which can not only correct the severe inhomogeneous intensity but also denoise in segmentation. Specifically, we first define an adaptive-scale representation term using the proposed adaptive diffusion mechanism to transform the image data towards diffusion-induced space, which successfully restrains different types/levels of noise while enhancing image details. Then, a new bias field correction term is constructed via estimating the bias in transformed domain to better correct the severe inhomogeneous intensity while segmentation. Finally, an enhanced fourth-order piecewise polynomial penalty term is designed to eradicate numerical calculation instability and tedious re-initialization during the evolution of the level set. The experimental results on synthetic and real images with severe intensity inhomogeneity and high noise demonstrate the superiority of the proposed method over most existing methods in both accuracy and robustness. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to perform a detailed review on the numerical modeling of multiphase and multicomponent flows in microfluidic system using phase-field method. The phase-field method is of emerging importance in numerical computation of transport phenomena involving multiple phases and/or components. This method is not only used to model interfacial phenomena typical to multiphase flows encountered in engineering and nature but also turns out to be a promising tool in modeling the dynamics of complex fluid-fluid interfaces encountered in physiological systems such as dynamics of vesicles and red blood cells). Intrinsically, a priori unknown topological evolution of interfaces offers to be the most concerning challenge toward accurate modeling of moving boundary problems. However, the numerical difficulties can be tackled simultaneously with numerical convenience and thermodynamic rigor in the paradigm of the phase field method. Design/methodology/approach: The phase-field method replaces the macroscopically sharp interfaces separating the fluids by a diffuse transition layer where the interfacial forces are smoothly distributed. As against the moving mesh methods (Lagrangian) for the explicit tracking of interfaces, the phase-field method implicitly captures the same through the evolution of a phase-field function (Eulerian). In contrast to the deployment of an artificially smoothing function for the interface as used in the volume of a fluid or level set method, however, the phase-field method uses mixing free energy for describing the interface. This needs the consideration of an additional equation for an order parameter. The dynamic evolution of the system (equation for order parameter) can be described by Allen–Cahn or Cahn–Hilliard formulation, which couples with the Navier–Stokes equation with the aid of a forcing function that depends on the chemical potential and the gradient of the order parameter. Findings: In this review, first, the authors discuss the broad motivation and the fundamental theoretical foundation associated with phase-field modeling from the perspective of computational microfluidics. They subsequently pinpoint the outstanding numerical challenges, including estimations of the model-free parameters. They outline some numerical examples, including electrohydrodynamic flows, to demonstrate the efficacy of the method. Finally, they pinpoint various emerging issues and futuristic perspectives connecting the phase-field method and computational microfluidics. Originality/value: This paper gives unique perspectives to future directions of research on this topic. [ABSTRACT FROM AUTHOR]

Active contour model (ACM) is an important branch in the field of image segmentation, since it adapts to different image types and scenes. However, traditional ACMs rely on local image information, which makes them sensitive to initial contours and time-consuming. In this paper, a Laplace operator based ACM (LOACM) with improved image edge detection performance is proposed. LOACM combines the global pre-fitting function which is constructed by using the image's second-order gradient information with the adaptive boundary indicator function to build a hybrid model. Its compact code size allows it to be executed on a wide range of edge devices. To substantiate the segmentation capability of the LOACM model, the BSD500 dataset was utilized for experimentation. The results indicate that LOACM exhibits excellent performance, with average IOU and DSC scores of 0.861 and 0.924 respectively. Additionally, it consistently handles processes within an average time of less than 0.3 s, significantly less than that of comparative models, providing compelling evidence of LOACM's exceptional efficiency and precision. [ABSTRACT FROM AUTHOR]

Our paper proposes an innovative approach for modeling Fluid–Structure Interaction (FSI). Our method combines both traditional monolithic and partitioned approaches, creating a hybrid solution that facilitates FSI. At each time iteration, the solid mesh is immersed within a fluid–solid mesh, all while maintaining its independent Lagrangian hyperelastic solver. The Eulerian mesh encompasses both the fluid and solid components and accommodates various physical phenomena. We enhance the interaction between solid and fluid through anisotropic mesh adaptation and the Level-Set methods. This enables a more accurate representation of their interaction. Together, these components constitute the Adaptive Immersed Mesh Method (AIMM). For both solvers, we utilize the Variational Multi-Scale (VMS) method, mitigating potential spurious oscillations common with piecewise linear tetrahedral elements. The framework operates in 3D with parallel computing capabilities. Our method's accuracy, robustness, and capabilities are assessed through a series of 2D numerical problems. Furthermore, we present various three-dimensional test cases and compare their results to experimental data. • A novel hybrid coupling method for FSI that takes the advantages of the partitioned approach, and retaining the advantages of the monolithic approach. • Ability to handle 2D/3D sharp membrane like geometries and interfaces through tetrahedral anisotropic unstructured finite elements.. • The level set method is used in the immersion of the solid mesh onto the fluid–solid mesh for interface tracking. • Variational Multi-Scale (VMS) stabilization for piece-wise linear finite elements to damp out spurious pressure oscillations and highly advective flows. • Moving Mesh Method (MMM) that considers the solid dynamics and helps track the FSI interface on the solid mesh. [ABSTRACT FROM AUTHOR]

Phase change problems are investigated numerically in this study. A combined precise time-domain expanding boundary element method (PTEBEM) and the level set method is proposed. The PTEBEM is employed on one hand to solve the temporal-spatial field partial differential equations of the transient heat transfer problem. The radial integral method is used to transform the domain integral of the governing equation into a boundary integral. On the other hand, the level set method which is widely used to track crack trajectories is here employed to handle the complicated topological changing during phase change, to record the position of material phase interface during moving, merging or slipping. The formed numerical framework is further enhanced for higher stability. To demonstrate the accuracy and robustness of the proposed method, a few examples are provided. [ABSTRACT FROM AUTHOR]

The transient crevice corrosion behavior of 304 stainless steel in NaCl solution has been investigated by a multiphysics coupling model. The model considers local electrochemical reactions, transport of different species, and homogeneous reactions. The moving mesh method is used to obtain the geometrical change of the crevice wall with time due to corrosion. The level set method is employed to quantitatively describe the influence of the precipitation process on electrochemical reactions. The transient crevice corrosion morphology, potential and current distributions, and pH and chloride ion concentration distributions are obtained by simulation. The effect of crevice geometry factors on the corrosion process is also discussed. The simulation results are in good agreement with the experiments, showing that the model has high reliability. [ABSTRACT FROM AUTHOR]

Purpose: Moving interface problems exist commonly in nature and industry, and the main difficulty is to represent the interface. The purpose of this paper is to capture the accurate interface, a novel three-dimensional one-layer particle level set (OPLS) method is presented by introducing Lagrangian particles to reconstruct the seriously distorted level set function. Design/methodology/approach: First, the interface is captured by the level set method. Then, the interface is corrected with only one-layer particles advected with the flow to ensure that the level set function value of the particle is equal to 0. When interfaces are merged, all particles in merged regions are deleted, while the added particles near the generated interface are used to determine the interface as the interface is separated. Findings: The OPLS method is validated with well-known benchmark examples, such as the long-term advection of a sphere, the rotation of a three-dimensional slotted disk and sphere, single vortex in a box, sphere merging and separation, deformation of a sphere. The simulation results indicate that the proposed method is found to be highly reliable and accurate. Originality/value: This method exhibits excellent conservation of the area bounded by the interface. The extraordinary performance is also shown in dealing with complex interface topological changes. [ABSTRACT FROM AUTHOR]

We propose a new segmentation method based on multiple walking particles (WP) bouncing from the image edges. The particles are able to segment objects characterized by deep concavities as narrow as one pixel and handle single or multiple objects characterized by a noisy background and broken boundaries ("weak edge", "boundary leakage"). The particles are designed to segment the image by permanently staying inside the object and repairing the boundaries where necessary. The proposed WP combine the advantages of the continuous diffusion models with the principles of multi-agent systems. WP have been tested against recent active contours and the distance regularized level set method on a set of complex-shaped synthetic images and ultrasound (US) images of breast cancer (http://onlinemedicalimages.com). The method has also been compared with localizing region-based active contours, the fuzzy C-mean level set method, and morphological active contours. The WP are faster and more accurate for images characterized by low contrast, noise, broken boundaries, or boundary leakage. However, for good quality, simple shaped objects the WP work similarly to the conventional methods. There is still an important difference even in this case: the WP do not require initialization. A video demo of the algorithm is at https://drive.google.com/drive/folders/1SlTphINKtdUwvdjjxiakFrwI2dDlIUAU [ABSTRACT FROM AUTHOR]

The current work is mainly about the implementation of the local radial basis functions (LRBFs) within the level set framework for structural optimization of two-dimensional linear elastic problems. The implicit representation of the structural geometry is accomplished through the LRBFs based level set function (LSF), and the geometry modification during the optimization process is carried out through an update of the LSF using a system of coupled ordinary differential equations (ODEs) instead of the Hamilton-Jacobi (HJ) type equation. This new implementation of LRBFs and level set method (LSM) allows essential topological changes automatically, i.e hole nucleation, hole merging with each other, and with the boundary to obtain the optimal structures. The coefficient matrix of the LRBFs is less sensitive to the values of shape parameter as well as the proposed method is mesh independent as explored during the numerical experiments performed. This new implementation is applied to distinct benchmark problems for minimum compliance with single and multiple load cases. The numerical experiments performed reveal significant insightful of the use of radial basis functions (RBFs) within the LSM framework, which may be considered as a step forward for further exploration of their intrinsic capabilities and improved performance for the solution of structural optimization problems. [ABSTRACT FROM AUTHOR]

This work presents the method to combine isogeometric analysis coupled to symmetric Galerkin boundary element method (IGA-SGBEM) and parametric level set (PaLS)-based optimization scheme for the analysis of linear problems in two-dimensional piezoelectric media. IGA-SGBEM is used to obtain field variables (i.e. generalized displacement and traction) in the forward analysis. Then, inverse analysis of flaw detection in piezoelectric structures is attempted by combining IGA-SGBEM with PaLS-based optimization scheme. In this proposed method, the versatility of isogeometric analysis (IGA) is proved in the inverse progress, where the iso-line of the level set function can be easily reconstructed and incorporated into the IGA framework. Numerical examples are examined to validate and to demonstrate the robustness of the proposed method in solving both forward and inverse problems in piezoelectricity. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to develop an effective numerical algorithm for a gas-melt two-phase flow and use it to simulate a polymer melt filling process. Moreover, the suggested algorithm can deal with the moving interface and discontinuities of unknowns across the interface. Design/methodology/approach: The algebraic sub-grid scales-variational multi-scale (ASGS-VMS) finite element method is used to solve the polymer melt filling process. Meanwhile, the time is discretized using the Crank–Nicolson-based split fractional step algorithm to reduce the computational time. The improved level set method is used to capture the melt front interface, and the related equations are discretized by the second-order Taylor–Galerkin scheme in space and the third-order total variation diminishing Runge–Kutta scheme in time. Findings: The numerical method is validated by the benchmark problem. Moreover, the viscoelastic polymer melt filling process is investigated in a rectangular cavity. The front interface, pressure field and flow-induced stresses of polymer melt during the filling process are predicted. Overall, this paper presents a VMS method for polymer injection molding. The present numerical method is extremely suitable for two free surface problems. Originality/value: For the first time ever, the ASGS-VMS finite element method is performed for the two-phase flow of polymer melt filling process, and an effective numerical method is designed to catch the moving surface. [ABSTRACT FROM AUTHOR]

This work presents the development of a higher-order finite element method for modeling unsteady, incompressible and inviscid two-phase flows using the level set method. A new explicit projection method is introduced to solve the incompressible Euler equation, where the pressure and the velocity fields are solved separately. To implement high order temporal schemes, the Hodge decomposition in this projection method is not applied to the velocity but to its time derivative. A discontinuous Galerkin discretization is used to solve both the level set and the nonlinear advection terms present in the Euler equations, while a Galerkin discretization is used to solve the pressure Poisson equation. The present method is a fully high order numerical approach, both in space and temporal dimensions. Numerical results provided by several 2D benchmark test cases in naval hydrodynamics (i.e hydrostatic equilibrium, sloshing and dam break) validate the computational code, illustrating the power of the proposed method. Compared to the CFD codes based on low order VOF/finite-volume methods, the present approach demonstrates greater accuracy on coarse meshes, leading to reduced CPU time. • The finite element method offers high order convergence (i.e. > =2). • High order schemes on coarse meshes save simulation CPU time compared to low order schemes on fine meshes. • The high order finite element method can provide more accurate results than a low order finite volume method on coarse meshes. • Smoothing methods destroy the expected order of convergence of the numerical method. [ABSTRACT FROM AUTHOR]

The variational level set model is widely used in image segmentation tasks due to its sound theoretical basis and reliable performance. However, it often faces limitations when dealing with images that contain intensity inhomogeneity and noise. To address this challenge, a novel variational level set model based on local-global function approximation (LSM-LGA) is proposed in this paper. In this approach, an approximation function space is first introduced for the input image. This space defines the function as a linear combination of a local approximation image and a global one, weighted by two coefficients and two complementary characteristic functions defined by a level set function. To achieve the optimal representation of the input image within this approximation function space, a hybrid-metric strategy that combines Euclidean distance and Jeffreys divergence is introduced. An alternating direction method of multiplier (ADMM) based on Euclidean distance is developed to solve for the optimal weight coefficients of the local and global approximation images. Additionally, gradient descent based on Jeffreys divergence is utilized to solve for the optimal level set function. Furthermore, the existence and uniqueness of the optimal approximation function are proven using the theory of projection onto convex sets. Extensive numerical experiments on natural and synthetic images with intensity inhomogeneity, textures, and noise validate that the LSM-LGA exhibits superior performance compared with several state-of-the-art models in terms of segmentation quality and computational efficiency. [ABSTRACT FROM AUTHOR]

In many practical applications of image segmentation problems, employing prior information can greatly improve segmentation results. This paper continues to study one kind of prior information, called prior distribution. Within this research, there is no exact template of the object; instead only several samples are given. The proposed method, called the parametric distribution prior model, extends our previous model by adding the training procedure to learn the prior distribution of the objects. Then this paper establishes the energy function of the active contour model (ACM) with consideration of this parametric form of prior distribution. Therefore, during the process of segmenting, the template can update itself while the contour evolves. Experiments are performed on the airplane data set. Experimental results demonstrate the potential of the proposed method that with the information of prior distribution, the segmentation effect and speed can be both improved efficaciously. [ABSTRACT FROM AUTHOR]

Based on our previous sharp interface method (SIM) for smoothed particle hydrodynamics (SPH) [Zhang M and Deng X-L. A sharp interface method for SPH. Journal of Computational Physics 2015; 302 469–484], a robust SIM for SPH is developed. According to Lagrangian nature of SPH, the interface is located between two types of SPH particles. It is different from the previous method, in which the initial interface is defined by the user. The main consequence of the interface definition in the current method is that minimum value of level set function is around half the initial inter-particle distance. Therefore the calculation of level set function becomes more robust. The interface status is determined by jump conditions at the interface. Then the interface status is extended to the ghost fluid particles. Various benchmark tests are given to show the performance of the robust SIM for SPH. Comparing with the previous SIM for SPH, current method is more robust and accurate in the simulation of low-speed multiphase flows of high density ratios with clear interface. [ABSTRACT FROM AUTHOR]

A convenient and efficient approach to simulate the excavation-induced rock fracturing process from continuity to discontinuity is proposed. The excavation boundary is considered to be an internal discontinuity, which is enriched by a Heaviside function. By using partition of unity concept and level set method, the cellular automaton updating rule for elasto-plastic fracturing induced by excavation is developed. The excavation induced rock mass strain localization is described by plasticity. A plastic strain-dependent criterion is proposed to link continuity and discontinuity, by which crack initiation and propagation of rock mass are described. By using the cellular automaton neighborhood information and level set method, the crack propagation path and excavation boundary can be tracked efficiently. The excavation and the induced crack initiation and propagation can be represented and simulated without explicit remeshing. This approach is implemented in a self-developed numerical model, i.e. a rock continuous-discontinuous cellular automaton (CDCA). The reliability and versatility of CDCA in the modeling of excavation-induced crack initiation, propagation, coalescence and block formation in rock mass are well demonstrated. The method helps estimate the onset of stable and unstable failure development, as well as the magnitude of plastic strain before cracking in rocks. [ABSTRACT FROM AUTHOR]

In this paper, we propose a robust region-based active contour model driven by fuzzy c-means energy that draws upon the clustering intensity information for fast image segmentation. The main idea of fuzzy c-means energy is to quickly compute the two types of cluster center functions for all points in image domain by fuzzy c-means algorithm locally with a proper preprocessing procedure before the curve starts to evolve. The time-consuming local fitting functions in traditional models are substituted with these two functions. Furthermore, a sign function and a Gaussian filtering function are utilized to replace the penalty term and the length term in most models, respectively. Experiments on several synthetic and real images have proved that the proposed model can segment images with intensity inhomogeneity efficiently and precisely. Moreover, the proposed model has a good robustness on initial contour, parameters and different kinds of noise. • We define the cluster center functions and fuzzy c-means energy. • A novel active contour model driven by fuzzy c-means energy is proposed. • An improvement of the penalty and length terms is utilized. • The proposed model shows better segmentation accuracy and robustness. [ABSTRACT FROM AUTHOR]

• We constructed a topology optimization method for fluid dynamics problems using the MPS method. • Optimization problems are formulated based on the level set method and the MPS method. • The sensitivity analysis was performed based on the adjoint variable method. • The adjoint equations were rewritten from the Eulerian coordinate system to the Lagrangian coordinate system. • The validity and the availability of our proposed method are confirmed through several numerical examples. Topology optimization for fluid field problems has been studied for many years, but most of them use the Eulerian coordinate system in the numerical analysis methods such as the finite element method and the finite volume method. The moving particle semi-implicit (MPS) method is one of the particle methods, which can be used to analyze incompressible free surface fluid flows. The MPS method is a meshless method based on the Lagrangian coordinate system without surface tracking by a mesh or a scalar quantity. It has attracted attention in recent years since this has several advantages such as the easy expression of the free boundaries. This paper presents a new topology optimization method for fluid dynamics problems using the MPS method. First, the optimization problems are formulated based on the level set method and the MPS method. Next, the design sensitivities are derived using the Lagrange multiplier method and adjoint variable method. The optimization algorithm is constructed based on those formulations, and the validity and the availability of the proposed method are confirmed through several numerical examples. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to propose dot sensitivity analysis of ferromagnetic materials for topology optimization in an axi-symmetric magnetostatic system. Design/methodology/approach: The dot sensitivity formula for the axi-symmetric system is derived as a closed form using the continuum shape sensitivity formula. The dot sensitivity method is combined with the level set method to perform topology optimization. Findings: Derived dot sensitivity analysis can generate a ferromagnetic ring torus in a vacant region. Thus, an initial design is not needed for the design material. Two design problems are tested to demonstrate the usefulness of dot sensitivity. Originality/value: By simultaneously using the shape sensitivity and dot sensitivity, in axi-symmetric magnetic system, the design space is expanded and it includes the interface and the inside of the vacant region. This property can reduce the possibility of local optimum convergence. [ABSTRACT FROM AUTHOR]

We address the optimal control of level sets associated with the solution of the normal flow equation. The problem consists in finding the normal velocity to the front described by a certain level set in such a way to minimize a given cost functional. First, the considered problem is shown to admit a solution on a suitable space of functions. Then, since in general it is difficult to solve it analytically, an approximation scheme that relies on the extended Ritz method is proposed to find suboptimal solutions. Specifically, the control law is forced to take on a neural structure depending nonlinearly on a finite number of parameters to be tuned, i.e., the neural weights. The selection of the optimal weights is performed with two different approaches. The first one employs classical line-search descent methods, while the second one is based on a quasi-Newton optimization that can be regarded as neural learning based on the extended Kalman filter. Compared with line-search methods, such an approach reveals to be successful with a reduced computational effort and an increased robustness with respect to the trapping into local minima, as confirmed by simulations in both two and three dimensions. [ABSTRACT FROM AUTHOR]

Researchers at Changchun University of Science and Technology in China have published a new study on malocclusion, a condition characterized by misalignment of the teeth. The study aimed to develop an accurate method for segmenting teeth under complex oral conditions, such as tooth rotation and displacement caused by dental crowding. The researchers used cone-beam computed tomography (CBCT) images and proposed a three-step solution, including a global convex level-set model and a local level-set model with adaptive edge feature enhancement. The experimental results showed promising outcomes, with high accuracy in segmenting different types of teeth. The proposed method is considered more robust than other existing methods and can provide valuable data for further research and clinical practice. [Extracted from the article]

One-layer particle level set (OPLS) has been developed by using Lagrangian particles that are employed to correct both advection and re-initialization procedures of the level set function. In which, a level set function is utilized to smooth physical properties of the interface, while one-layer Lagrangian particles are used to track the interface directly. This method exhibits excellent mass conservation properties compared to the LS method. As a special aspect, the OPLS method enables management of merging and stretching of interface in an effective way. This capability is similar to the particle level set (PLS) method. However, the new approach of the OPLS method offers a more straightforward technique. This approach is validated with classical benchmark test cases, such as the long term advection of a circle, rotation of a slotted disk, single vertex in a box, merging and separating of circle. The results from the proposed method show good agreement with the numerical experiments published results and the OPLS method is verified to be highly reliable and accurate. [ABSTRACT FROM AUTHOR]

Pixel-wise active contour models usually utilize local edge information and/or region statistics. These models are unable to ideally segment real-world objects, especially those in heterogeneous or cluttered images because of a lack of local spatial correlations. To represent the characteristics of the targets precisely, a kernel-descriptor-based active contour model is proposed to address the problem of a lack of local spatial correlations in image segmentation. First, image patch features are extracted and are clustered into several clusters. The initial contour is obtained from user inputs, and then the corresponding template feature sets of the clusters are constructed. Second, we utilize the template feature sets to formulate our energy functional, subject to a constraint on the total length of the region boundaries. Finally, a level set method is employed to estimate the resulting evolution. The proposed method utilizes the kernel descriptor as the high-dimensional feature and performs well on heterogeneous and cluttered images. Experimental results on real images suggest a clear superiority of the proposed method. [ABSTRACT FROM AUTHOR]

We present an advection velocity correction (AVC) scheme for interface tracking using the level-set method in this paper. The key idea is to apply a correction to the interface advection velocity at points adjacent to the zero level-set, so as to enforce the preservation of the signed distance function property at these points. As such, the AVC scheme eliminates the need for explicit sub-cell fix approaches as reinitialization at points adjacent to the zero level-set is not needed. This approach of correcting the advection velocity field near the interface and computing the signed distance function; SDF to a high order of accuracy near the interface, rather than applying an explicit sub-cell fix during the reinitialization step represents the key novel aspect of the AVC scheme. We present results from using the AVC scheme along with advection and reinitialization schemes using upwind finite differencing on uniform meshes in this paper. These results are determined for four canonical test problems: slotted disk rotation, deforming sphere, interacting circles and vortex in a box. We compare these results with corresponding results determined using a recently proposed explicit sub-cell fix based reinitialization scheme (CR2). These comparisons show that the AVC scheme yields significantly improved conservation of enclosed volume/area within the interface. Note, the present AVC scheme achieves this by only modifying velocity field values at mesh points. Therefore, the AVC algorithm can in principle be used within the framework of nearly any numerical scheme used to compute interface evolution using the level-set method, even on non-uniform and unstructured meshes, in order to achieve improvements in solution quality. [ABSTRACT FROM AUTHOR]

In this paper, first we prove that making abstraction of the output obtained from the interactive extension principle based on a joint possibility distribution, in the case of unimodal fuzzy numbers and when the function that generates the operation is continuous and strictly increasing in each argument restricted to the support of each fuzzy number used in the process, then we can use joint possibility distributions with the property that the left/right side of the output is obtained from the convolution of the values in the left/right side of these fuzzy numbers. Then, considering joint possibility distributions with the aforementioned property, we find an Nguyen type characterization of the level sets of the output based on interactive extension principle, in terms of the level sets of the fuzzy numbers used in the process. These two key results complete well-known results obtained in the case of Zadeh's extension principle and also in the case of triangular norm-based extension principle. As an interesting corollary, in the special case of unimodal fuzzy numbers, the Nguyen theorem can be used to present a new proof concerning necessary and sufficient conditions on the equality of the outputs based on joint possibility distributions, respectively based on Zadeh's extension principle. [ABSTRACT FROM AUTHOR]

• Topology optimization of natural convection process using metal foam is studied. • The adjoint model based on the lattice Boltzmann method is derived in detail. • The level-set based optimization method is validated by the pipe bend problem. • Passive heat sink designs under different parameters are obtained and analyzed. • Three-dimensional performance examination of the optimized designs are given. In this work, the level-set based topology optimization (TO) method for optimizing the distribution of porous metal foam in the fully-coupled natural convection system is developed. The respective adjoint lattice Boltzmann (LB) model and the sensitivity expression are derived. The forward LB model is validated by natural convection in cavity partially filled with porous medium and the TO method is validated by the pipe bend optimization problem. The validated TO method is utilized to design the two-dimensional passive heat sink made up of metal foam. It is found that the optimized design can approach the heat transfer enhancement of the conventional design with 100% filling while using only 40% material. For the base case, the average Nusselt number can be increased by 3.96∼6.74 times with the optimized designs mounted on the heating element when the Grashof number ranges from 15.7 to 2.8 × 104. Effects of increasing the Darcy number, decreasing the thermal conductivity ratio and decreasing the maximum foam volume fraction on the optimized designs and the heat transfer performance are discussed in detail. The two-dimensional TO structures are further stretched to three-dimension for further verification, and a 13.1%∼41.4% lower temperature than the conventional design is achieved by the optimized designs, indicating the superiority of the TO method. [ABSTRACT FROM AUTHOR]

This paper introduces a three-phases model based on the finite element method to simulate the generation and propagation of landslide-generated impulse waves, and this model can be employed to predict and prevent wave-induced hazards. The fluid-like landslide mass is treated as a non-Newtonian viscoplastic fluid. The motion of landslides, water and air is modelled by the incompressible Navier–Stokes equations and the interfaces between these three phases are captured with the n -phases improved conservative level set method which can preserve mass and provide precious interface parameters, including normals and curvatures. The conservative feature of this method is proven by the three-phases Zalesak slotted disk test case. This method is then adopted to simulate the impulse wave generated by the Lituya Bay landslide and the current outputs are compared with other existing results. Finally, this verified model is utilized to model the impulse waves generated by the Halaowo landslide near the Xiangjiaba Dam in the Jinsha River and the results could provide references for further protective activities. [ABSTRACT FROM AUTHOR]

Dam-break flow over an immersed stationary object is investigated using a coupled level set (LS)/immersed boundary (IB) method developed in Cartesian grids. This approach adopts an improved interface preserving level set method which includes three solution steps and the differential-based interpolation immersed boundary method to treat fluid–fluid and solid–fluid interfaces, respectively. In the first step of this level set method, the level set function ϕ is advected by a pure advection equation. The intermediate step is performed to obtain a new level set value through a new smoothed Heaviside function. In the final solution step, a mass correction term is added to the re-initialization equation to ensure the new level set is a distance function and to conserve the mass bounded by the interface. For accurately calculating the level set value, the four-point upwinding combined compact difference (UCCD) scheme with three-point boundary combined compact difference scheme is applied to approximate the first-order derivative term shown in the level set equation. For the immersed boundary method, application of the artificial momentum forcing term at points in cells consisting of both fluid and solid allows an imposition of velocity condition to account for the presence of solid object. The incompressible Navier–Stokes solutions are calculated using the projection method. Numerical results show that the coupled LS/IB method can not only predict interface accurately but also preserve the mass conservation excellently for the dam-break flow. [ABSTRACT FROM AUTHOR]

A new direct re-initialization algorithm of a level set method is proposed for two- and three-dimensional unstructured meshes. In this method, the signed distances (level set values) to an interface are to be computed for all of the nodes inside a narrow band. In the 2D case, simple geometrical relations are employed for efficient calculation of the distance from a node inside a narrow band of an interface segment to the segment without finding the foot of the perpendicular drawn from the node onto the line including the interface segment. In the 3D case, an algorithm similar to the algorithm for the 2D case is introduced to determine nodes with feet far from the interface segment quickly. For the remaining nodes, a new technique to determine the existence of the foot on the interface segment is proposed in the re-initialization procedure. Benchmark problems with prescribed velocities are simulated to validate the proposed method for various mesh resolutions. The proposed method is not only demonstrated to be accurate but also highly efficient. Furthermore, assessment of the proposed method with simulations related to free surface flows governed by the incompressible Navier–Stokes equations is successfully performed in the present study. [ABSTRACT FROM AUTHOR]

The article offers information on several methods of topology optimization. Topics discussed include the evolutionary methods of optimization, the finite element analysis model in evolutionary optimization, and the level set method of topology optimization. Also mentioned are the topological sensitivity parameter in level set method, and.

A new topology optimisation algorithm is implemented and presented for compliance minimisation of continuum structures using a volume preserving mechanism which effectively handles a volume constraint. The volume preserving mechanism is based on a unique combination of the level set method and a boundary element based bi-directional evolutionary structural optimisation approach using a bisectioning algorithm. The evolving structural geometry is implicitly represented with the level sets, efficiently handling complex topological shape changes, including holes merging with each other and with the boundary. Numerical results for two-dimensional linear elasticity problems suggest that the proposed adaptation provides smooth convergence of the objective function and a more robust, smoother geometrical description of the optimal design. Moreover, this new implementation allows for efficient material re-distribution within the design domain such that the objective function is minimised at constant volume. The proposed volume preserving mechanism can be easily extended to three-dimensional space. [ABSTRACT FROM AUTHOR]

In this paper we present approaches that address two issues that can occur when the level-set method is used to simulate two-fluid flows in engineering practice. The first issue concerns regularizing the Heaviside function on arbitrary meshes. We show that the regularized Heaviside function can be non-smooth on non-uniform meshes. Alternative regularizing definitions that are indeed smooth and monotonic, are introduced. These new definitions lead to smooth Heaviside functions by taking the changing local meshsize into account. The second issue is the computational cost and fragility caused by the necessity of redistancing the level-set field. In [1, 2] it is shown that strongly coupling the level-set convection with the flow solver provides robustness and potentially efficiency and accuracy advantages. The next step would be to include redistancing within the strong coupling part of the algorithm. The computational cost of current redistancing procedure prohibit this. Four alternative approaches for circumventing the expensive redistancing step are proposed. This should facilitate a fully coupled level-set approach. Some benchmark cases demonstrate the efficacy of the proposed approaches. These includes the standard test case of the vortex in a box. Based on these results the most favourable redistancing approach is selected. [ABSTRACT FROM AUTHOR]

Keywords for this news article include: Alexandria University, Oncology, Brain Cancer, Health and Medicine. Keywords: Brain Cancer; Cancer; Health and Medicine; Oncology EN Brain Cancer Cancer Health and Medicine Oncology 811 811 1 07/24/23 20230725 NES 230725 2023 JUL 24 (NewsRx) -- By a News Reporter-Staff News Editor at Clinical Oncology Week -- Investigators discuss new findings in brain cancer. [Extracted from the article]

Cancer, Health and Medicine, Mathematics, Oncology The news reporters obtained a quote from the research from University of Malaysia Sarawak: "Simulating invadopodia replication in order for it to be biologically relevant is important since it helps us to understand cancer invasion and metastasis better as well as giving some insight into investigating ways to stop the spread of this fatal disease. Keywords: Cancer; Health and Medicine; Mathematics; Oncology EN Cancer Health and Medicine Mathematics Oncology 558 558 1 07/24/23 20230725 NES 230725 2023 JUL 25 (NewsRx) -- By a News Reporter-Staff News Editor at Cancer Weekly -- Research findings on cancer are discussed in a new report. [Extracted from the article]

Bioengineering, Convolutional Network, Emerging Technologies, Health and Medicine, Machine Learning, Magnetic Resonance, Networks, Neural Networks Keywords: Bioengineering; Convolutional Network; Emerging Technologies; Health and Medicine; Machine Learning; Magnetic Resonance; Networks; Neural Networks EN Bioengineering Convolutional Network Emerging Technologies Health and Medicine Machine Learning Magnetic Resonance Networks Neural Networks 3907 3907 1 07/10/23 20230714 NES 230714 2023 JUL 14 (NewsRx) -- By a News Reporter-Staff News Editor at Medical Imaging Week -- Current study results on bioengineering have been published. [Extracted from the article]

Keywords: Changchun; People's Republic of China; Asia; Cancer; Colorectal Research; Convolutional Network; Emerging Technologies; Gastroenterology; Health and Medicine; Machine Learning; Networks; Neural Networks; Oncology EN Changchun People's Republic of China Asia Cancer Colorectal Research Convolutional Network Emerging Technologies Gastroenterology Health and Medicine Machine Learning Networks Neural Networks Oncology 1608 1608 1 06/19/23 20230620 NES 230620 2023 JUN 20 (NewsRx) -- By a News Reporter-Staff News Editor at Cancer Weekly -- Data detailed on Cancer have been presented. Changchun, People's Republic of China, Asia, Cancer, Colorectal Research, Convolutional Network, Emerging Technologies, Gastroenterology, Health and Medicine, Machine Learning, Networks, Neural Networks, Oncology. [Extracted from the article]

Deep neural networks have achieved good progresses in smoke segmentation, but it is a challenging task to accurately segment smoke images due to smoke semi-transparency and large variance. To improve performance, we propose a Cross-scale Mixed-attention Network (CMNet) by designing multi-scale and mixed attention modules. We first concatenate the results of average and maximum pooling along each axis to learn powerful attention coefficients, which are used to weight the original input for producing a directional attention map along each axis. Then we use point-wise additions for combining three directional attention maps to propose a module of Fused 3D Attention (F3A). In addition, we adopt atrous convolutions to generate multi-scale feature maps, then point-wisely add the results of average and maximum pooling on each scale feature map, and design a bottleneck structure to produce an effective attention map for each scale and reduce learnable parameters simultaneously. All attention feature maps with different scales are concatenated to obtain Multi-scale Channel Attention (MCA). Finally, we cross-wisely stack the modules of F3A and MCA on both shallow and deep feature maps to propose Mixed Cross Enhancement (MCE) for fully fusing information across scales. Experiments show that our method surpasses most existing methods. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this study is to present a detailed quantitative and qualitative fuzzy approach to the Allee effect that permits dealing with uncertainty.Design/methodology/approach The Allee effect is related to those aspects of population dynamics that are connected with a decrease in individual fitness when the population size diminishes to very low levels. It allows to model the evolution of certain sectors or clusters which, due to their low population density, may have problems of survival. In uncertain environments, an estimate of the effect’s parameters can be performed in the form of fuzzy numbers, which means that this study is using the methodology of fuzzy arithmetic.Findings This study reveals that fuzziness changes the behavior of the set of solutions when the strong Allee effect is studied under uncertainty from the point of view of standard difference or generalization of the Hukuhara difference.Originality/value The value and originality of the work consists in offering a set of tools for studying the evolution of a group of firms subject to an Allee effect in uncertain environments. [ABSTRACT FROM AUTHOR]

An efficient three-dimensional two-phase flow model for simulation of free surface flows is developed. The method is based in the solution of Navier-Stokes equation for quasi-incompressible flows. The equations in generalized coordinates are solved by extension of the fully explicit MacCormack scheme, second order in time and fourth order in space. The free surface is implicitly captured by the zero Level Set of a smooth function and by the Ghost Fluid Method to capture accurately shape discontinuities for properties in the vicinity of the interface. Finally, the Volume of Fluid method is used to ensure mass conservation. Turbulence is described by large eddy simulation, where only the large-scale eddies are solved, while the small scales are modeled by using the selective structure function subgrid-scale model. Boundary shapes are represented through the immersed boundary method on the Cartesian grid. The numerical model is validated by some free surface problems. Numerical predictions by all cases are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to carry out a finite element simulation of a physically non-linear phase change problem in a two-dimensional space without adaptive remeshing or moving-mesh algorithms. The extended finite element method (XFEM) and the level set method (LSM) were used to capture the transient solution and motion of phase boundaries. It was crucial to consider the effects of unequal densities of the solid and liquid phases and the flow in the liquid region. Design/methodology/approach – The XFEM and the LSM are applied to solve non-linear transient problems with a phase change in a two-dimensional space. The model assumes thermo-dependent properties of the material and unequal densities of the phases; it also allows for convection in the liquid phase. A non-linear system of equations is derived and a numerical solution is proposed. The Newton-Raphson method is used to solve the problem and the LSM is applied to track the interface. Findings – The robustness and utility of the method are demonstrated on several two-dimensional benchmark problems. Originality/value – The novel procedure based on the XFEM and the LSM was developed to solve physically non-linear phase change problems with unequal densities of phases in a two-dimensional space. [ABSTRACT FROM AUTHOR]

The structural topology optimisation method presented in this paper is based on the boundary element method, level set method and shape sensitivity analysis for two-dimensional linear elastic problems. The proposed method automatically nucleates holes within the design domain during the optimisation process using a topological derivative based hole insertion criterion. The level set method is used to provide an implicit description of the structural geometry, which is capable of automatically handling topological changes, i.e. holes merging with each other or with the boundary. During the optimisation process non-uniform rational b-splines are fitted through the zero level set contours, which links an implicit geometry representation to its structural model. In addition, this provides an optimal design in standard CAD format, and without intermediate material densities, which can be directly used in other design processes. The proposed optimisation method is tested against different benchmark examples and the optimal geometries generated are in close agreement those available in the literature of topology optimisation. [ABSTRACT FROM AUTHOR]

A coupled level-set and volume-of-fluid (CLSVOF) method is proposed for tracking interface of incompressible two-phase flows, where the VOF advection is carried out only, and a zero level-set (LS) formula and LS reinitialization equation are employed to reestablish the signed distanced field near the interface, which can program easily. Meanwhile, a mass-correction scheme based on the interface curvature is used to conserve the liquid mass correctly. Firstly, the performance of the CLSVOF method is evaluated through two- and three-dimensional deformation field tests. Then, the CLSVOF method is adopted to simulate the rising bubble and droplet falling problems. Finally, a shape LS function is used to describe and treat the irregular surface (immersed boundary) of mold cavity. With the aid of the shape function, the coupled immersed boundary (IB) and CLSVOF (IB-CLSVOF) method is applied to the melt filling process in the complex mold cavity with insets. The numerical results show that the proposed IB-CLSVOF method has the capability to cope with complex interface variations accurately. And also, the numerical results demonstrate that IB-CLSVOF method is able to successfully depict the phenomena of race-tracking, air entrapment and weldline development, which are very helpful for determining processing conditions and designing mold cavities. [ABSTRACT FROM AUTHOR]