Level Of Refinement Research Articles

Dynamic adaptive and fully unstructured tetrahedral gridding: Application to CO2 sequestration with consideration of full fluid compressibility

Numerical simulations of complex subsurface flow problems and geomechanics will advance enormously by dynamic adaptive gridding. Only a small part of a large domain where sharp changes occur may require fine gridding. In this work, we introduce a methodology to carry out dynamic adaptive gridding for large-scale flow problems. The algorithm allows 2D and 3D unstructured gridding with consideration of full fluid compressibility in single-phase, and two-phase compositional flow. We divide a triangular element into four and a tetrahedron element into eight which creates hanging nodes at each level of refinement. The handing nodes are eliminated by splitting extra elements. As a result, a transition region exists between the fine and coarse grid regions of the domain. We have applied the method to CO2 sequestration in subsurface aquifers. The conditions are selected such that gravity fingers develop from density increase by the dissolution of CO2 in the aqueous phase. The selected examples include large domains where neither systematic studies nor dynamic adaptive gridding have been reported in the past. Results from comparison with uniform gridding reveal a speedup of up to three orders of magnitude in 3D.

Three-dimensional simulation of a floating wind turbine platform

Abstract As the need for renewable energy has grown in recent years, the possibility of creating and collecting deep-sea wind energy has become a research hotspot. Floating wind turbines need platforms to provide a stable working state and structural safety. This article focuses on the study of the dynamics of the deep-water semi-submersible floating platform OC4-DeepCwind. The open-source computational fluid dynamic toolbox OpenFOAM is used for comparative analysis of the floating structure motion response. In order to eliminate the influence of grid size and refinement level on the simulation results, a grid refinement study was conducted before detailed hydrodynamic discussions. In absence of wind, the dynamic response of the platform is studied under the influence of the impact with regular waves with different amplitudes. The effect of the presence of the tower supporting the wind turbine on the dynamics of the platform is investigated as well. Results show that the addition of the tower exerted a slight destabilising influence on the support’s dynamic behaviour, confirming its stability against different wave height. Finally, the model has demonstrated its efficacy as a highly valuable tool for the simulation of wind turbines on floating foundations.

Maturity Assessment of Knowledge Management in the Transition of Organizational Transformation at PT Telkom Indonesia (Persero) Tbk

The telecommunications industry is rapidly and significantly changing due to rising customer demands and digitization. Telecom businesses are exploring new strategies to maintain a competitive advantage. As the biggest telecommunication provider, PT Telkom Indonesia (Persero) Tbk (Telkom) consistently innovates and collaborates to foster a fair digital environment. This drive motivates Telkom to accelerate its transformation and lead Indonesia’s digitalization efforts. During this transformation process, Telkom needs to assess its knowledge management (KM) maturity level. This study will explore Telkom’s KM maturity, highlight gaps, and recommend business solutions. Using a mixed-methods approach, quantitative data were collected from surveys based on the Asian Productivity Organization (APO) framework, while qualitative data were gathered through in-depth interviews. This holistic approach ensures a comprehensive understanding of the key success factors of knowledge management. The research shows that the KM maturity level of Telkom is categorized as the 4th level or refinement level. This level indicates that Telkom’s KM progress aligns with the organization’s vision, mission, objectives, and priorities. However, there is still potential for continuous evaluation and improvement. Based on the data analysis, Telkom can implement several proposed business solutions, informed by 11 key success factors, to enhance the critical programs for organizational transformation.

Robust treatment for the coarse/fine interface of adaptive mesh in the simulation of two-phase flow

We propose a numerical framework for simulating two-phase flow considering gravity and surface tension, and implement it with adaptive mesh. The framework employs a pressure compensation method and a jump model, ensuring accurate modeling of gravity and surface tension when the interface crosses between adaptive meshes of different refinement levels. Additional treatments have been developed to accommodate existing interface capturing and curvature estimation approaches for the adaptive mesh. The method is straightforward to implement and significantly reduces the unnecessary refinement around the free surface. Numerical validations demonstrate the robustness of the treatment for coarse/fine interfaces, with overall accuracy converging and comparable to results obtained with a uniform mesh. Furthermore, the numerical approach accurately reproduces the physics of bubble rising and jet capillary breakup.

A Comparison of Free and Mapped Meshes for Static Structural Analysis

Abstract This study addresses the challenge faced by Finite Element Analysts when choosing between free and mapped meshes, especially in terms of convergence stability and solution accuracy. The investigation focuses on 3D solid models under static structural loading, analyzed using Ansys® and MSC Patran®. Both free and mapped mesh types, employing equivalent 3D solid elements, are used to assess an aircraft structural component under design load conditions, with fixed boundaries. For free meshes, Tet10 elements in Patran (equivalent to Solid 72 in Ansys) are used, whereas for mapped meshes, CPENTA / CHEXA elements in Patran (equivalent to Wed6 / Hex8 in Ansys) are employed. Mesh convergence studies ensure that discretization does not affect the numerical solution. Notably, a significant stress increase is observed with successive refinement of free meshes, while mapped meshes achieve mesh independence at coarser refinement levels. Comparison of fringe plots indicates the same location for maximum deformation and equivalent stress in both free and mapped mesh models. The findings demonstrate that free meshes tend to underpredict maximum deformation and equivalent stress compared to mapped meshes, with both meshes showing deformation and stress at consistent locations. The findings underscore the importance of carefully choosing the appropriate mesh type, particularly when analyzing critical structural components, to ensure reliability and accuracy in FEA simulations.

A practical multiscale analysis for nonlinear RC structures using a smart substructure replacement strategy

This paper presents a novel practical multiscale analysis (MSA) method for simulating local damages in large reinforced concrete (RC) structures during seismic events. Traditional techniques like the finite element (FE) method often struggle to balance computational costs with detailed simulation. The proposed method facilitates sequential local refinement from macroscopic to mesoscopic scales of RC structures, focusing strategically on critical areas prone to damage and cracking. Key features include: (1) 'Correction forces' enable integration and collaboration among models of different refinement levels, keeping models unchanged (i.e., without additions, deletions, or further refinement of elements), streamlining analysis and independent implementation across methods, scales, and platforms. (2) A smart replacement strategy ensures smooth transitions and prevents abrupt force changes between models at different refinement levels. (3) A ‘training process’ before performing the replacement and a semi-explicit method guarantee the accuracy and efficiency of the MSA method. (4) Parallel and distributed computing is seamlessly applied, significantly accelerating the analysis at each level. Implemented in the open-source software OpenSees, this method is illustrated through three examples that efficiently capture both the macroscopic mechanical responses and detailed local damage behaviors. This approach provides a valuable tool for the refined analysis of large-scale RC structures.

A greedy MOR method for the tracking of eigensolutions to parametric elliptic PDEs

In this paper we introduce a Model Order Reduction (MOR) algorithm based on a sparse grid adaptive refinement, for the approximation of the eigensolutions to parametric problems arising from elliptic partial differential equations. In particular, we are interested in detecting the crossing of the hypersurfaces describing the eigenvalues as a function of the parameters.The a priori matching is followed by an a posteriori verification, driven by a suitably defined error indicator. At a given refinement level, a sparse grid approach is adopted for the construction of the grid of the next level, by using the marking given by the a posteriori indicator.Various numerical tests confirm the good performance of the scheme.

The refinement paradox and cumulative cultural evolution: Complex products of collective improvement favor conformist outcomes, blind copying, and hyper-credulity.

Social learning is common in nature, yet cumulative culture (where knowledge and technology increase in complexity and diversity over time) appears restricted to humans. To understand why, we organized a computer tournament in which programmed entries specified when to learn new knowledge and when to refine (i.e. improve) existing knowledge. The tournament revealed a 'refinement paradox': refined behavior afforded higher payoffs as individuals converged on a small number of successful behavioral variants, but refining did not generally pay. Paradoxically, entries that refined only in certain conditions did best during behavioral improvement, while simple copying entries thrived when refinement levels were high. Cumulative cultural evolution may be rare in part because sophisticated strategies for improving knowledge and technology are initially advantageous, yet complex culture, once achieved, favors conformity, blind imitation and hyper-credulity.

Unilateral buckling of thin plates by complementarity eigenvalue analyses

In this work, the analysis by the finite element method of thin plates subjected to buckling in the presence of unilateral punctual obstacles, that is, supports that allow the plate to move in one direction but prevent the motion in the opposite direction, is addressed. An appropriate algorithm based on the solution of a semi-smooth system of equations, that results from the formulation of the unilateral buckling problem as a complementarity eigenvalue problem, is used. Rectangular and square plates are analysed under various membrane loadings, including compression and shear. The conformal Bogner–Fox–Schmit (BFS) finite element is employed to compute the bifurcation loads and the corresponding instability modes in scenarios with and without unilateral obstacles. For each plate and type of loading, the six lowest bifurcation loads and corresponding modes are computed for different levels of mesh refinement. The results confirm that the convergence of bifurcation loads obtained using the BFS element is monotonically decreasing as the mesh is refined. It is also confirmed that, when unilateral obstacles are present, the lowest bifurcation load, known as the critical load, can never be lower than the one of the homologous problem without unilateral obstacles.

An adaptive lattice Green's function method for external flows with two unbounded and one homogeneous directions

We solve the incompressible Navier-Stokes equations using a lattice Green's function (LGF) approach, including immersed boundaries (IB) and adaptive mesh refinement (AMR), for external flows with one homogeneous direction (e.g. infinite cylinders of arbitrary cross-section). We hybridize a Fourier collocation (pseudo-spectral) method for the homogeneous direction with a specially designed, staggered-grid finite-volume scheme on an AMR grid. The Fourier series is also truncated variably according to the refinement level in the other directions. We derive new algorithms to tabulate the LGF of the screened Poisson operator and viscous integrating factor. After adapting other algorithmic details from the fully inhomogeneous case [1], we validate and demonstrate the new method with transitional and turbulent flows over a circular cylinder at Re=300 and Re=12,000, respectively.

A hp-adaptive finite element approach for 3D controlled source electromagnetic forward modeling

Accurate and efficient 3D controlled-source electromagnetic (CSEM) forward modeling is crucial for deciphering CSEM responses in complex geological contexts and for assessing the efficacy of survey designs. It also serves as the foundation for 3D inversion, a critical technique for interpreting CSEM data. We present a novel hp-adaptive finite element method for 3D CSEM forward modeling. This method enhances the traditional h-adaptive approach, which only refines the mesh while keeping the polynomial degree of the basis functions constant, by enabling simultaneous refining mesh and increasing polynomial degree of basis functions. High-order elements yield superior approximations when the solution exhibits sufficient smoothness, while mesh refinement enhances accuracy in regions with less smooth solutions. The adaptive refinement process is guided by a goal-oriented error estimator that relies on the residual of the governing equation and the continuity of electromagnetic fields. The hp-adaptive strategy, which determines whether to refine elements or increase their polynomial degree, is based on the refinement levels of the elements. Constraints are applied to hanging nodes, introduced during the refinement process, to ensure the continuity of the finite element space. We validate the accuracy, efficiency, and convergence of the hp-adaptive method through tests on two layered models. Further simulations on a topographic model and a realistic model corroborate its effectiveness. Our findings indicate that the hp-adaptive method outperforms the traditional h-adaptive method in terms of accuracy, convergence rate and computational cost, making it a promising technique for 3D CSEM forward modeling.

High-fidelity fluid-structure interaction applied to static aeroelasticity in transonic flows

Transonic flows at high Reynolds numbers can lead to high dynamic pressures and, consequently, to aerostructural deflections of aircraft structures. This study aims to develop and validate a high-fidelity static aeroelastic analysis environment that is efficient and that can be used in an industrial setting. The aerodynamics is represented by numerical solutions of the Reynolds-averaged Navier-Stokes equations with appropriate turbulence closures. The load transfer process uses finite element shape functions in order to distribute the aerodynamic loads into the structural discretization. The structural analysis employs a modal basis approach, and a wingtip deflection convergence study is performed to find an adequate modal basis size. Radial basis functions are used for the fluid mesh displacement, and the influence of the support radius is evaluated to determine the optimal values relative to the wing mean aerodynamic chord. The capability is tested using the static aeroelastic benchmarks of the High Reynolds Aerostructural Dynamics Project (HIRENASD) and NASA's Common Research Model (CRM). The static aeroelastic results demonstrate robustness and consistency for the aerodynamic coefficients, pressure distributions, and structural deflection predictions at different normalized dynamic pressure values and grid refinement levels.

Development assessment of regional rooftop photovoltaics based on remote sensing and deep learning

Assessing the development of rooftop photovoltaic (PV) plays a positive role in promoting the deployment of solar installations. In response to the problem that previous studies did not consider the PV already installed on rooftops and thus had a low level of refinement, this study proposes a dual-branch framework based on remote sensing imagery and deep learning to effectively monitor the current status and estimate the future potential of regional rooftop PV installations. Based on the dual-branch framework, a semantic segmentation network called MANet is designed that integrated multi-attention modules for more accurate extraction of roofs and PV panels from remote sensing imagery. Finally, the methodology is validated through an application in Taihuyuan Town, Hangzhou City. Model comparisons show that MANet achieves the best accuracy in both roof and PV panel extraction, with IoU scores of 88.17% and 91.58%, respectively. The difference between the existing PV installed capacity and the roof area extracted by the framework and the corresponding statistical data is 8.1% and 11.7%, respectively. The framework calculates the existing rooftop PV installed capacity to be 16,173.74 kW, and estimates the PV installed capacity potential of the remaining rooftops to be 403 MW.

The Security Threat and Precautionary Measures of QR Code of Internet of Things Technology

The Internet of Things (IoT) is the expansion and extension of the traditional network. It is a network that connects goods and objects, which has been widely used in today's social development process. It occupies an important position in various industries. The emergence of the Internet of Things has greatly improved the refinement level of human management. The QR code (Quick Response Code) is a part of the perception layer of the IoT, which belongs to the perception and recognition technology of the IoT. The QR code not only brings convenience to users but also becomes the carrier and disseminator of malware, phishing, and other attacks. Therefore, it is of great significance for the security of the IoT to understand the potential threats of the QR code, analyze its potential attack methods, and put forward defense plans. This paper briefly introduces the basic characteristics of the QR code, as well as some attack methods and potential threats against the QR code, and put forward some preventive measures from both technical and non-technical aspects. The technical aspect includes the combination of cryptography and the introduction of third-party management. The non-technical aspects are discussed at the national and individual user levels.

Pharmaceutical emissions on the example of the Baltic Sea catchment: comparing measurements with multi-tier predictive models

Currently, there is uncertainty about emissions of pharmaceuticals into larger closed ecosystems that are at risk such as the Baltic Sea. There is an increasing need for selecting the right strategies on advanced wastewater treatment. This study analysed 35 pharmaceuticals and iodinated X-ray contrast media in effluents from 82 Wastewater Treatment Plants (WWTPs) across Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland and Sweden. Measured concentrations from Finland and Denmark were compared to predicted effluent concentrations using different levels of refinement. The concentrations predicted by the Total Residue Approach, as proposed by the European Medicines Agency, correlated with R2 of 0.18 and 0.031 to measured ones for Denmark and Finland, respectively and the predicted data were significantly higher than the measured ones. These correlations improved substantially to R2 of 0.72 and 0.74 after adjusting for estimated human excretion rates and further to R2 = 0.91 and 0.78 with the inclusion of removal rates in WWTPs. Temporal analysis of compound variations in a closely monitored WWTP showed minimal fluctuation over days and weeks for most compounds but revealed weekly shifts in iodinated X-ray contrast media due to emergency-only operations at X-ray clinics during weekends and an abrupt seasonal change for gabapentin. The findings underscore the limitations of current predictive models and findings (...) demonstrate how these methodologies can be refined by incorporating human pharmaceutical excretion/metabolization as well as removal in wastewater treatment plants to more accurately forecast pharmaceutical levels in aquatic environments.

Multi-spacecraft study with the Icarus model. Modelling the propagation of CMEs to Mercury and Earth

Coronal mass ejections (CMEs) are the main drivers of the disturbances in interplanetary space. Earth-directed CMEs can be dangerous, and understanding the CME interior magnetic structure is crucial for advancing space weather studies. It is important to assess the capabilities of a numerical heliospheric model, as a firm understanding of the nature and extent of its limitations can be used to improve the model and the space weather predictions based on it. The aim of the present study is to test the capabilities of the recently developed heliospheric model Icarus and the linear force-free spheromak model that has been implemented in it. To validate the Icarus space weather modelling tool, two CME events were selected that were observed by two spacecraft located near Mercury and Earth, respectively. This enables us to test the heliospheric model computed with Icarus at two distant locations. The source regions for the CMEs were identified, and the CME parameters were determined and later optimised. Different adaptive mesh refinement levels were applied in the simulations to assess its performance by comparing the simulation results to in situ measurements. The first CME event erupted at 15:25 on July 9, 2013. The modelled time series were in good agreement with the observations both at MESSENGER and ACE. The second CME event started at 10:25 on February 16, 2014, and was more complicated, as three CME interactions occurred in this event. It was impossible to recover the observed profiles without modelling the other two CMEs that were observed, one before the main CME and one afterward. The parameters for the three CMEs were identified and the three CMEs were modelled in Icarus. For both CME studies, AMR level 3 was sufficient to reconstruct small-scale features near Mercury, while at Earth, AMR level 4 was necessary due to the radially stretched grid that was used. The profiles obtained at both spacecraft resemble the in situ measurements well. The current limitations of the space weather modelling tool result in an excessively small deceleration of the CME propagation during the CME--CME interaction as measured by MESSENGER and ACE.

Complexity analysis of quasi continuous level Monte Carlo

Continuous level Monte Carlo is an unbiased, continuous version of the celebrated multilevel Monte Carlo method. The approximation level is assumed to be continuous resulting in a stochastic process describing the quantity of interest. Continuous level Monte Carlo methods allow naturally for samplewise adaptive mesh refinements, which are indicated by (goal-oriented) error estimators. The samplewise refinement levels are drawn in the estimator from an exponentially-distributed random variable. Unfortunately in practical examples this results in higher costs due to high variance in the samples. In this paper we propose a variant of continuous level Monte Carlo, where a quasi Monte Carlo sequence is utilized to ''sample'' the exponential random variable. We provide a complexity theorem for this novel estimator and show that this theoretically and practically results in a variance reduction of the whole estimator.

Complex unstructured-grid groundwater modeling using centroidal Voronoi tessellation refinement and curve fitting

An unstructured grid is a powerful data structure for a proper depiction of various geological features such as faults and pinch-outs and for groundwater simulation in a complex aquifer system. This study presents a mesh generation methodology based on 2.5D centroidal Voronoi tessellations (CVTs), which provides a great flexibility in specifying grid connections in 3D, matching irregular geometries, and adding high levels of refinement in areas of interest. Lloyd relaxation approximation is introduced to effectively guarantee the generation of centroidal Voronoi grids. A curve-fitting Voronoi gridding approach is developed to construct Voronoi cell edges conforming to intricated geological traces in the horizontal 2D projection with unstructured vertical discretization. A controlled refinement in spatial grid resolution has been demonstrated to prevent adverse impacts on groundwater flow simulations. The methodology is applied to the Southern Hills aquifer system in the Capital Area of Louisiana, USA. Significant groundwater depletion has occurred due to continuous and excessive withdrawals over decades for public supplies and industries. The Baton Rouge fault and the Denham-Springs Scotlandville fault are leaky barriers and have a significant influence on groundwater flow. A curve-fitting centroidal Voronoi grid is developed to simulate the effects of the two faults as leaky barriers. CVT-based high-fidelity unstructured multi-model groundwater modeling is conducted using MODFLOW 6 to allow more flexibility in model design. Complex groundwater flow in the Southern Hills aquifer system was revealed through the centroidal Voronoi unstructured grid.

Enhancing the wearing resistance of TC17 alloy by nano/micro-TiC ceramic through directed energy deposition

Micro-TiC (m-TiC), nano-TiC (n-TiC), and nano/micro-TiC (n/m-TiC) ceramic particles reinforced TC17 composites were prepared using directed energy deposition (DED) technology. The microstructure, microhardness and wear properties of the composites were systematically studied. Under the same conditions, m-TiC partially melted, while n-TiC fully melted. The varying degrees of melting resulted in differences in both the level of grain refinement and the in-situ TiCX morphologies. The average grain sizes of the TC17 alloy, m-TiC/TC17, n-TiC/TC17, and n/m-TiC/TC17 composites are 76.96 μm, 39.43 μm, 20.76 μm, and 21.32 μm, respectively. The n-TiC demonstrated a superior grain refinement effect compared to m-TiC. The m-TiC/TC17 composite precipitated diverse small primary and eutectic TiCX. The n-TiC/TC17 and n/m-TiC/TC17 composites were mainly composed of primary dendritic and rod-like TiCX, with no eutectic phases observed. The n/m-TiC/TC17 composite showed the highest hardness (∼ 579.417 HV0.2) and best wear resistance (0.0592 mg/m), with a 44.4% hardness increase and a 51.4% wear rate decrease compared to TC17 alloy. In contrast, m-TiC/TC17 and n-TiC/TC17 composites showed hardness increases of 4.55% and 35.99%, and wear rate reductions of 18.7% and 43%, respectively.

Multi-Objective Topology Optimization of Conjugate Heat Transfer Using Level Sets and Anisotropic Mesh Adaptation

This study proposes a new computational framework for the multi-objective topology optimization of conjugate heat transfer systems using a continuous adjoint approach. It relies on a monolithic solver for the coupled steady-state Navier–Stokes and heat equations, which combines finite elements stabilized by the variational multi-scale method, level set representations of the fluid–solid interfaces and immersed modeling of heterogeneous materials (fluid–solid) to ensure that the proper amount of heat is exchanged to the ambient fluid by solid objects in arbitrary geometry. At each optimization iteration, anisotropic mesh adaptation is applied in near-wall regions automatically captured by the level set. This considerably cuts the computational effort associated with calling the finite element solver, in comparison to traditional topology optimization algorithms operating on isotropic grids with a comparable refinement level. Given that we operate within the constraint of a specified number of nodes in the mesh, this allows not only to improve the accuracy of interface representation and motion but also to retain the high fidelity of the numerical solutions at the grid points just adjacent to the interface. Finally, the remeshing and resolution steps both run within a highly parallel environment, which makes it possible for the proposed algorithm to tackle large-scale problems in three dimensions with several tens of millions of state degrees of freedom. The developed solver is validated first by minimizing dissipation in a flow splitter device, for which the method delivers relevant optimal designs over a wide range of volume constraints and flow rate distributions over the multiple outlet orifices but yields better accuracy compared to reference data from literature obtained using uniform meshes (in the sense that the layouts are more smooth, and the solutions are better resolved). The scheme is then applied to a two-dimensional heat transfer problem, using bi-objective cost functionals combining flow resistance and thermal recoverable power. A comprehensive parametric study reveals a complex arrangement of optimal solutions on the Pareto front, with multiple branches of symmetric and asymmetric designs, some of them previously unreported. Finally, the algorithmic developments are substantiated with several three-dimensional numerical examples tackled under fixed weights for heat transfer and flow resistance, for which we show that the optimal layouts computed at low Reynolds number, that are intrinsically relevant to a broad range of microfluidic application, can also serve as smooth solutions to high-Reynolds-number engineering problems of practical interest.