A new high-order RKDG method based on the TENO-THINC scheme for shock-capturing

In recent years, Runge-Kutta Discontinuous Galerkin (RKDG) methods have gained substantial attention in solving hyperbolic conservation laws, attributed to their high-order accuracy and adaptability to unstructured meshes. However, standard RKDG methods cannot capture discontinuities without oscillation unless they are supplemented with troubled cell indicators and limiters. Existing indicators, such as the total variation bounded (TVB) minmod indicator and the KXRCF indicator, typically depend on a critical parameter tied to the equation's solution, necessitating tuning for different cases. In terms of limiters, the popular limiters even fail to guarantee the high-order property in the smooth regions. The advent of Weighted Essentially Non-Oscillatory (WENO) schemes prompts the implementation of WENO limiters for RKDG methods, preserving high-order properties. However, WENO-family schemes exhibit significant numerical dissipation, potentially smearing small-scale flow structures. In this work, the Targeted Essentially Non-Oscillatory (TENO) indicator [1] is utilized, which leverages the nonlinear weighting strategy of the TENO scheme to separate high-wavenumber physical fluctuations and genuine discontinuities from smooth regions with a unified set of parameters. For troubled cells, a novel limiter is proposed for structured meshes, which combines a TENO scheme for resolving high-wavenumber physical fluctuations and a novel non-polynomial Tangent of Hyperbola for the INterface Capturing (THINC) scheme for resolving genuine discontinuities with extremely low numerical dissipation. Furthermore, the shifting between the TENO and THINC schemes is based on a new boundary variation diminishing (BVD) strategy, which only relies on compact neighborhoods and is significantly simpler than its predecessors. Meanwhile, a new strategy is proposed to ensure the consistency of the new limiter applied for 1D and 2D cases. A set of 1D and 2D benchmark cases including strong shockwaves and a broad range of flow length scales is simulated with uniform meshes for 1D cases and structured quadrilateral meshes for 2D cases to demonstrate the performance of the new numerical scheme. The indicator does not activate any limiters in the accuracy test cases to ensure the high-order property of the whole numerica

Ablation mechanisms of 2D C/SiC-Ti3SiC2 composite irradiated by combined laser: Experimental and numerical study

The combined laser has been applied in laser processing due to the accelerated damage behavior and processing efficiency. However, the best-combined scheme is uncertain for C/SiC composites due to multiple ablation modes and damage effects at various input laser parameters. In this paper, the combined laser, composing the continuous-wave and short-pulsed or long-pulsed lasers, is experimentally investigated in terms of the efficiency of ablation behavior. An in-situ observation system is established to obtain the instantaneous ablation process. The numerical simulation procedure, which includes an efficient and phenomenological multi-scale ablation model, is also proposed to reveal the ablation mechanism of the combined laser. The experimental and numerical results reveal the governing ablation mechanism of the different composed schemes: When combined with continuous-wave laser, the short-pulsed laser induces the plasma impact effect can reduce the oxidation resistance of the 2D C/SiC-Ti3SiC2 composite, whereas the long-pulsed laser can significantly accelerate the ablation rate. The multi-scale ablation model in this work can provide an effective analytical tool for studying the efficient processing mechanisms of the combined laser

Optimized dynamic similarity models to predict SGS backscatter in 2D decaying turbulence

Large eddy simulation (LES) of two-dimensional (2D) turbulence is often used in the geostrophic flows. However, some basic dynamics underlying traditional SGS models are absent in 2D turbulence, e.g. the vortex stretching. Hence, this research proposes an optimized dynamic similarity model (DSM) for the SGS stress, which is constructed through the dynamic procedure based on the Germano identity. In addition, a modification is made to the dynamic mixed model (DMM) for the sake of realizability condition. The optimized DSM is justified in comparison with the DMM, through the a priori and a posteriori verifications, in the context of the 2D decaying turbulence with turbulent Reynolds number of Re = 3.7 x 104 and turbulent Mach number of Mt = 0.1. Special attention is paid to the consistency of the verification procedure, so that the filtering operations used in the direct numerical simulation (DNS) and LES are optimally equivalent. The SGS transport phenomena, especially the SGS backscatter, predicted by these two models are studied in detail. In addition, the optimized DSM and the DMM are extended for the modified SGS transport vectors of passive scalars to show their capability in calculating 2D turbulent mixing. The numerical results show the optimized DSM provides larger correlation coefficient, better locality, and stronger SGS backscsatter than the DMM does, and therefore it is more suitable for the LES of 2D turbulence

Wave generation, energy conversion, and sediment accumulation in a real-scale channel-like reservoir by landslide using a soil-water coupling SPH model

For reservoirs located in mountainous regions, often referred to as channel-like reservoirs, the dynamics of landslide-generated impulse waves (LGIWs) differ considerably. The LGIW disaster resulted from the Huangtian landslide, which occurred in southwestern China, exemplifies a typical event in such channel-like reservoirs. However, survey data is limited due to the challenges of field observations. For instance, the evolution of LGIWs and the landslide movement process remain unknown. To investigate this practical event, a soil-water coupling model utilizing the Smoothed Particle Hydrodynamics (SPH) method is introduced. The results demonstrate a close alignment with actual observations. Notably, the evolution of the leading wave within the channel-like reservoir reveals significant differences, as the water body transitions from the common three-dimensional spreading propagation characteristic of reservoirs to a unidirectional movement along the river channel. This transition complicates the direct application of empirical formulas derived from conventional physical modeling experiments to wave phenomena in channel-like reservoirs. Moreover, the head velocity of the landslide diverges from its average velocity, offering a more accurate characterization of the landslide's impact on the water body. The energy conversion coefficient peaks at approximately 15% around the moment the landslide impacts the opposite bank, highlighting the substantial influence of topographic characteristics on the energy conversion process. The analysis also addresses the degree of siltation in the channel following the landslide and its implications for navigation

A compressed sensing based framework for surface pressure field reconstruction from sparse measurement

Traditional experimental methods usually measure the aerodynamic load characteristics of an object by deploying a large number of pressure sensors on its surface, which are often challenging to economically and efficiently obtain accurate surface pressure distribution due to limitation imposed by experimental space, the complexity of geometry, and the cost of measurement instruments. To address this, a compressed sensing (CS) based framework has been proposed in this paper to investigate the reconstruction of the original surface pressure field from extremely sparse measurement data. The proposed framework integrates the generalized proper orthogonal decomposition method for flow field dimensionality reduction, the CS technique for accurate reconstruction of the original signal, and the improved particle swarm optimization algorithm for optimizing sensor placement strategies. Unlike image and unsteady flow field reconstructions, the method presented in this paper has been successful in reconstructing surface pressure fields of high-speed train under various conditions. Based on the accurate reconstruction of surface pressure fields, further aerodynamic load data can be obtained. Additionally, this paper optimizes the traditional pressure sensor layout using a particle swarm optimization method, which not only improves reconstruction accuracy but also significantly reduces the deployment of redundant sensors. Moreover, traditional point selection strategies based on experience can still be incorporated into the pressure sensor layout scheme and effectively reduce reconstruction errors under crosswind conditions. Comparison of the results showed that the proposed framework can accurately and efficiently reconstruct the surface flow field of three-dimensional complex-shaped objects from sparse measurement

Strengthening copper matrix composites by in situ synthesized amorphous carbon nanosheet reinforcements

Graphene-like carbon nanosheets with large specific surface areas present a great potential to enhance the mechanical properties of copper matrix composites. To achieve the homogeneous dispersion of nanosheet reinforcements in the copper matrix, in-situ synthesis strategies using solid carbon sources have been developed in recent years. However, the influence of in-situ synthesis factors on the microstructures of carbon nanosheets and the corresponding mechanical behaviors are far from clear. In this work, an amorphous carbon nanosheets reinforced copper matrix composite with significantly enhanced strength had been in-situ synthesized. The dependence of the microstructures and tensile mechanical properties of the composite on the amorphous carbon nanosheet concentration was investigated. The in-situ grown amorphous carbon nanosheets induced remarkably refined Cu grains and they could effectively bear the loads transferring from the matrix. Consequently, the copper matrix composite with 0.6 wt% amorphous carbon nanosheets showed the highest yield strength and ultimate tensile strength of 196.5 MPa and 306.4 MPa, respectively, which are 2.56 and 1.51 folds of the pure copper bulk. The strengthening mechanisms of the amorphous carbon nanosheets/Cu composite were further revealed through the microstructure characterizations and theoretical model analysis. The load transfer was considered as a dominant mechanism for the strengthening

Strong detonation behaviours in stratified media bound by non-reactive gases

In this study, the propagation behaviour of detonation waves in a channel filled with stratified media is analysed using a detailed chemical reaction model. Two symmetrical layers of non-reactive gas are introduced near the upper and lower walls to encapsulate a stoichiometric premixed H2-air mixture. The effects of gas temperature and molecular weight of the non-reactive layers on the detonation wave's propagation mode and velocity are examined thoroughly. The results reveal that as the non-reactive gas temperature increases, the detonation wave front transitions from a 'convex' to a 'concave' shape, accompanied by an increase in wave velocity. Notably, the concave wave front comprises detached shocks, oblique shocks and detonation waves, with the overall wave system propagating at a velocity exceeding the theoretical Chapman-Jouguet speed, indicating the emergence of a strong detonation wave. Furthermore, when the molecular weight of non-reactive layers varies, the results qualitatively align with those obtained from temperature variations. To elucidate the formation mechanism of different detonation wave front shapes, a dimensionless parameter $\eta$ (defined as a function of the specific heat ratio and sound speed) is proposed. This parameter unifies the effects of temperature and molecular weight, confirming that the specific heat ratio and sound speed of non-reactive layers are the primary factors governing the detonation wave propagation mode. Additionally, considering the effect of mixture inhomogeneity on the detonation reaction zone, the stream tube contraction theory is proposed, successfully explaining why strong detonation waves form in stratified mixtures. Numerical results show good agreement with theoretical predictions, validating the proposed model

The detection, extraction and parameter estimation of extreme-mass-ratio inspirals with deep learning

One of the primary goals of space-borne gravitational wave detectors is to detect and analyze extreme-mass-ratio inspirals (EMRIs). This task is particularly challenging because EMRI signals are complex, lengthy, and faint. In this work, we introduce a 2-layer convolutional neural network (CNN) approach to detect EMRI signals for space-borne detectors, achieving a true positive rate (TPR) of 96.9% at a 1% false positive rate (FPR) for signal-to-noise ratio (SNR) from 50 to 100. Especially, the key intrinsic parameters of EMRIs such as the mass, spin of the supermassive black hole (SMBH) and the initial eccentricity of the orbit can also be inferred directly by employing a neural network. The mass and spin of the SMBH can be determined at 99% and 92% respectively. This will greatly reduce the parameter spaces and computing cost for the following Bayesian parameter estimation. Our model also has a low dependency on the accuracy of the waveform model. This study underscores the potential of deep learning methods in EMRI data analysis, enabling the rapid detection of EMRI signals and efficient parameter estimation

重稀土晶界扩散工艺制备高矫顽力钕铁硼磁体研究进展与应用现状

重稀土晶界扩散技术是目前制造高矫顽力钕铁硼磁体最重要的一种技术手段。本文简要介绍了重稀土晶界扩散的概念及用于工程化制备高性能钕铁硼磁体的应用现状，重点分析了重稀土晶界扩散技术近年来最新的代表性研究成果，提出了该技术当前亟待攻克的几个主要问题。文章对重稀土晶界扩散制备高性能钕铁硼磁材的进一步发展和工程化应用具有一定的指导意义

Impact response of pearlitic steel dominated by ferrite/cementite interface

It is experimentally difficult to ascertain the role of ferrite/cementite interface in the impact properties and structural evolution of pearlitic steel. In this paper, we propose a solution based on molecular dynamics simulations of planar shocks of pearlitic steel. It is found that the ferrite/cementite interface reflects the part of a shock wave and facilitates the nucleation of voids and dislocations. Consequently, the disturbance and plastic wave details are added to free surface velocity-time profiles. The evolution of voids contributes to the subsequent occurrence of spallation at interface, generating a power law relationship between the tensile strain rate and spall strength with an exponent of 2.7, which differs from that of 4.0 as spallation happens in polycrystalline ferrite regions