The discontinuous Galerkin (DG) method has been widely adopted due to its excellent properties such as high accuracy and ease of parallelization. The adaptive mesh refinement (AMR) technique has been widely adopted to improve computational efficiency with much less computational cost compared with uniform global refinement to the same level with AMR. This paper combines the advantages of DG and AMR, and a new hybrid limiter is applied to the DG method on adaptive Cartesian grid based on p4est, an open-source library. The limiter exhibits advantages of high precision, compactness, robustness, and ease of implementation. The shock wave is captured with a shock indictor and the performance of the new hybrid limiter is compared with that of the total variational bounded (TVB) limiter in this paper. The result shows that the performance of the former is significantly better than that of the latter. A series of numerical examples for Euler equations and Navier-Stokes equations are used to verify the feasibility and efficiency of the proposed method. The results show that the new hybrid limiter performs very well in the AMRDG method, it has lower dissipation and great shock capture ability, and the computational efficiency is greatly improved while the accuracy is guaranteed.

Considering the issue that low frequency and broadband of elastic wave metamaterials cannot coexist, this paper realizes a low-frequency band gap by rotating asymmetric mechanical metamaterials, and further widens the low-frequency bandgap by introducing multiple orders. By utilizing the node rotation and ligament bending deformation characteristics of anti-chiral materials, the vibration body size and ligament stiffness of the anti-tetra chiral unit cell diagonal are gradually adjusted through ligament folding, and the multi-order asymmetric unit cell design is realized. The generation and change mechanism of elastic wave bandgap are explained by analyzing the resonance mode and transmission characteristics of the upper and lower bounds of the bandgap. The study shows that: in the asymmetric mode, the node rotation and ligament bending deformation characteristics of chiral materials are utilized to realize the rotation resonance of the mass block and open the bandgap, and the band gap is widened by the resonant superposition between two pairs of different mass blocks arranged alternately. Finally, the proposed asymmetric mechanical metamaterial is verified by experiments to have to demonstrate improved broadband and low-frequency vibration isolation performance.

Damage and fracture are the main causes of structural failure, which have a significant impact on engineering safety. Crack propagation problem is also a fundamental scientific challenge that needs to be solved urgently. In this paper, the relevant theoretical basis for simulating damage and fracture, such as a fracture mechanics model, damage evolution model and numerical calculation methods, such as the finite element method, boundary element method and peridynamics theory, are introduced in the form of literature review. This paper also reviews the commonly used CAE software for structural damage and fracture analysis, including general-purpose finite element programs such as the damage and fracture analysis module that comes with ABAQUS, as well as specialized fracture analysis software, damage tolerance tools, fatigue life analysis tools, etc. The development status of some autonomous CAE software is also discussed. Finally, this paper analyzes some challenges faced by CAE software for damage and fracture simulation, and looks forward to the future development direction of domestic CAE software.

The Euler equation is one of the fundamental equations describing fluid motion in Computational Fluid Dynamics, and the existence of discontinuous solutions poses challenges in constructing numerical algorithms for solving this type of equation. To achieve high-resolution numerical results for the Riemann problem of the two-dimensional Euler equation, this paper constructs a pressure-difference adaptive rotating entropy stable scheme. Utilizing the rotating invariance of the equations, the normal vector outside the boundary is decomposed into two orthogonal components, and an entropy stable scheme is implemented in each directions. The determination of the components of the two components relies on the rotation angle. In this paper, a pressure function is introduced to adaptively adjust the rotation angle of the scheme based on local pressure variations. The resolution of the entropy stable scheme is enhanced by introducing the adaptive rotation angle. Numerical examples show that the numerical results obtained by this scheme exhibit good symmetry and high resolution.

This paper presents an analytical method, namely interface stiffness transfer method, for evaluating the responses of multilayered elastic structures. Based on the Love function and general solutions, the stiffness matrix relationship of the displacement-stress state vectors is introduced to obtain the interface stiffness transfer matrix equation between adjacent layers, which satisfies an algebraic Riccati matrix equation. When the elastic layer is a half-space, an explicit solution is obtained directly for the interface stiffness matrix. The interface stiffness transfer matrix method starts from the bottom layer with a known stiffness, and then deals with one layer at a time until the uppermost layer is reached, obtaining the interface stiffness of the multilayered structure. Finally, by solving the symmetric equilibrium equations of the boundary conditions, the displacement-stress state vector of an arbitrary layer is obtained. This method keeps the advantages of the classical transfer matrix method, but naturally excludes its exponential growth terms. In particular, the proposed method is a powerful candidate for efficiently solving the algebraic Riccati equation for the optimal control problems. Numerical examples show the properties of the interface stiffness transfer method.

In order to investigate the effect of cable damage on in-plane free vibration characteristics of cable-beam composite structures, three dimensionless parameters of cable damage intensity, extent and position are introduced in this paper to establish an in-plane dynamic model of single-cable cantilever beam composite structures with cable damage. The eigenvalue problem of in-plane free vibration of a single cable-cantilever beam model is solved by the method of separation of variables. At the same time, the finite element models under undamaged and damaged conditions of the cable are established for verification, and the results are in good agreement with the theoretical results. The results show that the frequency of the combined structure will decrease obviously only when the sag or damage intensity and extent of the cable are large. When the damage intensity and extent of the cable increase to a certain value, 1∶1 in-mode resonance phenomena tend to appear for high order frequencies. The asymmetric initial configuration caused by damage can increase the frequency of the combined structure, and some mixed modes of the combined structure change to local modes, while some local modes change to mixed modes.

In computational fluid dynamics, mesh quality greatly affects the accuracy and computational efficiency of numerical simulation results. The Bubble does not require the consideration of intersection judgments and has a relatively simple data structure, which has significant advantages in mesh generation efficiency and quality. The process of improving the mesh quality by moving nodes based on the traditional Bubble is optimized in this article, and we define it as the Bubble-Opt method. In this method, a bubble radius selection method combined with neural networks is used to generate the initial bubbles, and an improved bubble dynamic movement technique is used to adjust the bubbles to the appropriate position. The Delaunay method is used to connect the center of bubbles to form the final optimized mesh. Then, the optimization effects of different bubble radius selection methods and Bubble-Opt methods are compared under different process parameters. Taking the flow around a 2D cylinder as an example, the geometric quality and transition ratio of the mesh before and after optimization are tested. For this example, there is a set of optimal parameters and a radius selection method that achieve the best mesh quality optimization effect. The average transition ratio can be improved by about 17.37%, the average mesh quality can be improved by about 13.60%, and the minimum transition ratio and minimum mesh quality can be significantly improved. Finally, under the radius selection method and process parameters, taking two-dimensional cylindrical flow and NACA0012 airfoil flow as examples, the numerical simulation results are compared with experimental data from both qualitative and quantitative perspectives, indicating a significant improvement in the overall grid quality.

The computation mechanism of the calculation method for the completed state of existing suspension bridges is unclear, and the target state is unreasonable. A reasonable numerical analysis algorithm is proposed for bridge formation state. The cable theory consisting of the initial end angle and horizontal cable force is validated based on the relationship between the initial end angle and cable force in the theory of catenary equations. A system of bridge state analytical equations are constructed based on the optimization principle of the target parameters of each component of the suspension bridge. The calculation equation for the main cable configuration based on the geometric closure conditions of the suspension bridge's main cable. The mechanical equilibrium equations are constructed for each component based on the mechanical equilibrium conditions of the suspension cables and stiffening beams. Based on the principle of minimizing the bending moment of the stiffening beam components and the principle of uniform cable force of the suspension cable components in the completed state of the suspension bridge, a calculation equation system for the stiffening beam and suspension cable is established. The intelligent algorithm GRG is used to optimize the numerical solution of the objective function of the completed state of a suspension bridge. A case study of a kilometer-long level suspension bridge project. The derived analytical algorithm is compared with the calculation results of the finite element model and rigid supported continuous beam algorithm. The results show that the difference between the analytical algorithm and the finite element model calculation is relatively small in terms of force of main cable, shape-finding of main cable, and the bending moment of the stiffening beam. Compared with the rigid support continuous beam algorithm, the analytical algorithm has computational advantages in ensuring the uniformity of cable forces in bridge suspension cables and the extreme bending moment of stiffening beams.

To investigate the evolution of dimpling and the mechanism of interface separation in bimetal clad pipes under external mechanical loading, a stress model was established. The study analyzed the effects of the ratio of diameter to thickness for the inner and outer pipes, forming pressure, initial forming clearance, and operational internal pressure on dent formation and interface separation. Results indicate that interface separation distance and rebound rate correlate positively with the ratio of diameter to thickness for the inner pipes, forming pressure, and initial forming clearance, and negatively with the ratio of diameter to thickness for the outer pipes. Higher operational internal pressure reduces interface separation but increases rebound rate. Internal pressurization of dented pipes decreases interface separation; for instance, under 2-MPa operating pressure, interface separation is 5% less compared with conditions under 2-MPa pressurization. Additionally, the difference in separation between these conditions decreases with increasing pressure. Adjacent dimpling results in increased interface separation in intermediate pipe segments, causing a broader interface separation area compared with isolated dimpling.

Addressing the challenge of accurately solving unstable stick-slip vibration problems in non-smooth dynamics, this paper proposes a solution algorithm based on Physics-informed Neural Networks (PINN). Firstly, the classical stick-slip vibration problem is dynamically modeled using the linear complementarity theory under unilateral constraints. Then, the linear complementarity relationship is designed as a loss function to guide the training of the neural network, constructing a PINN algorithm for solving multi-point friction-induced stick-slip vibration problems. The accurate simulation of complex responses of multiple sliders'stick-slip vibrations in frictional systems is conducted. By comparing the numerical results with the Switching Model method that includes event detection and the traditional Time-Stepping method without event detection, the accuracy of the PINN algorithm is verified. The proposed PINN algorithm transforms the traditional optimization problem calculation into network training of the machine learning algorithm, making it suitable for stick-slip vibration analysis with multiple contact points. This method achieves accurate nonsmooth state transitions and provides a convenient and easy-to-use new approach for the accurate simulation of complex nonlinear vibration responses in multi-degree-of-freedom frictional systems.