Acta Mechanica Sinica最新文献

An efficient method is developed in this work for the modal analysis of multistage cyclic structures considering gyroscopic, stress stiffening, and spin softening effects. The eigen-solution analysis for gyroscopic systems is redefined as the eigen-solution analysis of a Hamiltonian matrix within a state-space framework, and an improved adjoint symplectic subspace iteration method is employed to determine the eigenvalues and eigenvectors of the Hamiltonian matrix. The algorithmic cost of the improved adjoint symplectic subspace iteration method is reduced by exploiting the matrix properties of the structure. Specifically, we demonstrate that for the Hamiltonian matrix corresponding to the gyroscopic system, the eigenvectors associated with a pair of conjugate eigenvalues exhibit a symmetry: their real and imaginary parts are invariant under mutual exchange. This property enables the required dimension of the iterative subspace to be halved. Subsequently, recognizing that the stress stiffening matrix is numerically much smaller than the stiffness matrix, a tailored preconditioner is designed to ensure the rapid convergence of the preconditioned conjugate gradient method with minimal iterations. Furthermore, the Guyan reduction and group theory are utilized to further reduce the computational cost of solving the linear algebraic equations by exploiting the cyclic symmetry of each stage. The proposed method achieves an accuracy comparable to full-order modal analysis while demonstrating superior computational efficiency. The computational accuracy and efficiency of the proposed method are validated through three case studies.

In an extreme ultraviolet (EUV) vessel, intense heating occurs when a high-power laser irradiates tin droplets, generating extreme thermal pressure gradients that drive complex flow dynamics. This review focuses on two critical aspects governing flow properties and debris transport within the vessel: main shock behavior and thermal expansion dynamics. Key considerations include finite-source shock dynamics, environmental effects on shock propagation, gas contact motion, and interface instabilities. The evolution of the main shock and gas contact is primarily determined by the initial pressure ratio and sound speed ratio between the heat source and ambient gas. Furthermore, Rayleigh-Taylor and Richtmyer-Meshkov instabilities dominate the evolution of gas-gas interfaces. This work presents a comprehensive analysis of the complex flow mechanisms underlying early-stage, high-temperature flow expansion in EUV source vessels.

The determination of the steady configuration of flexible spacecrafts in the challenging space environment holds paramount importance for the prediction of structural mechanical behaviors and the monitoring of failures during in-service conditions. In this paper, based on the nonlinear Euler-Bernoulli beam model, the differential equations describing the steady configuration of an ultra-large spacecraft are transformed into polynomial equations by introducing the moment integration function and Taylor expansion, facilitating rapid and accurate solutions. Furthermore, accounting for the additional moment effect induced by axial component of the gravity-gradient force, the steady configuration under all loads is iteratively calculated starting from the equilibrium configuration under normal loads, resulting in a novel integral and iterative solving method under the combined action of gravity-gradient force and thermal load. Based on the above method, an empirical formula for the steady configuration involving multiple parameters is developed to solve the problem of rapid and accurate prediction of static configurations of large-scale spacecraft under different assembly states. The numerical results show that the proposed method can obtain highly accurate and stable solutions with only a few iterations. Additionally, it sheds light on the impact of spacecraft configuration asymmetry in the space force-thermal environment. Parameter analysis reveals that increasing the spacecraft’s length significantly amplifies the geometric nonlinearity of the structure, and adjusting the spacecraft’s attitude effectively constrains its deformation in the face of force-thermal conditions.

In order to monitor and predict the failure of water-saturated rocks effectively, such as landslides, sudden mud flows, and debris flows, which are geological disasters, understanding the effect of water on infrared radiation is crucial. To investigate this influence, infrared monitoring experiments were conducted on intact sandstones and sandstones with pre-set crack, each with varying water content, under uniaxial compression condition. The infrared precursor information of water-bearing rocks was quantitatively discussed, and the spatiotemporal variations in infrared radiation were analyzed. The temperature distribution and energy evolution patterns during rock failure were also examined. The results show that the peak stress, total strain energy, and failure intensity of water-bearing rock under uniaxial loading are significantly lower than those of dry rock, which is one reason for the reduced infrared radiation temperature (IRT) in water-bearing rock samples. On the basis of the maximum and minimum changes in the IRT during rock loading and failure, the “ΔMax-ΔMin change characteristic” is proposed as an infrared precursor of rock failure. For dry sandstone, the precursor information typically exhibits “sudden increase-sudden increase” or “sudden increase-stable fluctuation”, whereas for water-bearing sandstone, it consistently shows a “sudden increase-sharp decrease”. Additionally, statistical analysis reveals a gradual increase in the frequency of high-temperature intervals during the failure process of dry sandstone, whereas the frequency of low-temperature intervals increases for water-bearing rock. This indicates that water reduces the infrared radiation intensity emitted during rock loading. Elucidating the impact of water on infrared radiation is crucial for guiding the use of infrared technology in monitoring the failure of water-bearing rocks.

Inerter is a basic two-terminal dynamic element. To explore the theory of inerter and obtain new mode control method of large unmanned underwater vehicle propulsion motor floating raft system, novel accurate mode control based on inerter array is proposed. First, accurate mode control based on triangular inerter array is researched. Then, method of accurate mode control based on rectangular inerter array is explained. Then, accurate mode control based on cross inerter array is researched. Dynamic models and accurate mode control methods are verified by experiments. The percentage deviations between experimental and theoretical natural frequencies are within 12%. It is concluded that accurate mode control based on inerter array is effective. Triangular inerter array and rectangular inerter array with equal inertances and nonzero distances must change all points to change a mode. Isosceles triangular inerter array which contains zero distance and cross inerter array need to change two points to change a torsional mode. Inerter arrays with a centroid inerter can accurately change the translational mode.

Helicoidal schemes and designs in biological composite constructions enable them to absorb high-impact energy with amazing efficiency and offer exceptional resistance against damage. However, little research has been done on how reorienting and redirecting fibers inside a helicoid structure’s matrix affects the structure’s response and mechanical performance. This study is innovative in that it uses isogeometric analysis in conjunction with modified first-order strain theory to examine the forced and free oscillation response of a doubly curved shallow shell made of bio-inspired helicoid laminated composite (B-iHLC) under low-velocity impact load in a hygro-thermal environment. The B-iHLC shallow shell lying on a visco-Pasternak medium is defined by two stiffness coefficients and one damping coefficient. In this article, the impact load model is described analytically using a single spring-mass model. The equilibrium equations of the shell are derived based on Hamilton’s Principle, and then Newmark’s direct integration approach is used to derive the transient responses of the B-iHLC shell and load during the collision. A series of numerical comparisons with reputable publications is performed to assess the accuracy of the model and the article’s calculation technique. The validity of the article’s model and methodology is verified by conducting numerical comparisons with well-regarded publications. These discoveries may be used in the building of civil works and military applications when the shell is exposed to extreme forces.

In this paper, we propose a high-order energy-conserving semi-Lagrangian discontinuous Galerkin (ECSLDG) method for the Vlasov-Ampère system. The method employs a semi-Lagrangian discontinuous Galerkin scheme for spatial discretization of the Vlasov equation, achieving high-order accuracy while removing the Courant-Friedrichs-Lewy (CFL) constraint. To ensure total energy conservation, we incorporate the energy-conserving technique proposed by Liu et al. Temporal accuracy is further enhanced through a high-order operator splitting strategy, yielding a method that is high-order accurate in both space and time. The resulting ECSLDG scheme is unconditionally stable and conserves both mass and energy at the fully discrete level, regardless of spatial or temporal resolution. Numerical experiments demonstrate the accuracy, stability, and conservation properties of the proposed method. In particular, the method achieves more accurate enforcement of Gauss’s law and improved numerical fidelity over low-order schemes, especially when using a large CFL number.

Minute amounts of long-chain flexible polymers dissolved in fluid flows can significantly alter the flow behaviors, including polymer drag reduction in wall-bounded turbulence and elastic turbulence in low Reynolds number flow. Polymer-turbulence interaction, a combination of two fields with many interacting degrees of freedom deviated far from equilibrium, is the key to understanding these intriguing phenomena. In this paper, we review the recent progress of polymer-turbulence interaction in homogeneous isotropic turbulence. For integrity, we first list the governing equations for the flow of a dilute polymer solution. Afterwards, we summarize related theories for the critical length scale below which the energy cascade of Newtonian turbulence is affected by polymers. We then review the theoretical, experimental, and numerical results about the scaling and statistical properties in those affected range of scales. We also include the implications of these results for polymer drag reduction in wall-bounded turbulence. The review has ended up with conclusions from our present understanding and outlooks for future work.

In this paper, a symplectic finite element method (SFEM) for linear Hamiltonian system is proposed. First, the SFEM is derived by applying the finite element method to the linear Hamiltonian equation, and it is shown to strictly preserve the symplectic structure. Furthermore, the implementation of the high-order iterative scheme is achieved through mathematical software. In addition, the flexibility of SFEM for linear Hamiltonian system is analyzed. Several numerical examples verify the excellent performance of SFEM in structural dynamic response problems and prove that SFEM offers significant advantages over traditional numerical methods due to its ability to maintain energy conservation during long-term dynamic simulation, as well as its superior stability.

Intraocular pressure (IOP) is a key parameter to diagnose glaucoma disease and assess the treatment effect of cornea after refractive surgery. Current refractive surgeries inevitably change the configuration of the cornea, making it difficult to measure IOP accurately using conventional methods. The prediction method proposed in this article can accurately measure the IOP after refractive surgery. In this study, firstly, the finite element models of cornea free of IOP depicted by various vertex height, thickness, and radius are established, and the deformation of the cornea under different IOP is predicted. Based on the dataset obtained from the numerical simulations and the multi-layer perceptron neural network algorithm, two prediction models for the vertex height and thickness of the cornea free of IOP and for the configuration under IOP are developed, and a prediction method for IOP is then proposed by combining the two models. Following the similar way, two prediction models respectively for the parameters of the presumptive initial configuration of the cornea to undergo refractive surgery and for those of the cornea after surgery are constructed, and a prediction method for IOP of cornea after the surgery is presented. The validity of the prediction methods for regular IOP and that after refractive surgery is demonstrated using the clinical data from some volunteers. The proposed methods provide an efficient prediction method for regular IOP and that after refractive surgery.