Abstract: The problems of aircraft multi-body separation, such as airborne weapon delivery separation, spacecraft series/parallel stage separation, fairing separation and submunition scattering, are common in the aerospace field at present. Safe and controllable multi-body separation is an important prerequisite for aircraft to perform aerospace tasks. In recent years, with the expansion of flight boundaries and the diversification of flight missions, aircraft are facing more complex multi-body separation scenarios, so it is necessary to carry out refined multi-body separation scheme design, which puts forward higher requirements for the fidelity and fineness of multi-body separation numerical simulation. In recent years, CFD has made great progress in high-fidelity simulation of complex scenes, aiming at the extremely complex and challenging multi-body separation problem. In this paper, the latest research progress of high-fidelity numerical simulation methods and applications of aircraft multi-body separation is reviewed and prospected. Firstly, the refined simulation methods of aircraft multi-body separation are summarized, including coupled grid dynamic optimization technology, coupled separation vortex simulation method and high-precision time-marching coupling algorithm. Secondly, the coupling simulation method of aircraft multi-body separation under complex constraints/flow field/control and its application are introduced. Then, the understanding of complex mechanism of dynamic interference of aircraft multi-body separation in typical complex scenes is introduced. Finally, the existing problems and future development direction of high fidelity numerical simulation of aircraft multi-body separation are pointed out.
Li H, Cui P C, Jia H Y, Tang J, Zhang J, Gong X Q, Wu X J, Zhang C, Zhang P H, Zhou N C, Zhang Y B. Numerical simulation method and application of aircraft multi-body separation. AdvancesinMechanics, in press. doi: 10.6052/1000-0992-24-040.
Abstract: Researching the coupling vibration of wind-train-bridge systems is one of the crucial means to ensure the safe operation of trains on bridges under strong wind conditions. In the last two decades, domestic and foreign scholars have conducted extensive research in this field, accumulating fruitful research results. The study of the coupling vibration of the wind-train-bridge system mainly includes three aspects: the aerodynamic characteristics of the train-bridge system, the calculation of the coupling vibration of the wind-train-bridge system, and the evaluation, prevention, and control of driving safety. Firstly, the primary purpose of studying the aerodynamic characteristics of the train-bridge system is to analyze the aerodynamic interference mechanism of the train-bridge system and accurately obtain the wind loads acting on the train and bridge. Depending on whether the train on the bridge is stationary or moving, it can be divided into two cases, i.e., stationary train and moving train. Secondly, on the basis of obtaining wind loads on the train-bridge system, it is necessary to solve the dynamic response of the wind-train-bridge system to obtain the response time-history curve of the entire process of the train passing through the bridge. This research mainly involves modeling methods for the train-bridge system, solving theories of wind-train-bridge coupling vibration equations, and using efficient calculation methods. Thirdly, based on the obtained dynamic response, the ultimate goal is to evaluate the driving safety of trains on the bridge and propose prevention and control measures. This research mainly includes the evaluation indicators and methods of driving safety and the main preventive and control measures for ensuring the driving safety of trains under strong wind conditions. Finally, in conjunction with the main issues existing in the field of the coupling vibration of wind-train-bridge systems, prospects for future research directions are provided to promote the development of this research field.
Han Y, Hu P, Wang L D, Liu H Y, Cai C S. Research Advances in Wind-Train-Bridge Coupling Vibration. AdvancesinMechanics, in press. doi: 10.6052/1000-0992-24-032.
Abstract: This paper is intended to reconcile the stress-based and strain-based formulations for material failure criteria, where a longstanding and deep division is present. The two approaches do not naturally agree with each other, and they not genuinely complement each other, either. Most popular criteria are stress-based when originally proposed, including the maximum stress, Tresca, von Mises, Raghava-Caddell-Yeh and the Mohr criteria. Their formulations are unique and self-consistent, i.e. capable of reproducing the input data. Their strain-based counterparts, with the maximum strain criterion being considered as the strain-based counterpart of the maximum stress criterion, are neither unique nor necessarily self-consistent. It has been proven that the self-consistent ones reproduce their respective stress-based counterparts identically in effect with a disadvantage of requiring an additional material property to apply, without a single benefit. For the Mohr criterion as a special case, a strain-based counterpart is simply infeasible in general. All undesirable features of strain-based criteria are rooted in a single source: the failure strains can only be measured under a uniaxial stress state, which corresponds to a combined strain state in general, not a uniaxial strain state! Given the arguments presented, the reconciliation proves to be biased completely towards the stress-based side if mathematics, logic and common sense prevail over perception and prejudice.
Li S G. Stress or Strain?. AdvancesinMechanics, in press. doi: 10.6052/1000-0992-24-035.
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