Theoretical study on the nonlinear behavior of a fluid micro-vibration isolator

Vibration isolation is an important method of spacecraft vibration control, and the study of vibration isolation performance (VIP) is the theoretical basis to design the interior structure of isolator and analyze its transmissibility characteristics. In the present study, a new type of fluid micro-vibration isolator used for space engineering is investigated, thus its nonlinear multi-parameter model whose pth power damping and qth power stiffness are placed in series is firstly constructed. After the application of harmonic balance method (HBM), the force and absolute displacement transmissibility curves under different parameters are obtained, and the corresponding transmissibility characteristics are estimated based on self-defined evaluation indices of VIP. Besides, the effects of some key factors, e.g., excitation amplitude and stiffness ratio, on the VIP are also analyzed. The results show that if the isolator is excited by external force in orbit, the linear model can be approximately used to analyze the VIP. However, if the isolator is excited by foundation displacement during the launch stage, only the nonlinear model can accurately describe its vibration behavior. Moreover, the numerical algorithm Runge-Kutta method is adopted to validate the above results, and a stability analysis is also carried out to show their practicability. Finally, an actual application of the nonlinear model is accomplished with the use of an optimization method called generalized pattern search (GPS) algorithm. The presented theory and method can also provide a reference and a theoretical basis for the design and engineering application of this type of fluid micro-vibration isolators

Experimental research and numerical simulation on vibration characteristics of a rectangular plate structure in fast time-varying thermal environments

Plate attitude control structures such as rudders and vertical tails of high-speed aircraft are faced with the compound effect of fast time-varying thermal environments and vibration during the high maneuvering flight. In this paper, a thermal/vibration test system was established by combining a transient aerodynamic heating simulation system with a vibration test system. A rectangular plate structure made of nickel-based stainless steel was tested at different heating rates and its modal frequencies in fast time-varying thermal environments were obtained. Numerical calculation was performed accordingly. The calculated results coincide well with the experimental results, verifying the credibility and effectiveness of the experimental methods. The research results can provide an important test method and reference basis for the dynamic performance analysis and safety design for the plate-like structures of high-speed aircraft in fast time-varying thermal environments

Experimental investigation of high temperature thermal-vibration characteristics for composite wing structure of hypersonic flight vehicles

A thermal-vibration test system is established by combining the high-temperature transient heating simulation system and vibration test apparatus, and this system can carry out experimental research on the thermal modal of high-temperature-resistant composite wing structure of hypersonic flight vehicles under high temperature environment with 1100°C. The vibration signals of the composite wing structure in high-temperature environments are transmitted to non-high temperature field by using self-developed extension configurations and then the vibration signals are measured and identified by using ordinary acceleration sensors. Based on a time-frequency joint analysis technique, the experimental data is analyzed and processed to obtain the key vibration characteristic parameters of composite wing structure, such as the natural frequency and mode shapes, in a thermal-vibration coupled environment up to 1100°C. The experimental results provide an important basis for the dynamic performance analysis and safety design of composite wing structure under high-temperature thermal-vibration conditions

Theoretical study on the nonlinear behavior of a fluid micro-vibration isolator

Vibration isolation is an important method of spacecraft vibration control, and the study of vibration isolation performance (VIP) is the theoretical basis to design the interior structure of isolator and analyze its transmissibility characteristics. In the present study, a new type of fluid micro-vibration isolator used for space engineering is investigated, thus its nonlinear multi-parameter model whose pth power damping and qth power stiffness are placed in series is firstly constructed. After the application of harmonic balance method (HBM), the force and absolute displacement transmissibility curves under different parameters are obtained, and the corresponding transmissibility characteristics are estimated based on self-defined evaluation indices of VIP. Besides, the effects of some key factors, e.g., excitation amplitude and stiffness ratio, on the VIP are also analyzed. The results show that if the isolator is excited by external force in orbit, the linear model can be approximately used to analyze the VIP. However, if the isolator is excited by foundation displacement during the launch stage, only the nonlinear model can accurately describe its vibration behavior. Moreover, the numerical algorithm Runge-Kutta method is adopted to validate the above results, and a stability analysis is also carried out to show their practicability. Finally, an actual application of the nonlinear model is accomplished with the use of an optimization method called generalized pattern search (GPS) algorithm. The presented theory and method can also provide a reference and a theoretical basis for the design and engineering application of this type of fluid micro-vibration isolators

Taxonomic reconsideration of Prunus veitchii (Rosaceae)

Prunus veitchii was published in 1912 and was treated as a synonym of P. serrulata var. pubescens. The information about this taxon is relatively scarce. When consulting specimens of Prunus L., type materials of Prunus veitchii were found to belong to three taxa and P. veitchii, P. concinna, P. japonica var. zhejiangensis, C. jingningensis and C. xueluoensis were found to be conspecific. The taxonomic status of P. veitchii is reconsidered in the present paper. Morphometric analyses were performed to evaluate the significance of differences between P. veitchii and P. serrulata var. pubescens. The results show that the leaves of P. veitchii are significantly smaller and narrower than the leaves of P. serrulata var. pubescens and the peduncle and pedicels are shorter. According to the results of morphometric analyses, P. veitchii should be treated as a separate species. To address these results, a lectotype of P. veitchii is designated here and P. concinna, Cerasus jingningensis and C. xueluoensis are here designated as synonyms of P. veitchii

Review of research on evaluating the ecological security of cultivated land

Cultivated land provides fundamental land-related resources, and its ecological security is, thus, an important means of protecting it. The ecological security of cultivated land has emerged as an important and challenging area of research in recent years. In this study, we summarize the progress in research on the evaluation of the ecological security of cultivated land through visual analysis. We review the concepts, characteristics, driving factors, scales and methods of evaluation, technologies, and simulations used in the relevant literature. The results show that while the relevant concept has been preliminarily established, research on the ecological security of cultivated land remains in its infancy, and comprehensive work on the subject is lacking. The Prevalent research has mainly focused on analyzing the current situation, but lacks a dynamic analysis of the driving mechanism of the ecological security of cultivated land based on simulations. This has made it difficult to understand the spatiotemporal mechanism of the ecological security of cultivated land. Future research in the area should discuss the complex driving mechanism of interactions between the social economy system and the ecological system and focus on an integrated model to assess its dynamic spatial and multi-scale characteristics of ecological security of cultivated land because this can inform the theory of protecting cultivated land and the design of plans for land use to mitigate global climate change

Experimental investigation of high temperature thermal-vibration characteristics for composite wing structure of hypersonic flight vehicles

A thermal-vibration test system is established by combining the high-temperature transient heating simulation system and vibration test apparatus, and this system can carry out experimental research on the thermal modal of high-temperature-resistant composite wing structure of hypersonic flight vehicles under high temperature environment with 1100°C. The vibration signals of the composite wing structure in high-temperature environments are transmitted to non-high temperature field by using self-developed extension configurations and then the vibration signals are measured and identified by using ordinary acceleration sensors. Based on a time-frequency joint analysis technique, the experimental data is analyzed and processed to obtain the key vibration characteristic parameters of composite wing structure, such as the natural frequency and mode shapes, in a thermal-vibration coupled environment up to 1100°C. The experimental results provide an important basis for the dynamic performance analysis and safety design of composite wing structure under high-temperature thermal-vibration conditions

Revisiting the Marrow Metabolic Changes after Chemotherapy in Lymphoma: A Step towards Personalized Care

Purpose. The aims were to correlate individual marrow metabolic changes after chemotherapy with bone marrow biopsy (BMBx) for its potential value of personalized care in lymphoma. Methods. 26 patients (mean age, 58 ± 15 y; 13 female, 13 male) with follicular lymphoma or diffuse large B-cell lymphoma, referred to FDG-PET/CT imaging, who had BMBx from unilateral or bilateral iliac crest(s) before chemotherapy, were studied retrospectively. The maximal standardized uptake value (SUV) was measured from BMBx site over the same area on both initial staging and first available restaging FDG-PET/CT scan. Results. 35 BMBx sites in 26 patients were evaluated. 12 of 35 sites were BMBx positive with interval decrease in SUV in 11 of 12 sites (92%). The remaining 23 of 35 sites were BMBx negative with interval increase in SUV in 21 of 23 sites (91%). The correlation between SUV change over the BMBx site before and after chemotherapy and BMBx result was significant (P < 0.0001). Conclusions. This preliminary result demonstrates a strong correlation between marrow metabolic changes (as determined by FDG PET) after chemotherapy and bone marrow involvement proven by biopsy. This may provide a retrospective means of personalized management of marrow involvement in deciding whether to deliver more extended therapy or closer followup of lymphoma patients