共查询到20条相似文献，搜索用时 15 毫秒
1.
畸变屈曲作为控制冷弯薄壁卷边槽钢柱承载力的重要模式之一，正逐步受到国内外研究人员的重视。本文针对畸变屈曲的变形特征，通过12根试件在不同连杆布置方式下的轴心受压和偏心受压试验研究，验证在冷弯薄壁卷边槽钢的卷边处设置连杆用以提高其承载力这一方法的有效性．得出了最有效的连杆布置方式。同时，采用有限元软件ABAQUS对试件进行了模拟分析，探讨了初始缺陷、双向偏心等因素的影响。 相似文献
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Using Lu's continuation theorem, the extension one of Manásevich-Mawhin, we study the existence of periodic solutions for p-Laplacian neutral Liénard equation of the form
(?p(x(t)-cx(t-σ))′)′+f(x(t))x′(t)+β(t)g(x(t-τ(t))=e(t). 相似文献
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By means of Mawhin's continuation theorem, we study a third-order p-Laplacian differential equation
(?p(u″(t)))′+f(t,u′(t),u″(t))+g(t,u(t-τ(t)))=e(t). 相似文献
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Guy Jumarie 《Journal of The Franklin Institute》2010,347(10):1797-1813
The usual model for (Poissonian) linear birth-death processes is extended to multiple birth-death processes with fractional birth probabilities in the form λi(Δt)α+o((Δt)α, 0<α<1. The probability generating function for the time dependent population size is provided by a fractional partial differential equation. The solution of the latter is obtained and comparison with the usual model is made. The probability of ultimate extinction is obtained. One considers the special case of fractional Poissonian processes with individual arrivals only, and then one outlines basic results for continuous processes defined by fractional Poissonian noises. The key is the Taylor’s series of fractional order f(x+h)=Eα(hαDxα)f(x), where Eα(·) is the Mittag-Leffler function, and Dxα is the modified Riemann-Liouville fractional derivative, as previously introduced by the author. 相似文献
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In this paper, we use the coincidence degree theory to establish new results on the existence of T-periodic solutions for the Rayleigh equation with two deviating arguments of the form
x″+f(x′(t))+g1(t,x(t-τ1(t)))+g2(t,x(t-τ2(t)))=p(t). 相似文献
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By means of Mawhin's continuation theorem, we study a kind of fourth-order p-Laplacian neutral functional differential equation with a deviating argument in the form:
(φp(x(t)−cx(t−δ))″)″=f(x(t))x′(t)+g(t,x(t−τ(t,|x|∞)))+e(t). 相似文献
7.
国家游泳中心"水立方"的多面体空间刚架结构中.采用了配合方钢管、且承受轴力与弯矩共同作用的焊接空心球节点.本文的主要目的是通过试验研究轴力、弯矩及两者共同作用下方钢管焊接空心球节点的受力性能和承载能力,为理论公式提供佐证,共选择了3种不同规格球径的6个节点.本文较详细地介绍了在轴力、弯矩及两者共同作用下方钢管焊接空心球节点模型试验过程,包括为实现轴力与弯矩共同作用的荷载条件而设计的试件、加载装置以及测点布置、加载方案等.对于模型的应力发展过程及试验结果,也逐一进行了分析.试验结果表明,有限元计算的可靠性是有保证的:节点承载力随弯矩的增大而减小. 相似文献
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AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (fc), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above fc. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H+] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5fc). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H+] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 Vpp potential, and voltage dependency was explored from 3.5 to 7.5 Vpp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position. 相似文献
11.
Chien-Chun Kung 《Journal of The Franklin Institute》2008,345(8):851-876
In this paper, an analytic solution of nonlinear H∞ robust controller is first proposed and used in a complete six degree-of-freedom nonlinear equations of motion of flight vehicle system with mass and moment inertia uncertainties. A special Lyapunov function with mass and moment inertia uncertainties is considered to solve the associated Hamilton-Jacobi partial differential inequality (HJPDI). The HJPDI is solved analytically, resulting in a nonlinear H∞ robust controller with simple proportional feedback structure. Next, the control surface inverse algorithm (CSIA) is introduced to determine the angles of control surface deflection from the nonlinear H∞ control command. The ranges of prefilter and loss ratio that guarantee stability and robustness of nonlinear H∞ flight control system implemented by CSIA are derived. Real aerodynamic data, engine data and actuator system of F-16 aircraft are carried out in numerical simulations to verify the proposed scheme. The results show that the responses still keep good convergence for large initial perturbation and the robust stability with mass and moment inertia uncertainties in the permissible ranges of the prefilter and loss ratio for which this design guarantees stability give same conclusion. 相似文献
12.
In this paper, we use Leggett-Williams multiple fixed point theorem to obtain different sufficient conditions for the existence of at least three nonnegative periodic solutions of the first order functional differential equation of the form
y′(t)=-a(t)y(t)+λf(t,y(h(t))). 相似文献
13.
采用数值模拟方法,以力学性能优异的C-BAR筋代替钢筋混凝土短柱的纵筋及箍筋,提高了短柱的轴压承载力,总结了C-BAR筋代替钢筋的一般规律性,并以实例证明此代替可一定程度地减轻结构的自重。 相似文献
14.
Liuqing Yang Ce Zhang Xiwen Yu Yingfang Yao Zhaosheng Li Congping Wu Wei Yao Zhigang Zou 《国家科学评论(英文版)》2021,8(8)
Aerospace milestones in human history, including returning to the moon and manned Martian missions, have been implemented in recent years. Space exploration has become one of the global common goals, and to ensure the survival and development of human beings in the extraterrestrial extreme environment has been becoming the basic ability and technology of manned space exploration. For the purpose of fulfilling the goal of extraterrestrial survival, researchers in Nanjing University and the China Academy of Space Technology proposed extraterrestrial artificial photosynthesis (EAP) technology. By simulating the natural photosynthesis of green plants on the Earth, EAP converts CO2/H2O into fuel and O2 in an in-situ, accelerated and controllable manner by using waste CO2 in the confined space of spacecraft, or abundant CO2 resources in extraterrestrial celestial environments, e.g. Mars. Thus, the material loading of manned spacecraft can be greatly reduced to support affordable and sustainable deep space exploration. In this paper, EAP technology is compared with existing methods of converting CO2/H2O into fuel and O2 in the aerospace field, especially the Sabatier method and Bosch reduction method. The research progress of possible EAP materials for in-situ utilization of extraterrestrial resources are also discussed in depth. Finally, this review lists the challenges that the EAP process may encounter, which need to be focused on for future implementation and application. We expect to deepen the understanding of artificial photosynthetic materials and technologies, and aim to strongly support the development of manned spaceflight. 相似文献
15.
碳纤维加固混凝土柱通过横向约束作用,提高柱的轴心受压承载力,增加柱的延性。利用碳纤维材料作围套加固混凝土轴心抗压柱,具有施工简单、抗腐蚀能力强、约束效果好等优点。 相似文献
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《Journal of The Franklin Institute》2019,356(11):5611-5629
In the rapidly expanding size and complexity of the electricity network, automatic generation control (AGC) is contemplated to be the most remarkable option for offering good quality electric power supply to the end users. An AGC system entails highly vigorous, competent and intelligent control technique to deliver a healthy power under stochastic nature of consumers’ power demand. Hence, in this paper, a hybrid fuzzy fractional order proportional integral-fractional order proportional derivative (FFOPI-FOPD) controller is proposed as a new expert control technique to tackle AGC profitably in isolated and interconnected multi-area power systems. A recently developed imperialist competitive algorithm (ICA) is utilized for the optimization of the output gains (KP/KP1/KI/KD) and other parameters such as order of integrator (λ) and differentiator (μ) of FFOPI-FOPD controller exercising integral of squared error criterion. The proposed technique is firstly implemented on 1-area thermal system, then to express its potential and extensibility, the work is extended to 2-area hydro-thermal and 3-area thermal power systems widespread in the literature. The eminence of the method is betokened by comparing the results with the various newly published control methodologies and FPI/FFOPI controller designed in the study via ICA in terms of minimum values of various error criteria and undershoots/overshoots/settling times of frequency and tie-line power deviations following a sudden load demand in an area. The sensitivity analysis substantiates that the suggested controller is robust and performs staunchly under the wide variations in the system parameters, random load pattern and in the company of physical constraints to produce more clean electricity. 相似文献
18.
Srinivas Velugotla Steve Pells Heidi K. Mjoseng Cairnan R. E. Duffy Stewart Smith Paul De Sousa Ronald Pethig 《Biomicrofluidics》2012,6(4)
Assessment of the dielectrophoresis (DEP) cross-over frequency (fxo), cell diameter, and derivative membrane capacitance (Cm) values for a group of undifferentiated human embryonic stem cell (hESC) lines (H1, H9, RCM1, RH1), and for a transgenic subclone of H1 (T8) revealed that hESC lines could not be discriminated on their mean fxo and Cm values, the latter of which ranged from 14 to 20 mF/m2. Differentiation of H1 and H9 to a mesenchymal stem cell-like phenotype resulted in similar significant increases in mean Cm values to 41–49 mF/m2 in both lines (p < 0.0001). BMP4-induced differentiation of RCM1 to a trophoblast cell-like phenotype also resulted in a distinct and significant increase in mean Cm value to 28 mF/m2 (p < 0.0001). The progressive transition to a higher membrane capacitance was also evident after each passage of cell culture as H9 cells transitioned to a mesenchymal stem cell-like state induced by growth on a substrate of hyaluronan. These findings confirm the existence of distinctive parameters between undifferentiated and differentiating cells on which future application of dielectrophoresis in the context of hESC manufacturing can be based. 相似文献
19.
This study presents a model for predicting the low-cycle fatigue life of steel reinforcing bars using Artificial Neural Network (ANN). A Radial Basis Function (RBF) artificial neural network topology with two additional hidden layers and four neurons (processing elements) in each of these layers is used. The input parameters for the network are the maximum tensile strain (εs,max) and the strain ratio (R) and the output of the ANN is the number of cycles to fatigue failure (Nf). Low-cycle fatigue tests were conducted by the authors in a previous study for different types of steel reinforcing bars subjected to different strain amplitudes and at different strain ratios. The data resulted from these tests were used to train and test the ANN. It is observed that the ANN prediction of low-cycle fatigue life of steel reinforcing bars is within ±2 cycles of the experimental results for the majority of the test data. A parametric study had been carried out to investigate the effect of maximum strain and strain ratio on the fatigue life of steel reinforcing bars. It is concluded that both the strain ratio and the maximum strain have significant effect on the low-cycle fatigue life of such bars, especially at low values of maximum strain and their effect should be considered in both analysis and design. Other observations and conclusions were also drawn. 相似文献
20.
Recent research in concrete analysis and design has revealed that the shear capacity contributed by concrete correlates well with the neutral axis depth. While nonlinear analysis calculation of the neutral axis depth is trivial for reinforced concrete beams, it is iterative for prestressed concrete beams and does not lend itself to straightforward hand calculations. In this study, a program is developed to simulate the response of prestressed concrete rectangular sections subjected to monotonic bending taking into account cracking, yielding and ultimate states. This program is used to benchmark a simplified analytical procedure devised to perform the same task by hand. Accordingly, critical observations made to a large pool of experimental and analytical results reveal that the moment-curvature and moment-extreme fiber strain can be accurately modeled as trilinear relationships. The four key points that define the trilinear functions (initial, cracking, yielding and ultimate) may be computed analytically from simple equations derived based on consistent assumptions with the true behavior. Once the simplified analysis is performed, the computation of the neutral axis depth becomes a simple hand calculation. A parametric study was performed to further simplify the analytical procedure by computing the four key points that define the trilinear functions through linear relationships that were derived based on regression analysis of a large number of beam solutions. The neutral axis depth was calculated using the analytical and the simplified procedures for three beams with different ratios of prestressing steel and concrete strength. The results compared well with the iterative numerical procedure. 相似文献