Drum instability of thinning spinning ultra thin-walled tubes with large diameter-to-thickness ratio

In order to explore drum instability problems of thinning spinning ultra thin-walled tubes with large diameter-to-hickness ratio, experiments of thinning spinning ultra thin-walled tubes with different clearances between the mandrel and the tube were carried out. The phenomena of drum instability were analyzed. Drum instability mechanism was studied. The important influence of the mandrel-locked ring on stable thinning spinning was found. Besides, two important parameters, namely drum ratio and drum stiffness, were proposed to characterize the drum instability of spinning ultra thin-walled tubes with large diameter-to-thickness ratio. What's more, numerical simulations were applied to explore the influences of different clearance ratios and diameter-to-thickness ratios on the drum instability. As a result, it is found that the mandrel-locked ring is the key to the stability and precision of spinning; drum ratio can reflect the degree of the deformation of the tubes; drum stiffness is a comprehensive index to measure the influences of the tube's own parameters on the spinning instability; both the clearance ratio and diameter-thickness ratio have significant influences on the drum ratio and drum stiffness.

Study on semi-active control of mega-sub controlled structure by MR damper subject to random wind loads

The recently proposed mega-sub controlled structure （MSCS）, a new type of structure associated with the design and construction of super-tall buildings, has attracted the attention of designers for use in enhancing the control effectiveness in mega-frame buildings. In this paper, a dynamic equation and method to assemble parameter matrixes for a mega-sub controlled structure under random wind loads is presented. Semi-active control using magnetorheological dampers for the MSCS under random wind loads is investigated, and is compared with a corresponding system without dampers. A parametric study of the relative stiffness ratio and relative mass ratio between the mega-frame and the substructures, as well as the additional column stiffness ratio that influences the response control effectiveness of the MSCS, is discussed. The studies reveal, for the first time, that different control mechanisms exist. The results indicate that the proposed structure employing semi-active control can offer an effective control mechanism. Guidelines for selecting parameters are provided based on the analytical study.

Higher mode effects in hinged wall with BRBsin base-frame structures using distributed parameter models

To investigate the effect of higher modes on the displacement and inner forces in HWBB(hinged wall with buckling-restrained braces in base)-frame structure,distributed parameter models for both the HWBB-hinged frame structure and the HWBB-MRF(moment resisting frame)structure are built.The hinged wall is simplified as a flexural beam.BRBs(bucking-restrained braces)are simplified to a rotational spring.MRF is simplified to a shear beam.Vibration equations of distributed parameter models are derived.Natural periods,natural modes of vibration,inner forces and displacements of the distributed parameter models are derived based on the vibration equations using numerical methods.The effect of the relative stiffness ratio and the rotational stiffness ratio on the higher mode effects is investigated.For elastic structures,the global displacement and shear in MRF are predominantly controlled by the first mode,while the shear and bending moment in the wall are significantly affected by higher mode effects.The effect of the yielding of BRB on the inner forces distribution in the HWBB-hinged frame is investigated.The results indicate that the first mode will no longer contribute to the inner forces and the contribution from higher modes to inner forces increases after the BRBs yield.Displacement is not sensitive to higher mode effects and it is controlled by the first mode after the BRBs yield.Parameter analysis demonstrates that the displacement amplitudes are reduced with the increase in the flexural stiffness of the wall before the flexural stiffness reaches a certain value.The first three periods decrease with the increase in the rotational stiffness.With the increase in the rotational stiffness ratio,the contribution from the first mode decreases while contributions from both the second mode and third mode increase.

Elastic stability of shallow pin-ended parabolic arches subjected to step loads

Buckling could be induced when shallow arches were subjected to vertical step loads. In-plane static and dynamic buckling of shallow pin-ended parabolic arches with a horizontal cable was investigated. Based on the equations of motion derived from Hamilton's principle, nonlinear equilibrium equations and static buckling equilibrium equations were deduced. Through the pseudo-static analysis, approximate solutions to the lower and upper dynamic buckling loads under step loads were obtained, for shallow parabolic arches. The results show that dynamic buckling and snap-through buckling are impossible when modified slenderness ratio λ<λc and λ>λs, where λc and λs denote critical slenderness ratios of bucking and snap-through buckling, respectively; effects of the stiffness of the horizontal cable on the dynamic buckling are significant; and the dynamic buckling loads under a equivalent central concentrated step load are lower than the loads under a distributed load appreciably.

Perturbation analysis on post-buckling behavior of pile

The nonlinear large deflection differential equation, based on the assumption that the subsoil coefficient is the 2nd root of the depth, was established by energy method. The perturbation parameter was introduced to transform the equation to a series of linear differential equations to be solved, and the deflection function according with the boundary condition was considered. Then, the nonlinear higher-order asymptotic solution of post-buckling behavior of a pile was obtained by parameter-substituting. The influencing factors such as bury-depth ratio and stiffness ratio of soil to pile, slenderness ratio on the post-buckling behavior of a pile were analyzed. The results show that the pile is more unstable when the bury-depth ratio and stiffness ratio of soil to pile increase, and although the buckling load increases with the stiffness of soil, the pile may ruin for its brittleness. Thus, in the region where buckling behavior of pile must be taken into account, the high grade concrete is supposed to be applied, and the dynamic buckling behavior of pile needs to be further studied.

Catastrophic destabilization of tunnel under rocks slipping in faultage

The model of catastrophic destabilization of tunnel under rock slipping in fault zone based on catastrophic theory and the potential function of fault movement were pre- sented.On the basis of the results above,through Taylor series expansion of the equation of equilibrium surface,its standard form was obtained.Analysis show that catastrophic destabilization of tunnel will occur only when stiffness ratio between elastic sector and strain weakening sector of soft rocks was larger than or equal to 1.On the other hand, sliding behavior and evolution path of fault were directly affected by exogenous process, and it was a major extraneous factor which leads to catastrophic destabilization of tunnel. In the condition of system catastrophe could be generated,if external forces vary from smaller to larger,firstly,fault sticks or creeps,and secondly,when external force equal to or larger than critical value,fault turns to slip suddenly.Inverse,if external forces vary from larger to smaller,fault smoothly slips firstly,when external force equal to or smaller than critical value,and fault turns to stick or creep suddenly.

Relationship between Neutrophil-to-Lymphocyte Ratio and Pulse Wave Velocity in Young Patients with Systemic Lupus Erythematosus

Background： The incidence of atherosclerosis-related myocardial infarction can be as much as 50-fold greater in young patients with systemic lupus e~,thematosus （SLE） than in age-matched controls. There are several explanations for this phenomenon, all of which result in a chronic state of low-grade inflammation. Recently, the neutrophil-to-lynlphocyte ratio （NLR） has been proposed as a useliil biomarker of inflammation. Pulse wave velocity （PWV） is a reliable indicator of vascular damage and atherosclerosis. There is a paucity of data concerning the relationship between NLR and atherosclerosis as measured by PWV in patients with SLE. This study aimed to verify whether there is a positive correlation between NLR and PWV and to explore factors that influence PWV in young SLE patients. Methods： A total of 90 female patients with SLE were enrolled in this cross-sectional investigation. Traditional and nontraditional cardiovascular risk factors were assessed on the same day that brachial-ankle PWV （baPWV） was examined. The patients were divided into three groups according to their mean baPWV values： patients whose mean baPWV value was lower than the first tertile were placed in Group 1 ： patients whose mean baPWV value was between the first tertile and the second tertile were placed in Group 2： and patients whose mean baPWV value was higher than the second tertile were placed in Group 3. SPSS 20.0 was used to perform all statistical analyses in this study. Both univariate linear regression and multivariate regression models were utilized to analyze the association between NLR and arterial stiffness. Results： Systolic blood pressure, diastolic blood presstire （DBP）. and triglycerides were all significantly different among Groups 1,2, and 3 （ 111.90 ± 12.85 mmHg vs. 114.60 ± 12.88 mmHg vs. 129.43 ±16.21 mmHg, P 〈 0.001 ： 68.77 ± 8.63 mmHg vs. 71.87 ± 9.77 mmHg vs. 82.57 ± 14.89 mmHg, P 〈 0.001 ; and 1.44 [0.91-2.47] mmol/L vs. 0.98 [0.78-1.26] mmol/L vs. 2.20 [0.94-3.66] mmol/L P = 0.030： respectively）, as were creatinine （57.50 [52.00-69.00] mmol/L vs. 55.50 [49.00-64.00] mmol/L vs. 64.00 [56.00-86.00] mmol/L P = 0.045） and blood urea nitrogen （4.27 [3.79-6.22] mmol/L vs. 4.16 [3.47-4.84] mmol/L vs. 5.88 [4.04-8.19] mmol/L, P = 0.011 ）. NLRs were significantly different among Groups 1, 2, and 3 （2.16 [1.56-3.42] vs. 3.12 [1.91-4.19] vs. 5.29 [2.63-7.25], P = 0.001）. N LR, together with DBP and the SLE disease activity index, independently predicts PWV. Conclusions： This study demonstrated that there was a positive correlation between NLR and PWV. Moreover, we found that disease activity and DBP were also positively correlated with PWV.

Discrete element modeling of the effect of particle size distribution on the small strain stiffness of granular soils

Discrete element modeling was used to investigate the effect of particle size distribution on the small strain shear stiffness of granular soils and explore the fundamental mechanism controlling this small strain shear stiffness at the particle level. The results indicate that the mean particle size has a negligible effect on the small strain shear modulus. The observed increase of the shear modulus with increasing particle size is caused by a scale effect. It is suggested that the ratio of sample size to the mean particle size should be larger than 11.5 to avoid this possible scale effect. At the same confining pressure and void ratio, the small strain shear modulus decreases as the coefficient of uniformity of the soil increases. The Poisson＇s ratio decreases with decreasing void ratio and increasing confining pressure instead of being constant as is commonly assumed. Microscopic analyses indicate that the small strain shear stiffness and Poisson＇s ratio depend uniquely on the soil＇s coordination number.

Fatigue crack propagation of new aluminum lithium alloy bonded with titanium alloy strap

A new type of aluminum lithium alloy （Al–Li alloy） Al–Li–S–4 was investigated by test in this paper. Alloy plate of 400 mm · 140 mm · 6 mm with single edge notch was made into samples bonded with Ti–6Al–4V alloy （Ti alloy） strap by FM 94 film adhesive after the surface was treated. Fatigue crack growth of samples was investigated under cyclic loading with stress ratio （R） of 0.1 and load amplitude constant. The results show that Al–Li alloy plate bonded with Ti alloy strap could retard fatigue crack propagation. Retardation effect is related with width and thickness of strap. Flaws have an observable effect on crack propagation direction.