16 research outputs found
Flutter analysis for bridge decks using Lattice Boltzmann Method
Aiming at using the Lattice Boltzmann Method for flutter analysis of the bridge decks, a fluid- structure interaction algorithm is developed within the framework of multiple ârelaxation- time Lattice Boltzmann Method. In the present algorithm, the unsteady fluid dynamics is computed by the extended two-dimensional Lattice Boltzmann Method by incorporating the dynamic Smagorinsky subgrid scale model, while the structure is modelled by an elastically suspended rigid body and its dynamic analysis is performed by using a RungeâKutta method. A staggered coupling strategy is adopted to couple the fluid solver and the structure solver. To demonstrate the applicability of the presented algorithm, flutter analyses of the Second Forth Road Bridge and the GuamĂĄ River Bridge are employed. The numerical results are compared with wind tunnel measurements. It is shown that the presented algorithm has a good prediction for the flutter onset velocities of the Forth Road Bridge and the GuamĂĄ River Bridge and thus indicates, to a certain extent, the applicability of the presented algorithm
Effect of Surcharge on the Stability of Rock Slope under Complex Conditions
In this paper, a general analytical expression for the factor of safety of the rock slope against plane failure is proposed,
incorporating most of the practically occurring under complex conditions such as depth of tension crack, depth of water
in tension crack, seismic loads and surcharge. Several special cases of this expression are established, which can be found
similarly to those reported in the literature. A detailed parametric analysis is presented to study the effect of surcharge on
the stability of the rock slope for practical ranges of main parameters such as depth of tension crack, depth of water in
tension crack, the horizontal seismic coefficient and the vertical seismic coefficient. The parametric analysis has shown
that the factor of safety of the rock slope decreases with increase in surcharge for the range of those parameters in this
paper. It is also shown that the horizontal seismic coefficient is the most important factor which effects on the factor of
safety in the above four influence factors. The general analytical expression proposed in this paper and the results of the
parametric analysis can be used to carry out a quantitative assessment of the stability of the rock slopes by engineers and
researchers
Suppressing the vortex-induced vibration of a bridge deck via suction
This paper presents experimental and numerical study with the objective of exploring the effect of suction control on vortex-induced vibration (VIV) of a bridge deck. The vertical and torsional responses of the model with or without suction control during this experiment were measured. The results demonstrate that the suction decreases the vibration amplitudes. The suction holes arranged on the undersurface near the leeward of the model has the best effect. To study the mechanism of the suction control, the aerodynamic stability of the model is analysed by the forced vibration method. The results demonstrate that the aerodynamic stability of the model is increased by the suction control
Flutter analysis for bridge decks using Lattice Boltzmann Method
Aiming at using the Lattice Boltzmann Method for flutter analysis of the bridge decks, a fluid- structure interaction algorithm is developed within the framework of multiple ârelaxation- time Lattice Boltzmann Method. In the present algorithm, the unsteady fluid dynamics is computed by the extended two-dimensional Lattice Boltzmann Method by incorporating the dynamic Smagorinsky subgrid scale model, while the structure is modelled by an elastically suspended rigid body and its dynamic analysis is performed by using a RungeâKutta method. A staggered coupling strategy is adopted to couple the fluid solver and the structure solver. To demonstrate the applicability of the presented algorithm, flutter analyses of the Second Forth Road Bridge and the GuamĂĄ River Bridge are employed. The numerical results are compared with wind tunnel measurements. It is shown that the presented algorithm has a good prediction for the flutter onset velocities of the Forth Road Bridge and the GuamĂĄ River Bridge and thus indicates, to a certain extent, the applicability of the presented algorithm
Syringin exerts antiâinflammatory and antioxidant effects by regulating SIRT1 signaling in rat and cell models of acute myocardial infarction
Abstract Introduction This study aimed to investigate the role of syringin in improving heart function during myocardial ischemia/reperfusion (I/R) and to determine whether the sirtuin 1/peroxisome proliferatorâactivated receptor gamma coactivator 1 alpha (SIRT1/PGCâ1α) pathway contributes to this cardioprotective effect in vivo and in vitro. Methods H9c2 cells were incubated with H2O2 for 12âh. The effect of syringin was assessed by measuring cell viability; the apoptotic rate; Keap1/NRF2/HOâ1 activation; and the levels of proinflammatory cytokines, oxidative products, and antioxidative enzymes. In addition, SIRT1 was silenced via short hairpin RNA (shRNA)âSIRT1 transfection to evaluate its involvement in syringinâmediated protection. Syringin rescued cells from H2O2âinduced reductions in viability, antioxidative enzyme levels, and NRF2/HOâ1 activation; likewise, syringin inhibited apoptosis, inflammation, and oxidative stress. We also created a rat model of I/R by ligating the left anterior descending coronary artery for 30âmin, followed by reperfusion for 12âmin. Syringin was then intraperitoneally injected, and the effect on infarct size and cardiac function was examined after 7 days. NRF2/HOâ1 activity and the levels of myocardial proinflammatory cytokines, oxidative products, and antioxidative enzymes were measured. Results In comparison to the untreated I/R group, the syringin treatment group exhibited improved cardiac function and reduced cardiac lesion and infarct size. Syringin administration also markedly reduced the levels of proinflammatory cytokines and reactive oxygen species and promoted antioxidative enzyme expression and NRF2/HOâ1 pathway activation. Conclusions Syringin may serve a protective role in animal and cell models of I/R by improving cardiac function, inhibiting the inflammatory response, and activating the antioxidative response
Synchronous Gastrointestinal Tumor and Abdominal Aortic Aneurysm or Dissection Treated with Endovascular Aneurysm Repair Followed by Tumor Resection
Objective. To evaluate the strategy in the management of patients with synchronous gastrointestinal tumor and abdominal aortic aneurysm (AAA) or abdominal aortic dissection (AAD) undergoing endovascular repair followed by tumor resection. Materials and Methods. Five patients with synchronous gastrointestinal tumor and AAA or AAD were treated by endovascular repair followed by tumor resection. Clinical data were retrospectively analyzed with respect to the management strategy, safety, and outcome. Results. Endovascular repair was technically successful in all patients. All the stents were well positioned and well patent, and the AAA (n=3) or AAD (n=2) were correctly excluded without endoleaks. After endovascular repair, all patients underwent resection of gastrointestinal tumor. No late mortality or major complications related to the two procedures were observed in the subsequent follow-up. Conclusion. Our results demonstrate that EVAR could significantly shorten the delay between AAA and gastrointestinal procedure with an excellent postoperative outcome. If the anatomical criteria are satisfied, EVAR followed by tumor resection might be an effective treatment for concomitant AAA and gastrointestinal tumor
Impact Analysis of Initial Cracks’ Angle on Fatigue Failure of Flange Shafts
A fatigue test on the failure mode of flange shafts was conducted. The propagation characteristics of the initial crack at the junction between the shaft and the flange as well as its angle effect were studied. This study developed an analysis program of fatigue crack propagation, based on the APDL (ANSYS Parametric Design Language). It obtained the effective angle interval within which the initial crack is able to propagate. The fitting calculation formula was derived and the results showed that: (1) The initial crack at the junction between the shaft and the flange would propagate in the radial and axial directions; the unstable crack propagation would cause an abrupt fracture of the cross-section, failing connection; and the angle of initial crack was uncertain. (2) The crack followed the I-II-III mixed mode, which was dominated by mode I. An initial crack with a larger angle showed more noticeable II-III characteristics; KII and KIII affected the crack’s propagation angle in the radial and axial directions and they also affected the structure’s surface direction. (3) The deepest point A of the crack was located at the junction between the shaft and the flange. Its crack propagation can be divided into three stages: rapid growth (stage 1), steady decline (stage 2, buffer stage), and instability (stage 3). The initial crack angle not only affected the propagation rate at stage 1 but also influenced the fatigue life distribution of the structure during propagation. The larger the initial crack angle was, the smaller the proportion of buffer stage in the total fatigue life would be. Moreover, the propagation of crack with a larger initial angle reached instability faster after stage 1, which would cause an abrupt fracture of the cross-section. This was unfavorable for deciding the crack detection time or carrying out maintenance and reinforcement. (4) The crack propagation at the junction between the shaft and the flange was determined by the size relation between ΔKI and ΔKth, instead of the effective stress intensity factor. The effective stress intensity factor can partly reflect the law of crack propagation, but cannot serve as the only criterion for crack propagation; it must be combined with the effective angle interval, which was negatively correlated with the crack’s shape ratio, to determine whether the crack would propagate
Improving Yield and Water Productivity of Rainfed Summer Maize in Smallholder Farming: A Case Study in Hebei Province, China
Because of the strong competition for a limited resource of water and demand for food production, understanding yield and water productivity (WP) potentials and exploitable gaps in the current production of intensively rainfed maize (Zea mays L.) is essential on the regional scale in China. In this study, we conducted 411 siteâyear on-farm trials to assess the actual yield and WP of rainfed summer maize and its yield and WP potentials in Hebei Province, China. Each on-farm trial contained detailed information of three different treatments: no fertilizer application (CK), current farmersâ practices (FP, depending on local farmer field fertilization management), and optimum fertilizer application (OPT, depending on soil testing and balanced fertilization). Results revealed that the yield and WP of rainfed summer maize in Hebei Province were 7635 kg haâ1 and 20.7 kg haâ1 mmâ1, respectively, and the yield and WP potentials were 12,148 kg haâ1 and 32.0 kg haâ1 mmâ1, respectively. Thus, the farmers attained 62.8% of the yield potential and 64.7% of the WP potential. A wide variation was observed in terms of the yield and WP across various types of farming. Compared with high-yield and high-WP (HYHW) farming, in low-yield and low-WP (LYLW) farming, the yield decreased by 24.9% and WP decreased by 44.4%. Nitrogen fertilizer application rate and rain were the most significant factors for yield and WP gaps among farmers, respectively. Other factors, such as solar radiation (tSola), soil available phosphorus content (AP), potassium fertilizer application rate, and grass-referenced evapotranspiration from planting to maturity (ET0), contributed the most to the variations in the yield and WP. Scenario analysis indicated that the optimization of fertilization levels from current to optimal for each farming could increase the yield and WP by 9.7% and 14.8%, respectively; closing gaps between the farming groups and achievement of the standard of HYHW farming by all farmers could increase the yield and WP by 14.8% and 35.5%, respectively; and achieving the yield and WP potentials could increase the yield and WP by 59.1% and 54.8%, respectively. These findings provided farming-based evidence that optimal nutrient management, advanced and climate-adapted agronomy practices, and higher soil fertility are essential for future maize production