•A stress contour lines according to J2 theory is used to define the shape of damper.•The axial deformation in the specimen has been identified to quantify the energy dissipation.•The stress ...concentration is significantly reduced by the optimized damper shape.•All dampers can be easily installed or replaced because of the all-bolt connections.
A metallic shear panel damper with the shape optimized by stress contour lines is proposed in this study to mitigate stress concentration, reduce the effect of hot welds, and improve energy consumption efficiency. The stress contour line is defined according to the J2 plasticity theory, and the optimized shape is obtained by assuming that the points on the same contour line yield simultaneously. Different optimized shapes are developed considering various loading conditions. The design formulas for the stiffness and the strength are then derived, and further examined by nine dampers tested quasi-statically. Four are tested laterally under the vertical axial load to simulate real boundary conditions. All dampers can be easily installed or replaced because of the all-bolt connections. The test results demonstrate that the proposed metallic shear damper has a stable energy-dissipation capacity and a better low-cycle fatigue capability than traditional shear dampers without shape optimization. The stiffness and strength design values match the test values very well. The axial deformation in the specimen has been observed and identified due to the interaction among the cyclic axial-shear coupled plasticity, the geometric nonlinearity, and the higher lateral buckling modes. Compared with the non-optimized damper, the distribution of plastic deformation in the proposed dampers is more uniform, and the stress concentration is reduced significantly.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The smart vehicles construct Internet of Vehicle (IoV), which can execute various intelligent services. Although the computation capability of a vehicle is limited, multi-type of edge computing nodes ...provide heterogeneous resources for intelligent vehicular services. When offloading the complex service to the vehicular edge computing node, the decision for its destination should be considered according to numerous factors. This paper mostly formulate the offloading decision as a resource scheduling problem with single or multiple objective function and constraints, where some customized heuristics algorithms are explored. However, offloading multiple data dependence tasks in a complex service is a difficult decision, as an optimal solution must understand the resource requirement, the access network, the user mobility, and importantly the data dependence. Inspired by recent advances in machine learning, we propose a knowledge driven (KD) service offloading decision framework for IoV, which provides the optimal policy directly from the environment. We formulate the offloading decision for the multiple tasks as a long-term planning problem, and explore the recent deep reinforcement learning to obtain the optimal solution. It can scruple the future data dependence of the following tasks when making decision for a current task from the learned offloading knowledge. Moreover, the framework supports the pre-training at the powerful edge computing node and continually online learning when the vehicular service is executed, so that it can adapt the environment changes and can learn policy that are sensible in foresight. The simulation results show that KD service offloading decision converges quickly, adapts to different conditions, and outperforms a greedy offloading decision algorithm.
Rheological behavior of fiber suspensions in a turbulent channel flow was investigated theoretically and numerically. A model of turbulent fiber suspensions was proposed to predict the orientation ...distribution of fibers. The fluctuating equation for the orientation distribution function (ODF) of fibers was theoretically solved using the method of characteristics. The self-governed mean equation for orientation distribution function (ODF) was derived by relating the fluctuating ODF and angular velocities-correlated terms to the gradient of mean ODF. Then the ODF of fibers was predicted by numerically solving the mean equation for ODF. Finally the shear stress and first normal stress difference of suspensions were obtained. The results, some of which agree with the available relevant experimental data, show that the orientation distribution of fibers in the vicinity of the center of the flow is relatively broad in turbulent regime, and becomes broader with the increase of Reynolds number. The shear stress of fiber suspensions increases, while the first normal stress difference decreases, from the wall to the center of the flow for varying Reynolds number.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We subjected nine full-scale masonry infilled reinforced concrete frame specimens to quasi-static cyclic loading to critically review the methods for determining the damage state of masonry infill ...walls to develop reliable in-plane fragility functions. Among the three methods, the method based on maximum crack widths gave the smallest dispersion, whereas the skeleton curve-based methods generated excessive dispersions and the phenomena-based method was shown to be self-contradictory in certain circumstances. If the damage states were determined by maximum crack widths, neither the brick type nor the plaster had a significant influence on the fragility functions.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
In the tip clearance flow, the dominant vortex is the tip leakage vortex (TLV), which has a significant impact on the hydraulic and cavitation performance of axial flow machinery. Thus, the ...suppression methods of the TLV are necessary in turbomachinery. Casing groove is an effective and economical technique among many control methods. However, its mechanism is still not completely understood. In order to reveal the effect mechanism of the casing groove on the TLV, numerical investigations of gap flow with groove configurations are carried out. A NACA0009 hydrofoil with tip gap is selected as the research object. Two typical groove types (vertical groove and horizontal groove) are applied on the solid wall respectively. Efforts are made to analyze the difference of velocity distributions between the two groove cases and the smooth wall case. Combing with the vortex stability theory, the suppression mechanisms of the two types of casing groove are distinguished and uncovered. For the vertical groove, the TLV intensity is reinforced via the secondary leakage vortex (SLV) at first, and then the supply of the axial momentum in the TLV center is cut off, leading to a less stable TLV. For the horizontal groove, the dissipation effect caused by viscosity on the TLV is strong, resulting in a weakened TLV.
•Numerical investigations of gap flows with different solid wall configurations are conducted.•Suppression mechanisms of two types of grooves on the tip leakage vortex (TLV) are distinguished.•A type of secondary leakage vortex (SLV) is found in the vertical groove case.•The viscous dissipation effect is a crucial factor for the stability of the TLV cavitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Unsteady cavitation is an important topic due to its potential to cause huge damage to the hydraulic machinery. To control the shedding of cloud cavitation, the cavitation over a flat hydrofoil with ...an obstacle is investigated experimentally and numerically. A series of experiments around the flat hydrofoil without/with obstacle are carried out to study the evolution of cavitation. Periodic re-entrant jet and large shedding of cloud cavitation are observed in the case without obstacle, while the shedding of cloud cavitation in the case with obstacle is much weaker. Numerical simulations of the 2D unsteady cavitating flows around the hydrofoil are also performed. The transient and averaged fields of numerical simulations are presented and compared with the experimental data. The results show that in cases without obstacle, the averaged cavity length becomes longer with the decrease of the cavitation number. While in cases with obstacle, there is a range of cavitation number, in which the averaged cavity length almost keeps constant. The existence of obstacle changes the strength and direction of the transient re-entrant jet as well as the pressure distribution at the tail part of the cavity, leading to the weaker shedding of the cloud cavitation.
•Period shedding and re-entrant jet are detected in the case with/without obstacle, while the shedding is much weaker in the case with obstacle.•The thickness and the length of the cavity in the case with obstacle both decrease apparently compared with the case without obstacle.•A peak can be found in the adverse pressure gradient distribution in the case without obstacle, while it decreases obviously in the case with obstacle.
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•Seismic responses of steel frames with self-centering braces were decomposed to analysis the contribution of each model.•Quantification measures of higher modes were proposed to highlight the ...influence of duration and peak value.•A novel dual self-centering variable friction damper (DSC-VFD) brace was developed to control the higher mode effect.•Parameter analysis of DSC-VFD frames was conducted to evaluate the influence of post-yield stiffness and energy dissipation capability.
Self-centering energy dissipation braced frames (SCEDFs) have been developed to satisfy the requirements of resilience. However, low post-yield stiffness in such systems often leads to a higher mode effect, resulting in a significant deformation concentration that may exceed the design objectives. A novel dual self-centering variable friction damper (DSC-VFD) brace with high post-yield stiffness and enhanced energy dissipation capability was proposed. Its hysteretic behavior, characterized by a loading stiffness that is larger than the unloading stiffness, was developed by incorporating the C++ language into the OpenSees platform. To evaluate the higher mode effect in different types of frames, a quantification measure based on the higher mode results of the steel frames, considering the seismic responses around the peak value, was therefore established. Then, the seismic responses of the DSC-VFD frames (DSC-VFDFs) using the proposed uniaxial material were calculated and compared with those of the traditional moment resisting frame (MRF) and SCEDF with the same design process. Finally, the four parameters, including the first stiffness modification coefficient α1, second stiffness ratio α2, strength ratio β, and fourth stiffness ratio α4, were considered to evaluate their influences on nonlinear seismic responses and the higher mode effect of the DSC-VFDF by the above-mentioned quantification measures. The results indicate that the influence of higher modes should not be ignored in the design of self-centering braced frames, and the higher mode quantification results of base shear are more sensitive than those of effective displacement. The DSC-VFD brace can more effectively improve the seismic responses and control the higher mode effect than the traditional SCEDF.
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•First full-scale test on IP-OOP interaction of lightly-reinforced masonry infills.•OOP strength reduction due to IP damage is dependent on wall slenderness.•Tie bars have marginal effect on OOP ...strength reduction due to IP damage.•Two-parameter empirical equation was proposed for IP-OOP interaction.•Neglecting the IP-OOP interaction may greatly underestimate seismic loss.
Out-of-plane collapse is one of the most important failure modes for masonry infill walls in frame structures during earthquakes and may result in significant economic loss, blocked evacuation pathways and even injuries and fatalities. To investigate the effect of prior in-plane damage on the out-of-plane behavior of masonry infill walls, a series of full-scale masonry infilled RC frame specimens that conform to the Chinese practice were subjected to sequential in-plane and out-of-plane quasi-static loading. The results show that the out-of-plane strength of the masonry infill walls was reduced by 22% and 47% at 1/500 and 1/200 prior in-plane drift ratios, respectively, whereas the out-of-plane stiffness was not significantly affected by the prior in-plane damage. Based on the test results of the present experiment and the collected data available in the literature, an empirical equation was derived to relate the out-of-plane strength reduction factor with both the prior in-plane drift ratio and the slenderness of the wall panel. According to the equation, the out-of-plane strength starts to degrade when the in-plane drift ratio reaches approximately 0.1% to 0.3% depending on the wall slenderness. Both the rate and extent of the strength degradation are greater for slenderer wall panels. Through a numerical example, we demonstrate that neglecting such an in-plane-out-of-plane interaction may lead to substantial underestimation of the loss by seismic damage of masonry infill walls in buildings.
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