In this work, a novel approach to couple ordinary state-based peridynamics (OSPD) with node-based smoothed finite element method (NS-FEM) is proposed. In present method, the solution domain is ...partitioned into two regions, one is discretized by OSPD, the other by NS-FEM, and more importantly, no transition region is introduced. The physical information is transmitted mutually from local to non-local regions, which is governed by the unified coupling equations of motion. The coupling takes full advantage of the generality of OSPD and the efficiency of NS-FEM. The parts of regions where damage and fracture either exist or are expected to propagate are described by OSPD, and the rest of regions are described by NS-FEM to reduce the computational cost and surface effect. Additionally, the critical bond work in OSPD is assumed to depend on the bond length, which is derived by the relation with the critical energy release rate in this study. Several numerical examples involving crack propagation are investigated under either dynamic or quasi-static conditions and satisfactory results have been obtained demonstrating the validity and efficiency of the proposed coupling approach.
•Innovative strategy to couple OSPD with NS-FEM.•No blending function, mapping parameters or interface elements are required.•The coupling approach is free of ghost forces.•It takes full advantages of both OSPD and NS-FEM.
In this study, we systematically investigated the effect of the carbon content on the phase structure evolution and macro and nanomechanical properties of the equiatomic CoCrFeNi alloy. A series of ...CoCrFeNi-based high-entropy alloys with 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, and 0.9 wt% carbon were fabricated by vacuum arc melting. The results showed that the alloys retained their single face-center-cubic (FCC) structure with large grains at the carbon contents up to 0.2 wt%. However, in the case of the alloys with carbon contents higher than 0.3 wt%, the single phase structure transformed into the dendrite structure. The inter-dendrite regions of these alloys were eutectic carbides containing lath M7C3 carbides and the FCC phase. The tensile yield strength of the CoCrFeNi alloy increased from 295 to 512 MPa with the addition of 0.9 wt% carbon. The strengthening mechanisms of the alloys were investigated, including the solid solution strengthening due to the interstitial carbon atoms and the precipitation strengthening due to the M7C3 carbides. In addition, the nanoindentation results revealed that the M7C3 carbides showed a high nanohardness of ~17.7 GPa, which is almost four times of that of the FCC phase. We also investigated the elasto-plastic relationships, plastic properties and wear resistance of the FCC phase, while elucidating the eutectic carbide regions and M7C3 carbides. The eutectic carbide regions exhibited brittle fracture, whereas the FCC phase showed plastic fracture.
The impact of impurity ions on a pedestal has been investigated in the HL-2A Tokamak, at the Southwestern Institute of Physics, Chengdu, China. Experimental results have clearly shown that during the ...H-mode phase, an electromagnetic turbulence was excited in the edge plasma region, where the impurity ions exhibited a peaked profile. It has been found that double impurity critical gradients are responsible for triggering the turbulence. Strong stiffness of the impurity profile has been observed during cyclic transitions between the I-phase and H-mode regime. The results suggest that the underlying physics of the self-regulated edge impurity profile offers the possibility for an active control of the pedestal dynamics via pedestal turbulence.
The evolutions of MHD instability behaviors and enhancement of both electrostatic and electromagnetic turbulence towards the plasma disruption have been clearly observed in the HL-2A plasmas. Two ...types of plasma disruptive discharges have been investigated for similar equilibrium parameters: one with a distinct stage of a small central temperature collapse (Formula: see text 5-10%) around 1 millisecond before the thermal quench (TQ), while the other without. For both types, the TQ phase is preceded by a rotating 2/1 tearing mode, and it is the development of the cold bubble from the inner region of the 2/1 island O-point along with its inward convection that causes the massive energy loss. In addition, the micro-scale turbulence, including magnetic fluctuations and density fluctuations, increases before the small collapse, and more significantly towards the TQ. Also, temperature fluctuations measured by electron cyclotron emission imaging enhances dramatically at the reconnection site and expand into the island when approaching the small collapse and TQ, and the expansion is more significant close to the TQ. The observed turbulence enhancement near the X-point cannot be fully interpreted by the linear stability analysis by GENE. Evidences suggest that nonlinear effects, such as the reduction of local Formula: see text shear and turbulence spreading, may play an important role in governing turbulence enhancement and expansion. These results imply that the turbulence and its interaction with the island facilitate the stochasticity of the magnetic flux and formation of the cold bubble, and hence, the plasma disruption.
Rotating radio transients (RRATs) are sporadically emitting pulsars detectable only through searches for single pulses. While over 100 RRATs have been detected, only a small fraction (roughly 20%) ...have phase-connected timing solutions, which are critical for determining how they relate to other neutron star populations. Detecting more pulses in order to achieve solutions is key to understanding their physical nature. Astronomical signals collected by radio telescopes contain noise from many sources, making the detection of weak pulses difficult. Applying a denoising method to raw time series prior to performing a single-pulse search typically leads to a more accurate estimation of their times of arrival (TOAs). Taking into account some features of RRAT pulses and noise, we present a denoising method based on wavelet data analysis, an image-processing technique. Assuming that the spin period of an RRAT is known, we estimate the frequency spectrum components contributing to the composition of RRAT pulses. This allows us to suppress the noise, which contributes to other frequencies. We apply the wavelet denoising method including selective wavelet reconstruction and wavelet shrinkage to the de-dispersed time series of eight RRATs with existing timing solutions. The signal-to-noise ratio (S/N) of most pulses are improved after wavelet denoising. Compared to the conventional approach, we measure 12%-69% more TOAs for the eight RRATs. The new timing solutions for the eight RRATs show 16%-90% smaller estimation error of most parameters. Thus, we conclude that wavelet analysis is an effective tool for denoising RRATs signal.
Listeria monocytogenes poses an increasing challenge to cheese production. To minimize the risk of bacterial contamination, a chitosan-coated nisin-silica liposome was engineered for the present ...study. We investigated the characteristics of nisin-silica liposomes and the anti-listeria effects of a chitosan-coated nisin-silica liposome on Cheddar cheese. The encapsulation efficiency of nisin in a liposome was sharply increased after it was adsorbed on a silica particle surface. Chitosan-coated nisin-silica liposomes displayed sustained antibacterial activity against L. monocytogenes, without affecting the sensory properties of the cheese. Chitosan-coated nisin-silica liposomes could be a promising active antimicrobial for cheese preservation.
•Two novel submerged JIMHS were proposed and investigated by overall numerical simulation and experiment.•The maximum relative error between simulation and experiment is less than 9%.•The oblique ...ribs can cause better fluid disturbance and reduce the adverse effect of horizontal cross-flow.•The average heat transfer surface temperature is lower than 60°C at low flow rates and maximum heat flow.
In this work, two submerged jet impingement/microchannel heat sink (JIMHS) models were proposed, i.e., straight-rib jet impingement/microchannel heat sink (SJIMHS) and oblique-rib jet impingement/microchannel heat sink (OJIMHS). The heat transfer and flow characteristics of the two models were investigated by overall numerical simulation and experiment. In the numerical simulation, the effects of heat flux, pressure drop and rib arrangement on the internal flow and heat transfer of the heat sink were studied. The results indicate that under the same heat flux and inlet condition, the heat transfer surface of OJIMHS achieves more uniform and lower temperature distribution compared with that of SJIMHS, and the average convective heat transfer coefficient of the OJIMHS is obviously higher than that of SJIMHS in all calculation cases, with an increase of about 20%. In addition, the performance of OJIMHS was tested experimentally. The comparison indicates that the maximum relative errors of average temperature and heat transfer coefficient between simulation and experiment were less than 9%. When the volume flow rate is 0.5 L/min and the heat flux is 100 W/cm², the average temperature of the heat transfer surface is still lower than 60°C. Besides, the averaged heat transfer coefficient of 2.8W/(cm2·K) was achieved under the inlet fluid temperature of 283K and volume flow rate of 2.5 L/min in the experiment.
•We present a novel concept for hotspot-targeted, energy efficient HT-JIHS for electronic chips.•The optimized jet hole arrangement and target plate can efficiently alter the flow distribution.•The ...total pressure drop will be dramatically reduced by enlarging the inlet diameter.•Optimized design is suitable for highly non-uniform heat flux maps.•The pumping power consumption for optimized design is less than 0.1%.
Jet impingement as a highly efficient cooling method has been broadly used in the field of heat dissipation for high heat flow electronics. Well-designed structures including jet hole and pin–fin arrangement can significantly alter flow fields to provide a favorable trade between increased heat transfer performance and total pressure loss. In order to solve the imbalance problem of temperature uniformity and power consumption caused by non-uniform heat flux distribution in multi-core integrated circuits, a novel jet impingement cooling concept, for hotspot-targeted, energy efficient cooling of non-uniform heat generation electronics, was proposed in this paper. A three-dimensional numerical simulation was carried out to investigate the effects of jet hole diameter and distribution, heat transfer plate type and inlet area on heat transfer and resistance performance. The heat transfer coefficient, total pressure drop, maximum temperature rise and temperature non-uniformity were selected as the performance parameters. Compared with the traditional jet impingement heat sink, the well-designed heat sink in this work achieves an improvement of 58% in temperature non-uniformity while the total pressure drop is reduced by 68.7% at the same mass flow rate. In addition, the pumping power consumption is only 0.093% and 0.061% of the total heating power for 150 W/cm2 and 300 W/cm2 hotspot heat flux respectively while ensuring the acceptable temperature non-uniformity.
This study investigated the influence of Ta content (i.e. 0 wt%, 2 wt%, and 4 wt%) on microstructure and creep behavior of a Ni–Co base disc superalloy at 760 °C/480 MPa. It was found that creep ...rupture life and the minimum creep strain rate showed a trend of first increase and then decrease with the increase of Ta content. The microstructure observations indicated that Ta addition promoted the increase of volume fraction of γ′, the precipitation of MC carbide and η-phase, but inhibited the growth of γ′ and the precipitation of M23C6 carbide at grain boundaries during creep. The mechanisms related to creep behavior were discussed, and it was deemed that the higher γ′ volume fraction, finer size of γ′, larger γ/γ′ misfit, lower atomic diffusion rate, inhibited M23C6 carbide and the palisade-like distribution of η-phase may be responsible for the enhancement of the primary and tertiary creep resistance.
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