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The reliability and accuracy of finite element models of metal machining are heavily reliant on the underlying material flow stress models. The aim of this study is to characterize the relation between the flow stress models and the chip morphology to provide a deeper insight into the process of serrated chip formation. Firstly, in the context of a flow stress model, the critical conditions for generation of the serrated chips are theoretically analyzed. Then, simulations are performed using two different constitutive models with five parameters sets, and the results are discussed in relation to how they verify the theoretical results. In order to better understand the process of serrated chip formation, attention is concentrated on the critical steps characterizing the formation of a single chip segment. The cutting process parameters (stress, strain, and temperature) are discussed. In addition, the mechanism by which the chip morphology transforms from continuous to serrated with increasing cutting speed is investigated in terms of the variation of flow stress curves. The results show that the slope of decrease and the strain value at the peak point of flow stress curves both greatly affect chip morphology. That is, the slope of decrease of the flow stress curve largely controls the formation of serrated chips, while the strain point at the peak determines the frequency and degree of serration of chips. It is found that simulations by manipulating well the flow stress models can produce results for chip morphology, cutting forces, etc. that are closer to those obtained experimentally. [ABSTRACT FROM AUTHOR]

To research an effective measure of reducing the soot and NOx in engine at the same time, different nozzle hole diameters coupled with exhaust gas re-circulation were adopted in this study based on KH-ACT spray breakup model, which takes the aerodynamic- induced, cavitation-induced, and turbulence-induced breakup into account. The SAGE detailed chemistry combustion and the new atomization model used in the simulation have been verified with the experiment data from YN4100QBZL engine. Different diesel nozzles were adopted in the study combined with different exhaust gas re-circulation rates ranging from 0% to 40%. The simulation results show that the NOx emission could be reduced effectively for both small (0.1 mm) and large (0.15 mm) diesel nozzles when increasing exhaust gas re-circulation ratio. The soot emission increases for the small nozzle hole size as the exhaust gas re-circulation increasing. However, when it comes to the large diesel nozzle, the emission increases slightly firstly and decreases quickly when the exhaust gas re-circulation rate above 20%. [ABSTRACT FROM AUTHOR]

Refractive indices of the highly polar compounds are evaluated by computation from first principles combined with molecular dynamics simulation. The molecular polarisability is obtained by density functional theory (DFT) using the B3LYP potential; the equilibrium density in the liquid phase is calculated utilising the GROMOS force field simultaneously. This combination of method is shown to provide an economical methodology for estimating the refractive indices of a wide range of polar species. All the evaluation data for the considered highly polar compounds are good agreement to the available data based on the standard of experiment. [ABSTRACT FROM PUBLISHER]

The three-dimensional premixed H2-O2 detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space–time conservation element and solution element (CE/SE) scheme. The simulation reproduces three typical cellular structures by setting appropriate cross-sectional size and initial perturbation in square tubes. As the cross-sectional size decreases, critical cellular structures transforming the rectangular or diagonal mode into the spinning mode are obtained and discussed in the perspective of phase variation as well as decreasing of triple point lines. Furthermore, multiple cellular structures are observed through examples with typical aspect ratios. Utilizing the visualization of detailed three-dimensional structures, their formation mechanism is further analyzed. [ABSTRACT FROM AUTHOR]

Abstract We propose a novel 8-level multidimensional intensity modulation scheme with the goal of achieving transmission rates higher than 200 Gbps when using only commercially available components. The generation of this modulation scheme is explained here and it is shown to increase the noise tolerance when compared with the 8-level pulse amplitude modulation (PAM-8), at the expense of spectral efficiency. We show that the proposed 3-dimensional (3D) modulation provides the same relative minimum distance gain for both non-duobinary (non-DB) and duobinary (DB) signaling. Gains ranging from 1 dB and up to 1.9 dB are shown in simulations for bit-error rates (BER) equal to or below 4x10−3, when comparing with the classic PAM-8. We demonstrate experimentally that 3D PAM-8 lowers the BER by up to 10 times for non-DB transmissions and by up to 3 times for DB transmissions. The proposed multidimensional modulation increases the maximum achievable bit rate from 205 Gbps (with PAM-8) up to roughly 240 Gbps, enabling 200 Gbps net rate single-lambda transmissions for next generation intra- and inter-datacenter optical transmission systems. [ABSTRACT FROM AUTHOR]