Mesoscopic investigation of size effect in notched concrete beams: The role of fracture process zone

A comprehensive mesoscopic investigation has been conducted into the classic topic of size effect, using notched plain concrete beams subjected to three-point bending as a test bed. The concrete beams are modelled as random heterogeneous material containing three components, coarse aggregates, mortar and the interface transition zone. Mesoscopic numerical simulations using a 2D mesoscale continuum damage-based model, enhanced by a nonlocal treatment, is used to capture the whole fracture process in concrete materials. Both global and local numerical results are then examined and verified with relevant experimental evidence from the literature. A stress field interaction theory based on the strip yield model is proposed to interpret the size effect phenomenon and the role of detailed fracture process zone features is discussed accordingl

Mesoscale modelling of concrete under high strain rate tension with a rate-dependent cohesive interface approach

This paper presents the investigation of the dynamic behaviour of concrete material under high strain rate tension using an interface approach in a mesoscale model framework. A ratedependent cohesive constitutive description is introduced into the mesoscale framework to account for the effects of viscosity occurring in the dynamic fracture process. An algorithm is developed to insert cohesive elements throughout the mesoscale mesh grids in a concrete specimen, and to identify the cohesive element properties based on the original mesoscale structure. After parameter studies in terms of the cohesive element properties, the proposed model is validated against representative experimental data. The model is then employed to 2 investigate the dynamic tensile behaviour of concrete under high strain rates. The underlying mechanisms of the dynamic tensile strength increase of concrete, including the influence of viscous effect from rate-dependent material description, the inertial effect from cracking and the material heterogeneity, are discussed and identified respectively. Results demonstrate that the viscous effect should be incorporated into the cohesive constitutive law to account for the Stefan effect at low and moderate strain rates and the micro-crack inertial effect only plays a significant role at a relatively high strain rate. Material heterogeneity does influence the strength enhancement under dynamic loading and the significance of this effect increases with the strain rate

A Comprehensive Study on Off-path SmartNIC

SmartNIC has recently emerged as an attractive device to accelerate distributed systems. However, there has been no comprehensive characterization of SmartNIC especially on the network part. This paper presents the first comprehensive study of off-path SmartNIC. Our experimental study uncovers the key performance characteristics of the communication among the client, SmartNIC SoC, and the host. We find without considering SmartNIC hardware architecture, communications with it can cause up to 48% bandwidth degradation due to performance anomalies. We also propose implications to address the anomalies.Comment: This is the short version. Full version will appear at OSDI2

Adaptive neural network control of underactuated surface vessels with guaranteed transient performance: Theory and experimental results

In this paper, an adaptive trajectory trackingcontrol algorithm for underactuated unmanned surfacevessels (USVs) with guaranteed transient performance isproposed. To meet the realistic dynamical model of USVs,we consider that the mass and damping matrices are notdiagonal and the input saturation problem. Neural Networks(NNs) are employed to approximate the unknown externaldisturbances and uncertain hydrodynamics of USVs. Moreover,both full state feedback control and output feedbackcontrol are presented, and the unmeasurable velocities ofthe output feedback controller are estimated via a highgainobserver. Unlike the conventional control methods,we employ the error transformation function to guaranteethe transient tracking performance. Both simulation andexperimental results are carried out to validate the superiorperformance via comparing with traditional potential integral(PI) control approaches