Numerical study of separated boundary layer transition under pressure gradient

Large-eddy simulation (LES) is conducted to study the transition process of a separated boundary layer on a flat plate with an elliptical leading edge. A streamwise pressure distribution is imposed and the free stream turbulence intensity is 3% to mimic the suction surface of a low-pressure turbine (LPT) blade. A dynamic sub-grid scale model is employed in the study and the current LES results compare well with available experimental data and previous LES results. The transition process has been analysed with a particular focus on primary instabilities at work. Streaky structures further upstream of the separation, known as the Klebanoff Streaks, have been observed. Typical two-dimensional Kelvin-Helmholtz (K-H) rolls are distorted in the separated region. When Klebanoff streaks passing over a full-span K-H roll, portion of the two-dimensional roll merges with the Klebanoff streaks and develop into chaotic three-dimensional structures, whereas the remaining undisrupted two-dimensional K-H rolls develop into Λ-vortex indicating that despite the disturbances before separation, the K-H instability may still be the main instability at work

Empirical Study of Travel Time Estimation and Reliability

This paper explores the travel time distribution of different types of urban roads, the link and path average travel time, and variance estimation methods by analyzing the large-scale travel time dataset detected from automatic number plate readers installed throughout Beijing. The results show that the best-fitting travel time distribution for different road links in 15 min time intervals differs for different traffic congestion levels. The average travel time for all links on all days can be estimated with acceptable precision by using normal distribution. However, this distribution is not suitable to estimate travel time variance under some types of traffic conditions. Path travel time can be estimated with high precision by summing the travel time of the links that constitute the path. In addition, the path travel time variance can be estimated by the travel time variance of the links, provided that the travel times on all the links along a given path are generated by statistically independent distributions. These findings can be used to develop and validate microscopic simulations or online travel time estimation and prediction systems

Uncertainty analysis of environmental loads response for fixed offshore platform in climate change condition

Peer Reviewe

Data-Driven Robust Control of Unknown MIMO Nonlinear System Subject to Input Saturations and Disturbances

This paper presented a new data-driven robust control scheme for unknown nonlinear systems in the presence of input saturation and external disturbances. According to the input and output data of the nonlinear system, a recurrent neural network (RNN) data-driven model is established to reconstruct the dynamics of the nonlinear system. An adaptive output-feedback controller is developed to approximate the unknown disturbances and a novel input saturation compensation method is used to attenuate the effect of the input saturation. Under the proposed adaptive control scheme, the uniformly ultimately bounded convergence of all the signals of the closed-loop nonlinear system is guaranteed via Lyapunov analysis. The simulation results are given to show the effectiveness of the proposed data-driven robust controller

Theoretical Modeling of Protective Oxide Layer Growth in Non-isothermal Lead Alloy Coolant Systems

The goal of this research project is to provide a basic understanding of the protective oxide layer behaviors and to develop oxide layer growth models of steels in non-isothermal lead alloys (lead or lead-bismuth eutectic) coolant systems. Precise studies and simulations of all hydrodynamics with thermal conditions encountered in practical coolant loop systems by use of different flowing conditions in the laboratory are difficult and expensive, if not impossible. Therefore it is important and necessary to develop theoretical models to predict the protective oxide layer behaviors at the design stage of a practical lead-alloy coolant system, to properly interpret and apply experimental results from test loops, and to provide guidance for optimization in lead alloys nuclear coolant systems. The research project, therefore, is aimed at filling the gaps of protective oxide layer growth and the oxygen concentration level before lead-alloys nuclear coolant is ready for programmatic implementations and industrial applications