Comparative Study of Machine Learning Modeling for Unsteady Aerodynamics

Modern fighters are designed to fly at high angle of attacks reaching 90 deg as part of their routine maneuvers.These maneuvers generate complex nonlinear and unsteady aerodynamic loading.In this study,different aerodynamic prediction tools are investigated to achieve a model which is highly accurate,less computational,and provides a stable prediction of associated unsteady aerodynamics that results from high angle of attack maneuvers.These prediction tools include Artificial Neural Networks(ANN)model,Adaptive Neuro Fuzzy Logic Inference System(ANFIS),Fourier model,and Polynomial Classifier Networks(PCN).Themain aim of the predictionmodel is to estimate the pitch moment and the normal force data obtained from forced tests of unsteady delta-winged aircrafts performing high angles of attack maneuvers.The investigation includes three delta wing models with 1,1.5,and 2 aspect ratios with four determined variables:change rate in angle of attack(0 to 90 deg),non-dimensional pitch rate(0 to.06),and angle of attack.Following a comprehensive analysis of the proposed identification methods,it was found that the newly proposed model of PCN showed the least error in modeling and prediction results.Based on prediction capabilities,it is seen that polynomial networks modeling outperformed ANFIS and ANN for the present nonlinear problem.

Crack Propagation in Pipelines Under Extreme Conditions of Near-Neutral PH SCC

Stress Corrosion Cracking(SCC)process through which cracks occur in a variety of susceptible materials is a result of a combination of residual or applied stresses and corrosion.In oil and gas field,buried pipeline steels are made of low-alloy steels with a ferritic-pearlitic structure,such as X70.In dilute solutions,these materials are prone to SCC failure.The Near-neutral simulated soil solution(NS4)solution is established to imitate SCC conditions and subsequently became the industry requirement for crack growth experiments in the majority of laboratories.The strainassisted active crack pathways are considered while modelling SCC growth as an oxide film rupture and anodic dissolution process.It’s been hypothesized that increasing the strain concentration can help with dissolution at the filmfree crack tip.This research focuses on estimating the SCC crack growth rate under various environmental conditions in oil and gas pipelines using finite element modelling.The simulation is carried out using the J-integral theory in the COMSOL Multiphysics program.Simulations are performed to model the crack growth rate(CGR)using slip anodic dissolution(film rupture)mechanism.The plastic strain gradient is required to compute the SCC CGR(da/dt).Because the plastic strain located at crack tip increases proportionally to the crack length as it propagates,the CGR increases as the stress intensity factor(SIF)increases.The crack growth rates increase when constant loads are applied and as the temperature rises,and elevating the cathodic potential has a minimal influence on the propagation rate of cracks but raises the material yield strength and imparts brittle behavior to it.