Comparitive Analysis in Non-linear Model of Pre-stressed Concrete Beam

The author presents a detailed procedure to model a pre-stressed concrete beam in ATENA Engineering and ABAQUS, considering a series of load cases. One of the main purposes of the thesis is to investigate the time effort required and the additional knowledge gained by modeling techniques of increasing accuracy, and based on different software packages. The two software packages differ in several substantial ways: mechanical models available, visualization, time costs, primary fields of application, and models for concrete cracking. This effort is part of a larger initiative with contributors from the USA and Europe to study the value of advanced modeling within the life-cycle cost of a major structure. Moreover, the thesis focuses on numerical problems arising from independent meshing of the multiple parts of the beam. Sensitivity analyses are performed to evaluate the effect of misalignment of the various local meshes on the global failure modes of the beam

Flow Dynamics of a Dodecane Jet in Oxygen Crossflow at Supercritical Pressures

In advanced aero-propulsion engines, kerosene is often injected into the combustor at supercritical pressures, where flow dynamics is distinct from the subcritical counterpart. Large-eddy simulation combined with real-fluid thermodynamics and transport theories of a N-dodecane jet in oxygen crossflow at supercritical pressures is presented. Liquid dodecane at 600 K is injected into a supercritical oxygen environment at 700 K at different supercritical pressures and jet-to-crossflow momentum flux ratios (J). Various vortical structures are discussed in detail. The results shown that, with the same jet-to-crossflow velocity ratio of 0.75, the upstream shear layer (USL) is absolutely unstable at 6.0 MPa (J = 7.1) and convectively unstable at 3.0 MPa (J = 13.2). This trend is consistent with the empirical criterion for the stability characteristics of a jet in crossflow at subcritical pressures (Jcr = 10). While decreasing J to 7.1 at 3.0 MPa, however, the dominant Strouhal number of the USL varies along the upstream jet trajectory, and the USL becomes convectively unstable. Such abnormal change in stability behavior can be attributed to the real-fluid effect induced by strong density stratification at pressure of 3.0 MPa, under which a point of inflection in the upstream mixing layer renders large density gradient and tends to stabilize the USL. The stability behavior with varying pressure and J is further corroborated by linear stability analysis. The analysis of spatial mixing deficiencies reveals that the mixing efficiency is enhanced at a higher jet-to-crossflow momentum flux ratio

Fault Mode Probability Factor Based Fault-Tolerant Control for Dissimilar Redundant Actuation System

This paper presents a Fault Mode Probability Factor (FMPF) based Fault-Tolerant Control (FTC) strategy for multiple faults of Dissimilar Redundant Actuation System (DRAS) composed of Hydraulic Actuator (HA) and Electro-Hydrostatic Actuator (EHA). The long-term service and severe working conditions can result in multiple gradual faults which can ultimately degrade the system performance, resulting in the system model drift into the fault state characterized with parameter uncertainty. The paper proposes to address this problem by using the historical statistics of the multiple gradual faults and the proposed FMPF to amend the system model with parameter uncertainty. To balance the system model precision and computation time, a Moving Window (MW) method is used to determine the applied historical statistics. The FMPF based FTC strategy is developed for the amended system model where the system estimation and Linear Quadratic Regulator (LQR) are updated at the end of system sampling period. The simulations of DRAS system subjected to multiple faults have been performed and the results indicate the effectiveness of the proposed approach

Active Fault Tolerant Control for Vertical Tail Damaged Aircraft with Dissimilar Redundant Actuation System

This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system (DRAS) that has suffered from vertical tail damage. A damage degree coefficient based on the effective vertical tail area is introduced to parameterize the damaged flight dynamic model. The nonlinear relationship between the damage degree coefficient and the corresponding stability derivatives is considered. Furthermore, the performance degradation of new input channel with electro-hydrostatic actuator (EHA) is also taken into account in the damaged flight dynamic model. Based on the accurate damaged flight dynamic model, a composite method of linear quadratic regulator (LQR) integrating model reference adaptive control (MRAC) is proposed to reconfigure the fault-tolerant control law. The numerical simulation results validate the effectiveness of the proposed fault-tolerant control strategy with accurate flight dynamic model. The results also indicate that aircraft with DRAS has better fault-tolerant control ability than the traditional ones when the vertical tail suffers from serious damage. © 2016 Chinese Society of Aeronautics and Astronautic

WCCNet: Wavelet-integrated CNN with Crossmodal Rearranging Fusion for Fast Multispectral Pedestrian Detection

Multispectral pedestrian detection achieves better visibility in challenging conditions and thus has a broad application in various tasks, for which both the accuracy and computational cost are of paramount importance. Most existing approaches treat RGB and infrared modalities equally, typically adopting two symmetrical CNN backbones for multimodal feature extraction, which ignores the substantial differences between modalities and brings great difficulty for the reduction of the computational cost as well as effective crossmodal fusion. In this work, we propose a novel and efficient framework named WCCNet that is able to differentially extract rich features of different spectra with lower computational complexity and semantically rearranges these features for effective crossmodal fusion. Specifically, the discrete wavelet transform (DWT) allowing fast inference and training speed is embedded to construct a dual-stream backbone for efficient feature extraction. The DWT layers of WCCNet extract frequency components for infrared modality, while the CNN layers extract spatial-domain features for RGB modality. This methodology not only significantly reduces the computational complexity, but also improves the extraction of infrared features to facilitate the subsequent crossmodal fusion. Based on the well extracted features, we elaborately design the crossmodal rearranging fusion module (CMRF), which can mitigate spatial misalignment and merge semantically complementary features of spatially-related local regions to amplify the crossmodal complementary information. We conduct comprehensive evaluations on KAIST and FLIR benchmarks, in which WCCNet outperforms state-of-the-art methods with considerable computational efficiency and competitive accuracy. We also perform the ablation study and analyze thoroughly the impact of different components on the performance of WCCNet.Comment: Submitted to TPAM

Dynamic Friction Parameter Identification Method with LuGre Model for Direct-Drive Rotary Torque Motor

Attainment of high-performance motion/velocity control objectives for the Direct-Drive Rotary (DDR) torque motor should fully consider practical nonlinearities in controller design, such as dynamic friction. The LuGre model has been widely utilized to describe nonlinear friction behavior; however, parameter identification for the LuGre model remains a challenge. A new dynamic friction parameter identification method for LuGre model is proposed in this study. Static parameters are identified through a series of constant velocity experiments, while dynamic parameters are obtained through a presliding process. Novel evolutionary algorithm (NEA) is utilized to increase identification accuracy. Experimental results gathered from the identification experiments conducted in the study for a practical DDR torque motor control system validate the effectiveness of the proposed method