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Van Tu Vu,Quang Huy Tran,Thanh Loc Pham,Phuong Nam Dao 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.3
This article addresses a trajectory tracking control approach for an uncertain surface vessel using the new cascade structure of adaptive reinforcement learning (ARL) algorithm and kinematic controller, feed-forward term. Since a surface vessel is decoupled by kinematic sub-system and dynamic sub-system, the cascade control system is an ideal method for obtaining the tracking problem. In the proposed control structure, the dynamic control loop is designed to be the optimized method of the corresponding dynamic sub-system and the kinematic control loop is implemented by a nonlinear controller combining with feed-forward term. The online actor-critic architecture is considered in ARL algorithm to overcome the challenge of solving the Hamilton-Jacobi-Bellman (HJB) equation. Additionally, the proposed controller is able to handle the difficulty of the non-autonomous optimal control problem by designing the ARL technique for the corresponding system with a small number of state variables. Based on theoretical analysis, the ARL based control design has been made to guarantee the uniformly ultimately bounded (UUB) stability of the closed system. Finally, the simulation results are illustrated to verify the effectiveness of the proposed control scheme.
A chemosystematic investigation of selected Stichococcus-like organisms (Trebouxiophyta)
Van, Anh Tu,Karsten, Ulf,Glaser, Karin The Korean Society of Phycology 2021 ALGAE Vol.36 No.2
The taxonomy of green microalgae relies traditionally on morphological traits but has been rapidly changing since the advent of molecular methods. Stichococcus Nägeli is a cosmopolitan terrestrial algal genus of the class Trebouxiophyceae that has recently been split into seven lineages, which, along with Pseudostichococcus, comprise the Stichococcuslike group; there is a need to further characterize these genera, since they are morphologically enigmatic. Here we used organic osmolytes as chemotaxonomic marker to verify the phylogenetic position of Stichococcus-like strains and were also able to exclude a strain hitherto identified as Gloeotila contorta from this group. Stichococcus-like organisms, including those recently revised, were characterized by the production of the polyol sorbitol and the disaccharide sucrose in high amounts, as is typical of Prasiola-clade algae. The results demonstrate that organic osmolyte chemotaxonomy can support green algal taxonomic designations as fundamental research.
APPLICATION OF MOVING CHIMERA GRID TECHNOLOGY IN NUMERICAL SIMULATIONOF WATER IMPACT PROBLEM
Van-Tu Nguyen,Duc-Thanh Vu,Warn-Gyu Park 한국전산유체공학회 2014 한국전산유체공학회 학술대회논문집 Vol.2014 No.5
A numerical scheme based on unsteady three-dimensional (3D), incompressible Navier-Stokes equations is applied to simulate water impact flows. The implicit method employs a dual-time, preconditioned algorithm with multi-block and parallel computing to improve our productivity in doing CFD analysis in a very effective way. A moving Chimera grid scheme were integrated with the Navier-Stokes solver to allows to assemble the computational grid by a collection of subgrids. The chimera domain decomposition scheme uses overlapping, embedding, and moving approach to facilitate the flow simulations of arbitrary translational and rotational complex geometries among various computational blocks. The domain-communication module is fully parallel and is ideally suited for handling moving body problems. The numerical scheme was validated by comparing present results of three free falling bodies including a hemisphere, a cone and a wedge entering the water with available experimental data and others numerical/theoretical results. A good obtained agreement between those results demonstrated the effectiveness of the methodology.
Influence of incident angles of earthquakes on inelastic responses of asymmetric-plan structures
Van Tu Nguyen,김두기 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.3
This paper presents the influence of incident angles of earthquakes on inelastic dynamic responses of asymmetry single story buildings under seismic ground motions. The dynamic responses such as internal forces and rotational ductility factor are used to evaluate the importance of the incident angles of ground motions in the inelastic range of structural behavior. The base shear and torque (BST) response histories of the resisting elements and of the building are used to prove that the shape of the BST surface of the building can be a practical tool to represent those of all resisting elements. This paper also shows that the different global forces which produce the maximum demands in the resisting elements tend to converge toward a single distribution in a definable intensity range, and this single distribution is related to the resistance distribution of the building.
Extended Airtime Fair Scheduling Method for a Zigbee Network
Van-Tu Chau,T.T. Quyen Bui,Anh-Tuan Do,Quang-Vinh Thai 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10
In a Zigbee network, when many nodes simultaneously send data packets to a Zigbee coordinator through routes (branches), the Zigbee coordinator cannot deal with all signals. Interference and noises are existed during data transmission. This problem is still one of challenges in the network communication. In this paper, we propose an extended airtime fair algorithm in which throughput of a Zigbee network is maximized and fractions of airtime are taken into account. We adapt a utility function that is proposed by Kelly (1997) in maximizing the network throughput; nevertheless, throughput of each branch is multiplied by a fraction of airtime. Fractions of airtime play a role in creating a balance of throughputs of branches: the throughput and fairness of each branch is guaranteed. Moreover, the usefulness of our proposed algorithm for a Zigbee network is presented; simulation results show that the throughput and fairness are better than those of a case of not using airtime fair.
Numerical investigation of ventilated supercavitation of a projectile by hot exhaust gas
Van-Tu Nguyen,Thanh-Hoang Phan,Dong-Hyun Kim,Warn-Gyu Park 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In this study, physical characteristics of supercavitation generated by high-temperature exhaust gas were numerically investigated. The hot gas in a range from 400 C° to 1000 C° was exhausted from the base of a shkval-shape projectile with a high velocity (approximately Ma = 2 in the air), while the velocity of the projectile is 120 m/s. The hot gas was also ventilated near the nose of the projectile with the same velocity as the projectile. With a very high temperature and high pressure, it is difficult to implement not only experiments but also CFD. In particular, since boiling due to temperature and cavity due to pressure must be considered together, a very high level of numerical analysis is required. In this study, the analysis of the multiphase flow was performed using a numerical program based on a fully compressible multiphase Navier-Stokes system with a phase change model. The numerical results provide detailed the temperature profile and shock structure that occurred in the wake flow.