chihyung wen - Academia.edu (original) (raw)

Papers by chihyung wen

Proceedings, Oct 19, 2023

Aerospace

Unmanned Ground Vehicles (UGVs) and Unmanned Aerial Vehicles (UAVs) are commonly used for various... more Unmanned Ground Vehicles (UGVs) and Unmanned Aerial Vehicles (UAVs) are commonly used for various purposes, and their cooperative systems have been developed to enhance their capabilities. However, tracking and interacting with dynamic UAVs poses several challenges, including limitations of traditional radar and visual systems, and the need for the real-time monitoring of UAV positions. To address these challenges, a low-cost method that uses LiDAR (Light Detection and Ranging) and RGB-D cameras to detect and track UAVs in real time has been proposed. This method relies on a learning model and a linear Kalman filter, and has demonstrated satisfactory estimation accuracy using only CPU (Central Processing Unit)- in GPS (Global Positioning System)-denied environments without any prior information.

Advances in Aerodynamics, Apr 6, 2022

This paper reports a modified steady one-dimensional Zel’dovich–von Neumann–Doring detonation mod... more This paper reports a modified steady one-dimensional Zel’dovich–von Neumann–Doring detonation model that considers a vibrational nonequilibrium effect. The Landau–Teller model is adapted for the translational–rotational to vibrational mode exchange rate, and Park’s two-temperature model is applied in the single-step Arrhenius equation. The Millikan and White method is chosen to model the vibrational relaxation time. In this modified model, α is introduced and is defined as the ratio of the specific heat capacity related to the translational–rotational mode only versus the total specific heat capacity at constant pressure. Changes in half-reaction zone length and predicted postshock thermodynamic properties are observed in this modified profile across the postshock state to the Chapman–Jouguet state. The findings agree with a previous numerical simulation of gas detonation with detailed chemistry assessment, in which detonation cell size changes under a vibrational nonequilibrium assumption.

The effects of vibrational non-equilibrium and vibration–chemistry coupling on hydrogen–air deton... more The effects of vibrational non-equilibrium and vibration–chemistry coupling on hydrogen–air detonation are numerically investigated by solving reactive Euler equations coupled with a multiple vibrational temperature-based model. Detailed hydrogen–air reaction kinetic is utilized, Landau–Teller model is adopted to solve the vibrational relaxation process, and the coupled vibration–chemistry vibration model is used to evaluate the vibration–chemistry coupling. It is shown that the relaxation process and vibration–chemistry coupling considerably influence the hydrogen–air detonation structure, highlighting the importance of correct treatment of vibrational non-equilibrium in detonation simulations.

Physics of Fluids

This paper investigates a Mach 6 oblique breakdown via direct numerical simulation in conjunction... more This paper investigates a Mach 6 oblique breakdown via direct numerical simulation in conjunction with stability and quadrant analyses. Particular emphasis is placed on, first, the heat transfer and mean flow distortion in the near-wall and outer transitional boundary layer, and, second, the flow events that are responsible for the production of the Reynolds stress. The energy budget reveals that enhancement of viscous dissipation due to mean flow distortion dominates the heat transfer overshoot, while the dissipation due to fluctuations is lesser but not negligible. Downstream of the location of the peak mean heat flux, the wall temperature gradient (non-dimensionalized by the freestream temperature and local boundary layer thickness) varies little, owing to the occurrence of breakdown and the establishment of self-similarity. Renormalized by the boundary layer thickness, a new correlation of the Stanton number shows no overshoot or difference between the original overshoot region ...

Sensors

Simultaneous localization and mapping (SLAM) system-based indoor mapping using autonomous mobile ... more Simultaneous localization and mapping (SLAM) system-based indoor mapping using autonomous mobile robots in unknown environments is crucial for many applications, such as rescue scenarios, utility tunnel monitoring, and indoor 3D modeling. Researchers have proposed various strategies to obtain full coverage while minimizing exploration time; however, mapping quality factors have not been considered. In fact, mapping quality plays a pivotal role in 3D modeling, especially when using low-cost sensors in challenging indoor scenarios. This study proposes a novel exploration algorithm to simultaneously optimize exploration time and mapping quality using a low-cost RGB-D camera. Feature-based RGB-D SLAM is utilized due to its various advantages, such as low computational cost and dense real-time reconstruction ability. Subsequently, our novel exploration strategies consider the mapping quality factors of the RGB-D SLAM system. Exploration time optimization factors are also considered to se...

AIAA Journal, Feb 11, 2022

The effect of nonequilibrium recombination after a curved two-dimensional shock wave in a hyperve... more The effect of nonequilibrium recombination after a curved two-dimensional shock wave in a hypervelocity dissociating flow of an inviscid Lighthill-Freeman gas is considered. An analytic solution is obtained with the effective shock values derived by Hornung (1976) and the assumption that the flow is ‘quasi-frozen ’ after a thin dissociating layer near the shock. The solution gives the expression of dissociation fraction as a function of temperature on a streamline. It can then provide a rule of thumb to check the validity of binary scaling for the experimental conditions and a tool to determine the limiting streamline which delineates the validity zone of binary scaling. The effects upon the nonequilibrium chemical reaction of the large difference in free stream temperature between free-piston shock tunnel and equivalent flight conditions are discussed. Numerical examples are presented and the results are compared with solutions obtained with two-dimensional Euler equations using Ca...

Volume 1A, Symposia: Turbomachinery Flow Simulation and Optimization; Applications in CFD; Bio-Inspired and Bio-Medical Fluid Mechanics; CFD Verification and Validation; Development and Applications of Immersed Boundary Methods; DNS, LES and Hybrid RANS/LES Methods; Fluid Machinery; Fluid-Structu..., 2016

Droplet impingement is the basic module in both ice accretion and anti-icing numerical calculatio... more Droplet impingement is the basic module in both ice accretion and anti-icing numerical calculation. A three dimensional finite volume approach with the capacity of modeling the in-flight droplet impingement on a wide range of subsonic regime is therefore established in this research, using OpenFOAM®. The Eulerian model is applied to estimate the droplet flow field with the same computational grid sets as those of the air flow calculation. The roughness effect caused by ice accretion is considered in the wall function modeling. Thus, the collection efficiency could be investigated for further icing numerical simulations. This approach is validated on both cylinder and sphere benchmark cases. The results are compared with the corresponding experimental and LEWICE (LEWis ICE accretion program) simulation data.

AIAA Journal, 2020

The dielectric barrier discharge (DBD) plasma actuator is a popular technology for active flow co... more The dielectric barrier discharge (DBD) plasma actuator is a popular technology for active flow control; however, the influence of the heat generated by the actuator on its performance is seldom mentioned. In this work, an experimental investigation is conducted to evaluate the interaction between spontaneous heat generation and the performance of an AC-DBD plasma actuator. The characteristics of the AC-DBD plasma actuator are examined temporally in quiescent air, including the profile of the induced flow, capacitance properties, power consumption, plasma light emission, and surface temperature. The particle image velocimetry shows that the velocity profile of the induced flow increases temporally, indicating enhanced momentum injection by the AC-DBD plasma actuator. The capacitance, power consumption, plasma brightness and surface temperature increase with the operation time analogously to exponential curves (f (x) = a − b exp −cx). And values of these properties are proportional to 3.5 power of the applied voltage. The dielectric surface is categorized into three typical streamwise regions according to the heat generation characteristics: the plasma region, the insulated electrode region, and the far field region. The dominant heat generation occurs in the plasma region due to the plasma discharge. The temperature increase of the local dielectric and the gas-plasma mixture enlarges the actuator capacitance, benefits the local induced electric field, and results in longer mean free paths of particles and stronger discharges accordingly. Thus, the spontaneous heat generation affects the induced ionic wind, and the performance of the AC-DBD plasma actuator is time dependent during the early period of the operation.

Journal of Electrochemical Energy Conversion and Storage, 2020

A valveless impedance pump is designed and applied for the first time to supply the liquid fuels ... more A valveless impedance pump is designed and applied for the first time to supply the liquid fuels for a direct sodium borohydride–hydrogen peroxide fuel cell (DBHPFC). This valveless pump consists of an amber latex rubber tube, which is connected at both ends to rigid stainless-steel tubes of different acoustic impedance, and a simple actuation mechanism with a small direct control (DC) motor and a cam combined. The cam is activated by the motor and periodically compresses the elastic tube at a position asymmetrical from the tube ends. The traveling waves emitted from the compression combine with the reflected waves at the impedance-mismatched rubber tube/stainless-steel tube interfaces. The resulting wave interference creates a pressure gradient and generates a net flow. When connected to a DBHPFC with an active area of 25 cm2, the pump can deliver the fuel at a maximum pumping rate of 30 ml/min, resulting in corresponding DBHPFC maximum power and a current of 13.0 W and 25.5 A, res...

Journal of Aerospace Engineering, 2016

International Journal of Heat and Mass Transfer, 2019

Hypervelocity flows of nitrogen and air over a 30°-55° double-wedge configuration are numerically... more Hypervelocity flows of nitrogen and air over a 30°-55° double-wedge configuration are numerically investigated under the condition corresponding to recent experiments conducted with total enthalpy of 8.0 MJ/kg. Time-accurate twodimensional and three-dimensional simulations are performed to resolve the unsteady shock interaction process. For the nitrogen flow, it is found that the three-dimensional simulation predicts a much smaller separation bubble and reduced surface heat flux and pressure peaks. Good agreement can be observed with the experiments in terms of the shock location, the flow structure, and the time-averaged surface heat flux when the three-dimensional effects are considered. For the air flow, the shock interaction mechanisms are similar to those in nitrogen. The real-gas effects tend to decrease the separation bubble and reduce the standoff distance of the detached shock induced by the second wedge, leading to a lower surface heat flux peak compared with the nitrogen result. However, the trend of the experimental heat flux data shows the opposite. To explain the discrepancies, effects of thermochemical nonequilibrium models are investigated. The results indicate that the air flow under the current condition is insensitive to air chemistry and vibration-dissociation coupling models. Suggestions for further study are presented.

2018 AIAA Modeling and Simulation Technologies Conference, 2018

This paper investigates the application of Model Predictive Control (MPC) for path tracking of a ... more This paper investigates the application of Model Predictive Control (MPC) for path tracking of a vertical takeoff and landing (VTOL) tail-sitter unmanned aerial vehicle (UAV) in hover flight. In this work, the nonlinear dynamic model of a quad-rotor tail-sitter UAV including the aerodynamic effect of the wing, propellers, and slipstream was developed. The cascaded MPC controllers were then built upon linearized dynamic models. Path tracking simulations were conducted in a hardware-in-loop (HIL) environment where the UAV model and controllers were running on a PC and a flight computer independently. The simulation results show that the proposed MPC controllers enable the UAV to perform good path tracking and the ability of disturbance rejection under limited onboard computation resource.