arXiv subjects

Yen-Chen Chen

Publications and source records attributed to Yen-Chen Chen.

6 recordsLinked to original sources

arXiv2025

Numerical Study on Jet-Like Outwash Induced by Multi-Rotor eVTOLs and Engineering Approaches for Outwash Mitigation

This study presents a comprehensive computational investigation of outwash phenomena generated by electric vertical takeoff and landing (eVTOL) aircraft, with particular emphasis on how rotor geometry and alignment shape hazardous airflow patterns at vertiports. Using nondimensional Reynolds-averaged Navier-Stokes (RANS) simulations with the k-omega SST turbulence model implemented in OpenFOAM, the research systematically characterizes jet-like outwash across a range of multi-rotor configurations. Results demonstrate that propeller count and inter-propeller spacing are primary determinants of outwash intensity, orientation, propagation range, and boundary-layer structure. For power-lift eVTOLs, low propeller counts combined with narrow spacing produce highly directional, intensified jet-like outwash with propagation ranges far exceeding current FAA EB105a safety standards. Conversely, higher propeller counts and larger spacings reduce peak velocities and propagation distances, enabling safer and more compact vertiport layouts. High-propeller-count designs further exhibit vertically stratified and thickened outwash boundary layers, requiring tailored mitigation strategies. Targeted engineering solutions-such as modular blast deflectors aligned with predicted outwash directions-are shown to reduce required vertiport safety areas by up to 82% without compromising operational safety. These findings establish a direct link between aircraft design, regulatory compliance, and infrastructure optimization, offering practical pathways for safe and scalable urban air mobility. The study also provides a foundation for future research on optimal mitigation device geometries and system-level integration of eVTOL operations within urban environments.

physics.flu-dyn↗

arXiv2025

Confinement geometry governs the impact of external shear stress on active stress-driven flows in microtubule-kinesin active fluids

Active fluids generate internal active stress and exhibit unique responses to external forces such as superfluidity and self-yielding transitions. However, how confinement geometry influences these responses remains poorly understood. Here, we investigate microtubule-kinesin active fluids under external shear stresses in two geometries. In slab-like confinement (a narrow-gap cavity), external stresses propagated throughout the system, leading to stress competition and a kinematic transition that shifted dynamics from active stress-dominated to shear stress-dominated flow. At the transition, we estimate the active stress to be ~1.5 mPa. Simulation supported that this transition arises from stress competition. In contrast, in ring-like confinement (a toroidal system), external forces acted locally, inducing a mini cavity flow that triggered self-organized reconfiguration rather than direct entrainment. These findings show that the response of active fluids to external forcing depends not only on the magnitude of the applied stress but also on how confinement geometry directs and redistributes that stress, revealing a new approach to controlling active fluid behavior by combining static geometrical design with dynamic external stimuli for real-time modulation of flow patterns. Such control strategies may be applied to microfluidic systems, where external inputs such as micromechanical actuators can dynamically tune active fluid behavior within fixed device geometries, enabling transitions between chaotic and coherent flows for tasks such as mixing, sorting, or directed transport.

cond-mat.soft↗

arXiv2021

Flow coupling between active and passive fluids across water-oil interfaces

Active fluid droplets surrounded by oil can spontaneously develop circulatory flows. However, the dynamics of the surrounding oil and their influence on the active fluid remain poorly understood. To investigate interactions between the active fluid and the passive oil across their interface, kinesin-driven microtubule-based active fluid droplets were immersed in oil and compressed into a cylinder-like shape. The droplet geometry supported intradroplet circulatory flows, but the circulation was suppressed when the thickness of the oil layer surrounding the droplet decreased. Experiments with tracers and network structure analyses and continuum models based on the dynamics of self-elongating rods demonstrated that the flow transition resulted from flow coupling across the interface between active fluid and oil, with a millimeter-scale coupling length. In addition, two novel millifluidic devices were developed that could trigger and suppress intradroplet circulatory flows in real time: one by changing the thickness of the surrounding oil layer and the other by locally deforming the droplet. This work highlights the role of interfacial dynamics in the active fluid droplet system and shows that circulatory flows within droplets can be affected by millimeter-scale flow coupling across the interface between the active fluid and the oil.

physics.flu-dyn↗

arXiv2020

Boost the Public Demand for Soft Matter Education and Career Opportunities with a Homemade Video

The study aims to promote the awareness and education of soft matter which has become a popular research topic owing to its capability of developing self-assembling materials for numerous industries such as self-healing materials. To pursue after this aim, we composed a homemade video to illustrate the soft matter concepts, followed by distributing a pre/post attitudinal survey to evaluate the effectiveness of the video on promoting the awareness of soft matter. The survey showed that the video effectively stimulated the public interest in soft matter-related knowledge, research, and careers by 27.8 percent on average. Moreover, the participants demanded more investment and soft matter education, suggesting that WPI provide more resources on developing soft matter education.

physics.ed-ph↗

arXiv2019

Emission Line Luminosity Distributions of Seyfert 2 Galaxies

We probed the relation between line activities of Seyfert 2 galaxies and their host galaxies. We selected Seyfert 2 galaxies from the Sloan Digital Sky Survey Data Release 10 with redshifts less 0.2. We used the luminosity of the emission lines as indicators of AGN power. We found that the Seyfert 2 galaxies seem to have two populations in the emission line luminosity distributions. We considered the L[OIII]/Lbulge ratio as an accretion rate indicator and found that the two Seyfert 2 distributions seem to have different accretion rates. We found that these two Seyfert 2 populations, although classified by their emission line distributions, turned out to have different morphology distributions. These results indicate that these different populations of the Seyfert 2 galaxies might be significantly different in their physical conditions.

astro-ph.GA↗

arXiv2017

Morphology of Seyfert Galaxies

We probed the relation between properties of Seyfert nuclei and morphology of their host galaxies. We selected Seyfert galaxies from the Sloan Digital Sky Survey with redshifts less 0.2 identified by the Véron Catalog (13th). We used the "{\it{FracDev}}" parameter from SDSS galaxy fitting models to represent the bulge fractions of the Seyfert host galaxies. We found that the host galaxies of Seyfert 1 and Seyfert 2 are dominated by large bulge fractions, and Seyfert 2 galaxies are more likely to be located in disk galaxies whereas most of the Seyfert 1 galaxies are located in bulge-dominant galaxies. These results indicate that the types of AGNs are related to their host galaxies and can not be explained by the traditional unification model of Seyfert galaxies.

astro-ph.GA↗