arXiv subjects

Valentin Dichtl

Publications and source records attributed to Valentin Dichtl.

3 recordsLinked to original sources

arXiv2026

Nature of granular drag in microgravity

The influence of gravity on the drag force acting on a projectile impacting granular media is investigated experimentally via embedded inertial measurement unit (IMU) sensor and numerically through discrete element method (DEM) simulations. As gravity approaches zero, inertial drag dominates, yielding qualitatively different scaling laws and cavity dynamics. Analogous to fluid dynamics, we define a dimensionless granular drag coefficient $C_{\rm gd}$, which is found to stay largely at a constant $\sim 1.2$ in microgravity while an additional term inversely proportional to impact velocity arises in the presence of gravity. The constant term can be understood from momentum transfer along the penetration direction while the additional term suggests the influence of internal stress built-up due to gravity. Similar discrepancy is also found for the initial peak of the drag force. This analogy provides novel insights into the nature of granular drag in microgravity and sheds light on future space missions.

cond-mat.soft↗

arXiv2025

The nonlinear limit of Babinet's Principle

Babinet's principle is a powerful tool for predicting the scattering behavior of planar structures where the solution for the complementary structure is already known. This makes it ubiquitous in the design of aperture antennas or metamaterials. Even for plasmonic nanostructures, a qualitative match of the behavior for complementary structures has been reported. Here, we discuss whether Babinet's principle can be extended to nonlinear scattering. We compare the third harmonic emission of plasmonic nanorods and complementary nanoslits by far field imaging and simulation. We find significantly different far field images, in agreement between experiment and simulation. We explain these differences by the higher spatial resolution at the third harmonic wavelength and by additional eddy currents in slits that are not present in rods. Within these limits, Babinet's principle can guide the design of inverted nonlinear plasmonic resonators, which promise to be more stable at high excitation power due to better thermal conductivity.

physics.optics↗

arXiv2019

The role of initial speed in projectile impacts into light granular media

Projectile impact into a light granular material composed of expanded polypropylene (EPP) particles is investigated systematically with various impact velocities. Experimentally, the trajectory of an intruder moving inside the granular material is monitored with a recently developed non-invasive microwave radar system. Numerically, discrete element simulations together with coarse-graining techniques are employed to address both dynamics of the intruder and response of the granular bed. Our experimental and numerical results of the intruder dynamics agree with each other quantitatively and are in congruent with existing phenomenological model on granular drag. Stepping further, we explore the `microscopic' origin of granular drag through characterizing the response of granular bed, including density, velocity and kinetic stress fields at the mean-field level. In addition, we find that the dynamics of cavity collapse behind the intruder behaves qualitatively different with different impact velocities. Moreover, the kinetic pressure ahead of the intruder decays exponentially in the co-moving system of the intruder. Its scaling gives rise to a characteristic length scale, which is in the order of intruder size. This finding is in perfect agreement with the long-scale inertial dissipation type that we find in all cases.

cond-mat.soft↗