arXiv subjects

Ching Lok Chong

Publications and source records attributed to Ching Lok Chong.

3 recordsLinked to original sources

arXiv2024

Observability-Aware Control for Quadrotor Formation Flight with Range-only Measurement

Cooperative Localization is a promising approach to achieving safe quadrotor formation flight through precise positioning via low-cost inter-drone sensors. This paper develops an observability-aware control principle tailored to quadrotor formation flight with range-only inter-drone measurements. The control principle is based on a novel approximation of the local observability Gramian (LOG), which we name the Short-Term Local Observability Gramian (STLOG). The validity of STLOG is established by proving its link to directional estimation precision in nonlinear systems. We propose the Observability Predictive Controller (OPC), a receding-horizon controller that generates optimal inputs to enhance information gain in weakly observable state directions by maximizing the minimum eigenvalue of the STLOG. This reduces the risk of estimator divergence due to the unbounded growth of uncertainty in weakly observed state components. Monte Carlo simulations and flight experiments are conducted with quadrotors in a GNSS-denied ferrying mission, showing that the OPC improves positioning confidence and estimator robustness.

cs.RO↗

arXiv2022

A Poisson map from kinetic theory to hydrodnamics with non-constant entropy

Kinetic theory describes a dilute monatomic gas using a distribution function $f(q,p,t)$, the expected phase-space density of particles. The distribution function evolves according to the collisionless Boltzmann equation in the high Knudsen number limit. Fluid dynamics is an alternative description of the gas using hydrodynamic variables that are functions of position and time only. These hydrodynamic variables evolve according to the compressible Euler equations in the inviscid limit. Both systems are noncanonical Hamiltonian systems. Each configuration space is an infinite-dimensional Poisson manifold, and the dynamics is the flow generated by a Hamiltonian functional via a Poisson bracket. We construct a map $\mathcal{J}_1$ from the space of distribution functions to the space of hydrodynamic variables that respects the Poisson brackets on the two spaces i.e. a Poisson map. It maps the $p$-integral of the Boltzmann entropy $f\log f$ to the hydrodynamic entropy density. This map belongs to a family of Poisson maps to spaces that include generalised entropy densities as additional hydrodynamic variables. The whole family can be generated from the Taylor expansion of a further Poisson map that depends on a formal parameter. If the kinetic-theory Hamiltonian factors through the Poisson map $\mathcal{J}_1$, an exact reduction of kinetic theory to fluid dynamics is possible. This is not the case, but by ignoring the relative entropy of $f$ to its local Maxwellian, we can construct an approximate Hamiltonian that factors through the map. The resulting reduced Hamiltonian generates the compressible Euler equations. We can thus derive the compressible Euler equations as a Hamiltonian approximation to kinetic theory. We also give an analogous Hamiltonian derivation of the compressible Euler--Poisson equations with non-constant entropy, starting from the Vlasov--Poisson equation.

math-ph↗

arXiv2019

Double bracket formulation for the distribution function approach to multibead-chain suspensions

A suspension of elastic chains of small beads in a Newtonian fluid is a common model for a viscoelastic polymer solution. The configuration of these multibead chains can be described by a distribution function that evolves according to a Liouville or Fokker--Planck equation. For example, when we consider a suspension of Hookean bead-spring pairs, this approach leads to the well-known upper-convected Maxwell model. This is done by taking the second moment of the Fokker--Planck equation that governs the distribution function, which describes the stress of the bead-spring pairs on the fluid. The evolution of these multibead-chain suspensions can be described using a double bracket formulation with a Hamiltonian functional. The conservative part of the dynamics is described by a Poisson bracket, and the dissipative part by an additional symmetric bracket. We treat the configuration space of multibead chains as a higher order tangent bundle. Lifting the fluid velocity field to the bundle leads naturally to a semidirect product Lie--Poisson bracket for the conservative dynamics. The elastic stress exerted by the chains then follows directly from the Hamiltonian functional. For chains with three or more beads, the possible bending of the chain introduces an angular momentum flux that is absent for chains with two beads. This flux appear as an asymmetric elastic stress whose antisymmetric part is the divergence of a rank-$3$ tensor, as in the Cosserats' theory of couple stresses. We investigate the possibility of an exact closure, passing from a distribution function description to a closed internal state variable description of the fluid suspension, and obtain some sufficient conditions for their existence. The resulting exactly closable models are generalisations of the upper-convected Maxwell model to Hookean bead-spring chains.

physics.flu-dyn↗