Formation of Warped Disks by Galactic Fly-by Encounters. I. Stellar Disks

Warped disks are almost ubiquitous among spiral galaxies. Here we revisit and test the `fly-by scenario' of warp formation, in which impulsive encounters between galaxies are responsible for warped disks. Based on N-body simulations, we investigate the morphological and kinematical evolution of the stellar component of disks when galaxies undergo fly-by interactions with adjacent dark matter halos. We find that the so-called `S'-shaped warps can be excited by fly-bys and sustained for even up to a few billion years, and that this scenario provides a cohesive explanation for several key observations. We show that disk warp properties are governed primarily by the following three parameters; (1) the impact parameter, i.e., the minimum distance between two halos, (2) the mass ratio between two halos, and (3) the incident angle of the fly-by perturber. The warp angle is tied up with all three parameters, yet the warp lifetime is particularly sensitive to the incident angle of the perturber. Interestingly, the modeled S-shaped warps are often non-symmetric depending on the incident angle. We speculate that the puzzling U- and L-shaped warps are geometrically superimposed S-types produced by successive fly-bys with different incident angles, including multiple interactions with a satellite on a highly elongated orbit.Comment: 16 pages, 13 figures, 3 tables. Accepted for publication in Ap

Localized-Based Control Algorithm For Passenger Ride Comfort

In this thesis, a new localized-based suspension control strategy is developed, simulated and validated with experimental results. Basic concepts of mathematical vehicle models, suspension systems, and conventional control algorithms, namely skyhook, groundhook, and hybrid controllers, used for ride comfort and road holding are also studied and implemented for comparison. The conventional control algorithms are for the vertical motion of a sprung mass, or an unsprung mass at each corner of a vehicle. The proposed localized-based control algorithm is a controller that can change its target location in a vehicle to where it is needed most. Simulation results show that the localized-based controller provides better ride comfort on targeted locations than the conventional control algorithms. Experimental results using a Cadillac STS test vehicle are used to compare the localized-based control algorithm with the conventional algorithms in vehicle comfort and holding. The results show that the new controller improves ride comfort more than other controllers. The prospect of easily adapting the new control algorithm to various vehicles is promising