We examine two dimensional properties of vortex shedding past elliptical cylinders through numerical simulations. Specifically, we investigate the vortex formation length in the Reynolds number regime 10 to 100 for elliptical bodies of aspect ratio in the range 0.4 to 1.4. Our computations reveal that in the steady flow regime, the change in the vortex length follows a linear profile with respect to the Reynolds number, while in the unsteady regime, the time averaged vortex length decreases in an exponential manner with increasing Reynolds number. The transition in profile is used to identify the critical Reynolds number which marks the bifurcation of the Karman vortex from steady symmetric to the unsteady, asymmetric configuration. Additionally, relationships between the vortex length and aspect ratio are also explored. The work presented here is an example of a module that can be used in a project based learning course on computational fluid dynamics.

This paper analyzes the aiming errors in a stationary controlled turret system given target location as input. Turret control system research is limited to demonstrating the viability of a proposed control strategy. However, there is no standard procedure for evaluating turret system accuracy when there is uncertainty in the turret model and the aimpoint measurement. Therefore, we propose a methodology for analyzing the accuracy of a stationary turret system against static targets. In our approach, we derive a turret model and design a proportional–integral–derivative controller and a model predictive controller to rotate the turret to the centroid of the target in simulations. We then perform numerical experiments that analyze the impact of uncertainty in the turret model parameters and the aimpoint measurement on the aiming errors. Our results indicate that the turret rotational movement is more sensitive to uncertainty in the moment of inertia than the damping coefficient, which could lead to reduced accuracy. The results also support the assumption of higher aiming errors over larger turret rotations and, assuming no time constraints, accuracy improves the longer the controller stabilizes the turret, though this may not always be practical. The results quantify the impact of uncertainty on turret system accuracy.

The gravitational wave signal produced by the merger of two compact objects includes both an oscillatory transient and a nonoscillatory part, the so-called memory effect. This produces a permanent displacement of test masses and has not yet been measured. We use general relativistic magnetohydrodynamic simulations, including neutrinos, with several representative viable equations of state, to quantify-for the first time-the effects of the neutron star magnetic field, neutrino emission, and the ejected mass on the linear and nonlinear displacement memory in binary neutron star mergers. We find that the additional contributions due to the emission of electromagnetic radiation, neutrinos and baryonic ejecta can be ∼15% of the total memory for moderate magnetic fields and up to ∼50% for extreme magnetic fields. The memory is most affected by changes in the equation of state, the binary mass, and the magnetic field. In particular, for moderate premerger field strengths, the dominant impact of the electromagnetic field is the change in the gravitational wave luminosity, and the associated gravitational wave null memory, due to the unstable growth of the magnetic field and the resulting redistribution of angular momentum it induces in the remnant. While the direct electromagnetic contribution to the null memory is additive, the change in the gravitational wave null memory can-in some cases-result in the total memory being smaller than that from the corresponding nonmagnetized binary. Furthermore, in contrast to binary black hole mergers, the growth of the memory in binary neutron star mergers is extended due to the long emission timescale of electromagnetic fields, neutrinos, and ejecta. These results necessitate the consideration of the magnetic field, as well as the equation of state, for accurate parameter estimation in future analyses of gravitational wave memory data.