Habitat Bennu: Design Concepts for Spinning Habitats Constructed From Rubble Pile Near-Earth Asteroids

The authors explore the possibility that near-earth, rubble pile asteroids might be used as habitats for human settlement by increasing their rotation to produce spin gravity. Using previously published scaling by Maindl et al. and studies of asteroid populations, it is shown that there is no class of hollowed body that would survive the spin-up process on its own without additional reinforcement. Large solid-rock asteroids (diameter D > 10 km) would not have the tensile strength to withstand the required rotation rates and would fracture and break apart. Smaller asteroids, being ‘rubble piles’, have little tensile strength and would quickly disperse. The possibility of containing the asteroid mass using higher-strength materials like carbon nanofiber is instead considered. It is found that a moderate tensile strength container can maintain the integrity of a large spinning cylinder composed of dispersed asteroid regolith. The research extends the range of possible asteroid habitat candidates, since it may become feasible to construct habitats from the more numerous smaller bodies, including NEAs (Near Earth Asteroids). The required tensile strength of the container material scales with habitat radius and thickness and is ∼ 200 MPa for a starting asteroid body of radius 300 m that is spun up to provide 0.3 g⊕ while increasing its radius to 3 km and maintaining a rubble and regolith shield thickness of 2 m to protect against cosmic rays. Ambient solar power can be harvested to aid in spin-up and material processing.

Orientation of Electrospun Magnetic Nanofibers Near Conductive Areas

Electrospinning can be used to create nanofibers from diverse polymers in which also other materials can be embedded. Inclusion of magnetic nanoparticles, for example, results in preparation of magnetic nanofibers which are usually isotropically distributed on the substrate. One method to create a preferred direction is using a spinning cylinder as the substrate, which is not always possible, especially in commercial electrospinning machines. Here, another simple technique to partly align magnetic nanofibers is investigated. Since electrospinning works in a strong electric field and the fibers thus carry charges when landing on the substrate, using partly conductive substrates leads to a current flow through the conductive parts of the substrate which, according to Ampère’s right-hand grip rule, creates a magnetic field around it. We observed that this magnetic field, on the other hand, can partly align magnetic nanofibers perpendicular to the borders of the current flow conductor. We report on the first observations of electrospinning magnetic nanofibers on partly conductive substrates with some of the conductive areas additionally being grounded, resulting in partly oriented magnetic nanofibers.

Feasibility of Reduced-Size Spinning Cylinder Specimens for Pressurised Thermal Shock Testing

Pressurised Thermal Shock (PTS) is one potential risk to the integrity of the reactor pressure vessel in a pressurised water reactor. It has been postulated that PTS could occur as a result of various initiating events such as loss-of-coolant accidents with subsequent re-pressurisation. Experimental studies of PTS are typically very difficult and expensive to perform because both a severe thermal shock and a primary load must be applied to the test specimen, while the specimen itself must be very large to imitate the behaviour of the RPV wall. We investigated the feasibility of using scaled-down PTS test specimens based on the spinning-cylinder concept. The use of scaled-down specimens could greatly reduce the difficulty and cost of experimental PTS testing. To explore this concept, we used a particularly well-characterised spinning-cylinder PTS test: the NESC-1 test which was performed in the late 1990s. A large parametric set of elastic-plastic finite element models was used determine a combination of specimen dimensions and test conditions that would very closely mimic the crack tip conditions which occurred during NESC-1. Specifically, the modelling demonstrated that it was indeed possible to replicate the KJ vs. temperature trajectory, and crack tip constraint, at a critical point on the crack tip line from which tearing initiated during the actual NESC-1 test. The reduced-size specimen must be carefully designed: it cannot be a simple linear scale-down due to the inherent non-linearity of both the thermal and mechanical processes which occur during PTS.

MODEL PENGENDALIAN KATODIK DALAM ELEKTRODE DISK PEMUTAR SISTEM KOROSI

The effect of fluids flow rate onto necessity of current density cathodic protection which characterized using Rotatingdisk electrode (RDE) model has been researched on an electrochemistry manner. This research was done to AISI 1018 steel as the electrode spinning cylinder-shaped inside aerated dissolvable NaCl 3.5%. using variation spinning rate 0–2000rpm and 25–75° C temperature. Current density cathodic protection necessity determined from the steel interface potential - 800mV with reference anode Ag/AgCl. Experiment result shows that the increasing of electrode rate, cathodic protection current density needs increased due to diffusion layer tare faction and also because corrosion potential become more positive. Higher temperature would increase cathode protection current density needs and makes corrosion potential more negative. Oxygen activation energy value to be diffused onto electrode surface support the corrodibility AISI 1018 toward temperature increment, because cathodic reaction controlled by transfer mass of dissolved oxygen.

Three-Dimensional Instabilities in Flow Past a Rotating Cylinder

Flow past a spinning circular cylinder placed in a uniform stream is investigated via three-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier-Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and freestream speed of the flow is 200. The nondimensional rotation rate, α, (ratio of the surface speed and freestream speed) is 5. It is found that although the two-dimensional flow for α=5 is stable, centrifugal instabilities exist along the entire span in a three-dimensional set-up. In addition, a “no-slip” side-wall can result in separation of flow near the cylinder ends. Both these effects lead to a loss in lift and increase in drag. The end conditions and aspect ratio of the cylinder play an important role in the flow past a spinning cylinder. It is shown that the Prandtl’s limit on the maximum lift generated by a spinning cylinder in a uniform flow does not hold.

Study of Aerodynamic Forces on a Rotating Wind Driven Ventilator

A wind driven ventilator is a simple, cost-effective and environmentally-friendly device that can improve comfort and the working environment. Unfortunately very little is known about the complex flow field associated with the operation of this device. A wind tunnel investigation of the flow associated with a rotating wind ventilator was, therefore, carried out at the aerodynamic laboratory of the University of New South Wales within the Reynolds number range of 1.1 times 105 to 5.5 times 105. An attempt was also made to study some of the important features associated with operation of a rotating wind ventilator using a simple model of a stationary and a spinning cylinder. The results were encouraging and several flow features were identified for future improvement in the performance of a wind ventilator.