Spin bearing retainer design optimization

The dynamics behavior of spin bearings for momentum wheels (control-moment gyroscope, reaction wheel assembly) is critical to satellite stability and life. Repeated bearing retainer instabilities hasten lubricant deterioration and can lead to premature bearing failure and/or unacceptable vibration. These instabilities are typically distinguished by increases in torque, temperature, audible noise, and vibration induced by increases into the bearing cartridge. Ball retainer design can be optimized to minimize these occurrences. A retainer was designed using a previously successful smaller retainer as an example. Analytical methods were then employed to predict its behavior and optimize its configuration

Modelling of high pressure binary droplet collisions

AbstractDroplet collision efficiency is a rather uncharted area for real hydrocarbon systems under non-atmospheric conditions. It is also of great interest in many industrial applications. In this work binary head-on droplet collisions at high pressure have been simulated using the lattice Boltzmann method. A model that captures the physics of the coalescence process is used where no external criterion for coalescence is needed. The collision process is described in terms of hydrodynamic variables and through a quantitative study of energy loss. At high pressures, low inertia collisions are the most frequent. Distinguishing between bouncing and coalescence under these conditions is needed in order to provide closure conditions for macroscopic CFD models. A limit of Re<170ρlg is found to predict coalescence in all the cases simulated. In addition this paper explains the stochastic behaviour of low inertia coalescence at high pressure. This has major implications both when building macroscopic models for predicting industrial process efficiencies and in the optimization of equipment internals working with droplets at high pressure as is the case for combustion chambers and gas–liquid separators

Correlation of Wear and Mechanics for Subjects having a Metal-on-Polyethylene Total Hip Arthroplasty Measured in vivo

Femoral head separation from the acetabular shell has been recorded, but clinical significance of this phenomenon has not yet been established. The objective of the study was to determine if there is a correlation between femoral head separation (sliding of the femoral head away from the acetabular cup), hip joint forces, and acetabular liner wear. Twenty subjects were strategically selected to participate in this study. All subjects were asked to perform gait on a treadmill while under fluoroscopic surveillance. The number of incidences involving femoral head separation was tallied and acetabular bearing surface forces were determined for each subject. A statistical correlation was done todetermine if femoral head sliding is related to the kinetics of the hip joint. Forty percent of the subjects were determined to have greater than 0.25 mm of wear. Twelve subjects demonstrated femoral head sliding leading to separation. Ten percent of the subjects tested demonstrated both wear and separation. The forces determined at the hip joint ranged from 1.75 to 1.85 times body weight. Although it was expected that subjects having more wear would have greater magnitudes of femoral head separation, the opposite was true. Kinematic data resulted in increased force magnitudes for a subject with separation then a subject with separation

Recent Advances in Graph Partitioning

We survey recent trends in practical algorithms for balanced graph partitioning together with applications and future research directions

Electromagnetic pulse accelerator of projectiles

Tato práce se zabývá použitím magnetického pole k urychlení projektilů v zařízení zvaném coilgun. Je složena ze dvou částí, z nichž první je teoretická diskuze o magnetismu a jeho využití, druhá část je o vlastním coilgunu, jeho výhodách a nevýhodách. Následuje série měření na dvou experimentálně postavených coilgunech a jejich optimalizace pro dosažení co nejlepších výsledků. První část probírá více témat. Na začátku je krátká kapitola, ve které se definuje magnetické pole a s ním související konstanty a jevy. Další dvě kapitoly jsou zaměřeny na různé typy materiálů, především feromagnetik, jak reagují na přítomnost magnetického pole a jakými parametry jsou specifikovány. Dále je výčet některých aplikací magnetizmu napříč lidskou společností. V druhé části se popíše princip coilunu a jak byly prototypy vyrobeny. Měření na prvním prototypu je zaměřeno na testování různých materiálů projektilu, jeho rozměrů a přínosy externího magnetického obvodu okolo cívky. Taktéž je tam kapitola pojednávající o způsobu měření rychlosti projektilu. Druhý prototyp se snaží eliminovat nedostatky zjištěné na prvním a prozkoumat výhody vícenásobného urychlení na dalších stupních.This work focuses on using magnetic field to accelerate projectile in a device called coilgun. It consists of two parts, first is theoretical discussing magnetism and its use, the other part is about coilgun itself, its benefits and drawbacks. Followed by series of measurements on two experimentally built coilguns and trying optimize it to achieve best results. First part discusses multiple topics. In the beginning, there is a small section defining magnetic field and other constants and phenomenons connected with it. Next two chapters are focused on different types of material, mainly ferromagnetics, how they react to magnetic field and what parameters we can follow, followed by a list of several applications of magnetic field in different areas of human society. The second part describes main principle of coilgun and how the prototypes were made. Measurements on a first prototype consist of trying different materials for projectile, various dimensions of it and benefits of using external shell for accelerating coil. There is also a chapter discussing velocity measurement of a projectile. Second prototype is trying to avoid all the flaws, which were found on the first prototype and find a benefits of using multiple acceleration stages.

A Digital Solar Aspect Sensor

The solar aspect sensor described herein performs the analog-to-digital conversion of data optically. To accomplish this, it uses a binary "Gray code" light mask to produce a digital indication, in vehicle-fixed coordinates, of the elevation and azimuth angles of incident light from the sun. This digital solar aspect sensor system, in Explorer X, provided measurements of both elevation and azimuth angles to +/- 2 degrees at a distance of over 140,000 statute miles

Design of an inert fluid injection system, phase 3 Final report

Research, development, and design of velocity trim system for third stage of Delta launch vehicl

Wet steam drying: Microwave-assisted droplet evaporation in open-cell ceramic foams

In many energy and process engineering systems where fluids are processed, droplet-laden gas flows may occur. As droplets are often detrimental to the system’s operation, they are required to be removed. According to the state-of-the-art, industrial droplet removal is achieved through a sequential arrangement of several separators followed by droplet collection and discharge. This results in a high-quality gas stream, yet at the expense of bulky and expensive systems that are difficult to retrofit to existing facilities. In addition, the multiple sequential separators produce high pressure drops, further increasing operating costs. Alternatively, a single droplet separation stage and in situ evaporation would provide compact solutions for facilities. However, compact engineering solutions for the removal of entrained droplets are difficult to achieve with conventional flow control and conduction heat transfer approaches such as Joule heating. Joule heating requires a well-defined and homogeneous electrical resistance to ensure uniform heating, which is technically challenging to apply in fine separators and thus compact removal devices are hence often costly and ineffective. Therefore, it becomes necessary to investigate alternative heating approaches to overcome these challenges, such as volumetric heating using microwaves. The research conducted in this thesis aims to analyze the potential of a compact microwave solution approach for droplet removal. The compactness of the approach relies on a novel fine separator structure enhanced by microwave-heat transfer for efficient in-flow droplet evaporation. The investigation targets at fundamental studies of the combined effect of droplet flow filtering and heat transfer from numerical calculations and experimentation. As novel fine separators, solid open-cell foams are a promising alternative for the separation of liquid droplets suspended in gas flows at comparably low pressure drops. Using susceptors, such as dielectric materials, for the skeleton and exposing them to microwaves is an efficient way to use them as heating elements. Silicon carbide (SiC) based open-cell foam samples were considered for the study as they are good susceptor materials. First, pore-scale fluid numerical simulations on representative foam models were used to obtain a deeper insight into the effects of pore size and pore density on the droplet retention time within foams. Numerical findings were reported considering the pressure gradient and the residence time distribution of droplets under different superficial flow velocities, droplet sizes, porosities and pore densities. Next, the temperature-dependent permittivity of SiC-based foam materials was determined by the cavity perturbation technique using a waveguide resonator at a microwave frequency of 2.45 GHz up to 200 °C. The permittivity was of particular interest as it is a crucial parameter for predicting and designing systems utilizing microwave heating. Along the permittivity measurements, electromagnetic wave propagation simulations were used to derive novel mixing relations describing the effective permittivity of foams while considering their skeletal morphology. The derived relations facilitate an efficient and reliable estimation of the effective permittivity of open-cell foams, producing good agreement to experimental data. Using the foams dielectric properties and the fluid characteristics of droplet-laden streams, a microwave applicator was designed to concentrate the electric field on the open-cell foams. The applicator was constructed for carrying out experimental studies on droplet evaporation removal under different flow velocities, microwave power and different SiC-based foams. Measurements of droplet size, velocity, number density and flux at the inlet and outlet streams of the applicator were performed using a 2D-phase Doppler interferometer. Eventually, it was found from the experimental data analysis that the application of open-cell ceramic foams as a filter medium reduced 99.9 % of the volumetric flow of droplets, while additional microwave exposure increased the reduction to 99.99 %. In addition, microwave-heated foams prevent droplet re-entrainment and structure-borne liquid accumulation within foams, thus avoiding water clogging and flooding. Hence, open-cell foams can be used as fine droplet separators as long as microwave heating may effectively evaporate accumulations of liquid. An important factor in designing future devices based on this microwave heating approach is the temperature, as it changes the arcing breakdown voltage of the gas, thus limiting the microwave input power and droplet flow velocity. Although more investigations are needed to develop an applicable and optimal product, the results presented in this thesis provide a first insight into the viability of using microwave heating and fine filtering as a compact solution for droplet removal