A bibliography /with abstracts/ on gas-lubricated bearings Interim report

Gas lubricated bearings - annotated bibliograph

Index to NASA Tech Briefs, January - June 1966

Index to NASA technological innovations for January-June 196

Cumulative Index to NASA Tech Briefs, 1963 - 1966

Cumulative index of NASA Tech Briefs dealing with electrical and electronic, physical science and energy sources, materials and chemistry, life science, and mechanical innovation

Damping of piezoelectric MEMS oscillators – fundamentals and applications

A limiting parameter for the performance of micromechanical oscillators is the damping induced by the surrounding medium. In this work, the damping losses of micromechanical oscillators with piezoelectric actuation and detection are investigated in nine different gas atmospheres over a pressure range of six decades. In addition, the influence of the distance to a spatial boundary is examined, covering a range from narrow gaps with squeeze film damping to an almost freely oscillating structure. This reveals a superposition of four different damping mechanisms, which occur in varying strength depending on pressure, distance and eigenmode. Using an analytical approach, the individual damping phenomena can be separated from each other and subsequently evaluated in a targeted manner. Based on these results, new insights are gained for the molecular flow regime as well as the transitional flow regime, which include the impact of the number of active degrees of freedom of the gas molecules as well as thermal resonance effects. In addition, an electrical equivalent circuit was designed for the entire measurement range, which shows very good agreement with the experimental data. Finally, the damping effects are exploited for applications in sensor technology and a wide range pressure sensor using the nonlinear regime of the oscillators as well as a concept for the measurement of the oxygen concentration are presented.Eine für die Leistungsfähigkeit mikromechanischer Oszillatoren limitierende Größe stellt die Dämpfung durch das umgebende Medium dar. In dieser Arbeit werden daher die Dämpfungsverluste mikromechanischer Oszillatoren mit piezoelektrischer Anregung und Detektion in neun verschiedenen Gasatmosphären über einen Druckbereich von sechs Dekaden untersucht. Zusätzlich wird der Einfluss des Abstandes zu einer räumlichen Begrenzung betrachtet und dabei ein Bereich von engen Spalten mit Squeeze Film Dämpfung bis hin zu fast frei schwingenden Strukturen untersucht. Dabei ergibt sich eine Überlagerung von vier verschiedenen Dämpfungsmechanismen, welche in Abhängigkeit von Druck, Abstand und Eigenmode in unterschiedlich starker Ausprägung auftreten. Durch einen analytischen Ansatz lassen sich die einzelnen Dämpfungsphänomene voneinander separieren und in der Folge gezielt auswerten. Anhand dieser Ergebnisse wurden für den molekularen sowie den Übergangsbereich neue Erkenntnisse gewonnen, welche die Anzahl aktiver Freiheitsgrade der Gasmoleküle sowie thermische Resonanzeffekte miteinbeziehen. Darüber hinaus wurde für den gesamten Messbereich ein elektrisches Ersatzschaltbild konzipiert, das eine sehr gute Übereinstimmung mit den experimentellen Daten zeigt. Abschließend werden die Dämpfungseffekte für Anwendungen in der Sensorik erschlossen und ein Mehrbereichsdrucksensor mit Hilfe des nichtlinearen Bereichs der Oszillatoren sowie ein Konzept zur Messung des Sauerstoffgehaltes präsentiert.German Research Foundation (DFG

National Educators' Workshop: Update 1989 Standard Experiments in Engineering Materials Science and Technology

Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 89, held October 17 to 19, 1989 at the National Aeronautics and Space Administration, Hampton, Virginia. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

Cumulative index to NASA Tech Briefs, 1963-1967

Cumulative index to NASA survey on technology utilization of aerospace research outpu

12th International Conference on Vibrations in Rotating Machinery

Since 1976, the Vibrations in Rotating Machinery conferences have successfully brought industry and academia together to advance state-of-the-art research in dynamics of rotating machinery. 12th International Conference on Vibrations in Rotating Machinery contains contributions presented at the 12th edition of the conference, from industrial and academic experts from different countries. The book discusses the challenges in rotor-dynamics, rub, whirl, instability and more. The topics addressed include: - Active, smart vibration control - Rotor balancing, dynamics, and smart rotors - Bearings and seals - Noise vibration and harshness - Active and passive damping - Applications: wind turbines, steam turbines, gas turbines, compressors - Joints and couplings - Challenging performance boundaries of rotating machines - High power density machines - Electrical machines for aerospace - Management of extreme events - Active machines - Electric supercharging - Blades and bladed assemblies (forced response, flutter, mistuning) - Fault detection and condition monitoring - Rub, whirl and instability - Torsional vibration Providing the latest research and useful guidance, 12th International Conference on Vibrations in Rotating Machinery aims at those from industry or academia that are involved in transport, power, process, medical engineering, manufacturing or construction

Composites for machine tool beds

In general, machine tool structures like lathe, milling, broaching, and grinding machines, etc. are subjected to regular unwanted vibrations. These machine tool vibrations or chatter are deleterious to machining operations. It results in degraded quality on the machined parts, shorter tool life, and unpleasant noise, hence are to be necessarily damped out. The important characteristics of the machine tool structures for metal cutting are high damping and static stiffness which ensure manufacture of work pieces of the required geometries with acceptable surface finish at the required rate of production in the most economical way. The unwanted vibrations must be arrested in ordet to ensure higher accuracy along with productivity. In the present work, the chatter vibrations on a slotted table Horizontal Milling Machine have been damped out using composite structure as a substitute for the base of the work piece. Glass Fiber Polyester and Glass Fiber Epoxy plates are fixed on to the slotted table as a secondary bed material and the workpiece is mounted on this bed for feeding to the rotating milling cutter. Initially four holes are drilled on each plate of the composite and a set of five plates of each type of composite are mounted for conducting the experiments. A mild steel specimen of similar dimension of the composite plate is placed on the pile of the composites and the setup is fixed to the slotted table using bolts and nuts. An up milling operation is carried out and the vibration signal is recorded on the screen of the digital phosphorus storage oscilloscope. The signal and RMS amplitude, frequency and time period of vibrations are recorded. The experiment is repeated for different sets of composite plates by decreasing the number and the corresponding readings are recorded and tabulated. Moreover, experiments are also conducted without any composite material below the mild steel specimen. It is observed that the vibration amplitude decreases with increase in number of layers of sheets of composites and then increases with increase in number of plates. Moreover, the optimum number of composites are also experimentally determined. The design of the experimental setup has been modeled using CatiaV5R15. Apart from total damping of the system, emphasis has also been focused to find out the material damping of the composite materials so as to select the same for effective damping of the structures. An energy balance approach has been used for calculating the material damping of the fiber reinforced composites used in the experiment

Development and demonstration of a pico-Watt calorimeter for optical absorption spectroscopy

An optical calorimeter for sensitive absorption measurements of non-radiative samples at 4 K was designed, built, and demonstrated. It consists of a cryostat cooled by a commercial pulse tube (PTC) refrigerator, a measurement chamber housing the sample and thermometers, and various fiber-coupled light sources. By employing measures to damp mechanical noise from the environment and active temperature stabilization of critical components of the instrument temperature noise as low as 6 nK/√Hz at 50 mHz was achieved under 15 mW of optical excitation. An optical absorption induced temperature increase of the sample as small as 2.5 nK could be resolved using paramagnetic temperature sensors with SQUID (Superconducting Quantum Interference Device) readout. This resulted in an absorption sensitivity of 0.3 ppm and 0.6 ppb for tunable 30 μW optical excitation from 330 nm to 1700 nm and for 15-mW laser excitation, respectively. The instrument was applied to the characterization of stacks of dielectric films for material science studies and laser mirror development