Quiet Air Research Articles

Stability Analysis of Ice Crystal Orientation

Abstract The stability of ice crystal orientation is studied by modeling the airflow around ice crystals at moderate Reynolds number, where an ice crystal is approximated by a cylinder with three parameters: diameter D, length L, and zenith angle of the axis θ. In this paper, the torque acting on ice crystals is simulated at different θ first, and then a special θ with zero horizontal torque, denoted as θe, is sought as an equilibrium of ice crystal orientation. The equilibrium is classified into two kinds: stable and unstable. Ice crystals rotate to θe of stable equilibriums while deviating from θe of unstable ones once they are released into quiet air. Multiple equilibriums of ice crystal orientation are found via numerical simulations. A cylinder with D/L close to one has three equilibriums, two of which are stable (i.e., θe = 0° and 90°). A cylinder with D/L away from one has only two equilibriums, one of which is stable (i.e., either θe = 0° or 90°). In addition, an asymmetric cylinder has two, three, or five equilibriums, and their θe is sensitive to the distance between its geometrical center and its center of gravity. The sensitivity of θe to crystal asymmetry suggests large symmetric ice crystals tend to become asymmetric (or irregular) and subsequently oriented randomly. Significance Statement Ice crystal orientation impacts high-cloud reflectance and satellite-based observations of high clouds significantly. However, its laboratory and field observations look dissimilar: the percentage of horizontally oriented ice crystals (HOICs) observed in the laboratory is quite high, while in the field it is often low and varies greatly in space and time. The motivation for this study is to elucidate what causes the difference between the laboratory and field observations. The torque acting on ice crystals are computed by modeling the airflow around ice crystals, revealing the conditions for nonhorizontal orientations of ice crystals. In quiet air, an ice crystal is oriented either horizontally or vertically when its shape is close to sphere. When its shape is elongated in one direction, its orientation depends on its asymmetry in density and shape. The sensitivity of ice crystal orientation to ice crystal asymmetry explains the low percentage of HOICs in the field, because asymmetric ice crystals are common in clouds. As an application, this sensitivity together with the observed percentage of HOICs can be used to infer the processes of ice crystal growth in clouds, providing clues to better representation of ice crystals in weather and climate models.

Bound to the Land: Cove Fort in Kesler Family History and Memory

Bound to the Land: Cove Fort in Kesler Family History and Memory

Mechanical properties of heat-resistant superalloy Inconel 718 obtained by selective laser melting and heat treatment under different load directions

Additive manufacturing is a promising modern direction that allows quickly and with high accuracy layer-by-layer manufacture of complex-shaped products using a computer model from almost any metal powders. This work is devoted to the study of the influence of specimen orientation during 3-D printing and heat treatment modes on the mechanical properties of specimens made of Inconel 718 heat-resistant nickel alloy manufactured using SLM technology. In the study of the position of the specimen during printing, it was found that the strength indicators are slightly higher for vertical specimens (up to 9%), and the plasticity is lower on average by 20%. After standard heat treatment, which consists of two stages (quenching and aging) with cooling in quiet air, the strength values of vertically and horizontally constructed specimens are very close (the difference is up to 3%).The plasticity values for the horizontal position of the specimen when printing are 10% and 30% higher. According to macrogeometry, the specimens under study have cup fracture; according to microfractors, it was established that the fracture mechanism is viscous and quasi-brittle. In the initial state, which is formed by 3-D printing, there were signs of viscous fracture: the crack propagates mainly by separating the metal in planes that do not coincide with the crystallographic planes of the sections, mainly the fracture surface in the form of pits - microdepressions on the fracture surface. representing the exposed surfaces of the microvoids formed during the plastic flow of the metal. In the study of the metal of the test specimens in the polished state, it was found that specimens No. 1-5 had high integrity (low porosity), a small amount of oxide inclusions was observed. The study found that the presence of defects in the form of micropores did not lead to a significant reduction in the mechanical properties of the test samples.

The Effect of Weld Reinforcement and Post-Welding Cooling Cycles on Fatigue Strength of Butt-Welded Joints under Cyclic Tensile Loading

This research deals with the fatigue behavior of butt-welded joints, by considering the geometry and post-welding cooling cycles, as a result of cooling in quiet air and immersed in water. ASTM A-36 HR structural steel was used as the base metal for the shielded metal arc welding (SMAW) process with welding electrode E6013. The welding reinforcement was 1 mm and 3 mm, respectively; axial fatigue tests were carried out to determine the life and behavior in cracks propagation of the tested welded joints, mechanical characterization tests of properties in welded joints such as microhardness, Charpy impact test and metallographic analysis were carried out. The latter were used as input for the analysis by finite elements which influence the initiation and propagation of cracks and the evaluation of stress intensity factors (SIF). The latter led to obtaining the crack propagation rate and the geometric factor. The tested specimens were analyzed, by taking photographs of the cracks at its beginning in order to make a count of the marks at the origin of the crack. From the results obtained and the marks count, the fatigue crack growth rate and the influence of the cooling media on the life of the welded joint are validated, according to the experimental results. It can be concluded that the welded joints with a higher weld reinforcement have a shorter fatigue life. This is due to the stress concentration that occurs in the vicinity of the weld toe.

Experimental characterization of fatigue strength in butt welded joint considering the geometry and the effect of cooling rate of the weld

In this work the experimental characterization of fatigue strength in butt welded joints considering the geometry and the post-weld cooling cycle was performed. ASTM A-36 structural steel was used as the base metal for the shielded metal arc welding process, with welding electrode E6013. Two experimental factors were established: weld bead geometry and the post-weld cooling rate. Two levels for each factor, the welding reinforcement (1 and 3 mm), and the rate of cooling, slow (quiet air) and fast (immersion in water) are evaluated respectively. For the uniaxial fatigue tests, 8 samples were selected for each treatment for a total of 32 specimens. The mechanical and fractomechanical properties of fusion zone, heat affected zone and base metal in relation to the analysis of failure mechanisms were analysed. The fatigue crack growth rates were estimated based on the counting of microstrations. Furthermore, experimental tests, such as uniaxial tension, microindentation hardness, Charpy impact and metallographic analysis, were made to know the influence of the experimental factors in the fatigue strength. On this research, about the 78.13% of the samples obtained a resistance higher than the recommended one by class FAT 100. The results showed that the geometry of the joint is the factor of greatest influence on fatigue strength for butt welded joints; the greater the weld reinforcement the lower the fatigue strength of the joint. Although it is also important to consider other geometric factors of less impact as it is the weld toe radius and the welding chord width.

Oxidation resistance and strength of a molybdenum fiber–oxide matrix composite material

The oxidation kinetics of a composite material, which consists of an Al2O3–Al5Y3O12 matrix and molybdenum fibers and has a high cracking resistance, is studied. The mass loss of the composite material during oxidation is shown to be several orders of magnitude lower than that of molybdenum. Oxidation in quiet air at 1250°C for several hours weakly changes the strength of the composite material at temperatures from room temperature to 1300°C. It is also shown that the strength of the composite material as a function of the oxide matrix composition (Al: Y ratio) changes nonmonotonically. The maximum strength shifts from the Al2O3–Al5Y3O12 eutectic point toward garnet.

An experimental investigation on the effects of surface gravity waves on the water evaporation rate in different air flow regimes

Estimating rate of evaporation from undisturbed water surfaces to moving and quiet air has been the topic a vast number of research activities. The obvious presence of various shapes of gravity waves on the water body surfaces was the motivation of this experimental investigation. In this investigation experimental measurements have been done to quantify evaporation rate from wavy water surfaces in free, mixed and forced convection regimes. The effects of a wide range of surface gravity waves from low steepness, round shaped crest with slow celerity, to steep and very slight spilling crest waves, on the water evaporation rate have been investigated. A wide range of \({\text{Gr}}/{\text{Re}}^{2} (0.01 \le {\text{Gr}}/{\text{Re}}^{2} \le 100)\) was achieved by applying different air flow velocities on a large heated wave flume equipped with a wind tunnel. Results reveal that wave motion on the water surface increase the rate of evaporation for all air flow regimes. For free convection, due to the effect of wave motion for pumping rotational airflows at the wave troughs and the dominant effect of natural convection for the air flow advection, the maximum evaporation increment percentage from wavy water surface is about 70 %. For mixed and forced convection, water evaporation rate increment is more sensitive to the air flow velocity for the appearance of very slight spilling on the steep wave crests and the leeward air flow structures.

Clean, quiet air

Clean, quiet air

Where next for the laser?

We all know that turbulence in the atmosphere makes stars twinkle, but it also severely blurs telescope images. Newton realized this back in 1730, when he wrote in Opticks that “the Air through which we look upon the Stars, is in perpetual Tremor… The only Remedy is a most serene and quiet Air, such as may perhaps be found on the tops of the highest Moun tains above the Grosser Clouds”.

In vitro comparison of the cutting efficiency and temperature production of 10 different rotary cutting instruments. Part I: Turbine

Standards to test the cutting efficiency of dental rotary cutting instruments are either nonexistent or inappropriate, and knowledge of the factors that affect their cutting performance is limited. Therefore, rotary cutting instruments for crown preparation are generally marketed with weak or unsupported claims of superior performance. The purpose of this study was to examine the cutting behavior of a wide selection of rotary cutting instruments under carefully controlled and reproducible conditions with an air-turbine handpiece. Ten groups of rotary cutting instruments (n=30) designed for tooth preparation were selected: 9 diamond rotary cutting instruments (7 multi-use, 2 disposable) and 1 carbide bur. One bur per group was imaged with a scanning electron microscope (SEM) at different magnifications. Macor blocks (n=75) were used as a substrate, and 4 cuts were made on each specimen, using a new rotary cutting instrument each time, for a total of 300 cuts. The cuts were performed with an air-turbine handpiece (Midwest Quiet Air). A computer-controlled, custom-made testing apparatus was used to monitor all sensors and control the cutting action. The data were analyzed to compare the correlation of rotary cutting instrument type, grit, amount of pressure, cutting rate, revolutions per minute (rpm), temperature, and type of handpiece, using 1-way ANOVA and Tukey's Studentized Range test (alpha=.05). Compared to the baseline temperature, all rotary cutting instruments showed a reduction of temperature in the simulated pulp chamber. The Great White Ultra (carbide bur) showed a significantly higher rate of advancement (0.15 mm/s) and lower applied load (106.46 g) and rpm (304,375.97). Tooth preparation with an adequate water flow does not cause harmful temperature changes in the pulp chamber, regardless of rotary cutting instrument type. The tested carbide bur showed greater cutting efficiency than all diamond rotary cutting instruments.

Boron isotopic fractionation during seawater evaporation

Laboratory experiments were undertaken to investigate the behaviour of boron at the seawater–air interface during seawater evaporation. Seawaters adjusted to different pH values were heated to 27, 33 and 40 °C inside a quartz evaporator. The vapor was collected with a quartz condenser using a cold trap. A natural seawater–vapor process in quiet air conditions and excluding the sea-spray component was realized using this arrangement. The results indicate an enrichment of 11B in the condensate. This implies that in the natural environment, rainfall with δ 11B values lower than that of seawater has been affected either by continental boron sources or by the boron extracted from seawater under airflow conditions. While the net flux of boron carried away from the ocean by air masses due to seawater evaporation is significant compared to other fractionation-associated processes removing boron from the ocean, the effect of isotopic fractionation as boron enters the vapor phase on the isotopic composition of boron in the ocean over time is small.

Preserving the acoustics of the Mahaiwe Theater

The Mahaiwe Theater, Great Barrington, Massachusetts, opened in 1905. It has been home to vaudeville, traveling Broadway shows, opera, concerts, and movies. In 2003, the theater began a multi-phase renovation project. The renovation project includes restoration of historic finishes, new seating, installation of air conditioning and heating systems, and installation of sound and projection systems. A stage shell for music performances will also be installed. A key aspect of the renovation is the preservation of what has been widely regarded as excellent acoustics. Some aspects of the original structure contributed to this reputation (e.g., room shaping, finishes), while others undoubtedly were less helpful (e.g., the 1905-era ventilation system). The renovation provides an opportunity to preserve the positive attributes of the room, while correcting the deficiencies. Among the key issues discussed are the design of historically-sensitive finishes that respect the acoustic requirements of the multi-use space, acoustical design of a new quiet air conditioning system, and design of an enclosure for music ensembles.

Analyse spectrométrique, in vivo, de l'impédance électrique de la première feuille de maïs ( Zea mays L.) en fonction des conditions hydriques du sol et de l'atmosphère

We have measured the electrical resistance and capacitance of the first leaf of maize aged 14 days. The plants were cultivated at different levels of soil and atmospheric humidity and submitted to quiet or agitated air. In ‘control’ plants cultivated in quiet air under moderate relative humidity (HRA) (50 to 60%), the amplitude of the spectrometric bioimpedance spectrum (CSB) increased with the quantity of water available to the roots. Agitated air or elevated HRA increased the magnitude of the CSB in plants cultivated at 40% of the maximal retention capacity (CRM) of the soil. On the other hand, the CSB decreased in plants cultivated at 60% of the CRM or in hydroponics. This was accompanied by a dramatic decrease in the electrical resistance. The action of the atmospheric factors studied depends on the quantity of water where the roots are bathing. To cite this article: S. Laarabi et al., C. R. Biologies 328 (2005).

On retrieving the microphysical properties of cirrus clouds using the moments of the millimeter‐wavelength Doppler spectrum

Techniques that use only measurements provided by millimeter‐wavelength Doppler radar for retrieving the properties of clouds provide certain practical advantages over techniques that require measurements from multiple instruments. We concentrate on the capacity of the moments of the Doppler spectrum to provide information suitable for retrieving the microphysical properties of cirrus clouds. Specifically, we present an algorithm that uses the zeroth and first moments of the Doppler spectrum (radar reflectivity and mean Doppler velocity) to retrieve the cloud particle size distribution. We also discuss a methodology for evaluating the second moment of the Doppler spectrum for information related to the width of the particle size distribution. The properties of observed cirrus particle spectra are first examined to ascertain what degree of complexity is required of assumed functional representations of particle spectra in cirrus volumes. We find that although particle spectra with bimodal tendencies are common, single‐mode functions are able to capture the essential characteristics of these spectra to within observational uncertainty for most cirrus. Furthermore, two‐parameter functions such as the exponential function are shown to be adequate representations of cirrus particle spectra in situations where the radar reflectivity factor is less than about −5 dBZe and the temperatures are colder than about 253 K. A technique for separating air motion contributions from the Doppler velocity is examined, and an approach for similarly processing the Doppler spectral width is introduced. In comparison to aircraft data, we find uncertainty in the derived quiet air velocity and spectrum width to be on the order of 20% and 40%, respectively. Using recent parameterizations of ice crystal terminal velocity, mass, and backscatter cross section, we present a straightforward algorithm for retrieving cirrus cloud microphysical properties from observations of radar reflectivity and Doppler velocity. A simulation experiment with variable particle habits and realistic observational error shows that the retrieval uncertainties are on the order of 60% and 40% for ice water content and mass median particle size, respectively. These uncertainty magnitudes are supported by comparison to aircraft data.

Experimental verification of the quasi-steady approximation for aerodynamic sound generation by pulsating jets in tubes.

Voice production involves sound generation by a confined jet flow through an orifice (the glottis) with a time-varying area. Predictive models of speech production are usually based on the so-called quasi-steady approximation. The flow rate through the time-varying orifice is assumed to be the same as a sequence of steady flows through stationary orifices for wall geometries and flow boundary conditions that instantaneously match those of the dynamic, nonstationary problem. Either the flow rate or the pressure drop can then be used to calculate the radiated sound using conventional acoustic radiation models. The quasi-steady approximation allows complex unsteady flows to be modeled as steady flows, which is more cost effective. It has been verified for pulsating open jet flows. The quasi-steady approximation, however, has not yet been rigorously validated for the full range of flows encountered in voice production. To further investigate the range of validity of the quasi-steady approximation for voice production applications, a dynamic mechanical model of the larynx was designed and built. The model dimensions approximated those of human vocal folds. Airflow was supplied by a pressurized, quiet air storage facility and modulated by a driven rubber orifice. The acoustic pressure of waves radiated upstream and downstream of the orifice was measured, along with the orifice area and other time-averaged flow variables. Calculated and measured radiated acoustic pressures were compared. A good agreement was obtained over a range of operating frequencies, flow rates, and orifice shapes, confirming the validity of the quasi-steady approximation for a class of relevant pulsating jet flows.

Waves on panel structures from turbulent boundary layer excitations

Response and acoustic radiation measurements from aircraft-type panels forced to vibrate by turbulent boundary layer flow are made in a quiet air duct facility and in a wind tunnel. Two types of aluminum structure are used: a newly developed panel with irregular, protruding, varying-thickness wedges at the upstream and downstream boundaries (fractal-type geometry) and a standard aircraft fuselage sidewall panel. Both panels have the same mass and exposed surface area to the flow. The new panel boundary has an extended perimeter with a gradual change in mass stiffness toward the center. The objective is to control the radiated acoustic pressure field. This is achieved by controlling the convective waves reflecting at the upstream and downstream boundaries of the panel. The geometry of the boundary is designed to induce a mismatch and randomness in wave motion along the direction of flow, resulting in significant attenuation of the amplitude of the incident and reflected waves.

Contribution to the discussion of '1987 ampacity tables-demystifying the myths'

The author discusses J. Nasilowski's remarks (see ibid., vol.26, no.4, p.605, 1990) on a paper by D.W. Zipse (see ibid., vol.25, no.5, pp.910-17, 1989). Nasilowski claimed that in M=(hS/R)/sup 1/2/, where M is the current coefficient of heating, h is the heat transfer coefficient, including both convection and radiation, S is the surface area of the conductor, and R is the resistance, M is constant for a specific material for a range of currents and for temperature rises up to about 60 K. The author argues that M is approximately constant only for a specific conductor and for restricted ranges of temperature rise and ambient temperature. In his reply, Nasilowski stresses the utility of the assumption that M=constant for calculations of steady state temperature rise of the conductors in a quiet air. >

A study of the analogue compensating monopole system for active attenuation of noise in a duct

This paper describes theoretically the feedback effect of the secondary source on the primary source in a monopole system for active attenuation of noise in a duct, and gives a more accurate mathematical model. Based on the model mentioned above, a new monopole system called the Analogue Compensating Monopole System, or ACM-System for short, is established. An analogue method for compensating the non-ideal phase response of the system is suggested and discussed, and measures for improving the non-ideal amplitude response are proposed. In order to improve the working stability of the system, a directional sound detector is introduced, and the absolute stability condition of the ACM-System is given. Test results show that the method for compensating for the phase errors and improving the amplitude characteristics of the system is effective. Experimental data from the ACM-System in conditions of flowing and quiet air in the duct are processed. Test results show that the ACM-System has a noise reduction ability superior to that of other monopole systems, whether in narrow or wider frequency bandwidths.

Mixing process in turbulent diffusion flames.

The flame height of diffusion flames rising vertically from a cylindrical burner tube in quiet air extends with increasing the gas exit velocity and becomes constant in f fully developed turbulent region. The turbulence intensity at the burner exit which is measured by LDV increases linearly with the gas exit velocity for nonswirling flames. The mixing length at the burner exit calculated from the flame height and the turbulence intensity is shortened gradually with the gas velocity and then becomes constant for nonswirling flames. For swirling turbulent diffusion flames, the mixing length decreases with the swirl intensity at the burner exit. The coefficient of the tube diameter in the mixing length for burning flow is less than half the value of than the tube flow or round jet.

Three-dimensional steady parabolic calculations of large scale methane turbulent diffusion flames to predict flare radiation under cross-wind conditions

Results obtained during a program geared to the development of a computer code to predict flare radiation in off-shore platforms are presented. Emphasis is put on the novel features included in this diffusion flame model viz: o i) a pseudo stream function formulation of the three dimensional parabolic flow structure which describes strong cross-wind flare interactions. ii) an improved radiation model where the “equivalent emitting body” approach is developed to adequately describe radiation fluxes coming out of the flame and, iii) an improved soot production and oxidation model to take care of the soot contribution to the emitted radiative fluxes. Turbulent combustion is modelled via the k -ω technique coupled with Magnussen's turbulent rate of mixing approach. A short description of the developed numerical solution procedures is given with emphasis on the self consistency of the boundary condition formulations. Comparisons are shown between large scale experimental flare data (obtained for round methane gas flares) and calculated results. A±15% accuracy is obtained for methane flow rates ranging from 0.8 up to 15 kg/sec (gas exit velocities not superior to 300 m/sec) under both quiet and windy air conditions. Temperature and soot concentration profiles are presented under windy conditions to illustrate how weak aerodynamic interactions may generate very drastic changes on received radiative fluxes, especially for down-wind located targets.