Multi-part Paper Research Articles

One project begets many: The role of one seminal project in the development of many design solutions (Part 2)

In the second part of this multi-part paper, the solution for the cap of the organ chamber at Verizon Hall will be presented. The original cap was a lightweight material, allowing significant low frequency energy—critical to the success of any pipe organ—to escape the acoustic volume of the room. The solutions implemented to improve the sound of the organ were limited by structural capacities, and were ultimately developed as lightweight but very stiff honeycomb core panels. The strategy of lightweight-yet-stiff materials has been implemented in numerous other projects to achieve low frequency reflectivity. Examples will be presented illustrating development of this strategy over the past decade.

One project begets many: The role of one seminal project in the development of many design solutions (Part 3)

In the third and final part of this multi-part paper, computer modeling will be described as a tool for presentation to client groups (often skilled listeners but not expert acousticians). Over the course of the Verizon Hall project, computer models were used to present visual illustrations that explained the acoustic concerns experienced by the orchestra. Starting with this project, Threshold began to develop computer models as tools to translate acoustic phenomena in ways that clients could understand visually and, over time, aurally. The development of customized computer modeling techniques has further supported communication with non-acousticians, and examples of these techniques will be presented.

Discrete element modelling of large scale particle systems—I: exact scaling laws

The discrete element method has emerged as a powerful predictive tool for the numerical modelling of many scientific and engineering problems involving discrete and discontinuous phenomena. There are nevertheless computational challenges to resolve before industrial scale applications can be effectively simulated. This multi-part paper aims to address some of the theoretical and computational issues central to achieving this goal. In the first part of this paper, a simple but generic theoretical framework is established for the development of a comprehensive set of scaling conditions, under which a scaled discrete element model can exactly reproduce the mechanical behaviour of a physical model. In particular, three basic physical quantities and their scale factors can be freely chosen. A special selection leads to a unique set of scale factors governing an exact scaling, which also gives rise to the requirement that all the interaction laws employed in a scaled model be scale-invariant. The subsequent examination reveals that most commonly used interaction laws, if all material (mechanical and physical) properties are treated as constant, do not possess such a feature and therefore cannot be directly employed in a scaled model. The problem can be solved by treating the scaled particles as pseudo-particles and by properly scaling the interaction laws. The resulting scaled interaction laws become scale-invariant and thus can be used in a scaled model.

The Discrete Fourier Transform, Part 1.

This paper describes an implementation of the Discrete Fourier Transform (DFT) and the Inverse Discrete Fourier Transform (IDFT). We show how the computation of the DFT and IDFT may be performed in Java and show why such operations are typically considered slow. This is a multi-part paper, in part 2, we discuss a speed up of the DFT and IDFT using a class of algorithms known as the FFT (Fast Fourier Transform) and the IFFT (Inverse Fast Fourier Transform). Part 3 demonstrates the computation of the PSD (Power Spectral Density) and applications of the DFT and IDFT. The applications include filtering, windowing, pitch shifting and the spectral analysis of re-sampling.

Diurnal Winds in the Himalayan Kali Gandaki Valley. Part III: Remotely Piloted Aircraft Soundings

Abstract In 1998 a field campaign has been conducted in the north–south-oriented Kali Gandaki valley in Nepal to explore the structure of its extreme valley wind system. Piloted ballon (pibal) observations were made to map the strong upvalley winds as well as the weak nocturnal flows (Part I). The stratification of the valley atmosphere was not explored. In Part II of this multipart paper, numerical simulations are presented that successfully simulate most of the wind observations. Moreover, the model results suggest that the vigorous upvalley winds can be seen as supercritical flow induced by contractions of the valley. Here, the results of a further campaign are reported where remotely piloted airplanes were used to obtain vertical profiles of temperature and humidity up to heights of ∼2000 m above the ground. Such profiles are needed for an understanding of the flow dynamics in the valley and for a validation of the model results. This technique is novel in some respects and turned out to be highly rel...

Atmospheric effects of friction, friction noise and wear with silicon and diamond. Part III. SEM tribometry of polycrystalline diamond in vacuum and hydrogen

In this part III of a multi-part paper series, the results of additional SEM tribometric experiments are described, performed with polished, mostly C(100)-oriented polycrystalline CVD diamond film [PCDC(100) vs. PCDC(100)] counterfaces sliding in \(\sim 1 \times 10^{ - 5}\) Torr and in 0.1–0.3 Torr partial pressures of pure hydrogen gas. These tests were completed under a 28 g (0.27 N) normal load, under standard and slow thermal ramping conditions at temperatures ranging from room temperature to 1000°C. The friction data were examined per the computer logging and analysis techniques described in part I. The treatment of the data is similar to that of Si in part II: the maximum and the average coefficients of friction (MAX.COF and COF) and their ratios (the friction noise FN) are employed to measure possible lubricative interaction of the diamond surfaces with rarefied hydrogen. The results indicate that excited species of molecular hydrogen enter into tribothermally catalyzed reactions not only with Si but with PCDC(100) surfaces as well. Similar to the behavior of Si, the most beneficial friction-reducing regime occurs in a temperature range just before the thermal desorption of adsorbates. The general magnitudes of MAX.COF, COF and the FN are significantly lower than those of the Si crystallinities, in both vacuum and \(P_{{\text{H}}_{\text{2}} }\). The wear rate of the PCDC(100) film characteristic of the standard thermal ramping test procedure performed mostly in \(P_{{\text{H}}_{\text{2}} }\) is around \(4 \times 10^{ - 16} {\text{m}}^3 /({\text{Nm)}}\), in good agreement with the wear rate previously measured in vacuum for unpolished, fine-cauliflowered diamond films. The data indicate that smooth polycrystalline diamond is a significantly better bearing material for miniaturized moving mechanical assembly applications than Si.

Atmospheric effects of friction, friction noise and wear with silicon and diamond. Part I. Test methodology

This multi-part paper series gives evidence of tribothermally catalyzed, lubricative interactions of low partial pressures of hydrogen, water vapor and oxygen with silicon and polycrystalline diamond employed as bearing materials in moving mechanical assemblies (e.g., miniaturized rotors, bearings and gears) of microelectromechanical systems. In part I a test methodology is described, whereby wide environmental range SEM-tribometric friction data are combined with friction noise analysis and applicable literature information to further assist in interpreting atomic-level interactions governing the macroscopic friction and wear behavior of Si and diamond. To further correlate the wear- and thermal desorption-induced generation, re(de)construction and adsorbate-passivated annihilation of dangling σ bonds with high and low adhesion and friction, previously generated average coefficient of friction (COF) values are complemented with the concept of the associated MAX.COF: the highest coefficient of kinetic friction gleaned from the raw computer-logged friction force data of each oscillatory cycle of an experiment. The MAX.COF/COF ratios are used as measures of the friction noise as a function of temperature and atmospheric environment. These quantities, sampled at the appropriate data logging rate to circumvent test machine-related vibrational disturbances, demonstrated signs of friction- and friction noise-reducing gas-phase interactions of dry hydrogen with silicon (part II) and diamond (part III). Future installments will deal with similar lubricative properties of low partial pressures of wet hydrogen and dry oxygen.

Investigations of a Winter Mountain Storm in Utah. Part III: Single-Doppler Radar Measurements of Turbulence

This Part III of a multipart paper deals with the analysis of turbulent motion in a winter storm, which occurred over the mountains of southwest Utah. The storm was documented with a long duration single Doppler radar dataset (∼21 h) comprised of volume scan observations acquired at 10-min intervals. Turbulence parameters were determined using a new technique of volume processing of single Doppler radar data. Physical analysis of turbulence is restricted to three particular storm regions: a prefrontal region far removed from a cold frontal discontinuity, a frontal zone aloft, and a low layer in the post-frontal region where a long lasting (∼6 h) wind-maximum existed. The prefrontal period showed enhancement of turbulent parameters near 2.6 km height, apparently due to disturbed flow caused by an upwind mountain range. Turbulence parameters in this prefrontal region showed good agreement with K-mixing length theory. Within the frontal zone most turbulence parameters reached peak values, but were generally less than orographically induced turbulence values in the prefrontal period. Turbulence in the low-level postfrontal period experienced periodic oscillations consistent with precipitation and kinematic variables described in Parts I and II, and associated with mesoscale precipitation bands. Acceleration of the valley-parallel wind component was apparent in prefrontal and postfrontal periods and was related to the specific valley configuration through a Venturi effect.

Investigations of a Winter Mountain Storm in Utah. Part I: Synoptic Analyses, Mesoscale Kinematics, and Water Release Rates

Abstract A winter storm passing across the north–south-orientated Tushar Mountains in southwest Utah is investigated in this multipart paper. This Part I describes the evolving synoptic pattern, mesoscale kinematics, and calculated water release rates (condensation or deposition) in clouds over the western upstope part of the mountains. Horizontal mesoscale kinematic variables come from direct application of Volume Velocity Processing to single C-band Doppler radar data. Water release rates are computed from updrafts derived from the radar data and from the vertical gradient of saturation mixing ratio obtained from soundings. In Stage I of the storm altostratus was present on the leading side of a long-wave trough. Weak updrafts occurred only at the higher altitudes within the clouds where there was convergence and large-scale synoptically forced lift. Downdrafts as great as −0.6 m s−1 occurred in the lower parts of the cloud where there was divergence. The downdrafts were induced in part by sublimation c...