Automatic cryogenic liquid level controller is safe for use near combustible substances

Automatic mechanical liquid level controller that is independent of any external power sources is used with safety in the presence of combustibles. A gas filled capillary tube which leads from a pressurized chamber, is inserted into the cryogenic liquid reservoir and becomes a liquid level sensing element or probe

Membrane structures and their use in civil engineering

This paper is focused on the static analysis of membrane structures, which are typical for their ability to transfer only tensile forces. Membrane structures are becoming more popular owing to their lower initial cost and potential for use in structures with higher aesthetic claims. However, the designs of membrane face some challenges related to the specific properties of these support systems. This paper aims to analyse the current possibilities for using membrane structures and to evaluate these structures in terms of materials and design details and using numerical methods

New technique for the direct measurement of core noise from aircraft engines

The core noise levels from gas turbine aircraft engines were measured using a technique which requires that fluctuating pressures be measured in the far field and at two locations within the engine core. The cross spectra of these measurements are used to determine the levels of the far-field noise that propagated from the engine vore. The technique makes it possible to measure core noise levels even when other noise sources dominate. The technique was applied to signals measured from an Avco Lycoming YF102 turbofan engine. Core noise levels as a function of frequency and radiation angle were measured and are presented over a range of power settings

Combustion noise from gas turbine aircraft engines measurement of far-field levels

Combustion noise can be a significant contributor to total aircraft noise. Measurement of combustion noise is made difficult by the fact that both jet noise and combustion noise exhibit broadband spectra and peak in the same frequency range. Since in-flight reduction of jet noise is greater than that of combustion noise, the latter can be a major contributor to the in-flight noise of an aircraft but will be less evident, and more difficult to measure, under static conditions. Several methods for measuring the far-field combustion noise of aircraft engines are discussed in this paper. These methods make it possible to measure combustion noise levels even in situations where other noise sources, such as jet noise, dominate. Measured far-field combustion noise levels for several turbofan engines are presented. These levels were obtained using a method referred to as three-signal coherence, requiring that fluctuating pressures be measured at two locations within the engine core in addition to the far-field noise measurement. Cross-spectra are used to separate the far-field combustion noise from far-field noise due to other sources. Spectra and directivities are presented. Comparisons with existing combustion noise predictions are made

Application of 3-signal coherence to core noise transmission

A method for determining transfer functions across turbofan engine components and from the engine to the far-field is developed. The method is based on the three-signal coherence technique used previously to obtain far-field core noise levels. This method eliminates the bias error in transfer function measurements due to contamination of measured pressures by nonpropagating pressure fluctuations. Measured transfer functions from the engine to the far-field, across the tailpipe, and across the turbine are presented for three turbofan engines

Prediction of the noise from a propeller at angle of attack

An analysis is presented to predict the noise of a propeller at angle of attack. The analysis is an extension of that reported by Mani which predicted the change in noise due to angle of attack to both unsteady loading and to azimuthal variation of the radiation efficiency of steady noise sources. Mani's analysis, however, was limited to small angles of attack. The analysis reported herein removes this small angle limitation. Results from the analysis are compared with the data of Woodward for a single rotation propeller and a counter rotating propeller. The comparison shows that including the effect of angle of attack on the steady noise sources significantly improves the agreement with data. Including higher order effects of angle of attack, while changing the predicted noise at far forward and aft angles, has little effect near the propeller plane

Přímý Optimalizovaný Pravděpodobnostní Výpočet

pravděpodobnostní výpočet, posudek spolehlivosti, pravděpodobnost poruchy, návrhová pravděpodobnost, funkce spolehlivosti, rezerva spolehlivosti, histogram, rozdělení pravděpodobnosti, náhodná proměnná Přímý Optimalizovaný Pravděpodobnostní Výpočet, POPV, Direct Optimized Probabilistic Calculation, DOProC, grupování, intervalová optimalizace, zónová optimalizace, trendová optimalizace, paralelizace, ProbCalc, HistAn, HistAn2D, HistAn3D, HistOp únavová trhlina, plocha oslabení, lineární lomová mechanika, přípustný rozměr, měřitelný rozměr, iniciační rozměr, šíření z okraje, šíření z povrchu, podmíněná pravděpodobnost, prohlídka konstrukce, FCProbCalc kotevní výztuž, redukovaná pevnost, geomechanický klasifikační koeficient, délka kotvy, únosnost kotvy, Ancho

Propagation of high frequency jet noise using geometric acoustics

Spherical directivity of noise radiated from a convecting quadrupole source embedded in an arbitrary spreading jet is obtained by ray-tracing methods of geometrical acoustics. The six propagation equations are solved in their general form in a rectangular coordinate system. The noise directivity in the far field is calculated by applying an iteration scheme that finds the required radiation angles at the source resulting in propagation through a given observer point. Factors influencing the zone of silence are investigated. The caustics of geometrical acoustics and the exact locations where it forms is demonstrated by studying the variation in ray tube area obtained from transport equation. For a ring source convecting along the center-axis of an axisymmetric jet, the polar directivity of the radiated noise is obtained by an integration with respect to azimuthal directivity of compact quadrupole sources distributed on the ring. The Doppler factor is shown to vary slightly from point to point on the ring. Finally the scaling of the directivity pattern with power -3 of Doppler factor is investigated and compared with experimental data

Probabilistic calculation of fatigue crack progression using FCProbCalc code

Příspěvek je zaměřen na jeden z možných způsobů posouzení spolehlivosti cyklicky namáhané ocelové konstrukce s ohledem na vznik únavových trhlin z okraje a povrchu, které vede k návrhu systému prohlídek konstrukčních detailů náchylných na únavové poškození. Pro řešení pravděpodobnostní úlohy byla použita nově vyvíjená metoda Přímého Optimalizovaného Pravděpodobnostního Výpočtu (zkráceně POPV), implementovaná do programu FCProbCalc.The paper gives examples of the probabilistic assessment of a steel cyclic loaded structure. Fatigue progression of the cracks from the edge and from the surface is used as a basis for proposing a system of inspections of details which tend to be damaged by fatigue. The newly developed method Direct Optimized Probabilistic Calculation (DOProC method) was used for solution. The method was applied in FCProbCalc code

A theoretical model for the cross spectra between pressure and temperature downstream of a combustor

A theoretical model developed to calculate pressure-temperature cross spectra, pressure spectra, temperature spectra and pressure cross spectra in a ducted combustion system is presented. The model assumes the presence of a fluctuating-volumetric-heat-release-rate disk source and takes into account the spatial distribution of the steady-state volumetric-heat flux. Using the model, pressure, velocity, and temperature perturbation relationships can be obtained. The theoretical results show that, at a given air mass flow rate, the calculated pressure-temperature cross spectra phase angle at the combustor exit depends on the model selected for the steady-state volumetric-heat flux in the combustor. Using measurements of the phase angle, an appropriate source region model was selected. The model calculations are compared with the data. The comparison shows good agreement and indicates that with the use of this model the pressure-temperature cross spectra measurements provide useful information on the physical mechanisms active at the combustion noise source