China
Africa
Explore chapters and articles related to this topic
Internal pressures
Published in John D. Holmes, Seifu A. Bekele, Wind Loading of Structures, 2020
John D. Holmes, Seifu A. Bekele
Applying Equation (6.13) for the Helmholtz resonance frequency, and setting po = 105 Pascals (atmospheric pressure), ρa = 1.2 kg/m3(air density), γ = 1.4 (ratio of specific heats), and le equal to 1.0 √A, we have the following approximate Equation (6.15) for nH: nH≈55A1/4Vo1/2[1+(KA/KB)]1/2
Slideways for Long Range Precision Motion
Published in S.T. Smith, D.G. Chetwynd, Foundations of Ultraprecision Mechanism Design, 2017
By definition, hydrostatic bearings require a pressurized supply. This causes a continuous energy input additional to that dissipated by viscous drag. With oil based bearings, the temperature of the inlet can be regulated and the outflow used to extract heat so that the bearing and its associated structures remain close to thermal equilibrium. Being a compressible medium, the situation with air bearings is less simple in both principle and practice. There will always be adiabatic expansion of the gas as it passes through restrictors and when it exits the bearing. Local cooling of regions around the bearing ensues and is not readily compensated by adjusting the inlet temperature. Its effect can be reduced by maintaining a small gap, which may not always be desirable on other grounds. An additional problem within air bearings is Helmholtz resonance. This is caused by an elastic wave travelling between the exit and supply orifices in a manner analogous to the sounding of a wind instrument. Although it is generally acknowledged to exist, there is very little information regarding its minimization, which seems a well preserved proprietary secret of the manufacturers.
Noise and Vibration
Published in Charles E. Baukal, Industrial Combustion Pollution and Control, 2003
Froud et al. [53] studied Helmholtz resonance in swirl burners. Experimental results in pilot-scale tests showed that the air/fuel ratio, the mode of fuel entry, and the length of the exhaust pipe attached to the exit of the furnace were all important variables. The experiments showed that the resonance can become severe enough virtually to extinguish the flame from the burner and cause highly complex transient flows in the furnace.
Distributed transfer function approach for one-dimensional thermoacoustic combustor models
Published in Combustion Theory and Modelling, 2023
Another good way to compare the two models is to see the pole-zeros of their transfer functions in Figure 12. The imaginary parts of the poles characterise the resonances, and the real (growth rate) parts the damping of the resonance, equivalently, the sharpness of the peaks in Figure 11. The zeros determine anti-resonances, the downward peaks in Figure 11. We can see in Figure 12 that two sets of pole-zeros have similar imaginary parts but different real parts. The missing Helmholtz resonance of the network model is related to the lack of a pole whose imaginary part is close to the Helmholtz resonance. In fact, the network model does have a pole with frequency 106 Hz and growth rate 449, which is out of the growth rate range of Figure 12.
Low-Noise pavement technologies and evaluation techniques: a literature review
Published in International Journal of Pavement Engineering, 2022
Peter Mikhailenko, Zhengyin Piao, Muhammad Rafiq Kakar, Moises Bueno, Sahand Athari, Reto Pieren, Kurt Heutschi, Lily Poulikakos
The tire/road sound generation mechanisms can be traced to the following: (i) tread impact, (ii) air pumping, (iii) stick-slip and (iv) stick-snap. In addition to these, three sound enhancement mechanisms can play a role: (i) horn effect, (ii) Helmholtz resonance and (iii) pipe resonance (Ohiduzzaman et al.2016, Sandberg and Ejsmont 2002). While it is not the goal of this review to look at these mechanisms, they can be used to explain the performance of different pavement types. A summary of the pavement properties which have been found to affect these mechanisms is shown in Table 1. Although in most studies, the vibrations contribution to the generated noise is considered the dominant one (Sandberg and Ejsmont 2002), models that incorporate the air pumping effect have shown that the contribution of the latter can be more significant than previously thought (Winroth et al.2013).
Natural ventilation in cities: the implications of fluid mechanics
Published in Building Research & Information, 2018
Jiyun Song, S. Fan, W. Lin, L. Mottet, H. Woodward, M. Davies Wykes, R. Arcucci, D. Xiao, J.-E. Debay, H. ApSimon, E. Aristodemou, D. Birch, M. Carpentieri, F. Fang, M. Herzog, G. R. Hunt, R. L. Jones, C. Pain, D. Pavlidis, A. G. Robins, C. A. Short, P. F. Linden
Smoke flow visualization (Figure 5) provided an overview of flow conditions and highlighted specific features, such as the wake of the tall Building 45. A two-component laser Doppler anemometer (2D-LDA; Carpentieri, Hayden, & Robins, 2012; Durst, Melling, & Whitelaw, 1976) provided quantitative measurements of mean and fluctuating air velocity with a typical sampling rate of 50 Hz. The instrument was used in two alignments in order to obtain three flow components. Dispersion studies used a passive hydrocarbon tracer, the concentration of which was measured with a fast-flame ionization detector (FFID) with a frequency response near 200 Hz (Carpentieri et al., 2012; Fackrell & Robins, 1982). Turbulent mass fluxes were determined by simultaneous LDA and FFID measurements. The external surface pressure distribution on the model Clarence Centre (Building 147) was measured by 88 pressure taps on the roadside, courtyard side and roof of the test site model. Each tap was connected to a pressure transducer by 400 mm of 1 mm internal diameter plastic tubing. Pressures were measured with transducers (RSCDRRM2.5MDSE3, Honeywell International) at 200 Hz, this being about twice the frequency response of the transducer. No interference from Helmholtz resonance in the tubing system was observed.