On sources of damping in water-hammer

Various potential causes of damping of pressure waves in water-hammer-like flows are discussed, with special attention being paid to their qualitative influences on measured pressure histories. A particular purpose is to highlight complications encountered when attempting to interpret causes of unexpected behaviour in pipe systems. For clarity, each potential cause of damping is considered in isolation even though two or more could exist simultaneously in real systems and could even interact. The main phenomena considered herein are skin friction, visco-elasticity, bubbly flows and porous pipe linings. All of these cause dispersive behaviour that can lead to continual reductions in pressure amplitudes. However, not all are dissipative and, in such cases, the possibility of pressure amplification also exists. A similar issue is discussed in the context of fluid–structure interactions. Consideration is also given to wavefront superpositions that can have a strong influence on pressure histories, especially in relatively short pipes that are commonly necessary in laboratory experiments. For completeness, attention is drawn towards numerical damping in simulations and to a physical phenomenon that has previously been wrongly cited as a cause of significant damping

High-Speed Vehicles in Low-Pressure Tunnels—Influence of Choked Flows

The aerodynamics of high-speed vehicles in evacuated tunnels is studied with particular reference to the consequences of choked flow conditions at the tails of the vehicles. It is shown that this has a dominant influence on overall conditions (pressure, temperature, velocity). Together with the need for the evacuated tunnel system to be closed, the high speeds cause the aerodynamic behaviour to differ greatly from that in conventional railway tunnels. A key purpose of the paper is to assess the relative importance of a large range of parameters and, for clarity, this is completed by focussing on a single vehicle in a single tunnel that is closed at both ends. Consideration is then given to interactions between more than one vehicle and to a twin-tube tunnel configuration in which interactions occur between vehicles moving in opposite directions. The paper closes with a brief mention of system-dependent matters that need to be considered in addition to the generic parameters investigated herein.</p

The story so far: A systematic review of the dialogic reading literature

Background: Dialogic reading (DR; Whitehurst et al., 1988) is an evidence-based intervention that promotes children's active participation in shared reading (Towson, 2016; Urbani, 2020; WWC, 2007, 2010). Since the development of DR, there has been a proliferation of studies evaluating the conditions and populations with which it is effective. However, to date, there has not been a systematic review of the literature focusing specifically on the impact of DR on the literacy and non-literacy skills of children under 10 years old. As DR research evolves, it is important that a review of the existing literature is undertaken to capture these advances and guide future research. / Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol, the aim of this review is to systematically explore, synthesise and critically evaluate the extant literature. A systematic search of electronic databases identified 46 relevant studies, and the overall methodological quality of the studies was assessed using the MMAT. / Results: Findings are organised according to sample and population, country of origin and setting, programme duration, language and literacy outcomes, social-emotional and other cognitive outcomes, impact and effect sizes to provide overview and insight into where and with whom DR is most effective. / Conclusions: The review findings suggest DR can positively impact a wide range of language and literacy skills for children under 5 years. There is some evidence that DR can have positive effects on enjoyment of reading, reading motivation, parental–child attachment, parental confidence and stress. However, the extant research is subject to limitations, and more methodologically robust research is needed to enable thorough assessment of the conditions in which DR is most effective

Alleviation of pressure pulse effects for trains entering tunnels. Volume 1: Summary

The degree to which it is possible to attenuate the effects of pressure pulses on the passengers in trains entering tunnels by modifying the normally abrupt portal of a constant-diameter single track tunnel was investigated. Although the suggested modifications to the tunnel entrance portal may not appreciably decrease the magnitude of the pressure rise, they are very effective in reducing the discomfort to the human ear by substantially decreasing the rate of pressure rise to that which the normal ear can accommodate. Qualitative comparison was made of this portal modification approach with other approaches: decreasing the train speed or sealing the cars. The optimum approach, which is dependent upon the conditions and requirements of each particular rail system, is likely to be the portal modification one for a rapid rail mass transit system

Pre-stack full waveform inversion of ultra-high-frequency marine seismic reflection data

The full waveform inversion (FWI) of seismic reflection data aims to reconstruct a detailed physical properties model of the subsurface, fitting both the amplitude and the traveltime of the reflections generated at physical discontinuities in the propagation medium. Unlike reservoir-scale seismic exploration, where seismic inversion is a widely adopted remote characterization tool, ultrahigh-frequency (UHF, 0.2–4.0 kHz) multichannel marine reflection seismology is still most often limited to a qualitative interpretation of the reflections’ architecture. Here we propose an elastic FWI methodology, custom-tailored for pre-stack UHF marine data in vertically heterogeneous media to obtain a decimetric-scale distribution of P-impedance, density and Poisson’s ratio within the shallow subseabed sediments. We address the deterministic multiparameter inversion in a sequential fashion. The complex trace instantaneous phase is first inverted for the P-wave velocity to make up for the lack of low frequency in the data and reduce the nonlinearity of the problem. This is followed by a short-offset P-impedance optimization and a further step of full offset range Poisson’s ratio inversion. Provided that the seismogram contains wide reflection angles (>40°), we show that it is possible to invert for density and decompose a posteriori the relative contribution of P-wave velocity and density to the P-impedance. A broad range of synthetic tests is used to prove the potential of the methodology and highlights sensitivity issues specific to UHF seismic. An example application to real data is also presented. In the real case, trace normalization is applied to minimize the systematic error deriving from an inaccurate source wavelet estimation. The inverted model for the top 15 m of the subseabed agrees with the local lithological information and core-log data. Thus, we can obtain a detailed remote characterization of the shallow sediments using a multichannel sub-bottom profiler within a reasonable computing cost and with minimal pre-processing. This has the potential to reduce the need of extensive geotechnical coring campaigns

Pressure radiation from a perforated duct exit region

Acknowledgements The authors are grateful to the following bodies that provided financial support for the project: (i) China Scholarship Council, (ii) National Natural Science Foundation of China (Grant no. U1334201) and (iii) UK Engineering and Physical Sciences Research Council (Grant no. EP/G069441/1).Peer reviewedPublisher PD

Perforated exit regions for the reduction of micro-pressure waves from tunnels

The authors are grateful to the following bodies that provided financial support for the project: (i) China Scholarship Council (20117 00029), (ii) National Natural Science Foundation of China (Grant no. U1334201) and (iii) UK Engineering and Physical Sciences Research Council (Grant no. EP/G069441/1).Peer reviewedPostprin

Perforated tunnel exit regions and micro-pressure waves:geometrical influence

ACKNOWLEDGEMENTS The authors are grateful to the following bodies that provided financial support for the project: (i) China Scholarship Council, (ii) National Natural Science Foundation of China (Grant No. U1334201 and (iii) UK Engineering and Physical Sciences Research Council (Grant No. EP/G069441/1).Peer reviewedPublisher PD

Hamming weights and Betti numbers of Stanley-Reisner rings associated to matroids

To each linear code over a finite field we associate the matroid of its parity check matrix. We show to what extent one can determine the generalized Hamming weights of the code (or defined for a matroid in general) from various sets of Betti numbers of Stanley-Reisner rings of simplicial complexes associated to the matroid