K.A. Kuo

Public Engagement with Biotechnologies Offers Lessons for the Governance of Geoengineering Research and Beyond

This Perspective looks back on recent experience of public engagement with biotechnologies and asks what can be learned for the governance of another controversial emerging area—geoengineering.

Prediction uncertainties and inaccuracies resulting from common assumptions in modelling vibration from underground railways

Underground railways produce significant ground-borne vibration that is reported to disturb people living or working near subways. Designers and engineers use numerical models to predict vibration levels so as to meet the increasingly strict vibration standards. These models commonly include simplifying assumptions to reduce the complexity and cost of the simulation. This paper reviews six commonly disregarded aspects of the underground railway environment and their respective effects on vibration prediction values: a second (twin) tunnel, piled foundations, track with discontinuous slabs, soil inhomogeneity, inclined soil layers, and irregular contact at the tunnel–soil interface. Results suggest that accounting for each of these simplifying assumptions can result in predictions that vary from the simplified cases by at least 5 dB and potentially up to 20 dB. This is a significant level of uncertainty and should be considered when estimating the predictive accuracy of numerical models using simplifying assumptions.

The use of sub-modelling technique to calculate vibration in buildings from underground railways

In this paper, a method is presented for the calculation of the vibration created in buildings by the operation of underground railways. The method is based on the sub-modelling approach which is used to couple a model of a building on a piled foundation to another model that calculates the vibration generated in the soil in underground railway tunnels. The method couples a building on a piled foundation to the soil at discrete points by satisfying equilibrium and compatibility requirements at those points. The method results in efficient numerical calculations. A two-dimensional frame made of beam elements is used to model the building and its piled foundation. The elements are formulated using a dynamic stiffness matrix which accounts for Euler–Bernoulli bending and axial behaviour. Vibrations created by a train moving in an underground tunnel are calculated using the well-known pipe-in-pipe (PiP) model. The model calculates the power spectral density (PSD) of the displacement in the soil. The excitation mechanism is the roughness of the rail and the PSD is calculated for a train moving on a floating-slab track in an underground railway tunnel for a stationary process. The current version of PiP accounts for a tunnel embedded in a half-space. The building frame is coupled in this paper at 90° to the tunnel’s centreline. The main result of this paper illustrates the significant contribution of the building’s dynamics to the displacement wave field received by the building. The example presented in this paper shows a decrease of more than 20 dB in the displacement PSDs at frequencies larger than 10 Hz when accounting for the change in this wave field.

Recent developments in the pipe-in-pipe model for underground-railway vibration predictions

The Pipe-in-Pipe (PiP) model is a fast-running model that calculates vibration levels from an underground railway within a layered halfspace. This model contains many simplifying assumptions, but its fast computation time makes it useful as an early design tool.

Isothermal pumping analysis for high-altitude tethered balloons

High-altitude tethered balloons have potential applications in communications, surveillance, meteorological observations and climate engineering. To maintain balloon buoyancy, power fuel cells and perturb atmospheric conditions, fluids could be pumped from ground level to altitude using the tether as a hose. This paper examines the pumping requirements of such a delivery system. Cases considered include delivery of hydrogen, sulfur dioxide (SO2) and powders as fluid-based slurries. Isothermal analysis is used to determine the variation of pressures and velocities along the pipe length. Results show that transport of small quantities of hydrogen to power fuel cells and maintain balloon buoyancy can be achieved at pressures and temperatures that are tolerable in terms of both the pipe strength and the current state of pumping technologies. To avoid solidification, transport of SO2 would require elevated temperatures that cannot be tolerated by the strength fibres in the pipe. While the use of particle-based slurries rather than SO2 for climate engineering can reduce the pipe size significantly, the pumping pressures are close to the maximum bursting pressure of the pipe.