The parameterisation of turbulence in the marine environment

There are many problems in the fields of flow modelling around structures and tidal stream energy yield analysis which require a thorough understanding of the turbulent and time-averaged flow speeds in marine environments. In this paper we examine the relationship between the turbulence intensity and mean tidal flow speed at a potential tidal stream power site. We report data from the Humber Estuary wherein an Acoustic Doppler Current Profiler were used to capture vertical profiles of the high frequency and mean tidal flow speeds throughout Spring and Neap, Flood and Ebb cycles. We show not only that our results extend earlier work but also suggest that the turbulence intensity, IT, can be described parametrically in terms of the mean flow, U, by an inverse power function IT = α Uᵖ where the coefficient appears to be dependent upon the anisotropic nature of the turbulence. For the data reported here, the coefficient has value of about 17–18 and the exponent lies between −0.6 and −1.0. Confirmation of this relationship should not only improve engineering design work and energy yield analyses in turbulent tidal flows but also be applicable to other problems such as the prediction of sediment mass transport and pollution dispersal in estuarine management studies

Helios is a key transcriptional regulator of outer hair cell maturation

The sensory cells that are responsible for hearing include the cochlear inner hair cells (IHCs) and outer hair cells (OHCs), with the OHCs being necessary for sound sensitivity and tuning1. Both cell types are thought to arise from common progenitors; however, our understanding of the factors that control the fate of IHCs and OHCs remains limited. Here we identify Ikzf2 (which encodes Helios) as an essential transcription factor in mice that is required for OHC functional maturation and hearing. Helios is expressed in postnatal mouse OHCs, and in the cello mouse model a point mutation in Ikzf2 causes early-onset sensorineural hearing loss. Ikzf2cello/cello OHCs have greatly reduced prestin-dependent electromotile activity, a hallmark of OHC functional maturation, and show reduced levels of crucial OHC-expressed genes such as Slc26a5 (which encodes prestin) and Ocm. Moreover, we show that ectopic expression of Ikzf2 in IHCs: induces the expression of OHC-specific genes; reduces the expression of canonical IHC genes; and confers electromotility to IHCs, demonstrating that Ikzf2 can partially shift the IHC transcriptome towards an OHC-like identity

Experiments with point absorbers for wave energy conversion

Although many existing and proposed wave energy devices operate as point absorbers, for which the overall efficiency depends upon the frequency and magnitude of the buoy's displacement, there is little experimental data presently available with which to optimise power outputs. A harmonic model is presented for the resonant frequency and absorption efficiency of bodies that oscillate in heave mode. The model is tested with a series of still water experiments and with monochromatic wave experiments in a laboratory flume incorporating an axi-asymmetric buoy. The results support the theoretical analysis. Empirical relationships are derived for the added mass and damping of the system. The laboratory experiments demonstrate an empirical absorption efficiency in excess of 80% at resonance

Modelling and testing the vertical axis, impulse rotor tidal power pontoon

The specification of a new tidal power pontoon is described. The device consists of a 500kW asynchronous generator connected through gearbox and drive shaft to a twelve bladed, vertical axis rotor 4.00m x 4.00m mounted at the impact point of a jet in a symmetrical Bernoulli duct beneath a 16.00 m x 10.00m pontoon. Analytical models are developed for (1) the flow through the duct, (ii) the torque and speed of the rotor and (iii) the efficiency as functions of the device's dimensions and the tidal current speed. Results from computational fluid dynamic simulations confirm the principles of the theory and emphasise the importance of the duct as both accelerator and diffuser. The overall efficiency is shown to depend upon the tip speed ratio of the blade to the Jet velocities. Results from laboratory experiments with a 1/40(th) scale model in a unidirectional flume support the theoretical considerations, provide empirical relationships for the device's efficiency as a function of the jet Reynolds Number and confirm that the optimum TSR lies in the range 0.45-050