R.W.F. Thurley

Shallow Angle Wave Profiling LIDAR

A LIDAR scanning system is described which is primarily designed to measure sea wave shape. The device is capable of measuring real-time spatial profiles over distances of hundreds of metres and as the LIDAR must inevitably operate from modest elevations, eg., from a vessels mast head it is inherently a very shallow angle metrology device. This results in a highly nonuniform distribution of the wave elevation values. The vertical and horizontal resolution is primarily set by the characteristics of the optical system employed and range/data capacity is set by signal to noise ratio considerations. Illustrative data is presented as consecutive profiles taken 0.2 sec apart for highly trochoidal wave under conditions where the height was recorded to +_ 0.03 m and horizontal sample separation to +_0.025 m. A comparison is presented with traditional wave staff measurements.

Early Stages of Combustion in Internal Combustion Engines Using Linked CFD and Chemical Kinetics Computations and its Application to Natural Gas Burning Engines

Abstract The paper describes a numerical model for the early stages of combustion in Natural Gas engines using linked CFD and detailed chemical kinetics. The importance of such a combustion device stems from the characteristics of natural gas which make it an attractive near-term olution for the automotive emissions problem. The 3-D simulation, which incorporates a chemical model, turbulence model and ignition model is taken under engine-like conditions. This is achieved by coupling the numerical codes KIVA II, developed to solve the transient equations of conservation of turbulent chemically reacting mixture of ideal gases, CHEMKIN II, designed to facilitate simulations of elementary chemical reactions in flowing systems, TRANSPORT, used for the evaluation of gas-phase multicomponent transport properties, and LIOR - a linking code. The numerical tool has predictive capability for combustion behaviour under various conditions, an ability to interpret observed combustion phenomena and ability to guide the ...

Combustion inhomogeneity and percolation

This paper briefly examines the scale and consequences of inhomogeneity in the fuel/air system within the cylinder of a petrol IC engine. This work serves as the basis around which to introduce a percolation network approach as the natural description for combustion inhomogeneity. The underlying structural elements of the percolation model link in a very direct way with the various physical quantities concerned. This allows the general aspects of the theory to offer new concepts in combustion which appear attractively obvious once they have been stated. The most important point to emerge is that the percolation approach generates very clear design guidelines, particularly for operation under lean conditions.

Non-uniform sampling issues arising in shallow angle wave profiling LIDAR

Non-uniform sampling has been identified as a fundamental property in the shallow angle remote sensing required to collect the data required to build DSWP prediction models for moving vessels. The dependence of typical DSWP models on traditional discrete spectral techniques introduces the requirement to re-map sets of N non-uniform sea profile data onto uniformly sampled equivalents. The high computational cost of the general change of basis involved in this process and its detrimental effects upon prediction time motivated an examination of approximation methods. A metric IF is discussed which measures the degree of departure from uniformity in terms of the Primary Band Limitation property which is associated with a generalisation of Nyquists theorem. Various levels of approximation are examined based upon the extent of the departure of /spl Gamma/ from unity. The major conclusion is that for each set of N remotely sensed data values which constitute a sea profile scan it is possible to assess the level of computational sophistication required to render the data set suitable for use in DSWP. This ability is central to the design of an the intelligent system architecture which is required to operate a viable DSWP unit.

Some consequences for marine simulators of statistical coherence within the phase spectrum of sea waves

Statistical dependence within the phase spectrum of simulated swell seas are examined in terms its effect upon the precision of short term deterministic wave prediction models. Numerical experiments show that such local coherence increases the prediction accuracy. Analytic models are developed of the prediction which explain the sensitivity of the prediction model parameters when neighbouring phase values are uncorrelated. The possibility of some degree of coherence in certain types of sea-wave are considered and sectional phase autocorrelations are presented which demonstrate such coherence in real sea data.

A novel design for surface following buoys for oceanography and wave prediction

The new science of detenninistic sea wave prediction (DSWP)J.2,M requires the development of economically viable sea surface profile measuring devices. For some applications, remote sensors such as laser scanners are appropriate but other applications (including temporary emergency deployment systems) will require the use of low-cost sUlfacefollowing buoys. This low-cost requirement mitigates against the possibility of using conventional motion reference units with large Vibrating Structure Gyroscopes (YSGs). Additionally the precision available from such units is not required for the applications discussed here. This paper describes the architecture and signal processing requirements of a novel surface following buoy. Two prototype buoys have been built and deployed for short-tel1l1 data collection in the English Channel.

Methods for Examining Anisotropies in Early Combustion Part I: Multi-Scale Experimental Determinations

ABSTRACT Experimental measures are developed for the description of anisotropic growth in the early stages, of the flame kernel development in an operating spark ignition internal combustion engine. These measures are developments of the support area concept introduced by Bradley and Abdel-Gayed. By applying the technique of multi-scale analysis derived from texture analysis to such anisotropy measures it has shown to be possible to obtain time dependent information about the effect of the various local length scales in the processes that influence early flame growth. The analysis techniques employed are demonstrated to offer very wide scope for characterising anisotropic time varying combustion and the basis is laid for a formal development of this topic as presented in the companion paper. An interesting observation is that for cycles other than partial combustions the largest length scale of process effecting the flame kernel on tends to increase with time during the early flame growth.