M.R. Belmont

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.

Combustion of methane and ethane with CO2 replacing N2 as a diluent. Modelling of combined effects of detailed chemical kinetics and thermal properties on the early stages of combustion

Abstract Simulations of methane combustion are developed for a synthetic atmosphere system where nitrogen is replaced as diluent with carbon dioxide. Special attention is given to the role of the detailed chemistry, using a scheme containing ∼100 separate reactions. The sensitivity of the results to the major reactions is analysed, and the approach to equilibrium is considered. Examination of a set of model problems shows that where there is a large initial concentration of carbon dioxide, the chemical effects are very important. The results for constant-pressure combustion coincide with conventional expectations, whereas those for a constant-volume system initiated by isotropic auto-ignition are very much counter to intuition. The methods are validated by simulating a plug-flow reactor, for which agreement with experiment is good. The typical application of this work is to subsea vehicles and other closed-environment machines, and the recognition of the importance of chemical effects points to the possibility of chemically modifying performance.

Synthesis of four n-alkanes with terminal dipolar substituents

Abstract 12-Nitrododecanol, 1,12-dinitrododecane, 1,24-dinitrotetracontane and 2,15-diaminohexadecan-1,16-dioioc acid were prepared from the common intermediate 12-bromododecanol. This bromoalcohol, being prepared from cyclododecanone, is free of homologous bifunctional impurities. The functionalised 24 carbon chain was prepared by a Wittig reaction of 12-bromododecanal with the triphenylphosphonium salt of 12-bromododecanal ethylene acetal using ‘naked’ carbonate anion to provide the base. The resulting bromoacetal was converted to 24-bromotetracont-12-enol, both this and the 12-bromododecanol were converted to the corresponding α,ω-di-iodides and then to the desired α,ω-dinitro compounds. The α-amino acid functionality can be introduced on an α,ω-dihalide with the anion of either diethyl 2-acetylaminopropan-1,3-dioate or benzylidene glycine ethyl ester. Also detailed is the previously unreported reduction of a carboxylic acid to an alcohol by borane-dimethyl sulphide in dichloromethane.

A lower bound estimate of the gains stemming from quiescent period predictive control using conventional sea state statistics

The principle of quiescent period prediction control (QPPC) is introduced in the context of sea wave energy capture (WEC) devices. The QPPC strategy is compared to approaches using statistical wave parameters for adaptive control of WECs and is shown to offer considerable increases in the average power captured. Assessing the quantitative benefits of QPPC would normally be based on wave by wave sea surface elevation data. Such data are not typically available from commercial wave sensors, and hence the present work describes a technique for assessing a lower bound estimate to QPPC benefits using conventional statistical sea state parameters. A case study is presented for a site off Southern Ireland where over a 12 month period QPPC can deliver more than 100% increase in the average power captured.

IGNITION SOURCE CHARACTERISTICS FOR NATURAL-GAS-BURNING VEHICLE ENGINES

Abstract Natural gas is a promising alternative fuel to petrol for vehicles. However, one of the factors hampering the design of natural gas burning engines for domestic cars is the long delay from the time of ignition to the commencement of significant heat release. This is mainly due to the substantially endothermic phase during the early development of the combustion in natural gas. It is well known that high-energy, extended or multiple ignition sources can reduce this problem. The present article uses a large-scale computer simulation of a natural gas engine to examine the issues affecting the optimization of such ignition sources.

Ultrafast heating and resolution of recorded crystalline marks in phase-change media

This work presents an analytical study of the thermally activated amorphous-to-crystalline phase-change process when the heating source has a delta function temporal profile. This simulates the case of ultrafast heating where crystallization in the amorphous phase-change medium occurs during cooling. The study produced closed-form expressions that predict the necessary peak temperature, and hence energy density, in the phase-change medium for successful crystallization during ultrafast annealing as functions of the kinetic and thermal parameters of the medium. Closed-form expressions were also derived that provide estimates of the final crystalline mark widths and tail lengths when phase change has ceased. The analysis indicated the need to reduce the activation energy of crystallization and the thermal diffusivity of the medium to reduce the initial peak temperature, produced by the heating source, to avoid melting, to increase the crystallization rate, to achieve sufficient levels of crystalline fractio...

Avoidance of phase shift errors in short term deterministic sea wave prediction

Short term deterministic sea wave prediction (DSWP) offers the promise of considerably extending the operational envelope of many marine activities such as aircraft launch and recovery onto vessels, cargo transfers, station-keeping roles and shuttle tanker activities. A short term prediction model first builds a description of the local sea surface profile then appropriately shifts this in time and space to the prediction site. It is shown that using the discrete Fourier series description conventionally proposed for DSWP implies assumptions about spectral resolution which can give rise to large errors in the shifting process. By reformulating the traditional linearised gravity wave equations it is possible to remove the need for discrete approximations to the shifting process and thus entirely avoid the consequent errors. The resulting shifting algorithms are shown to involve little increase in computational overhead compared to the fully discretised DSWP methods, and thus do not significantly detract from the available prediction times.

Generalized cross-correlation functions for engineering applications, part I: Basic theory

Traditional cross-correlation considers situations where two functions or data sets are linked by a constant shift either in time or space. Correlation provides estimates of such shifts even in the presence of considerable noise corruption. This makes the technique valuable in applications like sonar, displacement or velocity determination and pattern recognition. When regions are decomposed into patches in applications such as Particle Image Velocimerty it also allows estimates to be made of whole displacement/flow fields. The fundamental problem with traditional correlation is that patch size and hence statistical reliability must be compromised with resolution. This article develops a natural generalization of cross-correlation which removes the need for such compromises by replacing the constant shift with a function of time or space. This permits correlation to be applied globally to a whole domain retaining any long-range coherences present and dramatically improves statistical reliability by using all the data present in the domain for each estimate.

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 ...

Conduction transients using a Lagrangian formulation. Part II: Transients in polarized specimens

Abstract The problem examined concerns bipolar charge flow in an insulator containing a large polarization field produced by a uniform distribution of trapped charge and an external applied bias. The self-field of the two mobile species is considered negligible compared with the polarization. The analysis is performed with a view to analysing drift mobility experiments in heavily polarized insulators. The detailed shapes of transients and the variation of total induced charge with applied charge are determined. Novel features, including polarity reversals during the transient, are discussed.