The use of physics engines in quantifying breakwater damage

The response of proposed breakwater packing strategies to incident waves is usually tested and evaluated in a model hall. There is currently also increasing interest in using numerical simulations to model both the packing of a breakwater, and its response to storms. In this paper, we test the use of physics engine software, which provides fast modelling of hundreds of units, as a means of gaining insight into damage quantification and breakwater disorder. Both dolosse and Antifer armour units are investigated. An order parameter P2 is proposed which is shown, using the numerical models, to be a useful measure of orientational order or disorder when the randomness of the packing is in question. A rootmean-square displacement parameter is proposed as a measure of the movement of armour units from their original positions under cyclic forces. Both parameters are easy to use in simulations, and the use of these parameters in model halls and in the field is discussed.This paper was transferred from the original CD ROM created for this conference. The material was published using Adobe Acrobat 10.1.0 Technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: nigel@doctech URL: http://www.doctech.co.zaPaper presented at the 32nd Annual Southern African Transport Conference 8-11 July 2013 "Transport and Sustainable Infrastructure", CSIR International Convention Centre, Pretoria, South Africa.mv201

Adsorption and two-body recombination of atomic hydrogen on 3^3He-4^4He mixture films

We present the first systematic measurement of the binding energy $E_a$ of hydrogen atoms to the surface of saturated $^3$He-$^4$He mixture films. $E_a$ is found to decrease almost linearly from 1.14(1) K down to 0.39(1) K, when the population of the ground surface state of $^3$He grows from zero to $6\times10^{14}$ cm$^{-2}$, yielding the value $1.2(1)\times 10^{-15}$ K cm$^2$ for the mean-field parameter of H-$^3$He interaction in 2D. The experiments were carried out with overall $^3$He concentrations ranging from 0.1 ppm to 5 % as well as with commercial and isotopically purified $^4$He at temperatures 70...400 mK. Measuring by ESR the rate constants $K_{aa}$ and $K_{ab}$ for second-order recombination of hydrogen atoms in hyperfine states $a$ and $b$ we find the ratio $K_{ab}/K_{aa}$ to be independent of the $^3$He content and to grow with temperature.Comment: 4 pages, 4 figures, all zipped in a sigle file. Submitted to Phys. Rev. Let