Swash Zone Modeling Essay Example | Topics and Well Written Essays - 1250 words

Swash Zone Modeling - Essay Example However, an accurate model is still lacking for at least a couple of reasons (Nielsen et al., 2001). Firstly, the water motion in the swash zone is quite different from that in the inner surf zone and not well understood. In particular, the bed shear stresses have not been measured. Secondly, there is a possibility that perpendicular to the sand surface (in/exfiltration or ventilation) and/or strong horizontal pressure, gradients near bore fronts could influence the sediment motion significantly in the swash zone. In the swash zone, the bore collapses at the shore, surface rollers are not present and consequently the velocity distribution given by Eq. (1) is not valid. Thus, this dissipation mechanism (i.e. surface roller concept) cannot be applied in this region. Instead of this, the eddy viscosity concept is adopted in order to simulate the dissipation due to turbulence in the swash zone (the run-down point is considered as the offshore limit of the swash zone). Details can be found in Karambas and Koutitas (2002). The numerical solution of the Boussinesq-type equations is based on an accurate higher order numerical scheme, which has been developed by Wei and Kirby (1995). They used a fourth-order predictor-corrector scheme for time stepping and discretize the first-order spatial derivatives to fourth-order accuracy. This discretization automatically eliminates error terms that would be of the same form as the dispersive terms, and which must therefore be corrected for if lower order scheme are used. In order to validate the above model, Karambas and Koutitas (2002) compared the numerical results with experimental data (including swash zone). As mentioned by Turner and Masselink (1998), vertical flow through a porous bed induces two effects: (a) bed stabilization-destabilization, and (b) thickening or thinning of the boundary layer. On the uprush, downwards-directed piezometric head gradients (infiltration) will increase the effective weight of sediment (i.e. bed stabilization), thereby decreasing the potential for sediment transport

Construction Law Essay Example | Topics and Well Written Essays - 2000 words - 1

Construction Law - Essay Example In this case, the tender arrived on time, but lay in the letterbox, therefore it was deemed to be a valid offer. A unilateral contract would turn into a bilateral contract through a valid acceptance, signified by a performance of the stipulated terms within the offer. According to I.M. Wormser, the justification for fixing acceptance to a unilateral contract upon completed performance of the stipulated terms is based upon symmetry3. Therefore in terms of the tender, there is no obligation upon the offerer, neither is there any obligation upon the offeree unless and until the stipulated terms of the offer have been completed. An offeree need not perform the stipulated terms, in which case no contract exists. Therefore, the initial tender was sent to Widget by Dig-it Builders but when accepted by Widget, did not yet constitute a formal contract because Dig-it sent a counter offer and when it was not accepted within the stipulated time period, they sent the fax withdrawing their offer. However the original term of the tender is 60 days so the tender still remains open, since only one party has wi thdrawn the offer. The mail indicating acceptance by Widget was posted by the architect on the same day, and the courts have deemed acceptance when a letter is posted4. However it is received on the subsequent day (the 35th) day of the tender. Therefore, this will still be subject to the general rule regarding acceptance, which is the requirement of actual communication5. No legal commitment will be deemed to exist until the acceptance of the offer is communicated to the offerer and up to that point, either party is free to change their minds.6 However, Dig-it’s fax will be construed to be a counter offer in the sense that it is a withdrawal of the original offer, which no longer exists. But the tender is not yet closed because Dig-it has made a counter offer reducing the price, although this will still not be a contract until acceptance is obtained