On the relative utility of different methods to increase the vertical height in an otter trawl

Comparative fishing experiments to study the relative utility of different methods for increased vertical spread of bottom trawl and the availability of off bottom fishes in the region were made using gussets, kite, separate float line and side panels on a two seam net. The catch rates as well as composition of fish were studied. The opening of the trawl mouth, both horizontally and vertically, under different operating gears and towing tension on warps were measured and estimated for comparison purposes. Better catch rate with good quality fishes was obtained with the gear operated with separate float line. With kite, the vertical spread was increased with less catch indicating poor concentration of off bottom fishes.

KNOCK DETECTION BY AUDIBLE, ACCELEROMETER, PRESSURE AND IONIC CURRENT METHODS.

This paper describes the ways which are used at the present time by the Ford Motor Company for the detection of knock. A description of the available methods is given, and their relative effectiveness is assessed by analysing data taken simultaneously by all of these methods. It is shown that no one technique has an overwhelming advantage, but that each technique has its individual merits and demerits.

A comparison of methods for assessing the lifetime reliability of a moored FPSO

Current design codes for floating offshore structures are based on measures of short-term reliability. That is, a design storm is selected via an extreme value analysis of the environmental conditions and the reliability of the vessel in that design storm is computed. Although this approach yields valuable information on the vessel motions, it does not produce a statistically rigorous assessment of the lifetime probability of failure. An alternative approach is to perform a long-term reliability analysis in which consideration is taken of all sea states potentially encountered by the vessel during the design life. Although permitted as a design approach in current design codes, the associated computational expense generally prevents its use in practice. A new efficient approach to long-term reliability analysis is presented here, the results of which are compared with a traditional short-term analysis for the surge motion of a representative moored FPSO in head seas. This serves to illustrate the failure probabilities actually embedded within current design code methods, and the way in which design methods might be adapted to achieve a specified target safety level.

Circulation system and areas of potentially successful tuna fishing with surface methods off Mozambique

Charts with 3-months running means of thermal data collected during 1977-1982 are used to describe the seasonal variability of the circulation pattern off Mozambique, and to identify the areas of tuna vulnerability to surface gears. The main conclusions reached by Sætre and Jorge da Silva (1984) have received further support. Areas of potentially successful exploitation of tunas by surface methods have been identified during the whole year, with emphasis for November-April.

Centrifuge modelling-based verification of response spectra design methods for some vulnerable structures

Residential RC framed structures suffered heavily during the 2001 Bhuj earthquake in Gujarat, India. These types of structures also saw severe damage in other earthquakes such as the 1999 Kocaeli earthquake in Turkey and 921 Ji-Ji earthquake in Taiwan. In this paper the seismic response of residential structures was investigated using physical modelling. Idealised soft storey and top heavy, two degrees of freedom (2DOF) portal frame structures were developed and tested on saturated and dry sand models at 25 g using the Schofield Centre 10-m Beam Centrifuge. It was possible to recreate observed field behaviour using these models. As observed in many of the recent earthquakes, soft storey structures were found to be particularly vulnerable to seismic loads. Elastic response spectra methods are often used in the design of simple portal frame structures. The seismic risk of these structures can be significantly increased due to modifications such as removal of a column or addition of heavy water tanks on the roof. The experimental data from the dynamic centrifuge tests on such soft storey or top-heavy models was used to evaluate the predictions obtained from the response spectra. Response spectra were able to predict seismic response during small to moderate intensity earthquakes, but became inaccurate during strong earthquakes and when soil structure interaction effects became important. Re-evaluation of seismic risk of such modified structures is required and time domain analyses suggested by building codes such as IBC, UBC or NEHRP may be more appropriate. © Springer 2006.

Blind equalization and sequence estimation using Markov chain Monte Carlo methods

This paper discusses the problem of restoring a digital input signal that has been degraded by an unknown FIR filter in noise, using the Gibbs sampler. A method for drawing a random sample of a sequence of bits is presented; this is shown to have faster convergence than a scheme by Chen and Li, which draws bits independently. ©1998 IEEE.

Fishing gear and methods for off-shore fishing in Sri Lanka

The author describes the commercial viable off-shore fishing methods for catching known commercial resources available around Sri Lanka. He also describes the in-shore fishing methods such as bait fishery which are related and of prime importance for carrying out certain off-shore methods. The paper is intended as a background for the description of fishing methods. The methods discussed are: (1) Longlining for large pelagic species such as large tuna (yellow fin, big eye), shark, spearfish and others; (2) Drift-netting for small and large tuna species (skipjack, yellow fin and others), shark, spearfish, etc.; (3) Pole and line for all deep-sea pelagic species such as skipjack, yellow fin, frigate mackerel, etc.; and (4) Purse seining (small scale) for small pelagic species suitable as bait fish for pole and line and longline fisheries.

Improved chemical methods for extraction of fin rays from shark fins

A survey was undertaken of methods available for the extraction of fin rays from shark fins. The development of new, quicker and easier methods of processing is presented.

A comparison of methods for the coupled analysis of floating structures

The dynamic analysis of a deepwater floating platform and the associated mooring/riser system should ideally be fully coupled to ensure a reliable response prediction. It is generally held that a time domain analysis is the only means of capturing the various coupling and nonlinear effects accurately. However, in recent work it has been found that for an ultra-deepwater floating system (2000m water depth), the highly efficient frequency domain approach can provide highly accurate response predictions. One reason for this is the accuracy of the drag linearization procedure over both first and second order motions, another reason is the minimal geometric nonlinearity displayed by the mooring lines in deepwater. In this paper, the aim is to develop an efficient analysis method for intermediate water depths, where both mooring/vessel coupling and geometric nonlinearity are of importance. It is found that the standard frequency domain approach is not so accurate for this case and two alternative methods are investigated. In the first, an enhanced frequency domain approach is adopted, in which line nonlinearities are linearized in a systematic way. In the second, a hybrid approach is adopted in which the low frequency motion is solved in the time domain while the high frequency motion is solved in the frequency domain; the two analyses are coupled by the fact that (i) the low frequency motion affects the mooring line geometry for the high frequency motion, and (ii) the high frequency motion affects the drag forces which damp the low frequency motion. The accuracy and efficiency of each of the methods are systematically compared. Copyright © 2007 by ASME.

Ground improvement methods for liquefaction remediation

Soil liquefaction continues to be a major source of damage to buildings and infrastructure after major earthquake events. Ground improvement methods are widely used at many sites worldwide as a way of mitigating liquefaction damage. The relative success of these ground improvement methods in preventing damage after a liquefaction event and the mechanisms by which they can mitigate liquefaction continue to be areas of active research. In this paper the emphasis is on the use of dynamic centrifuge modelling as a tool to investigate the effectiveness of ground improvement methods in mitigating liquefaction risk. Three different ground improvement methods will be considered. First, the effectiveness of in situ densification as a liquefaction resistance measure will be investigated. It will be shown that the mechanism by which soil densification offers mitigation of the liquefaction risk can be studied at a fundamental level using dynamic centrifuge modelling. Second, the use of drains to relieve excess pore pressures generated during an earthquake event will be considered. It will be shown that current design methods can be further improved by incorporating the understanding obtained from dynamic centrifuge tests. Finally, the use of soil grouting to mitigate liquefaction risk will be investigated. It will be shown that by grouting the foundation soil, the settlement of a building can be reduced following earthquake loading. However, the grouting depth must extend the whole depth of the liquefiable layer to achieve this reduction in settlements.