Breaking Cone Research Articles

Experimental study of dynamic conical ice force

Dynamic ice force is one of the key factors in the design and operation of narrow offshore structures in ice-covered areas. In the paper, a series of physical model tests were carried out to simulate field ice conditions on the oil jacket structures with an ice breaking cone in the Bohai Sea. The model tests involved two geometric scale factors (3 and 6), 3 structural models, and 3 ice sheets. In the total 17 groups of tests, the controlled parameters of ice velocity, ice friction coefficient, and the shape of the ice-resistant structure at the waterline were different. The time history of ice forces, accelerations of the model, and the ice–cone interaction process were recorded synchronously. Ice failure modes and global ice loads obtained from the model tests were compared with the data measured on the JZ20-2MUQ oil jacket platform. Similar to the results in the field measurements, two ice failure modes were observed on the cones in the lab test. The plate failure mode was observed on the inverted cone. For the upright cone, when the cone diameter was increased, the ice failure mode was transformed from the wedge failure mode into the plate failure mode and the ice load on unit area was decreased.

Geomorphological features of the Manengouba Volcano (Cameroon Line): assets for potential geopark development

Mount Manengouba is a volcanic complex, age between 1.5 and 0 Myr, situated in the Cameroon Line in Cameroon, approximately 120 km NE of Mount Cameroon. It comprises some important geomorphological features, of geoheritage significance, i.e., geomorphosites, namely, two nested sub-circular calderas, broken cones, crater lakes (Female Lake, Male Lake, and Beme Lake), domes and basins. The scientific values, aesthetic appeal, and the uniqueness of Mt Manengouba geomorphosites are suitable for geotourism. However, there are conflicting land-use values as its fertile soils favor farming in the downslope areas of the volcano, and the pyroclastic cones are quarried for pozzolana. While there are field excursions and research programs undertaken by Universities to educate the public about its geoheritage values, currently, tourism at Mt Manengouba is not well developed. It is proposed to promote better local environmental management of the area, improve roads to facilitate the accessibility to these geomorphosites, and produce interpretative panels, guide books and postcards to educate tourists on the geological setting and geoheritage values of the Mt Manengouba area.

Performance evaluation of a new ice-resistant jacket platform based on field monitoring

A new ice-resistant jacket platform was designed and constructed in the Bohai Sea, equipped with a series of techniques to mitigate the ice-induced vibrations. The vibration mitigating techniques include the following: 1) Single-leg design with double-ward fixed ice breaking cone at water level, so as to reduce ice load and dynamic response of the structure; 2) the steel-rubber bearing isolators and magnetorheological (MR) dampers, installed between the upper and lower deck of the platform, so as to reduce the vibration of upper deck and to protect the pipeline system transporting natural gas. In order to evaluate the performance of the new platform, different sensors were deployed on the structure to measure the accelerations of the deck levels and the relative displacement between the two decks. Based on the measured data, the ice-resist performance is discussed. It is shown that the conceptual design and related techniques used on this platform can be adopted during the design process of other structures in the future. ► A new ice-resistant jacket platform was designed in the Bohai Sea ► A field monitoring system was built to evaluate the ice-resistant performance ► The vibration of the structure with mitigating facilities gets smaller than that without mitigating facilities ► The new designed platform and accompanying vibration mitigating facilities are effective ► The conceptual design and related techniques can be adopted in the future.

Model tests of ice forces on fixed and oscillating cones

A series of model tests has been carried out on downward breaking conical structures using low salinity model ice. Comparison with information in the literature showed that a downward breaking cone experiences lower ice forces than an upward breaking cone. Fixed cones of angles of 15, 30, 45 and 60 deg were tested in 50-mm-thick ice of 60 kPa flexural strength at velocities ranging from 0.01 to 0.5 m/s. The effects of thickness and flexural strength variations were also investigated. Horizontal forces were observed to increase with increasing velocity. Ice thickness variation was observed to have a stronger influence on the vertical forces than on the horizontal forces. Vertical and horizontal forces showed a decrease with decreasing flexural strength. Two test series were run with the 45 deg conical structure arranged so that it oscillated. Horizontal force reductions of up to two thirds were observed.