Adel Younan

Design of a Shipboard Local Load Measurement System to Collect Managed Ice Load Data

Abstract Due to a lack of data, currently (and justifiably) conservative ice load assumptions are made in rig assessments allowing only very small floe sizes to contact non-Polar classed drilling r ...

Determination of Wave Impact Loads for the Hebron Gravity Based Structure (GBS)

ExxonMobil Canada Properties and its co-venturers are building a gravity based structure (GBS) in Newfoundland and Labrador to be installed on the Hebron Field offshore Eastern Canada. This area is characterized by harsh storms with large waves and high winds. The geometry of the Hebron GBS has an effect on the behavior of the incident waves with regards to their likelihood of breaking onto the shaft. Model tests of the structure in storm waves were executed to provide local wave impact load data on the shaft of the GBS. These tests required significant planning and design of the model, environment, and instrumentation in order to properly satisfy the test objectives. The results of the test showed that the measured wave impact loads on the structure were highly variable, requiring a long-term, response based method to quantify the design loads on an annual exceedance basis. In this paper, we discuss the salient aspects of the model testing effort and the long-term analysis approach which was utilized to define the wave impact loads that were incorporated into the Hebron GBS structural design.Copyright

Modelling Iceberg-Topsides Impacts Using High Resolution Iceberg Profiles

Platforms operating in arctic and subarctic regions such as the Grand Banks, Labrador Sea, Barents Sea and offshore Greenland are exposed to the risk of iceberg impacts. These structures must be designed to withstand the impact from an iceberg or be designed to disconnect and move offsite to avoid the impact. Offshore Newfoundland, gravity based structures (GBS) such as the Hibernia and Hebron platforms are designed to withstand an impact from an iceberg. However, current accepted practice is not to design the topsides for impact, but to reduce impact risk to an acceptable level by varying the facility geometry (i.e., topsides elevation or footprint). An analytical model was developed to estimate the frequency of icebergs impacting the topsides using three dimensional (3D) models of the platform and the icebergs. Random shapes and sizes are simulated for each iceberg and 3D shapes are generated using a database of measured 2D iceberg profiles. The iceberg shapes are placed randomly in close proximity to the structure and are set to drift towards the structure in a straight line. The initial point of contact between the iceberg and the structure is determined. Crushing of the iceberg against the platform caisson is considered. The process is repeated a large number of times and the total number of contacts with the topsides are determined. In 2012, Hibernia Management and Development Company Ltd. (HMDC) sponsored a field program in which high resolution iceberg profile data were collected. The high resolution iceberg profiles contain detailed 3D information of the above water and below water shape of the iceberg. This paper describes updates to the existing-topsides impact model to take full advantage of the detailed 3D iceberg profiles. These updates include new iceberg shape databases for simulation, and the addition of a detailed iceberg management model and a graphical user interface (GUI) to improve the functionality of the software. Introduction Icebergs can pose a significant risk to oil and gas exploration, development and production facilities operating on the Grand Banks, off Canada’s east coast. The Terra Nova and White Rose floating production storage and offloading (FPSO) vessels are designed to disconnect and move off location to avoid impacts for icebergs which cannot be managed. The Hibernia GBS was designed with an outer ice wall capable of resisting impacts from large icebergs (Hoff et al. 1994; Huynh, Clark, and Luther 1997). The Hebron GBS is also designed to withstand impacts from large icebergs (Widianto et al. 2013). With both GBS platforms, the caisson can withstand large impact forces. However, it is not practical or feasible to design the various components of the topsides structure (e.g. walkways, lifeboat stations, generators, etc.) to withstand such large impacts forces. Instead, the topsides layout and elevation above the sea surface are designed such that the risk of iceberg impact is minimized. The Iceberg-Topsides Impact Model was developed to provide guidance to designers. This software tool can be used during the early concept selection stage of a project to optimize the basic GBS-topsides configuration such that the risk of an iceberg impact with the topsides is minimized. The tool can also be used later during detailed engineering design to verify that a particular design meets ISO 19906: 2010 guidelines. During the summer of 2012, HMDC sponsered an extensive field program to collect high resolution iceberg profiles (Younan et al. 2016). Multibeam sonar was used to collect below water iceberg shape information and a photogrammetry system was used to collect above water information. The data were combined resulting in complete 3D iceberg profiles.

Seismic Design of Hebron Platform: An Integrated Soil-Structure-Interaction Approach

Seismic analysis of an offshore platform requires an integral model combining all its elements: foundation, substructure, deck, modules, appurtenances, and even pipeline and riser tie-ins. With typical breakdown of project scope amongst several EPC contractors, the task of creating a seismic model and ensuring proper input, output and updates for EPC contractors’ design always rests with the operator’s engineering team. This model is complicated by the nature of dynamic soil-structure-interaction characterized by radiation of earthquake wave and energy to the far field. This radiation of energy is significant for short squatty gravity-base structures while most structural software lack this capability. This problem has been worked by the nuclear industry, but in this paper we summarize ExxonMobil practice for carrying this task in this scope breakdown environment. The need for this practice emerged during the engineering of Orlan (Sakhalin), was first used on the Adriatic LNG Terminal (Italy) and applied since on Berkut (Sakhalin) and Hebron (Canada).Copyright