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Ship traffic via navigable freezing ice channels causes a gradual accumulation of small ice floes mixed with water, known as brash ice. The thickness of the brash ice layer may reach the values when ship navigation becomes difficult or even impossible. This paper introduces a computational model intended to predict ice channel evolution in winter. The model considers the thermodynamics of the ice-growing process and allows the estimation of the parameters of the cross-section of the ice channel depending on the number of freezing degree-days and the schedule of ship passages. Unlike existing models, the described scheme of channel evolution takes into account that some brash ice is pushed beneath ice channel edges by passing vessels, and therefore the obtained cross-section profile is similar to that observed in full-scale conditions.
Ship navigation in freezing waters is conducted via ice channels made in the ice cover. A channel behind the icebreaker remains but is filled with broken ice fragments. Ships may use the same ice channel time and again. Between ship passages, a fresh ice cover grows in the channel under freezing temperatures. At each ship passage, the ice cover is broken again, and ice blocks are split into smaller pieces. Frequently used channels accumulate smaller ice floes (mean size 50 cm) mixed with water (“brash ice”). The water content is defined by the porosity of the brash ice, which influences the intensity of ice accumulation in the channel.
Ship navigation in ice channels filled with brash ice involves two main issues. First, it is necessary to know the current state of the ice channel. The second issue is related to ship performance in the ice channel, including the hull resistance and the effect of brash ice on propeller operation. This study examines only the first issue, the evolution of the ice channel during the winter season.
The extended lift operation to deliver the Wellbay module (M5) combined with the Flare Tower (M8) from the Miller Platform in the North Sea to the shore using the Semi-Submersible Crane Vessel S7000 was sensitive to the wave environment. Weather and response forecasts were used to assist go or no go decision. Responses of interest such as main hook loads, crane tip motions and clearances between the M5/M8 and vessel crane booms were forecasted and monitored. The results of the weather and response forecasts and the data from the monitored parameters are compared to identify some uncertainties in the weather and response forecasts. To reduce these uncertainties, a method using the sea states measured from the wave rider buoy (WRB) deployed in the Miller Platform Removal campaign has been developed.
Marine operations to install jackets/towers and topsides for new fixed offshore platforms or to remove them after the end of their service life are performed within allowable weather windows. These windows are conventionally based on the comparison of weather forecasts and limiting sea states. The limiting sea states for a particular operation such as topside removal from an offshore platform are found from a dynamic analysis using standard wave spectra (typically JONSWAP spectra), during an engineering phase. The uncertainty in wave spectra used in the engineering analysis can be taken into account using a risk parameter (γ) in the calculation of most probable maximum/minimum (MPM) responses to define the limiting sea states. However, the γ factor is not considered, as the inaccuracy in wave spectra is addressed through an alpha factor (α) to account for uncertainty in weather forecasts. The value of the α factor, recommended by the DNV-GL classification society may be used to de-rate the operational limits (DNV-GL AS, 2016). This approach is generally conservative.
With the increase in computational power, and improvement in numerical weather prediction (NWP) models, the general pattern of the forecast weather is quite accurate up to about three days. For 48 hour weather forecasts wind speed is within 5 m/s 94% of the time and wave height is within 0.5 m 78% of the time (Galvin, 2014). Combining forecast two-dimensional (2D) wave energy spectra output from the NWP models with vessel response amplitude operators (RAOs) has made vessel response forecasts possible (Lai, et al, 2006).
Design of offshore structures for arctic and subarctic regions requires consideration of wave, wind and ice actions. If individual actions are not mutually exclusive, then combined actions also need consideration. ISO 19906 recommends that, when possible, extreme level combined actions should be determined based on the joint probability distribution of the actions. As an alternative, ISO 19906 provides a framework where a user can determine principal and companion extreme actions independently, and sum these with calibrated combination factors applied. While the combination factors in ISO 19906 were calibrated over a range of conditions and platforms, site-specific information is not taken into account when applying the method. In this paper, a procedure is presented for determining extreme level combined actions for sea ice and waves based on site-specific sea ice and wave information, accounting for the joint probability distribution of the actions. The procedure is demonstrated for an example fixed structure on the Grand Banks off Canada's east coast. The results are compared with extreme actions determined using the ISO 19906 combination factors.
New environmental regulations have substantially reduced the permissible level of sulfur oxide emissions from ocean vessels. An economical means of meeting the regulations is through the use of a diesel exhaust scrubber. The scrubber environment includes chlorides, high temperatures, and acidic conditions and requires the use of corrosion resistant alloys. This study will build upon a previous study that compared the corrosion resistance of multiple corrosion resistant alloys in several simulated scrubber environments. The current study evaluates the effect of welding and the presence of a crevice on five alloys. The alloys include a common austenitic alloy, UNS S31603; two superaustenitic alloys, N08367 and N08031; and two Ni-Cr-Mo alloys, N10276 and N06059. These comparisons are essential for proper material selection as the demand for marine exhaust scrubbers grows to meet the new regulations.
Due to new environmental regulations, substantial growth is expected for marine diesel exhaust scrubbers. The new regulations limit the allowable sulfur content in heavy fuel oil (HFO). Marine vessels use HFO as the primary fuel. Current regulations are in effect in certain regions, referred to as Emission Control Areas (ECAs). The ECAs established under MARPOL (International Convention for the Prevention of Pollution from Ships) Annex VI for sulfur oxides are: the Baltic Sea area, the North Sea area, the North American area (covering designated coastal areas off the United States and Canada) and the United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands)1. The sulfur content in HFO in the ECAs is limited at 0.10%. In 2020, new regulations will be applied globally. Currently, outside the emission control areas, the limit for sulfur content of fuel oil is 3.50 wt.%. However, it is scheduled to be reduced to 0.50 wt.% in 2020. Available options to meet the regulations are to burn more expensive low sulfur fuel, switch to natural gas, or install an exhaust scrubber system. Because the scrubber option is not subject to fuel price fluctuations, it is becoming a preferred choice for the marine vessel industry. Therefore, understanding the corrosion behavior of available materials for reliable scrubber design is of increasing importance.
This paper shares results from three DeepStar® Phase XII efforts championed by the X800 Metocean Committee. The first project, 12801, examined marine growth profiles for the Gulf of Mexico. The profile presently used by industry is based on limited data collected nearly thirty years ago, and was shown by the study to under-represent the amount of growth that should be expected on platforms in the Gulf. In addition, flaws in the survey processes currently used to evaluate growth as part of inspections were identified and documented. The second project, 12802, evaluated the design wind speed relationships used by industry to characterize extra-tropical storms, through analysis of high-quality overwater wind measurements collected for elevations up to 100 m made at three locations in the North Sea and Baltic Sea. The evaluation demonstrated the present NORSOK relations are adequate for extra-tropical storms, and hence going forward, industry will use separate design wind speed relationships for extra-tropical storms and tropical cyclones, a revised set for the latter being developed previously under project 11802. The third and final project, 12803, sponsored the development of an updated 54-year free-running simulation of currents in the Gulf of Mexico, with refined modeling of bottom currents in areas near steep bathymetry such as the Sigsbee Escarpment, in order to better represent topographically-enhanced Rossby waves (TRWs), which are a critical design consideration for risers and tendons. The resulting database provides an excellent basis for the development of Loop Current and TRW criteria for use in deepwater Gulf of Mexico projects.
Growing commercial activities in the High North increase the possibility of unwanted incidents. The vulnerability related to human safety and environment as well as a challenging context, call for a strengthening of the maritime preparedness system, cross-border and cross-institutional collaboration. In this paper, we look into the different stressors and risk factors of the sea regions in the High North. We elaborate on emergencies where integrated operations like mass evacuation is needed. We build upon in-depth studies of two cruise ship incidents close to the Spitsbergen Islands, and full-scale exercises in the Arctic region. We claim that coordination of such operations where several institutions and management levels are included demands significant integration and communication efforts. Implications for the training of key personnel responsible for coordinating such operations are discussed.
Emergency situations are often characterized by lack of overview and uncertainty about cause, consequences and suitable safety barriers. In areas like the High North, due to limited infrastructure and the scarcity of emergency capacities, a simple emergency situation can quickly turn into a crisis involving significant risk for people, nature and vulnerable societies. The turbulent weather conditions facing emergency actors, makes rescue and relief operations a challenging and time consuming task. In this paper, we examine how the emergency management has to be configured to overcome challenges related to large-scale emergencies with limited local infrastructure, long distances and harsh weather conditions in icy waters. In addition, we consider the limited availability of emergency support systems and the time delays caused by the geographical distances.
By examining the various emergency situations we reflect on suitable composition of the infrastructure, emergency groupings, and coordination mechanism.
Emergency Management and Emergency Response Pattern
High levels of uncertainty combined with a need for fast and reliable action are the main characteristic of emergencies (Kyng, Nielsen, and Kristensen 2006). Major incidents like shootouts and terror action, or cruise ship groundings with mass rescue operations (MRO) are categorized by lack of sufficient resources to meet the emergency situation. These situations are often chaotic and stressful with a large number of causalities, and a mix of SAR capacities. Thus, obtaining and maintaining an overview for such an incident become extremely hard for the coordinators and the different levels of command.
ABSTRACT: Samples of anisotropic gneiss oriented at 0, 30, 60 and 90 degrees to the maximum loading stress were tested in a true-triaxial deformation cell. The loading path was designed to simulate the in situ stresses that rock would be exposed to during the excavation, heating and cooling of canister holes created for the proposed containment of radioactive waste. The results show that the deformation response would not be replicated with a traditional triaxial test were the intermediate and minimum stress are assumed to be equal. In two situations the loading history induced failure when the intermediate stress was reduced. Acoustic emission and velocity data are used to characterize the damage and the sensitivity of the velocity data provide a future method to link laboratory to in situ observations.
Understanding damage around boreholes and tunnels in rock is significant to numerous engineering applications. Borehole breakout and spalling, where the preferential orientation of stresses can induce failure, is a classic manifestation of this damage. Ever since the early work of Kirsch over a century ago we have endeavored to understand the complex interactions of stress and geometry on failure. More recently rock mechanics experimental testing and discrete particle numerical models have been used to deconvolve the complex fracture processes that lead to crack coalescence and the various modes of failure in rock materials (Hoek & Martin 2014). One application, which requires an understanding of failure around underground openings, is the concept of deep geological disposal of radioactive waste. Several countries have proposed schemes that involve the placement of spent fuel in canisters that will be placed in large diameter boreholes in tunnel complexes that are between 300 m and 500 m below the surface. Three such countries include Canada, Sweden and Finland where extensive investigations have been undertaken in crystalline rock to create a design that will be safe for the long term management, storage and disposal of radioactive waste.
In situ rock stresses are directly associated with the stability of underground openings and thus the state of in situ rock stress is a crucial factor for the design of underground excavations. The consequences of the rock stresses are rock deformation and rock failure. Concerns have to be taken into account when the in situ stresses are in such magnitudes so that rock failure would occur after excavations. The modes of rock failure observed in fields will be first presented as the base for subsequent discussions in the article. Some rock mechanics principles aiming to improve the stability of underground openings are also presented. For instance, a wide opening can be excavated in a rock mass where the horizontal stresses are high enough. In a case of extremely high horizontal stresses, the stability of the roof could be improved by increasing the width of the opening. The basic design principles with regard to in-situ stresses will be illustrated through a few examples in the article. Finally, measures dealing with instability issues caused by in situ rock stresses are presented through a few case studies. Among others, the case studies include positioning of a mine shaft in a rockburst-prone condition, excavation of a shaft that was subjected to uneven lateral rock deformations, assessment of the causes for the rock failure in a deeply located underground workshop, and field observations of mine pillars in an abandoned open stope.
Underground excavation is affected by three factors from viewpoints of design and stability. They are the quality of the rock mass, the state of in situ stresses and the size and shape of the excavation, Figure 1. The quality of the rock mass essentially describes the “strength“ of the excavation material - the rock mass. One has nothing to do with the material, as soon as the excavation location is determined. The state of in-situ stresses in the rock mass cannot be changed by human either. What one can do with these two factors is to carry out assessment and measurement in order to form a solid base for engineering design. Excavation method is the only factor, among the three, which one can interfere. The stability of an underground opening is not only determined by the quality of the rock mass, but also the state of in-situ stresses. The state of in-situ stresses refers to the magnitude and the orientation of the principal stresses in the rock mass prior to excavation. The stability of the underground opening can be improved by employing some principles related to in-situ stresses. For instance, a wide opening can be excavated in a rock mass where the horizontal stresses are large enough. In a case of extremely high horizontal stresses, the stability of the roof could be improved through increasing the width of the opening. The basic design principles with regard to in-situ stresses will be illustrated through examples in this paper.