Karina Hjelmervik

A simple approach to adjust tidal forcing in fjord models

To model currents in a fjord accurate tidal forcing is of extreme importance. Due to complex topography with narrow and shallow straits, the tides in the innermost parts of a fjord are both shifted in phase and altered in amplitude compared to the tides in the open water outside the fjord. Commonly, coastal tide information extracted from global or regional models is used on the boundary of the fjord model. Since tides vary over short distances in shallower waters close to the coast, the global and regional tidal forcings are usually too coarse to achieve sufficiently accurate tides in fjords. We present a straightforward method to remedy this problem by simply adjusting the tides to fit the observed tides at the entrance of the fjord. To evaluate the method, we present results from the Oslofjord, Norway. A model for the fjord is first run using raw tidal forcing on its open boundary. By comparing modelled and observed time series of water level at a tidal gauge station close to the open boundary of the model, a factor for the amplitude and a shift in phase are computed. The amplitude factor and the phase shift are then applied to produce adjusted tidal forcing at the open boundary. Next, we rerun the fjord model using the adjusted tidal forcing. The results from the two runs are then compared to independent observations inside the fjord in terms of amplitude and phases of the various tidal components, the total tidal water level, and the depth integrated tidal currents. The results show improvements in the modelled tides in both the outer, and more importantly, the inner parts of the fjord.

Organizing data from industrial internet of things for maritime operations

The enormous amount of data collected from different sources in an Industrial Internet of Things (IIoT) will have to be processed, analyzed, and visualized in a timely manner. In this paper, we present a strategy for organizing IIoT data to facilitate data processing, storage, analysis, and visualization based on a typical oil combat operation scenario. A web-based system has been implemented and deployed and real-time data streams from the oil detectors are presented interactively, satisfying different users needs.

Advance Use of Training Simulator in Maritime Education and Training: A Questionnaire Study

Simulator training has seen its growth and effectiveness since last two decades across all socio-technical complex systems including maritime. The adaption of simulator training in Maritime Education and Training has been well embraced in the education programs, as they provide enhanced learning, as well as possibilities of simulating abnormalities and malfunctions. One way of understanding the impact and benefits of various features of training/education simulators is by the user themselves. This can be achieved by a well-designed questionnaire study, which is the focus of this work. An experiment was designed and conducted to investigate the effect on learning outcome based on the realistic currents in the simulator, which was compared with those who were trained with simple (uni-directional) currents. Apart from objective performance indicators – e.g., cross track error, speed, etc. – a questionnaire was developed and conducted to acquire various parameters that are linked to overall performance and learning of the participants.

Fuel Saving in Coastal Areas: A Case Study of the Oslo Fjord

Fossil fuels such as marine diesel oil (MDO) account for a significant part of the shipping industry’s total operating costs and have a certain negative impact on the environment. Maritime transport emits around 1000 million tonnes of CO2 annually and is responsible for about 2.5% of global greenhouse gas emissions. To focus on fuel saving is therefore important for both economic and environmental reasons. It is indicative that ship owners are now using weather routeing to save fuel and reduce emissions, particularly on long passages. In coastal areas, navigation is limited by traffic rules. This study examines whether fuel consumption can be reduced with current routeing in confined coastal areas, in this case a relatively short voyage in the Oslo Fjord, Norway. An advanced bridge simulator is used, where different current fields from a high-resolution ocean model are implemented. The results reveal that if the voyage is conducted on a typical field with following currents, instead of a typical counter current field, the travel time will be reduced by 12% for a typical vessel with speed through water set to 16.7 knots. On following currents, the vessel speed can be reduced to 15.7 knots and the voyage is completed within the same time as if no currents are present. This implies approximately a 15% reduction in fuel consumption for the vessel tested. The results also reveal that fuel consumption can be reduced if the vessel is operated within most favourable or least unfavourable currents inside the main traffic lanes.

Characterising piezoelectric material parameters through a 3D FEM and optimisation algorithm

Self heating in underwater transducers can act as a limit for high performance transducers. Understanding the physical processes which drive ultrasound transducer self heating requires characterisation of the internal energy loss mechanisms. This study focuses on the energy loss mechanisms of the active part of the transducer, the piezoelectric component. A method which involves a 3D FEM model nested within an iterative simulated annealing scheme which determines the material parameters, including the energy loss parameters, is used to characterise a piezoelectric rod. This type of piezoelectric structure is commonly used in underwater transducers. A cost function is used to compare the difference between the measured electrical admittance and the modelled electrical admittance. The choice of the cost function used has an impact on which material parameters the method is able to optimise efficiently. In the case of the cost function used in this study, the method is successful at characterising the real values of the material constants. However, a more tailored cost function is needed to characterise the loss tangents successfully.

Adjusting modelled sound speed profiles for use in sonar operations

Realistic descriptions of vertical sound speed profiles are essential for modelling underwater acoustic fields. Errors in the vertical sound speed profile will have negative impact on the acoustic propagation modelling. Ocean models provides vertical profiles of temperature and salinity, from which sound speed can be derived, covering large areas with high spatiotemporal resolution. Previous experience with ocean models shows that vertical sound speed profiles are difficult to model with sufficient accuracy to be useful for acoustic modelling. A method for adjusting sound speed profiles from an ocean model to better represent measured profiles is proposed. The method is based on replacing the mean sound speed profile from the ocean model data set with mean profile of an observed data set. The method is illustrated on data from the Norwegian coast where the coastal current causes well-defined fronts and eddies. The proposed method reduces the mean root-mean-square error in the model data, particularly in the upper layers. On the other hand, comparisons of observed and modelled sound speed profiles on a one-to-one basis, is still challenging in both space and time.

Detection of oceanographic fronts using empirical orthogonal functions

Oceanographic fronts are boundaries between water masses with differences in hydrography. Often the presence of fronts coincide with oceanographic currents. The detection of fronts has traditionally been carried out by looking for sudden horizontal changes in the sea surface temperature or salinity. Applications involving temperature or salinity alone, may therefore overlook significant oceanic fronts. Also some fronts may be more exaggerated below the sea surface and therefore missed by approaches that rely on sea surface values only. Here we suggest a parametrical approach that combines both salinity and temperature profiles simultaneously using empirical orthogonal functions. This ensures that both salinity and temperature based fronts may be detected even if they are present below the sea surface. The suggested parametrisation allows the user to customise the emphasis on salinity or temperature, and even put an emphasis on particular depth regions. The method is demonstrated on data from two different dynamical ocean models. The same parametrisation is used for both data sets. No calibration or tuning was required and the resulting fronts are comparable. The method is also applied on a full year of data with unchanged parametrisation. The detected fronts exhibit expected behaviour, which builds confidence in the methods robustness and versatility.