Wave energy is one among several resources of renewable energy which needs to be utilized in the future to solve human’s energy demand. Several technologies have been proposed but yet there are few commercial concepts that have been connected to the grid. The floating wave energy converters (WECs) will have an important role in the supply of electricity in the future. But there are several challenges in their designs on systems and component levels that need to be overcome and solved. There are also challenges related to installation and maintenance. The current paper presents and discusses examples of challenges on component and systems level, with reference to floating WECs. One specific concept is studied in detail with an emphasis on mooring design, fatigue life of elastic mooring systems and umbilical cables, power performance of individual WECs vs WECs installed in wave parks. The levelized cost of electricity method is used to compare some configurations that have been studied in more detail. Examples of results from numerical simulations and full-scale measurements on a floating heave point-absorber are presented.

The Northeast Passage in the Arctic between Europe and Asia offers a significantly shorter voyage compared to the Southern route through the Suez Canal. In 2017, the EU research project “Safe maritime operations under extreme conditions: the Arctic case (SEDNA)” was established to perform a comprehensive analysis of Arctic transit shipping and to promote technical solutions for this purpose. This paper is based on the deliverables of the SEDNA project. A voyage planning tool (VPT) for Arctic applications was developed to plan the optimal route regarding ship’s fuel consumption and safety. One of the most advanced metocean and ice forecast model is utilized to provide comprehensive environmental conditions that are synchronized and will be updated frequently during the voyage. The ship energy system model takes into account the various environmental variables as well as ship’s operational conditions to compute the ship performance in both open and ice infested waters. For Arctic operations, specific ice resistance models are implemented in the VPT, and a user has the options of either relying on icebreaker assistance or going for unassisted navigation in part of the entire Arctic passage. Case study voyages of different ship types, route options, staring time, home/destination ports are simulated to demonstrate how various optimal routes are planned and how the transit time and fuel consumption vary. This information is considered being crucial for ship owners for planning their voyages in advance. The continuously updated voyage information from the VPT is particularly helpful for the ship crew if there are specific ship operations and risk mitigation actions that need to be taken care of during the voyage. In addition, this study underlines that a safe and fuel-efficient Arctic passage requires viable voyage planning tools that combine reliable ship performance with weather and ice forecasts.

With the effects of global warming, the Arctic is presenting a new environment where numerous ice floes are floating on the open sea surface. Whilst this has unprecedentedly improved Arctic shipping navigability and brought about significant opportunities, the interaction of such floes with ships has yet to be understood, thus hindering appropriate assessment of corresponding ship performance. This paper presents work on developing empirical equations to estimate the effects of such floes on ship resistance. Based on extensive data from validated computational simulations, the ice-floe resistance has been shown to correlate with ship beam, ship speed, ice concentration, ice thickness and floe diameter, and the regression powers of each the parameter on resistance are ascertained for a container ship. This leads to an empirical equation that can immediately predict ice-floe resistance in a given condition. The proposed approach has the potential to facilitate propulsion power estimates for Arctic shipping, as well as providing valuable insights into ship design for these environmental conditions.

Composite sandwich ships have laminated joints that contribute to a significant part of the ship’s weight. Their construction requires an extensive number of man-hours. There is great potential for weight and production-time-reduction through alternative joint designs. According to class rules, one is not allowed to benefit from the load-carrying capability of the core, i.e. the strength characteristics of the core shall be disregarded and geometry at the joint location is disregarded as well. The objective of the current investigation was to investigate the possibility of constructing a joint where the load-carrying capability of the foam core is accounted for, leading to a reduction in weight and production time. One specific joint in a 23 m composite sandwich catamaran was selected for study — a side wall-wet deck T-joint. This joint is considered to be crucial for the structural integrity of the current vessel. A global finite element (FE) model of the catamaran was designed and analysed in ANSYS. The loads and boundary conditions were applied to the global model according to DNV GL’s HSLC rules. Two local FE models of the joints (2D and 3D) were utilized for a parametric analysis with respect to structure response (stress concentrations and compliance with failure and fracture criteria). Finally, the results and conclusions from the study show the possibilities and advantages of incorporating the foam core material as a load-carrying member in joint design without compromising safety.

The paper presents a decision-support tool for maritime operations in Arctic seas. This tool targets at improving the safety and fuel efficiency of existing and future cargo vessels that are designed to operate in Arctic and in open water conditions. It is achieved by smart voyage planning using meteorological, oceanographic and ice forecasting. A single-objective optimization for minimizing the fuel consumption in various scenarios of Arctic transits is established, with the transit time and the safety as the two major constraints. The tool is implemented in an in-house Matlab code, which is based on Dijkstra’s algorithm, a grid-based approach that aims at finding the most cost-efficient path connecting any chosen nodes in a given grid. Results from case studies along the Northern Sea Route indicate that the tool generates appropriate routes in ice-infested Arctic waters. The fuel consumption accounting for ice-induced extra resistance is optimized and the risk of collision with icebergs has been considered.

The study presents analyses of key parameters that affect the performance of the point absorbing wave energy converter (WEC). Performance is assessed by running hydrodynamic and structural response simulations and calculating the power absorption of the WEC and fatigue damage in the mooring lines from the output data. The baseline model of the WEC input to the simulation is modelled after the WaveEL 3.0 device, designed by Waves4Power and installed in Runde, Norway. Simulations are run for single buoy and small array configurations, varying environmental conditions, mooring system, and WEC buoy shaft length. Environmental conditions are chosen to reflect locations studied as potential future installation sites. Select configurations are further analyzed through an analysis of LCOE and LCA. The results show that optimal mooring line geometry depends on water depth, and that optimal shaft length depends on the average sea conditions at the location. The array simulations show that small WEC separating distances will limit the mooring line length, which will result in lower power absorption and lower fatigue lives in the mooring lines. The LCOE shows that the four-buoy array configuration is the most profitable, and both the LCOE and LCA show that the main process contribution to climate change and the total product cost is the manufacturing of the WEC buoy itself. The research in this study demonstrates the importance of using simulations to make effective WEC design choices for a given environment.

Most of the ocean energy technologies are considered to be in a pre-commercial phase and need technical development. This study focuses on design of mooring solutions and compares array systems of a specific floating point-absorbing wave energy converter (WEC) developed by the company Waves4Power. A full-scale prototype of the WEC is installed in Runde (Norway) where it is moored with three polyester mooring lines, each having one floater and one gravity anchor. Based on this reference installation, the method of systems engineering was used to propose twenty-two conceptual mooring solutions for different array systems. They were compared and reduced to four top concepts in a systematic elimination procedure using Pugh and Kesselring matrices. The top concepts were assessed in detail by means of LCOE (levelised cost of energy), LCA (life cycle analysis) and risk analyses. The fatigue life of the mooring lines and the energy capture were calculated using results obtained from coupled hydrodynamic and structure response analyses in the DNV-GL DeepC software. Two final concepts were proposed for the water depths 75 and 200 m.

Shock load caused by underwater explosion in naval battles can lead to malfunction of the equipment on-board naval vessels. It makes the ships vulnerable and they can lose the ability to accomplish their missions. This study presents a shock analysis, using the dynamic design analysis method (DDAM), of a naval ship stern ramp subjected to a non-contact underwater explosion. The objective is to evaluate the performance of the ramp subjected to a shock load, identify areas for structural improvements and recommend design changes. The DDAM in the commercial software ANSYS is used in the evaluation of the ramp. The structural response to the shock load is estimated by combined modal and response spectrum analyses. The shock load is applied in three directions (vertical, fore and aft, athwart ships) and the results show that the vertical direction is the most severe loading direction and critical to the functionality of the ramp. A parametric study is presented which shows which parameters that influence the most the structural response. The results from this study are used to suggest improvements of the ramp structure to make it more resistant to shock loads.

This study presents the determination of structural response due to sloshing impact loads in LNG carriers with membrane type cargo tanks. These loads are characterized by very short durations and are thus likely to inflict a dynamic amplification in the response of the hull. Finite element analyses are presented using a model representing parts of an LNG membrane tank. The objective was to find and quantify the dynamic amplification factor (DAF) for the structural response towards sloshing impact pressures. The influence of variations in the load characteristics such as load duration, extent of the loaded area, load location as well as the influence of the insulation system was evaluated. The study shows that the response in the studied region of the hull structure experiences significant levels of dynamic amplification during impact loads with specific durations. The response sensitivity analysis also shows that the insulation system (MARK III type) has a large effect on the dynamic behaviour of the hull structure. It has been found to alter the magnitude of the stress and deflection response for key structural members. It also changes the load time durations for which the maximum dynamic amplification occurs and increases the magnitude of the corresponding response DAF. Finally, it has been found that dynamic response gives DAF values of up to 2. The effects have been found to be present for temporal load characteristics commonly occurring in sloshing model tests and full-scale measurements and are therefore likely to occur for a vessel in operation.

The connection between column and deck-box on a semi-submersible platform is often subjected to high stress concentrations that can be governing for the structural strength. One common design used to withstand the high stresses is a cast integral in high tensile material, which is both heavy and expensive to manufacture, which is why an alternative cut-out design is investigated. This study presents an analysis of a node connection with regard to yield stresses, buckling, fatigue damage, weight and cost in order to propose an alternative cut-out design using the same criteria. The cast integral, which is analysed as a reference case and used for comparison of designs, is of a typical design used today. A parametric study shows that the use of a cut-out design may be advantageous in the centre bulkhead connection between the column and the deck-box. The adjacent geometry is of simple character and the cut-out does not affect the overall structural design. The cut-out is found to be a feasible alternative to the cast integral, with yield stresses and fatigue damage in the same range. Further refinements of the cut-out design could, however, decrease both yield stresses and fatigue damage. A suggested cut-out solution leads to a decrease of 4.5% in weight for a reference structure. For the same reference structure the production cost is estimated to decrease by 9%, hence, the cut-out design is recommended for the centre bulkhead connection.

The development of Sandwich PULS, a semi-analytical calculation tool for predicting the ultimate limit state (ULS) of FRP composite sandwich plates is presented. This was done by extending DNV GL’s semi-analytical calculation tool Composite PULS, which is used for quick estimation of the ULS for unstiffened composite plates. ULS was evaluated in terms of the first buckling load and the first ply failure (FPF). The Sandwich PULS code was developed by implementing formulations for sandwich plate theory. First-order shear deformation theory (FSDT) was implemented to include the transverse shear deformations that are highly important for sandwich plates with poor shear stiffness of the core. The Sandwich PULS code was evaluated against nonlinear finite element analyses (FEA). It was concluded that Sandwich PULS shows good agreement with FEA-predicted critical buckling loads. For all inspected plates, Sandwich PULS shows improved results compared to Composite PULS. Differences between Sandwich PULS and FEA are caused by the difference in evaluating shear stiffness. It has been shown that neglecting shear stiffness of faces results in good agreement between Sandwich PULS and FEA, while use of conventional shear correction factors proved to be unfavourable for sandwich plates. It was found that Sandwich PULS is limited in terms of slenderness. Sandwich plates with soft core should not have slenderness below 20 to assure an accurate solution.

Increased fuel prices and public awareness of environment impacts from shipping have attracted large efforts in maritime sector to increase its energy efficiency as a factor of competitiveness. Weather routing has become a recognized measure, which can partly help to achieve the targets as well as enhancing safety. A routing system requires a reliable optimization algorithm to consider a ship’s operational costs, expected time of arrival, and cargo safety etc. simultaneously. Hence, the service provided by a weather routing system is highly dependent on a properly selected optimization algorithm and associated input parameters. In this paper the concept of weather routing is broken down into many elements for further analysis. Focus is given to algorithms, constraints and weather forecasts used in the optimized routing plan. Two different aspects of state-of-the-art have been considered. The first is a study of software already in use and the second is a study of methods investigated in the research community. Furthermore, this paper also provides examples of development trends, for example the fatigue based routing, and the risk based routing, as well as its integration with onboard monitoring systems for more reliable weather and ship specific response information.

The renewable energy resource of offshore wind is believed to have a great potential in playing an essential role on the future energy market in Europe, but there are complications such as harsh weather and low accessibility. To manage this, most offshore wind turbines of today are installed and maintained using self-elevating units (SEUs). In this study, a method is presented that enables the analysis of weather window assessments for the installation and retrieval phases of a SEU. The method of analysis takes site-specific parameters, defined as soil type and water depth, into account in addition to vessel-specific and environmental parameters. The inclusion of site-specific parameters is the novel contribution compared to assessment methodologies used today. A simulation model is presented that incorporates a coupled non-linear time-domain analysis of vessel motion and soil-structure interaction. Soil deformation behaviour during impact is described by resistance curves based on a bearing capacity theory. A structural evaluation criterion against which impact forces are compared is used for weather window assessments. The simulation model is applied on a case study utilizing different soil types to study impact forces and the capacity of the structure for withstanding such impacts and eventually performing a weather window assessment. The results show that the jacking operation can be divided into two phases when it comes to loads on the spudcan: a phase dominated by vertical forces followed by a phase dominated by horizontal forces. It is found that including soil deformation behaviour is of paramount importance to the magnitude of the resulting impact forces and that class-recommended practice does indeed produce rather large force estimates. Thus, assessments where site-specific parameters are incorporated could definitely increase the operable weather window for SEUs, and, consequently, increase the economic competitiveness of, for example, the offshore wind industry.

Design against impact loads (slamming) can be challenging and time consuming and can involve complex calculations. Application of simplified, quasi-static calculation approaches will make the design process much easier. In this paper, such simplified methods are discussed using free fall lifeboats as a case. Results from non-linear FE-analysis show that the response is non-linear due to large deformations. The impact pressure is then mainly carried by membrane stress and the dynamic response is small. A non-linear beam theory approach for hand calculation is established. As the non-linear calculation model is the most realistic, it is recommended that this is used in an initial design assessment. Although the results are on the conservative side, simple hand calculations including non-linear geometry can be used to predict the maximum strain. Linear methods are also investigated. However, these methods should be used with more rigid structures such as stiffened steel and aluminium panels.

Ice-induced global forces that affect a ship’s hull when colliding with heavy ice features are analysed. The objective was to increase the knowledge of what structural loads a ship encounters during Arctic operations and thereby contribute to safer shipping in the Arctic. In the study, a model was created that used recorded motions of a ship when it collided with a heavy ice feature in order to calculate the global forces that affect the ship hull. The motion data were collected by Det Norske Veritas during the Coldtech research project on board of the Norwegian Coast Guard vessel KV Svalbard. To give an understanding and background to the problems that the model needs to handle, the paper includes a brief review of ice-ship interaction and hull monitoring. The model developed is limited to perpendicular collisions and the first impact sequence, since only then the impact location can be considered as known. The forces resulting from the model are compared with the design loads of ice class rules, since the same impact type is considered. The results are also compared with previous work done in the area. From the comparisons it can be seen that the forces calculated with the current model seem to be reasonable as they are in the same order of magnitude. However, more measurements are required in order to fully verify the model and the measured motions.

In stress-based fatigue design and analysis of marine structures, a stress concentration factor (SCF) is used to compute the local stress in structural details when the hot-spot approach is used. For a typical steel material, the fatigue damage is computed as proportional to the power 3–5 of the stress values, defined by the chosen S-N curve. This means that a small change in the SCF value can lead to a large difference in the fatigue damage result and corresponding fatigue life prediction. Thus, the methodology used to compute the SCF should be clearly defined in classification society guidelines. This study presents a review of different direct calculation procedures for how to obtain the SCF based on fatigue assessment guidelines. The effect of different element types and local stress extrapolation methods to the fatigue damage estimation is studied for both longitudinal load and bending load conditions in a container ship. A simple structural detail with cracks observed after only a few years in service is used for the case study. For this structural detail, two alternative methods to compute the local stress for fatigue assessments are compared. The difference in fatigue life prediction using the proposed approaches is compared; with at least 50% difference expected even within the guidelines from the same classification society. It is further discussed how to reduce the SCF with the objective to increase the fatigue life.

This paper presents a comparison made of different fatigue calculation methods used in the maritime industry today, with the aim of having a higher control of a fatigue failure site. To provide an overview of the different fatigue calculation methods, a comparison study was performed, as well as a local weld parameter study for two typical fillet welded joints. The two methods used for this study were the structural hot spot and effective notch stress method. Two fillet welded joints were provided by Aker Solutions MMO AS, Bergen, Norway. The first joint is a rectangular hollow section from a davit, built as a truss. The second model is a part of a K-joint from a semi-submersible (Aker H3 design). Both joints were analysed using fine 3D finite element models. The two different fatigue life calculation methods yielded different fatigue lives for the weld toe, with inconclusive results regarding their conservatism which is discussed in the paper. An increased weld toe radius gave a higher fatigue life for the weld toe, while the larger weld size increased the fatigue life in the weld root. Any weld size effect regarding fatigue life in the weld toe could not be established. Based on the effective notch stress method calculations, there was an indication of weld root failure for the K-joint of the drilling unit. Fatigue life improvement methods only increasing weld toe fatigue life are not recommended based on these results.

Numerous methodologies for estimating the reliability of composites have been published in the past few decades. This paper presents the experiences and findings by the authors regarding an assessment of different mechanical and probabilistic models for the calculation of reliability estimates of fibre-reinforced plastic laminates. The assessment was performed to determine the manner by which the models influence the reliability estimations. This knowledge is used to determine the most suitable combination of models for reliability-based design optimization of marine structures made out of fibre-reinforced plastics. The assessment consists of a brief overview of a number of probabilistic and mechanical models as well as the computation of reliability estimates for a number of fibre-reinforced laminates through Monte Carlo simulations. Among some of the findings, it was found that the definition of matrix cracking and the choice of mechanical model (description of damage initiation and development) influence significantly the reliability estimations of fibre-reinforced plastic laminates.