An issue that ROVs experience during operations is disturbances from the tether, making navigation and control more difficult as real-time measurements are not currently available. This paper proposes the development of an innovative sensor that can measure tether forces in multiple degrees of freedom. These tether forces apply an external disturbance during operation, which is difficult to model and predict. The sensor provides real-time input on the effect the tether has on the ROV, which can be utilized in feed-forward in the control system in combination with a feedback loop. There are 2 proposed designs: a 4 DOF sensor design using a plastic bottle and a 6 DOF version utilizing an aluminum cross with hollowed sections. Both designs use strain gauges to measure and determine the direction and magnitude of the force from the tether.
The sensors are implemented to a modified BlueROV2 using ROS. Station-keeping tests in a harbor and test basin are done for the 4 DOF version to evaluate performance. The sensor shows potential, improving response in heave but worsening it in yaw. It removes and adds oscillations both in frequency and amplitude depending on the orientation of the waves relative to the sensor. Indicating alternative control strategies might be more suitable. The 6 DOF version is not tested on the BlueROV2. In future work, additional development is required to ensure the viability of the tether force sensor as a commercial product.
The European maritime transport policy recognizes the importance of the waterborne transport systems as key elements for sustainable growth in Europe. A major goal is to transfer more than 50% of road transport to rail or waterways within 2050. To meet this challenge waterway transport needs to get more attractive and overcome its disadvantages. Therefore, it is necessary to develop new knowledge and technology and find a completely new approach to short sea and inland waterways shipping. A key element in this is automation of ships, ports and administrative tasks aligned to requirements of different European regions. One main goal in the AEGIS project is to increase the efficiency of the waterways transport with the use of higher degrees of automation corresponding with new and smaller ship types to reduce costs and secure higher frequency by feeders and provide multimodal green logistics solutions combining short sea shipping with rail and road transport.
With increasing demand for renewable energy resources, the development of alternative concepts is still ongoing. The wave energy sector is still in vast development on the way to contribute to the energy production world wide. The present study presents the development of the Exowave wave energy converter made so far. A numerical model has been established supported by wave flume tests performed at Aalborg University during the first phase of the development. Furthermore, a successful open sea demonstration has been performed on 7 meters of water at Blue Accelerator, Belgium, from which the concept has been proven. As part of the ongoing research, verification of the numerical model will be made through experimental testing in the wave tank of Aalborg University, and an open sea demonstration at 14 meters of water depth will be executed off the coast of Hanstholm, Denmark.
Coupled mooring analysis using CFD with dynamic mooring models is becoming an established field. This is an important step for better predictions of responses of moored marine structures in extreme sea states and also for capturing the low-frequency response correctly. The coupling between the CFD and mooring solvers are most often carried out by exchanging the fairlead/anchor points and fairlead forces. In this paper we will discuss the effects of using (i) viscous fluid flow on a mooring component level (submerged buoys and clump weights) and (ii) the fluid-structure coupling between the viscous fluid solver and the mooring system.
Ship engines are subject to a very demanding work environment, where maximum availability is a must. In this project we look at different operational variables of a marine engine from large cargo ships, with the aim of detecting and trending damage onset on different engine sub-components. This information can be used by owners to expedite O&M interventions and maximize ship availability.
The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measurement and analysis of the generated directional wave field. Most of the existing methods assume a double summation sea state to be present which is valid in the prototype. However, waves in the laboratory are usually generated by single summation. The current paper presents a method to analyze short-crested waves generated by the single summation method. Compared to similar methods oblique reflections are considered instead of only in-line reflections. The results show that the method successfully decomposes the incident and reflected wave fields in the time domain. Thus, for example the incident wave height distribution may be obtained. The sensitivity of the new method to additional reflective directions, noise, calibration errors and positional errors of the wave gauges was found small.
Under complex sea conditions, the energy demand for each device of renewable-energy ships presents a random situation, which makes the complex energy demand of the ship integrated energy system (SIES) uncertain during ship navigation. To ensure the economical, stable, and efficient operation of the SIES, this paper proposes a distributed stochastic energy management method to solve the energy management problem (EMP). Firstly, a framework for the SIES including both renewable energy and traditional energy is constructed. Based on the energy efficiency operation index (EEOI) and the operation mode of energy supply devices during navigation, the EMP of the SIES is raised. Then, considering the distributed structure and limited computing resources of the SIES, a distributed stochastic energy management method is proposed. Through this method, the disturbances of load demand can be effectively suppressed, and a stable energy supply is provided for devices such as power propellers. Furthermore, it is analyzed that the proposed method can converge to the O(η) (η is the fixed step size of the proposed method) neighborhood of the optimal energy management decision in the mean-square-error sense. Finally, the simulation results verify that the mean-square-error-optimal energy management decision of the SIES can be obtained by the proposed method in different scenarios, and the proposed method can solve the EMP of SIES under complex sea conditions.
Infrastructure-led development is driving geopolitical agendas in the Global South, and Djibouti is a case in point. Strategically situated in the Horn of Africa, Djibouti's seaports and related infrastructure have been modernized through foreign investments to serve international trade and growing African hinterlands. Scholarship often posits foreign logistics investors as hegemons driven by geopolitical interests, and host states as passive recipients. This paper questions such claims. It examines the relationship between "hegemon" and "host state" from the perspective of the latter, in this case the Djibouti government's interactions with Emirati and Chinese infrastructure companies. Methodologically, the analysis is based on interviews, secondary data and document analysis. It applies a conflict-sensitive controversies approach from critical logistics studies to trace contestation over authority in Djibouti's logistics sector. It shows how Djibouti's government applies various strategies (discursive, legal and political) to exercise agency in its logistics sector. The paper concludes that the geopolitics of infrastructure-led development is a reciprocal effort that goes beyond conventional logics of hegemons imposing on host states.
Aims and objectives: Seagoing employees must undergo medical examinations every second year. Even though International Organisations issued guidelines for these pre-employment medical examinations there is a lack of an internationally accepted continuous training programme for the maritime doctors who perform these examinations. The aim of this survey was to examine the Danish maritime doctors perceived training needs as part of a planned comprehensive maritime occupational health prevention programme.
Methods: A questionnaire based on international standards was distributed to all the maritime doctors (110) electronically in May 2017. The completed questionnaires were 46.4%. STATA was used for the statistical analysis of the data and correlations among the self-rated needs as dependent variables and the doctors characteristics were performed with Fisher exact test, with significance level at α=0.05%.
Results: The maritime doctors considered very important to receive training in “Fitness evaluation and medical examinations guidelines” (76.47%) followed by “Rules and regulations within maritime medicine” (68.63%) and “Working conditions and health risks on board” (62.75%). The number of examinations influenced their preference with those with more than 20 patients to express a more pressing need for training. Age, gender and years of practice did not have any influence in their self-rated needs. Furthermore, they pointed out flexible ways of training including distance learning and
the establishment of a webpage by the respective Authorities as one stop-shop.
Conclusion: Maritime doctors are in favour of continuous education and training. The survey may help the respective Authorities to organise such short courses on targeted topics in the country.
This paper examines if eco-rating schemes improve environmental outcomes in the context of the
international shipping industry. Shipping faces global environmental challenges and has recently
witnessed the introduction of several eco-rating schemes aiming to improve the environmental
performance of ships. Extending the private environmental governance literature into a mature
service industry with global operations, the paper shows that concerns about eco-rating schemes’
effectiveness also have relevance here. Shipping eco-rating schemes fall short of best practices for
design and governance, and this hampers improvement efforts. The study has policy implications for
the achievement of improved environmental outcomes in the shipping industry.