A split hopper barge is a dredging vessel that can split over its longitudinal axis to discharge its cargo. To allow for such an operation, the barge consists of two half-hulls that are connected by hinges at the top and hydraulic cylinders at the bottom. Any forces that act at the interface between the half-hulls have to be transferred by the hinges and cylinders as a result. The aim of this thesis is to develop a method to determine the workability limits of split hopper barges in irregular seas. For this workability of the barge, the design limits of the hinges and hydraulic cylinders are assumed to be governing. A quasi-static model is formulated to determine the effects of roll, different types of cargo, opening the barge and discharging the cargo on the forces in the hinges and cylinders. The results of the quasi-static model are a set of governing load cases for the split hopper barge. From the quasi-static model, it is found that the forces of interest are the largest for a closed split hopper barge and that either a solid or a liquid cargo will yield the governing load case. To account for the dynamics in irregular sea conditions, a calculation method is proposed based on Ansys AQWA. Since AQWA is not able to account for liquid cargo motions, its effects are incorporated separately. Using WAMIT simulations, the influences of the liquid cargo to the added mass and stiffness of the barge are determined. Based on the WAMIT results the AQWA model is adjusted. Superimposing the results from the quasi-static and dynamic models, the maximum forces in the hinges and hydraulic cylinders are obtained for the governing load cases. By comparing the obtained maximum forces to the design forces, a conclusion on the workability limits of the split hopper barge is drawn.
For the barge carrying a solid cargo only one resonance frequency is found, while, due to the liquid cargo motions, the barge with a liquid cargo has two resonance frequencies. As a result, a larger number of combinations of wave directions and periods yield considerable forces. For a 3-hour-extreme with a significant wave height of 3 meters, the governing hydraulic cylinder forces are found for a barge carrying a liquid cargo. The maximum resulting hinge forces however, are found for a barge carrying a solid cargo. Because the limits of the hinges are exceeded before the limits of the hydraulic cylinders, it is concluded that the workability limits of the split hopper barge in irregular waves are most limited, and therefore governing, for a barge carrying a solid cargo.

A new development aiming to improve the safety and/or operability of offshore operations is deterministic motion forecasting. Various parties target at developing a radar which is able to detect wave trains. This deterministic wave forecast can be used to forecast vessel motions up to several minutes ahead. With such a forecast a quiescent period can be searched for, where ship motions are at a minimum. Possible advantages considered for a heavy lift operation are: Safer operations, less waiting on weather and extended lifetime of equipment. With the use of the Heerema Simulation Center (HSC), the possibilities to extend a deterministic wave forecast into a motion forecast is investigated. Thewave components are known in the HSC, so a perfect wave radar is available and the focus is entirely on (1) predicting motions and (2) presenting it in a useful way. The first part of the objective is approached by investigating the possibilities and limitations of making a motion forecast in the frequency domain. This method is convenient since the calculation is easy to understand and very fast, a quality which is most wanted when making a future prediction. To quantify the quality of a wave- andmotion forecast, the correlation coefficient (½) and RMS ratio (¾) are used (forecastedvs logged motion). The model showed good results for heave roll and pitch (½ 0.85 - 1.0, ¾ 0.86 - 1.15) for mild, severe and complex sea-states (all wave directions, respectively). For extreme swell a forecast could not be made. This can be explained by the fact that when motions become larger, a frequency domain approach is no longer valid. However, it should be noted that it is very unlikely a lift operation will take place with Hs > 2m. The sensitivity of themodel to variations in the center of gravity and radii of gyration of the vessel (model input), is found to be within acceptable bounds. The impact is negligible on the phase and small (<10%) on the amplitude of the forecast. With data offshore available with an accuracy of +- 2m, this is acceptable. Two test cases are investigated. A single crane lift (1000 mT module) and a dual crane (7000 mT module). In both cases the model proved to be well capable of forecasting themotion of interest (Heave) of the module (relative to a fixed and floating platform). The second part of the objective has a more qualitative character, where the use of a forecast is tested in the HSC by using a tool that is created for this purpose: the VirtualWave Radar Tool (VWRT). This tool is able to make and display a forecast in the HSC. The tests executed in the HSC showed positive results for the use of a forecast in the crane cabin during a lift operation. A reduction of secondary impact loads in a challenging environment was realized due to the use of the VWRT. Furthermore, a forecasted time span of two minutes (current performance of wave radars on the marked) proved to be long enough to benefit from during a lift operation. The tool demonstrated that simplicity of the dashboard is key and should be understandable at a glance. With many possible sources causing a forecast to deviate from the actual motion, a self learning, optimization model could reduce the need for exact model input offshore (not always available), even without knowing the source of deviation. v

Large-scale changes in ocean conditions caused by installing and operating Ocean Thermal Energy Conversion (OTEC) have not been studied in depth. Conversely, the effect on an OTEC plant by oceanographic features are not researched in depth either. The aim of this research is to describe the natural patterns and variability of the ocean currents around Curaçao, an island in the Caribbean Sea and a potential OTEC deployment location. This research is carried out in order to assess possible implications for the OTEC industry. Ten years of data from the Mercator Ocean Model with a spatial resolution of 1/12˚ and temporal resolution of one day was analyzed. The model is forced by wind data from ECMWF. A strong current jet is found to dominate the flow from east to west in the Caribbean Sea. The jet is identified as the Caribbean Current and it is forced by currents in the north equatorial Atlantic Ocean and large-scale wind patterns. The Caribbean Low Level Jet, an intensification of the Trade Winds over the Caribbean Sea, is strongest in winter and weakest in fall. Consequently, the current jet is found to have a peak from December to March and a trough in October and November. The largest surface velocities of the order of 1 m/s are found along the coast of Venezuela, where wind-driven upwelling enhances surface flow to the west. Along the Venezuelan coast, subsurface currents to the east, in the opposite direction to the surface currents, are also found. The period from April to September is characterized by the meandering of the jet and the formation of large (diameter > 200 km) anticyclonic eddies that cause large local surface velocities. These eddies contribute to the great variability observed in the Caribbean Sea. The origin of these eddies has not been clearly identified. Due to upwelling, no OTEC system should be deployed more than 50 km south of Curaçao to avoid cold surface water decreasing the system's performance. Hydrodynamic forces due to the calculated expected maximum velocity of 1.8 m/s, induce stresses in the cold-water pipe that do not exceed the yield stress.