5 research outputs found
Development of a numerical model for Cutter Suction Dredgers: A time domain analysis of a CSD in operation
No full textA Cutter Suction Dredger (CSD) is a vessel that is used to cut hard soils with precision. It is moored stiffly through a spud pile while the soil is being cut. This, in combination with wave loads, causes the whole system to be dynamically challenging and nonlinear. Previous attempts to model a CSD in operation have been limited to the frequency domain. However, in order to be able to include these nonlinear effects occurring during the operation of a CSD, a time domain analysis is necessary. The hydrodynamic forces in the time domain analysis will be calculated using Ansys AQWA. The external forces which occur during operation will be calculated by a custom script written in Python. The script consists out of 3 modules; a spud module, a winch module and a soil module. The spud module is responsible for calculating the mooring forces on the spud pile in order to maintain its position. The spud has been modeled as a beam with 3 pinned supports. This linear model has been expanded to include the option to take the presence of a flexible spud carriage into account. This means that if the buffer of the flexible carriage is activated, the stiffness of the system changes accordingly in order to reduce the loading on the spud with increasing displacements. The winch module is responsible for determining the force required to achieve the swing around the spud at the desired velocity. Within the module, the application of a PID controller ensures that the tension in the side wires is adjusted dynamically in order to maintain a stable swing velocity throughout the whole process. Tuning the controller correctly is critical to avoid unnecessary tension peaks while at the same having a sufficiently quick response to sudden changes. The soil module is responsible for calculating the reaction forces on the CSD as a consequence of the cutting of the soil. The soil is characterized by the specific energy characteristic, which enables the module to be applied to all types of soil, from soft clay to hard rock. The 3D force vector on the cutterhead is then calculated using the volume cut and the rotational torque of the cutterhead. Furthermore, the module keeps track of where the soil has been cut, adjusting the new height as the cutterhead passes. This enables to realistically create a time series where the volume cut during each timestep will vary due to the oscillations of the cutter. The final result is a model in 7 degrees of freedom which can dynamically respond to the nonlinear reactions caused by cutting soil, wave loads, mooring through a flexible carriage and varying side wire forces. This model is now ready to be used to investigate the effects of different combinations of soil types and wave conditions
Hydrodynamic loads on an inclined monopile in the splash zone
No full textOffshore and Dredging Engineerin
VARIATION IN AGGRESSIVENESS AND AFLP AMONG Alternaria solani ISOLATES FROM INDONESIA
Get PDF<p><em>Alternaria solani </em>is a necrotroph fungus that causes three-phased diseases in tomato. Management of the pathogen by using resistant cultivars requires knowledge on the aggressiveness and genetic diversity of the fungus. The aims of this study were to isolate <em>A. solani </em>from major tomato and potato producing areas in Indonesia and to study their aggressiveness and genetic variability. Twenty two<strong> </strong><em>A. solani</em><strong> </strong>isolates were recovered from early blighted tomato and potato in Central and West Java.<strong> </strong><em>A. alternata</em><strong> </strong>was also isolated from tomato leaves in West Java and North Sumatra, indicating that early blight in Indonesia may be caused by more than one <em>Alternaria </em>species. Resistance tests of four tomato genotypes to selected<strong> </strong><em>A. solani</em><strong> </strong>isolates revealed that local isolates were more aggressive in inciting early blight and stem lesion than an imported isolate from USA. This implies that introduced breeding materials must be tested to local isolates to obtain effective resistance genes. Cluster analysis based on amplified fragment length polymorphism (AFLP) obtained from <em>Eco</em>RI+AG and<strong> </strong><em>Mse</em>I+C primer amplification separated 28 local and Taiwan isolates from the US isolate, which was coincided with aggressiveness separation between the local isolates and the US isolate. Three clusters of AFLP genotypes which did not associate with geographic origin were observed among tropical isolates. The low genetic diversity among the Indonesian isolates suggests clonal population structure with wide distribution. Successful local tomato breeding requires the availability of local<strong> </strong><em>A. solani </em>collection with well-characterized aggressiveness level and molecular diversity to obtain effective resistance genes.</p></jats:p
Offshore Wind Turbine Monopile Foundation Installation with a Dynamic Positioned Vessel: A feasibility study by modeling
No full textAfter years of using fossil fuel, the transition to renewable energy sources need to be made to limit the increase in temperature and to support the future energy demand. To support and speed up the transition phase from fossil fuels to renewables it is necessary to decrease the costs. Offshore Wind Turbines are widely used for the production of renewable energy and several Offshore Wind Turbine projects are planned for the future. Most of the Offshore Wind Turbines are founded by monopile, large steel tube, to support the wind turbine. Nowadays, these monopile be installed by either jack-up vessel or moored floating vessel. However, these installation method come with a major drawback: the installation procedure is time consuming. A new installation method is propose to reduce the installation time. This thesis focus of the feasibility to install the monopile with a dynamically positioned (DP) vessel. Therequired station keeping situation is faster achieved with a DP vessel. Due to the footprint of the DP vessel relative to an earth fixed position, a vessel motion compensated pile gripper is used to maintain the upright position of the monopile and to decrease the interaction forces between vessel and monopile. Adding the monopile to the vessel is an off-design condition for the DP controller. During the early hammering phase of the monopile, the monopile have limited interaction with the soil and is unstable. The upright position is maintain by the gripper frame. The forces from the gripper frame on the monopile are reaction forces on the vessel. Beside these forces, environmental forces are acting on the monopile and via the gripper frame acting on the vessel. The forces on the vessel could lead to unstable behavior and/or increased vessel footprint. A simulation model is build to investigate the behavior of the DP vessel during the operation. A industry used DP simulator and a simulation model of the Bokalift1 is used. A model of a typical shallow water and deep water monopile is build. A hydraulic based gripper frame is simulated with an inclination controller and a induced vessel motion controller which needto maintain the upright position of the monopile. The inclination controller is tuned with a higher bandwidth compare to the bandwidth of the DP controller to prevent motions of the monopile is the same frequency range as the linear motions of the vessel. The forces from the gripper frame are fed into the Kalman filter of the DP controller. This is done to prevent a drift of the vessel when the gripper frame starts acting on the vessel. In all simulation cases with governing environmental conditions, the vessel could maintain stable behavior. The rotations of the monopile are in the same frequency as the first order wave forces on the vessel. This relative high frequency motions to not significantly amplify the position of the DP vessel. However, despite the fact of feeding the Kalman filter, a larger drift is observed in case of the large, deep water monopile in the operation stage when the gripper frame force is introduced to the vessel. This increase the requirement on the envelope of the gripper frame. The requirement on the gripper frame is given in terms of power, force and envelope based on governing environmental conditions. The requirements on the gripper frame are assumed to be within an acceptable magnitude. The operation seams to be promising in the future.Marine Technology | Ship Design, Production and Operation
VARIATION IN AGGRESSIVENESS AND AFLP AMONG Alternaria solani ISOLATES FROM INDONESIA
Get PDFAlternaria solani is a necrotroph fungus that causes three-phased diseases in tomato. Management of the pathogen by using resistant cultivars requires knowledge on the aggressiveness and genetic diversity of the fungus. The aims of this study were to isolate A. solani from major tomato and potato producing areas in Indonesia and to study their aggressiveness and genetic variability. Twenty two A. solani isolates were recovered from early blighted tomato and potato in Central and West Java. A. alternata was also isolated from tomato leaves in West Java and North Sumatra, indicating that early blight in Indonesia may be caused by more than one Alternaria species. Resistance tests of four tomato genotypes to selected A. solani isolates revealed that local isolates were more aggressive in inciting early blight and stem lesion than an imported isolate from USA. This implies that introduced breeding materials must be tested to local isolates to obtain effective resistance genes. Cluster analysis based on amplified fragment length polymorphism (AFLP) obtained from EcoRI+AG and MseI+C primer amplification separated 28 local and Taiwan isolates from the US isolate, which was coincided with aggressiveness separation between the local isolates and the US isolate. Three clusters of AFLP genotypes which did not associate with geographic origin were observed among tropical isolates. The low genetic diversity among the Indonesian isolates suggests clonal population structure with wide distribution. Successful local tomato breeding requires the availability of local A. solani collection with well-characterized aggressiveness level and molecular diversity to obtain effective resistance genes
