676 research outputs found
Austin Papers: Series IV, 1828-1829
No full textCopy of transcript for a letter from B. M. Cutter to Stephen F. Austin, in which Cutter inquires about the physical and legal status of a half league of land that he purchased from William S. Brown
Development of a cutter ladder vibration model
No full textStructural vibrations are a known cause of damage to offshore structures and equipment. A Cutter Suction Dredger (CSD) is a dredge vessel known to vibrate heavily during operation. Primary cause of these vibrations is the cutting process, performed to cut and excavate soil from the seabed. A component prone to damage is the cutter ladder, a component of the CSD used to position the cutter head at the seabed. Cutter ladders are known to suffer from failures including large cracks in the structural members, of which the cause is sometimes unclear. Current methods for developing a cutter ladder involve detailed quasi-static finite element modeling for strength analysis and sometimes modal analysis to identify natural frequencies and mode shapes. Structural vibrations due to dynamic loading are usually not taken into account. In 2015 Boskalis performed extensive vibration measurements on its Taurus II CSD, hereby setting the stage for research into the dynamics of cutter ladders. By taking a closer look at dynamics of the cutter ladder, a cause for structural damage might be identified. This thesis therefore aims to investigate the vibrations of a cutter ladder as a possible cause for damage. In order to obtain knowledge about the dynamic behavior of the cutter ladder in operation, data obtained during the vibration measurements were investigated using operational modal analysis. This investigation gave further insight in how to approach the development and validation of a vibration model. A vibration model using finite beam elements was developed to take a closer look at the characteristics of the cutter ladder structure. This vibration model was obtained through simplification of a detailed plate-element model, which was developed in an earlier project. The dynamic characteristics of the obtained vibration model where validated to the detailed plate element model by comparison of modal analysis results. It was chosen to update the vibration model using the measurements obtained on the cutter ladder, as it was hereby possible to investigate the influence of dynamic parameters on which uncertainties exist, such as the water added mass surrounding the structure, the damping and the stiffness parameters at the boundary conditions. Use was made of the transmissibility of vibrations between the locations where measurements were obtained. Measured transmissibility was compared to modeled transmissibility, as in this manner it was possible to look into dynamic behavior of the cutter ladder, apart from the external loading. The model was updated by varying various dynamic parameters on which uncertainties existed, including water added mass, damping and stiffness parameters at the boundary conditions. Investigating the data obtained during measurements showed that the forced vibrations caused by the cutting process dominate the dynamic behavior in the cutter ladder. Natural vibrations of the cutter ladder were found to be minor. Updating the model revealed that the water surrounding the structure has a significant influence on the dynamic behavior. In vertical direction, a quantity of water close to the weight of the cutter ladder itself had to be added to have the vibration model meet the design parameters. Quite an amount of structural damping had to be added too, for which the cause is again sought for in the water surrounding the structure. Using transmissibility functions as design parameters was found to yield accurate results, especially at the sections where no external loading was introduced. It is recommended to continue investigating the influence of the forced vibrations on the fatigue life of the cutter ladder on a more local scale, as this might provide new insights for future cutter ladder designs.Civil Engineering and GeosciencesHydraulic EngineeringOffshore and Dredging Engineerin
A Cutter Suction Dredger in Operational Condition: Implementation of a Cutter Force Function in a dynamic multi-body model
No full textModern large Cutter Suction Dredgers utilize anchors, swing wires, a cutter head and a spud, which enables the CSD to excavate sand and tough rock masses with a relatively high accuracy. A drawback of the relatively stiff is that the ship often encounters problems in certain wave conditions. Several models exist which study the dynamic effects of the mooring system, when the cutter is not being operated. These models have led to innovations in the development of new spud mooring systems which are more reliable and allow the operators to safely work up to the operability boundaries.From the desire to study innovative concepts for the cutter ladder as well to improve the range of operability, IHC has offered a thesis project to examine a dynamic simulation program of a CSD in operational condition. This project is based on the program DODO which couples the hydrodynamic solutions of a diffraction solving algorithm (DIFFRAC) to multi-body dynamics. The RK4-method is used for the numerical integration of the equations of motion. Although IHC already has several highly detailed cutting models, none of them were used since early on in the project it became clear that they were unsuitable in combination with the multi-body models of CSDs in DODO. Especially the level of detail and the scale size of these programs eventually led to the idea of developing a new and computationally cheaper model. This new Cutter Force Function is based on a case study. The model for the case study is constructed according to a conventional multi-body method in which the cutter ladder body and the floater body are connected to each other via constraints. The hydrodynamic coefficients and the Froude-Krylov wave forces of the external DIFFRAC solution are applied to the floater body. The transfer functions of the Linear Time Invariant-system are studied to verify the system and to act as a stepping stone for future simulations that include the Cutter Force Function. In the Cutter Force Function an orthogonal spacial discretization is used for a cutter and a seabed matrix which store a template of force unit vectors and the instantaneous surface height of the seabed, respectively. With an elementwise overlay method the cut volumes and their according force vectors are determined for each time step. The Cutter Force Function provides a framework to which clay- and sand cutting models can be added as well as other effects such as bulldozing forces, snow-plough effects, etcetera.Several time domain simulations have been run to verify the functionality of the Cutter Force Function. The primary results indicated that the function gave adequate signal forms although their amplitudes were not limited to a maximum power. Due to the fact that this could generate energy in the system at moments at which it should not be physically possible, a feedback control loop based on the cutter drive torque should be implemented. The LTI-model of the CSD and the transfer functions are ready to be used for the study of implementing PID-controls on swing wires.Offshore and Dredging Engineerin
Towards simulating flow induced spillage in dredge cutter heads using DEM-FVM
No full textWhen dredging rock using a Cutter Suction Dredger the high amount of spillage is problematic, since it prevents an energy efficient removal process. This papers presents a coupled DEM-FVM method to simulate spillage, that can be used for optimizing the design and working method of the Cutter Suction Dredger. In these simulations, the challenge was to model relatively large particles in a complex and rotating geometry. To ensure stability and reduce computational time we used smoothing kernels to map the forces and the concentration between the discrete elements and the fluid mesh. The method is validated for the fluid flow in the rotating cutter head. This model incorporates all physical processes to predict flow induced spillage in cutter heads within feasible calculation times.Offshore and Dredging Engineerin
Open Access Cookie Cutter
No full textPrint your own cookie cutter on a 3D printer using one of these files designed by Chip Wolfe, Digitization Specialist/Access Services Technician at Embry-Riddle Aeronautical University.
The .dae file does not need to scaled; the .stl file will need to be scaled. The cutter was designed to be 14 mm deep and 85 mm top to bottom, but can be rescaled to whatever size you like.
UPDATE 10-25-16: Stephen Gray of University of Bristol modified the file (it reportedly had a spike that prevented it from fitting on the printer bed). The modified version is being shared here in hopes that it will be helpful to others. Check the additional files area at the bottom of this record
Modelling Spillage in Rotating Cutter Suction Heads: A combined Finite Volume and Discrete Element Model
No full textDue to an increased demand for transport, ships become larger, needing a larger navigable depth. For these reasons a waterway needs to be dredged and a Cutter Suction Dredger is a vessel suitable for this operation.A Cutter Suction Dredger is a floating vessel which removes sand, clay or soft rock from sea or river beds. It has a cutter head with pickpoints attached to it. By rotating and swinging, the pickpoints are pushed into the soil, disintegrating it. The soil enters the cutter head where it is mixed with water. From inside the cutter head it is hydraulically transported to the vessel via the suction mouth and pipe. The rotational speed of the cutter head can be varied by the vessel operator. When increasing the rotational velocity and swing speed, more production can be obtained. However, this leads to an outflow of water and dredged material near the ring, spilling the soil. When the Cutter Suction Dredger is employed for cutting sand, the sand particles are easily kept in suspension due to the rotating motion before it is sucked up. A cutter suction dredger is also used for cutting rock, leading to large pieces, which are more influenced by gravity and the centrifugal force. Due to these forces, the pieces are thrown out of the cutter head more easily than smaller sand particles. The pieces of rock which are thrown out of the cutter are considered spilled. This spillage is unfavourable since this material has to be dredged a second time or is left on the sea floor. When the material is left on the sea floor, a larger layer of soil needs to be dredged for creating the same navigable depth. To reduce spillage, the processes contributing to spillage should be quantified in order to design a better cutter head or working method. This dissertation contributes to this goal by presenting a validated model for simulating the spillage of rock particles inside a rotating cutter head. Such a model can be used to quantify different processes and test new cutter head designs… Offshore and Dredging Engineerin
Computer controlled metal cutter
No full textThe study presents an automated oxygen-acetylene metal plate cutter entitled Computer Controlled Metal Cutter. The machine\u27s cutting path is determined by X and Y rail movements. A Z assembly decides the height of the cut. The mechanical components are driven by DC motors interfaced to a microcomputer. A feedback system using rotary shaft encoders is employed to monitor the cutting path and position of the torch at any time. Shapes of any form can be cut by the machine using the developed software capable of reading any DXF compatible file format. Control algorithms are implemented to ensure smoothness of cut and compensate for real world imperfections
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