Auswahl der wissenschaftlichen Literatur zum Thema „Metoda 6DOF“

Emergency gates are important safety feature of hydropower plants. They are used to close the flow in order to protect power plant equipment in case of emergency. In this diploma the-sis are realized CDF simulations of emergency closure of wheel-mounted gate on two-dimensional model of the Slapy hydropower plant. Simulations were performed for the case of constant lowering gate speed and for the case of gravitational closure. Dynamic mesh was used to enable the gate motion. The 6DOF method was used for the case of gravitational clo-sure and user defined function was defined to control movement of the gate. User defined function include gravitational force, hydrodynamic forces and friction force. Simulations were used to verify forces acting on gate and volume flow through gate during closing process. In case of gravitational closure the speed and orientation of closing process and closing process time were determined.

Thesis (MSc)--Stellenbosch University, 2015.<br>ENGLISH ABSTRACT: There are several ports around the world currently experiencing problems with moored vessel motions. Extreme vessel motions are mainly caused by long waves, which can become trapped inside a harbour basin. The extreme motions can cause downtime in port operations and in some instances cause mooring lines to break. Methods and procedures currently available to measure motions of moored vessels require vessel specific information as input. The implementation of these methods is seen as impractical to implement on every vessel visiting the port and require the physical measurement of some points on the vessel and/or the placement of some kind of measurement device on the vessel. A new Six Degree of Freedom (6DOF) motion measurement system for a moored vessel is presented in this document. The system analyses a video image sequence from one camera. The method estimates the 3D rigid motion for an object of known size by using a Pose from Orthography and Scaling with ITerations (POSIT) algorithm. The object for which the motion is estimated is located on the deck of the vessel and within the camera field of view. Geometric rigid body calculations allow for the calculation of camera perspective rotations and translation of an object on the vessel. Further geometric calculations allow for converting camera perspective motions to the 6DOF object motions. The primary objective of this study was to validate and verify the motions obtained from two proof-of-concept tracking systems. For evaluation purposes, the validation was done by using a small scale physical model set-up in a hydraulics laboratory and using a known method as reference. The Keoship system from the Council for Scientific and Industrial Research (CSIR) is currently one of the most accurate small scale vessel motion measurement systems and was used as reference. The first method tested was the tracking of a 2D LED rectangle mounted on the vessel. This method tracked a 2D object and was primarily used as a stepping stone to measure movement of a 3D object. The second method tracked a 3D object on the vessel. Each tracking method was tested for four different wave conditions with each condition additionally repeated twice as repeatability tests, resulting in a total of 12 tests for each tracking method. When comparing the 2D LED tracking and 3D Object tracking data to data measured with the Keoship system, results show that in general, the 3D Object tracking data compared better to the Keoship data. Tests under controlled conditions enabled a direct estimation of the absolute accuracy of the two developed methods. The verification and accuracy test results, indicated that the 2D LED tracking system should not be pursued further. The results also indicated that for prototype motions exceeding 0.6 m (i.e. storm events) the 3D Object tracking system would have an accuracy close to the maximum allowable accuracy criterion of 0.1 m. This makes the system viable at its current proof-of-concept stage for further development which would enable rapid deployment during a storm event in a prototype situation.<br>AFRIKAANSE OPSOMMING: Daar is verskeie hawens regoor die wêreld wat tans bewegings probleme op gemeerde skepe ervaar. Hierdie buitensporige bewegings word veroorsaak deur lang periode golwe wat binne die hawe bekkens vasgekeer word. Dit kan daartoe lei dat hawe bedrywighede tot stilstand kom en in ernstige gevalle ook veroorsaak dat meringslyne breek. Huidige metodes vir die meet van skeepsbewegings op vasgemeerde skepe, vereis skeep spesifieke inligting as inset. Die toepassing van hierdie metodes op elke skip wat die hawe besoek, word as onprakties beskou, aangesien dit die fisiese meting van sekere punte op die skip behels. In sekere gevalle is dit selfs nodig om meet toestelle op die skip te plaas. In hierdie dokument word ‘n nuwe metode aangebied om die ses grade van vryheid bewegings vir ‘n vasgemeerde skip te meet. Hierdie stelsel analiseer ‘n video beeld reeks van een kamera. Die metode bereken die 3D rigiede beweging van ‘n voorwerp, waarvan die grootte bekend is. ’n ‘Pose from Orthography and scaling with Iterations’ (POSIT) algoritme word hiervoor gebruik. Die voorwerp waarvoor beweging gemeet word is op die dek van die skip en in kamera sig. Rigiede geometriese voorwerp berekeninge word gebruik om die rotasie en translasie vanuit ‘n kamera perspektief te bereken. Verdere geometriese berekeninge maak dit moontlik om die bewegings vanuit die kamera perspektief te omskep in die ses grade van vryheid bewegings van die voorwerp. Die hoof doelwit van hierdie ondersoek was om die gemete bewegings van twee beweging stelsels te valideer en te verifieer. Die validasie en verifiëring was in ‘n hidrolise laboratorium met ‘n klein skaal model opstelling getoets. ‘n Meet metode van skeepsbeweging op klein skaal wat reeds bekend is, is gebruik as ‘n verwysingsraamwerk waarteen die metings vergelyk kan word. Die Keoship stelsel van die Wetenskaplike Nywerheids Navorsings Raad (WNNR) is tans een van die mees akkurate klein skaal skeepsbeweging meet stelsels, en was as verwysing gebruik. Die eerste bewegings metode is getoets op ‘n 2D reghoek vervaaridig uit ligstralede diodes. Hierdie metode het die 2D voorwerp gevolg en is hoofsaaklik gebruik as ‘n boublok om die beweging van ‘n 3D voorwerp te volg. Die tweede metode het die beweging van ‘n 3D voorwerp op ‘n skip gevolg. Vir elke meet metode was daar vier verskillende golf toestande. Elke golf toestand was ook ‘n verdere twee keer herhaal vir herhaalbaarheids doeleindes. Saam met die herhaalbaarheids toetse was daar in totaal, 12 toetse vir elkeen van die twee metodes gedoen. Met die Keoship metode as verwysing, bewys hierdie toetse dat die 3D metode beter resultate lewer as die 2D metode. Toetse onder beheerde toestande, het dit moontlik gemaak om die absolute akkuraatheid van albei sisteme wat ontwikkel was, te evalueer. Verifikasie en akuraatheids toetse het aangedui dat verdere ontwikkeling van die 2D metode gestuit moet word. Die resultate het ook aangedui dat die 3D metode ‘n akuraatheid baie na aan die maatstaf van 0.1 m sal hê wanneer prototipe bewegings 0.6 m oorskrei (b.v. gedurende ‘n storm). Dit sal die oplossing lewensvatbaar maak by die huidige bewys van konsep fase vir die verdere ontwikkeling wat vinnige ontplooiing gedurende ‘n storm sal moontlik maak.

Recently, unsteady aerodynamics has been drawing many attention because it is becoming clear that unsteady aerodynamics have a big effect on running stability, safety and ride comfort of vehicles. In order to estimate unsteady aerodynamics, it is necessary to reproduce the actual running condition including an atmospheric disturbance and vehicle motion. However, it is difficult to investigate the effect of unsteady aerodynamics in the road test because it has a lot of errors in measurement. In this study, a coupled simulation method between the 6DoF motion of a vehicle and aerodynamics was developed for these problems. Large Eddy Simulation (LES) was used to estimate the aerodynamics, and the motion equations of a vehicle was used to estimate vehicle motion. Vehicle motion in aerodynamic simulation was reproduced by using Arbitrary Lagrangian-Eulerian (ALE) method. In addition, sliding mesh method was used to reproduce overtaking and passing motions of two vehicles. By using the methods, aerodynamics and vehicle dynamics simulations are treated interactively (2-way) by exchanging each result at each time step. The 2-way results were compared with the 1-way coupled simulation estimating vehicle motion from aerodynamics results posteriori to investigate how vehicle’s motion itself further affects its aerodynamics during the pass-by and overtaking motions. Our main focus is, by using this method, to study the effect of unsteady aerodynamics on the running stability of a vehicle. The results of 1-way and 2-way coupling analysis showed difference with respect to behavior of a vehicle. It is believed that such differences result in the different aerodynamic forces and moments, which is caused by the vehicle’s posture changes in the 2-way coupling simulation.

A 6DOF Stewart platform driven by piezoelectric actuators was designed for applications in need of nanoscale positioning. By using flexural joints and an error compensation model based on a minimum-points-3-axes measurement method, the manufacturing and assembly errors can be offset. The design of a feedforward controller that is able to reduce the nonlinear hysteresis effect of the piezoelectric actuator is the focus of this article. A dynamic Preisach model is developed to improve the accuracy of hysteresis model, whose inverse model is used as the feedforward controller. Such a control scheme is cost-effective without employing expensive sensors for feedback control. Experimental data shows that the platform can achieve the objective of nanoscale positioning.

The paper reports on the predictive prospects of the Smoothed-Particle-Hydrodynamics (SPH) method for jacket launching and foundation installation simulations. The type of considered applications usually involves the interaction between floating structures (e.g. barges and jackets) as well as structures and seabeds. Such scenarios pose challenges to mesh-based solvers, particle methods like SPH therefore are of advantage. The presented procedure captures floating body motions using a quaternion based 6DOF motion solver. Fluid/Soil interaction is predicted by an adequate suspension model. An efficient parallelization strategy is applied together with a dynamic variable resolution approach to handle large computational domains and structural details requiring a rather fine discretization.

A 6DOF Stewart platform using piezoelectric actuators for nanoscale positioning objective is designed. A measurement method that can directly measure the pose (position and orientation) of the end-effector is developed so that task-space on-line control is practicable. The design of a sensor holder for sensor employment, a cuboid with referenced measure points, and the computation method for obtaining the end-effector parameters is introduced. A control scheme combining feedforward and feedback is proposed. The inverse model of a hysteresis model derived by using a dynamic Preisach method is used for the feedforward control. Hybrid control to maintain both the positioning and force output for nano-cutting and nano-assembly applications is designed for the feedback controller. The optimal gain of the feedback controller is searched by using relay feedback test method and genetic algorithm. In experiment, conditions with/without external load employed with feedforward, feedback, and feedforward with feedback control schemes respectively are carried out. Performance of each control scheme verifies the capability of achieving nanoscale precision. The combined feedforward and feedback control scheme is superior to the others for gaining better precision.

Global response of a flexible catamaran due to wetdeck slamming in head sea regular waves is studied. A 6DOF structural model is used to model the test catamaran. The catamaran has a wetdeck with horizontal transverse cross-sectional shape. The flow due to the water impact is assumed 2D in the longitu-dinal cross-sectional plane. Both a direct method and a modal based method are applied to predict the global response. Vertical shear forces and bending moments are compared with experimental data and show reasonable agreement. Theoretical and experimental error sources are presented and the influence on global response is discussed.

This paper introduces a new 6DOF parallel manipulator with a ‘3-3’-PSS structure for the space docking test system. The objective of the paper is to present a design method for determine the geometrical parameters of the 6-DOF manipulator according to a prescribed workspace and required performances. By the study of the relationships between the geometrical parameters and the performance indices of the manipulator, a new method is presented for finding all the appropriate parameters on the contour maps of the performance indices. With this method, the smallest manipulator whose workspace involves the prescribed workspace and whose performances fit the requirements could be found.