Browsing by Author "Kirk, Colin L."
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Item Open Access Compounded normal modes of free vibration of cantilever plates(College of Aeronautics, 1967-04) Kirk, Colin L.Experimental determination of the natural frequencies of a stiffened cantilever plate reveals the simultaneous excitation of two normal modes of vibration. Comparison is made between the experimental nodal pattern and the nodal pattern calculated by assuming characteristic beam functions for the vibration form of the plate.Item Open Access The dynamic analysis of flexible riser systems(Cranfield University, 1988-01) Ryan, M. S.; Kirk, Colin L.The aim of this thesis is to provide a design tool for the engineering analysis of the dynamics of a flexible riser system. The design tool is piovided in the form of a computer program. The two main requirements of such a program are that it is realistic and practical to use. The necessary theory is developed to allow these requirements to be satisfied. To ensure accuracy checks are made against model tests and known analytical solutions. How the computer program may be used is shown by analysing a particular riser configuration.Item Open Access Dynamic analysis of flexible space shuttle remote manipulator system with large payloads(Cranfield University; School of Engineering, 2005-06-27T15:48:00Z) Wiedemann, Simon M.; Kirk, Colin L.This paper presents a new approach for determination of vibration response of the triply articulated Space Shuttle Remote Manipulator System (SRMS) with large rigid overhanging payloads. In contrast to other researchers dynamic modelling is based on the exact eigenvalue analysis of the two main flexible links with a rigid end effector and payload, including the effect of interaction of the Shuttle. A wide range of SRMS configurations and payloads with joints free and locked is examined for bang-bang slews and with all joints locked for payload positioning using Shuttle thruster firing.Item Open Access The dynamic analysis of offshore mooring terminals(Cranfield University, 1983-02) Langley, R. S.; Kirk, Colin L.This Thesis investigates the methods which are currently avail- able for the dynamic analysis of Offshore Mooring Terminals, particular regard being paid to Single Point Mooring (SPM) Terminals. Various aspects of the problem are considered in turn, these being the random vibration of non-linear systems, the analysis of catenary mooring lines, buoy dynamics, ship motions, second order (or slow drift) forces and motions, and low frequency motions caused by instabilities. These various aspects are then applied to the dynamic analysis of a Single Buoy Storage (SBS) System and the effect of the method of analysis employed, the system dimensions and the environmental conditions on the computed response is investigated. A Time Domain investigation of the stability of the SBS System in the presence of wind and current alone reveals that the system is only unstable for combinations of wind and current which are unlikely to occur in practise. A static offset position is then assumed and the calculation of the three-dimensional first and second order response to random waves is performed in the Frequency Domain, linear wave theory being used. The first order wave forces are calculated by using strip theory for the tanker and Morison's equation for the buoy. The second order response in surge, sway and yaw is calculated by a reflection coefficient method, these coefficients being obtained from published literature. The non-linear mooring system and the drag forces acting on the buoy are linearised using the equivalent linearisation method, due account being taken of the coupling between the first and second order response. The model developed for the first order response of the system allows the use of a spreading function in the incident wave spectrum. The accuracy of linearisation techniques and the statistics of the second order force and response are also investigated.Item Open Access Dynamics and control of flexible articulated space manipulators with large payloads(2002-03) Wiedemann, Simon M.; Kirk, Colin L.This thesis studies the dynamics and control of flexible articulated space manipulators with large payloads similar to the Space Shuttle Remote Manipulator System. For dynamic response analyses an exact analytical method to compute natural frequencies and mode shapes of space manipulator systems with varying degrees of complexity is developed. Dynamic response analyses are performed comparing the results obtained using the exact mode shapes with those obtained when using assumed mode shapes for a series of different manipulator slew manoeuvres and Shuttle thruster firings. Possible methods for active vibration damping control of the manipulator are discussed, including the methods presented by other researchers. In this thesis it is proposed to use reaction wheels in a closed-loop control scheme, and its advantages and disadvantages compared to other methods are discussed. The problem of payload capturing and post-capture dynamics are addressed, as well as the dynamics following an emergency braking of the robot. For these cases, a simple method to estimate upper limits of dynamic responses is developed, and results obtained with this method for various example cases are compared with results computed by professional software. Finally the dynamic responses of a space station to various robot manoeuvres are analysed. These responses can have detrimental effects on micro-gravity and similar experiments. The analyses are performed using a simplified model of the International Space Station and its Mobile Remote Manipulator System.Item Open Access Nonlinear dynamic analysis of offshore structures(Cranfield University, 1986-03) Ghadimi, R.; Kirk, Colin L.In this thesis consideration is given to a selection of nonlinear dynamic problems in the field of offshore engineering. Hydrodynamic loading on fixed horizontal and vertical tubular members and the dynamic response of articulated towers together with the distribution of shear force and bending moment along the tower are investigated using various wave theories. Effects of nonlinear convective acceleration terms in the calculation of fluid inertia forces and moments are examined and attention is given to integration of wave forces up to the free surface for vertical members. Calculation of fluid loading at the displaced position of the articulated tower and any Mathieu type instabilities that may occur have been considered. The dynamic analysis of a damaged Single Anchor Leg Storage (SALS) system subject to loss of buoyancy in the yoke chamber is studied. The equations of motion of the yoke/riser system are derived assuming large displacements and solved in the time domain. Time histories of the response, variations of the riser tension, velocities of riser top end and the time histories of pivot reactions are given. Natural periods and mode shapes for small displacements of the system are calculated. Two methods of simulating random seas, both represented by a sum of harmonic wave components, are used to simulate second order low frequency (slow drift) force on a tanker in head seas by Pinkster's time domain method. In one method the wave amplitudes are generated randomly from a Rayleigh distribution and in the other they are obtained deterministically via the wave spectrum. Time histories of slow drift force and response together with simulation results with various duration lengths are presented and compared. Estimates of the extreme vessel response and its relation to rms value are compared with the result of a commonly used method of determining peak/rms ratios. The results of these investigations highlight the importance of accurately simulating nonlinear effects in both fixed, floating and compliant offshore structures from the point of view of safe design and operation of such- systems.Item Open Access Static and dynamic analysis of marine pipelines and risers(Cranfield University, 1985-03) Shanks, J. M.; Kirk, Colin L.This thesis investigates two slender body problems, namely the static and dynamic analysis of submarine pipeline spans and the dynamic analysis of marine risers. In view of structural and environmental similarities, these problems are closely related and where possible common analysis procedures have been developed. For the problem of pipe spanning, attention is focused on the possibility of vortex induced vibration and the associated question of span assessment. This situation arises when following the discovery of a span, an assess- ment is required to determine if any remedial repair work required. To assist in this assessment, and also to provide a more fundamental understanding of span behaviour, number of mathematical models are developed. First linear beam-column theory is used to determine the span natural frequencies and buckling load for a single span supported continuously on either side by an elastic foundation. The effects of internal/external pressures and product temperature are included and the results presented terms of two independent nondimensional parameters. Next the effects of pipe/soil friction and change in geometry are considered utilising a nonlinear Finite Element model. Theories are developed for a nonlinear pipe element with axial/bending coupling and a nonlinear nonconservative pipe/soil friction element. The effects of initial seabed geometry and finite amplitude vibration are included and it shown that span frequencies are sensitive to both end friction constraints and seabed geometry. . For marine riser dynamics, an attempt is made to synthesise the best parts from the many and varied analysis methods developed to date, into a simple but flexible design-orientated program. The riser is represented using a Finite Element model similar to that employed for the pipeline spans, and a reduced set of equations obtained using a component mode synthesis method. Several riser/ articulated column designs are considered and the results found to agree with published data.Item Open Access Vibration of structures with non-linear damping(Cranfield University, 1978-03) Gabri, B. S.; Kirk, Colin L.The work reported here is directed towards the problem of measuring and modeling non-linear damping in steel space frame civil engineering structures. In order to gain a better understanding of the damping mechanism in such structures, tests were performed on a full scale bolted lattice structure and the results of section A show that the joint' damping can be represented approximately in the form: FD =C (1 +e IXIn) where n=1. Other situations. where this form of non-linear damping occurs is in the case of fluid flow past a solid body. In offshore structures the hydro-dynamic force due to drag effects are found to be proportional to velocity squared. For non linear material damping, n, takes a value of 6. In section B. various methods of solution to the non-linear dynamical system under random excitation were studied and it was found that the 'Equivalent Non- Linear Differential Equationl, (ENL) method yields a better measure of the response of the non-linear system to white noise excitation than other approximate methods. Analytical expressions are derived for the mean-square response, probability density function and level crossing rates. With the modified IENLI method (MENL) it is shown how one can extract the non-linear damping and excitation power spectral density. A good correlation is obtained between experimental and theoretical results.