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The turned mass damper (TMD) system has found extensive applications in vibration control nowadays. The main disadvantage of the system is to add additional mass to the structures. In order to make use of its merits and overcome its disadvantage the developed turned mass damper (DTMD) vibration control system is studied in this paper. It uses the equipment set on the structure instead of additional mass to control the vibration of structures. The theory analysis shows that the frequency range is enlarged and the resonant band is reduced with the mass ratio increasing. The FEM simulation shows that the DTMD vibration control system could absorb more vibration energy when the frequency of the DTMD is near the excitation frequency. The results of the simulation also showed that the DTMD is more effective in the vibration control for the jacket platforms.

A wideband METMD (multiple extended tuned mass dampers) system has been developed for reducing the multiple resonant responses of the platforms to all kinds of loads such as earthquake typhoon tsunami and big ice load. This system is composed of several sub-systems each of which consists of one set of ETMD (extended tuned mass damper) unit covering a specific frequency bandwidth and its average frequency is tuned to one of the first resonant frequencies of the platform. The offshore platform is simplified to a single DOF (degree-of-freedom) system to which a METMD subsystem (composed of m ETMDs) is attached and constitutes m+1 DOFs system. The total mass ratio of the METMD subsystem to the platform is 14% and the frequency ratio of the exciting frequency to the platform's natural frequency varies in [0.51.5]. The theory analysis results are described. The FEM simulation shows that the METMD has a better vibration control effect on the mega-platforms' vibration control under the random ocean wave load

The successful use of mega-frame theory for big buildings on the ground to control the vibration acts as a reminder to investigate a new kind of platform using the theory. The concept platform is made up of major columns and major beams. The major columns stand vertical and horizontal load. The major beams endure the horizontal load and averagely transfer the weight of the platform to the columns. The static analysis mode analysis and simulation of vibration control are performed for the concept platform and three other types of platforms for comparison. It is concluded that the concept platform is feasible in functionality since the platform has high holistic intensity and can avoid the partial breakage because of the columns of the MFPs being more equal burden under static loadings as compared with other kinds of platforms.

The work in this paper is concerned with the application of a strain based shallow shell finite element to study the natural frequencies of cylindrical panels with cut outs. Eccentrically located holes as well as holes having their centre coinciding with the centre of the panels are dealt with. Simply supported panels or held rigidly along the four edges are considered. The sub-space iteration technique which is shown to have an economising effect is used to obtain the natural frequencies and the associated modes of vibration. Investigations are carried out to study the effects of the size and location of the openings on the natural frequencies and the corresponding mode shapes.

Vortex-induced vibrations (VIVs) can be detrimental to slender tubulars such as the anchor tethers of floating platforms steel risers and submarine pipelines that have free span over an irregular seabed. A new type of low-cost easy-to-install vortex- shedding suppression device has been developed. A laboratory test programme was undertaken to determine its ability to reduce vibrations in both the cross-flow and in-line direction. During the tests the efficiency of the device was verified for different incident angles between the flow direction and the pipe axis and for increased velocities exciting the higher modes. The results show that the device is as efficient as conventional helical strakes. Efficiency decreases for oblique flow and for velocities where the higher modes lock-on.

The differential quadrature element method (DQEM) and the extended differential quadrature (EDQ) have been proposed by the author. The EDQ is used to the differential quadrature element vibration analysis of bar beam and frame structures. The element can be a nonprismatic beam considering the warping due to torsion. The EDQ technique is used to discretize the element-based differential eigenvalue equations the transition conditions at joints and the boundary conditions on domain boundaries. An overall discrete eigenvalue system can be obtained by assembling all of the discretized equations. A numerically rigorous solution can be obtained by solving the overall discrete eigenvalue system. Mathematical formulations for the EDQ-based DQEM vibration analvsis of frame structures considering the effect of warping torsion are carried out. By using this DQEM model accurate results of frame problems can efficiently be obtained. Numerical results demonstrate this DQEM model.

This paper is the second in a series of two papers documenting the research activities in the area of vision-based navigation for unmanned underwater vehicles. The earlier paper published in Part B7 of IMarEST Proceedings covered tracking of pipelines and cables and moving targets such as fish. This paper covers the topics of motion estimation and station-keeping and then goes on to explain how this can be used in mosaicbased positioning. The most significant of the previous efforts at each are examined including an overview of the image processing techniques used the various motion estimation algorithms employed and the different styles of approach. Methods for reducing the error in each technique are discussed. Both monocular and binocular vision is examined and the outstanding challenges still to be solved are presented. Finally some conclusions from both papers are offered.

SLAM (simultaneous localisation and mapping) is an approach to localisation in which the vehicle uses relative observations of environment landmarks to incrementally construct an environment map and simultaneously localise itself within this map. A virtual SLAM system has been implemented and optimised for real-time deployment on an AUV equipped with calibrated stereo cameras. The system incorporates a novel approach to landmark description in which landmarks are local submaps that consist of a cloud of 3D points and their associated SIFT-SURF descriptors. Landmarks are also sparsely distributed which simplifies and accelerates data association and map updates. In addition to landmark-based localisation the system uses visual odometry to estimate the pose of the vehicle in six degrees of freedom by identifying temporal matches between consecutive local submaps and computing the motion. Both the extended Kalman filter and unscented Kalman filter have been considered for filtering the observations. The output of the filter is also smoother using the RTS (Rauch-Tung-Striebel) method to obtain a better alignment of the sequence of local submaps and to deliver a large-scale 3D acquisition of the surveyed area.

VIV (vortex-induced vibrations) are a well-known phenomenon to engineers. Several structures subjected to wind or water currents may experience VIV: common posts chimneys suspended cables for bridges power transmission lines in air and pipes risers towing cables mooring lines in water. Sometimes this has to be carefully taken into account in their design as a major cause of fatigue damage e.g. for offshore structures. Recent development of oil fields in deeper ocean sea in particular deals with structures of increasing length to diameter aspect ratio for which VIV remain a challenging problem. The VIV (vortex-induced vibrations) of two circular cylinders in tandem arrangement are studied both analytically and numerically. A low-order model for transverse VIV of one degree-of-freedom elastically supported rigid cylinders is analysed. The model based on van der Pol oscillators is first developed addressing the response of a single structure and then extended to describe vortex-induced oscillations of two interfering circular cylinders in tandem arrangement.

The VLCC HAVEN was carrying a cargo of heavy crude oil when it exploded in April 1991. It was towed towards shore but sank one nautical mile offshore after burning for 70 hours. Because of the burning the petroleum hydrocarbons became heavier than the seawater and sank dispersing tar depositions on a wide sea bottom area in the Gulf of Genoa. Taking into account the occurrence of re-suspension phenomena from the shoreline to a depth of 20 meters tar depositions were detected by means of a towed video-camera and using scuba divers. It is described how the oil residues were recovered from the shoreline to a depth of 10 meters using submerged pumps manual works and a number of techniques and devices specially developed.

The prediction of vortex-induced vibration (VIV) in mooring cables and deepwater production risers requires a combination of structural response dynamic response hydrodynamic excitation and damping models. The key factors to be considered when estimating the dynamic response of risers to vortex shedding in sheared currents are summarised. Several important dimensionless parameters are considered and their effect on dynamic response is explained. Two new sets of results are presented. The first highlights the possibility of lock-in under highly sheared conditions. The second introduces an improved model for hydrodynamic damping which includes still water damping as well as the effects of reduced velocity and response amplitude. The VIV response prediction program SHEAR7 is used to demonstrate the response characteristics of three different example structures: a cable that behaves as though it is nearly infinite in length a vertical "rigid" riser and a steel catenary riser.

The initial exploratory analysis into the effects on military survivability of adopting commercial style in warships is described. The paper describes a vulnerability study comparing two patrol combatants: one corvette designed in a conventional military style and one cost-expedient conversion of an off-the-shelf PSV (platform supply vessel). Both ships were designed to carry the same payload and carry out the same role. The UPC (unit procurement cost) and annual fuel cost were estimated for each ship. A comparative study was then carried out which examined the vulnerability of each of five top-level functional systems in each design to attack by a series of generic threat weapons. The results showed that the converted PSV exhibited considerably better system vulnerability. It is likely that the Corvette may exhibit significantly better susceptibility and recoverability characteristics than the PSV due to a combination of lower signatures reduced size and better distributed damage control equipment.

Aspects of water quality and quantity problems in the Amu Darya basin are presented. Local people depend on the fresh water of the Aral Sea tributaries. Numerous oases have existed since ancient times and were supported by the favourable flow regime of the Amu Darya including the low saline summer flood. Today the problem lies in the scale of irrigation the choice of cultivated crops and the decline in water quality due to the use of agro-chemicals. Past environmental destruction has led to a reduction in the level of the Aral Sea and is also endangering human existence in the deltas. The hydrography of the Amu Darya basin water quality and the dynamics of the Tuyamuyn Hydro-engineering Complex (THC) are discussed.

Conf held 22-23 October 1991 in Aberdeen Papers are Water injection and treatment - a changing environment The improved design of scale inhibitor squeeze treatments Bacterial sulphide generation in oil production systems New trends in oilfield injection water treatment The Puritech seawater filter Efficient and chemical-free system for water deoxygenation Legal environmental and monitoring considerations for the discharge of oily aqueous wastes from offshore installations A review of chemical additives used in offshore topsides processing Experiences with the injection of unfiltered produced water On-line monitoring of oil in water in oil field brines Produced water disposal trials Produced water solids removal Advances in liquid hydrocyclone technology Oily water treatment by coalescence - techniques and applications developed by Elf-Aquitaine The development of the Leo centrifuge for produced water de-oiling

Importation of fresh water carried by tankers, as a substitute for sea water ballast and backhaul cargoes, can make an important contribution towards achieving a better balance between demand and supply of water. This report presents work done by INTERTANKO in cooperation with others to promote water transportation in tankers. Part 1, Water supply improvements in the next decade, is a summary of INTERTANKO's recommendations over the years. Part 2 , Experimental investigation of irrigation with oil-contaminated freshwater, is an extract from a paper presented on research by Professor Arnulf R. Persson. Part 3 is a summary of investigations in Middle East countries, 4-17 March 1979. Part 4 contains appendices.

The book aims to present a self-contained introduction to the mathematical and physical aspects of the theory of water waves. It consists of 10 chapters, arranged into 3 parts as follows: Basic fluid mechanics and solutions techniques, Water waves, Advanced water waves. Chapter 1 gives an overview of the specification of fluid motion. Chapter 2 describes the basic equations of fluid motion from the viewpoint of general fluid dynamics. Chapter 3 contains the classical solution techniques for partial differential equations governing the physical situation of the problems. Chapters 4 and 5 are devoted to the development of wave terminology. Chapter 7 is primarily concerned with wave statistics and wave energy spectra. The application of the wave theory is demonstrated in Chapter 8 which is about wave forces on offshore structures. In Chapter 9 non-linear long waves in shallow water are examined from a mathematical viewpoint. The final chapter deals with the solution method of the solitary wave problem by an inverse scattering technique.

Conventional linear added mass and damping can be obtained when a floating body is forced to oscillate in the calm water. However with the presence of the incident waves there exists an alternative source of added mass and damping caused by the nonlinear interactions between waves and low-frequency oscillations. Proportional to the square of the wave amplitude they are called the wave drift added mass and the wave drift damping. The problem of a circular cylinder array slowly oscillating in both diffraction and radiation wave fields is considered in the present work. The frequency of the low frequency oscillation is assumed to be much smaller than the wave frequency. Perturbation expansion based on two time scales is performed to simplify the problem. Wave loads including the wave drift added mass are formulated by integration of the hydrodynamic pressure over the instantaneous wetted body surface.

Nortek's AWAC (acoustic wave and current) has traditionally measured both the pressure and orbital velocities to estimate the wave frequency and directional spectrum. Recently the firmware has been modified to allow the free surface to be detected using the vertical beam. The modification eliminates the constraint from the attenuation of wave properties with depth. Therefore the AWAC is now capable of measuring higher frequency waves in deeper water with a greater degree of accuracy. This approach of measuring waves is not a new concept. However it represents a considerable step forward from existing bottom-mounted sensors now available which generally rely just on the pressure and velocity measurements. The development and validation of the surface tracking was carried out over three separate experiments. The first was carried out at Drobak south of Oslo. The second was carried out in Carqueiranne France. Here it could be compared directly to a DataWell WaveRider buoy. Once it was established that the surface track measurements were in good agreement with the wave buoy the surface track firmware in an AWAC online in Hwa Lien Taiwan was implemented.

A simulation model developed to predict wax deposition in wells and pipelines is described. The model uses a standard steady-state multiphase point model to predict pressure drop and liquid hold-up along the pipeline. By integration in time the effect of wax deposition on pressure drop and temperature is calculated. A multi- component wax model is used to give a continuous estimation of the wax precipitation along the pipeline and the viscosity of the current composition. The wax deposition is estimated from the diffusion of wax from the bulk towards the wall as a result of temperature gradients as well as shear dispersion effects. Varying inner pipe wall friction due to wax deposition is also included. Two case studies are presented.

The Gdansk University of Technology's Department of Acoustics has a measurement laboratory on Wdzydze Lake. The lake's hydrological conditions are presented such as its bathymetric map and seasonal range distribution of sound velocity. The laboratory's technical equipment and watercraft are also presented. Thanks to these research facilities tests can be carried out such as measuring the beam patterns of large hydroacoustic antennas in the far field or determining the range of devices in an actual and difficult hydroacoustic channel. It also enables longer studies to be carried out and tests to be run in most weather conditions except when the lake freezes over. The laboratory's teaching programme is also presented. This consists of practical training and presentations devised for environmental telemonitoring automation of mobile objects and sound engineering students.