Thèses sur le sujet « FLOATING COLUMNS »

Renewable energy is a critical component in combating climate change. Ocean wave energy is a source of renewable energy that can be harvested using Wave Energy Converters (WECs). One such WEC is the floating Oscillating Water Column (OWC), which has been successfully field tested and warrants further exploration. This research implements a publicly accessible code in MatLab and SimuLink to simulate the dynamics of a floating OWC in the time domain. This code, known as the Floating OWC Iterative Time Series Solver (FlOWCITSS), uses the pressure distribution model paired with state space realization to capture the internal water column dynamics of the WEC and estimate pneumatic power generation. Published experimental results of floating moored structures are then used to validate FlOWCITSS. While FlOWCITSS seemed to capture the period and general nature of the heave, surge, and internal water column dynamics, the magnitude of the response sometimes had errors ranging from 1.5% −37%. This error could be caused by the modeling techniques used, or it could be due to uncertainties in the experiments. The presence of smaller error values shows potential for FlOWCITSS to achieve consistently higher fidelity results as the code undergoes further developments. To demonstrate the use of FlOWCITSS, geometry variations of a Backward Bent Duct Buoy (BBDB) are explored for a wave environment and mooring configuration. The reference model from Sandia National Labs, RM6, performed significantly better than a BBDB with an altered stern geometry for a 3 second wave period, indicating that stern geometry can have a significant impact on pneumatic power performance.
Master of Science
Renewable energy is a critical component in combating climate change. Ocean wave energy is a source of renewable energy that can be converted into electricity using Wave Energy Converters (WECs). One such WEC is the floating Oscillating Water Column (OWC), which has been successfully field tested and warrants further exploration. Floating OWCs are partially submerged floating structures that have an internal chamber which water oscillates in. The motions of the water displace air inside this chamber, causing the air to be forced through a high speed turbine, which generates electricity. This research develops a publicly accessible code using MatLab and SimuLink to evaluate the motions and power generation capabilities of floating OWCs. This code is then validated against physical experiments to verify its effectiveness in predicting the device's motions. This publicly accessible code, known as the Floating OWC Iterative Time Series Solver (FlOWCITSS), showed error ranging from 1.5 % - 37% for the most important motions that are relevant to energy harvesting and power generation. These errors could be caused by the numerical models used, or uncertainties in experimental data. The presence of smaller error values shows potential for FlOWCITSS to achieve consistently higher fidelity results as the code undergoes further developments. To demonstrate the use of FlOWCITSS, geometry variations of floating OWCs are explored.

ABSTRACT A LABORATORY MODEL STUDY ON SETTLEMENT REDUCTION Effect OF STONE COLUMNS IN SOFT CLAY Sü
nnetcioglu, Mehmet Emrah M.Sc., Department of Civil Engineering Supervisor: Prof. Dr. Mehmet Ufuk Ergun August 2012, 177 pages An experimental study was conducted in order to examine settlement reduction ratios of footing supported by both floating and end bearing type of stone columns. For the floating types, tests were done with varying column lengths of one and two widths of footing (L=B,2B). Tests were conducted in 200 mm* 200 mm* 200 mm cubic loading tanks. The reinforcement effect was achieved by the installation of four stone columns with 20 mm diameter under 70 mm* 70mm model footing. Parameters such as area replacement ratio (a_s), loading plate dimensions, consolidation and vertical pressures applied, and the relative density (D_R) of the granular column were kept constant, the column length (L) was set as the only variable in the experimental tests conducted. In the tests, footing settlements together with subsurface settlements at depths equal to footing width (B) and two times the footing width (2B) were measured by specially designed telltales. The settlement reduction ratios both at surface and subsurface were evaluated in order to determine the effect of column length on settlement improvement. It has been found out that as the column length increases the settlement reduction ratios decrease for all depth intervals. However, there exists a threshold column length (L=2B), beyond which the composite ground demonstrates little settlement improvement.

â Reflectionâ is an experiment with what I call â symbolic architectureâ i.e. design where the features of the building have a profound meaning or a strong recall to some familiar aspect in our lives. It is a meditation center designed to rejuvenate visitors by providing an ideal environment to practice and teach meditation. The design is inspired by concepts of Hindu philosophy and each element of the building, the light, the materials, the water and the structure is likened to an element of the spiritual being that helps a meditator achieve a connection between the body and the soul.
Master of Architecture

In a world with ever increasing energy demands, there is a need to find new ways to harvest renewable energy. Floating offshore wind turbines could be an important energy source in the future. To make this possible a better understanding of offshore wind turbines is essential. This thesis has dealt with fatigue associated challenges related to a column-pontoon connection in a semi-submersible floating wind turbine developed at CeSOS, NTNU.The specific design investigated in this report has a transition hull from the cylindrical column to the rectangular pontoon. A finite element model of the connection was available and revealed very high stress concentration at some areas. The sub-modeling technique was applied at two crucial areas for a detailed stress analysis. The design of the connection was changed in order to reduce the stress concentration.Fatigue analysis were carried out at the intersection between the midpoint at the upper hull of the pontoon and the transition piece. The same was done at 13 points along the weld between the hull of the transition piece and the hull of the column. Load time series from global dynamic response analysis from 13 sea states, representing wave and wind conditions at deep water in the North Sea with 0, 30, and 60 degree wave heading, were available and used in fatigue calculations. Load time series from -30 and -60 degree heading were created assuming symmetry around the vertical midplane of the structure. 10 one hour simulations of every sea state were used.Cumulative fatigue damage at all sea states and wave headings were calculated and compared using rainflow counting, an appropriate S-N curve and Miner's rule. Estimated time to failure is calculated assuming a constant wave heading over the lifetime of the structure. The estimated fatigue life is also determined for a combined wave heading. The combined wave heading corresponds to the column-pontoon connection where 0 degree heading is dominating.There will be a multiaxial stress state at the different hot spots. A simplified method for including the fatigue damage contribution from all the different stress components (stress parallel with the weld, stress normal to the weld and shear stress) is proposed. The method has large limitations, but is intended to be used when there is a close to linear relationship between the different stress components. This method has been used when predicting fatigue life at all hot spots and the results have been evaluated.Estimated fatigue life at the most critical hot spot is 1.9 years under a combined wave heading. Multiple hot spots have a fatigue life under 10 years. More design changes is needed to achieve acceptable fatigue life. The method proposed for including multiaxial fatigue effects show promising results at some hot spots. The accuracy depends on which hot spot is analyzed and wave heading.

This study uses a 3D finite element program, calibrated with the results of a full scale instrumented load test on a limited size footing, to estimate the settlement improvement factor for footings resting on rammed aggregate pier groups. A simplified 3D finite element model (Composite Soil Model) was developed, which takes into account the increase of stiffness around the piers during the ramming process. Design charts for settlement improvement factors of square footings of different sizes (B = 2.4m to 4.8m) resting on aggregate pier groups of different area ratios (AR = 0.087 to 0.349), pier moduli (Ecolumn = 36MPa to 72MPa), and with various compressible clay layer strengths (cu = 20kPa to 60kPa) and thicknesses (L = 5m to 15m) were prepared using this calibrated 3D finite element model. It was found that, the settlement improvement factor increases as the area ratio, pier modulus and footing pressure increase. On the other hand, the settlement improvement factor is observed to decrease as the undrained shear strength and thickness of compressible clay and footing size increase. After using the model to study the behaviour of floating piers, it was concluded that, the advantage of using end bearing piers instead of floating piers for reducing settlements increases as the area ratio of piers increases, the elasticity modulus value of the piers increases, the thickness of the compressible clay layer decreases and the undrained shear strength of the compressible clay decreases.

Despite the developments in the last decades, field performance information for short aggregate pier improved ground is needed for future design and to develop a better understanding of the performance of the short (floating) aggregate piers. A full-scale field study was performed to investigate the floating aggregate pier behavior in a soft clayey soil. Site investigations included five boreholes and sampling, four CPT soundings, and SPT and laboratory testing. The soil profile consisted of 8m thick compressible clay overlying weathered rock. Four large plate load test stations were prepared. A rigid steel footing having plan dimensions of 3.0m by 3.5m were used for loading. Four 65cm diameter reaction piles and steel cross beams were used to load the soil in each station. First test comprised of loading the untreated soil up to 250 kPa with increments, and monitoring the surface settlements. Moreover, distribution of settlements with depth is recorded by means of deep settlement gages installed prior to loading. Other three tests were conducted on clay soil improved by rammed aggregate piers. In each station, seven stone columns were installed, having a diameter of 65cm, area ratio of 0.25, placed in a triangular pattern with a center to center spacing of 1.25m. The length of the columns were 3m, 5m in the two station resembling floating columns, and 8m in the last station to simulate end bearing columns to observe the level of the improvement in the floating columns. Field instrumentations included surface and deep settlement gages, and load cell placed on a aggregate pier to determine distribution of the applied vertical stress between the column and the natural soil , thus to find magnitude of the stress concentration factor, n , in end bearing and floating aggregate piers. It has been found that, the presence of floating aggregate piers reduce settlements, revealing that major improvement in the settlements takes place at relatively short column lengths. It has been also found that the stress concentration factor is not constant, but varies depending on the magnitude of the applied stress. The magnitude of stress concentration factor varies over a range from 2.1 to 5.6 showing a decreasing trend with increasing vertical stress.

The non-uniform dc glow discharge plasma system is studied by using isolated computer controlled three couples of double probe system (TCDP) in argon gas, simultaneously. TCDP system has been developed to use for magnetized, unmagnetized, and for low oscillating plasma systems by using low pass filter with optically isolated circuitry to minimize the measurement errors with higher resolution and accuracy. Difference in the shapes and diameters of the discharge tube from region to region leads to change in the positive column glow discharge properties. This is because the positive column inhomogeneities, rising from the increase in the electron densities at the small tube radius region than the large one. Therefore, the axial electric field and the electron temperature have been diverted from their normal behavior in the positive column. However, at the large radius regions, the axial electric field seams to stay approximately constant at higher discharge currents. On the other hand, In this work the radial dependence of the electron temperature, density, floating potential, and the normalized probe radius (&
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D) has been investigated. Since, the probe radius is smaller than Debye length, the orbital motion limited (OML) theory has been used. As a result, the electron temperature (at the center) decreased and density increased with decreasing tube radius, and they have maximum values at the first probe (near the cathode). The electron density ne was observed to decrease and electron temperature Te to increase with increasing the discharge current. The floating potential has less negative value with decreasing tube radius except at the higher currents. Finally, it has been found that the &
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is proportional with electron density, but it remains constant depending on the value of Te and ne.

Suite à la mise en place de politiques publiques favorisant les énergies renouvelables, la construction de fermes éoliennes offshore est en plein essor aux quatre coins du monde. Or, la technique de l'éolienne offshore posée, la seule utilisée actuellement, n'est pas viable économiquement dans des eaux trop profondes. Ceci représente un sérieux frein au développement de l'énergie éolienne. Pour cette raison, la communauté scientifique s'intéresse depuis plusieurs années aux éoliennes sur plates-formes flottantes. En eau profonde, cette technologie est intéressante. Mais le fait que l'éolienne ne soit pas encastrée au fond de la mer augmente très significativement les sollicitations mécaniques induites par les vagues.Pour réduire ces sollicitations qui ont de nombreux effets néfastes, différentes approches sont possibles. Essayer de compenser les oscillations « avant-arrière » du mât de l'éolienne en pilotant la force de poussée exercée au niveau du rotor a déjà été écarté dans la littérature. Nous nous sommes concentrés sur l'ajout d'un dispositif de stabilisation interne à la plate-forme, de type Tuned Liquid Column Damper (un tube en U contenant un liquide, TLCD, encore appelé tube anti-roulis), utilisé dans d'autres contextes. Le dispositif que nous proposons est un dispositif actif où les paramètres du TLCD sont ajustés en temps réel, au cours du mouvement induit par les vagues. La mise à jour des paramètres suit une stratégie reposant sur une analyse des interactions entre le TLCD et la plate-forme (appelée ici barge) sur laquelle est installée l'éolienne. Nous avons modélisé le mouvement de la barge seul et son couplage avec le TLCD dans le plan grâce à une approche Lagrangienne. Nous avons étudié les effets des interactions du TLCD avec la barge dans le cas où le coefficient de perte de charge dans le tube était constant. Les limites de cette approche ont été détaillées grâce aux résultats classiques de la littérature sur les oscillateurs mécaniques couplés. Nous nous sommes ensuite concentrés sur une approche active consistant à modifier les caractéristiques du système en temps réel. Nous avons proposé des stratégies de type Linear Quadratic Regulator et de type Model Predictive Control agissant sur le coefficient de perte de charge. Dans un deuxième temps, les simulations nous ont ensuite permis d'écarter la commande MPC dont le rapport performance / complexité n'est pas favorable par rapport à la commande LQR dans ce cas précis.Une étude plus générale du système, en trois dimensions, nous a permis de vérifier que le TLCD classique dans sa version passive ou dans la version active que nous proposions n'est pas du tout robuste à l'incidence de la houle. Nous avons donc imaginé et modélisé des dispositifs inspirés du TLCD mais permettant d'amortir les oscillations de la houle de manière efficace, indépendamment de l'incidence de la houle. Nous avons nommé ces dispositifs TLMCD, pour Tuned Liquid Multiple Columns Damper.Les dispositif que nous proposons sont des systèmes TLMCD actifs. Ils sont conçus d'après les modélisations 3D que nous avons développées et une étude des coûts. Pour ces dispositifs, nous avons aussi détaillé les spécificités de la synthèse des stratégies LQR pour amortir les oscillations de la barge indépendamment de l'incidence de la houle.La performance de ces solutions d'amortissement a finalement été évaluée par simulation pour un large éventail de conditions de houle, couvrant les spécifications d'un “ cahier des charges ” que nous présentons. On observe une réduction des oscillations en roulis de la barge qui peut atteindre un facteur 4 par rapport à l'éolienne flottante sans TLCD. Ces résultats nous montrent que le dispositif TLMCD que nous proposons est un dispositif intéressant pour amortir de manière significative, robuste et économiquement abordable notre système
Thanks to the recent policies of subsidizing renewables energies, constructions of offshore wind farms are booming all over the world. Yet, fixed-bottom wind turbine technology, the only one currently deployed, are too costly for deep waters. This hinders the development of wind power. This is why the scientific community has an interest in floating wind turbines (FWT). The cost of these wind turbines does not depend much on water depth. But since the wind turbine is not fixed into the seabed, the mechanical stress caused by the waves significatively raises.To reduce these detrimental loads, different approaches can be used. The litterature already discarded the control of the wind thrust applied on the rotor to compensate the "fore-aft" oscillations of the tower. We focused on stabilizing floating wind turbine by means of an attached damping system placed inside the float, it is a Tuned Liquid Column Damper (a U-tube containing a liquid, TLCD, also known as anti-roll tank), used in other areas. The damper we propose is an active system where TLCD parameters are continuously modified. Parameters are updated according to a strategy defined thanks to an analysis of the interactions between TLCD and the float (referred to as barge) supporting the wind turbine. We modelled the coupled dynamics of the barge and the TLCD in the vertical plan using a Lagrangian approach. We studied the motions of the damped system for a constant head-loss coefficient in the TLCD. The limits of this approach were detailed thanks to the classic results in double oscillators literature. Then, we focused on an active approach involving a time varying of the head-loss coefficient. We proposed Linear Quadratic Regulator and Model Predictive Control strategies to determine the head-loss coefficient. At a later stage, simulations enabled us to discard the MPC strategy as its complexity/performance ratio is rather bad compared to the LQR strategy in this particular case.A more general study of the system, in three dimensions, showed us that the TLCD is not robust against wave incidence. Therefore, we imagined and modeled new dampers inspired by the TLCD, which can damp the float effectively, regardless of the wave incidence. We named those dampers Tuned Liquid Multiple Column Damper (TLMCD).The dampers we propose are active TLMCD. Their designs are based on their dynamic properties and a cost study. We also detailed the specificities of LQR design to ensure the best possible robustness against wave incidence.The performance of the proposed TLMCD dampers was assessed through numerical simulations for a wide range of sea conditions. We observe that barge roll can be reduced by a factor of four compared to the undamped FWT. These results show us that the TLMCD we propose is interesting to damp significantly, robustly and economically our FWT

In present scenario buildings with floating column is a typical feature in the modern multistory construction in urban India. Such features are highly undesirable in building built in seismically active areas. This study highlights the importance of explicitly recognizing the presence of the floating column in the analysis of building. Alternate measures, involving stiffness balance of the first storey and the storey above, are proposed to reduce the irregularity introduced by the floating columns. The study is carried out on a building with floating columns. The plan layout of the building is shown in the figure. The building considered is a residential building having G+9. Height of each storey is kept same as other prevalent data.

碩士
淡江大學
土木工程學系碩士班
106
This study investigates the bearing behavior of individual geosynthetic-laminated sand columns embedded in very soft clay and medium hard clay through model tests. Similarity analysis was first executed to determine the suitable properties of the constituents used in the model test to ensure comparable behavior between the prototype-scale and model-scale geosynthetic-laminated sand columns. The model tests were divided into plane strain and axisymmetric,with rigid column and 5、10 or 20 layers in cross direction of geosynthetic sheets horizontally placed in these model sand columns. Loading tests performed on soft clay, ordinary sand column (OSC) and laminated reinforced sand column (LRSC) were employed to explore the effectiveness of reinforcement and various horizontal spacing. Experimental results showed that horizontally inserted reinforcements improve the bearing capability of the model sand columns. With the more layers of geosynthetic, the stiffening effect tends to be critical.Rigid columns are advantageous when the amount of settlement is very small, but with the increase of settlement easily lead to destruction through；In a large amount of settlement, reinforced sand columns began to develop its value, can allow the columns to moderate swelling also have the bending force of geosynthetics, Making the columns body bundling force increases, the axial force increases. If the full load represents the average pressure of view, geosynthetics to enhance the carrying capacity of the effect is more limited.

In present scenario buildings with floating column is a typical feature in the modern multistory construction in urban India. Such features are highly undesirable in building built in seismically active areas. This study highlights the importance of explicitly recognizing the presence of the floating column in the analysis of building. Alternate measures, involving stiffness balance of the first storey and the storey above, are proposed to reduce the irregularity introduced by the floating columns. FEM codes are developed for 2D multi storey frames with and without floating column to study the responses of the structure under different earthquake excitation having different frequency content keeping the PGA and time duration factor constant. The time history of floor displacement, inter storey drift, base shear, overturning moment are computed for both the frames with and without floating column.

碩士
國立臺灣海洋大學
河海工程學系
97
Abstract A numerical model was developed by usage of Boundary Element Method in this study to analyze the characteristics of floating body’s motion which has the equipment of the tuned liquid column damper. Theoretic analysis is based on linear wave theory and assumes the body moving with a synchronous small amplitude of waves. The tuned liquid column damper is assumed to have a contant dimension and set up inner the floating structure. Coupling with three freedoms motion of floating body, the motion of liquid surface was gotten by means of momentum conservation of the tuned liquid column damper. After neglected higher order terms and lineaized the second order terms and associated with the dynamic condition of floating structure, amplitude of damper and floating body’s motion will be gotten. Discussions were focusedon the influences of damper for floating body’s motion. The parameters of damper, such as width, vertical height and horitional length of liquid column were discussed one by one. It was found that motion of structures will be similar to free floating body if the width of damper approchs to zero. When the floating body was influence by the tuned liquid column damper then the second resonant frequency should be induced. It is showed that the influential phenomenon of the liquid is more significant, the peak of the first resonant frequency has a tender to the long period and the peak of the second resonant frequency will to the short period. The phenomenon is caused by the natural frequency of tuned liquid column damper has transformed, the relationship between the natural frequency of the floating body and the wave frequency was influenced further, and the relationship between the natural frequency of the floating body and the natural frequency of tuned liquid column damper, too. Keywords: floating structure, Boundary Element Method, tuned liquid column damper, amplitude, resonant frequency.

The increasing population density and the industrial expansion significantly affect the availability of land. In this context, the high modularity of Very Large Floating Structures (VLFSs) may indeed represent a promising alternative for multipurpose use. Furthermore, the interest for the sea as a source of renewable marine energy, particularly for wave energy, has tremendously increased in the last decade and years. Among the large diversity of Wave Energy Converters (WECs), the Oscillating Water Column (OWC) is one of the most promising concept. Moreover, when an OWC is incorporated in a VLFS, its efficiency in terms of wave energy absorption is not only increased, but also it has additionally the benefit of attenuating the heave motion of the floating structure. Hence, there is a growing interest in the development of an innovative VLFS equipped with OWC devices. In this scope, the mitigating effect of the OWC on the heave motion of the VLFS can be combined with an increased efficiency of the OWC, thus better contributing to supply energy for the facilities located on the floating system. The main goal of this PhD research is the investigation of a VLFS-OWC System conceived for a hypothetical installation in a Mediterranean area, characterized by a moderate wave climate. For this purpose, small-scale experiments have been carried out in the wave-current flume of the Maritime Engineering Laboratory (LABIMA) of Florence University. The laboratory tests focused on the effect of: (i) the OWC design parameters (i.e., OWC geometry); (ii) the incident wave conditions (i.e., regular and irregular wave trains); (iii) the damping induced by a non-linear air turbine (i.e., a self-rectifying impulse turbine) idealised by vents with different diameters in the OWC chamber roof; (iv) the length and the heave motion of the VLFS on the performance of the OWC, including the attenuating effect of the incorporated OWC on the heave motion of the VLFS-OWC system. The design of the fixed OWC, VLFS and VLFS-OWC models as well as the testing programme and laboratory procedures, are based on an extensive literature review of the available numerical and physical models on OWC devices and VLFS technologies. The main findings of this study may be summarized as follows: - the most dominant parameters affecting the performance of a fixed OWC are the chamber width (in wave propagation direction), the front wall draught and the damping induced by the air turbine; - the additional parameters affecting the efficiency of an OWC integrated in a VLFS are the length of the structure and the heave motion; - formulae are developed for predicting the heave motion of the VLFS-OWC system respectively, for regular waves and irregular waves; - formulae are developed for improving the prediction of the performance of a fixed OWC for a floating OWC (integrated in a VLFS) respectively, for regular irregular waves. These findings have contributed to improve the understanding of the functioning of the OWC device and the relative importance of the aforementioned parameters affecting the device under moderate wave climate.

This research was performed with a focus on two key aspects of energy cost–reduction for offshore OWC devices; improving the power extraction efficiency and reducing the excess margin in structural safety factors by a better understanding of wave–induced loads on these devices. This study utilised information from three different resources. First, 2D and 3D numerical results from fully nonlinear Computational Fluid Dynamics (CFD) simulations performed using the commercial code STAR–CCM+ that was validated in good agreement with physical scale model measurements at each stage of increasing complexity during this research. Second, published experiments in the literature for 2D OWC devices subjected to unidirectional regular waves to validate the 2D CFD models of this study. Third, experiments conducted in the towing tank of the Australian Maritime College (AMC) for 3D offshore stationary and floating–moored OWC devices (at a model–scale of 1:50) subjected to unidirectional regular and irregular waves. These experiments were designed to (1) compare the hydrodynamic performance of both devices, (2) estimate wave–induced loads on the fixed device during operating conditions, (3) investigate the survivability of the floating–moored device with intact and damaged mooring systems and (4) validate the 3D CFD models of this study. Using the combined CFD and experimental approach, it was found that optimizing the underwater geometry of an offshore stationary OWC device could significantly improve the power extraction efficiency up to 0.97. However, this efficiency could be reduced due to air compressibility effects at full–scale. The surge motion of the floating–moored device improved device efficiency in regular and irregular waves. Furthermore, the effectiveness of deploying offshore OWC devices in deep–water where waves are more energetic was proven by increasing the extracted pneumatic energy by a maximum of about 7.7 times when wave height was doubled (incident wave energy increased four times). The instantaneous position of the floating–moored OWC device and its interactions with a certain wave train was more important than the maximum wave height in an irregular sea state when assessing device survivability. Survivability with a damaged mooring system was the key analysis for mooring design. For this analysis, using an equivalent design regular wave condition along with the current safety factors recommended for offshore oil and gas platforms was found to over–design the mooring system of the floating OWC device. The good agreement between CFD experiments for survivability analysis with intact and damaged mooring systems in regular waves highlighted that CFD is a very promising tool a designer can employ to investigate and assess device survivability under different conditions upon further validations in irregular waves.