APPLICATION OF TUNED LIQUID DAMPERS TO MITIGATE WIND- INDUCED TORSIONAL MOTION

The tuned liquid damper (TLD) is a proven and an increasingly popular auxiliary device for mitigating the dynamic effects induced by wind loading on tall buildings. During a dynamic loading event, the water inside a TLD will slosh against the end walls of the tank, thereby imparting a force approximately anti-phase to the motion of the building. The current study uses a multi-modal TLD system to reduce the resonant torsional responses of a real high-rise building. The building is sensitive to torsion in the first two vibration modes; therefore, a unique TLD system is designed to damp these two modes by displacing the tanks away from the center of mass of the building. The TLD system is capable of reducing the serviceability responses to an acceptable level. In addition, the current study demonstrates the possible reduction in wind loading experienced by the building. The reduced wind loading leads to a 16.9% reduction in the cost of steel reinforcement in the concrete shear walls. Furthermore, the robustness of the TLD system is evaluated and practical TLD design issues are discussed

APPLICATION OF TUNED LIQUID DAMPERS TO MITIGATE WIND- INDUCED TORSIONAL MOTION

The tuned liquid damper (TLD) is a proven and an increasingly popular auxiliary device for mitigating the dynamic effects induced by wind loading on tall buildings. During a dynamic loading event, the water inside a TLD will slosh against the end walls of the tank, thereby imparting a force approximately anti-phase to the motion of the building. The current study uses a multi-modal TLD system to reduce the resonant torsionalresponsesofarealhigh-risebuilding. Thebuildingissensitivetotorsioninthe first two vibration modes; therefore, a unique TLD system is designed to damp these two modes by displacing the tanks away from the center o f mass o f the building. The TLD system is capable of reducing the serviceability responses to an acceptable level. In addition, the current study demonstrates the possible reduction in wind loading experienced by the building. The reduced wind loading leads to a 16.9% reduction in the cost of steel reinforcement in the concrete shear walls. Furthermore,the robustness of the TLD system is evaluated and practical TLD design issues are discussed

Numerical simulation of low gravity draining

A boundary value problem was solved numerically for a liquid that is assumed to be inviscid and incompressible, having a motion that is irrotational and axisymmetric, and having a constant (5 degrees) solid-liquid contact angle. The avoidance of excessive mesh distortion, encountered with strictly Lagrangian or Eulerian kinematics, was achieved by introducing an auxiliary kinematic velocity field along the free surface in order to vary the trajectories used in integrating the ordinary differential equations simulating the moving boundary. The computation of the velocity potential was based upon a nonuniform triangular mesh which was automatically revised to varying depths to accommodate the motion of the free surface. These methods permitted calculation of draining induced axisymmetric slosh through the many (or fractional) finite amplitude oscillations that can occur depending upon the balance of draining, gravitational, and surface tension forces. Velocity fields, evolution of the free surface with time, and liquid residual volumes were computed for three and one half decades of Weber number and for two Bond numbers, tank fill levels, and drain radii. Comparisons with experimental data are very satisfactory

Switching control systems and their design automation via genetic algorithms

The objective of this work is to provide a simple and effective nonlinear controller. Our strategy involves switching the underlying strategies in order to maintain a robust control. If a disturbance moves the system outside the region of stability or the domain of attraction, it will be guided back onto the desired course by the application of a different control strategy. In the context of switching control, the common types of controller present in the literature are based either on fuzzy logic or sliding mode. Both of them are easy to implement and provide efficient control for non-linear systems, their actions being based on the observed input/output behaviour of the system. In the field of fuzzy logic control (FLC) using error feedback variables there are two main problems. The first is the poor transient response (jerking) encountered by the conventional 2-dimensional rule-base fuzzy PI controller. Secondly, conventional 3-D rule-base fuzzy PID control design is both computationally intensive and suffers from prolonged design times caused by a large dimensional rule-base. The size of the rule base will increase exponentially with the increase of the number of fuzzy sets used for each input decision variable. Hence, a reduced rule-base is needed for the 3-term fuzzy controller. In this thesis a direct implementation method is developed that allows the size of the rule-base to be reduced exponentially without losing the features of the PID structure. This direct implementation method, when applied to the reduced rule-base fuzzy PI controller, gives a good transient response with no jerking

Three-dimensional sloshing in a scaled membrane LNG tank under combined roll and pitch excitations

This paper experimentally investigates the three-dimensional sloshing in a membrane-type LNG (liquefied natural gas) tank under combined roll and pitch excitations. Seven groups of roll and pitch amplitudes are studied. For each group, the roll and pitch have the same frequency, and around ten frequencies are tested in a frequency band that ranges from 0.5 times of the resonance frequency in the length direction of the tank to 1.4 times of the resonance frequency in the tank breadth. The characteristics of the sloshing waves and impact pressures are analysed in detail. It is found that the steady-state sloshing waves can be classified into four patterns: the length-dominant wave, swirling wave, diagonal wave, and breadth-dominant wave. Highlighted is the swirling wave that is observed in most of the cases where the roll and pitch amplitudes are significant and the excitation frequency locates between the resonant frequencies in the two directions. It is hypothesized that the rotational motion of the tank imposes necessary initial conditions to trigger the swirling wave. The swirling wave is always associated with wave impingements at tank corners and induce violent impact pressures. The practical implementation is that reinforcements of the membrane layer should be added or the sloshing wave should be suppressed near the tank corner to mitigate the damages to the interior layer of the membrane-type LNG tank

Three SPH Novel Benchmark Test Cases for free surface flows.

Benchmark Test Cases have been used by SPHERIC interest group members for the validation of SPH models and their corresponding computer implementations. Since the use of SPHERIC benchmark test cases as validation reference for SPH implementations has slightly declined in the most recent editions, we think it might be interesting to document three novel test cases with the aim of enriching the database with complementary validation data. The first proposed test case is a wave impact problem in a rectangular tank. The time history of the motion of the tank and the pressure of the first instances of lateral and roof impacts for both water and oil are provided. An analysis of the two-dimensionality and repeatability of the pressure peaks is provided. The second proposed test case treats the coupling of the angular motion of a sloshing tank and a single degree off reedom structural system. Finally, the third proposed test case, is a canonical fluid structure interaction problem consisting in the interaction between a free surface sloshing flow and an elastic body. As both SPH practitioners and experimentalists, regard less of the discussion provided in this paper, we are committed to improving these test cases for future use. We hope to increase our experimental skills and capabilities not only in light of experience from our own simulations but mainly by receiving a feedback from the SPH communit

Second All-Union Seminar on Hydromechanics and Heat and Mass Exchange in Weightlessness, summaries of reports

Abstracts of reports are given which were presented at the Second All Union Seminar on Hydromechanics and Heat-Mass Transfer in Weightlessness. Topics include: (1) features of crystallization of semiconductor materials under conditions of microacceleration; (2) experimental results of crystallization of solid solutions of CDTE-HGTE under conditions of weightlessness; (3) impurities in crystals cultivated under conditions of weightlessness; and (4) a numerical investigation of the distribution of impurities during guided crystallization of a melt

Nonlinear hydrodynamic modelling of wave energy converters under controlled conditions

One of the major challenges facing modern industrialized countries is the provision of energy: traditional sources, mainly based on fossil fuels, are not only growing scarcer and more expensive, but are also irremediably damaging the environment. Renewable and sustainable energy sources are attractive alternatives that can substantially diversify the energy mix, cut down pollution, and reduce the human footprint on the environment. Ocean energy, including energy generated from the motion of wave, is a tremendous untapped energy resource that could make a decisive contribution to the future supply of clean energy. However, numerous obstacles must be overcome for ocean energy to reach economic viability and compete with other energy sources. Energy can be generated from ocean waves by wave energy converters (WECs). The amount of energy extracted from ocean waves, and therefore the profitability of the extraction, can be increased by optimizing the geometry and the control strategy of the wave energy converter, both of which require mathematical hydrodynamic models that are able to correctly describe the WEC- uid interaction. On the one hand, the accuracy and representativeness of such models have a major in uence on the effectiveness of the WEC design. On the other hand, the computational time required by a model limits its applicability, since many iterations or real-time calculations may be required. Critically, computational time and accuracy are often mutually contrasting features of a mathematical model, so an appropriate compromise should be defined in accordance with the purpose of the model, the device type, and the operational conditions. Linear models, often chosen due to their computational convenience, are likely to be imprecise when a control strategy is implemented in a WEC: under controlled conditions, the motion of the device is exaggerated in order to maximize power absorption, which invalidates the assumption of linearity. The inclusion of nonlinearities in a model is likely to improve the model's accuracy, but increases the computational burden. Therefore, the objective is to define a parsimonious model, in which only relevant nonlinearities are modelled in order to obtain an appropriate compromise between accuracy and computational time. In addition to presenting a wider discussion of nonlinear hydrodynamic modelling for WECs, this thesis contributes the development of a computationally efficient nonlinear hydrodynamic model for axisymmetric WEC devices, from one to six degrees of freedom, based on a novel approach to the nonlinear computation of static and dynamic Froude-Krylov forces