Non-supercell tornadoes frequently occur on the gust fronts of cold outflows intruding to environmental flow. It is quite difficult to predict the genesis of such tornadoes because the generations of parent cumulonimbi and cold outflows are not represented by ordinal environmental indices. Therefore, we need to establish new indices to represent non-supercell tornado genesis. The present laboratory experiment aims to clarify the environment of non- supercell tornadoes which are generated on gust front of cold outflow intruding environmental flow. We reproduced such flow situation by using a cold outflow simulator and an environmental flow simulator. In the present experiment, we set the cold outflow simulator at 30 deg. in attack angle. We made stereo dynamic PIV and measured 3-D velocity field on the horizontal plane. The results showed that the rotating direction of tornado-like vortices was changed with velocities of the cold outflow and the environmental flow. A counter-rotating vortex pair was observed to generated by tilting. The tornado-like vortices are also found to have the downdraft region partially.
近年報告される竜巻等の突風による被害調査をみると，過大な風圧力による構造骨組や部材，屋根ふき材，外装材の損傷とともに，飛来物による外装材，建具等への被害が数多く報告されている。外装材の耐衝撃性能については，ASTM E 1996-4， ISO16932等に加撃体の条件や試験方法が規定されており，日本でも災害拠点建築物に対して，河井らによる飛来物対策評価法が提案されている。これらの飛来物による影響は衝撃試験によることが多く，2×4角材等を飛来物の代表として，外装材などの対象物に高速で衝突させる衝撃実験が工夫されている。また，原子力発電施設のような重要構造物では飛来物の影響評価が求められており，衝撃試験が行われている。衝撃試験に際して，加撃体射出速度をコントロールするためには加撃体発射に用いる空気タンクの空気圧と射出速度の関係が既知である必要があるが，これまでの衝撃試験では，本試験前に予備実験を実施して，加撃体毎に経験式を求める必要があった。本研究では，衝撃試験装置を開発し，合わせガラスとアルミサッシ試験体への衝撃試験を試みた。特に，衝撃試験に先立って実施される加撃体の衝撃速度の調整に必要な予測式を導出し提案した。
An extended theoretical approach is proposed to predict the average power of wind turbines in a large finite-size wind farm. The approach is based on the two-scale momentum theory proposed recently for the modelling of ideal very large wind farms, but the theory is now generalised by introducing the effect of additional pressure difference induced by the farm between the upstream and downstream sides of the farm, making the approach applicable to real wind farms that are large but not as large as the size of the relevant atmospheric system driving the flow over the farm. To validate the generalised theoretical model, 3D Reynolds-averaged Navier-Stokes simulations of boundary layer flow over a large array (25 x 25) of actuator (drag) discs are conducted at eight different conditions. The results suggest that the generalised model could be embedded in a regional-scale atmospheric model to predict the average power of a given wind farm effectively. This approach may also be combined with the blade element momentum (BEM) theory for coupled wind turbine/farm optimisation.
In this study, a control logic of wind turbines by using fuzzy function is proposed and the effect of control logic on the power performance and the load on supporting structure is investigated. By using proposed control logic which uses fuzzy function and use the gain values calculated by loop shaping, the fluctuation of the rotor speed can be reduced. By adding additional loop from acceleration of the nacelle is introduced and it is shown that this method can effectively add additional damping and resulting damage equivalent fatigue load of the tower base moment is reduced while the other fatigue load does not increase. This indicates that the tower acceleration feedback is a effective tool to reduce tower load.
Motivated by occasional difficulties to install anemometers with fixed towers, the present study aims at developing a way for measuring wind speed with anemometers attached to moving or unstable objects such as tree tops or captive balloons. The objective of this paper is to propose a way to estimate wind speed relative to ground based on the posture and motion as well as wind speed identified and measured by sensors and moving anemometers. The proposed way consists of (1) correction of anemometer output, (2) motion and posture identification by sensor fusion and (3) summation of corrected wind speed vector and motion vector as estimate of wind speed relative to ground. The performance of the proposed way is investigated through a simple case where a hotwire anemometer is attached to a frame under pendulum motion. The result of the investigation suggests that the proposed way can work well.