Normal Wind Conditions Research Articles

Oceanographic conditions in the sandsfjord system, western Norway, after a bloom of the toxic prymnesiophytePrymnesium parvumcarter in August 1990

Abstract As in 1989 the algal bloom was toxic and mortal to Atlantic salmon and rainbow trout in fish-farms. The brachish layer, with salinities between 5 and 25 ‰ was characterized by a high N : P ratio reflecting the low phosphate content in the freshwater supplied to the fjord system. An overflow discharge of freshwater close to the power plarit-at Hyfen created a vigorous ‘upwelling’ and dominated the hydrographical conditions in Hylsfjorden and Sandfjorden during the bloom. As a result a compensation current in Hylsfjorden was created resulting in a prolonged residual time in the upper 1–2 m, where most of the P. parvum was observed. The entrainment of seawater into the brackish layer at Hylen was about four times greater than that under normal wind conditions in the fjord system. The calculated nitrate consumption in the fjord system was about 2 800 kg day-1 and compared well with the measured in situ production of about 900 mgC m-2 day-1. The supply of phosphate from fresh and seawater into the brackish layer could only support about 20 % of the theoretical normal phosphate requirements for phytoplankton growth. As in 1989 there was a close relationship between the start of the freshwater discharge, the associated upwelling at Hylen and the time of onset of a pelagical phase of the P. parvum bloom. It is suggested that the low salinity conditions, the prolonged residence time in the surface layer and the artifical ‘upwelling’ in Hylsfjorden set the stage for the bloom. The high N : P ratio and the associated phosphate limitation, probably played a major role in causing P. pMVum to become toxic.

Interference excitation of twin tall buildings

The enhanced dynamic response of a tall square building under interference excitation from neighbouring tall buildings has been studied in a series of wind-tunnel model tests. In a low-turbulence wind environment and under normal strong wind conditions, the dynamic loads on the upstream of an identical pair of tall buildings may increase by a factor of up to 4.4. The dynamic loads on the downstream building of the pair may increase by a factor of up to 3.2 due to “resonant buffeting”. Measurements of along-wind and cross-wind force spectra and a number of wake spectra provide an explanation for the observed behaviour. Possible excitation mechanisms are discussed and critical building arrangements presented. The large interference loads found in this study indicate that interference excitation should be carefully considered in the design of tall buildings.

Self-regulating composite bearingless wind turbine

The Composite Bearingless Rotor (CBR) concept has been shown to have characteristics ideally suited for wind turbine applications. Originally developed for helicopters to reduce weight, costs and complexity, the CBR eliminates blade bearings and hinges through the utilization of the unique structural characteristics of uniaxial composite materials. This rotor concept was further developed under an ERDA contract to provide a fully self-regulating and self-aligning wind turbine. Such a system was achieved without the need for auxiliary controls or sensors. These features allow self-starting for wind initiating from any direction and automatic pitch and yaw variations to optimize performance under all normal wind conditions. The work described in this report consists of the design and fabrication of a 4.5 ft dynamically scaled wind turbine model and the successful testing of this model in the United Technologies Research Center low speed wind tunnel.

Wind response of the Interama Tower of the Sun

The proposed Interama Tower of the Sun is an 830 ft high tower supported by 168 guy cables with a skyhouse located between the 650 and 740 ft levels. The tower was to be located approximately 5 miles north of Miami, Florida. The site is flat open land, only a few feet above sea level, located a short distance inland from the seacoast—sufficiently close that no reduction in hurricane wind magnitude due to landfall can be allowed. A study was undertaken to determine overall loads and local pressures by means of wind-tunnel tests, and to determine the dynamic response of the tower to wind loads by means of computer simulation. Wind-tunnel modeling was used to obtain overall wind loading on the tower, to investigate possible vortex shedding phenomena, and to obtain local pressures on the skyhouse and legs. The computer simulation used to determine dynamic response modeled primary structural components of the tower as well as the guy cables, the latter introducing geometric nonlinearity into the model. Appropriate beam-column and cable elements were utilized to represent the structure, with wind loading being considered on all elements. Primary results are presented in the form of response plots. These indicate relatively minor tower responses for normal wind conditions, but increasing rapidly in the higher wind range of 75–130 mph.