Air Density

The most accurate value of air density is obtained by a calculation based on the equation using measured atmospheric parameters approved by the International Committee for Weights and Measures in 1981. When a 1-kg steel weight was calibrated against the prototype kilogram using the international expression for determining the density of air, experimental results showed that the estimated uncertainty of the air density was 1.45x10 -4 mg.cm -3 and the uncertainty of air buoyancy was 11.3 µg.

This paper provides realistic values of wind shear coefficients calculated using measured values of wind speed at 20, 30 and 40 m above the ground for the first time in Saudi Arabia in particular and, to the best of the authorsÕ knowledge, in the Gulf region in general. The paper also presents air density values calculated using the measured air temperature and surface pressure and the effects of wind shear factor on energy production from wind machines of different sizes. The measured data used in the study covered a period of almost three years between June 17, 1995 and December 1998. An overall mean value of wind shear coefficient of 0.194 can be used with confidence to calculate the wind speed at different heights if measured values are known at one height. The study showed that the wind shear coefficient is significantly influenced by seasonal and diurnal changes. Hence, for precise estimations of wind speed at a height, both monthly or seasonal and hourly or night time and day time average values of wind shear coefficient must be used. It is suggested that the wind shear coefficients must be calculated either (i) using long term average values of wind speed at different heights or (ii) using those half hourly mean values of wind speed for which the wind shear coefficient lies in the range P0 and 60.51. The air density, calculated using measured temperature and pressure was found to be 1.18 kg/m 3. The air density values were also found to vary with the season of the year and hour of the day, and hence, care must be taken when precise calculations are to be made. The air density values, as shown in this paper, have no significant variation with height. The energy production analysis showed that the actual wind shear coefficient presented in this paper produced 6% more

In this paper, wind shear coefficient has been determined and analyzed at coastal wind sites of Bangladesh. For searching the wind energy for scale up contribution to renewable energy in rural, pre-urban and urban areas some research work has been done. This is in line with the proposed renewable energy policy of Bangladesh targeting on solar-wind hybrids power generation by renewable energy to meet 5% of the total power demand by 2015. In this work, considering a coastal wind site such as Kuakata where wind shear coefficient has been determined and the effect of wind shear on velocity profile has been analyzed. It is evident that the heating and cooling cycle of the air adjacent to the earth during 24 h of the day influences the wind shear coefficients. During early hours of the day i.e. between 00:00 and 07:00 h, higher and almost constant values of α 1 , α 2 and α 3 were observed while from 07:00 h onwards, as heating of the ground surface and the air above it took place, these values started decreasing and after reaching a minimum at 09:00 h remained almost constant up to 18:00 h for α 2. But at 12:00 h the wind shear coefficient becomes minimum both α 1 and α 3. After 16:30 h, the values of α 1 and α 3 again started increasing and after reaching a maximum at 21:00 h showed a decreasing pattern during rest of the night hours, which may be accounted for cooling of the ground surface and the air above it.

The aeroclynamie friction between air and sea is an important part of the momentum balance in the development of tropical cyclones. Measurements of the clrag eoef/ïcient, relating the tangential stress (frictional drag) betwccn wincl ancl water to the wind speed ancl air clensity, have yieldccl rcliable information in wincl speeds less than 20 mis (about 39 Imots). ln these moclerate conclitions it is generally acceptecl that the clrag coeffïeient (or equivalently, the "aeroclynamic roughness") increases with the wincl spcccl. Can one merely extrapolate this wincl speecl tenclency to clescribe the aeroclynamic roughness of the ocean in the extreme wind speecls that OCCLU' in hurricanes (wincl speeds greater than 30 mis)? This paper attempts to answer this question, guicled by laboratory extreme wind experiments, and eoncludes that the aeroclynamic roughness approaches a limiting value in high wincls. A nuidmechanical explanation of this phenomenon is given.

The most accurate value of air density is obtained by a calculation based on the equation using measured atmospheric parameters approved by the International Committee for Weights and Measures in 1981. When a 1-kg steel weight was calibrated against the prototype kilogram using the international expression for determining the density of air, experimental results showed that the estimated uncertainty of the air density was 1.45x10 −4 mg.cm −3 and the uncertainty of air buoyancy was 11.3 µg.

This paper provides realistic values of wind shear coefficients calculated using measured values of wind speed at 20, 30 and 40 m above the ground for the first time in Saudi Arabia in particular and, to the best of the authorsÕ knowledge, in the Gulf region in general. The paper also presents air density values calculated using the measured air temperature and surface pressure and the effects of wind shear factor on energy production from wind machines of different sizes. The measured data used in the study covered a period of almost three years between June 17, 1995 and December 1998. An overall mean value of wind shear coefficient of 0.194 can be used with confidence to calculate the wind speed at different heights if measured values are known at one height. The study showed that the wind shear coefficient is significantly influenced by seasonal and diurnal changes. Hence, for precise estimations of wind speed at a height, both monthly or seasonal and hourly or night time and day time average values of wind shear coefficient must be used. It is suggested that the wind shear coefficients must be calculated either (i) using long term average values of wind speed at different heights or (ii) using those half hourly mean values of wind speed for which the wind shear coefficient lies in the range P0 and 60.51. The air density, calculated using measured temperature and pressure was found to be 1.18 kg/m 3 . The air density values were also found to vary with the season of the year and hour of the day, and hence, care must be taken when precise calculations are to be made. The air density values, as shown in this paper, have no significant variation with height. The energy production analysis showed that the actual wind shear coefficient presented in this paper produced 6% more

This paper provides realistic values of wind shear coefficients calculated using measured values of wind speed at 20, 30 and 40 m above the ground for the first time in Saudi Arabia in particular and, to the best of the authorsÕ knowledge, in the Gulf region in general. The paper also presents air density values calculated using the measured air temperature and surface pressure and the effects of wind shear factor on energy production from wind machines of different sizes. The measured data used in the study covered a period of almost three years between June 17, 1995 and December 1998. An overall mean value of wind shear coefficient of 0.194 can be used with confidence to calculate the wind speed at different heights if measured values are known at one height. The study showed that the wind shear coefficient is significantly influenced by seasonal and diurnal changes. Hence, for precise estimations of wind speed at a height, both monthly or seasonal and hourly or night time and day time average values of wind shear coefficient must be used. It is suggested that the wind shear coefficients must be calculated either (i) using long term average values of wind speed at different heights or (ii) using those half hourly mean values of wind speed for which the wind shear coefficient lies in the range P0 and 60.51. The air density, calculated using measured temperature and pressure was found to be 1.18 kg/m 3. The air density values were also found to vary with the season of the year and hour of the day, and hence, care must be taken when precise calculations are to be made. The air density values, as shown in this paper, have no significant variation with height. The energy production analysis showed that the actual wind shear coefficient presented in this paper produced 6% more

This paper provides realistic values of wind shear coefficients calculated using measured values of wind speed at 20, 30 and 40 m above the ground for the first time in Saudi Arabia in particular and, to the best of the authorsÕ knowledge, in the Gulf region in general. The paper also presents air density values calculated using the measured air temperature and surface pressure and the effects of wind shear factor on energy production from wind machines of different sizes. The measured data used in the study covered a period of almost three years between June 17, 1995 and December 1998. An overall mean value of wind shear coefficient of 0.194 can be used with confidence to calculate the wind speed at different heights if measured values are known at one height. The study showed that the wind shear coefficient is significantly influenced by seasonal and diurnal changes. Hence, for precise estimations of wind speed at a height, both monthly or seasonal and hourly or night time and day time average values of wind shear coefficient must be used. It is suggested that the wind shear coefficients must be calculated either (i) using long term average values of wind speed at different heights or (ii) using those half hourly mean values of wind speed for which the wind shear coefficient lies in the range P0 and 60.51. The air density, calculated using measured temperature and pressure was found to be 1.18 kg/m 3. The air density values were also found to vary with the season of the year and hour of the day, and hence, care must be taken when precise calculations are to be made. The air density values, as shown in this paper, have no significant variation with height. The energy production analysis showed that the actual wind shear coefficient presented in this paper produced 6% more

SUMMARYThe alpine environment is likely to challenge insect locomotion because of low mean temperatures and reduced barometric pressure. In this study, we measured the direct and interactive effects of these factors on walking and flight performance of wild-caught Drosophila melanogaster Meigen. We found that decreased temperature and decreased air pressure both reduced walking speed and flight performance. Flies walked more slowly at 18°C and in the lowest air pressure treatment (34 kPa). This treatment, equivalent in air pressure to the top of Mount Everest, was the only air pressure that significantly reduced fly walking speed. Therefore, walking performance in the wild is likely limited by temperature, but not oxygen availability. In contrast to walking performance, low but ecologically realistic air pressures dramatically reduced overall flight performance. The effects of reduced air pressure on flight performance were more pronounced at colder temperatures. Reduced flight perf...

Conditions are considered of inception of DC corona discharges in air near spherical and cylindrical anodes. The parameter K (ionization integral) in the standard discharge inception criterion is evaluated for a wide range of electrode radii and air densities.