Air Lake Research Articles

Effect of stress waveform and hold-time on environmentally assisted fatigue crack propagation inC-Mn structural steel

AbstractFatigue crack propagation rates were measured in a carbon-manganese structural steel in laboratory air, distilled water, and natural lake water over a wide range of testing frequencies with triangular waveforms at low values of stress ratio R. The aqueous environments were found to increase the crack propagation rates over the values measured in air by up to a factor of 7, but the degree of enhancement was found to be frequency dependent. Waveforms with a very fast rise-time such as negative sawtooth or square wave did not lead to environmental enhancement of fatigue crack propagation rates. In addition, extended hold periods of up to 600 s at the maximum stress of the fatigue cycle did not affect fatigue crack growth for the conditions studied. Growth rates increased with increasing water temperature over the range 25–85°C, with an apparent activation enthalpy of 19.2 kJ mol−1 (4.6 kcal g−1 mol−1).

Cold Air Lake in an Orange Orchard opened in a Reclaimed Salt-field in Urato, Ehime Prefecture

Cold Air Lake in an Orange Orchard opened in a Reclaimed Salt-field in Urato, Ehime Prefecture

An Example of the Formation of Gold Air Lake

It is generally believed that at clam nights cold air drainage flows downslope forming cold air lakes at the bottom of the slopes. In this survey, the air temperature, the speed and direction of the wind were measured 50 cm above the ground on the s1Ope of Sugadaira Plateau (Fig. 1) in Nagano from Oct. 31 to Nov. 1, 1969. Results are illsutrated in Fig. 2, 3, 4.We tried to recognzie the pass of cold air drainage in three manners:1) The change of wind direction when cold air drainage passes.2) The low temperature for shrot time and the high value of the standard deviation f the temperature.3) We assumed that the air temperature rises suddenly after cold air drainage passes. But the results attained did not agree with these hypotheses, for1) the wind speed is too slow to recognzie the pass of cold air drainage, 2) the high values of the standard deviation are releated to the rise of the air temperature and3) the rise of air temperature is reasonably explained by sensible and latent heat. Cold air lake is expanded and confirmed as time passes at St. 5 and 4 (Fig. 2). It may be said that cold air lake is formed without cold air drainage. The formation of cold air lake is thought as follows:At night there is a net loss of heat by radiation. Radiation flux divergence is a major cause of air cooling and the rate is equal in the forest and outside the forest. In the forest no wind blew, and outside the forest wind blew all night (Fig. 4). The eddy transfer component must be greater outside the forest than in the forest. So it gets cooler relatively in the forest.

Temperature distribution under radiation frost conditions in a central Pennsylvania valley

Air temperatures, measured with vehicle-mounted thermistor thermometers, are presented for traverses across a broad Pennsylvania valley under radiation frost conditions. The temperature range observed over the breath of the valley on clear, calm mornings was often as much as 10°C or 18°F. Comparisons of the temperature distributions between mornings indicated that the patterns were quite similar under cool, calm and clear conditions. This was interpreted as justification for a radiation frost condition category. Most of the variation in air temperature could be explained by the relative elevation above the bottom of the basin confining the cold air lake. A mean change in temperature of +6.2°C per 100 m change in relative elevation (or +3.4°F/100 ft.) was found to exist near dawn under calm and clear conditions. This value is suggested for approximating the relative frost danger from contour maps of similar valleys in which the distribution of temperature is unknown.

Distribution Patterns of Mandarin Orchards and Local Climates Along the River Okitsu, Shizuoka Prefecture

Predominance of mandarin orchards and tea gardens is a typical landscape on the Pacific coast of Shizuoka Prefecture. They are distributed not only on the climatically advantageous coastal strips but also some distance inland along river valleys where climatic conditions are less favourable. Mandarin having economical advantages over tea in recent years, there has been a tendency that mandarin orchards replace tea gardens, or even paddy fields in this region.A distinct contrast in the distribution patterns of mandarin orchards and tea gardens can be observed along the River Okitsu within a relatively short distance. The valley, only 20 kilometers in length, can be divided by the presence of a narrow gorge in the halfway into the upper and the lower parts (Fig. 1). The lower part is characterized by predominance of mandarin orchards. They cover the greater parts of the sunny side of the mountain slopes and the valley floors as well, although the floor has only recently been turned into mandarin from paddy fields. Tea gardens are found only on the windswept ridges. On the contrary, the upper part of the valley is quite dissimilar in that mandarin orchards are concentrated to the height of 200400 meters above sea level and tea gardens are distributed both on the ridges and on the lower parts of the slopes (Fig. 2 and Photo 1). There seems to be no such tendency for the tea gardens in the valley bottom to be replaced by mandarin.This areal difference in landscape is expected to be accounted for, at least partly, by the different local climatic conditions. Two of the students of Tokyo Metropolitan University, S. TAKABAYASHI and H. KITAJIMA, conducted some meteorological observations along the valley and reported the results in manuscript forms. The authors try to supplement their works and to make a further discussion in this paper.The observations were made mostly during the nighttime in different seasons. Bimetal thermographs and mercury minimum thermometers were installed at different heights (ranging from 90 meters at the valley bottom to 400 meters at the top) of the slopes, and simultaneous temperature observations were carried out at some 20 localities with the help of high school pupils and university students. In addition, moving observations was conducted by using a thermister thermometer installed on a car.Temperature inversion was commonly observed on clear nights in the colder seasons both in the upper and the lower parts of the valley, whereas it seems to be absent in summer. Particularly in winter the temperature difference between the valley bottom and the upper part of the slope (relative height being 250 meters) may reach 4.0°C or even greater (Fig. 3 and 4). The top of the inversion was not ascertained by the observations, but the ridge appear to be cooler irrespective of the altitudes.There was no significant difference in the intensity of the inversion between the upper and the lower parts of the valley. Presence of temperature inversions itself does not explain the difference of the mandarin distribution. The explanation seems to lie in the fact that there is a remarkable difference in temperature. Many of the simultaneous observations revealed that there is a greater temperature gradient near the boundary between the upper and the lower parts of the valley (Fig. 5). In other words, the valley bottom of the lower part is much less frequently exposed to low temperatures. On the contrary, the upper valley is filled up with cold air, which is not easily drained out to the downstream. Consequently a typical cold air lake results, and the valley bottom there is subject to extremely low temperature.