Circumferential winding

This section is devoted to the definition of the vessel dimension as long as the material properties. Typically, the dimension of the prototypes which are mannfactnred in onr Laboratory is a 1 litre bottle of 250 mm long for a 75.3 mm inside diameter. The thickness of the aluminium liner is 1.85 mm and the thickness of each layer of the laminate is 0.27 mm. The stacking sequence of the laminate is the following [+30] + [+50]4 + [90]3. This sequence means the liner is reinforced with 13 layers of composite 2 layers with a 30° angle, 8 layers with a 50° angle and finally 3 layers with a circumferential winding. 

The primary classes of FW are hoop, polar, and helical. The simplest is hoop or circumferential winding, in which fibers are wound approximately normal to the mandrel axis of rotation with the fiber payout head advancing one band width for each revolution of the spindle. Hoop winding is usually combined with helical winding in more complex parts. Polar or tumble machines are used for parts wound using a planar winding path (such as for a short closed-end pressure vessel). These machines normally have the mandrel mounted vertically, over which a rotating arm wraps fiber onto the mandrel. 

In the tumble-type winder (Fig. 22), the mandrel is tumbled end over end during a polar wind, whereas the feed eye is traversed and the mandrel rotated in the normal lathe-type fashion for helical or circumferential winds. This type is widely used for high volume commercial products such as water-softener tanks and pool filter tanks. 

This paper discusses the impact of wind action on natural-draft cooling towers. The structure of the wind load may be divided into a static, a quasistatic, and a resonant part. The effect of surface roughness of the shell and of wind profile on the static load is discussed. The quasistatic load may be described by the variance of the pressure fluctuations and their circumferential and meridional correlations. The high-frequency end of the pressure spectra and of the coherence functions are used for the analysis of the resonant response. It is shown that the resonant response is small even for very high towers, however, it increases linearly with wind velocity. Equivalent static loads may be defined using appropriate gust-response factors. These loads produce an approximation of the behavior of the structure and in general are accurate. 11 refs, cited. 

Wind, seismic and vibrational stresses and accumulated dead weight compression loadings primarily affect the axial stress and produce only a small effect as a result of Poisson s relationship on the circumferential stress. Therefore, the shell thickness of the upper portion of a tall vertical vessel designed to operate under either internal pressure or vacuum is determined by the circumferential stress. 

We will now consider the special problems in tall tower design which are not described in the ASME Code for Unfired Pressure Vessels. As discussed previously, circumferential stresses control the design of cylindrical vessels if external loads are of small magnitude. In tall vertical vessels, four major factors (wind load, seismic loads, dead weight and vibration) may contribute to axial stresses — in addition to axial stress produced by the operating pressure or vacuum of the vessel. 

Fl = longitudinal force due to wind, seismic, expansion, contraction, etc., lb Ft = transverse force, wind or seismic, lb CTx = longitudinal stress, internal pressure, psi = circumferential stress, internal pressure, psi CT,. = longitudinal stress, external pressure, psi CTs = circumferential stress in stiffening ring, psi <7h = latitudinal stress in head due to internal pressure, psi... 

In the application of bidirectional patterns, the end domes can be formed by fibers that are laid down in polar winding patterns. The best geometrical shape of the dome is an oblated hemispheroid. Theoretically, the allowable stress level in the two perpendicular directions should be identical. However, the efficiency of the longitudinal fibers is less than that of the circumferential fibers. It is possible to estimate an optimum or length-to-diameter ratio of a cylindrical case for a given volume. 

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