A Study Of Wind Powered Turbine Generation

CHAPTER FOUR
DESIGN SPECIFICATION FOR WIND TURBINE
4.0    STRENGTH CALCULATION FOR STRUCTURAL ANALYSIS & SAFETY
It is usually the common practice in Engineering field to have prior knowledge of the properties of the materials that will be used in a design so that the design could be carried out with the awareness of the materials properties. With such prior knowledge adequate provision could be made to compensate the inadequacies of the material available for use in design.
It is in the light of the above that the strength calculation of these materials must be done before and during the fabrication process. The most important test will be the strength of wood/aluminum airfoils under centrifugal load as flying broken pieces of airfoils are not welcomed especially in wind tunnel. The airfoils model can be fabricated using either solid woods or aluminum sheets with spar and rib.
Having a wind turbine test model as basic of my estimates and calculation these strength calculation/estimates can be sub-divided into.
different section as;
i)    Airfoil bending stress
ii)    Bolt tension at Airfoil joint and washed pressure
iii)    Support arm vibration and deflection
iv)    Shaft bending stress and vibration
v)    Bearing size selection
vi)    Pipe bending stress and vibration
i)    Airfoil Bending Stress:
Hear two main loads on the airfoils are the centrifugal force and the aerodynamic drop force. The rough comparison of these forces shows that the aerodynamic forces are small compared to the centrifugal force for the mode material, solidity and operating speed. The strength property of the wood airfoils will be supported at the centre so the centrifugal forces will cause highest stress at the centre where the airfoils join the support arm. To test the airfoil strength both sides of the airfoil will be loaded with dumbell weights and it will be lifted off the ground by holding the center of the airfoils. Note that stress concentration is definitely lower when balancing using hand instead of the actual support.
Aerodynamic force comparism to centrifugal force on the air force is thus

ii)    Bolt Tension at airfoil joint and washer pressure
Here each airfoil is to be supported by 4 bolts with pairs of nuts which clamp the wood airfoil. This bolts and nuts joint will further be tightened by using spring and plate washer. The plate washer will hopefully distribute the stress to a wider area of the wood.
Calculation on the tension in the bolts caused mainly by an assumed airfoil imbalance and partly by centrifugal forces showed sufficient strength.
The wood will probably be dented in after some time of fast rotation and repeating assembling/disassembling.
Bolt tension due to centrifugal Force