Building And Analysis Of Dynamic Model For Windthrow Of Spruce

Windthrow means the stem damage and uproot of trees, it's a common nature disaster after the wind balefulness in forest. The major factors to affect windthrow contain the biologic mechanical attribute of tree, the mutual action of soil and base, disturbance of wind and so on. The biologic mechanical attribute of tree is relative with age of tree, intensity of stem, shape and size of stem and crown of tree, and the health of tree; the mutual action of soil and base is affected by shear intensity,soil humidity,deep of base, and above two factors determined the resistance to wind of tree. The disturbance of wind mainly means the variety of speed and frequency of wind, and it's affected by forest density and the distribution of wind field under complex landform.In the paper, an appreciative mechanical model has been given and analyzed under the consideration of the shape of the spruce. First the spruce is described as a stretch staff whose cross section varies following the height in an exponential order, one end is fixed and the other is free which connects with a mass. Then the free vibration of the staff at the vertical position is analyzed, the frequency character is given and it's just the appreciative frequency character of the spruce. Upon the base of the frequency of vibration, change the coefficient of the cross section of the trunk of spruce and the mass of the crown of a tree (the mass connected to the free end), consider the effect of the external conditions and the self character to the vibration frequency of the system. In this part , the paper pay more attention on the vibration character of the stretch staff with variational cross section and a mass on the free end , and these were rarely discussed in other papers in the past.Then the paper analyzes the responses of the forced vibration under the considerations of the nature growth and the load of wind. Depending on the general solution of the vibration of system given in the front, considerate that the nature wind is always in a gust form, model the load of wind on the canopy and trunk of tree as a impulse load on the free end of the staff, and gets the responses of vibration under these conditions, then picture the curve of the vibration. The nature vibration frequency can be get by analyzing the curve of the staff, and...