134
L. Chen et al.
Fig. 1. 3D model of the femur
falls in the elderly, femoral (Fig. 1) intertrochanteric fractures or femoral neck fractures
account for more than 80% [8, 9].
According to relevant documents [10, 11], the airbag was designed to cover 95%
users aged from 36 to 60. Also, airbag should cover the complete hip and main possible
damage area. Considering the factor of the volume of air in the inflatable cylinder, the
diameter of the air bag is 22.5 cm and the material is nylon 66 (Fig. 2).
Fig. 2. 3D model of the airbag
3 Finite Element Analysis of Fall Protection with the Airbag
In this paper, the dynamic explicit nonlinear algorithm is used for the finite element
analysis of human falling:
M ¨
u = P − I
(1)
Where, Matrix is represented by M, node acceleration matrix is represented by ¨
u,
gravity is represented by P, internal force matrix is represented by I. The acceleration of
incremental step at time t is:
¨
u| (t) = (M)
−1
· (P−I)| (t)
(2)
The central difference method is used to integrate the acceleration in time:
˙
u| (t+
t
2 ) = ˙
u| (t−
t
2 ) +
((t| (t+t) + t| (t) )
2
¨
u| (t)
(3)
According the Eq. (3) and displacement conditions at the beginning of the
incremental step, the displacement at the end of the incremental step can be calculated:
u| (t + t) = ˙
u (t) + t| (t+t) ˙
u| (t+
t
2 )
(4)
L. Chen et al.
Fig. 1. 3D model of the femur
falls in the elderly, femoral (Fig. 1) intertrochanteric fractures or femoral neck fractures
account for more than 80% [8, 9].
According to relevant documents [10, 11], the airbag was designed to cover 95%
users aged from 36 to 60. Also, airbag should cover the complete hip and main possible
damage area. Considering the factor of the volume of air in the inflatable cylinder, the
diameter of the air bag is 22.5 cm and the material is nylon 66 (Fig. 2).
Fig. 2. 3D model of the airbag
3 Finite Element Analysis of Fall Protection with the Airbag
In this paper, the dynamic explicit nonlinear algorithm is used for the finite element
analysis of human falling:
M ¨
u = P − I
(1)
Where, Matrix is represented by M, node acceleration matrix is represented by ¨
u,
gravity is represented by P, internal force matrix is represented by I. The acceleration of
incremental step at time t is:
¨
u| (t) = (M)
−1
· (P−I)| (t)
(2)
The central difference method is used to integrate the acceleration in time:
˙
u| (t+
t
2 ) = ˙
u| (t−
t
2 ) +
((t| (t+t) + t| (t) )
2
¨
u| (t)
(3)
According the Eq. (3) and displacement conditions at the beginning of the
incremental step, the displacement at the end of the incremental step can be calculated:
u| (t + t) = ˙
u (t) + t| (t+t) ˙
u| (t+
t
2 )
(4)