Biomedical Engineering Reference
In-Depth Information
TABLE 4-3
Comparison Between Electrical and Mechanical Elements
Block
Describing Equation
Energy/Power
1
L
1
2
Li
2
Inductor
i
=
Vdt
E
ind
=
F
=
kx
=
k
1
2
kx
2
Spring
v
dt
E
spring
=
=
k
θ
=
k
1
2
k
θ
2
Torsion spring
T
ω
dt
E
spring
=
C
dV
dt
1
2
CV
2
Capacitor
i
=
E
cap
=
F
=
m
d
dt
=
m
d
2
x
1
2
m
v
2
Mass
E
mass
=
dt
2
I
d
2
I
d
dt
=
θ
dt
2
1
2
I
2
Moment of inertia
T
=
I
α
=
E
I
=
ω
V
R
1
R
V
2
Resistor
i
=
P
res
=
F
=
c
v
=
c
dx
dt
2
Dashpot
P
dash
=
c
v
=
c
ω
=
c
d
dt
2
Rotational damper
T
P
damp
=
c
ω
Hydraulic capacitance is the term that describes the potential energy storage by a fluid in
terms of its pressure head. Consider the diagram shown in Figure 4-11, where the rate of
change of volume,
V
(m
3
)
, in the reservoir is equal to the difference in the volume flow
rates into and out of the reservoir.
dV
dt
q
1
−
q
2
=
(4.46)
However, if the volume is written in terms of the cross sectional area,
A
(m
2
)
, and the
height of the fluid,
h
(m), in the reservoir, then
q
1
−
q
2
=
A
dh
dt
(4.47)
FIGURE 4-11
Potential energy of
fluid in a reservoir.
