Answer to Question #150068 in Mechanical Engineering for Tugberk Yıldız

Question #150068
An electric motor drives a co-axial rotor through a
single-plate clutch, which has two pairs of driving
surfaces, each of 275mm external and 200mm internal
diameter, the total spring load pressing the plates
together is 500N. The mass of the motor armature and
shaft is 800kg and its radius of gyration is 260mm; the
rotor has a mass of 1350kg and its radius of gyration is
225mm.
The motor is brought up to a speed of 1250rev/min; the
current is then switched off and the clutch suddenly
engaged. Determine the final speed of the motor and
rotor, and find the time taken to reach that speed and
the kinetic energy lost during the period of slipping.
How long would slipping continue if a constant torque
of 50Nm were maintained on the armature shaft? Take
=0.35
1
Expert's answer
2020-12-22T05:03:37-0500

Solution

1) Final speed ω3\omega_3

I1=m1k12=8000.262=54.08kgm2I_1=m_1k_1^2=800*0.26^2=54.08 kgm^2

I2=m2k22=13500.2252=68.34375kgm2I_2=m_2k_2^2=1350*0.225^2=68.34375 kgm^2

Conservation of energy

ω1=2πN160=2π30060=130.8997rad/sec\omega_1=\frac{2\pi N_1}{60}=\frac{2\pi*300}{60}=130.8997 rad/sec

ω2=2πN260=2π30060=62.8319rad/sec\omega_2=\frac{2\pi N_2}{60}=\frac{2\pi*300}{60}=62.8319 rad/sec (Assume the speed of the rotor was originally at 300 rpm)

I1ω1+I2ω2=(I1+I2)ω3I_1\omega_1+I_2\omega_2=(I_1+I_2)\omega_3

ω3=92.9004rad/sec=889.133rpm\omega_3=92.9004 rad/sec= 889.133 rpm


2) Energy lost

K.E(before)=12I1ω12+12I2ω22=598215.06NmK.E (before )=\frac{1}{2}*I_1*\omega_1^2+\frac{1}{2}*I_2*\omega_2^2=598215.06 Nm

K.E(after)=12(I1+I2)ω32=528267.3961NmK.E (after )=\frac{1}{2}*(I_1+I_2)\omega_3^2=528267.3961 Nm

Lostenergy=598215.06528267.3961=69947.66NmLost energy =598215.06-528267.3961=69947.66Nm


Time taken to reach the speed

T=12Wμ(R1+R2)=12906.25Nmm=12.906NmT=\frac{1}{2}W\mu(R_1+R_2)=12906.25 Nmm=12.906 Nm


Angular acceleration of the rotor

I2α2=T=12.906    α2=0.18885rad/secI_2\alpha_2=T=12.906 \implies\alpha_2=0.18885 rad/sec

ω3=ω2+α2t    t=159.22sec\omega_3=\omega_2+\alpha_2t \implies t = 159.22 sec

Now constant resisting torque is 50Nm is applied

Torque on motor = T1=12.90650=62.906NmT_1=-12.906-50=-62.906 Nm

ω3=ω1+α1t=ω1+T1I1t=130.899762.90654.08t\omega_3=\omega_1+\alpha_1t =\omega_1+\frac{T_1}{I_1}t =130.8997-\frac{62.906}{54.08}t

Considering the rotor

ω3=ω2+α2t=62.8319+0.18885t\omega_3=\omega_2+\alpha_2t= 62.8319+0.18885t

Equating the two implies that t = 50.35 sec


Need a fast expert's response?

Submit order

and get a quick answer at the best price

for any assignment or question with DETAILED EXPLANATIONS!

Comments

No comments. Be the first!

Leave a comment