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Gain - function of two non-identical warm standby system subject to failure due to voltage fluctuations and steep high acoustics with switch failure
Ashok Kumar Saini
Associate Professor, Department of Mathematics, BLJS College, Tosham, Bhiwani, Haryana, INDIA.
Email: [email protected]
Research Article
Abstract Introduction: Two-unit standby system subject to environmental conditions such as shocks, change of weather conditions etc. have been discussed in reliability literature by several authors due to significant importance in defence, industry etc. In the present paper we have taken two-non-identical warm standby system with failure time distribution as exponential and repair time distribution as general. The Role of voltage fluctuations and steep high acoustics under which the system operates plays significant role on its working. We are considering system under (i) voltage fluctuations and (ii) Steep high acoustics causing different types of failure requiring different types of repair facilities. Using semi Markov regenerative point technique we have calculated different reliability characteristics such as MTSF, reliability of the system, availability analysis in steady state, busy period analysis of the system under repair, expected number of visits by the repairman in the long run and gain-function and graphs are drawn.
Keyword: warm standby, voltage fluctuations, steep high acoustics, switches failure.
INTRODUCTION
The mathematical theory of reliability has grown out of the demands of modern technology and particularly out of experiences in World War II (1939-1945) with complex military systems although the concept of reliability is as old as man himself.
Assumptions
- The failure time distribution is exponential whereas the repair time distribution is arbitrary of two non-identical units.
- The repair facility is of four types :
Type I, II repair facility
- when failure due to voltage fluctuations and steep high acoustics of first unit occurs respectively and
Type III, IV repair facility
- when failure due to voltage fluctuations and steep high acoustics of the second unit occurs respectively.
- The repair starts immediately upon failure of units and the repair discipline is FCFS.
- The repairs are perfect and start immediately as soon as the voltage fluctuations and steep high acoustics of the system becomes normal. The voltage fluctuations and acoustics in both the units do not go steep high simultaneously.
- The failure of a unit is detected immediately and perfectly.
- The switches are perfect and instantaneous.
- All random variables are mutually independent.
SYMBOLS FOR STATES OF THE SYSTEM
Superscripts: O, WS, SO, FVF, FHA SFO
Operative, Warm Standby, Stops the operation, failure due to voltage fluctuations, failure due to steep High acoustics, Switch failed but operable respectively
Subscripts: nvf, vf, sha, ur, wr, uR
No voltage fluctuations, voltage fluctuations, steep high acoustics, under repair, waiting for repair, under repair continued respectively
Up states: 0, 1, 2, 9;
Down states: 3, 4, 5, 6, 7, 8, 10, 11
Regeneration point: 0, 1, 2, 4, 7, 10
States of the System
0(Onvf, WSnvf)
One unit is operative and the other unit is warm standby and there are no voltage fluctuations and no steep high acoustics in both the units.
1(SOnvf, Onvf)
The operation of the first unit stops automatically due to voltage fluctuations and warm standby unit’s starts operating with no voltage fluctuations.
2(FVFur, Onvf)
The first unit fails and undergoes repair after the voltage fluctuations are over and the other unit continues to be operative with no voltage fluctuations.
3(FVFuR, SOuvf)
The repair of the first unit is continued from state 2 and the operation of second unit stops automatically due to voltage fluctuations.
4(FVFur, SOsha) The first unit fails and undergoes repair after the voltage fluctuations are over and the other unit also stops automatically due to steep high acoustics.
5(FVFuR, FHAsha,wr) The repair of the first unit is continued from state 4 and the other unit is failed due to steep high acoustics in it and is waiting for repair.
6(Onvf, FHAur) The first unit becomes operative with no voltage fluctuations and the second unit is failed due to high acoustics is under repair.
7(SOnsha, SFOnvf, ur)
The operation of the first unit stops automatically due to steep high acoustics and during switchover to the second unit switch fails and undergoes repair and there is no voltage fluctuations.
8(FHAsha, wr, SFOnvf, uR)
The repair of failed switch is continued from state 7 and the first unit is failed after steep high acoustics is waiting for repair.
9(Onvf, SOsha)
The first unit is operative with no voltage fluctuations and the operation of warm standby second unit is stopped automatically due to steep high acoustics.
10(SOsha, SFur)
The operation of the first unit stops automatically due to steep high acoustics and the second unit switch fails and undergoes repair after the steep high acoustics is over.
11(FHAsha, wr, FuR)
The repair of the second unit is continued from state 10 and the first unit is failed due to steep high acoustics is waiting for repair.
Figure 1: The State Transition Diagram
TRANSITION PROBABILITIES
Simple probabilistic considerations yield the following expressions:
p01 = , P07 =
p09 = , p12 = , p14 =
P20= G1*( λ1), P22(3) = G1*( λ1)=p23, P72 = G2*( λ4),
P72(8) = G2*( λ4)= P78
We can easily verify that
p01 + p07 + p09 = 1, p12 + p14 = 1, p20 + p23 (=p22(3))= 1, p46(6)= 1 p60 = 1,
p72+ P72(5) + p74 = 1, p9,10 =1, p10,2 + p10,2(11) = 1 (1)
And mean sojourn time are
µ0 = E(T) = (2)
MEAN TIME TO SYSTEM FAILURE
We can regard the failed state as absorbing
,
(3-5)
Taking Laplace-Stiltjes transform of eq. (3-5) and solving for
= N1(s) / D1(s) (6)
Where
N1(s) = { +
D1(s) = 1 -
Making use of relations (1) and (2) it can be shown that θ0*(0) =1, which implies that θ0(t) is a proper distribution.
MTSF = E[T] = d/ds θ0*(s) = (D1’(0) - N1’(0)) / D1 (0)
s=0
= ( +p01 + p01 p12 + p09 ) / (1 - p01 p12 p20 )
where
+ + , + , + (3),
AVAILABILITY ANALYSIS
Let Mi(t) be the probability of the system having started from state I is up at time t without making any other regenerative state belonging to E. By probabilistic arguments, we have
The value of M0 (t), M1 (t), M2 (t), M4 (t) can be found easily.
The point wise availability Ai (t) have the following recursive relations
A0(t) = M0(t) + q01(t)[c]A1(t) + q07(t)[c]A7(t) + q09(t)[c]A9(t)
A1(t) = M1(t) + q12(t)[c]A2(t) + q14(t)[c]A4(t), A2(t) = M2(t) + q20(t)[c]A0(t) + q22(3)(t)[c]A2(t)
A4(t) = q46(3)(t)[c]A6(t), A6(t) = q60(t)[c]A0(t)
A7(t) = (q72(t)+ q72(8)(t)) [c]A2(t) + q74 (t)[c]A4(t)
A9(t) = M9(t) + q9,10(t)[c]A10(t), A10(t) = q10,2(t)[c]A2(t) + q10,2(11)(t)[c]A2(t) (7-14)
Taking Laplace Transform of eq. (7-14) and solving for
= N2(s) / D2(s) (15)
Where
N2(s) = (1 - 22(3)(s)) { 0(s) + 01(s) 1(s) + 09(s) 9(s)}+ 2(s){ 01(s) 42(s) + 07(s)72(s) + 73(8)(s)) + 09 (s) 9,10 (s)( 10,2 (s) + 10,2(11)(s))}
D2(s) = (1 - 22(3)(s)) { 1 - 46(5)(s) 60(s) ( 01(s) 44 (s) + 07(s) 74(s))
- 20(s)01(s)12(s)07(s)( 72(s)) + 72(8)(s) + 09 (s) 9,10 (s)
( 10,2 (s) + 10,2(11)(s))}
The steady state availability
A0 = = =
Using L’ Hospitals rule, we get
A0 = = (16)
Where
N2(0)= p20(0(0) + p011(0) + p09 9(0) ) + 2(0) (p01p12 + p07 (p72
+ p72(8) + p09 ))
D2’(0) = p20{ + p01 + (p01 p14 + p07 p74 )+ p07 + p07 + p09()
+ { 1- ((p01p14 + p07 p74 )}
, ,
The expected up time of the system in (0,t] is
(t) = So that (17)
The expected down time of the system in (0,t] is
(t) = t- (t) So that (18)
The expected busy period of the server for repairing the failed unit under steep high acoustics in (0,t]
R0(t) = S0(t) + q01(t)[c]R1(t) + q07(t)[c]R7(t) + q09(t)[c]R9(t)
R1(t) = S1(t) + q12(t)[c]R2(t) + q14(t)[c]R4(t),
R2(t) = q20(t)[c]R0(t) + q22(3)(t)[c]R2(t)
R4(t) = q46(3)(t)[c]R6(t), R6(t) = q60(t)[c]R0(t)
R7(t) = (q72(t)+ q72(8)(t)) [c]R2(t) + q74 (t)[c]R4(t)
R9(t) = S9(t) + q9,10(t)[c]R10(t), R10(t) = q10,2(t) + q10,2(11)(t)[c]R2(t) (19-26)
Taking Laplace Transform of eq. (19-26) and solving for
= N3(s) / D2(s) (27)
Where
N2(s) = (1 - 22(3)(s)) { 0(s) + 01(s) 1(s) + 09(s) 9(s)} and D2(s) is already defined.
In the long run, R0 = (28)
where N3(0)= p20(0(0) + p011(0) + p09 9(0) ) and D2’(0) is already defined.
The expected period of the system under steep high acoustics in (0,t] is
(t) = So that
The expected Busy period of the server for repairing the failed units under voltage fluctuations by the repairman in (0,t]
B0(t) = q01(t)[c]B1(t) + q07(t)[c]B7(t) + q09(t)[c]B9(t)
B1(t) = q12(t)[c]B2(t) + q14(t)[c]B4(t), B2(t) = q20(t)[c] B0(t) + q22(3)(t)[c]B2(t)
B4(t) = T4 (t)+ q46(3)(t)[c]B6(t), B6(t) = T6 (t)+ q60(t)[c]B0(t)
B7(t) = (q72(t)+ q72(8)(t)) [c]B2(t) + q74 (t)[c]B4(t)
B9(t) = q9,10(t)[c]B10(t), B10(t) = T10 (t)+ (q10,2(t) + q10,2(11)(t)[c]B2(t) (29- 36)
Taking Laplace Transform of eq. (29-36) and solving for
= N4(s) / D2(s) (37)
Where
N4(s) = (1 - 22(3)(s)) { 01(s)14(s) 4(s) + 46 (5)(s) 6(s)) + 07(3)(s) 74(s)( 4(s)
+ 46(5)(s) 6(s))+ 09(s)09,10(s) 10(s) )
And D2(s) is already defined.
In steady state, B0 = (38)
where N4(0)= p20 {( p01 p14 + p07 p74) (4(0) +6(0)) + p09 10(0) } and D2’(0) is already defined.
The expected busy period of the server for repair in (0,t] is
(t) = So that (39)
The expected Busy period of the server for repair of switch in (o,t]
P0(t) = q01(t)[c]P1(t) + q07(t)[c]P7(t) + q09(t)[c]P9(t)
P1(t) = q12(t)[c]P2(t) + q14(t)[c]P4(t), P2(t) = q20(t)[c]P0(t) + q22(3)(t)[c]P2(t)
P4(t) = q46(3)(t)[c]P6(t), P6(t) = q60(t)[c]P0(t)
P7(t) = L7(t)+ (q72(t)+ q72(8)(t)) [c]P2(t) + q74 (t)[c]P4(t)
P9(t) = q9,10(t)[c]P10(t), P10(t) = (q10,2(t) + q10,2(11)(t))[c]P2(t) (40-47)
Taking Laplace Transform of eq. (40-47) and solving for
= N5(s) / D2(s) (48)
where N2(s) = 07(s ) 7(s) 1 - 22(3)(s)) and D2(s) is defined earlier.
In the long run, P0 = (49 )
where N5(0)= p20 p07 4(0) and D2’(0) is already defined.
The expected busy period of the server for repair of the switch in (0,t] is
(t) = So that (50)
The expected number of visits by the repairman for repairing the non-identical units in (0,t]
H0(t) = Q01(t)[c]H1(t) + Q07(t)[c]H7(t) + Q09(t)[c]H9(t)
H1(t) = Q12(t)[c][1+H2(t)] + Q14(t)[c][1+H4(t)], H2(t) = Q20(t)[c]H0(t) + Q22(3)(t)[c]H2(t)
H4(t) = Q46(3)(t)[c]H6(t), H6(t) = Q60(t)[c]H0(t)
H7(t) = (Q72(t)+ Q72(8)(t)) [c]H2(t) + Q74 (t)[c]H4(t)
H9(t) = Q9,10(t)[c][1+H10(t)], H10(t) = (Q10,2(t)[c] + Q10,2(11)(t))[c]H2(t) (51-58)
Taking Laplace Transform of eq. (51-58) and solving for
= N6(s) / D3(s) (59)
Where
N6(s) = (1 – 22(3)*(s)) { 01(s)12(s)14(s)) 09 (s) 9,10 (s)}
D3(s) = (1 - 22(3)*(s)) { 1 - (01(s) 14 (s) + 07(s) 74(s))46(5)*(s) 60(s)}
- 20(s)01(s)12(s)07(s)( 72(s)) + 72(8)(s) +
09 (s)9,10 (s) ( 10,2 (s) +Q 10,2(11)*(s))}
In the long run, H0 = (60)
where N6(0)= p20 (p01 + p09) and D’3(0) is already defined.
The expected number of visits by the repairman for repairing the switch in (0,t]
V0(t) = Q01(t)[c]V1(t) + Q07(t)[c]V7(t) + Q09(t)[c]V9(t)
V1(t) = Q12(t)[c]V2(t) + Q14(t)[c]V4(t), V2(t) = Q20(t)[c]V0(t) + Q22(3)(t)[c]V2(t)
V4(t) = Q46(3)(t)[c]V6(t), V6(t) = Q60(t)[c]V0(t)
V7(t) = (Q72(t)[1+V2(t)]+ Q72(8)(t)) [c]V2(t) + Q74 (t)[c]V4(t)
V9(t) = Q9,10(t)[c]V10(t), V10(t) = (Q10,2(t) + Q10,2(11)(t))[c]V2(t) (61-68)
Taking Laplace-Stieltjes transform of eq. (61-68) and solving for
= N7(s) / D4(s) (69)
where N7(s) = 07 (s) 72 (s) (1 – 22(3)*(s)) and D4(s) is the same as D3(s)
In the long run, V0 = (70)
where N7(0)= p20 p07 p72 and D’3(0) is already defined.
GAIN- FUNCTION ANALYSIS
The gain- function of the system considering mean up-time, expected busy period of the system under voltage fluctuations when the units stops automatically, expected busy period of the server for repair of unit and switch, expected number of visits by the repairman for unit failure, expected number of visits by the repairman for switch failure.
The expected total cost-benefit incurred in (0,t] is
C(t) = Expected total revenue in (0,t] - expected total repair cost for switch in (0,t]
- expected total repair cost for repairing the units due to voltage fluctuations in (0, t ] when the units automatically stop in (0,t]
- expected busy period of the system under steep high acoustics
- expected number of visits by the repairman for repairing the switch in (0,t]
- expected number of visits by the repairman for repairing of the non-identical units in (0,t]
The expected total cost per unit time in steady state is
C = =
= K1A0 - K2P0 - K3B0 - K4R0 - K5V0 - K6H0
Where
K1: revenue per unit up-time,
K2: cost per unit time for which the system is under switch repair,
K3: cost per unit time for which the system is under repair due to voltage fluctuations when units automatically stop,
K4: cost per unit time for which the system is under repair due to steep high acoustics,
K5: cost per visit by the repairman for which switch repair,
K6: cost per visit by the repairman for units repair.
CONCLUSION
After studying the system, we have analyzed graphically that when the failure rate due to voltage fluctuations, failure rate due to steep high acoustics increases, the MTSF and steady state availability decreases and the cost function decreased as the failure increases.
REFERENCES
- Dhillon, B.S. and Natesen, J, Stochastic Anaysis of outdoor Power Systems in fluctuating environment, Microelectron. Reliab.. 1983; 23, 867-881.
- Goel, L.R., Sharma,G.C. and Gupta, Rakesh Cost Analysis of a Two-Unit standby system with different weather conditions, Microelectron. Reliab., 1985; 25, 665-659.
- Goel,L.R., Sharma G.C. and Gupta Parveen, Stochastic Behavior and Profit Analysis of a redundant system with slow switching device, Microelectron Reliab., 1986; 26, 215-219.
- Cao, Jinhua, Stochastic Behavior of a Man Machine System Operating under Changing Environment Subject to a Markov Process with two States, Microelectron. Reliab.1989, 28, pp. 373-378.
- Barlow, R.E. and Proschan, F., Mathematical theory of Reliability, 1965; John Wiley, New York.
- Gnedanke, B.V., Belyayar, Yu.K. and Soloyer, A.D., Mathematical Methods of Relability Theory, 1969 ; Academic Press, New York.
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