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### Modelling of repairable items for production inventory with random deterioration

2. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 57 |Page .This model is developed for deteriorating item by assuming that the deterioration rate is uniform and the finite production rate is proportional to the demand rate & the demand rate increasing exponentially. Repairable Items are collected at time of production run and repairs at time of no production no shortage completely. These repaired items as good as new and consumed at time of shortage. When shortages is maximum production start and items consumed from both the channels forward production and repaired items as well. We derive an expressions for different cost associated in the model and total average cost .We derive equations, solution of these equations gives the optimal cycle and optimal cost of repairable items. Fig. 1. Flow of inventory in the integrated supply system II. Assumption and Notation The mathematical model of the production inventory problem with repairable system considered herein is developed on the basic of the following assumptions-: a. A single item is considered over a prescribed period of T units of time, which is subject to a time dependent Random deterioration rate. b. Deteriorate D (t) is known and increasing exponentially t Ae)t(D   , 0t  , A is initial demand,  is a constant governing the increasing rate of demand. c. Production rate P(t) at any instant depends on the demand that is, at time t, t > 0, )()( tbDatP  , a > 0, 10  b and P(t) > D(t). d. Deterioration of the units is considered only after they have been received into the inventory. e. Items are returnable and are repaired. Repaired items are as good as new ones and they are used during the shortage period of forward production. f. The time horizon of the inventory system is infinite. Only a typical planning schedule of length T is considered, all remaining cycles are identical. g. Shortages are allowed and backlogged. h. The production time interval for forward production coincides with the collection time interval for reverse repairing system. Notations for production system and repairing system: (1) I(t) = Inventory level at any time t, 0t  (2) 0 ( )t    the items deterioration rate is random. (3) Im = Maximum inventory level. (4) Ib = Maximum shortages level. (5) C = Setup cost for new cycle. (6) CS = Shortage cost per unit. (7) K = The total average cost of system. (8) CHP=Holding cost per unit per unit of time during the production. (9) CDP=Deteriorating cost per unit per unit of time during the production. (10) Pcp = Production cost per item. (11) CHC= Holding cost per unit per unit of time during the collecting and consuming process for the repairing system. (12) CDC= Deteriorating cost per unit per unit of time during the collecting and consuming process for the repairing system. (13) CHR = Deteriorating cost per unit per unit of time during the repairing process for the repairing system. (14) CDR =Holding cost per unit per unit of time during the repairing process for the repairing system. (15) Ic(t) = Inventory level during the collecting process for the returnable items. (16) I1(t)= Inventory level during the repairing process for the returnable items. (17) z =Fraction of the production lot size 0 <z<1. (18) Rc =Rate of collection of returnable items. (19) M =Rate of repair of returnable items to be repaired.
3. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 58 |Page (20) t1 = Time when production stops and also the time when collecting process for returnable items stops. At this very time repairing of collected items start. (21) t2 = Time period when repairing of returnable items stops and also the time when accumulated inventory of production system vanishes. (22) t3 = Time when shortages is maximum.(t= t1+ t2+ t3) (23) t4 = Period of time when production starts again during the period of shortage. (24) T = )( 4321 tttt  is the cycle time. (25) IS = Maximum inventory level of repaired items. (26) Pcc= Cost of purchasing the returnable items per unit. (27) Pcr =Repair cost of repaired items per unit. III. Mathematical Model : Initially, the inventory level is start with zero. The forward production inventory level starts at time t=0 and it reaches at maximum inventory level Im unit after t1 time. At that time production is stopped and the inventory level is decreasing continuously and reaches zero at time t2,at this time shortages start developing at time t3 it reaches to maximum shortage level Ib . This time fresh production start to remove backlog by the time t4 . At the beginning of each cycle, the inventory is zero. The production starts at the very beginning of the cycle. As production progresses the inventory of finished goods piles up even after meeting the market demand, deterioration. At the beginning of each cycle, the process of collecting returnable items in a separate store also begins. At a point where the production from the forward production system stops; the collection process of returnable items also stops at the same point .It is assumed there is no collection of used items once the repairing of collected items starts. At this very point the repairing of reusable items begin at a constant rate. The accumulated inventory produced from the advanced production system in the meanwhile starts getting consumed and ultimately becomes nil. The accumulated inventory of repairing products, which are assumed to be as good as the newly produced products, is consumed when the shortages from the forward production system begin to surface. Thereafter, production starts when shortages is maximum in forward inventory system and shortages are gradually cleared after meeting demand by repairable items and produced item from forward system simultaneously and the cycle ends with zero inventories. Here our aim is to find out the optimal values of t1, t2, t3 , t4, Im & Ib that minimize the total average cost (K) over the time planning horizon cycle(0,T). Forward production system Repairing System Fig. 2. Inventory of production and repairing system The differential equation governing the stock status during the period Tt0  can be written as )()()1( )( 0 ttIAeba dt tdI t   , I(0) = 0,( I1) =Im, 10 tt  …(1)
4. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 59 |Page 0 ( ) ( ) ( )tdI t Ae tI t dt      , I(t1) =Im , I(t2) = 0 , 20 tt  … (2) ( ) tdI t Ae dt    , I(0) =o, I(t3) =Ib, , 30 t t  ….(3) ( ) ( 1) tdI t a b Ae dt     , I(0) = Ib,I(t4)=0, 40 t t  ….(4) Differential equations representing repairing system in collecting time & consuming time 0 ( ) ( )t ( )c c c dI t R I t dt    , Ic(0) = 0 10 tt  … (5) 0 ( ) ( )t ( )c c dI t M I t dt    , Ic(t1) = Bz , 20 t t  … (6) Where B=Production lot size during production system=Production- Deterioration 1 1 1 1 1 0 0 0 0 0 0 0 2 0 0 1 0 0 1 ( ) (1 ( ) )(a bAe ) {a bAe ( ) (a bAe )} ( ) ( ) ( )bA bAe { (1 ) } {1 ( ) ) } 2 t t t t t t t t Pdt tPdt t dt t dt a t t                                            Differential equations representing inventory of repaired items. 1 0 1 ( ) ( )t ( ) dI t M I t dt    , I1(0) = 0, I1(t2) =Is, 20 t t  , ….(7) 0 ( ) ( ) ( )tdI t Ae tI t dt      ,I(0) =Is,I 3 4( ) 0t t  , I(t3) =Ib1 , 3 40 t t t   … (8) Solution of equation (1) , (2) , .3) and (4) by adjusting the constant of integration using boundary condition are given by                             t Ae b e t tatI t t t )( 1 )1( 6 )( )( 02 )( 2)( 3 0 0 2 0       t t e et       2 0 2 0 2 0 )()( 2 )( , 10 tt  … (9) )(tI  A             2 020 2 02)( )()( 2 )( 1 2 2 0        tte e t t            2 00 2 0 )()( 2 )( 1     tt e t , 20 t t  … (10) )(tI )1( t e A    , 30 t t  … (11) )( )1( )()( 4 4 tt ee bA ttatI      , 40 t t  … (12) Solving (5) and (6)
5. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 60 |Page 2 0 3 ( ) 20 ( ) ( ) , 6 t c c t I t R t e           10 tt  … (13) 2 0 1 2 0 1 3 ( ) 20 1 1 1 ( ) 2 3 0 1 1 ( ) ( ) Bz, 6 ( ) 6 t c c t C t I t R t e Bze R t t                          2 2 0 0 1 3 3 ( ) 2 ( ) 20 0 1 1 ( ) ( ) ( ) , 6 6 t t c t t I t Bz M t e M t e                       20 t t  … (14) Solution of equation (7) and (8) by adjusting the constant of integration using boundary condition are given by 2 0 3 ( ) 20 1 ( ) ( ) , 6 tt I t M t e           20 t t  …(15) 0 ( ) 2 0 ( ) ( ) 1 t t tA I t e                  2 0 0 0 2 2 ( ) ( ) ( ) , 2 t tt e e                   3 40 t t t   …(16) 0 3 3 ( ) 2 0 3 1 ( ) 1 t t b tA I e                  3 3 2 0 3 0 0 2 2 ( ) ( ) ( ) , 2 t tt e e                   …(16) The inventory level of production start initially at time unit t = 0 to t = t1 at maximum level Im is obtained by equation (9)                             102 )( 2)( 3 10 1 )( 1 )1( 6 )( 1 10 2 10 t Ae b e t taI t t t m       1 1 2 0 2 0 2 10 )()( 2 )( t t e et                       1 )()( 2 )( 1 2 020 2 102       tt e A t … (17) and after time 1t the production is stopped and stock level is decreasing continuously and become zero at time t=t2 at that time shortages are develop and reaching to Ib at time 3tt  is obtained . 3 4 1 4 ( 1) (1 ) (1 )t t b b A A b I I e at e            … (.18) Thus by equation (17) we observed that 1t and 2t are dependent so they are related by the equation )( 12 tRt  … (19) and by equation (18) 3t and 4t are dependent to each other so related by the equation 3 1 4( )t R t … (20) Total amount of deteriorated units ( )DPI of production inventory )T,0( is given by 1 2 0 0 0 0 ( ) ( ) ( ) ( ) t t DPI tI t dt tI t dt     
6. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 61 |Page                          72 )( 8 )( 30 )( 2 )( 7 1 2 0 4 10 5 10 2 1 0 tttt a                             22 )5()6( )( )1)(( 3 1 2 1 3 1 0 0 2 1 tttAeb t                2 1 3 3 1 5 2 1 5 12 0 4 3 2 7 2 )123(42 )(     tttt                   2 3 1 2 0 3 1 2 001 2 0 6 )()()(66)1)((     ttttAb                        e t t ttAe 2 2 20 2 )(020 2 20 2 1 )()( 2 )( 1                  2 20 2 0 22 )()( 1       tt eetA 2 )( 22 0 t e              24 2 0 43 2 2 2 2 3 2 1)(366t3tt               43 2 2 2 2 3 2 2 0 663)( 2    ttt e A t 2 )( 2 0 t e          65 2 4 2 2 3 3 2 2 4 2 5 2 12012060205  ttttt                         4 2 32 2 2 2 2 0 6 0 4 22)()(606 2 ttt e A t         5354 2 3 3 2 2 3 2 2422424124  ttt … (21) Total amount of deteriorated units ( )DCI of collected items of repairable inventory channel in 2(0,t ) is given by 1 2 1 2 0 2 2 2 0 0 1 0 0 0 0 3 ( ) 20 0 0 3 3 ( ) 2 ( ) 20 0 1 0 1 0 3 2 5 0 1 0 1 0 2 ( ) ( ) ( ) ( ) ( ) ( ) 6 ( ) ( ) ( ) 6 6 ( ) ( ) ( ) 3 15 t t DC C C t t c t t t c I tI t dt tI t dt t tR t e dt t t t Bz M t e M t e dt t t Bzt R                                                                      2 0 1 2 3 2 5 0 2 0 2 2 3 ( ) 20 2 0 1 1 ( ) ( ) 2 3 15 ( ) ( ) 2 6 t t t M t M t t e                          … (22) Total amount of deteriorated units ( )DRI of Repaired items of repairable inventory channel is given by
7. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 62 |Page … (23) During period ),0( T total inventory of produced items ( )HPI in forward production channel can be obtained as 1 2 0 0 ( ) ( ) t t HPI I t dt I t dt                          1)1( 72 )( 6 )( 1 6 1 2 0 3 10 1 1 t eAbtat ta t                 42 354 )( 2 )( 4 1 2 3 1 3 2 1 4 12 032 1 0 11 tttt e t e tt 4 1                   543 1 3 3 12 03 3 1 2 1 05 726 6 )( 2 6 )( 6      tttt                          24 )( 2 )( 2222 3 2 4 22 02 2 230 tttt eteteteA     55444 2 2 2 3 2 2 2 2 2 3313 2 3 2 222222   tttttt eeetetetet          2 20 2 20 2 3 2 2 03 2022 )()( 6 )( )( 3 11 22 ttt tt Aee tt                    6 )( 12 )( 4 20 5 2 3 0 tt … (24) During period ),0( T total inventory of collected items ( )HCI can be obtained as 1 2 1 2 0 2 2 2 0 0 1 0 0 3 ( ) 20 0 3 3 ( ) 2 ( ) 20 0 1 1 0 2 2 4 2 2 4 0 1 0 1 0 2 0 2 0 2 ( ) ( ) ( ) 6 ( ) ( ) 6 6 ( ) ( ) ( ) ( ) ( ) 2 12 2 12 t t HC C C t t c t t t c I I t dt I t dt t R t e dt t t Bz M t e M t e dt t t t t R Bzt M                                                                     2 0 1 3 ( ) 20 1 0 2 1 ( ) ( ) 6 tt t M t e                  …(25) 3 42 2 2 0 03 4 0 1 0 0 0 3 ( ) 20 0 0 ( ) 2 2 0 0 0 0 0 2 2 0 3 2 5 0 2 0 2 0 ( ) ( ) ( ) ( ) ( ) ( ) 6 ( ) ( ) ( ) ( ) ( ) 1 2 ( ) ( ) ( 3 15 t tt DR t t tt t tt t I tI t dt tI t dt t tM t e dt t t eA t e e dt t t M A                                                                           2 3 4 3 4 3 4 0 3 4( ) ( ) ( )( ) ) 2 3 8 t t t t t t          
8. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 63 |Page During period ),0( T total inventory of repaired items ( )HRI can be obtained as 3 42 2 2 0 03 4 1 0 0 3 ( ) 20 0 0 ( ) 2 2 0 0 0 0 0 2 2 0 2 2 4 0 2 0 2 3 0 3 4 ( ) ( ) ( ) ( ) 6 ( ) ( ) ( ) ( ) ( ) 1 2 ( ) ( ) ( ( ) ( ) 2 12 t tt HR t t tt t tt t I I t dt I t dt t M t e dt t t eA e e dt t t t M A t t                                                                           2 3 4 0 3 4) ( )( ) 2 6 t t t       …(26) Total amount of shortage units (Is) during the period (0, T) is given by   43 00 )()( tt S dttIdttII                                     4 43 4 2 4 3 1)1( 2 1 t tt et ebAat t eA    … (27) P=Production cost +Collection cost +Repaired cost 1 1 2 1 0 0 0 1 1 2 ( ) ( ) t t t t CP CC c CR t CP CC c CR P P a bAe dt P R dt P Mdt bAe P at P R t P Mt               Hence the total average cost of the inventory system is K = setup cost +production cost+ deterioration cost + inventory carrying cost + shortage cost   1 DP DP DC DC DR DR HP HP HC HC HR HR S SC P C I C I C I C I C I C I C I T           … (28) and putting the value of IDP, IDC, IDR,IHP, IHC, IHR and IS we getting the total average cost of the inventory system. IV. The Approximation Solution Procedure In many cases  and )(0  are extremely small hence to use Maclaurin series for approximation 2 1 22 t te t    … (29) By using equation (4.29) the total average cost of system  1 1 1 2 2 3 3 2 2 4 4 20 1 0 1 0 2 2 24 1 [ ( ) ] ( ) ( )( 1) ( ) 2 2 2 2) 2 2 t DP CP CC c CR CbAe K C P at P R t P Mt T T at b At A t t t                                  2 0 1 3 2 5 2 3 2 5 0 1 0 1 0 2 0 2 0 2 2 3 ( ) 20 2 0 1 1 ( ) ( ) ( ) ( ) ( ) 3 15 2 3 15 ( ) ( ) 2 6 c DC t t t Bzt t t R M C T t M t t e                                             
9. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 64 |Page 3 2 5 2 3 4 0 2 0 2 3 4 3 4 0 3 4 0 ( ) ( ) ( ) ( ) ( )( ) ( ) 3 15 2 3 8 DR t t t t t t t tC M A T                               3 0 1 1 ( ) 6 HP a tC at T                  3 0 3 102 1 )(2 3 )()1(       At t Ab           2 0 2 2 20 2 00 2 )()()()( 2         t t                     4 2 00 23 202 222 0 2 6 )()(2 3 )(2)( 1 t t tt A       50 2 ( ) 6 t       2 0 1 2 2 4 2 2 4 0 1 0 1 0 2 0 2 0 2 3 ( ) 20 1 0 2 1 ( ) ( ) ( ) ( ) ( ) 2 12 2 12 ( ) ( ) 6 c HC t t t t t R Bzt M C T t t M t e                                              + 2 2 4 2 3 0 2 0 2 3 4 0 3 4 0 3 4 ( ) ( ) ( ) ( )( ) ( ) ( ) 2 12 2 6 HR t t t t t tH M A t t T                              2 2 23 4 4 ( 1) 2 2 2 SC At at A b t T         … (30) And  1 1 1 1 2 3 3 2 2 4 4 20 1 0 1 0 1 1 14 1 [ ( ) ( )] ( ) ( )( 1) ( ) ( ) ( ) 2 2 ( ) 2 2) 2 2 t DP CP CC c CR CbAe K C P at P R t P MR t T T at b At A R t R t R t                                  2 0 1 3 2 5 2 3 2 5 0 1 0 1 0 1 0 1 0 1 2 3 ( ) 20 1 0 1 1 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 3 15 2 3 15 ( ) ( ) ( ) 2 6 c DC t t t BzR t R t R t R M C T R t M t t e                                              2 3 1 4 4 1 4 4 3 2 5 0 1 0 1 0 4 0 1 4 4 ( ( ) ) ( ( ) ) ( ) ( ) ( ) ( ) 2 3 ( ) 3 15 ( )( ( ) ) 8 DR R t t R t t R t R tC M A T R t t                                  3 0 1 1 ( ) 6 HP a tC at T                  3 0 3 102 1 )(2 3 )()1(       At t Ab 2 0 0 0 1 0 1 2 2 2 ( ) ( ) ( ) ( ) ( ) ( ) 2 R t R t                        
10. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 65 |Page 3 2 2 40 0 1 0 0 1 1 12 2 ( ) 2 ( ) ( ) 2 ( ) ( ) 1 ( ) ( ) ( ) 3 6 R tA R t R t R t                              50 1 ( ) (t ) 6 R       2 0 1 2 2 4 2 2 4 0 1 0 1 0 1 0 1 0 2 3 ( ) 20 1 0 1 1 ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 12 2 12 ( ) ( ) ( ) 6 c HC t t t R t R t R Bzt M C T t R t M t e                                              + 2 1 4 4 2 2 4 1 4 4 0 1 0 1 0 3 0 1 4 4 ( ( ) ) ( ( ) ) ( ) ( ) ( ) ( ) 2 ( ) 2 12 ( )( ( ) ) 6 HR R t t R t t R t R tH M A T R t t                                  2 2 21 4 4 4 ( ) ( 1) 2 2 2 SC AR t at A b t T         … (31) According to equation (30) contain four variables t1, t2, t3 and t4 and these are dependent variable and related by equation (19) and (20). Also we have K > 0, hence the optimum value of t1 and t4 which minimize total average cost are the solutions of the equations 0 1    t K and 0 4    t K … (.32) Provided that these values of t1 satisfy the conditions 02 1 2    t K , 02 4 2    t K and 2 2 2 2 2 2 1 4 1 4 . 0 K K K t t t t             Now differentiating (31) with respect to t1 and t4, we get      1 1 1 1 12 2 1 2 3 3 2 2 4 4 20 1 0 1 0 1 1 14 1 1 [ ( ) ( )] 1 ( ) ( ) ( )( 1) ( ) ( ) ( ) 2 2 ( ) 2 2) 2 2 1 ( ) t DP CP CC c CR CK bAe C P at P R t P MR t R t t T T at b At A R t R t R t R t                                         2 0 1 3 2 5 2 3 2 5 0 1 0 1 0 1 0 1 0 1 2 2 3 ( ) 20 1 0 1 1 1 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 3 15 2 3 15 ( ) ( ) ( ) 2 6 1 ( ) c DC t t t BzR t R t R t R M C T R t M t t e R t                                                 3 2 5 0 1 0 1 2 3 1 4 4 1 4 4 12 0 4 0 1 4 4 ( ) ( ) ( ) ( ) 3 15 ( ( ) ) ( ( ) ) 1 ( ) 2 3 ( ) ( )( ( ) ) 8 DR R t R t M C R t t R t t R t T A R t t                                        
11. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 66 |Page 3 0 1 12 ( ) 6 HP a tC at T                  3 0 3 102 1 )(2 3 )()1(       At t Ab 2 0 0 0 1 0 1 2 2 2 ( ) ( ) ( ) ( ) ( ) ( ) 2 R t R t                         3 2 2 40 0 1 0 0 1 1 12 2 ( ) 2 ( ) ( ) 2 ( ) ( ) 1 ( ) ( ) ( ) 3 6 R tA R t R t R t                               50 1 1 ( ) ( ) 1 ( ) 6 R t R t          2 0 1 2 2 4 0 1 0 1 0 1 2 2 4 0 1 0 1 12 3 ( ) 20 1 0 2 1 ( ) ( ) ( ) ( ) 2 12 ( ) ( ) ( ) ( ) 1 ( ) 2 12 ( ) ( ) 6 c HC t t t R BzR t C R t R t M R t T t t M t e                                                       2 1 4 4 2 2 4 1 4 4 0 1 0 1 0 12 3 0 1 4 4 ( ( ) ) ( ( ) ) ( ) ( ) ( ) ( ) 2 ( ) 1 ( ) 2 12 ( )( ( ) ) 6 HR R t t R t t R t R tH M A R t T R t t                                      2 2 21 4 4 4 12 ( ) ( 1) 1 ( ) 2 2 2 SC AR t at A b t R t T            1 1 3 2 2 40 0 0 1 1 1 1 1 14 1 [ ( ) ( )] ( )( 1) ( ) ( ) 3 ( ) ( ) 2 ( ) ( ) 2 ( ) 2 t DP CP CC c CR C P a bAe P R P MR t T T b A A at R t R t R t R t R t                            2 2 0 1 0 1 2 2 4 0 1 0 1 0 1 1 2 2 4 0 1 1 0 1 1 3 2 2 ( ) 2 ( ) 20 1 1 0 1 0 1 0 1 1 2 0 3 ( ) ( ) 2 ( ) ( ) ( ) 3 3 2 3 ( ) ( ) ( ) ( ) ( ) ( ) 3 3 2 ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1 2 6 2 2 ( ) c DC t t t t BzR t R t R R t R t R t R t M C T R t R t M t R t M t t e e                                                           2 0 1 2 3 ( ) 21 1 0 1 1 t ( ) ( ) 2 6 tR t M t t e                                   2 2 4 0 1 1 0 1 13 ( ) ( ) ( ) ( ) ( ) ( ) 3 3 DR R t R t R t R tC M T              
12. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 67 |Page 2 0 1( ) 2 HP a tC a T      0 1 1 ( )( 1) 2 1 tb A A t              0 0 0 1 1 1 2 2 ( ) ( ) 2 ( ) ( ) ( ) ( ) 2 R t R t R t                      2 2 30 0 1 1 0 0 1 1 1 1 12 2 ( ) 2 ( ) ( ) ( ) 2 ( ) ( ) 1 ( ) 2 ( ) ( ) 2 ( ) ( ) 1 3 R t R tA R t R t R t R t R t                                 40 1 1 5 ( ) (t ) ( ) 6 R R t       2 2 0 1 0 1 2 3 2 3 0 1 0 1 0 1 1 0 1 0 1 3 2 ( ) 2 ( ) 20 1 0 1 0 1 1 0 1 2 2 0 1 1 0 1 2 ( ) ( ) 2 ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 3 2 3 ( ) ( ) ( ) ( ) ( ) ( ) 1 6 2 ( ) t ( ) ( ) 1 2 c t tHC t t R t R t R t R BzR t M C t t R t M t e R t M e T R t M t                                                                   2 0 1( ) 2t e                       + 2 3 0 1 1 0 1 12 ( ) ( ) ( ) ( ) ( ) ( ) 0 2 3 HR R t R t R t R tH M T               … (33)      1 1 1 1 1 42 2 4 2 0 1 0 1 0 4 1 4 3 3 2 2 4 4 2 1 1 1 1 [ ( ) ( )] 1 ( ) ( ) ( )( 1) ( ) 2 2 1 ( ) ( ) ( ) 2 2 ( ) 2 2) t DP CP CC c CR CK bAe C P at P R t P MR t R t t T T at b At A R t R t R t R t                                           2 0 1 3 2 5 2 0 1 0 1 0 1 3 2 5 0 1 0 1 1 42 2 3 ( ) 20 1 0 1 1 ( ) ( ) ( ) ( ) 3 15 2 ( ) ( ) ( ) ( ) 1 ( ) 3 15 ( ) ( ) ( ) 2 6 c DC t t t BzR t R C R t R t M R t T R t M t t e                                                      3 2 5 0 1 0 1 2 3 1 4 4 1 4 4 1 42 0 4 0 1 4 4 ( ) ( ) ( ) ( ) 3 15 ( ( ) ) ( ( ) ) 1 ( ) 2 3 ( ) ( )( ( ) ) 8 DR R t R t M C R t t R t t R t T A R t t                                        
13. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 68 |Page 3 0 1 12 ( ) 6 HP a tC at T                  3 0 3 102 1 )(2 3 )()1(       At t Ab 2 0 0 0 1 0 1 2 2 2 ( ) ( ) ( ) ( ) ( ) ( ) 2 R t R t                         3 2 2 40 0 1 0 0 1 1 12 2 ( ) 2 ( ) ( ) 2 ( ) ( ) 1 ( ) ( ) ( ) 3 6 R tA R t R t R t                               50 1 1 4 ( ) ( ) 1 ( ) 6 R t R t          2 0 1 2 2 4 2 2 4 0 1 0 1 0 1 0 1 0 1 2 3 ( ) 20 1 0 2 1 1 4 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 12 2 12 ( ) ( ) 6 1 ( ) c HC t t t R t R t R BzR t M C T t t M t e R t                                                 2 2 4 0 1 0 1 2 1 4 4 1 42 1 4 4 0 3 0 1 4 4 ( ) ( ) ( ) ( ) 2 12 ( ( ) ) 1 ( )( ( ) ) 2 ( ) ( )( ( ) ) 6 HR R t R t M H R t t R tR t tT A R t t                                           2 2 21 4 4 4 1 42 ( ) ( 1) 1 ( ) 2 2 2 SC AR t at A b t R t T           2 1 4 1 4 1 4 4 1 4 0 3 0 1 4 4 1 4 ( ( ) )( ( ) 1) ( ( ) ) ( ( ) 1) 1 1 ( ) ( )( ( ) ) ( ( ) 1) 2 DR R t t R t R t t R t C A T R t t R t                              + 2 0 1 4 4 1 41 4 4 1 4 0 1 4 ( )( ( ) ) ( ( ) 1)( ( ) )( ( ) 1) ( ) ( ( ) 1) 1 2 HR R t t R tH R t t R t A R t T                    1 4 1 4 4 4( ) ( ) ( 1) 0SC AR t R t at A b t T      … (34) Here we obtain two simultaneous non-linear equation in of t1 and t4 can be find out optimal value by using some suitable computational numerical method and the optimum value of t2, t3, Im, Ib and minimum total average cost „K‟ can be obtained from equations. V. Special Cases: Case I : If b = 0 then the discussed model convert to production inventory model in which production rate is constant and independent on the demand. Case II : If 0)(0  then the discussed model reduces to production inventory model with out deterioration Case III : If 0 , 0b  the model reduce to uniform production rate and constant demand.
14. Modelling of repairable items for production inventory with random deterioration DOI: 10.9790/5728-11145669 www.iosrjournals.org 69 |Page VI. Conclusion In the proposed model a production inventory model is formulated for random deteriorating item with a increasing market demand rate with time and production rate is dependent on the demand. Result in this study can provide a valuable reference for decision markers in planning the production and controlling the inventory. The model proposed here in is resolved by using maclaurin series and cost minimization technique is used to get the approximate expression for total average cost and other parameters & some special cases of model are also discussed. We derive an expressions for different cost associated in the model. We derive equations, solution of these equations gives the optimal cycle and optimal cost of repairable items. A future study will incorporate more realistic assumption in the proposed model. References [1]. Alamri, A.A. (2010). Theory and methodology on the global optimal solution to a Reverse logistics inventory model for deteriorating items and time varying rates. Computer & Industrial Engineering,(60), 236-247. [2]. Balkhi, Z. T. and Benkherouf, L. (1996 b)On the optimal replenishment schedule for an inventoy system with deteriorating items and time varying demand and production rates.Computers & Industrial Engineering, 30 ; 823-829.. [3]. Bhunia, A. K. and Maiti, M. (1998) A two warehouse inventory model for deteriorating items with a linear trend in demand and shortages.Jour of Opl. Res. Soc., 49 : 287-292. [4]. Chang, H. J. and Dye, C. Y. (1999) An EOQ model for deteriorating items with time varying demand and partial backlogging.Jour, of Opl. Res. Soc., 50 : 1176-1182. [5]. Chung, C. J., & Wee, H. M. (2011). Short life-cycle deteriorating product remanufacturing in a green supply chain inventory control system. International Journal of Production Economics, 129(1), 195-203. [6]. Covert, R.P., and Philip, G.C.,( 1973), An EOQ Model for Item with Weibull Distribution Deterioration, AIIE Transactions, 5, (4), 323-326, [7]. Dobos, I., & Richter, K. (2003), A production/recycling model with stationary demand and return rates.Central European journal of Operations Research, 11(1), 35-46. [8]. Dobos, I., & Richter, K. (2004), An extended production/recycling model with stationary demand and return rates. International Journal of production Economics, 90(3), 311-323. [9]. Dobos, I., & Richter, K. (2006), A production/recycling model with quality considerations. International Journal of Production Economics, 104(2), 571-579. [10]. El Saadany A. M. A., & Jaber M. Y. (2010)., A production/ remanufacturing inventory model with price and quality dependant return rate. Computers and Industrial Engineering, 58(3), 352–362. [11]. Ghare, P.M., and Schrader, G.F.,(1963), A Model for An Exponentially Decaying Inventory, The Journal of Industrial Engineering, 14, (5), 238-243. [12]. Goswami, A and Chaudhuri, K. S. (1991) EOQ model for an inventory with a linear trend in demand and finite rate of replenishment considering shortages.int. Jour. Syst ScL, 22, 181-187. [13]. Konstantaras, I., & Skouri, K. (2010), Lot sizing for a single product recovery system with variable set up numbers. European Journal of Operations Research, 203(2), 326-335. [14]. Perumal, V. and Arivarignan, G. (2002)A production inventory model with two rates of production and backorders.Int. Jour of Mgt. & Syst., 18 (1) : 109 -119. [15]. Pyke, D. (1990 )“Priority Repair and Dispatch Policies for Reparable-Item Logistics Systems.”Naval Research Logistics v37 n1 1- 30 Feb. [16]. Raafat, F., Wolfe, P.M. and Eldin, H.K. An Inventory Model for Deteriorating Item, Computers & Industrial Engineering, 20, (1), 89-94, 1991. [17]. Richter, K, (1996b). The extended EOQ repair and waste disposal model. International Journal of Production Economics, 45(1-3), 443-447. [18]. Richter, K. (1996), The EOQ repair and waste disposal model with variable setup numbers. European Journal of Operational Research, 95(2), 313-324. [19]. Richter, K., & Dobos, I. (1999). Analysis of the EOQ repair and waste disposal model with integer set up numbers. International journal of production economics, 59(1-3), 463-467. [20]. Schrady, D.A. (1967). A deterministic inventory model for repairable items. Naval Research Logistics Quarterly, 14, 391–398. [21]. Teng, J. T. & Chang, C. T. (2005). Economic production quantity models for deteriorating items with price and stock-dependent demand. Computational Operations Research, 32 (2), 297-308. [22]. Teng, J. T. (1996) A deterministic replenishment model with linear trend in demand. Opns. Res. Lett. 19 : 33-41.
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