Geri kazanımlı kapalı çevrim tedarik zinciri için dağıtım planlama
Distributon planning of a closed-loop supply chain with product recovery
Yazar: İREM OTAY
Danışman: PROF. DR. FERHAN ÇEBİ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İşletme Mühendisliği Ana Bilim Dalı
Derece: Doktora, 2015
Konu: İşletme = Business Administration

Özet:
Artan nüfus artışı, iklimsel değişiklikler  ve  doğal kaynakların hızla tükenmesi  gibi 
çeşitli  faktörler  işletmeleri  kaynak  tüketimini  azaltmaya  ve  böylece  maliyetleri 
düşürmeye  yönlendirmiştir.  Bunlara  ek  olarak,  günümüzün  zorlu  rekabet  ortamı, 
teknolojideki hızlı gelişmeler,  son yıllarda çevre bilincinin artmasıyla  müşterilerin 
ürün  ve/veya  hizmet  alırken  çevreci  yaklaşımlar  sergileyen  işletmelerden  yana 
tercihlerini yapmaları ve çeşitli yasal yükümlülükler, çevreye dost ürünlerin üretimi, 
atıkların  geri  dönüşümü  ve  ürün,  parça  ve  malzemelerin  yeniden  kazanımı  gibi 
konulara  verilen  önemi  arttırmıştır.  Bu  faktörler  tersine  lojistik  faaliyetlerini 
incelenmesi, ürün, parça ve malzemeler için ileri ve tersine lojistik faaliyetlerinin etkin 
bir şekilde yönetilmesini gerektirmiş ve ürün geri kazanım yaklaşımları gibi konulara 
olan rağbeti arttırmıştır. Araştırmalar göstermiştir ki, tüm bu konuların dikkatle ele 
alınması ve planlanması işletmelere rekabet avantajı sağlamaktadır.  
Bu kapsamda, bu doktora tez çalışması ürünlerin ileri ve geri akışlarını dikkate alan 
kapalı  çevrim  tedarik  zinciri  için  üretim  ve  dağıtım  faaliyetlerinin  planlanması 
konusunu incelemektedir. Kapsamlı bir literatür araştırmasıyla, kapalı çevrim tedarik 
zinciri  ve  tersine  lojistik  konularında  yapılan  çalışmalar  araştırılmıştır.  Ardından 
tersine lojistik ve kapalı çevrim tedarik zincirindeki belirsizlikler dikkate alınarak 
bulanık kapalı çevrim tedarik zinciri modelleri, bulanık kümeler ve bulanık modelleme 
konuları üzerinde durulmuştur. Bu bilgiler ışığında, farklı işletmelerin problemlerini 
çözmeye  yönelik  olarak  çeşitli  varsayımlar  altında  matematiksel  modeller 
geliştirilmiştir.  Geliştirilen  modeller  nümerik  örnekler  için  çözülerek  modellerin 
çalışıp çalışmadığı kontrol edilmiştir. Daha sonrada bu modeller göz önüne alınarak  
genelleştirilmiş  bir  model  oluşturulmuştur.  Uygulama  bölümünde  ise  geliştirilmiş 
modeller gerçek hayat problemine göre revize edilmiştir. Model, birden çok yeniden 
kullanılabilen ürün ve tek bir üretici, birden çok distribütör ve bölge deposu ile çok 
sayıdaki müşteriyi içermektedir.  Model tek bir dönem için planlama yapmakta ve 
birden  çok  amacı  göz  önüne  almaktadır.  Dikkate  alınan  amaçlardan  ilki,  kapalı 
çevrimdeki toplam maliyetin minimum kılınmasıdır. Diğer amaçlar sırasıyla, ileri ve 
tersine  ürün akışı  sırasında  meydana  gelen  sera  etkisi  yaratan  gazlardan  biri  olan 
karbondioksit  gazının  emisyonunun  minimum  kılınması  ve  müşterilerden  geri 
toplanamayan (kullanılmış) ürün miktarının minimum kılınması şeklindedir. 
Kapalı çevrim tedarik zincirinde birçok belirsizlik ve eksik bilgi bulunmaktadır. Bu 
belirsizlikler,  geri  dönüş  oranında,  geri  dönen  ürünün  kalitesinde,  geri  dönüş 
zamanında olabileceği gibi ürünlerin talebinde de olabilmektedir. Bu belirsizlik ve 
eksik  bilgilerle  başa  çıkabilmek  için  çok  amaçlı  karma  tam  sayılı  doğrusal 
programlama  modelinin  çözümünde  bulanık  küme  ve  bulanık  modellemeden 
yararlanılmıştır.  
Modeldeki  belirsizlik  iki  şekilde  incelenmiştir.  İlk  olarak  hedef  ve  kısıtlardaki 
bulanıklık ele alınmıştır. Modeldeki tüm hedeflerin erişim seviyeleri ile talep kısıtının 
bulanık olduğu durum değerlendirilmiştir. Bulanık çok amaçlı modelin geleneksel tek 
amaçlı  doğrusal  programlama  modeline  dönüştürülmesinde  ağırlıklı  toplamsal 
modelden yararlanılmıştır. Daha sonra ise, modeldeki çeşitli  parametrelerdeki  (geri 
dönüşüm oranı ve talep  gibi)  bulanıklık ele alınmıştır. Her iki durum gerçek hayat 
problemi için çözülmüştür. Modellerin çözümünde GAMS 24.02 - CPLEX solverdan 
yararlanılmıştır. Ek olarak, modellerin doğruluk ve geçerlilik analizleri ile duyarlılık 
analizleri  gerçekleştirilerek  sonuçlar  analiz  edilmiş  ve  gelecek  çalışmalar  için 
önerilerde bulunulmuştur.

Abstract:
Increasing population, climate changes, and rapid consuption of  natural resources are 
the  factors  that  led  organizations  to  reduce  sources  and  to  decrease  costs.  Today's 
highly  competitive  environment,  increasing  advancements  in  technology,  growing 
customers  environmental  consciousness  and  legislations  force  organizations  to 
produce environmentally friendly products, and to concentrate on waste management 
and  recovery  approaches  of  products,  components,  and  materials.  All  these  factors 
require  to  examine  reverse  logistic  activities,  to  plan  reverse  flows  of  products, 
components,  and  materials  and  to  manage  effectively  and  efficiently  forward  and 
reverse logistic activities. 
One  of  the  important  topics  in  reverse  logistics  is  recovery  approaches.   There  are 
different approaches which  vary depending on the organization operate and even on 
the  product,  component  and  material.  Therefore,  choosing  the  appropriate  recovery 
approach is both complex and important topic for the organizations. 
The researches have highlighted that consideration of all these issues and planning of 
forward  and  reverse  flows  of  products  help  organizations  for  decreasing  costs, 
reducing resource consumptions while increasing productivity and proficiency, as well 
as  protecting  environment.  Therefore,  effective  management  of  both  forward  and 
reverse flows allows organizations to gain competitive advantage in the market. 
For all these reasons, closed-loop supply chain and reverse logistics have been one of 
the critical and popular topics drawing attentions of researchers and practitioners for 
more than two decades. In the literature some of the studies concentrate only on the 
aspect of reverse flows while some other integrate both the forward and the reverse 
flows. In this dissertation, closed-loop supply chain integating both the forward and 
the reverse flows of the products is examined. 
By conducting a comprehensive literature review, papers with regard to closed-loop 
supply  chain  and  reverse  logistics  are  analyzed  and  classified  depending  on  the 
problem they handle. The literature review points out that the studies mainly focus on 
some of the topics such as network design, inventory control, life-cycle analysis, and 
routing  problems.  However,  this  dissertation  concentrates  on  production  and 
distribution planning problem of a closed-loop supply chain for recoverable products 
by considering forward and reverse flows of products.  
The review also highlights that there are few studies made on reuse which is one of 
the product recovery options.  However, a large  amount of  studies are conducted on 
particularly  recycling  and  remanufacturing  recovery  options.  In  addition,  there  are 
some  studies  integrating  couple  of  product  recovery  options  such  as  recycling  and repairing,  recycling  and  remanufacturing  while  there  are  a  few  number  of  studies 
conducted for reusable products and/or items.  
The  review  also  indicates  that  that  there  are  only  some  studies  using  fuzzy  logic 
methodology for recoverable products. However, researchers emphasize that the fuzzy 
logic  and  fuzzy  modelling  provide  efficient  solutions  for  handling  uncertainties, 
vaguness and lack of information in the real life applications. For this reasons, fuzzy 
closed-loop  supply  chain  models  are  reviewed  in  the  literature  by  considering 
uncertainties  and  lack  of  information  in  the  closed-loop  supply  chain  and  reverse 
logistics topics. 
In the dissertation, the fundamental concepts on fuzzy sets, extension principle, fuzzy 
numbers  and  fuzzy  arithmetic  operations  are  defined.  Then,  fuzzy  mathematical 
modelling  is  analyzed  in  two  different  ways  in  which  the  previous  deals  with  the 
fuzziness in the objectives and in the constraints while the last considers the fuzziness 
in  the  parameters  (technological  coefficients  and  right  hand  side  values  in  the 
constraints).  
By considering all these information stated above, in this dissertation, production and 
distribution planning problem for a closed-loop supply chain is analyzed under fuzzy 
environment. In this pursuit, a various mathematical models are developed for bringing 
solutions to production and distribution planning problems of different organizations.  
For  each  model,  graphical  illustrations  marking  forward  and  reverse  flows  of  the 
products are given in the dissertation to make the model more understandable. Also, 
indices, variables and parameters are defined and matematical models are formulated. 
The developed models are solved for numerical examples to check if the models are 
running.  The  results  obtained  from  the  solutions  are  presented  using  graphics.  The 
results show that all the developed models run. 
This  study  systematically  analyzing  the  closed  loop  supply  chain  production  and 
distribution problem from a broad perspective illustrates the application to the real life 
industrial problem. In the application part, the developed models are revised for the 
real-life industrial problem. All the necessary parameters are collected from the factory 
operating in Istanbul. The factory prefered to change proportionally the real data. The 
model  considering  multiple  reusable  products  is  composed  of  a  single  producer, 
multiple distributors and multiple regional  warehouses as well as a large  number of 
customers that demand the reusable products from the factory. The model is conducted 
for the city of Istanbul and constructed for a single time period.  
A  varity  of  objectives  are  evaluated  in  the  model.  One  of  the  objectives  having  an 
economical perspective is to minimized total costs of a closed-loop supply chain. The 
second  objective  having  enviromental  perspective  is  to  minimize  carbon  dioxide 
emissions occuring during forward and reverse flows of the products. This objective 
considers  all  the  forward  and  the  reverse  transportation  activities  between  a  factory 
and  distributors,  factory  and  regional  warehouses,  distributors  and  customers  in  the 
model. This is one of the important objectives since carbon dioxide is playing essential 
role  as  green  house  gas.  Additionally,  carbon  dioxide  emission  is  also  one  of  the 
popular  and  important  topics  that  researchers  and  practitionars  work  on.  The  last 
objective  deals  with  minimizing  total  number  of  products  that  can  not  be  collected 
back  from  the  customers.  The  objective  is  essential  especially  for  the  organizations 
that reuse products or components. The reduction in lost products help organization to 
reduce  consumption  of  sources,  to  protect  environment  and  to  reduce  costs  such  as procurement costs, and transportation costs. Thus, this objective is also essential for 
the organizations.  
On the other hand, in real life applications, there are uncertainties, vaguness and lack 
of information with regard to closed-loop supply chain and reverse logistics. One of 
the uncertainties are with regard to return rate of the products. The other uncertainty is 
on  quality  of  the  returned  products  or  items.  There  are  also  uncertainties  related  to 
timing of returning items and even demands of the reusable products. To deal with the 
uncertainties,  in  this  dissertation  the  developed  multiobjective  mixed-integer  linear 
programming model is solved by using the concepts of fuzzy sets and fuzzy modelling.  
In the application of the proposed model, the uncertainties associated to the problem 
are  determined  by  reviewing  the  literature  and  by  consulting  to  the  factory 
management. The uncertainties are evaluated in two different aspects. Firstly, all the 
mentioned objectives and demand constraint are taken as fuzzy. Demand constraint is 
specifically chosen in the analysis because it affects many important decisions that the 
managers should make on such as inventory, production and logistics. For the solution 
of  the  first  model,  weighted  additive  approach  is  used  for  converting  the  fuzzy 
multiobjective model into crisp linear mathematical model having a single objective. 
This approach is prefered for the solution of the problem since the approach is easy to 
understand  and  easy  to  conduct.  In  addition,  it  is  also  easy  to  apply  and  it  gives 
effective solutions. In the approach, weights obtained from fuzzy Analytic Hierarchy 
Analysis are assigned to the fuzzy objectives and fuzzy constraint. 
Secondly,  some  of  the  important  model  parameters  such  as  product  return  rate  and 
product demand, are also evaluated under fuzzy environment. In this approach, there 
is no weight attained to the objectives and constraints. The model aims to reach a single 
satisfaction level for all the uncertainties and maximize this level.  
For solving both of the single objective crisp mathematical models, an optimization 
software  called  GAMS  (general  algebraic  modelling  system)  24.04  with  CPLEX 
solver  is  used.  Both  of  the  models  are  solved  in  couple  of  seconds  and  optimal 
solutions are obtained for both of them.  
The  solutions  of  both  models  given  in  the  application  section  demonstrate  different 
results.  Even  though  demands  of  the  customers  are  all  satisfied,  there  are  some 
differences in the results related to  the distributors  that the factory have to send the 
products, the amount of products should be sent to distributors by the factory, and the 
distributors should serve to the customers.  
In  addition,  the  values  calculated  for  each  objective  also  changed.  For  instance, 
according to the first model total cost, total CO2 emissions and total lost products are 
calculated as 20.316.460 TL, 39,6 tonne and 668.540 products, respectively. On the 
other  hand,  total  costs,  total  CO2  emissions  and  total  lost  products  are  obtained  as 
22.552.820 TL, 47,5 tonne and 675.580 products, respectively.  
In this context, the verification and validation analysis are conducted. First, distributors 
are selected randomly and the capacity of them are assigned as "0". Then, the distances 
between factory and distributors are increased around 10.000 km. Thus, the model is 
tested if it gives rational results. The results of these analysis show that the model does 
not choose the distributor having the capacity of zero and choose the distributor which 
is far away from the factory.  
Sensitivity  analysis  is  also  performed  to  check  if  there  is  a  change  in  the  solutions 
when the parameters are changed. In this analysis, the weights of the fuzzy objectives and fuzzy constraints are systematically changed. Starting from the first objective, the 
weights are changed  in  the  range  of  [0,10;1.0]  with  an  incremental  increase  of 
0,10 while the rest of the weights are changed proportionally. The results are illustrated 
by figures. 
Lastly,  the  discussions,  conclusions  and  suggestions  for  the  further  studies  are 
represented.