فهرست مطالب
مجله مهندسی صنایع و مدیریت شریف
سال سی‌ام شماره 1 (بهار و تابستان 1393)
- تاریخ انتشار: 1393/03/16
- تعداد عناوین: 14
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صفحات 3-12روش تاگوچی، روشی موثر و کارا در افزایش کیفیت محصول یا فرایند است. هدف این روش کاهش میزان تاثیر عوامل اغتشاش بر مقدار متغیر پاسخ است به گونه یی که متغیر پاسخ نسبت به تغییرات عوامل اغتشاش مقاوم شود. تاگوچی به منظور بررسی و تجزیه و تحلیل متغیر پاسخ، نسبت سیگنال به اغتشاش را معرفی کرد. در این مطالعه یک شاخص نوین سیگنال به اغتشاش، براساس فاصله ی اقلیدسی و مساحت ناحیه ی فرایند برای متغیرهای پاسخ وابسته به هم ارائه می شود. معیار ارائه شده چنان است که هم معیاری است برای اندازه گیری فاصله تا هدف، و هم معیاری است برای اندازه گیری میزان تغییرات مشاهدات)مشتمل بر تغییرات ناشی از هر متغیر و ناشی از کواریانس بین متغیرها(. روش پیشنهادی در سه مثال مورد بررسی قرار گرفته، و کارایی روش پیشنهادی نشان داده شده است.
کلیدواژگان: نسبت سیگنال به اغتشاش، فاصله ی اقلیدسی، ناحیه ی فرایند، روش تاگوچی، پاسخ های وابسته به هم -
صفحات 13-24گلوگاه ها معمولا به عنوان منابع محدودی شناخته می شوند که عملکرد کل خط تولید را تحت تاثیر قرار می دهند. بنابراین زمان بندی برپایه ی گلوگاه را می توان رویکردی مفید برشمرد. از طرف دیگر یافتن بهترین مکان گلوگاه، برای معیارهای عملکردی مختلف سبب ارائه ی راهکارهای مناسب سرمایه گذاری برای افزایش ظرفیت می شود. در این تحقیق تاثیر مکان گلوگاه بر معیارهای $C_{m a x}$، میانگین مدت زمان توقف کارها، متوسط زمان چرخه، متوسط زمان انجام کار و متوسط تعداد قطعات نیمه ساخته در محیط سری انعطاف پذیر با ماشین های غیرمشابه مورد بررسی قرار گرفته است. برای بررسی این تاثیر یک روش ابتکاری مبتنی بر گلوگاه براساس ایده ی نظریه ی محدودیت ها توسعه داده شده است. نتایج نشان می دهد که برای حالات و مقادیر فرض شده، مکان گلوگاه بر معیارهای $C_{m a x}$ و متوسط زمان چرخه تاثیرگذار نیست، در حالی که بر معیارهای میانگین مدت زمان توقف کارها، متوسط زمان انجام کار و متوسط تعداد قطعات نیمه ساخته موثر است.
کلیدواژگان: محیط سری انعطاف پذیر_ معیارهای عملکردی، گلوگاه ها، زمان بندی بر پایه ی گلوگاه ها، روش ابتکاری -
صفحات 25-34گذرنامه ی الکترونیکی یکی از کاربردهای تکنولوژی شناسایی از طریق امواج (R F I D)، به عنوان سند مهم شناسایی و احراز هویت است. با توجه به اهداف سازمان ایکائومبنی بر مجهز شدن تمامی کشورها به گذرنامه ی الکترونیکی، افزایش امنیت و همچنین لزوم اجرای گذرنامه ی الکترونیکی در ایران، ضروری است تهدیدها و راهکارهای امنیتی گذرنامه ی الکترونیکی مورد تحقیق قرار گیرد. در این مقاله هدف بر آن است که برای اولین بار تهدیدهای امنیتی گذرنامه ی الکترونیکی بررسی و راهکارهای مربوطه پیشنهاد شوند. بدین منظور ابتدا تهدیدهای امنیتی و نقض حریم شخصی استخراج و سپس از طریق پرسش نامه راهکارهای موثر برای کاهش تهدیدها شناسایی می شوند. نتایج تحقیق نشان می دهد که مهم ترین مخاطرات تاثیرگذار بر گذرنامه ی الکترونیکی شنودگذاری، سرقت، جعل و افشای اطلاعات است؛ همچنین می توان راهکارهای تایید اعتبار فعال، کنترل دسترسی مقدماتی و کنترل دسترسی پیشرفته را به عنوان گزینه های قابل استفاده و موثر در گذرنامه ی الکترونیکی به کار گرفت.
کلیدواژگان: شناسایی از طریق امواج رادیویی، حریم شخصی، امنیت، گذرنامه ی الکترونیکی -
بهینه سازی حد کنترل در نگه داری و تعمیر مبتنی بر شرایط با فرض ثابت نبودن هزینه ی تعویض به دلیل خرابیصفحات 35-45در نگه داری و تعمیر مبتنی بر شرایط دستگاه هدف این است که با انجام بازرسی و کنترل شرایط، دستگاه به عمر واقعی تعویض نزدیک شد. در روش حد کنترل، تابع توام نرخ مخاطره دستگاه و تاثیر متغیرهای کنترل شرایط، با استفاده از مدل تلفیقی نرخ مخاطره (P H M)، و با توجه به سوابق اطلاعاتی دستگاه تخمین زده می شود. سپس، بهترین حد کنترل به گونه یی تعیین می شود که متوسط هزینه های تعویض به دلیل خرابی و تعویض پیشگیرانه در یک دوره ی طولانی کمینه شود. در مدل ارائه شده در این نوشتار، فرض ثابت بودن هزینه ی تعویض به دلیل خرابی حذف و هزینه ی این نوع خرابی، تابعی صعودی از عمر دستگاه و مقادیر متغیرهای تشخیص خرابی در نظر گرفته شده است. سپس مدلی برای تعیین بهترین حد کنترل ارائه شده است، به گونه یی که متوسط هزینه های تعویض کمینه شود. یک مثال عددی نیز به منظور تشریح بهتر مدل، ارائه شده است.
کلیدواژگان: نگه داری و تعمیرات براساس شرایط، مدل تلفیقی نرخ مخاطره، سیاست تعویض، برنامه ریزی پویا، هزینه ی تعویض متغیر -
صفحات 47-57سیستم های مرکز تماس یکی از پرکاربردترین سیستم های مورد استفاده در مراکز و سازمان ها برای پاسخ گویی به سوالات مشتریان است. طراحی و پیکربندی بهینه ی سیستم یکی از مسائل و حوزه های اصلی به خصوص برای مراکز تماس چندگانه است. در این ارتباط، افزایش کارایی امکانات سیستم، به ویژه نیروی انسانی از یک سو و افزایش رضایت مشتریان از سوی دیگر، مهم ترین اهداف سیستم های مرکز تماس است. طی سال های اخیر رویکردهای متنوعی برای حل این مسئله ارائه شده، اما بیشتر این رویکردها تنها به تحلیل عملکرد مرکز می پردازند. رویکردهای بهینه سازی ارائه شده نیز صرفا از دیدگاه مشتری یا کارفرما طراحی شده اند. در این مطالعه یک رویکرد بهینه سازی براساس متدولوژی سطح پاسخ و طراحی آزمایشات پیشنهاد شده، که نه تنها به طور همزمان رضایت مشتریان و بهره وری امکانات مرکز تماس را بیشینه می کند، بلکه همبستگی بالقوه بین اهداف را نیز ضمن تلاش برای کمینه سازی اثر متغیرهای غیر قابل کنترل)عوامل اختلال(روی اهداف لحاظ می کند.
کلیدواژگان: مرکز تماس چندگانه، طراحی آزمایشات، متدولوژی سطح پاسخ -
صفحات 59-67
در این نوشتار مسئله ی زمان بندی تولید کارگاهی انعطاف پذیردر حالت چندهدفه با سه معیار «دوره زمانی ساخت»، «مجموع بار کاری» و «بیشینه بار کاری ماشین ها» مورد بررسی قرار می گیرد. بدین منظور ابتدا مسئله بررسی و مدل ریاضی آن ارائه شده، و سپس با توجه به ماهیت بسیار پیچیده ی مسئله از یک نگرش یک پارچه برای حل آن استفاده شده است.
نگرش پیشنهادی با استفاده از یک رویه جست وجوی شناور و چندین الگوریتم ابتکاری جست وجوی محلی، مسئله را از حالت بررسی سلسله مراتبی به حالت یک پارچه تبدیل می کند و سپس با استفاده از یک الگوریتم مبتنی بر روش های پارتو و N S G A I I مجموعه جواب پارتو را به دست می آورد. به منظور تحلیل کارایی و اثربخشی الگوریتم پیشنهادی، تجزیه و تحلیل های عددی در ابعاد مختلف انجام و با نتایج تحقیق های قبلی مقایسه شده است. نتایج به دست آمده کارایی الگوریتم پیشنهادی را هم در کاهش تغییرپذیری جست وجو و هم در بهبود جواب های نهایی نشان می دهد.کلیدواژگان: تولید کارگاهی انعطاف پذیر_ تغییرپذیری، الگوریتم های ابتکاری چندهدفه، رویکرد جست وجوی شناور -
صفحات 69-79کارت امتیازی متوازن (B S C) از مدل های چندبعدی در ارزیابی عملکرد سازمانی است که وظیفه اش ایجاد توازن بین معیارهای مالی و غیرمالی، معیارهای قابل اندازه گیری و غیرقابل اندازه گیری، و محرک های عملکرد و نتایج است. درخصوص ارزیابی عملکرد و اجرای B S C تحقیقات بسیاری صورت گرفته، اما در بسیاری از آنها وجود روابط پویا بین ابعاد B S C نادیده گرفته شده است. در این تحقیق از هر دو روش فرایند تحلیل سلسله مراتبی (A H P) و تحلیل شبکه یی (A N P) در اجرای B S C به منظور ارزیابی عملکرد یک بانک، استفاده شده تا از این طریق نتایج حاصل از تاثیرات وابستگی بین معیارهای عملکرد بررسی شود. همچنین برای مواجهه با شرایط عدم اطمینان، نتایج حاصل از این روش ها در محیط فازی نیز مورد بررسی قرار گرفته است. نتایج نشان می دهد که A N P)هم در محیط قطعی و هم فازی(نسبت به A H P)در محیط قطعی و فازی(یک رویکرد قوی و مناسب برای تسهیل اجرای مدل های ارزیابی عملکرد برپایه ی B S C است.
کلیدواژگان: ارزیابی عملکرد، کارت امتیازی متوازن، فرایند تحلیل سلسله مراتبی فازی، فرایند تحلیل شبکه یی فازی -
صفحات 81-89هدف این مطالعه شناسایی بخش های متمایزی از مشتریان بازار موبایل کشور با کمک روش های کمی است. امروزه با توجه به اهمیت داده ها در ارائه ی مناسب تر خدمات، بازاریابی هدف مند و تخصیص بهینه ی منابع، «داده کاوی» به عنوان یکی از ابزارهای شناسایی الگوهای موجود بین حجم عظیمی از اطلاعات درهم ریخته، اهمیت یافته است. از آنجا که در صنعت تلفن همراه، دسترسی به حجم بالایی از اطلاعات مفید کاربران به آسانی ممکن است، می توان از این ابزار استفاده کرد. یکی از کاربردهای این ابزار «خوشه بندی مشتریان» است. در این مطالعه ضمن شناسایی و گردآوری، خوشه بندی و تحلیل داده ها، با کمک نرم افزار S P S S C l e m e n t i n e و الگوریتم دومرحله یی سری زمانی، داده های قبوض مشترکین تحلیل شد. نتایج خوشه بندی حاکی از وجود پنج خوشه ی متمایز است. با بررسی درآمد ناشی از گروه های پنج گانه، برقراری اصل پارتو مشهود است. همچنین مشترکین در خوشه هایی که ظاهرا سهم کمی از کل مشترکین را تشکیل می دهند، تا 20 برابر مشترکین بزرگ ترین خوشه ی شناسایی شده، درآمدزایی دارند.
کلیدواژگان: بخش بندی بازار، داده کاوی، خوشه بندی، الگوریتم دومرحله یی، صنعت تلفن همراه، اپراتور تلفن همراه، ایران -
صفحات 91-103علی رغم آشکار شدن مزایای فراوان برون سپاری فعالیت های لجستیک به شرکت های لجستیکی طرف سوم)3P L ها(هنوز در ایران شاهد انجام امور لجستیکی توسط خود بنگاه ها هستیم. یکی از دلایل اصلی این موضوع، نبود 3P L های قدرت مند و مدرن در کشور است. با توجه به برخورداری برخی از شرکت های لجستیکی سنتی داخلی از پتانسیل لازم برای تبدیل شدن به 3P L، در این نوشتار به دنبال ارائه ی راهکارهایی برای این منظور هستیم. براین اساس، نسبت به شناسایی عوامل تاثیرگذار بر توانایی هماهنگی مشتریان و توانایی تطبیق پذیری با مشتریان به عنوان دو عامل بحرانی در بنگاه های لجستیکی اقدام شده است. عوامل شناسایی شده عبارت اند از: سیستم های اطلاعاتی و مدیریت اطلاعات، پوشش جغرافیایی و دامنه ی خدمت رسانی، استانداردسازی خدمات، انعطاف پذیری پیش نگر و مدیریت تقاضا برای توانایی هماهنگی مشتریان و عوامل تخصص در صنعت خاص، انعطاف پذیری واکنشی و مدیریت تقاضا برای توانایی تطبیق پذیری با مشتریان. برای درک بهتر مطلب و مطالعه ی موردی در این خصوص، شرکت حمل ونقل بین المللی خلیج فارس موردی بررسی قرار می گیرد.
کلیدواژگان: لجستیک طرف سوم، توانایی هماهنگی مشتریان، توانایی تطبیق پذیری با مشتریان -
صفحات 105-111مسئله ی انتخاب تامین کننده یکی از مراحل مهم مدیریت زنجیره ی تامین است و به دلیل برخورداری از ماهیت چندشاخصه بودن، ذهن دانشمندان زیادی را به خود مشغول کرده است. از آنجا که در دنیای واقعی متغیرها غالبا غیرقطعی اند این پژوهش به استفاده از نظریه ی فازی در مسئله ی انتخاب تامین کننده می پردازد. بدین منظور مدلی با سه هدف کمینه کردن هزینه، بیشینه کردن کیفیت و بیشینه کردن تحویل به موقع با پارامترهای فازی مثلثی پیشنهاد شده است. به دلیل وجود محدودیت تامین تقاضای فازی، متغیرهای اندازه ی سفارش نیز به صورت فازی تعریف شده اند که درنتیجه مسئله حالت فازی کامل پیدا کرده است. برای حل این مسئله ی چندهدفه ی فازی کامل از روش برنامه ریزی فازی استفاده شده است. با حل این مدل در یک مثال عددی، الگوریتم حل مسئله به خوبی تبیین شده است.
کلیدواژگان: مسئله ی انتخاب تامین کننده، عدد فازی مثلثی، مدل فازی کامل و روش برنامه ریزی فازی -
صفحات 113-119در سال های اخیر پایش پروفایل ها، که در آن کیفیت محصول یا عملکرد فرایند به وسیله ی رابطه ی رگرسیونی بین یک متغیر پاسخ و یک یا چند متغیر مستقل توصیف می شود، مورد توجه محققین قرار گرفته است. این رابطه در پروفایل ها انواع مختلفی دارد نظیر رگرسیون خطی ساده، رگرسیون خطی چندگانه، رگرسیون غیرخطی و رگرسیون مبتنی بر مدل های خطی تعمیم یافته که برای پایش آنها روش هایی ارائه شده است. از سوی دیگر، محققین روش های تطبیقی مختلفی برای بهبود عملکرد نمودارهای کنترل در کشف شیفت های پدید آمده در پارامترهای مدل به کار گرفته اند. در این نوشتار نیز به طور خاص بر نمودار کنترل میانگین متحرک موزون نمایی چندمتغیره (M E W M A) برای پایش پروفایل های خطی چندگانه متمرکز شده و با تطبیقی کردن ضریب هموارسازی عملکرد روش را بهبود بخشیده ایم. این بهبود از طریق مطالعات شبیه سازی و مقایسه ی معیار متوسط طول دنباله در قالب دو مثال نشان داده شده است.
کلیدواژگان: نمودار کنترل تطبیقی، پروفایل، میانگین متحرک موزون نمایی چندمتغیره، متوسط طول دنباله -
صفحات 121-130مسئله ی چندین فروشنده ی دوره گرد (M T S P) گسترشی است مشهور از مسئله ی فروشنده ی دوره گرد (T S P)، که ثابت شده یک مسئله ی N P-h a r d است. اگرچه M T S P یک مسئله ی پیچیده ی بهینه سازی ترکیباتی است، می توان آن را به مسائل گوناگونی در مسیریابی و زمان بندی توسعه داد. به علاوه، تحقیقات روی این مسئله، برخلاف T S P که گستردگی آن توجه بسیار زیادی را به خود معطوف کرده، بسیار محدود بوده است. از این رو، در این نوشتار یک روش جدید بهینه سازی به نام «الگوریتم رقابت بهره جویانه (I C A)» برای حل این مسئله ارائه می شود. این روش ملهم از رقابت کشورهای مستقل و وابسته برای حل مسائل بهینه سازی ترکیباتی است. الگوریتم پیشنهادی روی دو دسته مسائل از ادبیات موضوع مورد آزمایش قرار گرفته است. نتایج محاسباتی نشان می دهد که الگوریتم رقابت خوبی با دیگر الگوریتم های فراابتکاری برای حل مسائل M T S P داشته است. همچنین چندین جواب بهینه به وسیله ی الگوریتم پیشنهادی به دست آمد.
کلیدواژگان: مسئله ی چندین فروشنده ی دوره گرد، الگوریتم رقابت بهره جویانه، مسائل بهینه سازی ترکیباتی، مسئله ی مسیریابی وسیله ی نقلیه -
صفحات 131-136توزیع به مراحلی اطلاق می شود که برای انتقال و انبار یک محصول از مرحله ی تامین کننده تا مرحله ی مشتری در زنجیره ی تامین انجام می گیرد. توزیع یکی از عوامل اصلی سودآوری در هر بنگاه است زیرا مستقیما بر هزینه ی زنجیره ی تامین و تجربه ی مشتری تاثیر می گذارد. از توزیع خوب می توان برای به دست آوردن اهداف مختلف زنجیره ی تامین از هزینه ی پایین گرفته تا پاسخ گویی بالآ بهره جست. برای طراحی شبکه ی توزیع می توان از ایجاد هاب استفاده کرد؛ هاب ها تسهیلات ویژه یی هستند که نقش ایستگاه های واسطه یی را در سیستم های توزیع ایفا می کنند، به طوری که با تعیین مسیر و سازمان دهی ترافیک بین جفت نقاط مبدا/مقصد (بسته به نوع مسئله) سبب کاهش زمان، هزینه، یا بهبود عوامل دیگر می شوند. در این نوشتار مدل برنامه ریزی ریاضی عدد صحیح مختلط برای طراحی شبکه ی توزیع محصولات کارخانه با استفاده از مکان یابی هاب و با در نظر گرفتن حدودیت های ظرفیت و سطح سرویس دهی ارائه می شود.
کلیدواژگان: زنجیره ی تامین، شبکه ی توزیع، مکان یابی هاب، P میانه، سطح سرویس دهی -
صفحات 137-150امروزه برای تبدیل خواسته های مشتریان به مشخصه های فنی محصول از رویکرد گسترش عملکرد کیفیت یا گسترش کارایی کیفی (Q F D) به طور وسیعی استفاده می شود. در این رویکرد رتبه بندی و وزن دهی صحیح هریک از خواسته های مشتریان حائز اهمیت است، چرا که این امر بر ارزش نهایی مشخصه های فنی محصول تاثیر خواهد گذاشت. هر فرد تصمیم گیرنده درک متفاوتی از ارزیابی متغیرهای زبانی در محیط فازی دارد، هدف از این تحقیق روش جدید وزن دهی به خواسته های مشتریان و مشخصه های فنی براساس اطلاعات رقبا و ارائه ی روش سیستماتیک Q F D فازی است. موفقیت یک محصول نه تنها به مطابقت با نیازهای شتریان، بلکه به مقایسه و ارزیابی محصولات رقبا نیز بستگی دارد. اکثر روش های پیشین تنها بر دیدگاه مشتری متمرکز بوده و از محیط رقابتی چشم پوشی کرده اند. روش پیشنهادی شامل موقعیت رقبا، وزن دهی متفاوت مشتریان گوناگون، عملکرد فعلی و نظر مشتریان به درک های متفاوت از متغیرهای زبانی،درنظر گرفتن سقف خانه ی کیفیت فازی، به علاوه استفاده از ریاضیات فازی به جای اعداد قطعی در مقایسه با روش های قبل است. این روش می تواند بهترین استراتژی طراحی محصول را در اختیار سازمان قرار دهد.
کلیدواژگان: گسترش عملکرد کیفیت، خانه کیفیت فازی، ندای مشتری، محیط رقابتی، قاعده ی پارتو، آنتروپی
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Pages 3-12The Taguchi method is an effective method for improving the quality of processes or products. This method tries to decrease the effects of noise factors on a response variable, so that a response variable would be robust towards variations in noise factors. Hence, changes in external circumstances will have a minimum effect on the response variable, and the product or the process can be used with little change in response variables under any situation. Taguchi introduced the signal to noise ratio (SNR) for considering and analyzing response variables. This method considers the distance of the process mean from the target, as well as the variation between observations, and tries to decrease variations and bring the response mean to the target. Although this index has some advantages, it is inefficient for considering a multivariate problem, because the correlation between responses is neglected using this index. Hence, another method should be applied to introduce single measurement or multi objective techniques which need weight vector for responses. In this paper, a new method is developed as an alternative for SNR according to the Euclidean distance and process region. It is based on correlations between variables, by which different patterns can be identified and analyzed. It is also a useful way of determining the similarity of an unknown sample set to a known one. It differs from Euclidean distance and takes into account the correlations of the data set. In addition, it is scale-invariant, i.e. not dependent on the scale of measurements. The process region represents observations, according to their variance and correlation. Hence, as the variation of observations increases, the volume of the process region increases. This concept is used in many methods, such as process capability indices, as a measurement of variation between observations.The proposed index accounts for the distance of the process mean from the target (using Euclidean distance) and variations of observations (using process region). This method is capable for application to multivariate normal cases and presents a single index to consider those problems. An important advantage of the proposed index (called MSN) is that the correlation between responses is considered. So, there is no need to apply any other techniques, such as principal component analysis or other multi criteria decision techniques to the problem.Keywords: Signal to noise ratio, Euclidean distance, Process region, Taguchi method, Correlated responses
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Pages 13-24Bottlenecks are known as constraint recourses, as they govern overall system performance. Thus, bottleneck based scheduling is a useful approach. In this research, a new heuristic algorithm, based on the bottleneck, is developed for scheduling in flexible flow shop scheduling with unrelated parallel machines. Flexible flow shop scheduling problems (FFS), with multiple unrelated machines, contain sequencing in the flow shop, where, at any stage, there exists one or more unrelated processor. The proposed algorithm is based on the theory of constraints (TOC); a manufacturing philosophy that states: ``bottleneck resources govern overall system performance''. Performance enhancement of the bottleneck stage can improve overall performance, whereas, also, finding the bottleneck stage and exploiting it can optimize the whole system performance. Based on this idea, this heuristic algorithm consists of four steps: 1) finding the bottleneck stage: a stage with the largest work load, 2) local search: in this algorithm, sequencing in the bottleneck stage is improved by applying a bottleneck-based multiple insertion procedure (BBMIP) to the initial sequence, 3) scheduling the jobs at the bottleneck stage: based on three indicators (minimum necessary time to bottleneck stage, minimum necessary time from bottleneck stage to last stage and largest processing time), this heuristic method schedules jobs in the bottleneck stage, 4) scheduling the jobs at the non-bottleneck stage; consisting of upstream stages (based on completion at a previous stage and start time in the bottleneck stage) and downstream stages (based on completion at the previous stage and minimum necessary time from the bottleneck stage). Afterwards, finding the best position of the bottleneck in a production system can help to make a good decision for investment. In this research, the influence of bottleneck position on various performance criteria is investigated. For this purpose, five different criteria are used: $C_{max}$ (maximum job completion time in the last stage), average job idle time, average cycle time, average lead time and average work-in process (WIP). Various experimental factors are used to design multiple scenarios to investigate the effect of the bottleneck position on performance criteria. For each scenario, 10 test problems are generated. These criteria contain bottleneck position, number of jobs, number of stages, number of machine stages, and processing time in bottleneck and non-bottleneck stages. Based on these experimental factors, 540 test problems have been generated. Results show that the bottleneck position has no significant influence on $C_{max}$ and average cycle time, but other criteria, such as average job idle time, average lead time and average work-in process, are influenced by bottleneck position.Keywords: Flexible flow shop, Performance criteria, Bottlenecks, Bottleneck, based scheduling, heuristic method
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Pages 25-34In the near future, millions of people around the world will be directly dealing with Radio Frequency Identification (RFID) technology. This technology is defined as a method for providing accurate and concurrent information, without human interference. Some RFID applications are: ATM cards and electronic passports. One of the most important and recent applications of RFID is the electronic passport, which uses biometric technology for authenticating passenger use. Inside the passport, a chip is embedded, in which personal and biometric information is stored. Considering the importance of the data, there is risk of information abuse, causing people to worry about a violation of their privacy. Information theft and eavesdropping are major threats, and, therefore, a method must be employed to ensure the strong security of e-passports to prevent these problems. Considering the ICAO goal, based on electronic passports in all countries, for improving passenger convenience and increasing security, the electronic passport project has been running since 1390 and all citizens should now have one. It is necessary that threats and security issues regarding electronic passports should be examined and investigated. The aim of this paper is identification of security threats when an electronic passport is used and proposing solutions to prevent these threats. Based on our knowledge, it is the first time that security and privacy violations are studied for e-passports in Iran. For this purpose, a questionnaire has been developed which covers the factors concerning privacy violations and solutions for their reduction. The questionnaire was prepared by 35 experts in the field of RFID and e-passports. The results show that major threats affecting the electronic passport are eavesdropping, disclosure of biometric information, theft, and fraud of information. Basic access control, advanced access control, and active and passive authentication can be used as effective solutions in electronic passports.Keywords: Radio frequency identification (RFID), Privacy, Security, E, passport
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Pages 35-45The primary goal of condition-based maintenance (CBM) is to extend system lifetime based on the information collected through periodic inspections. There have been many attempts to include economic considerations in the process of decision making in CBM. A well-known approach is called the control limit policy. In this approach, using historical data of the equipment and the values of condition monitoring covariates, the hazard rate function is first estimated. It is assumed that the inspections are performed at fixed and given intervals of time. The equipment is replaced whenever it fails. Also, after each inspection and based on the inspection results, if the cost-related failure rate reaches or exceeds a pre-determined limit, a preventive replacement is scheduled. The limit is, then, determined such that the expected average maintenance costs per unit time, due to preventive and failure replacements over a long time horizon, is minimized. However, it is assumed that the failure cost is constant, no matter when or at which state the failure occurs. Using the main principals of the control limit policy, this paper extends the approach assuming that the failure cost depends on both the age of the system and the value of the covariates observed. This assumption is more practical, as equipment usually incurs more failure cost as it deteriorates. However, determination of the function that can represent the variable failure cost is often difficult. In this paper, we consider a hypothetical non-decreasing failure cost function. This does not limit the scope of the application of the proposed method, as its relaxation only entails replacing the failure cost function with the one determined in a given application. The derivation of the required mathematical formulation to obtain the optimal control limit is presented in detail. A numerical example is also given to illustrate the proposed approach.Keywords: Condition, based maintenance, Proportional hazard, odel, Replacement policy, Dynamic programming, Variable failure cost
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Pages 47-57A call center is a centralized office used for the purpose of receiving and transmitting a large volume of requests by telephone. A call centre often operates through an extensive open workspace for call centre agents, with work stations that include a computer for each agent, a telephone set/headset connected to a telecom switch, and one or more supervisor stations. Call centers can operate independently or be networked with additional centers, called a multi call center.System configuration optimization is one of the main problems in multi call centers. Improvement of system utilization and customer satisfaction are the most important objectives in a call center system. In recent years, different approaches have been developed for solving this problem. Most of these approaches only stress the analysis of system performance. Furthermore, these approaches usually focus on either customer or employer viewpoints. In this paper, a multi-objective optimization approach, based on response surface methodology and the design of experiments, is proposed. The proposed approach maximizes customer satisfaction and system utilization simultaneously. Response surface methodology (RSM) is a collection of mathematical and statistical techniques that are useful for modeling and analysis in applications where responses of interest are influenced by several variables, and the objective is to optimize these responses simultaneously.In the proposed approach, decision variables are the number of operators in any center, number of links between centers and length of waiting queue. Simultaneous objectives include maximization of operator utilization and link utilization; minimization of the percentage of balking calls, and customers waiting time in the system. The proposed approach consists of three phases; design of experiments, simulation and optimization. First, a factorial design is developed to evaluate system performances. Then, an aggregated method is used to convert various objectives into a single objective function. In this study, the aggregation measure is the probability of all four objective functions simultaneously meeting their desirable regions (P(Y$in$S)). In order to estimate this measure, we simulate the system. In the next step, the response surface of the aggregated measure, with respect to design variables, is obtained. Finally, by maximization of P(Y$in$S), optimum values of factors are obtained. The validity and performance of the proposed method were investigated on the data of a multi call center system consisting of three call centers. The results of the proposed method were compared with the solutions of common methods in the literature. The result of the proposed method outperformed the results obtained by other approaches.Keywords: Multi call center, design of experiment, Response surface methodology
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Pages 59-67
Scheduling for flexible job shops is very important in both fields of production management and combinatorial optimization. However, it is quite difficult to achieve an optimal solution to this problem in medium and actual size problems with traditional optimization approaches, owing to the high complexity of computations. The flexible job shop scheduling problem (FJSP) extends the job shop scheduling problem (JSP) by assuming that, for each given operation, there is at least one instance of the machine type necessary to perform it. The scheduling problem of a FJSP consists of a routing sub-problem, i.e., assigning each operation to a machine out of a set of capable machines, and the scheduling sub-problem, i.e., sequencing the assigned operations on all machines, in order to obtain a feasible schedule minimizing a predefined objective function. The FJSP mainly presents two difficulties. The first is to assign each operation to a machine, and the second is to schedule these operations in order to make a predefined minimal objective. The FJSP is a much more complex version of the JSP, so the FJSP is strongly NP-hard and combinatorial. It incorporates all of the difficulties and complexities of its predecessor, JSP, and is more complex because of the additional need to determine the assignment of operations to machines. This paper attempts to simultaneously optimize three objectives, including minimization of the makespan, total workload and critical workload. Since the multi objective flexible job shop scheduling problem is strongly NP-Hard, an integrated heuristic approach is used for solving it. The proposed approach is based on a floating search procedure that uses some heuristic algorithms. The floating search procedure uses local heuristic algorithms, which make the considered problem into two sub problems, including assigning and sequencing sub problems. Then, a search is done on the assignment space. After achieving an acceptable solution, a search is done on the sequencing space, based on a heuristic algorithm. This paper used a multi-objective approach for producing a pareto solution. This proposed approach is adapted from the NSGA II algorithm and evaluates pareto-archives. The elements and parameters of the proposed algorithms are adjusted based on preliminary experiments. Then, computational results are used to analyze the efficiency of the proposed algorithm.
Keywords: Flexible job shop scheduling, Variability, Multi, objective meta heuristic algorithm, Floating search procedure -
Pages 69-79The balanced scorecard is a multidimensional model in organizational performance evaluation which creates a balance between financial and non-financial indicators, measurable and non-measurable criteria, internal and external aspects, performance drivers and results. Although numerous studies have been done in the field of performance evaluation and implementation of the BSC, in many of these studies, dynamic relationships and interdependencies between the dimensions of the BSC have been ignored. In this study, both methods of the analytic hierarchy process (AHP) and the analytic network process (ANP) in implementation of the BSC have been used to evaluate banking performance. Applying these methods, the dependency effect between performance criteria will be studied. In this regard, using a questionnaire and expert opinions, the final criteria of performance evaluation in the BSC framework are determined, and, after identifying the relation between these criteria, the network model of this study is designed. Finally, the weights of model criteria and sub-criteria will be calculated using AHP and ANP methods by MATLAB and Expert Choice software. Comparing both methods shows that ANP is a robust and appropriate approach to facilitate the implementation of performance evaluation models, based on the balanced scorecard, and it can also integrate the quantitative and qualitative data. Likewise, investigating dependency between dimensions and also determining the weights of BSC dimensions and related criteria, two significant aspects of implementing BSC, are described in this model.Furthermore, these methods have been implemented in the fuzzy environment for dealing with uncertainty and achieving more realistic decisions. Results show that a fuzzy environment provides simple conditions for making decisions, and, compared to a crisp environment, is more compatible with real conditions.As a result, the network performance evaluation model is designed, based on a combination of FANP and BSC approaches, to provide a more accurate and effective tool for decision-making.Keywords: Performance evaluation, balanced scorecard, Fuzzy analytic hierarchy process, Fuzzy analytic network process
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Pages 81-89The purpose of this study is to determine clusters of mobile subscribers, such that members within a cluster demonstrate common characteristics, while, at the same time, distinctive features can be uncovered among members of different clusters. Along with the increasing importance of data for organizations, it seems critical for managers to extract valuable information out of unstructured data through efficient access, sharing, extracting and implementing the data. Data mining is a promising tool to dig out patterns from a large amount of unsorted data. Telecommunication industry benefits from such data, opportunity. One of these favorable applications is consumer clustering, which leads to market segments. The study was conducted in three successive phases. First, the required data was determined and gathered through multiple expert panels. The second phase included running the clustering process, during which, the records were clustered. The last, but not the least, is analyzing the results. For the first phase, 16 million mobile post-paid bills were analyzed, using a two-step algorithm in SPSS Clementine. Each bill included 11 variables, out of which, 7 variables were chosen as important and effective for clustering and marketing purposes, due to technical and managerial insights. The other 4 variables were filtered. The clustering process was applied using these 7 variables as the input to the two-step clustering algorithm. The results revealed 5 distinctive clusters that demonstrated different behavior in various aspects, including the Pennywise, who just use limited voice call service, the Traditionalias who use a mid-level of voice service and a little of SMS, the Exorbitants use the maximum level of voice and medium level of SMS, pioneers who use newly offered services and provide the maximum revenue per user, and the followers, who are the biggest SMS users and use new services after pioneers. The Pareto principle was obviously observed when scrutinizing the earned revenue from each cluster. Dividing the revenues from each cluster by its size, we were able to plainly note that each member of the smallest cluster generated revenue 20 times greater than that of the largest one.Keywords: Market segmentation, Data Mining, Clustering, Two, step algorithm, Mobile industry, Mobile operator, Iran
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Pages 91-103In the modern competitive business environment, logistics activities of supply chains are not only considered an overhead cost, but also an important competitive advantage. Therefore, different companies have entrusted their logistics activities to specialists from organizations, using this competitive advantage, in addition to focusing on their core competencies and taking advantage of scale economies. These logistics specialists are called third party logistics service providers, or 3PL. 3PLs are service providers with high customer coordination and adaptation abilities, and provide a wide range of modern services in logistics. In spite of the benefits of outsourcing logistics, Iranian companies usually do their logistic activities themselves, and logistics outsourcing is limited in transportation and warehousing. One of the main reasons for this is the lack of a powerful and modern 3PL in Iran, even though there is a high potential for 3PLs in Iranian industries, such as automotive, oil and petrochemical, food and groceries, retail goods and etc. Therefore, formation of powerful and modern 3PLs in Iran is necessary. Two styles for formation of 3PLs are common. First, the companies start up directly the third party logistics business, and, second, traditional logistics firms try to enter this business by developing their abilities and facilities. In this article, the second one is studied. For this purpose, we look at the factors affecting customer coordination and adaptation abilities as critical factors for logistics firms. Information systems and information management ability, geographical coverage, proactive flexibility and demand management are factors that affect customer coordination abilities. Especially in industry, reactive flexibility and demand management are factors that affect customer adaptation abilities. With an improvement in these factors, traditional logistics firms can enter a third party logistics business. For better perusal of this issue, the Persian Gulf Transportation Company has been surveyed as a case study.Keywords: Customers adaptation ability, Customers coordination ability, Third party logistics
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Pages 105-111Supply chain management (SCM) is an important subject in competitive economics. A supply chain includes all activities related to the flow of goods from the raw material through to the customer, as well as information flow. Determination of appropriate suppliers in SCM is very significant. Therefore, a problem is defined, named the supplier selection, to evaluate each supplier. Supplier selection is a multi-criteria decision making (MCDM) problem. In MCDM problems there are two important issues: the method that should be selected and the criteria. A decision maker needs to use one of the MCDM methods to solve a problem. In this paper, a multi-objective model is proposed for the supplier selection problem. Objective functions, such as minimization of cost, and maximization of quality level and on-time delivery are considered criteria in this model. Since the parameters of the model cannot be predicted precisely, the fuzzy theory is used. Fuzzy set theory has been widely used to solve many complex problems. This theory has considered effective methods to manage both vagueness and uncertainty in different problems. In our proposed model, the parameters of objective functions, the demand constraint and all decision variables are defined as triangular fuzzy numbers. This type of problem, in which all parameters and variables are defined as fuzzy numbers, is called a fully fuzzy problem. So, our proposed model is a multi-objective fully fuzzy linear programming (MOFFLP) problem, and one of the most difficult to solve. In this study, for solving this MOFFLP problem, first a method is used which finds the fuzzy optimal solution of FFLP problems. This method has proved its efficiency in several problems and we have applied it to the supplier selection problem. In the next stage, a fuzzy programming technique, which is a common method used for solving multi-objective decision making (MODM) problems, is considered. Finally, a numerical example is given to illustrate the modeling idea and this example is solved step-by-step.Keywords: Supplier selection problem, Triangular fuzzy number, Fully fuzzy problem, Fuzzy programming technique
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Pages 113-119Statistical process control (SPC) is widely used in different industries to create high quality products through reducing the variability in processes. Among all SPC tools, the control chart is a powerful tool usually used by quality engineers. It can detect shifts in process parameters by distinguishing between common causes and special causes of variations. Quality characteristics can be univariate or multivariate and can be monitored by corresponding univariate or multivariate control charts. However, in some practical situations, the quality of a process or product is better characterized by a relationship between a response variable and one or more explanatory variables, which is usually referred to as a profile. In recent years, profile monitoring has been considered by many researchers and different applications of profile monitoring, such as calibration, are discussed in different papers. Different types of profile include simple linear regression, multiple linear and polynomial regression, nonlinear regression and logistic regression. Several methods are proposed in the literature of profile monitoring to monitor different types of profiles in both phases I and II. In phase I, one checks the stability of a process, while, in phase II, the aim is to detect shifts in the process parameters as quickly as possible.On the other hand, a variety of adaptive methods have been proposed by different researchers to improve the performance of control charts to detect small to large shifts in the process parameters quickly. When the adaptive control charts are applied, one or more design parameters vary during the production process, based on recent data obtained from the process. This paper proposes the use of an adaptive control chart for monitoring multiple linear regression profiles, and is focused on the proposed ultivariate xponentially weighted moving average (MEWMA) control chart by Zou et al. for monitoring general linear profiles. The proposed method improves the performance of the MEWMA control chart using an adaptive smoothing constant. This improvement is shown through simulation studies and comparison of an average run length criterion. The results show that in simple and multiple linear profiles, performance of the proposed method is better than the MEWMA method by Zou et al. [7] in the medium to large shifts considered in this paper.Keywords: adaptive control chart, Profile, Multivariate exponentially weighted moving average (MEWMA), average run length
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Pages 121-130The Multiple Traveling Salesmen Problem (MTSP) is a well-known generalization of the Traveling Salesman Problem (TSP). In general, The MTSP can be defined as follows:Given a set of n nodes (cities), let there be m salesmen located at a single depot node. The remaining nodes that are to be visited are called intermediate nodes. Then, the MTSP consists of finding tours for m salesmen. All of them start and end at the depot, such that each intermediate node is visited exactly once. Our aim is to minimize the total cost of visited nodes by the salesmen. There is a broad variety of versions of MTSP and a wide range of literature on this class of problems. The variants include MTSP with pickup and delivery, time windows, multi depots, and others. There have been important advances in the development of exact and approximate algorithms for solving the MTSP, as an important NP-hard combinatorial optimization problem. Although heuristic methods solve NP-hard problems, they become trapped in local optima and cannot gain a good suboptimal solution. As a result, in the last 30 years, a new kind of approximate algorithm called meta-heuristics has emerged. Basically, this type of algorithm tries to combine basic heuristic methods into higher level frameworks aimed at efficiently and effectively exploring a search space.In contrast, the research on the MTSP has received less attention than the TSP. Therefore, in this paper for the MTSP, a new meta-heuristic algorithm called the Imperialist Competitive Algorithm (ICA), is proposed. This algorithm has been motivated by the notion of imperialism and imperialistic competition in order to solve optimization problems. The proposed algorithm is tested using two benchmark data sets available from the literature. The computational results show that the ICA is competitive with other published results for solving MTSP. In addition, for some instances, the proposed algorithm gives better solutions.Keywords: Multiple traveling salesmen problem, Imperialist competitive algorithm, Combinatorial optimization problems, Vehicle routing problem
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Pages 131-136The system of transferring and storing a product from supplier to customer in the supply chain is called distribution. Keskinocak and Tayur (2001) established that the primary goal of supply chain management is to deliver the correct product to the correct place at the correct time, while maintaining cost efficiency. Designing a distribution network includes inventory holding, transportation and facilities, establishment costs and customer service. Distribution is one of the most important factors in the profitability of an enterprise because it affects supply chain cost directly. Increasing the number of distribution centers will increase inventory holding costs and decrease transportation costs and lead time for the customer. The hub location problem can be used in designing a distribution network. Hubs are special facilities that serve as switching, trans-shipment and sorting points in the distribution systems. Instead of serving each origin---destination pair directly, hub facilities concentrate flow in order to take advantage of he conomies of scale [20]. Hub-and-spoke networks are employed in various applications, such as cargo transportation, airline systems and telecommunication networks. Hub location problems deal with finding the location of hub facilities and the allocation of demand nodes to these located hub facilities. Hub network problems are divided into two categories; single allocation and multiple allocation. The difference between these two types is in the assignment of non-hub nodes to hubs. In single allocation, all the incoming and outgoing traffic of every demand center is routed through a single hub. In multiple allocation, each demand center can receive and send flow through more than one hub. In some research, only the allocation aspect was considered, but, it is important to know that optimal hub location is also effected by hub location. In this paper, we develop a MILP model for designing a istribution network using the hub location method, regarding hub capacity and service levels. The objective of this problem is minimizing transportation and construction costs.Keywords: Supply chain, Distribution network, Hub location problem, P, median, Service level
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Pages 137-150In a competitive environment, quality and price have an important role to play in the production of commodities. For this purpose, increasing the quality at a reasonable price is the first and most important issue for achieving a share in the market. Quality Function Deployment (QFD) has been one of the most successful tools for this purpose, for some years. Using QFD, we design and produce the finished goods or services which satisfy the needs of the customers. In fact, QFD transforms the needs of the customer to the technical characteristics of the product. However, usually, customer needs are presented in the form of subjective and verbal statements, which causes a reduction in the effectiveness of the questioners who are determining customer needs. The fuzzy approach has solved this problem. During the construction of QFD, using fuzzy numbers instead of crisp numbers, better results will be obtained. Fuzzy logic shows a range for each customer idea. Comparing the crisp with the fuzzy numbers, crisp numbers only identify one point in a wide range of possibilities. These issues are more highlighted when customer beliefs regarding one issue may be quite different from another.In this paper, all these possibilities are considered when the fuzzy environment for projecting the view of the customers is considered. First, the fuzzy environment and the house of quality are introduced. Then, a complete example, concerning the house of quality matrix as the most important factor in QFD, is presented.After determination of the technical characteristics of the product, the most important, determined by Pareto's law, are transmitted to the next step, which is the designing of the product. With emphasis on these important characteristics, by using fuzzy numbers for projecting the view of customer needs and by improving the design of the product based on them, we can be sure that customer satisfaction will be improved.Keywords: Quality function deployment, Fuzzy house of quality, Customer, Competition, Pareto's law
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