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1

Minimizing total tardiness in no-wait flowshops

Aldowaisan T., Allahverdi A.

Foundations of Computing and Decision Sciences

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2012

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Vol. 37, No. 3

149--162

EN

We address the m-machine no-wait flowshop scheduling problem where the objective is to minimize total tardiness. To the best of our knowledge, the considered problem has not been addressed so far. We propose heuristic solutions since the problem is NP-hard. Initially, we consider a number of dispatching rules commonly used for the considered objective in other scheduling environments. We identify through computational experiments the best performing dispatching rule and then propose simulated annealing (SA) and genetic algorithms (GA) by using the best performing dispatching rule as an initial solution. This achieves at least 50% improvement in the SA and GA performances. Next, we propose enhanced versions of SA and GA and show through computational experiments that the enhanced versions provide over 90% further improvement. The performance of enhanced GA is slightly better than that of enhanced SA however, the computation time of enhanced GA is about 10 times that of enhanced SA. Therefore, we conclude that the enhanced SA outperforms the enhanced GA.

2

Dwuskładnikowa mieszanina naturalnej pucolany z gipsem aktywowana klinkierem portlandzkim i chemicznym aktywatorem

Allahverdi A., Najafi Kani E., Abolhasani S.

Cement Wapno Beton

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2011

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R. 16/78, nr 3

139-147

PL

Badano mieszaniny naturalnej pucolany z gipsem oraz bez i z dodatkiem mielonego klinkieru portlandzkiego, a także z chemicznym aktywatorem. Dla porównania przeprowadzono także doświadczenia z klinkierem, lecz bez gipsu. Z mieszanin tych sporządzono zaczyny o stałej urabialności, jednak ze zmiennym stosunkiem wody do spoiwa w zakresie od 0,34 do 0,28. Oznaczono koniec czasu wiązania oraz wytrzymałość na ściskanie po 28 dniach, skurcz suszenia i powstawanie wykwitów, także po tym okresie. Wyniki doświadczeń wykazały, że wytrzymałość na ściskanie wzrasta z 17 MPa do 32 MPa, przy zwiększającym się dodatku klinkieru, jednak pewien dalszy wzrost wytrzymałości wystąpił przy równoczesnym dodatku chemicznego aktywatora. Mieszaniny te z 25% dodatkiem gipsu, kosztem pucolany, osiągnęły praktycznie taką samą wytrzymałość, niezależnie od mniejszego stosunku wody do spoiwa. Dodatek chemicznego aktywatora pociągnął za sobą znaczne zmniejszenie skurczu suszenia, natomiast zwiększenie wykwitów, szczególnie w przypadku jego 4% zawartości.

EN

The mixtures of natural pozzolana with gypsum without and with ground Portland cement clinker as well with chemical activator were investigated. For comparison also mixes with clinker, and witout gypsum were examined. Of these mixtures pastes were obtained with equal workability, but changeable water to binder ratio, in the range from 0.34 to 0.28. Final setting time, compressive strength after 28 days of hardening, drying shrinkage and the efflorescence also after 28 days were examined. The results of experiments have shown that the compressive strength increases from 17 MPa to 32 MPa with the increased ground clinker content, however a small increase is also found when chemical additive was simultaneously added to these mixtures. 25% content of gypsum, replacing pozzolana in these mixtures, gives practically the same strength, intedendently of lower water to binder ratio. The addition of chemical activator causes the significant decrease of drying shrinkage, but the efflorescence phenomena increased with the chemical activator content, especially in the case of 4%.

3

Chemiczna aktywacja naturalnej pucolany za pomocą stałego aktywatora

Allahverdi A., Rahmani A.

Cement Wapno Beton

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2009

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R. 14/76, nr 4

205-213

PL

Otrzymano spoiwo złożone w 77% z naturalnej pucolany pumeksowej, a w 23% z aktywatora zawierającego ponad 90% cementu portlandzkiego i niewielkie ilości substancji chemicznych złożonych z siarki i metali alkalicznych. Zbadano właściwości zaczynu i zapraw sporządzonych z tego spoiwa. Czas wiązania był zawarty w granicach od 210 minut (początek wiązania) do 300 minut (koniec wiązania). Wytrzymałość zaprawy wzrastała z około 23 MPa po 28 dniach do 45 MPa po rocznym dojrzewaniu. Badania wykazały, że opracowany aktywator pozwala na otrzymanie dobrej jakości spoiwa z naturalnej pucolany pumeksowej. Jest to spoiwo niezwykle przyjazne dla środowiska.

EN

The binder was produced consisting of 77% of natural pozzolana pumice-type and 23% of activator composed chiefly of Portland cement and small addition of chemical substances containing sulfure and alkali metals. The properties of paste and mortars prepared on the basis of this binder were investigated. Setting time of the binder was the range from 210 min (beginning of setting) to 300 minutes (final setting time). The compressive strength was 23 MPa after 28 days of hardening till 45 MPa after one year of curing. The experimental results showed that the elaborated activator gives the possibility for producing good quality binder from natural puzzolana of pumice-type. This binder is very environmental friendly.

4

Three-machine flowshop scheduling problem to minimize total completion time with bounded setup and processing times

Allahverdi A.

Decision Making in Manufacturing and Services

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2007

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Vol. 1, no. 1-2

5-23

EN

The three-machine flowshop scheduling problem to minimize total completion time is studied where setup times are treated as separate from processing times. Setup and processing times of all jobs on all machines are unknown variables before the actual occurrence of these times. The lower and upper bounds for setup and processing times of each job on each machine is the only information that is available. In such a scheduling environment, there may not exist a unique schedule that remains optimal for all possible realizations of setup and processing times. Therefore, it is desired to obtain a set of dominating schedules (which dominate all other schedules) if possible. The objective for such a scheduling environment is to reduce the size of dominating schedule set. We obtain global and local dominance relations for a three-machine flowshop scheduling problem. Furthermore, we illustrate the use of dominance relations by numerical examples and conduct computational experiments on randomly generated problems to measure the effectiveness of the developed dominance relations. The computational experiments show that the developed dominance relations are quite helpful in reducing the size of dominating schedules.