Pengembangan model dan algoritma Dynamic-Inventory Ship Routing Problem (D-ISRP)

Ketidakpastian tingkat kesibukan pelabuhan atau dwelling time menyebabkan ketidaksesuaian operasional kapal terhadap jadwal yang telah direncanakan. Lamanya waktu tunggu di pelabuhan mengakibatkan utilitas kapal menjadi rendah dan biaya distribusi meningkat karena pemberlakuan biaya pelabuhan. Dampak lainnya adalah memperbesar kemungkinan keterlambatan kapal yang berpotensi untuk menyebabkan terjadinya inventory stock out. Jika supplier menerapkan kebijakan vendor managed inventory (VMI), maka dalam hal ini supplier akan menanggung biaya penalti akibat keterlambatan tersebut. Untuk menghindari terjadinya keterlambatan, diperlukan evaluasi terhadap jadwal eksisting apabila terdapat informasi perubahan dwelling time. Oleh karena itu, pada penelitian ini dikembangkan model dynamic-inventory ship routing problem (D-ISRP), dimana proses re-routing berdasarkan informasi dwelling time akan dilakukan dengan mengevaluasi opsi perubahan kecepatan dan opsi perubahan urutan kunjungan. Kedua opsi tersebut kemudian dibandingkan untuk menentukan jadwal baru jika terjadi perubahan dwelling time. Model yang dikembangkan mempertimbangkan beberapa komponen biaya antara lain biaya konsumsi bahan bakar saat pelayaran, konsumsi bahan bakar saat berlabuh, biaya operasional kapal, biaya kepelabuhanan, biaya loading/unloading, serta biaya penalti keterlambatan. Permasalahan D-ISRP merupakan permasalahan NP-hard, maka pada penelitian ini dikembangkan juga algoritma heuristic berbasis interaction theory sebagai teknik solusi. Berdasarkan percobaan numerik yang dilakukan, disimpulkan bahwa algoritma yang dikembangkan dapat menyelesaikan permasalahan D-ISRP dan pada keseluruhan kondisi, opsi perubahan kecepatan menghasilkan performansi yang lebih baik dalam merespon perubahan informasi dwelling time. ============================================================================================= Uncertain dwelling time in a port can cause error in scheduling. The queue on a port will reduce ship utilization and increase the distribution cost because of higher port charge. Ship can also be late on other port that cause inventory stock out. These risks are disadvantages for supplier who implement Vendor Managed Inventory agreement. The supplier will be charged for lateness penalty cost. In order to cope with this problem, a model for dynamic inventory ship routing problem (D-ISRP) is developed in this research. The model will evaluate two alternative options, changing ship speed or changing route visiting sequence, if new information of dwelling time occured. The cost function to evaluate the scheduling options consists of sail bunker consumption, port bunker consumption, ship operational cost, port charge, loading/unloading cost, and penalty cost for late delivery. To solve this problem, an heuristic algorithm based on interaction theory has been developed. The algorithm determines the schedule based on the interaction coefficient of ships and ports. Finally, by some numerical experiments, we concluded that the algorithm has a high reliability in order to cope with DISRP and in general situations changing ship speed option will give better performance rather than changing ship route visiting sequence option

Model of Twin Automatic Stacking Crane Operation Strategy with Dynamic Handshake Area in an Automated Container Terminal

This paper proposes a new idea for allocating a handshake area of an automated container yard. A block of automated container yards (CY) consists of two areas, which are the import (waterside) and export (landside) areas. The CY has two major activities (loading and unloading), where both are served by Twin Automatic Stacking Cranes (Twin-ASCs). A handshake area in the middle of the CY serves as a temporary slot for both ASCs. This situation causes an imbalance between the ASCs when the demands of each side differ significantly. Thus, we proposed using a dynamic location of the handshake area corresponding to the proportion demand of export and import containers. We developed a heuristics model and algorithms of ASC’s operations to compare the efficiency of the ASC operations between the fixed and the dynamic location. Based on our model and algorithm, we developed simulation software. Finally, we explored some numerical experiments to compare the performance of both policies in dealing with different export and import demand scenarios. Our result showed that the proposed approach outperformed the existing one in reducing unnecessary ASC movements

Space-sharing Strategy for Building Dynamic Container Yard Storage Considering Uncertainty on Number of Incoming Containers

The implementation of AEC (Asian Economic Community) leads to demand increase at ports in Indonesia. This increasing demand is followed by operational efficiency at the port as well. In fact, ports in Indonesia have an average dwell time for 5 days. One of the causes of this long dwell time is container transfer inefficiencies during loading process. In this research, we will focus in yard management and increasing land utilization. To increase the land utilization, we develop the space-sharing concept to reduce the initial space needed for a given workload. Since the ships arrivals are also varying, this concept will be possible. We develop the concept by adding uncertainty on number of incoming containers at operational level as the determining factor in planning a shared yard area. We propose a simulation approach to evaluate strategies in making yard template

The effect of steam curing on chloride penetration in geopolymer concrete

In this paper, we present the result of our study on the effect of steam curing to chloride ion penetration in geopolymer concrete. Class F fly ash was activated using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The concrete specimens were then steam-cured at 40°C, 60°C, 80°C and room temperature at 24 hours. The treatment was followed by wet curing for 28 days, and then followed by immersion of all specimens in salt water for the durations of 30, 60, and 90 days. Cylindrical specimens were then prepared for compressive strength, chloride ion penetration, pH, and porosity tests. A 16 mm-steel bar was fixed at the center of the specimen concrete blocks (specimen size: 10cm × 10cm × 15cm). Corrosion probability was determined by conducting Half Cell Potential test. Our result showed that increasing the curing temperature to 80°C induced chloride ion penetration into the concrete’s effective pores, despite improvements in compressive strength. We also found that chloride ingress on the geopolymer concrete increases commensurately with the increase of the curing temperature. The corrosion potential measurement of geopolymer concrete was higher than OPC concrete even if corrosion was not observed in reinforcing. Based on our result, we suggest that the corrosion categorization for geopolymer concretes needs to be adjusted

The effect of steam curing on chloride penetration in geopolymer concrete

In this paper, we present the result of our study on the effect of steam curing to chloride ion penetration in geopolymer concrete. Class F fly ash was activated using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The concrete specimens were then steam-cured at 40°C, 60°C, 80°C and room temperature at 24 hours. The treatment was followed by wet curing for 28 days, and then followed by immersion of all specimens in salt water for the durations of 30, 60, and 90 days. Cylindrical specimens were then prepared for compressive strength, chloride ion penetration, pH, and porosity tests. A 16 mm-steel bar was fixed at the center of the specimen concrete blocks (specimen size: 10cm × 10cm × 15cm). Corrosion probability was determined by conducting Half Cell Potential test. Our result showed that increasing the curing temperature to 80°C induced chloride ion penetration into the concrete’s effective pores, despite improvements in compressive strength. We also found that chloride ingress on the geopolymer concrete increases commensurately with the increase of the curing temperature. The corrosion potential measurement of geopolymer concrete was higher than OPC concrete even if corrosion was not observed in reinforcing. Based on our result, we suggest that the corrosion categorization for geopolymer concretes needs to be adjusted