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Salhi S.,University of Canterbury | Imran A.,National Institute of Technology Bandung | Wassan N.A.,University of Canterbury
Computers and Operations Research | Year: 2013

The multi-depot fleet size and mix vehicle routing problem, also known as the multi-depot routing with heterogeneous vehicles, is investigated. A mathematical formulation is given and lower as well as upper bounds are produced using a three hour execution time of CPLEX. An efficient implementation of variable neighborhood search that incorporates new features in addition to the adaptation of several existing neighborhoods and local search operators is proposed. These features include a preprocessing scheme for identifying borderline customers, a mechanism that aggregates and disaggregates routes between depots, and a neighborhood reduction test that saves nearly 80% of the CPU time, especially on the large instances. The proposed algorithm is highly competitive as it produces 23 new best results when tested on the 26 data instances published in the literature. Crown Copyright © 2013.

Noersomadi,National Institute of Technology Bandung | Tsuda T.,Kyoto University
Annales Geophysicae | Year: 2016

We retrieved temperature (T) profiles with a high vertical resolution using the full spectrum inversion (FSI) method from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS radio occultation (GPS-RO) data from January 2007 to December 2009. We studied the characteristics of temperature perturbations in the stratosphere at 20-27 km altitude. This height range does not include a sharp jump in the background Brunt-Väisälä frequency squared (N2) near the tropopause, and it was reasonably stable regardless of season and latitude. We analyzed the vertical wavenumber spectra of gravity waves (GWs) with vertical wavelengths ranging from 0.5 to 3.5 km, and we integrated the (total) potential energy Ep T. Another integration of the spectra from 0.5 to 1.75 km was defined as Ep S for short vertical wavelength GWs, which was not studied with the conventional geometrical optics (GO) retrievals. We also estimated the logarithmic spectral slope (p) for the saturated portion of spectra with a linear regression fitting from 0.5 to 1.75 km. Latitude and time variations in the spectral parameters were investigated in two longitudinal regions: (a) 90-150°E, where the topography was more complicated, and (b) 170-230°E, which is dominated by oceans. We compared Ep T, Ep S, and p, with the mean zonal winds (U) and outgoing longwave radiation (OLR). We also show a ratio of Ep S to Ep T and discuss the generation source of Ep S. Ep T and p clearly showed an annual cycle, with their maximum values in winter at 30-50°N in region (a), and 50-70°N in region (b), which was related to the topography. At 30-50°N in region (b), Ep T and p exhibited some irregular variations in addition to an annual cycle. In the Southern Hemisphere, we also found an annual oscillation in Ep T and p, but it showed a time lag of about 2 months relative to U. Characteristics of Ep T and p in the tropical region seem to be related to convective activity. The ratio of Ep T to the theoretical model value, assuming saturated GWs, became larger in the equatorial region and over mountainous regions. © Author(s) 2016.

Nurbanasari M.,University of Sheffield | Nurbanasari M.,National Institute of Technology Bandung | Tsakiropoulos P.,University of Sheffield | Palmiere E.J.,University of Sheffield
ISIJ International | Year: 2014

Carbide precipitation in a H21 tool steel during conventional heat treatment was studied. The aim of this work was to study the exact microstructure and for better understanding of carbide formation during double tempering process of the H21 tool steel. The steel was austenised either at 1 100°C or 1 250°C for 1 hour, and water quenched. Double tempering was performed at 650, 750 and 800°C for 1 hour with air cooling in the first and second temper for each austenising temperature. The results showed that the double tempered microstructure consisted of tempered martensite, lower bainite and carbides. The current study confirmed previous findings and contributed to existing knowledge that depending on the tempering temperature, the types of carbide formed during double tempering were M2C, Fe3C, M6C and M23C6 carbides. The present study findings add substantially to our understanding of the carbide formation sequence in the H21 tool steel during double tempering. No secondary peak hardening was observed, and the highest hardness (505 HV) was obtained after austenising at 1 250°C and double tempering at 650°C, which implies that the double tempering of the H21 tool steel should be carried out below 650°C. © 2014 ISIJ.

Juwana I.,National Institute of Technology Bandung | Muttil N.,Victoria University of Melbourne | Perera B.J.C.,Victoria University of Melbourne
Science of the Total Environment | Year: 2012

In the past few decades, there have been extensive efforts on measuring sustainability. One example is the development of assessment tools based on sustainability indicators. Several individuals and organisations have suggested various indices for assessing sustainability. This paper focuses on the review of water sustainability assessment using the indicator-based approach. It discusses major definitions of sustainable development that have been proposed and more specific concepts of sustainability based on sustainability principles and criteria. It then proceeds with the review of existing definitions, principles and guidelines on sustainable water resource management. The paper then explores elements of indicator-based water sustainability assessment. These elements include the selection of components and indicators, obtaining sub-index values, weighting schemes for components and indicators, aggregation of components and indicators, robustness analysis of the index, and interpretation of the final index value. These six elements are explored considering four existing water sustainability indices and two other sustainability indices that are thought to be useful for the development and use of water sustainability indices.The review presented in this paper on indicator-based water sustainability assessment can provide significant inputs to water stakeholders worldwide for using existing indices, for customising existing indices for their applications, and for developing new water sustainability indices. These indices can provide information on current conditions of water resources, including identifying all factors contributing to the improvement of water resources. This information can be used to communicate the current status of existing water resources to the wider community. Also, the water sustainability indices can be used to assist decision makers to prioritise issues, challenges and programmes related to water resource management. © 2012 Elsevier B.V.

Nurbanasari M.,National Institute of Technology Bandung | Abdurrachim,Bandung Institute of Technology
Case Studies in Engineering Failure Analysis | Year: 2014

The failure of the first stage blade in a steam turbine of 55. MW was investigated. The blade was made of 17-4 PH stainless steel and has been used for 12 years before failure. The current work aims to find out the main cause of the first stage blade failure. The methods for investigation were metallurgical analysis, chemical composition test, and hardness measurement. The result showed that there was no evidence the blade failure was due to material. The damage found on the blade namely crack on the blade root. Two locations of the crack observed at the blade root, which was at the tang and the fillet, with different failure modes. In general, the damage of the blade was started by the corrosion occurred on the blade root. The crack at the blade root tang was due to corrosion fatigue and the crack occurred at the blade root fillet owing to stress corrosion cracking. © 2014 The Authors.

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