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Herawan T.,Ahmad Dahlan University | Vitasari P.,National Institute of Technology Bandung | Abdullah Z.,University of Malaysia, Terengganu
International Journal of Continuing Engineering Education and Life-Long Learning | Year: 2013

One of the commonly and popular techniques used in data mining application is association rules mining. The purpose of this study is to apply an enhanced association rules mining method, so called significant least pattern growth (SLP-growth) proposed by Abdullah et al. (2010a) for capturing interesting rules in student suffering language and social anxieties dataset. The datasets were taken from a survey among engineering students in Universiti Malaysia Pahang (UMP). The results of this research will provide useful information for educators to make a decision on their students more accurately, and to adapt their teaching strategies accordingly. It can be helpful to assist students in handling their fear of language and social. Furthermore, it is also useful in increasing the quality of learning. Copyright © 2013 Inderscience Enterprises Ltd.

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.

Salhi S.,University of Kent | Irawan C.A.,University of Portsmouth | Irawan C.A.,National Institute of Technology Bandung
Computers and Operations Research | Year: 2014

A special data compression approach using a quadtree-based method is proposed for allocating very large demand points to their nearest facilities while eliminating aggregation error. This allocation procedure is shown to be extremely effective when solving very large facility location problems in the Euclidian space. Our method basically aggregates demand points where it eliminates aggregation-based allocation error, and disaggregates them if necessary. The method is assessed first on the allocation problems and then embedded into the search for solving a class of discrete facility location problems namely the p-median and the vertex p-center problems. We use randomly generated and TSP datasets for testing our method. The results of the experiments show that the quadtree-based approach is very effective in reducing the computing time for this class of location problems. © 2014 Elsevier Ltd. All rights reserved.

Irawan C.A.,National Institute of Technology Bandung | Jones D.,University of Portsmouth | Ouelhadj D.,University of Portsmouth
Computers and Operations Research | Year: 2016

A bi-objective optimisation using a compromise programming approach is proposed for installation scheduling of an offshore wind farm. As the installation cost and the completion period of the installation are important aspects in the construction of an offshore wind farm, the proposed method is used to deal with those conflicting objectives. We develop a mathematical model using integer linear programming (ILP) to determine the optimal installation schedule considering several constraints such as weather condition and the availability of vessels. We suggest two approaches to deal with the multi-objective installation scheduling problem, namely compromise programming with exact method and with metaheuristic techniques. In the exact method the problem is solved by CPLEX whereas in the metaheuristic approach we propose Variable Neighbourhood Search (VNS) and Simulated Annealing (SA). Moreover, greedy algorithms and a local search for solving the scheduling problem are introduced. Two generated datasets are used for testing our approaches. The computational experiments show that the proposed metaheuristic approaches produce interesting results as the optimal solution for some cases is obtained. © 2015 Elsevier Ltd.

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.

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.

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.

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.

Nurbanasari M.,National Institute of Technology Bandung
Journal of Failure Analysis and Prevention | Year: 2014

The leakage of a supercritical boiler tube has been investigated. The leakage was observed during a working pressure hydrostatic test under 40.1 MPa. The internal geometry of the investigated leaking tube was multi-lead ribbed tube. Various methods for investigation namely radiography, microstructural analysis using optical and scanning electron microscopes, Vickers hardness testing and chemical analysis were conducted to investigate the main cause of leakage. The results revealed that the material tube met the standard for supercritical boiler tube (ASTM A 213 Grade T12). From the microstructural analysis, there was a crack, which initiated from the outer wall adjacent to the weld metal and propagated to the inner wall of the tube. The crack was due to a weld defect known as "excessive melt through" which is due to overheating during the welding process in joining the tubes. It is suggested that control of welding process parameters must be accomplished during fabrication to make a furnace wall, and placing strip of steel between the tubes to reduce the fit-up gap should be considered. © 2014 ASM International.

Herbudiman B.,National Institute of Technology Bandung | Saptaji A.M.,National Institute of Technology Bandung
Procedia Engineering | Year: 2013

Bad reinforcement concrete works could generate building failures after earthquake. Concrete pouring and compacting on structural element with dense reinforcement and beam column joint are difficult. Suitable solution on this problem is the use of self-compacting concrete that has flow-ability, filling-ability, and passing-ability. Traditional roof tile waste is available in Indonesian villages. The use of traditional roof tile powder in self-compacting concrete is an effort to recycle waste and new development in environmental friendly concrete material technology. This research tends to understanding contribution of traditional roof tile powder in development of workability and strength of self-compacting concrete. On this research, self compacting concretes are designed as follows: 1) water-powder ratio (w/p) is designed with 0.35, 0.32, and 0.29; 2) maximum dimension of coarse aggregate is limited by 15 and 20 mm; 3) dosages of traditional roof tile powder are 0%,10%,20%, and 30% from powder weight; 4) dosage of silica fume sets to be 5% for all trial mixes; 5) super-plasticizer is added with dosage of 0.5%, 1.0%, 1.2% and 1.5% from powder weight to achieve flow characteristic of self compacting concrete; 5) aggregates are washed before mixing. Indonesian standard (SNI 03-2834-2000) combined with simple mix design Okamura are used to calculate the compositions of self-compacting concrete. Test on fresh concrete is slump spread for all trial mixes. The mix that has the largest slump spread is tested with V-funnel and L-shaped box. Specimens of cylinder with diameter of 10 cm and height of 20 cm are used in this research to determine the compressive strength and split-tensile strength. Maximum diameter of slump spread could achieve 65 cm. Duration in V-funnel test is 14.6 second. In L-shaped box, duration to reach 40 cm and to reach box-end are 45 and 65 second, respectively. Blocking/passing ratio (H2/H1) is 4.5/32. Optimum dosage of traditional roof tile powder is 20% at w/p of 0.35 and dosage of super-plasticizer of 1% that has compressive strength of 44.11 MPa and split-tensile strength of 3.25 MPa. Washing aggregate before mixing could increase workability performance and increase compressive and split-tensile strength of 17.06 % and 42.37 %. Coarse aggregate with maximum dimension of 20 mm has compressive strength of 51.05 MPa. Optimum w/p is 0.32 and optimum dosage of super-plasticizer is 1.5% at dosage of traditional roof tile powder of 20%, dosage of silica fume of 5%, and proportion of coarse aggregate of 45% that has the largest compressive strength of 67.72 MPa. © 2013 The Authors.

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