7,201 research outputs found
REKOMENDASI PENEMPATAN DISTRIBUTED GENERATION (DG) DENGAN KAPASITAS YANG AMAN TERHADAP KOORDINASI PROTEKSI YANG SUDAH ADA
No full textSemakin bertambahnya permintaan konsumen terhadap energi listrik dari tahun ketahun tentu semakin besar pula daya listrik yang harus disediakan. Karena itu perlu adanya suatu upaya untuk menambah pasokan daya listrik pada sistem tenaga, salah satu cara yaitu mengaplikasikan unit pembangkit tersebar (Distributed Generation (DG)). Dengan adanya DG ini, kondisi sistem tenaga menjadi lebih rumit untuk dipahami karena setelah penambahan DG arus yang sebelumnya hanya berasal dari grid saja namun setelah ada DG arus juga disuplai dari DG. Oleh karena itu, sangat diperlukan untuk mengetahui pengaruh pemasangan DG terhadap perubahan sistem termasuk sistem proteksi yang sudah ada. Pengaruh DG pada koordinasi proteksi dipengaruhi oleh ukuran, jenis dan lokasi penempatan DG. Karena itu, perlu dianalisa besar arus gangguan yang dilihat oleh rele proteksi pada level distribusi. Hasil penelitian yang didapatkan, Pada bus 2, penambahan DG sebesar 1000 kW, 2000 kW dan 3000 kW tidak mempengaruhi setting rele yang ada. Pada bus 3, penambahan DG sebesar 1000 kW, 2000 kW aman untuk ditempatkan DG dan kapasitas DG 3000 kW tidak bisa ditempatkan DG karena merubah setting proteksi yang ada. Pada bus 6, penambahan DG sebesar 1000 kW juga berpengaruh terhadap setting rele yang ada walaupun untuk kondisi normal. Penambahan DG dengan kapasitas yang kecil sekalipun (500 kW) menyebabkan koordinasi rele sudah terganggu. Karena itu penempatan DG pada bus 6 sebaiknya dihindari. Maksimum kapasitas DG yang dapat ditempatkan adalah 3000 kW pada bus 2, 2000 kW pada bus 3 dan sebaiknya tidak ada penempatan DG pada bus 6
Two-stage real-time head tracking by an active camera based on multimodal information
No full textWe propose a two-stage real-time tracking algorithm for an active camera system having pan-tilt-zoom functions. The algorithm is based on the assumption that a human head has an elliptical shape and that its model color histogram has been acquired in advance. The algorithm consists of two stages, a color-based convergence stage for fast and reliable tracking and a refinement stage for accurate tracking based on multimodal information. In the first color convergence stage, we roughly estimate the target position by using the mean-shift method based on the histogram similarity between the model and a candidate ellipse. To better predict the initial position for the mean shift, the global motion is compensated; to enhance reliability of the mean shift, the model histogram is appropriately updated by referring to the target histogram in the previous frame. In the subsequent refinement stage, we refine the position and size of the ellipse obtained at the first stage by using multimodal information such as color, shape, and quasi-spatial information. In particular, to quantify the quasi-spatial information, we use a spatial color histogram obtained by properly dividing the ellipse into two regions. Extensive experiments verify that the proposed algorithm robustly tracks the head, even when the subject moves quickly, the head size changes drastically, or the background has many clusters and/or distracting colors. Also, the proposed algorithm can perform real-time tracking with a processing speed of about 10 fps on a standard PC. (c) 2006 Society of Photo-Optical Instrumentation Engineers
Effect of two-step sol-gel reaction on the mesoporous silica structure
No full textthe present study, we investigated the effects of two-step sol-gel reaction by abrupt pH change on the SBA-15 and mesocellular silica foams (MCF). Mesoporous silica was fabricated by using triblock copolymer templates (poly(ethylene oxide) and poly(propylene oxide)). The prepared silica structure was characterized by X-ray diffraction, transmission electron microscopy, and N-2 sorption experiment. Specifically, we prepared SBA-15 with long-range two-dimensional hexagonal arrangement of 3 to 6-nm feature spacing and MCF with larger pores of a few tens of nanometers. The pore size and ordering were influenced by pH change in a two-step sol-gel reaction and the concentration of organic solvent. Although well-ordered hexagonal arrangement of mesopores was prevalent in acidic conditions, the materials synthesized by a single-step reaction in neutral or basic conditions possessed gel-like structure without mesopores. However, the present two-step reaction (low pH sol-gel reaction followed by high pH reaction) not only produced mesoporous materials but also provided controllability of the pore size. In particular, mesoporous structures with pore sizes as large as those of MCF were successfully fabricated by the two-step reaction without using organic swelling agents. As expected, when xylene was added as a swelling agent, the pore size increased with the xylene/copolymer weight ratio. (C) 2003 Elsevier Science (USA). All rights reserved.This work has been supported partially by grants from
the Brain Korea 21 and IMT-2000 Projects. The authors
thank BASF for their kind donation of the Pluronic P123
block copolymer. The Korea Basic Science Institute is also
acknowledged for allowing us to use TEM (EM912, Carl
Zeiss)
shear-induced structure of semi-dilute aqueous micellar solutions of the cetylpyridnium chloride and additive effects
No full textSurface reconstruction for mid-slice generation on variable lamination manufacturing
No full textA new rapid prototyping process, variable lamination manufacturing (VLM), has been developed to reduce building time and to improve the surface finish of parts by using a 4-axis-controlled hotwire cutter and expandable polystyrene foam sheet as a laminating material of the part (VLM-S). The objective of this study is to reconstruct the surface of the original 3D computer-aided design (CAD) model in order to generate mid-slice data using the advancing front technique (AFT). The generation of 3D layers by a 4-axis-controlled hotwire cutter requires a completely different procedure to generate toolpath data unlike the conventional RP CAD systems. The cutting path data for VLM-S are created by VLM-Slicer, which is a special CAD/CAM software with automatic generation of 3D toolpath. For the conventional sheet type system like LOM, the STL file would be sliced into 2D data only. However, due to the use of thick layers and a sloping edge with the first-order approximation between the top and bottom layers, VLM-Slicer requires surface reconstruction, mid-slice, and toolpath data generation as well as 2D slicing. Surface reconstruction demands that the connection between the two neighboring cross-sectional contours use the triangular facets. VLM-S employs thick layers with finite thickness, so that surface reconstruction is necessary to obtain a sloping angle of a side surface and the point data at a half of the sheet thickness. In the process of the toolpath data generation the surface reconstruction algorithm is expected to minimize the error between the ruled surface and the original parts. (C) 2002 Elsevier Science B.V. All rights reserved
Calculation and verification of rotation angle of a four-axis hotwire cutter for transfer-type variable lamination manufacturing using expandable polystyrene foam
No full textMost rapid prototyping (RP) processes adopt a solid CAD model sliced into thin layers of constant thickness in the building direction. Each cross-sectional layer is successively deposited and, simultaneously, bonded onto the previous layer; eventually the stacked layers form a physical part of the model. A new RP process called the Transfer-type Variable Lamination Manufacturing process using expandable polystyrene foam sheet (VLM-ST) has been developed to reduce building time and to improve the surface finish of parts with thick layers and sloping surfaces. The objective of this study is to develop a method for calculating the rotation angles (theta(x), theta(y)) of a linear hotwire cutter in the three-dimensional space for the VLM-ST process using inverse kinematics. The method for calculating the rotation angles (theta(x), theta(y)) of the four-axis hotwire cutter to VLM-ST was applied and verified for a variety of free surface bodies
2D nano/micro hybrid patterning using soft/block copolymer lithography
No full textIn this work, we fabricated various 2D hybrid patterns with the feature resolution from micrometer to nanometer scale by using soft lithography and block copolymer lithography. Composite molds for the high-resolution with feature sizes from 135 nm to 50 mum were composed of a hard layer supported by soft PDMS layer. Polymer (PU) replica holes were made from the composite mold by replica molding. Block copolymers (PS-b-PMMA and PS-b-PI) were used as ink materials for the pattern smaller than 100 nm. UV and ozone etching was used for the selective removal of one block in the block copolymer. (C) 2003 Elsevier B.V. All rights reserved.This work was supported by the Brain Korea 21 program,
the IMT-2000 program and a grant (M102KN010001-
02K1401-00212) from Center for Nanoscale Mechatronics
and Manufacturing of 21st Century Frontier Research
Program
Mechanical properties and anisotropy of expanded polystyrene foam sheet for the VLM-S rapid prototyping process
No full textA study on the influence of the sloped cutting angle on kerfwidth and part quality in the hotwire cutting of EPS foam for the VLM-s rapid prototyping process
No full textThe VLM-s rapid prototyping process employs hotwire cutting of an EPS foam sheet using a four-axis synchronized automatic hotwire cutter. The dimensional accuracy and the quality of the cut part are highly dependent on cutting parameters such as effective heat input, and cutting angle, etc. The objective of this study is to investigate the influence of cutting angle on the kerfwidth and the part quality in hotwire cutting of EPS foam for the case of the sloped cutting including single-sloped cutting with one cutting angle and generally sloped cutting with two cutting angles. Experiments are carried out to obtain the relationship between kerfwidth and effective heat input for each cutting angle, and to find the relationship between the melted area and the cutting angle for each effective heat input. In order to investigate the influence of cutting angle on temperature distribution in EPS foam, transient heat transfer analysis using the sloped heat flux model and the conformed mesh structure is carried out. Through comparison of the results of the experiment and the transient heat transfer analysis, it has been shown that the sloped heat flux with an elliptical cross-section and the conformed mesh structure are needed to estimate the three-dimensional temperature distribution in the EPS foam in the sloped hotwire cutting. (C) 2003 Elsevier Ltd. All rights reserved
Influence of process parameters on the surface roughness in hotwire cutting of EPS foam sheet for VLM-S rapid prototyping process
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