8,748 research outputs found
Optimal placement of dispatchable and nondispatchable renewable DG units in distribution networks for minimizing energy loss
No full textThis paper presents a methodology for the integration of dispatchable and nondispatchable renewable distributed generation (DG) units for minimizing annual energy losses. In this methodology, analytical expressions are first proposed to identify the optimal size and power factor of DG unit simultaneously for each location for minimizing power losses. These expressions are then adapted to place renewable DG units for minimizing annual energy losses while considering the time-varying characteristics of demand and generation. A combination of dispatchable and nondispatchable DG units is also proposed in this paper. The proposed methodology has been applied to a 69-bus test distribution system with different scenarios. The results demonstrate that dispatchable DG units or a combination of dispatchable and nondispatchable DG units can lead to a substantial reduction in annual energy losses when compared to nondispatchable DG units. The results also show that a maximum annual energy loss reduction is achieved for all scenarios proposed with DG operation at optimal power factor. (C) 2013 Elsevier Ltd. All rights reserved
Surface 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
Mechanical properties and anisotropy of expanded polystyrene foam sheet for the VLM-S rapid prototyping process
No full textDesign and manufacture of composite high speed machine tool structures
No full textThe high transfer speed as well as the high cutting speed of machine tools is important for the productivity improvement in the fabrication of molds/dies because non-machining time, called the air-cutting-time, amounts to 70% of total machining time with complex shape products. One of the primary reasons for low productivity is large mass of the moving parts of machine tools, which cannot afford high acceleration and deceleration encountered during operation. Moreover, the vibrations of the machine tool structure are among the other causes that restrict high speed operations. In this paper, the slides of high speed CNC milling machines were designed with fiber reinforced composite materials to overcome this limitation. The vertical and horizontal slides of a large CNC machine were manufactured by joining high-modulus carbon-fiber epoxy composite sandwiches to welded steel structures using adhesives and bolts. These composite structures reduced the weight of the vertical and horizontal slides by 34% and 26%, respectively, and increased damping by 1.5-5.7 times without sacrificing the stiffness. Without much tuning, this machine had a positional accuracy of +/-5 mum per 300 mm of the slide displacement. (C) 2003 Elsevier Ltd. All rights reserved
A study of negative-bias temperature instability of SOI and body-tied FinFETs
No full textNegative-bias temperature-instability (NBTI) characteristics are carefully studied on SOI and body-tied pMOS FinFETs for the first time. It was observed that a narrow fin width degraded device lifetime more than a wider fin width. Electrons generated by the NBT stress are accumulated at the center of a silicon fin and cause energy-band bending. This results in an incremental hole population at the interface. The energy band is bent more steeply at the narrow fin than at the wide fin by the accumulated electrons. A body-tied FinFET shows better immunity to NBT stress due to a substrate contact.This work was supported in part by Samsung Electronics Co., Ltd., and in part by the National Research Program for the 0.1-Terabit Nonvolatile Memory Development, sponsored by the Korea Ministry of Science and Technology. The review of this letter was arranged by Editor B. Yu
A new twisted differential line structure on high-speed printed circuit boards to enhance immunity to crosstalk and external noise
No full textDifferential signaling has become a popular choice for high-speed interconnection schemes on Printed Circuit Boards (PCBs), offering superior immunity to external noise. However, conventional differential transmission lines on PCBs have problems, such as crosstalk and radiated emission. To overcome these, we propose a Twisted Differential Line (TDL) structure on a multilayer PCB. Its improved immunity to crosstalk noise and the reduced radiated emission has been successfully demonstrated by measurement. The proposed structure is proven to transmit 3 Gbps digital signals with a clear eye-pattern. Furthermore, it is subject to much less crosstalk noise and achieves a 13 dB suppression of radiated emission
Rapid prototyping and reverse engineering application for orthopedic surgery planning
No full textThis paper describes rapid prototyping (RP) and reverse engineering (RE) application for orthopedic surgery planning to improve the efficiency and accuracy of the orthopedic surgery. Using the symmetrical characteristics of the human body, CAD data of undamaged bone of the injured area are generated from a mirror transformation Of undamaged bone data for the uninjured area. The physical model before the injury is manufactured from Polyjet RP process. The surgical plan, including the selection of the proper implant, pre-forming of the implant and decision of fixation positions, etc., is determined by a physical simulation using the physical model. In order to examine the applicability and efficiency Of the Surgical planning technology, two case studies, Such as a distal tibia comminuted fracture and an iliac wing fracture of pelvis, are carried Out. From the results of the examination, it has been shown that the RP and RE can be applied to orthopedic surgical planning and can be an efficient surgical tool
Investigation into development of progressive-type variable lamination manufacturing using expandable polystyrene foam and its apparatus
No full textIn order to reduce the lead-time and cost, the technology of rapid prototyping (RP) has been widely used. However, RP techniques have disadvantageous characteristics according to their working principles: a low building speed caused by a thin-layer, stair-stepped surface of a part due to layer-by-layer stacking with a vertical edge, an additional post-processing and high cost for installation, operation and maintenance of the RP apparatus. The objective of this study is to propose a new RP process, progressive-type variable lamination manufacturing using expandable polystyrene foam (VLM-(SP)), to overcome the disadvantageous characteristics and to develop an apparatus for the implementation of the process. The proposed RP system employs several novel techniques such as a thick layer with the thickness less than 2 mm, a sloped surface with the first-order approximation between the top and bottom surfaces of each layer, a building sequence that performed stacking and bonding after cutting, the concept of a unit shape part (USP) and an automated synchronized four-axis hot-wire cutting system. In this paper, the characteristics of the proposed process and apparatus are discussed. The experiments are carried out to verify the bonding strength of the bonded area. Several three-dimensional shapes are fabricated on the prototype of the VLM-(SP) apparatus in order to investigate the applicability of the proposed process. In addition, in order to examine the efficiency of the VLM-(SP) process, the prototypes of VLM-sp are compared with those of commercial RP processes [LOM (laminated object manufacturing) and FDM (fused deposition modelling)] from the viewpoint of geometrical conformity, building time, building cost xand dimensional accuracy. As a result of the comparison, it has been shown that the proposed process is an efficient rapid prototyping process
A 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
- …
