Determination of optimal build direction in rapid prototyping with variable slicing

Several important factors must be taken into consideration in order to maximize the efficiency of rapid prototyping (RP) processes. The ability to select the optimal orientation of the build direction is one of the most critical factors in using RP processes, since it affects part quality, build time, and part cost. This study aims to determine the optimal build-up direction when a part is built with the variable layer thickness for different RP systems. The average weighted surface roughness (AWSR) that is generated from the stair stepping effect, the build time, and the part cost using the variable layer thickness are all considered in the process. Using the multi-attribute decision-making method, the best orientation is determined among the orientation candidates chosen from the convex hull of a model. The validity of the algorithm is illustrated by an example. The algorithm can help RP users select the best build-up direction of the part and create an efficient process planning.     

Modeling and controller design of manta-type unmanned underwater test vehicle

This paper describes the mathematical model and controller design for Manta-type unmanned underwater test vehicle (MUUTV) with 6 DOF nonlinear dynamic equations. The mathematical model contains hydrodynamic forces and moments expressed in terms of a set of hydrodynamic coefficients which were obtained through the PMM (planar motion mechanism) test. Based on the 6 DOF dynamic equations, numerical simulations have been performed to analyze the dynamic performance of the MUUTV. In addition, using the mathematical model PID and sliding mode controller are constructed for the diving and steering maneuver. Simulation results show that the control performance of the MUUTV compared with that of NPS (Naval Postgraduate School) AUV II. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Seung-Keon Lee received the B.S. and M.S. degrees from Pusan National University, in 1982 and 1984, respectively, and the Ph.D. degree from University of Tokyo in 1988. He is currently a Professor in the Department of Naval Architecture and Ocean Engineering, Pusan National University, Busan, Korea. His research interests are about the hydrodynamic force and mathematical model for the motion of surface and underwater vehicles. Joon-Young Kim received the B.S. and M.S. degrees from Inha University, in 1989 and 1993, respectively, and the Ph.D. degree from Hanyang University in 1999. He is currently a Professor in the Department of Ocean System Engineering, Jeju National University, Jeju, Korea. His current research interests are in unmanned underwater vehicle design and control.     

Experimental hover performance evaluation on a small-scale rotor using a rotor test stand

This paper presents the work being carried out in order to deduce hover performance of a small-scale single rotor blade as a preliminary study of a small coaxial rotor helicopter development. As an initial research, a test stand capable of measuring thrust and torque of a small-scale rotor blade in hover state was constructed and fabricated. The test stand consists of three parts; a rotating device, a load measuring sensor and a data acquisition system. Thrust and torque were measured with varying collective pitch angle at fixed RPM. Through this research, hover performance tests were conducted for a small-scale single rotor blade operating in low Reynolds numbers (Re ≈ 3 × 10⁵). The rotor blades investigated in this paper have maximum FM values varying from 0.59 to 0.65, which are low relative to modern full-scale helicopters. From these differences in FM between a small and a full-scale helicopter, the induced power factor is determined as varying from 1.35 to 1.42. Through this study, tests of hover performance were conducted for a single small-scale rotor blade, as well as verifying the test stand itself for the acquisition of hover performance.     

Analysis of primary drying of poly-γ-glutamic acid during vacuum freeze drying

Journal of Mechanical Science and Technology - This paper analyzes primary vacuum freeze drying of poly-γ-glutamic acid (γ-PGA), a biomaterial, by considering the variation in tortuosity...     

Analysis of nitrifying bacterial communities in aerobic biofilm reactors with different DO conditions using molecular techniques

In order to assess the relationship between the dissolved oxygen (DO) concentration and the characteristics of nitrifying bacterial communities in an aerobic biofilm reactor, molecular techniques including denaturing gradient gel electrophoresis (DGGE)/cloning based on PCR targeting 16S rRNA and the amoA gene and fluorescence in situ hybridisation (FISH) were conducted. The D-1, D-2, D-3 and D-4 reactors with different DO concentrations (1, 3, 5 and 7 mg/L, respectively) were set up in the thermostat and acclimated. The optimal DO concentration with stable nitrification efficiency was above 5.0 mg/L. As was shown by the results of DGGE and cloning, the community of ammonia-oxidising bacteria (AOB) and the ratio of Nitrosomonas sp. changed only slightly despite their differing nitrification efficiencies. The results of FISH indicated that higher DO concentrations resulted in an increase in AOB and nitrite-oxidising bacteria (NOB), and a reduction in heterotrophic microorganisms. The INT-dehydrogenase activity (DHA) test demonstrated that the activity of AOB decreased with reductions in the DO concentration. This means that the DO concentration does not influence the community of AOB, but rather the activity of AOB. In the relationship between the attached biomass and the nitrification efficiency, only the active biomass affected the nitrification efficiencies.     

A novel fault-detection technique of high-impedance arcing faults in transmission lines using the wavelet transform

This paper describes a novel fault-detection technique of high-impedance faults (HIFs) in high-voltage transmission lines using the wavelet transform. The wavelet transform (WT) has been successfully applied in many fields. The technique is based on using the absolute sum value of coefficients in multiresolution signal decomposition (MSD) based on the discrete wavelet transform (DWT). A fault indicator and fault criteria are then used to detect the HIF in the transmission line. In order to discriminate between HIF and nonfault transient phenomena, such as capacitor and line switching and arc furnace loads, the concept of duration time (i.e., the transient time period), is presented. On the basis of extensive investigations, optimal mother wavelets for the detection of HIF are chosen. It is shown that the technique developed is robust to fault type, fault inception angle, fault resistance, and fault location. The paper demonstrates a new concept and methodology in HIF in transmission lines. The performance of the proposed technique is tested under a variety of fault conditions on a typical 154-kV Korean transmission-line system.     

Preparation of laminated composite membranes by impregnation of polypropylene with styrene in supercritical CO2 for direct methanol fuel cells

Composite membranes were formed by grafting styrene using supercritical carbon dioxide (scCO_-2) impregnation and polymerization procedures. A polypropylene membrane, styrene monomer, divinylbenzene (DVB), and 2,2′-Azoisobutyronitrile (AIBN) were placed in a reactor, and CO₋₂ was injected into the reactor at 38 ‡C for the scCO₋₂ impregnation process. After impregnation, the polymerization process was carried out at 78 ‡C. The grafted membranes were sulfonated in concentrated sulfuric acid at 95 ‡C. These polypropylene grafted polystyrene sulfonic acid (PP-g-pssa) membranes were characterized by using various methods. The morphology and structure of the PP-g-pssa membranes were analyzed with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and energy dispersive spectrometer (EDS). The ion conductivity and methanol permeability were also measured. The ion conductivity of the PP-g-pssa membranes was higher and the methanol permeability of the laminated membrane was lower than that of Nafion membranes. The performance of the PP-g-pssa/Nafion laminated membranes was evaluated in a DMFC unit cell at 90 ‡C.     

Multi-view 3D reconstruction by random-search and propagation with view-dependent patch maps

This paper proposes an efficient multi-view 3D reconstruction method based on randomization and propagation scheme. Our method progressively refines a 3D model of a given scene by randomly perturbing the initial guess of 3D points and propagating photo-consistent ones to their neighbors. While finding local optima is an ordinary method for better photo-consistency, our randomization and propagation takes lucky matchings to spread better points replacing old ones for reducing the computational complexity. Experiments show favorable efficiency of the proposed method accompanied by competitive accuracy with the state-of-the-art methods.     

Photo patternable porous siloxane thin films using cyclodextrins as template materials

Photo patternable cyclic silsesquioxane (mCSSQ) compositions containing heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (tCD) as a porogen and photo acid generator (PAG) have been prepared, with the goal of achieving a photo resist free porous low dielectric constant precursor. The composition containing triphenylsulfonium based PAG could effectively create a patterned mCSSQ thin film with a resolution approaching ∼2 μm. The pore size of the mCSSQ film with PAG was smaller than that without PAG. Furthermore, the pore size distribution of the mCSSQ film with PAG was much narrower than that without PAG. This might be attributed to the disturbance effect of the agglomeration of tCD molecules through pre-vitrification of the matrix at the relatively low curing temperature. The mechanical property and dielectric constant of the photo-definable mCSSQ/tCD/PAG film were comparable to those of the mCSSQ/tCD counterpart.     

Design of fuzzy controller using schema coevolutionary algorithm

Researches on the design of the optimal fuzzy controller have been carried out for many years. Various approaches to fuzzy modeling have been proposed. In this paper, we introduce a novel algorithm, schema coevolutionary algorithm, for fuzzy modeling. We demonstrate the schema coevolutionary algorithm and compare it with other similar coevolutionary algorithms: virus-evolutionary genetic algorithm and coevolution of Handa. Then, we apply it to design the optimal fuzzy controller. The fuzzy controller is used to control the mobile robot and optimized by the schema coevolutionary algorithm. We verify the efficacy of this algorithm through the experiment and comparison with other algorithms.