Optimal replacement strategy for stochastic deteriorating system with random wear limit under periodic inspections

In this paper, we examine the preventive maintenance policies for systems/items which are degraded continuously in time and the degree of deterioration that can be observed through periodic inspection. The items will be replaced preventively if the wear process exceeds a limit at periodic inspection or replaced immediately on failure. The limit is assumed to be random in taking individual variation to withstand damages or unmeasurable variables latent to failure into account. Continuous wear process is modeled via a gamma process. We derive an optimal wear limit for preventive replacement so that the long-run total expected cost per unit time is minimized. The proposed method is applied to a problem of block mat inspection for the barrier’s seabed protection.     

Direct observation on the temperature-dependent change of magnetic domains in epitaxial MnAs film on GaAs (001)

We present a systematic change of the magnetic domain structure with temperature in epitaxial ferromagnetic MnAs film on GaAs (001), observed in a wide temperature range of 15-45 degrees C by magnetic force microscopy. Interestingly, it is found that, as temperature increases, the domain structure within the ferromagnetic alpha-MnAs stripes shows a mixture of head-on and simple domains at 15 degrees C and then, takes a complete transition to simple ones above 15 degrees C. This change could be understood by change in the demagnetizing factor of the cross-section of the ferromagnetic stripes with temperature.     

Miniaturized TIR Fresnel lens for miniature optical LED applications

Light-emitting diodes (LEDs) have been investigated to expand their application to very thin electronic devices, including various optical components in a single device. In such applications, the collimation of light produced by LEDs using a conventional Fresnel lens can be bent at angles greater than 45°, whereas most LEDs radiate at solid angles greater than 60°. This paper describes a miniaturized total internal reflection (TIR) Fresnel lens for such miniature optical LED applications. The proposed lens reduces the solid angle of a LED from 60° to 12°, and was designed to have a thickness of less than 1 mm with eleven facets on a single side. The overall geometry of the TIR lens was calculated numerically using Matlab, and the central hyperboloid was designed using Code V.     

Development of a motion simulator for testing a mobile surveillance robot

A 6-axis motion simulator has been developed, in order to regenerate UGV (unmanned ground vehicle) motion and to test the stabilization system of the mobile surveillance robot that is mounted on the UGV. For developing the 6-axis motion simulator, a simulation-based design procedure was introduced. The 3D geometric model of the motion simulator was created by using 3D CAD modeler ProE. The multibody dynamics model of the motion simulator has also been created by using the general purpose dynamic analysis program ADAMS to validate the design of the motion simulator. Dynamics and control co-simulation model for the motion simulator has been also established for control performance analyses. Actual hardware of the motion simulator has been fabricated based on the proposed simulation based design. Hardware test of the motion simulator has been tried to validate the design. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Oskar Wallrapp was awarded a Ph.D. degree in Mechanical Engineering at the Technical University of Berlin, Germany in 1989. Dr. Wallrapp is currently a Professor in the Department of Precision and Micro Engineering, Muenchen University of Applied Science, Munich, Germany. His research interests are mechanism analysis and design, robotics, and bio-mechanics. Sung-Soo Kim received a Ph.D. degree in Mechanical Engineering from the University of Iowa in 1988. Dr. Kim is currently a Professor in the Department of Mechatronics Engineering at Chungnam National University in Daejeon, Korea. His research interests are real-time multibody formulation and its application to the automotive systems and military robot systems.     

Experimental research on thermal comfort in the university classroom of regular semesters in Korea

This research has investigated physical variables affecting indoor thermal comfort and subjective responses of thermal comfort of students in a university in Korea in which the weather is oceanic temperate climate, and has been performed to contribute to the research fields of Sustainable Thermal Standard and Adaptive Thermal Comfort (ATC). This research is based on the ISO 7730-2005 standard and the ATC theories and 4 main variables of PMV such as dry bulb temperature (Ta), relative humidity (RH), black bulb temperature (Tg), and air velocity (Va) are measured once a week during two regular semesters. A clothing insulation, a thermal sensation vote (TSV), an acceptability of thermal environment, and a preference for cooling and heating are investigated at the same time using a questionnaire. This study was carried out for 26 weeks during the spring season, from March to June 2009, and the autumn season, from September to December 2009. The main achievements of this study are as follows. Monthly Mean Outdoor Temperature (MMOT) and Operative Temperature (OT) in the classroom during research periods are 7.4∼23.3°C and 17.5∼29.0°C, respectively. The acceptability ratio of thermal environment shows over 80% when the range of OT in the classroom is 17∼25°C, and the range can be applicable to operative index of heating and cooling of classroom. The mean TSV of respondents is almost “neutral (0)” when the PMV in the classroom moves to “neutral (0)” and “slightly cool (−1)”, and the TSV is almost “+1.5” when the PMV moves to “slightly warm (+1)”. The acceptability ratio of thermal environment is slightly different from ASHRAE Standard 55-2004. So it is necessary to more investigate standard range of acceptability of thermal environment in oceanic temperate climate region using much more databases.     

Ultrastructural investigation of intact orbital implant surfaces using atomic force microscopy

This study examined the surface nanostructures of three orbital implants: nonporous poly(methyl methacrylate) (PMMA), porous aluminum oxide and porous polyethylene. The morphological characteristics of the orbital implants surfaces were observed by atomic force microscopy (AFM). The AFM topography, phase shift and deflection images of the intact implant samples were obtained. The surface of the nonporous PMMA implant showed severe scratches and debris. The surface of the aluminum oxide implant showed a porous structure with varying densities and sizes. The PMMA implant showed nodule nanostructures, 215.56 ± 52.34 nm in size, and the aluminum oxide implant showed crystal structures, 730.22 ± 341.02 nm in size. The nonporous PMMA implant showed the lowest roughness compared with other implant biomaterials, followed by the porous aluminum oxide implant. The porous polyethylene implant showed the highest roughness and severe surface irregularities. Overall, the surface roughness of orbital implants might be associated with the rate of complications and cell adhesion. SCANNING 33: 211–221, 2011. © 2011 Wiley Periodicals, Inc.     

Winglet geometry effects on tip leakage loss over the plane tip in a turbine cascade

The effects of winglet offset distance, winglet coverage, and winglet cross section on the over-tip leakage loss for the plane tip have been investigated experimentally in a turbine blade cascade for a tip gap height-to-span ratio of h/s = 1.36 %. The results show that the over-tip leakage loss for the full coverage winglet increases steeply with increasing the winglet offset distance. This loss generation is attributed to flow disturbances over the forward-facing and backward-facing steps within the tip gap. The winglet flush mounted to the tip surface provides the best result. With the leading edge winglet portion or without it, the both-side winglet always provides better aerodynamic performance than the corresponding pressure-side winglet or suction-side winglet. Longer coverage of the both-side winglet leads to lower loss. Therefore, the full coverage winglet performs best in the loss reduction for the plane tip. In general, thinner winglet leads to better aerodynamic result, and the winglet cross section having a slant bottom surface with the smallest thickness at its outer end is recommended.     

Counter-current air-water flow in narrow rectangular channels with offset strip fins

Counter-current two-phase flows of air-water in narrow rectangular channels with offset-strip fins have been experimentally investigated in a 760 mm long and 100 mm wide test section with 3.0 and 5.0 mm gap widths. The two-phase flow regime, channel-average void fractions and two-phase pressure gradients were studied. Flow regime transition occurred at lower superficial velocities of air than in the channels without fins. In the bubbly and slug flow regimes, elongated bubbles rose along the subchannel formed by fins without lateral movement. The critical void fraction for the bubbly-to-slug transition was about 0.14 for the 3 mm gap channel and 0.2 for the 5 mm gap channel, respectively. Channel-average void fractions in the channels with fins were almost the same as those in the channels without fins. Void fractions increased as the gap width increased, especially at high superficial velocity of air. The presence of fins enhanced the two-phase distribution parameter significantly in the slug How, where the effect of gap width was almost negligible. Superficial velocity of air dominated the two-phase pressure gradients. Liquid superficial velocity and channel gap width has only a minor effect on the pressure gradients.     

Oxidation characteristics of phthalic and adipic acids by supercritical water

Supercritical water oxidation (SCWO) was carried out in a flow-type reactor for modeling of waste-water containing phthalic or adipic acid. For each acid, the reaction order and rate constant, k, were determined over a wide range of experimental conditions : temperatures from 633.15 to 713.15 K, pressures from 18 to 29 MPa, excess amounts of hydrogen peroxide from zero to 800 percent, and the mean residence time in the reactor from 1.1 to 49.1 seconds. The concentration of both acids in model wastewater was set by 500 ppm. For phthalic acid, we found that the orders of decomposition reaction with respect to the reactant concentrations were 0.56 for phthalic acid, 0.31 for hydrogen peroxide, and 0.53 for water. For adipic acid, the orders of oxidation were 0.78 for adipic acid, 0.53 for hydrogen peroxide, and 0.74 for water. Then measured activation energy for phthalic acid was 33.08 kcal/mol and that for adipic acid was 19.51 kcal/mol, respectively.     

Interfacial Structure of Ordered Domains in Barium Lanthanum Magnesium Niobate

Microstructural studies on the interfacial boundaries of 1:1 and 1:2 ordered domains in (Ba_0.9La_0.1)(Mg_0.37Nb_0.63)O₃ were conducted using high-resolution transmission electron microscopy and X-ray diffractometry. Both 1:2 and 1:1 ordered domains coexisted in a fully ordered single grain. Each ordered domain occupied its own region, and the interfaces were atomically sharp and coherent. The wavelength of the superlattice modulation was ∼0.47 nm in the 1:1 ordered domain and ∼0.71 nm in the 1:2 ordered domain. The transition from the 1:2 ordered region to the 1:1 ordered region was clearly shown at the interface. These observations well support the structural models that have been previously presented.