9,700 research outputs found
Transonic and low-supersonic aeroelastic analysis of a two-degree-of-freedom airfoil with a freeplay non-linearity
No full textA two-degree-of-freedom airfoil with a freeplay non-linearity in the pitch and plunge directions has been analyzed in the transonic and low-supersonic flow region, where aerodynamic non-linearities also exist. The primary purpose of this study is to show aeroelastic characteristics due to freeplay structural non-linearity in the transonic and low-supersonic regions. The unsteady aerodynamic forces on the airfoil were evaluated using two-dimensional unsteady Euler code, and the resulting aeroelastic equations are numerically integrated to obtain the aeroelastic time responses of the airfoil motions and to investigate the dynamic instability. The present model has been considered as a simple aeroelastic model, which is equivalent to the folding fin of an advanced generic missile. From the results of the present study, characteristics of important vibration responses and aeroelastic instabilities can be observed in the transonic and supersonic regions, especially considering the effect of structural non-linearity in the pitch and plunge directions. The regions of limit-cycle oscillation are shown at much lower velocities, especially in the supersonic flow region, than the divergent flutter velocities of the linear structure model. It is also shown that even small freeplay angles can lead to severe dynamic instabilities and dangerous fatigue conditions for the flight vehicle wings and control fins. (C) 2000 Academic Press
Clinical comparison of humeral-lateralization reverse total shoulder arthroplasty between patients with irreparable rotator cuff tear and patients with cuff tear arthropathy
No full textBackground: This study aimed to compare the clinical and radiologic outcomes between patients with irreparable cuff tears (ICTs) and those with cuff tear arthropathy (CTA) after reverse total shoulder arthroplasty (RTSA) with a humeral-lateralization prosthesis. Methods: A total of 127 patients with ICTs and CTA who underwent RTSA were enrolled and matched at a 1:2 ratio by propensity score. Preoperative shoulder function was assessed for all patients. Radiologic parameters including the acromion–deltoid tuberosity (ADT) distance, lateral humeral offset, and scapular notching were evaluated. Results: Thirty-four patients in the ICT group and 68 patients in the CTA group were matched for comparison. Preoperatively, mean active forward flexion in the ICT group (89.7° ± 29.4°) was significantly better than that in the CTA group (65.5° ± 24.0°, P <.001). In the CTA group, fatty infiltration of the supraspinatus was worse (3.7 ± 0.5) and the ADT distance was shorter (134.0 ± 12.0 mm) compared with the ICT group preoperatively (3.3 ± 0.8 [P =.008] and 140.7 ± 12.5 mm [P =.001], respectively). There was no significant difference in postoperative functional or radiologic outcomes between the 2 groups. However, gains in active forward flexion (37.9° in ICT group vs. 61.5° in CTA group, P <.01) and abduction (42.1° in ICT group vs. 60.6° in CTA group, P <.01) were significantly greater in the CTA group than in the ICT group. Conclusions: Shoulder function was significantly improved after RTSA regardless of the preoperative diagnosis. Postoperatively, radiologic findings were not significantly different between the 2 groups. Due to the fact that preoperative range of motion and rotator cuff status were better in patients with ICTs, improvements in active forward flexion and abduction were significantly greater in patients with CTA. © 2020 The Author(s
Heat transfer and quenching analysis of combustion in a micro combustion vessel
No full textCombustion phenomena in a millimeter scale combustor subjected to an intense heat loss were theoretically investigated. Although there has been much research on micro combustion devices, some basic questions on the combustion processes in such devices are yet to be answered. Two of the most prominent questions are the lower limit of the combustor size, and the combustion efficiency in a millimeter size combustor. As the combustor is reduced to a scale comparable to the laminar flame thickness, the existing theoretical model is not adequate for the prediction of the combustion process inside such a volume. On the other hand, many measurement techniques developed for macro scale combustion phenomena cannot be applied due to the size limitation further complicating the situation. In the present study, a simple theoretical analysis partially relying on experimental data is proposed. The analysis is based on the existing model of the flame propagation in a macro scale closed vessel. While the effect of heat loss to the wall is insignificant and ignored in a macro scale vessel, it is a decisive factor in a micro scale combustor. A heat loss model was derived from the measured data and the governing equation of conservation of mass and energy is integrated with constitutive thermodynamic relationships between gas properties. Calculations were compared with the measured data on quenching and resulted in a satisfactory agreement despite the simple nature of the proposed model
Nonlinear flutter characteristics of composite missile wing in transonic/low-supersonic flows
No full textThis work was supported through funding from the Korea Ministry
of Science and Technology. The authors acknowledge the
support (Subject 2000-N-NL-01-C-250) of the National Research
Laboratory Program
Slot error rate performance of DH-PIM with symbol retransmission for optical wireless links
No full textIn this paper we introduce the dual-header pulse interval modulation (DH-PIM) technique employing a simple retransmission coupled with a majority decision detection scheme at the receiver. We analytically investigate the slot error rate (SER) performance and compare results with simulated data for the symbol retransmissions rates of three, four and five, showing a good agreement. We demonstrate that the proposed scheme significantly reduces the SER compared with the standard single symbol transmission system, with retransmission rate of five offering the highest code gain of 5 dB
Fuzzy inference neural network for fuzzy model tuning
No full textIn fuzzy modeling, it is relatively easy to manually define rough fuzzy rules for a target system by intuition. It is, however, time-consuming and difficult to fine-tune them to improve their behavior. This paper describes a tuning method for fuzzy models which is applicable regardless of the form of fuzzy rules and the used defuzzification method. For this purpose, this paper proposes a fuzzy neural network model which can embody fuzzy models. The proposed model provides the functions to perform fuzzy inference and to tune the parameters for the shape of antecedent linguistic terms, the relative importance degrees of rules, and the relative importance degrees of antecedent linguistic terms in rules. In addition, to show its applicability, we perform some experiments and present the results
Error concealment technique of satellite imagery transmission through information hiding
No full textImperfect transmission of satellite imagery results in the loss of image lines. This paper proposes a novel error concealment technique using LSB-based watermarking. We generate block description information and insert it into the LSB bit plane of the image. Missing lines after transmission are restored by extracting this block description information. Simulation results show outstanding performance of the proposed technique
A methodology of constructing a decision path for IT investment
No full textInformation Technology (IT) may be used for organizational efficiency, but should also be flexible to adapt to the rapidly changing competitive business environment. In competitive business circumstances, management continually asks: (1) How flexible must the firm be in investing in IT in order to meet unknown business needs in the future? At the same time, how efficient must the firm be in order to meet current business needs?; (2) How well must the firm align its business strategy with IT investment in order for it to support its strategic goals?; (3) how to construct a decision path for IT investments with respect to flexibility, efficiency and alignment between business strategy and IT investments? Although many researchers have struggled to answer these questions, they generally provide no means for incorporating these factors into the rr investment decision process. This paper suggests a method that identifies the degree of flexibility required (alpha -value), and accounts for and incorporates the alpha -value in making IT investments. The proposed method is based on a product development method called Quality Function Deployment (QFD). It will be applied to a real case of the "H-company" in Korea to validate and evaluate the proposed methodology. (C) 2000 Elsevier Science B.V. All rights reserved
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