1,721,639 research outputs found
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
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
EXPERIMENTAL-STUDY OF TURBULENT AXISYMMETRICAL CAVITY FLOW
No full textAn experimental study is made of turbulent axisymmetric cavity flow. The flow configuration consists of a sudden expansion and contraction pipe joint. In using the LDV system, in an effort to minimize refraction of laser beams at the curved interface, a refraction correction formula for the Reynolds shear stress is devised. Three values of the cavity length (L=300, 600 and 900 mm) are chosen, and the cavity height (H) is fixed at 55 mm. Both open and closed cavities are considered. Special attention is given to the critical case L=600 mm, where the cavity length L is nearly equal to the reattachment length of the flow. The Reynolds number, based on the inlet diameter(D = 110 mm) is 73,000. Measurement data are presented for the static wall pressure, mean velocity profiles, vorticity thickness distributions, and turbulence quantities
ASSESSMENT OF TURBULENT SPECTRAL BIAS IN LASER-DOPPLER VELOCIMETRY
No full textA critical evaluation is made of the spectral bias which occurs in the use of a laser Doppler velocimeter (LDV). In order to accommodate the randomly sampled LDV data, statistical treatments of particle arrival times are needed. This is modeled as a doubly stochastic Poisson process which includes the intensity function of the velocity field. Three processing algorithms are considered for spectral estimates: the sample and hold method (SH), the modified Shannon sampling technique (SR), and the direct transform (RG). Assessment is made of these for varying data densities (0.05 less-than-or-equal-to d.d less-than-or-equal-to 5) and turbulence levels (t.i. = 30%, 100%). The effects of the values of the Reynolds stress coefficients and the transversal standard deviation on the spectral contents were examined. As an improved version of the spectral estimator, the utility of POCS (the projection onto convex sets) has been tested in the present study. This algorithm is found useful to be in the region when d.d. less-than-or-similar-to 3
Iterative procedures for multi-period order selection and loading problems in flexible manufacturing systems
No full textThis paper focuses on multi-period order selection and loading problems in flexible manufacturing systems. The multi-period order selection problem is the problem of selecting orders to be produced in each period during the upcoming planning horizon, and the loading problem involves allocation of operations and required tools to machines for orders selected in each period. The objective is to minimize earliness and tardiness costs and subcontracting costs. The earliness and tardiness costs are incurred if an order is not finished on time, while subcontracting cost is incurred if an order is not selected within the planning horizon (and must be subcontracted) due to limits in processing time capacity and the tool magazine capacity of the machines. To solve the two problems simultaneously, we develop four iterative procedures in which the multi-period order selection and loading problems are solved repeatedly until a good solution is obtained. To compare the four iterative procedures, computational experiments are done on randomly generated test problems and the results are reported.This research was supported in part by the Institute for Advanced Engineering of
Daewoo Business Group
A multi-period order selection problem in flexible manufacturing systems
No full textWe consider a multi-period order selection problem in flexible manufacturing systems, which is the problem of selecting orders to be produced in each period during the upcoming planning horizon with the objective of minimising earliness and tardiness costs and subcontracting costs. The earliness and tardiness costs are incurred if an order is not finished on time, while subcontracting cost is incurred if an order is not selected within the planning horizon (and must be subcontracted) due to processing time capacity or tool magazine capacity. This problem is formulated as a 0-1 integer program which can be transformed into a generalised assignment problem. To solve the problem, a heuristic algorithm is developed using a Lagrangian relaxation technique. Effectiveness of the algorithm is tested on randomly generated problems and results are reported
Scheduling algorithms for flexible manufacturing systems with partially grouped machines
No full textThis paper focuses on a scheduling problem in a flexible manufacturing system. Unlike most previous studies, this paper deals with the scheduling problem resulting from a loading plan obtained for the configuration of the partial machine grouping, where machines are tooled differently, but multiple machines can be assigned to each operation. The planned workload of each machine specified by the loading plan may or may not be maintained when scheduling and controlling part flows. In this paper, two solution algorithms in which a given planned workload is maintained are suggested based on decomposition of the entire problem into route selection and job shop scheduling problems. In one algorithm, the two subproblems are solved simultaneously by employing rules for part selection and machine selection, while in the other they are solved using a simulated annealing algorithm and dispatching rules. Performance of the suggested algorithms is tested on randomly generated test problems, and results show that the latter algorithms give better solutions and solve the problems in a reasonable amount of computation time. Also, it is shown from computational experiments that it is better to maintain planned workloads
Adsorption-free Microfluidic Encapsulation of Algal Cells using Lateral Flow in a PDMS-based Microchannel
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