Calculating the Efficiency of Complex-Shaped Fins

Calculation of fin efficiency is necessary for the design of heat exchangers. This efficiency can be calculated for individual finned tubes or continuous fins. Continuous fins are mostly used in plate-fin and tube heat exchangers (PFTHEs). In most cases, the basic elements of those PFTHEs are circular, oval or flattened pipes, which contain circular or polygonal fins. Continuous fins, as can be observed in PFTHEs, are divided into virtual fins. Those fins can have a rectangular shape for an inline arrangement of pipes or a hexagonal shape for a staggered arrangement of pipes. This research shows a methodology of using the finite element method for calculating the efficiency of fins of any shape, placed on pipes of any shape. This paper presents examples of determining the efficiency of seeming fins, which are most commonly used in PFTHEs. In the article, we also compare the precision of calculations of the efficiency of complex-shaped fins using exact analytical methods and approximated methods: the equivalent circular fin method (Schmidt’s method) and the sector method. The results of the analytical methods and the approximate methods are compared to the results of numerical simulations. The calculations for continuous fins with complicated shapes of virtual fins, e.g., hexagonal elongated or segmented, are also presented.

An improved approach for the fatigue calculation of rotor blades based on sector loads

In the design and calculation of rotor blades for wind turbines, a sector representation of the loads is often used. The investigation proposed in this paper indicates that, depending on the loading direction, the evaluated sector and the considered location on the rotor blade, the sector approach can result in a significant overestimation of the acting stresses. This translates in a higher calculated fatigue stress exposure (up to 101% in the considered example). However, under particular conditions, the stresses and therefore the stress exposure are correctly assessed. Based on the observation, an improvement of the current method is suggested. The improved method, called invariant-sector method, relies on the appropriate selection of the sector(s) to be evaluated. The method allows for an accuracy equal to the one of the direct method but with a computational effort that is orders of magnitude lower.

Mathematical modeling of the trajectory of a ship as a control object in local planning

In the article proposes the decomposition of the global planning task in local planning. It is proposed to combine the segment method and the sector method of division of the circle to construct the ship’s trajectory in local planning. Corrective coefficients were selected for the correct geometry of the turning trajectory, combining the segment method and the sector method of constructing the ship’s trajectory. The article uses formulas of spherical trigonometry; the trajectory of the turn depends on the rudder angle, which in turn depends on the turning ability of the vessel under the given conditions. In determining the value of the angle of the rudder, the control device must take into account the ship’s turning ability in the conditions set, the value of the angle of the turn and the constrained water area. The combination of all factors allows to differentiate the ship’s turning ability such as: high HG, middle MD or low LW with regard to passage area. The ME shifting operating modes matrix proposed in the article works as a filter of modes of operation and is completely dependent on the readings of pressure, temperature and vibration sensors. The ship’s trajectory is constructed using calculations in MS Excel and graphic simulations in the MATLAB environment.

Mathematical Model for Centralized Supply Chains with Decisions Involving Shared Resources

Context: Cooperation in supply chain management is an important issue considering the global performance of the different echelons of a specific supply chain. In this sense, applying logistic strategies such as VMI (Vendor Managed Inventory) allows a system to manage distribution processes from a central point or depot. Additionally, the components of the chain work more closely with it, which allows increasing global performance, instead of individually developing each sector. Method: A stochastic mathematical model is proposed which considers a network of customers, where products are delivered from a central depot. These customers can share part of their product with the central depot for redistribution, aiming to minimize shortage for other customers. A mathematical model is proposed which includes the elements involved in distribution processes. It is then reformulated to consider shortage and the linearization of some of its elements. Results: Results show that implementing or adapting logistic strategies, such as managing from a central point and sharing resources along the supply chain, allows companies to reduce the complexity of some decisions and improve performance. Conclusions: Implementing logistic strategies such as centralized management and sharing resources along a supply network allows companies to reduce the complexity of some decisions and, in turn, improve their performance.

Nursing diagnoses in the hemodynamics sector: an adaptive perspective

ABSTRACT Objective: To identify nursing diagnoses of NANDA-I Taxonomy II in patients treated in the Hemodynamics Sector. Method: A descriptive, cross-sectional study with a quantitative approach conducted in a teaching hospital in the interior of Rio Grande do Sul. Data were collected through a sociodemographic characterization instrument and information regarding the problems of physical-physiological adaptation. Results: 100 patients participated in the study. Defining characteristics, risk factors and related factors were identified through adaptation problems. In all, 28 nursing diagnoses were identified, and 13 were considered for the discussion which presented frequency above 50% and represented the main adaptive problems. Protection, neurological and activity and rest components were the most frequent. Conclusion: The recognition of nursing diagnoses facilitates a connection between the main problems of adaptation and nursing interventions.

Global Dynamics of Memristor Oscillator

In this paper, we investigate the global dynamics of a memristor oscillator [Formula: see text] which comes from [Corinto et al., 2011], where [Formula: see text], and [Formula: see text]. Clearly, the case [Formula: see text] is trivial. So far, all results of this oscillator were given only for the case [Formula: see text], where the set of equilibria may change among a singleton, three points and a singular continuum and at most one limit cycle can arise and no limit cycles arise from the continuum. Compared with the case [Formula: see text], this oscillator displays more complicated dynamics for the case when [Formula: see text]. More clearly, one limit cycle may arise from the continuum and at most three limit cycles appear in the case of three equilibria, where generalized pitchfork bifurcation, saddle-node bifurcation, generalized Hopf bifurcation, double limit cycle bifurcation and homoclinic bifurcation may occur. Finally all global phase portraits are given for [Formula: see text] cases on the Poincaré disc, where a generalized normal sector method is applied. Moreover, our partial analytical results are demonstrated by numerical examples.