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Francesco Amoroso, Angelo De Fenza, Giuseppe Petrone and Rosario Pecora

Abstract

The need to reduce pollutant emissions leads the engineers to design new aeronautic combustors characterized by lean burn at relatively low temperatures. This requirement can easily cause flame instability phenomena and consequent pressure pulsations which may seriously damage combustor’s structure and/or compromise its fatigue life.

Hence the need to study the combustor’s structural dynamics and the interaction between elastic, thermal and acoustic phenomena. Finite element method represent a largely used and fairly reliable tool to address these studies; on the other hand, the idealization process may bring to results quite far from the reality whereas too simplifying assumptions are made.

Constraints modelling represent a key-issue for all dynamic FE analyses; a wrong simulation of the constraints may indeed compromise entire analyses although running on very accurate and mesh-refined structural models.

In this paper, a probabilistic approach to characterize the influence of external constraints on the modal behaviour of an aircraft combustor-rig is presented. The finite element model validation was performed at first by comparing numerical and experimental results for the free-free condition (no constraints). Once the model was validated, the effect of constraints elasticity on natural frequencies was investigated by means of a probabilistic design simulation (PDS); referring to a specific tool developed in the ANSYS®software, a preliminary statistical analysis was at performed via Monte-Carlo Simulation (MCS) method. The results were then correlated with the experimental ones via Response Surface Method (RSM).

Open access

Adam Brański and Stanisław Szela

Quasi-optimal PZT distribution in active vibration reduction of the triangular plate with P-F-F boundary conditions

An active reduction of transverse vibration of the triangular plate with P-F-F boundary conditions is considered. The cracked plate is idealized research model as partially clamped on one edge with varying clamped length. The active reduction is realised with PZTs. In the paper, assuming the detached base clamped length, the influence of PZTs distribution on the bending moment and the shearing force at the clamped edge is investigated. To realize the purpose two cases are considered. At the former the PZTs are attached at points in which the curvatures of the surface locally take their maximum (MC sub-areas or quasi-optimal ones). At the latter, the PZTs are somewhat shifted. The plate is excited with harmonic plane acoustic wave. The second mode is considered only.

The active vibration reduction study with a finite element method (FEM) is carried out. The numerical calculations show that better results are obtained for MC distribution of the PZTs.

Open access

Georg Von Pfingsten, Andreas Ruf, Simon Steentjes, Marco Hombitzer, David Franck and Kay Hameyer Rwth

Abstract

Magnetic circuits of electromagnetic energy converters, such as electrical machines, are nowadays highly utilized. This proposition is intrinsic for the magnetic as well as the electric circuit and depicts that significant enhancements of electrical machines are difficult to achieve in the absence of a detailed understanding of underlying effects. In order to improve the properties of electrical machines the accurate determination of the locally distributed iron losses based on idealized model assumptions solely is not sufficient. Other loss generating effects have to be considered and the possibility being able to distinguish between the causes of particular loss components is indispensable. Parasitic loss mechanisms additionally contributing to the total losses originating from field harmonics, non-linear material behaviour, rotational magnetizations, and detrimental effects caused by the manufacturing process or temperature, are not explicitly considered in the common iron-loss models, probably even not specifically contained in commonly used calibration factors. This paper presents a methodology being able to distinguish between different loss mechanisms and enables to individually consider particular loss mechanisms in the model of the electric machine. A sensitivity analysis of the model parameters can be performed to obtain information about which decisive loss origin for which working point has to be manipulated by the electromagnetic design or the control of the machine.

Open access

Sandeep Kumar, Anal K. Jha and K. Prasad

Abstract

Single phase silver aluminum titanate (Ag1/2Al1/2)TiO3, later called AAT, nanoceramic powder (particle size 2 to 7.5 nm) was synthesized by a low-cost, green and reproducible tartaric acid gel process. X-ray, FT-IR, energy dispersive X-ray and high resolution transmission electron microscopy analyses were performed to ascertain the formation of AAT nanoceramics. X-ray diffraction data analysis indicated the formation of monoclinic structure having the space group P2/m(10). UV-Vis study revealed the surface plasmon resonance at 296 nm. Dielectric study revealed that AAT nanoceramics could be a suitable candidate for capacitor applications and meets the specifications for “Z7R” of Class I dielectrics of Electronic Industries Association. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were performed using the impedance data. Electric modulus studies supported the hopping type of conduction in AAT. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in AAT. The ac conductivity data were used to evaluate the density of states at Fermi level and minimum hopping length of the compound.

Open access

Janusz Gołdasz and Bogdan Sapiński

Abstract

The so-called squeeze flow involves a magnetorheological (MR) fluid sandwiched between two planar surfaces setting up a flow channel. The height of the channel varies according to a prescribed displacement or force profile. When exposed to a magnetic field of sufficient strength MR fluids develop a yield stress. In squeeze-mode devices the yield stress varies with both the magnetic field magnitude and the channel height. In this paper an unsteady flow model of an MR fluid in squeeze mode is proposed. The model is developed in Ansys Fluent R16. The MR material flow model is based on the apparent viscosity approach. In order to investigate the material's behaviour the authors prepared a model of an idealized squeeze-mode damper in which the fluid flow is enforced by varying the height of the channel. Using mesh animation, the model plate is excited, and as the mesh moves, the fluid is squeezed out of the gap. In the simulations the model is subjected to a range of displacement inputs of frequencies from 10 to 20 Hz, and local yield stress levels up to 30 kPa. The results are presented in the form of time histories of the normal force on the squeezing plate and loops of force vs. displacement (velocity).

Open access

Ana K. Spalding

Abstract:

Lifestyle migration, the flow of relatively affluent people from developed to developing countries, is characterized by the search for ‘lifestyle’ destinations with warm climates, reduced costs of living, and perceived higher quality of life. Mexico, Costa Rica, and Panama are three current major lifestyle migration destinations in Latin America. In this article I explore the emergence of this relatively new phenomenon in the Bocas del Toro Archipelago in Northwestern Panama by discussing the contradiction between lifestyle migrants’ idealized perception of place and local realities. I also introduce the implications of these contradicting versions of reality, and how they play out at the local level. Results show that, in general, foreign residents are attracted to Bocas del Toro as a physical manifestation of globally produced images and perceptions of tropical island living. However, an in-depth exploration reveals contradictions between expectations and reality. I suggest that foreigners exhibit a set of attitudes and behaviors towards their new home that are defined by a shared cultural and economic background that, on the ground, contribute to the creation of emerging markets, land conflicts, and changes in environmental practices. The ensuing narrative is contingent upon tensions between and within social, political, and ecological variables at the global and local levels.

Open access

Postmemory, Stereotype and the Return Home

Rewriting Pre-Existing Narratives in Sofi Oksanen’s Purge

Anna Estera Mrozewicz

Abstract

The article offers a discussion of Sofi Oksanen’s novel Purge, focusing on the book’s strategy of evoking stereotypical narratives about Eastern Europe, such as the (postcommunist) fallen woman and (Russian) return home narratives, as well as related intertexts, primarily Lukas Moodysson’s film Lilya 4-ever. I argue that Oksanen constructs the plot around clichés in order to challenge them in a subversive fashion, first and foremost, in the name of recuperating the notion of Home. Related to locality and the feeling of being at-home, where the wholeness of the (national) subject is possible, ‘home’ is staged as an alternative to stereotypes, associated with transnational travel and the apparatus of colonization. A significant counter-narrative embedded in the novel - and hitherto rarely discussed - is the exilic perspective with its idealization of the lost and imagined home(land). In Purge, this is mediated through the main character’s postmemory. By means of a postexilic narrative, home is reconfigured as a ‘third space’ - neither fully ideal and (ethnically) pure nor adhering to the aforementioned stereotypical narratives. The positive valorisation of home, despised by some critics as simplistic and conservative, does not prevent movement and dislocation from being included in the new experience of home(land) emerging from the post-Soviet condition.

Open access

Niklas Salmose

Abstract

This essay explores the modernist aesthetic involved in creating a fictive, nostalgic, childhood experience. Evoking the experience of childhood through fiction is as close to actually reliving childhood as we can get. The author argues that it is possible to actually transport the reader into not only the idealized world of childhood, but more so into an embodied experience of childhood through the use of different kinds of narrative and stylistic configurations. In a stylistic and narratological analysis of three modernist novels, Virginia Woolf’s The Waves (1931), Tarjei Vesaas’ The Ice Palace [Is-slottet] (1963) and William Faulkner’s The Sound and the Fury (1929), the author explores the different ways that literature can create (or re-create) the very experience of childhood through literary style. The strategies involved in establishing a fictive experience of childhood extend from narratological choices such as free indirect style, strict focalization through a child in the narrative (which implies limitations in perception and cognitive abilities, as well as in linguistic terms) to the use of a child-like temporality, the hyperbolic use of phenomena, and an emphasis of the sensorial aspects of perception.

Open access

Fazal Haleem, Muhammad Jehangir and Muhammad Khalil-Ur-Rahman

Abstract

Transformational leaders encourage their subordinates to achieve organizational goals and objectives and to reach their full potential by providing the needed resources. This increasing influence of transformational leaders on employees instigated us to find out the impact of transformational leadership on employees’ job satisfaction. The study was conducted in the public sectors universities of KPK, Pakistan. A sample size of 130 employees was selected using convenient sampling techniques. The data was collected from grade 16 and upper level of employees in the universities. Initially, 130 questionnaires were sent out to the target population for their participation in the survey; out of which 100 filled questionnaires were received forming percentage of 76.92%. These 100 properly filled questionnaires were used for statistical analysis. Both descriptive and advance multivariate statistical, correlation and regression analysis, were conducted to get a feel for the data and to test the postulated hypothesis respectively. Findings of the study revealed that there was non-significant influence of transformational leadership in terms of idealized influence, individualized consideration, and inspirational motivation on employees’ job satisfaction in the public sectors universities of KPK, Pakistan. However, the intellectual stimulation type of leadership had positive and significant impact on employees’ job satisfaction. The paper contributes to the literature review in context of non-forprofit organizations in a developing country and provides implications for universities’ executives to pay more attention to intellectual stimulation type of leadership to increase employees’ satisfaction and thus help achieve the universities goals and objectives.

Open access

Kintija Priedniece, Agris Nikitenko, Aleksis Liekna and Guntis Kulikovskis

Abstract

Kinematic model is the basic aspect in robot design and motion planning. Kinematic models are idealized, however there exist certain specific aspects of particular robot or environment, so that during navigation, the robot can significantly deviate from the planned trajectory. To increase the accuracy of motions, kinematic model can be improved and to achieve that the artificial intelligence methods can be used. In case of fixed base robots different approaches are used to train kinematics, at the same time, for the mobile base robots it proves to be a more complicated task. The reason is that a mobile robot can move unbound with respect to environment thus it is difficult to control the platform without deviation from the target position, which leads to inaccuracy in the position estimate. This paper presents the method meant for improvement of the accuracy of motion of differential drive platform. Genetic programming is used to obtain the wheel velocity function, from which the coefficient, which describes different factor influence on motion, is obtained. As a result, the kinematic model of a particular platform for a particular task is obtained. This method is effective because the developed kinematic model is more specific than the general one.