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Article
Publication date: 3 October 2019

Changmin Chen, Jianping Jing and Jiqing Cong

The infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the…

168

Abstract

Purpose

The infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the perturbed pressure is assumed being zero at leading edge of film, although it is usually not zero because of nonzero pressure gradient. This assumption is sufficiently accurate for most purpose in horizon rotors. However, for journal bearing in vertical rotor-bearing systems, the BC with the assumption in IP method will bring in significant errors in calculating linear dynamic coefficients. This paper aims to propose a method to obtain the dynamic coefficients of journal bearing in vertical rotors.

Design/methodology/approach

The stiffness and damping are approached based on IP method and the modified BC of perturbed pressure. As it is difficult to predict perturbed pressure at leading edge at a fixed coordinate system using IP method, a dynamic coordinate system is introduced in this method, of which the origin on circumferential direction is defined as the leading edge of film.

Findings

The effectiveness and accuracy of proposed IP method in dynamic coordinate (IPMDC) system are verified by comparing the obtained results with analytical solutions. The comparison shows that the results from IPMDC present a good agreement with the analytic solutions.

Originality/value

The proposed method can be applied in obtaining linear dynamic coefficients of journal bearing in vertical rotors with high precisions. Instead of the usual nonlinear analysis of vertical rotors, this method provides a feasibility of predicting the instability threshold of vertical rotor-bearing systems via linear models.

Details

Industrial Lubrication and Tribology, vol. 72 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

Available. Open Access. Open Access
Article
Publication date: 30 April 2015

Inkyo Cheong

Discussion of unification was for several decades focused on the costs rather than the benefits for Korea, until reports emphasizing the latter were published by Goldman Sachs…

372

Abstract

Discussion of unification was for several decades focused on the costs rather than the benefits for Korea, until reports emphasizing the latter were published by Goldman Sachs (2009) and various Korean think tanks over the past four to five years. Although these studies can be evaluated positively in pointing out the benefits of unification rather than the concerns about the costs, several questions can be raised. This paper tries to evaluate the quality and credibility of existing studies and suggests a new approach for estimating the impact of unification. It proposes a computational general equilibrium (CGE) model to be based on the social accounting matrix (SAM) and input-output (IO) table for the North Korean economy, in order to produce more reliable estimates of the benefits and costs of unification and the impact of various cooperative activities between the two Koreas.

Details

Journal of International Logistics and Trade, vol. 13 no. 1
Type: Research Article
ISSN: 1738-2122

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Book part
Publication date: 12 September 2017

Tiziana D’Alfonso and Valentina Bracaglia

Airport economics literature has recently included the supply of concession services among the factors that might affect airport pricing. In particular, there is only little…

Abstract

Airport economics literature has recently included the supply of concession services among the factors that might affect airport pricing. In particular, there is only little empirical analysis on whether: (i) the supply of airport concession services can stimulate the demand for travel (two-side complementarity) and (ii) the demand for airport concession services is independent of traveling activities (welfare neutrality). In this chapter, we survey papers that have addressed two-side complementarity and welfare neutrality in airport concessions. Our goal is to discuss the different assumptions that have shaped the models and to collect evidences, facts and empirical findings that may support analytical hypotheses. We argue that the notions of two-side complementarity and welfare neutrality might be interrelated – especially when airports invest in concessions in the area accessible to non-passengers. Welfare gains should be assessed on a case by case basis, depending on the type of airport in terms of ownership, size (and the relative mass of connecting passengers compared to origin–destination passengers), and the source of concession revenues. Our arguments might be particularly relevant to policy makers who need to understand (i) whether the supply of concessions reduces or increases the benefits of airport (aviation) price regulation and (ii) whether the effective control of market power may require the regulation of the prices of both the businesses.

Details

The Economics of Airport Operations
Type: Book
ISBN: 978-1-78714-497-2

Keywords

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