Signature of the Van der Waals like small-large charged AdS black hole phase transition in quasinormal modes

We calculate the quasinormal modes of massless scalar perturbations around small and large four-dimensional Reissner-Nordstrom-Anti de Sitter (RN-AdS) black holes. We find a dramatic change in the slopes of quasinormal frequencies in small and large black holes near the critical point where the Van der Waals like thermodynamic phase transition happens. This further supports that the quasinormal mode can be a dynamic probe of the thermodynamic phase transition.Comment: 20 pages,11 figures.The new version is accepted for publication in JHE

Design guidelines for FRP honeycomb sandwich bridge decks

Fiber-Reinforced Polymer (FRP) Bridge decks offer great advantages in highway bridge rehabilitation and new construction, due to reduced weight and maintenance costs, and enhanced durability and service-life. In practice, however, lack of bridge engineering design standards and guidelines have prevented wider acceptance and application of FRP bridge decks by transportation officials. This dissertation focuses on the study of an engineered FRP deck-steel stringer bridge system through experimental testing and both Finite Element analyses and analytical methods.;A prototype mechanical shear connection was developed and designed to be used with any type of FRP panels that can accommodate any panel heights. This non-grouted sleeve-type connector can secure the deck onto a welded stud and can sustain shear forces at FRP panel-steel stringer interface. Static and fatigue tests were conducted on push-out connection specimens, and later on a scaled bridge model. The strength, stiffness, and fatigue performance characteristics of the connection were fully investigated. Constructability issues were also evaluated, such as ease of installation and economic manufacturing of the connector. Design formulations were established based on the test results.;Following the connection study, a 1:3 scaled bridge model of a honeycomb FRP deck on steel stringers was evaluated. The deck was attached to three supporting steel stringers using the proposed sleeve-type mechanical connections. The model was designed as partially composite to satisfy AASHTO limits and requirements. Several issues were evaluated that included: (1) deck attachment procedures; (2) transverse load distribution factors; (3) local deck deflections; and (4) system fatigue behavior. After the bridge model was tested in the linear range, a 1.2-m wide T-section, of an FRP deck section attached to the middle stringer, was cutout from the bridge model and tested in bending for service and failure loads. The evaluations included: (1) Degree of composite action, (2) Effective deck-width, and (3) service-limit and ultimate-limit states under flexure loads. The behavior of the FRP deck under partial composite action was defined fully by these tests.;Finite element models of the scaled bridge model and T-beam section were formulated using ABAQUS. Besides the experimental tests and FE analyses, analytical solutions were developed to verify the test results. An explicit series solution for stiffened orthotropic plates was used to evaluate the bridge response and obtain load distribution factors of FRP deck-on-steel-stringer bridges. Also a harmonic analysis that was developed for FRP thin-walled sections was formulated to define effective-width for FRP decks as an explicit solution. The outcome of this study was to propose design guidelines and recommendations for FRP honeycomb bridge decks for applications in bridge engineering practice

Ships in ice : the interaction process and principles of design

For ships operating in arctic and sub-arctic waters, ice load is a major threat. Due to the uncertainties in ice conditions and varying operating situations, an accurate estimation on design ice load is difficult. The objective of the present research is to investigate the ice loads and the associated structural strength from aspects of mechanics, statistics and design principles. -- First, the ice-structure interaction process is investigated from the view point of mechanics. The interaction is characterized by ice fracture and damage. The ice load is highly localized within high pressure regions termed critical zones. A numerical analysis was carried out to investigate how a crack may propagate in an ice sheet and how the ice material is damaged during an ice-structure interaction. The analysis showed that small shear cracks, with mixed modes, are more likely the candidates for the fracture spalls and the formation of critical zones. -- Critical zones vary in space and time. These critical zones are characterized using parameters such as spatial density, zonal area, and the zonal force. These parameters in the model were calibrated using ship trial data of CCGS Louis St. Laurent. The ice loads on a design area were modelled as a random number of critical zones, each with a random force. Based on this model and extreme value theory, a design curve was proposed for the estimation of extreme ice loads. -- Third, the strength of the structure was investigated. A long plate, loaded by uniform pressure was proposed as the design model for the plating. Due to the randomness of ice load, there are uncertainties associated with the design model. To understand this uncertainty, various load scenarios were investigated using the finite element method. The results show that the plate fails at a dominant section, which fails in a way similar to an "equivalent long plate". Factors affecting the failure of the panel are lateral support and interaction between critical zones. These factors were investigated and empirical formula were derived based on finite element modelling. -- A simplified model was proposed to investigate the failure of the "equivalent long plate". This model was used, together with factors of lateral support, location and interactions between critical zones from empirical formula, in Monte Carlo simulation scheme to model the uncertainty of the design model of the structure. The simulated results of the uncertainty factor were approximated by a lognormal distribution. -- Finally, the results from the analysis on the ice loads and the structural resistance were used in discussion of the design principles. Two design methods, i.e., reliability design and code design methods, were discussed. Principles in selecting design load and resistance were discussed. These principles were applied in an example design of an offshore oil tanker. Reliability of the plates from different design strategies were evaluated. It was found that, for ultimate rupture, a yearly maximum with a probability of exceedance of 10⁻⁴ is appropriate as the design load