Strength assessment of stiffened blast walls in offshore installations under explosions

Offshore installations are exposed to hydrocarbon explosions and/or fire accidents. Especially, explosions lead to serious damages to human, safety, and environment. To minimise and prevent the damage from explosions, blast walls are generally installed in oil and gas production structures. Typical blast walls are classified into flat, corrugated, and stiffened types. Among them, corrugated blast walls are frequently used for reasons such as construction, cost, and energy absorption. However, it has been known that a corrugated type of blast wall buckles between the web and flange under the explosion loads, and loses its stiffness. It means that the buckling phenomenon of a blast wall is closely related to the structural strength. This study investigates on the structural characteristics of a blast wall under quasi-static and dynamic (explosion) loads with or without a flat-plated stiffener. Finally, it can be concluded that the flat type of stiffeners are located at the buckling region to delay the buckling and improve the strength of blast walls

Development and Applications of Nanoscale Scanning Electrochemical Microscopy

DEVELOPEMENT AND APPLICATIONS OF NANOSCALE SCANNING ELECTROCHEMICAL MICROSCOPY Jiyeon Kim, PhD University of Pittsburgh, 2012 After more than 20 years of basic nanoscience research, advances in nanotechnology have opened up unprecedented possibilities and opportunities in electrochemistry. Especially, fabrication, characterization, modification and the understanding of various electrochemical interfaces or electrochemical processes at the nanoscale have led to applications of electrochemical methods to novel technologies. Nanoscale characterization and theoretical analysis of electrochemical interfaces and reactions can lead to the understanding of these complicated chemical systems at the molecular level. This is not only scientifically interesting, but also crucial for the controlled applications of electrochemistry in nanotechnology. A theme of my PhD work is to seek the better understanding of important nanosystems such as single walled carbon nanotube (SWNT) and nanopores in biological as well as artificial nanoporous membrane. The understanding of the electrochemistry of carbon nanotubes as an attractive electrode material for electroanalysis and electrocatalysis is fundamentally and practically important. Also, the greater understanding of nucleocytoplasmic transport through the nuclear pores in nuclear envelope is highly significant because of its critical roles as a regulator of gene expression, a gateway for gene delivery, and a model of biomimetic transport systems. In addition, the quantitative understanding of membrane permeability at a single nanopore level is a prerequisite for the development and the application of nanoporous membrane for nanofiltration, biomedical devices, nano fluidics, and biomimetic membrane transport. To achieve these goals, I developed scanning electrochemical microscopy (SECM) as a powerful nanoscale tool and applied this technology to the kinetic study and high-resolution imaging of heterogeneous reactions at various interfaces. Therefore, this thesis is based on two sections. In the first section, I summarize the application of nanoscale SECM to the study of a few different nanostructures and the substantial findings. The second section is concerned about the development of nanoscale SECM. Based on these achievements, the capacity of nanoscale SECM will be greatly increased to characterize and understand various nanomaterials and interfaces at the nanoscale

Three-Dimensional Metal-Oxide Nanohelix Arrays Fabricated by Oblique Angle Deposition: Fabrication, Properties, and Applications

Three-dimensional (3D) nanostructured thin films have attracted great attention due to their novel physical, optical, and chemical properties, providing tremendous possibilities for future multifunctional systems and for exploring new physical phenomena. Among various techniques to fabricate 3D nanostructures, oblique angle deposition (OAD) is a very promising method for producing arrays of a variety of 3D nanostructures with excellent controllability, reproducibility, low cost, and compatibility with modern micro-electronic processes. This article presents a comprehensive overview of the principle of OAD, and unique structural and optical properties of OAD-fabricated thin films including excellent crystallinity, accurate tunability of refractive indices, and strong light scattering effect which can be utilized to remarkably enhance performances of various systems such as antireflection coatings, optical filters, photoelectrodes for solar-energy-harvesting cells, and sensing layers for various sensors.1114Ysciescopu

Methods for determining the optimal arrangement of water deluge systems on offshore installations

Offshore installations are prone to fire and/or explosion accidents. Fires have particularly serious consequences due to their high temperatures and heat flux, which affect humans, structures and environments alike. Due to the hydrocarbon explosions caused by delayed ignition following gas dispersion, fires can be the result of immediate ignition after gas release. Accordingly, it can be difficult to decrease their frequency, which is an element of risk (risk=frequency×consequence), using an active protection system (APS) such as gas detectors capable of shutting down the operation. Thus, it is more efficient to reduce the consequence using a passive protection system (PSS) such as water spray. It is important to decide the number and location of water deluge systems, thus the aim of this study is to introduce a new procedure for optimising the locations of water deluge systems using the water deluge location index (WLI) proposed herein. The locations of water deluge systems are thus optimised based on the results of credible fire scenarios using a three-dimensional computational fluid dynamics (CFD) tool. The effects of water spray and the effectiveness of the WLI are investigated in comparison with uniformly distributed sprays

Enhanced overall efficiency of GaInN-based light-emitting diodes with reduced efficiency droop by Al-composition-graded AlGaN/GaN superlattice electron blocking layer

AlxGa1-xN/GaN superlattice electron blocking layers (EBLs) with gradually decreasing Al composition toward the p-type GaN layer are introduced to GaInN-based high-power light-emitting diodes (LEDs). GaInN/GaN multiple quantum well LEDs with 5- and 9-period Al-composition-graded AlxGa1-xN/GaN EBL show comparable operating voltage, higher efficiency as well as less efficiency droop than LEDs having conventional bulk AlGaN EBL, which is attributed to the superlattice doping effect, enhanced hole injection into the active region, and reduced potential drop in the EBL by grading Al compositions. Simulation results reveal a reduction in electron leakage for the superlattice EBL, in agreement with experimental results. (C) 2013 AIP Publishing LLC.open1133sciescopu

A Preliminary Risk Assessment on the Development of a Small-Scaled Floating Power Plant

This paper introduces a preliminary risk assessment method carried out on a newly developed floating power plant. The small-scale floating power plant has been developed to provide electric power for areas on demand, and this is a kind of a new concept system which is not clearly classified in the maritime industry. To grant the feasibility for this novel system design, a set of risk assessment activities is essentially required, and in this context, a hazard identification (HAZID) study is conducted at the very early stage of the plant design. The aims of this HAZID study are to verify the inherent safety of the initial plant design and to provide any recommendations on the next design stages. For this purpose, the potential hazards are identified in view of personnel, structural, and asset effects in association with the operation of the power plant and all the identified hazards and relevant risks are assessed with the defined criteria using a simple risk matrix. As a result, the risk or safety level of the conceptual plant design is estimated, and some design changes are suggested to give a better balance between the safety and the cost of the plant system. Overall, this paper shows how the primitive risk assessment techniques are utilized as a practical engineering tool in the development of the marine system

Electron emission of Au nanoparticles embedded in ZnO for highly conductive oxide

We investigated the effect of embedded Au nanoparticles (Au NPs) on electrical properties of zinc oxide (ZnO) for highly conductive oxide semiconductor. Au NPs in ZnO films influenced both the structural and electrical properties of the mixture films. The electrical resistivity decreases by as much as five orders of magnitude. This is explained by the electron emission from Au NPs to the ZnO matrix. Temperature-dependent Hall effect measurements show that an electron emission mechanism changes from tunneling to thermionic emission at T = 180 K. The electron mobility in the mixture film is mainly limited by the grain boundaries at lower temperature (80-180 K), and the Au/ZnO heterogeneous interface at higher temperature (180-340 K). In addition to the electron emission, embedded Au NPs alter the ZnO matrix microstructure and improve the electron mobility. Compared to the undoped ZnO film, the carrier concentration of the Au NP-embedded ZnO film can be increased by as much as six orders of magnitude with a small change in the carrier mobility. This result suggests a way to circumvent the inherent tradeoff between the carrier concentration and the carrier mobility in transparent conductive oxide (TCO) materials. © 2014 AIP Publishing LLC

A study on fire design accidental loads for aluminum safety helidecks

The helideck structure must satisfy the safety requirements associated with various environmental and accidental loads. Especially, there have been a number of fire accidents offshore due to helicopter collision (take-off and/or landing) in recent decades. To prevent further accidents, a substantial amount of effort has been directed toward the management of fire in the safety design of offshore helidecks. The aims of this study are to introduce and apply a procedure for quantitative risk assessment and management of fires by defining the fire loads with an applied example. The frequency of helicopter accidents are considered, and design accidental levels are applied. The proposed procedures for determining design fire loads can be efficiently applied in offshore helideck development projects

Controlled release of human growth hormone fused with a human hybrid Fc fragment through a nanoporous polymer membrane

Nanotechnology has been applied to the development of more effective and compatible drug delivery systems for therapeutic proteins. Human growth hormone (hGH) was fused with a hybrid Fc fragment containing partial Fc domains of human IgD and IgG(4) to produce a long-acting fusion protein. The fusion protein, hGH-hyFc, resulted in the increase of the hydrodynamic diameter (ca. 11 nm) compared with the diameter (ca. 5 nm) of the recombinant hGH. A diblock copolymer membrane with nanopores (average diameter of 14.3 nm) exhibited a constant release rate of hGH-hyFc. The hGH-hyFc protein released in a controlled manner for one month was found to trigger the phosphorylation of Janus kinase 2 (JAK2) in human B lymphocyte and to exhibit an almost identical circular dichroism spectrum to that of the original hGH-hyFc, suggesting that the released fusion protein should maintain the functional and structural integrity of hGH. Thus, the nanoporous release device could be a potential delivery system for the long-term controlled release of therapeutic proteins fused with the hybrid Fc fragment.X111313sciescopu