Comparative analysis of BLEVE mechanical energy and overpressure modelling

The mechanical effects of a BLEVE are overpressure and ejection of fragments. Although fragments reach much longer distances, peak overpressure can be very strong over a certain area. Diverse authors have proposed methodologies for the estimation of the explosion energy and peak overpressure from these type of explosions, based on different thermodynamic and physical assumptions. Here these methodologies are commented and compared. Their predictions, which show an important scattering, are checked by comparison with two sets of experimental data taken from the literature. The results obtained indicate that none of the models take into account Reid’s theory. The models based on ideal gas behaviour and constant volume energy addition, isentropic expansion and isothermal expansion give quite conservative (i.e., high) values of both energy released and overpressure, while those assuming real gas behaviour and adiabatic irreversible expansion give lower values, much closer to the real/experimental ones. The diverse uncertainty factors affecting the prediction of peak overpressure are also commented.Postprint (published version

부직포의 젖음성과 기공 특성이 박테리아 부착성에 미치는 영향

학위논문(석사) -- 서울대학교대학원 : 생활과학대학 의류학과, 2021.8. 하나.Textiles can act as a media to deliver pathogenic organisms and spread infectious diseases. For controlling bacterial adhesion on surfaces, it is crucial to understand the substrate characteristics and how bacteria interact with substrates. For an accurate evaluation of textile-adhered bacteria, a proper evaluation method is necessary, because a complex 3D structure of fibrous material makes quantification of adhered bacteria challenging. Therefore, in the first phase of the study, colorimetric bacteria assay method using the iodonitrotetrazolium (INT) stain was tested for quantifying the textile-adhered bacteria. In the second phase of the study, the textile parameters including wettability, porosity, pore-volume, and pore size distribution were investigated in association with the bacterial adhesion property. Two different types of bacteria, gram-negative rod shape Escherichia coli (E. coli) and round shape Staphylococcus aureus (S. aureus) were used as model bacteria. Substrates with different levels of wettability and pore characteristics were employed to identify the critical factors influencing cell adhesion. The substrate’s wettability appeared to be the initial factor influencing the bacterial adhesion, where the hydrophilic surface showed considerably higher bacterial adhesion. Substrates with high wettability provided higher contact areas for bacteria to adhere to the substrates. Pore volume and pore size, rather than the porosity (%) itself, were other important factors affecting bacterial adhesion and retention. Compact spatial distribution of fibers resulted in limited bacterial intrusion into the pores, and eventually reduced the total amount of bacterial adherence. Thus, superhydrophobic textiles with reduced total pore volume and smaller pore size would reduce the adhesion. The findings of this study can be used as a design guide for anti-biofouling textiles.섬유상에 부착된 박테리아는 냄새를 유발하고 전염병 확산 매개체로 작용을 하는 등 위생 상의 문제를 일으키므로 박테리아의 부착을 억제하기 위한 연구가 다수 진행되고 있다. 본 연구의 목표는 부직포 직물의 표면 특성 및 직물 기공 구조에 따른 박테리아의 부착성을 조사하는 것이다. 첫 번째 단계로, 섬유상에 부착된 박테리아의 정량을 위해 INT(iodonitrotetrazolium) colorimetric bacteria assay를 이용한 박테리아 비색 검출을 수행했다. 이어서 연구의 두 번째 단계에서는 부직포 직물의 젖음성, 기공도(%), 기공 부피 및 기공 크기 분포를 포함한 섬유 물리화학적 특성이 박테리아 부착성에 어떻게 영향을 미치는지 조사하였다. 모델 박테리아로 그람 음성 간균인 대장균(E. coli)과 그람 양성 구균인 황색 포도상구균(S. aureus)을 사용했다. 표면의 젖음성은 박테리아 부착성에 영향을 미치는 주요 요인으로 조사되었으며, 친수성 표면에서 박테리아 부착량이 높게 나타났는데, 이는 젖음성이 높은 표면에서 박테리아와의 접촉면적이 크기 때문으로 사료된다. 기공도(%) 자체보다는 기공이 차지하는 절대적인 부피와 기공의 크기가 박테리아 부착에 더 큰 영향을 미치는 것으로 나타났다. 섬유의 solidity가 높고 기공크기가 박테리아보다 작은 고밀도 조직에서 박테리아의 침입 가능성이 낮아져서 부착성이 낮았으며, 기공크기가 매우 큰 부직포의 경우에도 직물에 침투한 박테리아가 잘 빠져나가기 때문에 부착성이 비교적 낮았다. 본 연구의 결과는 섬유의 방오성과 항균성을 증진시키는데 활용될 수 있을 것으로 기대한다.Chapter 1. Introduction 1 1. Background and Objectives 1 2. Theoretical Background 3 2.1. Microbial contamination of nonwoven substrates 3 2.2. Factors affecting bacterial adhesion to substrates 4 2.2.1. Surface energy 4 2.2.2. Morphology of nonwoven substrates 5 2.2.3. Wettability 6 2.3. Quantification methods of bacterial adhesion to substrates 7 Chapter 2. Experiment 9 1. Materials 9 2. Fabrication of Substrates 10 2.1. Spin coating and electrospinning 10 2.2. Surface chemical modifications 11 3. Characterization of Substrates 12 3.1. Substrate's solidity, porosity, and total pore volume 12 3.2. Wettability 13 4. Bacterial Adhesion Assay 16 4.1. Adhering bacteria to substrates 16 4.2. Quantification of adhered bacteria 17 4.2.1. Method 1: Extraction method 17 4.2.2. Method 2: Colorimetric method 20 Chapter 3. Results and Discussion 24 3.1. Comparison of bacterial adhesion assay methods 24 3.2. Effect of wettability on bacterial adhesion 28 3.3. Effect of nonwoven substrate's morphology and pore characteristics on bacterial adhesion 37 Chapter 4. Summary and Conclusions 45 Chapter 5. References 47 Abstract 55석

Sound Transmission Analysis of Circular Sandwich Panels Fully and Partially Treated with MR Fluid Core Layer

Magnetorheological (MR) fluid is categorized as smart material whose rheological properties can be varied instantaneously under the application of an external magnetic field. Utilization of these smart multifunctional materials into the devices and structures provides a unique opportunity to develop adaptive devices/structures capable of changing their dynamic characteristics in response to wide range of external disturbances. MR fluid have been recently utilized in sandwich panels to provide variable stiffness and damping to effectively control vibrations. The main objective of the present dissertation is to investigate the sound transmission loss (STL) capability of sandwich panels treated with MR fluids at low frequencies. This dissertation contributes in three major parts. First the effect of applied magnetic field on the structural and acoustical behavior of MR fluid sandwich panels is experimentally investigated. An experimental test setup including two anechoic chambers and an electro-magnet has been designed and fabricated to experimentally investigate the effect of applied magnetic field on the STL and natural frequency of sandwich panels having different thicknesses of MR core layer. The magnetic flux density generated inside the electromagnet is simulated using magneto-static finite element analysis and validated with the measured magnetic flux density using Gaussmeter. The results from the magneto-static analysis is used to derive approximate polynomial functions to evaluate the magnetic flux density as a function of the plate’s radius and applied current. In the second part, the sound transmission behavior of MR based-circular sandwich panels is investigated through development of efficient numerical models. The forced vibration equations of motion of the circular sandwich panel fully treated with MR fluid core layer is first derived utilizing Ritz and finite element (FE) methods using circular and annular elements. The transverse velocity in the transmitted side of the panel is then calculated and utilized to obtain the sound radiated from the panel and subsequently the STL. The theoretical models are validated comparing the simulation results with those obtained experimentally. The developed models have been subsequently used to conduct parametric studies in order to investigate the effect of the applied magnetic field, the thickness of the face sheets and the thickness of the MR core layer on the first axisymmetric natural frequency and STL of the MR based-clamped circular panels. The last part of the present study is devoted to the topology optimization of sandwich panels partially treated with MR fluid and silicone rubber core layer. The FE model of the sandwich panel partially treated with MR fluid and silicone rubber has been developed using circular and 4-node quadrilateral elements. The developed model is then utilized to investigate the vibroacoustic behavior of MR-based sandwich panels and to obtain their natural frequencies, loss factors and STL. Subsequently, systematic parametric studies on the effect of the position of the MR fluid and silicone rubber segments on the first axisymmetric natural frequency, corresponding loss factor and also STL are presented. It has been shown that the vibrational and acoustical behavior of the sandwich panel considerably changes by varying the location of the MR fluid treatment segments. A formal constrained and unconstrained design optimization strategy have been subsequently formulated to identify the optimal location of the MR fluid segments. Due to high computational cost associated with the FE model and considering that in each optimization iteration, FE model requires to be executed several times, approximate meta-models have been developed using random and D-optimal design points to conduct optimization problems efficiently without using the full FE model. The developed meta-models are then utilized to solve the topology optimization problems using the genetic algorithm (GA) and integer programing (IP) problems. The suitability of the identified optimal candidates are further evaluated using the developed finite element model to determine the true optimized topologies for the constrained and unconstrained problems

Fire as a primary event of accident domino sequences: The case of BLEVE

The domino sequences found in major accidents have been analyzed for a large set of cases (330); the first event triggering the domino effect was an explosion or a fire, both with approximately the same contribution; the same proportion has been found when all domino effect steps were considered. Although fire effects usually reach a distance much shorter than those of an explosion, as fire is the most frequent major accident it is often found as the first step of domino sequences. This is especially true in the case of BLEVEs. Both in fixed plants and in the transportation of hazardous materials, in the event of a fire, if flames affect a vessel and the fireproofing layer has been damaged, a BLEW can occur at any moment 127 BLEW accidents involving domino effect have been analyzed. It has been found that fire is significantly more frequent than explosion, both in triggering the domino effect sequence and in intermediate steps. The time to failure can range from 1 min or even less up to several hours, an aspect that should be very important for the management of the emergency. A set of conclusions are inferred from this survey. (C) 2015 Elsevier Ltd. All rights reserved.Postprint (author's final draft

A new procedure to estimate BLEVE overpressure

Several methodologies, based on different thermodynamic assumptions and requiring substance properties and thermodynamic data, have been proposed in the literature for the prediction of the mechanical energy released by a Boiling Liquid Expanding Vapour Explosion (BLEVE) and the associated overpressure. A new method, simple and easy to use, is presented which only requires the vessel filling degree and the temperature at failure as input variables to estimate this energy. The polynomial approach has been used to obtain the equation corresponding to the diverse substances most commonly involved in these explosions. The comparison of the predicted values with experimental data shows a good agreement.Peer ReviewedPostprint (author's final draft

The impact of poor cementing casing damage: A numerical simulation study

A good knowledge of the parameters causing casing damage is critically important due to vital role of casing during the life of a well. Cement sheath, which fills in the gap between the casing and wellbore wall, has a profound effect on the resistance of the casing against applied loads. Most of the empirical equations proposed to estimate the collapse resistance of casing ignore the effects of the cement sheath on collapse resistance and rather assume uniform loading on the casing. This paper aims to use numerical modeling to show how a bad cementing job may lead to casing damage. Two separate cases were simulated where the differences between good and bad cementation on casing resistance were studied. In both cases, the same values of stresses were applied at the outer boundary of the models. The results revealed that a good cementing job can provide a perfect sheath against the tangential stress induced by far-field stresses and reduce the chance of casing to be damaged

Nano-fabrication of complex functional structures using non- conventional lithography

In Chapter 1 I will present a brief introduction on the state of art of nanotechnologies, nanofabrication techniques and unconventional lithography as a technique to fabricate the novel electronic device as resistive switch so-called memristor is shown. In Chapter 2 a detailed description of the main fabrication and characterization techniques employed in this work is reported. Chapter 3 parallel local oxidation lithography (pLOx) describes as a main technique to obtain accurate patterning process. All the effective parameters has been studied and the optimized condition observed to highly reproducible with excellent patterned nanostructures. The effect of negative bias, calls local reduction (LR) studied. Moreover, the use of AC bias shows faster patterning process respect to DC bias. In Chapter 4 (metal/ e-SiO2/ Si nanojunction) it is shown how the electrochemical oxide nanostructures by using pLOx can be used in the fabrication of novel devices call memristor. We demonstrate a new concept, based on conventional materials, where the lifetime problem is resolved by introducing a “regeneration” step, which restores the nano-memristor to its pristine condition by applying an appropriate voltage cycle. In Chapter 5 (Graphene/ e-SiO2/ Si), Graphene as a building block material is used as an electrode to selectively oxidize the silicon substrate by pLOx set up for the fabrication of novel resistive switch device. In Chapter 6 (surface architecture) I will show another application of pLOx in biotechnology is shown. So the surface functionalization combine with nano-patterning by pLOx used to design a new surface to accurately bind biomolecules with the possibility of studying those properties and more application in nano-bio device fabrication. So, in order to obtain biochips, electronic and optical/photonics devices Nano patterning of DNA used as scaffolds to fabricate small functional nano-components

Aging, Osteocytes, and Mechanotransduction

status: publishe

BLEVE: The case of water and a historical survey

After a short update of the current more accepted definition of BLEVE, the special features of water BLEVEs are analyzed. The stronger overpressure wave generated in the case of water as compared to that of other substances is justified in terms of volume change. Through a comparison with liquefied pressurized propane, three possibilities are analyzed: the simultaneous contribution of both the liquid and the preexisting vapor, the contribution of the liquid flash vaporization, and the contribution of the pre-existing vapor. Also a historical survey on a set of 202 BLEVE accidents –the largest sample of BLEVE accidents surveyed until now– is presented. LPG was the most common substances in this set of accidents. However, water and LNG (11% of water and 4% of LNG in the studied cases) have also been involved. Impact failure (44.8%) and human factor (30.3%) were the most common causes of BLEVEs. Transport, storage, process plants, and transfer were the activities in which more accidents occurred.Peer ReviewedPostprint (published version

Trade negotiations and global relations: emerging players and actors (II)

The financial markets have regained grounds following losses in recent weeks. However the current global outlook remains largely uncertain. The decision of the Federal Reserve to announce its emergency rate cut on the 3rd March 2020, the first since the Financial Crisis, sent shock waves amongst investors with the Dow tumbling nearly 1,000 points following what was regarded as the “surprising” announcement . Even though stocks have fluctuated in recent weeks, stock markets have rebound since the Tuesday announcement. Recent events have demonstrated the importance of engaging technologies and techniques to address matters of global significance – particularly those which impact economically, socially and environmentally, in a holistic and futuristic manner – taking into account the interests of future generations. Humanity and global relationships are shaped and defined, not just through the manner in which global issues are addressed, but the techniques and responsibilities towards others, at a global level also, in deploying such techniques. (The show cased chapter Conflict Framing, Multilateral Leadership, and Coalition Formation in International Trade Disputes, 1995 – 2011 is funded in part by a grant from the Ewing Marion Kauffman Foundation). The major component of the volume "Rethinking Regulation and Monetary Policies: Recent Developments" accounting for 80 percent of the volume, cannot be highlighted/uploaded for copyright reasons