ASSESSMENT OF STABILITY MAPS FOR HEATED CHANNELS WITH SUPERCRITICAL FLUIDS VERSUS THE PREDICTIONS OF A SYSTEM CODE

Ambrosini, Walter,Sharabi, Medhat Beshir Korean Nuclear Society 2007 Nuclear Engineering and Technology Vol.39 No.5

The present work is aimed at further discussing the effectiveness of dimensionless parameters recently proposed for the analysis of flow stability in heated channels with supercritical fluids. In this purpose, after presenting the main motivations for the introduction of these parameters in place of previously proposed ones, additional information on the theoretical bases and on the consequences of this development is provided. Stability maps, generated by an in-house program adapted from a previous application to boiling channels, are also shown for different combinations of the operating parameters. The maps are obtained as contour plots of an amplification parameter obtained from numerical discretization and subsequent linearization of governing equations; as such, they provide a quantitatively clear perspective of the effect of different boundary conditions on the stability of heated channels with supercritical fluids. In order to assess the validity of the assumptions at the basis of the in-house model, supporting calculations have been performed making use of the RELAP5/MOD3.3 computer code, detecting the values of the dimensionless parameters at the threshold for the occurrence of instability for a heated channel representative of SCWR proposed core configurations. The obtained results show reasonable agreement with the maps, supporting the applicability of the proposed scaling parameters for describing the dynamic behaviour of heated channels with supercritical fluids.

Reinforced concrete wall as protection against accidental explosions in the petrochemical industry

Ambrosini, Daniel,Luccioni, Bibiana Maria Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.2

In this paper the study of a reinforced concrete wall used as protection against accidental explosions in the petrochemical industry is presented. Many alternatives of accidental scenarios and sizes of the wall are analyzed and discussed. Two main types of events are considered, both related to vessel bursts: Pressure vessel bursts and BLEVE. The liberated energy from the explosion was calculated following procedures firmly established in the practice and the effects over the structures and the reinforced concrete wall were calculated by using a CFD tool. The results obtained show that the designed wall reduces the values of the peak overpressure and impulse and, as a result, the damage levels to be expected. It was also proved that a reinforced concrete wall can withstand the blast load for the considered events and levels of pressure and impulse, with minor damage and protect the buildings.

ASSESSMENT OF STABILITY MAPS FOR HEATED CHANNELS WITH SUPERCRITICAL FLUIDS VERSUS THE PREDICTIONS OF A SYSTEM CODE

WALTER AMBROSINI 한국원자력학회 2007 Nuclear Engineering and Technology Vol.39 No.5

The present work is aimed at further discussing the effectiveness of dimensionless parameters recently proposed for the analysis of flow stability in heated channels with supercritical fluids. In this purpose, after presenting the main motivations for the introduction of these parameters in place of previously proposed ones, additional information on the theoretical bases and on the consequences of this development is provided. Stability maps, generated by an in-house program adapted from a previous application to boiling channels, are also shown for different combinations of the operating parameters. The maps are obtained as contour plots of an amplification parameter obtained from numerical discretization and subsequent linearization of governing equations; as such, they provide a quantitatively clear perspective of the effect of different boundary conditions on the stability of heated channels with supercritical fluids. In order to assess the validity of the assumptions at the basis of the in-house model, supporting calculations have been performed making use of the RELAP5/MOD3.3 computer code, detecting the values of the dimensionless parameters at the threshold for the occurrence of instability for a heated channel representative of SCWR proposed core configurations. The obtained results show reasonable agreement with the maps, supporting the applicability of the proposed scaling parameters for describing the dynamic behaviour of heated channels with supercritical fluids.

Reinforced concrete wall as protection against accidental explosions in the petrochemical industry

Daniel Ambrosini,Bibiana Maria Luccioni 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.2

In this paper the study of a reinforced concrete wall used as protection against accidental explosions in the petrochemical industry is presented. Many alternatives of accidental scenarios and sizes of the wall are analyzed and discussed. Two main types of events are considered, both related to vessel bursts: Pressure vessel bursts and BLEVE. The liberated energy from the explosion was calculated following procedures firmly established in the practice and the effects over the structures and the reinforced concrete wall were calculated by using a CFD tool. The results obtained show that the designed wall reduces the values of the peak overpressure and impulse and, as a result, the damage levels to be expected. It was also proved that a reinforced concrete wall can withstand the blast load for the considered events and levels of pressure and impulse, with minor damage and protect the buildings.

Microphysiological Engineering of Immune Responses in Intestinal Inflammation

Yoko M. Ambrosini,Woojung Shin,Soyoun Min,Hyun Jung Kim 대한면역학회 2020 Immune Network Vol.20 No.2

Microphysiological Engineering of Immune Responses in Intestinal Inflammation

Yoko M. Ambrosini,Woojung Shin,Soyoun Min,Hyun Jung Kim 대한면역학회 2020 Immune Network Vol.20 No.2

The epithelial barrier in the gastrointestinal (GI) tract is a protective interface that endures constant exposure to the external environment while maintaining its close contact with the local immune system. Growing evidence has suggested that the intercellular crosstalk in the GI tract contributes to maintaining the homeostasis in coordination with the intestinal microbiome as well as the tissue-specific local immune elements. Thus, it is critical to map the complex crosstalks in the intestinal epithelial-microbiome-immune (EMI) axis to identify a pathological trigger in the development of intestinal inflammation, including inflammatory bowel disease. However, deciphering a specific contributor to the onset of pathophysiological cascades has been considerably hindered by the challenges in current in vivo and in vitro models. Here, we introduce various microphysiological engineering models of human immune responses in the EMI axis under the healthy conditions and gut inflammation. As a prospective model, we highlight how the human “gut inflammation-on-a-chip” can reconstitute the pathophysiological immune responses and contribute to understanding the independent role of inflammatory factors in the EMI axis on the initiation of immune responses under barrier dysfunction. We envision that the microengineered immune models can be useful to build a customizable patient's chip for the advance in precision medicine.

TMD effectiveness in nonlinear RC structures subjected to near fault earthquakes

Martin N. Domizio,Daniel Ambrosini,Oscar Curadelli 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.24 No.4

The use of Tuned mass dampers (TMD) has proved to be effective in reducing the effects of vibrations caused by wind loads and far-field seismic action. However, its effectiveness in controlling the dynamic response of structures under near-fault earthquakes is still under discussion. In this case, the uncertainty about the TMD performance arises from the short significant duration of near-fault ground motions. In this work, the TMD effectiveness for increasing the safety margin against collapse of structures subjected to near-fault earthquakes is investigated. In order to evaluate the TMD performance in the proposed scenario, the nonlinear dynamic response of two reinforced concrete (RC) frames was analyzed. TMDs with different mass values were added to these structures, and a set of near-fault records with frequency content close to the fundamental frequency of the structure was employed. Through a series of nonlinear dynamic analysis, the minimum amplitude of each seismic record that causes the structural collapse was found. By comparing this value, called collapse acceleration, for the case of the structures with and without TMD, the benefit produced by the addition of the control device was established.

Nonlinear dynamic analysis of a RC bridge subjected to seismic loading

Germán Nanclares,Daniel Ambrosini,Oscar Curadelli,Martín Domizio 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.6

Collapse of bridges in recent earthquakes demonstrates the need to deepen the understanding of the behaviour of these structures against seismic actions. This paper presents a highly detailed numerical model of an actual bridge subjected to extreme seismic action which results in its collapse. Normally, nonlinear numerical models have high difficulties to achieve convergence when reinforced concrete is intended to be represented. The main objective of this work is to determine the efficiency of different passive control strategies to prevent the structural collapse of an existing bridge. Metallic dampers and seismic isolation by decoupling the mass were evaluated. The response is evaluated not only in terms of reduction of displacements, but also in increasing of shear force and axial force in key elements, which can be a negative characteristic of the systems studied. It can be concluded that the use of a metallic damper significantly reduces the horizontal displacements and ensures the integrity of the structure from extreme seismic actions. Moreover, the isolation of the deck, which in principle seems to be the most effective solution to protect existing bridges, proves inadequate for the case analysed due to its dynamic characteristics and its particular geometry and an unpredictable type of axial pounding in the columns. This unexpected effect on the isolation system would have been impossible to identify with simplified models.

Performance of TMDs on nonlinear structures subjected to near-fault earthquakes

Martín Domizio,Daniel Ambrosini,Oscar Curadelli 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.16 No.4

Tuned mass dampers (TMD) are devices employed in vibration control since the beginning of the twentieth century. However, their implementation for controlling the seismic response in civil structures is more recent. While the efficiency of TMD on structures under far-field earthquakes has been demonstrated, the convenience of its employment against near-fault earthquakes is still under discussion. In this context, the study of this type of device is raised, not as an alternative to the seismic isolation, which is clearly a better choice for new buildings, but rather as an improvement in the structural safety of existing buildings. Seismic records with an impulsive character have been registered in the vicinity of faults that cause seismic events. In this paper, the ability of TMD to control the response of structures that experience inelastic deformations and eventually reach collapse subject to the action of such earthquakes is studied. The results of a series of nonlinear dynamic analyses are presented. These analyses are performed on a numerical model of a structure under the action of near-fault earthquakes. The structure analyzed in this study is a steel frame which behaves as a single degree of freedom (SDOF) system. TMD with different mass values are added on the numerical model of the structure, and the TMD performance is evaluated by comparing the response of the structure with and without the control device.

Energy dissipation by friction for sliding blocks subjected to near-fault seismic base motion

Pablo M. Barlek Mendoza,Daniel Ambrosini,Bibiana M. Luccioni 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.5

The objective of this study was to determine friction ratios that maximize energy dissipation on a seismic damper. The aforementioned friction damper basically consists of mass blocks that are able to slide on a flat surface. To carry out this analysis, a numerical-experimental approach was used. Firstly, the theoretical background and equations of motion for a SDOF system consisting of a mass supported on a flat surface with friction are introduced. Special emphasis is made on the fundamentals of stick-slip motion as well as energy considerations. Secondly, experimental studies carried out on a shaking table with harmonic and seismic records are described. These tests consisted of lead blocks contained on a U-shaped channel type aluminum section with its open end facing upwards. This configuration allowed blocks to slide solely in the direction of the base motion. Five different types of contact interfaces were considered to determine potential friction coefficients for the damper's design. Additionally, computational models based on rigid-body dynamics are presented. Numerical results were satisfactory particularly when comparing model's dissipated energy with empirical results. An analysis was carried out by calculating dissipated energy for the experimentally-calibrated models with varying friction ratios. For this purpose, eight near-fault seismic records were selected. Intervals with friction coefficients that maximize energy dissipation are proposed for each record. Finally, relationships between the computed friction ratios and register's peak ground acceleration (PGA) and root mean square acceleration (RMS) are discussed.