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Westerberg, Lars-GöranORCID iD iconorcid.org/0000-0001-5294-1855
Publikationer (10 of 84) Visa alla publikationer
Schillings, A., Slapak, R., Nilsson, H., Yamauchi, M., Dandouras, I. & Westerberg, L.-G. (2019). Earth atmospheric loss through the plasma mantle and its dependence on solar wind parameters. Earth, Planets and Space, 71(70)
Öppna denna publikation i ny flik eller fönster >>Earth atmospheric loss through the plasma mantle and its dependence on solar wind parameters
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2019 (Engelska)Ingår i: Earth, Planets and Space, Vol. 71, nr 70Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Atmospheric loss and ion outfow play an important role in the magnetospheric dynamics and in the evolution of the atmosphere on geological timescales—an evolution which is also dependent on the solar activity. In this paper, we investigate the total O+ outfow [s−1 ] through the plasma mantle and its dependency on several solar wind param‑ eters. The oxygen ion data come from the CODIF instrument on board the spacecraft Cluster 4 and solar wind data from the OMNIWeb database for a period of 5 years (2001–2005). We study the distribution of the dynamic pressure and the interplanetary magnetic feld for time periods with available O+ observations in the plasma mantle. We then divided the data into suitably sized intervals. Additionally, we analyse the extreme ultraviolet radiation (EUV) data from the TIMED mission. We estimate the O+ escape rate [ions/s] as a function of the solar wind dynamic pressure, the interplanetary magnetic feld (IMF) and EUV. Our analysis shows that the O+ escape rate in the plasma mantle increases with increased solar wind dynamic pressure. Consistently, it was found that the southward IMF also plays an important role in the O+ escape rate in contrast to the EUV fux which does not have a signifcant infuence for the plasma mantle region. Finally, the relation between the O+ escape rate and the solar wind energy transferred into the magnetosphere shows a nonlinear response. The O+ escape rate starts increasing with an energy input of approxi‑ mately 1011W.

Ort, förlag, år, upplaga, sidor
Springer, 2019
Nyckelord
O+ outfow/escape, Plasma mantle, Solar wind, Interplanetary magnetic feld (IMF), Extreme ultraviolet (EUV), Coupling functions
Nationell ämneskategori
Rymd- och flygteknik Strömningsmekanik och akustik
Forskningsämne
Atmosfärsvetenskap; Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-74886 (URN)10.1186/s40623-019-1048-0 (DOI)000472492500001 ()2-s2.0-85067844890 (Scopus ID)
Anmärkning

Validerad;2019;Nivå 2;2019-08-15 (johcin)

Tillgänglig från: 2019-06-24 Skapad: 2019-06-24 Senast uppdaterad: 2019-10-11Bibliografiskt granskad
Schillings, A., Slapak, R., Nilsson, H., Yamauchi, M., Dandouras, I. & Westerberg, L.-G. (2019). Earth atmospheric loss through the plasma mantle and its dependence onsolar wind parameters. In: : . Paper presented at EGU General Assembly 2019, 7–12 April 2019, Vienna, Austria.
Öppna denna publikation i ny flik eller fönster >>Earth atmospheric loss through the plasma mantle and its dependence onsolar wind parameters
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2019 (Engelska)Konferensbidrag (Refereegranskat)
Nationell ämneskategori
Rymd- och flygteknik Strömningsmekanik och akustik
Forskningsämne
Atmosfärsvetenskap; Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-73466 (URN)
Konferens
EGU General Assembly 2019, 7–12 April 2019, Vienna, Austria
Tillgänglig från: 2019-04-05 Skapad: 2019-04-05 Senast uppdaterad: 2019-04-05Bibliografiskt granskad
Hamedi, N. & Westerberg, L.-G. (2019). Modelling of Flexible Fibres in Viscous Fluid Flow. In: : . Paper presented at IWNMNNF 2019, 19th International Workshop on Numerical Methods for Non-Newtonian Flows, Peso da Régua, Portugal, June 16 - 20th.
Öppna denna publikation i ny flik eller fönster >>Modelling of Flexible Fibres in Viscous Fluid Flow
2019 (Engelska)Konferensbidrag, Muntlig presentation med publicerat abstract (Refereegranskat)
Abstract [en]

The current study relates to the development of a multiphase model of flexible fibre suspensions. An understanding of the rheology and dynamics of the deformation of such suspension is desirable in order to be able to fully disclose the flow behaviour from very low to very high shear rates. We present an approach for numerically simulating the dynamics of flexible fibres employing a particle-level method. This is performed by investigating the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres [1-3] enabling the model to have all degrees of freedom (translation, rotation, bending and twisting). The three-dimensional Navier-Stokes equations which describes the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The simulations are performed using OpenFOAM and the numerical outcomes are validated against experimental data.The purpose of the modelling framework applied in this work is to enable the numerical model to be extended to a 4-way coupling model, capturing shear thinning, shear thickening and the yield stress properties of a fibrous fluid suspension.

Nationell ämneskategori
Strömningsmekanik och akustik
Forskningsämne
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-74058 (URN)
Konferens
IWNMNNF 2019, 19th International Workshop on Numerical Methods for Non-Newtonian Flows, Peso da Régua, Portugal, June 16 - 20th
Tillgänglig från: 2019-05-29 Skapad: 2019-05-29 Senast uppdaterad: 2019-05-29Bibliografiskt granskad
Westerberg, L.-G. (2019). MR-fluid Technology for Reduced Wear in Windturbine Bearings. In: : . Paper presented at STLE Annual Meeting, Nashville, Tennessee, USA, 19-23 May.
Öppna denna publikation i ny flik eller fönster >>MR-fluid Technology for Reduced Wear in Windturbine Bearings
2019 (Engelska)Konferensbidrag, Muntlig presentation med publicerat abstract (Refereegranskat)
Abstract [en]

Magnetorheology (MR) is a technology to enable active control of the viscosity of a material - typically afluid, but also semi-solid materials such as lubricating greases. Magnetic particles of nano to micron scale aremixed with the fluid and when subjected to a magnetic field the particles are aligned with the field, inducing ashear resistance - i.e. the effect of an increased viscosity - if applied in appropriate direction. This technology isfor example used in active dampers in sports cars, where electromagnets activated by a sensor systemcontrols the viscosity of the damper oil and the pressure in the dampers. This paper proposes a method ofusing MR technology to reduce wear in wind turbine bearings by enhancing the lubricant film in the maximumHertzian contact. Electromagnets are used to control the sequence of demagnetization and magnetization ofthe lubricant. Here the wear particles existing in the lubricant acts as guiding particles.

Nyckelord
Applied Tribology, Power Generation, Lubricants, Ferrofluids
Nationell ämneskategori
Strömningsmekanik och akustik
Forskningsämne
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-74087 (URN)
Konferens
STLE Annual Meeting, Nashville, Tennessee, USA, 19-23 May
Tillgänglig från: 2019-05-29 Skapad: 2019-05-29 Senast uppdaterad: 2019-09-17Bibliografiskt granskad
Karami, F., Nadooshan, A. A., Westerberg, L.-G. & Tadi Beni, Y. (2019). Nano-fluid flow in a catheterized tapered artery: Consistent couple stress-theory and wall slip. Journal of thermal analysis and calorimetry (Print), 137(1), 327-342
Öppna denna publikation i ny flik eller fönster >>Nano-fluid flow in a catheterized tapered artery: Consistent couple stress-theory and wall slip
2019 (Engelska)Ingår i: Journal of thermal analysis and calorimetry (Print), ISSN 1388-6150, E-ISSN 1588-2926, Vol. 137, nr 1, s. 327-342Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This study was conducted with the aim of investigating the Newtonian nanofluid flow in a catheterized tapered artery through using a completely consistent couple stress theory. In the process of carrying out this study, the slip condition at the arterial wall and the catheter, as well as, the permeability was taken into account. Further, the velocity, temperature, and concentration profiles were analytically modeled and the effect of the length scale on these profiles was well presented through the way it influences small-scale flows. The effect of the slip condition at the artery and catheter walls on the velocity was also investigated and revealed that any increase in the velocity leads to an increase in the slip velocity. Furthermore, the effect of other parameters such as the catheter diameter, shape, and height of the stenosis on these profiles was explored for all three artery geometries, i.e., diverging tapered artery, converging tapered artery, and non-tapered artery, respectively. The findings suggested that any increase in the catheter diameter and stenosis height can decrease the velocity and nanoparticle concentration profiles, while the temperature profile increases. It was also found that by increasing the stenosis shape parameter the velocity and concentration profiles increase and temperature decreases.

Ort, förlag, år, upplaga, sidor
Springer, 2019
Nyckelord
Catheterized artery, Couple stress, Nanofluid, Slip velocity, Galerkin method
Nationell ämneskategori
Strömningsmekanik och akustik
Forskningsämne
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-71601 (URN)10.1007/s10973-018-7930-3 (DOI)000470338100029 ()
Anmärkning

Validerad;2019;Nivå 2;2019-07-01 (johcin)

Tillgänglig från: 2018-11-15 Skapad: 2018-11-15 Senast uppdaterad: 2019-07-01Bibliografiskt granskad
Hamedi, N. & Westerberg, L.-G. (2019). On the deformation of fibrous suspensions. In: Transactions of the Nordic Rheology Society: . Paper presented at Nordic Rheology Conference, Gothenburg, aug 21-23, 2019. Nordic Rheology Society, 27
Öppna denna publikation i ny flik eller fönster >>On the deformation of fibrous suspensions
2019 (Engelska)Ingår i: Transactions of the Nordic Rheology Society, Nordic Rheology Society , 2019, Vol. 27Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

An understanding of the rheology and dynamics of the deformation of fibrous suspension as a multiphase fluid is important in order to be able to fully disclose the flow behaviour from very low to very high shear rates. In this study, a flexible fibre model has been implemented in an open source Computational Fluid Dynamics code. The three-dimensional Navier-Stokes equations which describe the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The aim of this study is to investigate the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres1-3 enabling the model to have all degrees of freedom - translation, rotation, bending and twisting. The simulations are performed using the OpenFOAM open source software.

Ort, förlag, år, upplaga, sidor
Nordic Rheology Society, 2019
Nationell ämneskategori
Strömningsmekanik och akustik
Forskningsämne
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-75701 (URN)
Konferens
Nordic Rheology Conference, Gothenburg, aug 21-23, 2019
Tillgänglig från: 2019-08-27 Skapad: 2019-08-27 Senast uppdaterad: 2019-08-28
Hamedi, N. & Westerberg, L.-G. (2019). On the Interaction of Side-By-Side Circular Cylinders in Viscoplastic Fluids. Fluids, 4(2), Article ID 93.
Öppna denna publikation i ny flik eller fönster >>On the Interaction of Side-By-Side Circular Cylinders in Viscoplastic Fluids
2019 (Engelska)Ingår i: Fluids, ISSN 2311-5521, Vol. 4, nr 2, artikel-id 93Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In this paper, the static interaction of a train of three cylinders in a Bingham fluid is studiednumerically using Computational Fluid Dynamics. The variation of drag forces for the cylinders inseveral configurations is investigated. Positions of the particles in relation to the reference particleare recognized by the separation distance between the cylinders. A steady state field is considered,with Bingham numbers between 5 and 150. Several separation distances (d) were considered, such that2.0D d 6.0D where D is the cylinder diameter. The Reynolds number was chosen in the range of5 Re 40. In particular, the eect of the separation distance, Reynolds number and Bingham numberon the shape and size of the unyielded regions was investigated. The functional dependence of thisregion and the drag coecient is explored. The present results reveal the significant influence of thegap between the cylinders on the drag force and the shape of the unyielded regions surrounding thecylinders. It was found that there are several configurations in which the drag forces over the first andthe third cylinders are almost equal depending on variation of the Bi, Re and the separation distance.

Ort, förlag, år, upplaga, sidor
MDPI, 2019
Nyckelord
particle interaction, viscoplastic fluid, Bingham fluid, computational fluid dynamics
Nationell ämneskategori
Strömningsmekanik och akustik
Forskningsämne
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-74059 (URN)10.3390/fluids4020093 (DOI)000475331700035 ()2-s2.0-85069779541 (Scopus ID)
Anmärkning

Validerad;2019;Nivå 2;2019-05-27 (oliekm)

Tillgänglig från: 2019-05-27 Skapad: 2019-05-27 Senast uppdaterad: 2019-08-21Bibliografiskt granskad
Schillings, A., Gunell, H., Nilsson, H., De Spiegeleer, A., Ebihara, Y., Westerberg, L.-G., . . . Slapak, R. (2019). The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations. Annales Geophysicae
Öppna denna publikation i ny flik eller fönster >>The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations
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2019 (Engelska)Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Artikel i tidskrift (Refereegranskat) Submitted
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:ltu:diva-76359 (URN)
Tillgänglig från: 2019-10-11 Skapad: 2019-10-11 Senast uppdaterad: 2019-10-17
Schillings, A., Gunell, H., Nilsson, H., De Spiegeleer, A., Ebihara, Y., Westerberg, L.-G., . . . Slapak, R. (2019). The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations.
Öppna denna publikation i ny flik eller fönster >>The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations
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2019 (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

Ion escape is of particular interest for studying the evolution of the atmosphere on geological time scales. Previously, using Cluster-CODIF data, we investigated the oxygen ion outflow from the plasma mantle for different solar wind conditions and geomagnetic activity. We found significant correlations between solar wind parameters, geomagnetic activity (Kp index) and the O+ outflow. From these studies, we suggested that O+ ions observed in the plasma mantle and cusp have enough energy and velocity to escape the magnetosphere and be lost into the solar wind or in the distant magnetotail. Thus, this study aims to investigate where do the ions observed in the plasma mantle end up. In order to answer this question, we numerically calculate the trajectories of O+ ions using a tracing code to further test this assumption and determine the fate of the observed ions. Our code consists of a magnetic field model (Tsyganenko T96) and an ionospheric potential model (Weimer 2001) in which particles initiated in the plasma mantle and cusp regions are launched and traced forward in time. We analysed 136 observations of plasma mantle or cusp events in Cluster data between 2001 and 2007, and for each event 200 O+ particles were launched with an initial parallel and perpendicular velocity corresponding to the bulk velocity observed by Cluster. From the observations, our results show that 93 % of the events have an initial parallel velocity component twice the initial perpendicular velocity. After the tracing, we found that 96 % of the particles are lost into the solar wind or in the distant tail. Out of these 96 %, 20 % escape into the dayside magnetosphere.

Nationell ämneskategori
Strömningsmekanik och akustik Rymd- och flygteknik
Forskningsämne
Atmosfärsvetenskap; Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-76814 (URN)10.5194/angeo-2019-146 (DOI)
Tillgänglig från: 2019-11-22 Skapad: 2019-11-22 Senast uppdaterad: 2019-11-22
Slapak, R., Schillings, A., Nilsson, H., Yamauchi, M. & Westerberg, L.-G. (2018). Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,2017 [Letter to the editor]. Annales Geophysicae
Öppna denna publikation i ny flik eller fönster >>Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,2017
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2018 (Engelska)Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Artikel i tidskrift, Letter (Refereegranskat) Published
Ort, förlag, år, upplaga, sidor
Copernicus Publications, 2018
Nationell ämneskategori
Rymd- och flygteknik Strömningsmekanik och akustik
Forskningsämne
Atmosfärsvetenskap; Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-68587 (URN)10.5194/angeo-35-721-2017-corrigendum (DOI)
Tillgänglig från: 2018-05-02 Skapad: 2018-05-02 Senast uppdaterad: 2018-11-20Bibliografiskt granskad
Organisationer
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0001-5294-1855

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