| 1. |
- Liefvendahl, Mattias, 1971, et al.
(författare)
-
Wall-Modeled LES for Ship Hydrodynamics in Model Scale
- 2021
-
Ingår i: Journal of Ship Research. - : Society of Naval Architects and Marine Engineers. - 1542-0604 .- 0022-4502. ; 65:1, s. 41-54
-
Tidskriftsartikel (refereegranskat)abstract
- A complete approach for wall-modeled large-eddy simulation (WMLES) is demonstrated for the simulation of the flow around a bulk carrier in the model scale. Essential components of the method are an a-priori estimate of the thickness of the turbulent boundary layer (TBL) over the hull and to use an unstructured grid with the appropriate resolution relative to this thickness. Expressions from the literature for the scaling of the computational cost, in terms of the grid size, with Reynolds number, are adapted in this application. It is shown that WMLES is possible for model scale ship hydrodynamics, with similar to 10(8) grid cells, which is a gain of at least one order of magnitude as compared with wall-resolving LES. For the canonical case of a flat-plate TBL, the effects of wall model parameters and grid cell topology on the predictive accuracy of the method are investigated. For the flat-plate case, WMLES results are compared with results from direct numerical simulation, RANS (Reynolds-averaged Navier-Stokes), and semi-empirical formulas. For the bulk carrier flow, WMLES and RANS are compared, but further validation is needed to assess the predictive accuracy of the approach.
|
|
| 2. |
- Larsson, Tobias, et al.
(författare)
-
Project: PIEp - Product Innovation Engineering Programme
- 2011
-
Annan publikation (populärvet., debatt m.m.)abstract
- PROJEKTSAMMANFATTNINGPIEp, Product Innovation Engineering Program är ett nationellt program som syftar till att stärka förmågan till innovativ produkt- och affärsutveckling. PIEp spänner över fältet från teori till praktik, från forskning om innovationssystem till proaktivt arbete för att stärka innovationskraft och därigenom uppnå en systemförändring inom forskning, utbildning och utveckling. PIEp skall pågå under tio år, 2007-2016 och engagera flera av Sveriges lärosäten och forskningsinstitut involverade i innovation och produktutveckling. PIEp leds och administreras vid KTH i partnerskap med Lunds Tekniska Högskola, Högskolan i Jönköping, Designhögskolan vid Umeå Universitet, Centrum för Teknik, Medicin och Hälsa, Luleå Tekniska Universitet, samt en rad företag och organisationer.
|
|
| 3. |
|
|
| 4. |
- Lind, Erik, et al.
(författare)
-
High Frequency Performance of Vertical InAs Nanowire MOSFET
- 2010
-
Ingår i: 2010 22Nd International Conference On Indium Phosphide And Related Materials (Iprm). - 1092-8669. - 9781424459193
-
Konferensbidrag (refereegranskat)abstract
- We report on RF characterization of vertical, 100-nm-gate length InAs nanowire MOSFETs, utilizing wrap-gate technology and Al2O3 high-kappa gate oxide. The transistors show f(t)=5.6 GHz and f(max)=22 GHz, mainly limited by parasitic capacitances. The RF device performance is described using a hybrid-pi model taking hole generation at the drain into account. Electrostatic modeling of the parasitic capacitances for arrays of vertical nanowires indicates that a strong reduction in extrinsic capacitances can be achieved for devices with a small inter-wire separation.
|
|
| 5. |
- Egard, Mikael, et al.
(författare)
-
Vertical InAs nanowire wrap gate transistors with f(t) > 7 GHz and f(max) > 20 GHz.
- 2010
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:3, s. 809-812
-
Tidskriftsartikel (refereegranskat)abstract
- In this letter we report on high-frequency measurements on vertically standing III-V nanowire wrap-gate MOSFETs (metal-oxide-semiconductor field-effect transistors). The nanowire transistors are fabricated from InAs nanowires that are epitaxially grown on a semi-insulating InP substrate. All three terminals of the MOSFETs are defined by wrap around contacts. This makes it possible to perform high-frequency measurements on the vertical InAs MOSFETs. We present S-parameter measurements performed on a matrix consisting of 70 InAs nanowire MOSFETs, which have a gate length of about 100 nm. The highest unity current gain cutoff frequency, f(t), extracted from these measurements is 7.4 GHz and the maximum frequency of oscillation, f(max), is higher than 20 GHz. This demonstrates that this is a viable technique for fabricating high-frequency integrated circuits consisting of vertical nanowires.
|
|
| 6. |
- Liu, Yu
(författare)
-
Integrating life cycle assessment into simulation-based decision support
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing marketing and legislative requirements put heavy demands on the environmental performance of future transportation solutions. The resulting need to reduce total environmental impacts presents both challenges and opportunities to the transport sector as a whole, including the automotive industry. Life cycle assessment (LCA) is commonly used to evaluate environmental performance in the automotive industry. However, the static nature of LCAlimits its usefulness for capturing dynamic environmental consequences in the manufacturing and operational phase. This thesis proposes a simulation-based approach to LCA that addresses this problem. Selected real-world case studies demonstrate the potential of the approach in both vehicle production processes and end-user applications. The work was preceded by a comprehensive review of the potential benefits and challenges of using simulation-based LCA in production processes. This review laid the foundation for the development and implementation of this method inthe automotive industry. Two real-world case studies demonstrate its value. The first was a waste collection case study in which LCA was integrated in an existing simulation-based decision support tool to optimize the company’s activities froma life cycle environmental impact perspective. A simultaneously developed simulation-based LCA model of an iron foundry production line extended the applicability of the method with a proposed decision support interpretation approach. The study shows that data and information from both simulation model and LCA databases can be integrated and utilized in the developed simulation-based LCA method. This allows different systems with different configurations to be combined to assess the relevant parameters, and eventually to provide information about overall environmental impacts to decision makers to improvethe environmental sustainability of the automotive industry.
|
|
| 7. |
- Lundberg, Mattias, 1985-
(författare)
-
Residual stresses, fatigue and deformation in cast iron
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The complex geometry of cylinder heads in heavy-duty diesel engines makes grey iron or compact graphite iron a preferred material choice due to its price, castability, thermal conductivity and damping capacity. Today’s strict emission laws have increased the demands on engine performance and engine efficiency. This means that material properties such as fatigue resistance need to be improved. Shot peening is often used to improve the fatigue resistance of components and the benefits of shot peening are associated with the induced compressive surface stresses and surface hardening. How different shot peening parameters can affect fatigue strength of grey and compact graphite iron has been investigated within the project underlying this thesis. To do this, X-ray diffraction (XRD) was utilized for residual stress measurements, scanning electron microscopy (SEM) for microstructural characterizations and mechanical fatigue testing for mechanical quantifications. The ultimate aim of this work has been to increase the fatigue resistance of cast iron by residual stress optimization.XRD measurements and SEM examinations revealed that the shot peening parameters shot size and peening intensity significantly influence residual stresses and surface deformation. Residual stress profiles, similar to the one general considered to improve the fatigue strength in steels, were obtained for both grey and compact graphite iron. Uniaxial push-pull fatigue testing on grey iron with these shot peening parameters reduced the fatigue strength with 15–20 %. The negative effect is likely related to surface damage associated with over peening and relatively high subsurface tensile residual stresses. With very gentle shot peening parameters, the uniaxial fatigue strength were unaltered from the base material but when subjected to bending fatigue an increase in fatigue strength were observed. An alternative way to increase the fatigue strength was to conduct a 30 min annealing heat treatment at 285 XC which increased the fatigue strength by almost 10 % in uniaxial loading. The improvement could be an effect of favourable precipitates forming during the annealing, which could hinder dislocation movement during fatigue.Measuring residual stresses using XRD and the sin2 -method demands accurate X-ray elastic constants (XEC) for meticulous stress analysis. The XEC referred to as 1~2s2 should therefore always be calibrated for the specific material used. The experiments conducted revealed that the XEC value is independent of the testing method used in this work. A small correction from the theoretical value should be applied when the material contains small amounts of residual stresses. The amount of residual stresses has a great impact on the XEC and thus on the stress analysis. Concluding that proper analysis of residual stresses in cast iron is not straight forward.
|
|
| 8. |
|
|
| 9. |
- Jalkanen, J. P., et al.
(författare)
-
Modelling of ships as a source of underwater noise
- 2018
-
Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0792 .- 1812-0784. ; 14:6, s. 1373-1383
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a methodology is presented for modelling underwater noise emissions from ships based on realistic vessel activity in the Baltic Sea region. This paper combines the Wittekind noise source model with the Ship Traffic Emission Assessment Model (STEAM) in order to produce regular updates for underwater noise from ships. This approach allows the construction of noise source maps, but requires parameters which are not commonly available from commercial ship technical databases. For this reason, alternative methods were necessary to fill in the required information. Most of the parameters needed contain information that is available during the STEAM model runs, but features describing propeller cavitation are not easily recovered for the world fleet. Baltic Sea ship activity data were used to generate noise source maps for commercial shipping. Container ships were recognized as the most significant source of underwater noise, and the significant potential for an increase in their contribution to future noise emissions was identified.
|
|
| 10. |
- Roupé, Mattias, 1975, et al.
(författare)
-
Immersive visualization of Building Information Models
- 2016
-
Ingår i: Living Systems and Micro-Utopias: Towards Continuous Designing, Proceedings of the 21st International Conference of the Association for Computer-Aided Architectural Design Research in Asia (CAADRIA 2016). - 9789881902672 ; , s. 673-682
-
Konferensbidrag (refereegranskat)abstract
- The design process of a building often involves many different actors and people with different experiences, level of knowledge and ability to interpret information. The most common information media in these processes are 2D-drawings, documents and 3D images of design. These media can be difficult to interpret and understand and could cause communication difficulties and design errors. However, in this context, Building Information Modelling (BIM) and Virtual Reality (VR) have been shown to offer an efficient communication platform. In this paper we present and evaluate a portable immersive visualization system that uses the BIMs directly from the design tools. The system is validated in a real construction project, where the dif-ferent disciplines in the design process used the system. The result was collected through interviews and observation during usage of the system. All the participants expressed that this type of visual interface helped them to get another level of understanding and perception of space, which lead to better decision-making process and resolving of design issues.
|
|
