| 9091. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Site-specific analysis of on wind turbines in complex terrain: A case study
- 2021
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Ingår i: WESC2021, Wind Energy Science Conference , The Conference Book (Intro) with the Book of Abstracts (Theme 01 - 10). ; Theme 02, s. 2-111-2-112
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study aims to analyse and understand how the structural and drivetrain loads on the turbines can vary within a wind farm situated in a complex terrain. To this end, the flow field is studied using computational fluid and aero-elastic simulations and a modified version of the FAST software is used to determine the turbine response Verification of the numerical results is performed by using data from turbine SCADA system for a case study of Röbergsfjället wind farm with 8 turbines located in the mid-western part of Sweden.
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| 9092. |
- Sarvazyan, Armen, et al.
(författare)
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Biomedical applications of radiation force of ultrasound : Historical roots and physical basis
- 2010
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Ingår i: Ultrasound in Medicine and Biology. - : Elsevier. - 0301-5629. ; 36:9, s. 1379-1394
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Forskningsöversikt (refereegranskat)abstract
- Radiation force is a universal phenomenon in any wave motion, electromagnetic or acoustic. Although acoustic and electromagnetic waves are both characterized by time variation of basic quantities, they are also both capable of exerting a steady force called radiation force. In 1902, Lord Rayleigh published his classic work on the radiation force of sound, introducing the concept of acoustic radiation pressure, and some years later, further fundamental contributions to the radiation force phenomenon were made by L. Brillouin and P. Langevin. Many of the studies discussing radiation force published before 1990 were related to techniques for measuring acoustic power of therapeutic devices; also, radiation force was one of the factors considered in the search for noncavitational, nonthermal mechanisms of ultrasonic bioeffects. A major surge in various biomedical applications of acoustic radiation force started in the 1990s and continues today. Numerous new applications emerged including manipulation of cells in suspension, increasing the sensitivity of biosensors and immunochemical tests, assessing viscoelastic properties of fluids and biological tissues, elasticity imaging, monitoring ablation of lesions during ablation therapy, targeted drug and gene delivery, molecular imaging and acoustical tweezers. We briefly present in this review the major milestones in the history of radiation force and its biomedical applications. In discussing the physical basis of radiation force and its applications, we present basic equations describing the relationship of radiation stress with parameters of acoustical fields and with the induced motion in the biological media. Momentum and force associated with a plane-traveling wave, equations for nonlinear and nonsteady-state acoustic streams, radiation stress tensor for solids and biological tissues and radiation force acting on particles and microbubbles are considered.
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| 9093. |
- Scholz, Matthias, 1971
(författare)
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The influence of a vibrating upper lip on the sound generation in flue organ pipes - A combined experimental/numerical study
- 2007
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Ingår i: Proceedings of the International Symposium on Musical Acoustics, Barcelona, Spain 9-12 September, 2007.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A combined experimental/numerical study investigating the relation between vibrations of the upper lip and the acoustical energy accumulated inside a flue organ pipe resonator will be presented. A characteristic flue organ pipe was mechanically excited at the upper labium. Input force, surface velocities of the pipe walls and sound pressure inside the pipe were measured for this load case. The measurements assumed steady state conditions, i.e. the pipe was driven using broadband noise and signal analysis was performed in the frequency domain.The experiment was then simulated using a finite element approach. Generally, due to uncertainties in material and geometrical data, modelling a crafted instrument is not easy. However, in the low frequency range numerical results matched well the experimental data. This allowed using the model to identify the energy flow from the excitation point to positions where the sound pressure was picked up with the microphone. Results indicate that an overly yielding labium can indeed have a strong influence on the sound generation. It will also be shown that in general this will not be desired, since the degree of coupling between sound field and vibrating labium is very sensitive to material and structural properties, i.e. hard to control.
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| 9094. |
- Segalini, Antonio, et al.
(författare)
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A spectral model for stably stratified turbulence
- 2015
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 781, s. 330-352
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Tidskriftsartikel (refereegranskat)abstract
- A solution of the inviscid rapid distortion equations for a stratified flow with homogeneous shear is proposed, extending the work of Hanazaki & Hunt (J. Fluid Mech., vol. 507, 2004, pp. 1-42) to the two horizontal velocity components. The analytical solution allows for the determination of the spectral tensor evolution at any given time starting from a known initial condition. By following the same approach as that adopted by Mann (J. Fluid Mech., vol. 273, 1994, pp. 141-168), a model for the spectral velocity tensor in the atmospheric boundary layer is obtained, where the spectral tensor, assumed to be isotropic at the initial time, evolves until the breakup time where the spectral tensor is supposed to achieve its final state observed in the boundary layer. The model predictions are compared with atmospheric measurements obtained over a forested area, giving the opportunity to calibrate the model parameters, and further validation is provided by additional low-roughness data. Characteristic values of the model coefficients and their dependence on the Richardson number are proposed and discussed.
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| 9095. |
- Shams Hakimi, Poja, 1988, et al.
(författare)
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High-cycle variable amplitude fatigue experiments and design framework for bridge welds with high-frequency mechanical impact treatment
- 2022
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Ingår i: Steel Construction. - : Wiley. - 1867-0520 .- 1867-0539.
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Tidskriftsartikel (refereegranskat)abstract
- Fatigue enhancement by way of high-frequency mechanical impact (HFMI) treatment can enable effective design and construction of steel bridges. However, bridges may experience high and varying mean stresses, the effects of which are not covered today by any design recommendation or in the literature on HFMI-treated joints. In this study, fatigue experiments were conducted with realistic in-service bridge loading, which revealed the same high fatigue performance as for constant amplitude loading. The effect of mean stress in spectrum loading was quantified and a method to account for it in an equivalent manner is proposed. A design framework has been developed for design and engineering purposes.
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| 9096. |
- Shankar, Vijay, et al.
(författare)
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Transient heat transfer and moisture load in cold attic constructions - A CFD analysis
- 2018
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Ingår i: AIP Conference Proceedings. - : Author(s). - 1551-7616 .- 0094-243X. ; 1978
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Konferensbidrag (refereegranskat)abstract
- Mold growth in cold attic constructions has become an increasing problem in Sweden and other countries with cold climates due to the demands on energy efficient building envelopes. Highly insulated building envelopes with cold ventilated attics lead to colder climates in the attic space, which increases the risk for mold growth. In this paper, the transient heat transfer process including natural and forced convection is investigated for a 24-hour cycle in a virtual 3D model of a ventilated attic construction by the use of CFD technology. The momentum and energy equations along with the realizable k-epsilon turbulence model are solved with commercial CFD software. Transient simulations are performed for daily temperature variations for various ventilation rates and a hygrothermal analysis is conducted to estimate the risk for mold growth at the inner roof boundary. A virtual model of a ventilated attic with an underlying layer of porous medium is used for the simulations and the CFD approach is based on a validated model from previous research. The results are the temperature field and the risk for mold growth for different ventilation rates presented as a function of time during the cycle.
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| 9097. |
- Shao, Xinyuan, 1997, et al.
(författare)
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A comparison of two wave energy converters’ power performance and mooring fatigue characteristics – One WEC vs many WECs in a wave park with interaction effects
- 2023
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Ingår i: Journal of Ocean Engineering and Science. - 2468-0133. ; 8:4, s. 446-460
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Tidskriftsartikel (refereegranskat)abstract
- The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution. Harnessing ocean energy from waves has attracted attention due to its high energy density. This study compares two generations of floating heaving point absorber WEC, WaveEL 3.0 and WaveEL 4.0, regarding their power performance and mooring line fatigue characteristics, which are essential in, e.g., LCoE calculations. The main differences between the two WECs are the principal dimensions and minor differences in their geometries. The DNV software SESAM was used for simulations and analyses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting, motion characteristics, mooring line forces, fatigue of mooring lines, and hydrodynamic power production. The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions. A verification of the two WECs’ motion responses and axial mooring line forces is made against measurement data from a full-scale installation. In the second part of the study, the influence of interaction effects is investigated when the WECs are installed in wave parks. The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method. Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are simulated and discussed. The study's main conclusion is that WaveEL 4.0, which has a longer tube than WaveEL 3.0, absorbs more hydrodynamic energy due to larger heave motions and more efficient power production. At the same time, the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short. Its motions in the horizontal plane are larger, which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects.
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| 9098. |
- Shao, Xinyuan, 1997
(författare)
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Analysis of Power Performance and Mooring Fatigue Damage for Wave Energy Parks
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave energy has been recognized as a promising alternative to traditional energy sources due to its cleanliness and sustainability. To harness this energy, wave energy converters (WECs) are utilized. These WECs operate using a variety of working principles and are typically deployed in large numbers in the form of wave energy parks to generate electricity with high efficiency and low levelized cost of energy (LCOE). However, the interaction effects between multiple WECs can positively or negatively impact power performance and mooring fatigue damage, highlighting the importance of numerical methodologies to evaluate such effects and facilitate agile wave energy park design processes. The primary objective of this thesis was to develop numerical methodologies and data post-processing techniques to effectively access single WECs and wave energy parks consisting of two different WEC concepts belonging to the point absorber group: WaveEL and NoviOcean. Specifically, two methodologies were built based on the potential theory and a computational fluid dynamics (CFD) method, for which the boundary element method (BEM) and direct numerical simulation (DNS) with volume of fluid (VOF) modelling were adopted, respectively. These methods were implemented using the software, DNV SESAM and STAR-CCM+. The WEC concepts were evaluated in terms of the performance and mooring fatigue damages of each WEC concept with varying WEC generations, wave conditions, wave incoming directions and wave park layouts. This thesis contributes to a better understanding of WEC system modelling, power performance and mooring fatigue damage estimation. Ultimately, these findings are anticipated to facilitate the development of optimized wave energy park layouts in the future.
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| 9099. |
- Shao, Xinyuan, 1997, et al.
(författare)
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Fatigue of mooring lines in wave energy parks
- 2023
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Ingår i: Advances in the Analysis and Design of Marine Structures - Proceedings of the 9th International Conference on Marine Structures (MARSTRUCT 2023). - London : CRC Press. - 9781032506364 - 9781032506364 ; , s. 205-211
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Konferensbidrag (refereegranskat)abstract
- This study analyzes the amount of fatigue damage accumulated by polyester mooring lines in different wave parks for six heaving point absorber wave energy converters (WECs). The wave park simulation uses a coupled non-linear method that calculates the motion of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated by the mooring lines is calculated using a relative tension-based fatigue analysis method. Several factors that influence the fatigue life of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are discussed in detail.
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| 9100. |
- Shao, Xinyuan, 1997, et al.
(författare)
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FSI simulations and analyses of a non-resonant buoyant wave energy converter
- 2023
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Ingår i: Proceedings of the International Conference on Ocean, Offshore and Arctic Engineering - OMAE 2023. - 9780791886908 ; 8
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Konferensbidrag (refereegranskat)abstract
- Deploying wave energy converters (WECs) in wave parks into the ocean requires detailed planning and numerical analyses to maximize the wave energy capture and keep the LCoE at the lowest possible level. High-fidelity simulation models can accurately simulate the fluid-structure interaction (FSI) between the WECs and the ocean’s waves. However, the computation cost is too high for simulations and analyses of large-scale WEC parks. This study presents fully coupled hydrodynamic-structure response simulations and analyses using the high-fidelity CFD software STAR-CCM+, which is compared with the DNV software package SESAM that adopts potential flow theory to model environmental loads. A novel non-resonant heave-point buoyant WEC called NoviOcean is investigated. The first case study, where only one WEC was modelled, showed that both simulation approaches/software gave comparable WEC motion results for moderate sea state conditions, but the SESAM software required significantly less computation cost. Hence, the SESAM model was used in systematic simulations of two WECs to investigate the effect of FSI on the energy capture by both WECs by varying the distance between the WECs and the wave direction. The results show which WEC distances and wave directions should be preferred to maximize the wave energy capture.
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