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  • 1.
    Andersson, Kjell
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Hagnestål, Anders
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM).
    A flexible chain proposal for winch based point absorbers2018In: Proceedings of the ASME 2018 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2018: August 26-29, 2018, Quebec City, Quebec, Canada, 2018Conference paper (Refereed)
    Abstract [en]

    Ocean wave power is a promising renewable energy source for future energy production. It has however been difficult to find a cost-effective solution to convert the wave energy into electricity. The harsh marine environment and the fact that wave power is delivered with high forces at low speeds makes design of durable mechanical structures and efficient energy conversion challenging. The dimensioning forces strongly depend on the wave power concept, the Wave Energy Converter (WEC) implementation and the actual Power TakeOff (PTO) system. A WEC using a winch as a Power Take-Off system, i.e. a Winch Based Point Absorber (WBPA), could potentially accomplish a low Levelized Cost Of Energy (LCOE) if akey component - a low-cost, durable and efficient winch that can deal with high loads - can be developed. A key problem for achieving a durable winch is to find a force transmitting solution that can deal with these high loads and handle up to 80 million cycles. In this article we propose a design solution for a force transmitting chain in a WBPA system where elastomeric bearings are used as a means to achieve the relative motion between the links in the chain. With this solution no sliding is present and the angular motion is achieved as a deformation in the elastomeric bearing when the chain is winded on a drum. The link was designed primarily to minimize the number of joints in the chain: Thereby the maximum allowed relative angle between the links when rolled up over the drum should be as large as possible within practical limits. The angle is to be handled by the elastomeric bearing. A detailed strength analysis of the link has been performed as well as topology optimization to increase the strength to weight ratio. A test rig for a first proof of concept testing has been developed and the first preliminary test results indicate that this concept with using elastomeric bearings can be a potential solution for a durable chain and should be analyzed further for fatigue conditions and under water operations. 

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  • 2.
    Andersson, Kjell
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Hagnestål, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A Flexible Chain Proposal for Winch-Based Point Absorbers2019In: Journal of mechanical design (1990), ISSN 1050-0472, E-ISSN 1528-9001, Vol. 141, no 10, article id 102301Article in journal (Refereed)
    Abstract [en]

    Ocean wave power is a promising renewable energy source. It has, however, been difficult to find a cost-effective solution to convert wave energy into electricity. The harsh marine environment and the fact that wave power is delivered with large forces at low speed make design of durable mechanical structures and efficient energy conversion challenging. The dimensioning forces strongly depend on the wave power concept, the wave energy converter (WEC) implementation, and the actual power take-off (PTO) system. A WEC with a winch as a power take-off system, i.e., a winch-based point absorber (WBPA), could potentially enable a low levelized cost of energy (LCOE) if a low-cost, durable and efficient winch that can deal with peak loads can be developed. A key challenge for realizing such a winch is to find a force transmitting solution that can deal with these peak loads and that can handle up to 80 million cycles during its life. In this article, we propose a design solution for a force transmitting chain with elastomer bearings connecting the links of the chain. With this solution no sliding is present, and the angular motion is realized as elastic shear deformations in the elastomer bearings when the chain is wound onto the winch drum. The elastomer bearings were designed for low shear stiffness and high compression stiffness, and the links were designed primarily to minimize the number of joints in the chain. Thereby, the maximum allowed relative angle between the links when rolled up over the drum should be as large as possible within practical limits. Finite element-based topological optimization was performed with the aim to increase the link strength to weight ratio. A test rig for a first proof of concept testing has been developed, and preliminary test results indicate that this chain concept with elastomer bearings can be a potential solution for a durable chain and should be analyzed and tested further for fatigue and sea operations.

  • 3.
    Andersson, Kjell
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Hagnestål, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Design of a flexible chain for winch based point absorbers2018In: Proceedings of NordDesign: Design in the Era of Digitalization, NordDesign 2018, 2018Conference paper (Refereed)
  • 4.
    Hagnestal, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    On the Optimal Pole Width for Direct Drive Linear Wave Power Generators Using Ferrite Magnets2018In: Energies, E-ISSN 1996-1073, Vol. 11, no 6, article id 1356Article in journal (Refereed)
    Abstract [en]

    In this work, ferrite magnet linear generators for wave power applications are considered. These machines operate at unusually low speeds, around and even below 1 m/s, at which the optimal geometry differs from standard machines, since the copper loss and the force density become considerably more important. The focus is on translator design, and analytical two-dimensional (2D) expressions for the optimal 2D geometry are derived. Finite Element Analysis (FEA) is also applied to verify the analytical expressions and to determine effects from leakage fluxes and iron saturation. Demagnetization of ferrite magnets is also discussed and calculations are made to show the demagnetization situation for the magnets in different geometries. Finally, an example generator design is made to illustrate the findings. This generator is compared to three other generator concepts. It is concluded that ferrite magnet generators can have at least nearly the same shear stress as surface mounted neodymium magnet generators at low speed if the airgap is 3 mm or less, provided that a proper pole length is chosen, and that they can be economically competitive to neodymium magnet generators for wave power. It is also concluded that the demagnetization situation for the magnets can be severe, and that the choice of magnet grade and pole length is crucial in this respect.

  • 5.
    Hagnestål, Anders
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    A generator for generating electric energy from movements of sea water2015Patent (Other (popular science, discussion, etc.))
  • 6.
    Hagnestål, Anders
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    A low cost and highly efficient TFM generator for wave power2016In: Proceedings of the 3rd Asian Wave and Tidal Energy Conference, 2016, p. 822-828Conference paper (Refereed)
    Abstract [en]

    A force-dense and very efficient direct drive transverse flux generator aimed for wave power applications is being developed at the Royal Institute of Technology in Sweden. The machine is specialized for low speeds, and the design of a linear version is presented in this paper. The basic electromagnetic design is given as well as an overview of the mechanical design. The benefits of such machines at low speeds are described in detail. The challenges that the machine type have are also presented, and suggestions are made on how they can be handled. Geometrical and calculated performance data is given for a prototype machine that is to be constructed during 2017. The possibility of using the machine type for control methods such as reactive control is also discussed. The machine is predicted to have an efficiency of 97-98% at speeds as low as 0.7 m/s, and a shear stress of 100-120 kN/m², corresponding to 200-240 kN/m² if only half the active area is counted as active which is custom for such machines.

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  • 7.
    Hagnestål, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Addressing the Magnet Mounting Problem for Double-Sided TFM Machines with Flux-Concentrating Setup2019In: ISSN 2332-7707Article in journal (Refereed)
    Abstract [en]

    Variable reluctance machines such as transverse fluxmachines (TFM) have very suitable properties for slow speedrenewable energy conversion applications such as wave power.The double-sided TFM variant with flux-concentrating magnetsetup has generally better performance than other variants, butis considerably more challenging to build. One of the mostchallenging parts to build for such machines is the magnetstructure, especially for larger machines where the magnetstructure is wide. In this text, the magnet mounting problemof such a structure for a linear wave power generator hasbeen analysed. A mounting method has been proposed and themounting forces involved for that method have been calculated.A mounting tool has been designed and built, and it has beenused to successfully build 12 magnet stacks for two linear wavepower generators that form a test setup. Through this work, ithas been demonstrated that it is fully feasible to construct suchmagnet structures and thereby a reference to how this rathercomplex practical problem can be handled is provided for othersin the field.

  • 8.
    Hagnestål, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Guldbrandzén, Erling
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    A highly efficient and low-cost linear TFM generator for wave power2017In: Proceedings of the 12th European Wave and Tidal Energy Conference 27th aug - 1st Sept 2017, Cork, Ireland, European Wave and Tidal Energy Conference , 2017, article id 1069Conference paper (Refereed)
    Abstract [en]

    A force-dense,low-cost and very efficient direct drive transverse flux generator aimed forwave power applications is being developed at the Royal Institute of Technologyin Sweden, and a linear version is currently being built. The machine isspecialized for low speeds, and the project is presented in this paper, wherewe focus on why TFMs are very suitable for low speed applications and why theyare so hard to build. The basic electromagnetic design is given as well as anoverview of the mechanical design. The benefits of such machines at low speedsare described in detail. The challenges that the machine type have are alsopresented, and suggestions are made on how they can be handled. Geometrical andcalculated performance data is given for a prototype machine that is to beconstructed during 2017. The machine is predicted to have an efficiency of about98% at speeds as low as 0.7 m/s, and a shear stress of 100-120 kN/m²,corresponding to 200-240 kN/m² if only half the active area is counted asactive which is custom for such machines.

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  • 9.
    Hagnestål, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Durable winch-based point absorbers2017In: Proceedings of the 12th European Wave and Tidal Energy Conference 27th Aug - 1st Sept 2017, Cork, Ireland, European Wave and Tidal Energy Conference , 2017Conference paper (Refereed)
    Abstract [en]

    Wave power could give a significant contribution to a

    future sustainable energy system if the Levelized Cost Of Energy

    can be reduced to a competitive level. Winch-based point

    absorbers could potentially accomplish this if a key component –

    a low-cost, durable and efficient winch that can deal with high

    loads – can be developed. In this article the possibilities of winchbased

    point absorbers and the challenges that need to be

    overcome are described. Further, the possibilities to design such

    winches are explored and several different design approaches are

    evaluated and compared. At present, we believe that such a

    winch solution can be found although more research is needed to

    develop a full concept, and the most promising solutions so far

    involve inverted tooth chains, flat UHMwPE fiber (Dyneema)

    bands and flat carbon fibre structures.

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1 - 9 of 9
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