Advertisement

Electromechanical System Simulation and Optimization Studies

  • Ercan M. DedeEmail author
  • Jaewook Lee
  • Tsuyoshi Nomura
Chapter
Part of the Simulation Foundations, Methods and Applications book series (SFMA)

Abstract

Multiphysics simulation and design optimization studies for electromechanical systems are provided herein. Electronic components are covered followed by magnetic components, radio frequency devices, actuators, and motors. The governing equations for each problem are reintroduced with the addition of defined optimization variables. In the first section, five different electronic component studies are introduced in order of increasing complexity. The optimization/design of 2-D electrothermal conductors is first presented. Next, 3-D design for thermal stress reduction of an electronics package is covered. Studies on thermal-fluid systems in 2-D and 3-D design domains are then presented for electronics cold plate design. This topic is extended to a unique case, where the motion of a magnetically susceptible coolant is controlled by designing the magnetic field. Finally, heat flow control in anisotropic composites for electronics applications is described. Moving to magnetic components, computational examples are presented including an inductor analysis and related topology optimization study. Higher frequency microstrip device and multiphysics antenna design studies are then explained. In the latter case, a sequentially solved multiphysics system is optimized with respect to both electromagnetic and structural response, with consideration of fabrication constraints. The chapter concludes with the design of actuators and motors. The magnetostructural design of a basic solenoid actuator is introduced followed by a linear actuator involving several materials, components, and design variables. Design of more complicated switched reluctance motors is finally described along with the multiphysics performance analysis of a traditional interior permanent magnet synchronous motor.

References

  1. 1.
    Aage N, Mortensen NA, Sigmund O (2010) Topology optimization of metallic devices for microwave applications. Int J Numer Meth Eng 83:228–248. doi: 10.1002/nme.2837 zbMATHMathSciNetGoogle Scholar
  2. 2.
    Alexandersen J, Andreasen CS, Aage N, Lazarov BS, Sigmund O (2013) Topology optimisation for coupled convection problems. 10th world Congress on structural and multidisciplinary optimization, Orlando, 19–24 May 2013Google Scholar
  3. 3.
    Andkjær J, Nishiwaki S, Nomura T, Sigmund O (2010) Topology optimization of grating couplers for the efficient excitation of surface plasmons. J Opt Soc Am B 27:1828–1832. doi: 10.1364/JOSAB.27.001828 CrossRefGoogle Scholar
  4. 4.
    Andreasen CS, Gersborg AR, Sigmund O (2008) Topology optimization for microfluidic mixers. Int J Numer Meth Fl 61:498–513. doi: 10.1002/fld.1964 CrossRefMathSciNetGoogle Scholar
  5. 5.
    Bendsøe MP (1989) Optimal shape design as a material distribution problem. Struct Multidiscip O 1:193–202. doi: 10.1007/BF01650949
  6. 6.
    Bendsøe MP, Sigmund O (2003) Topology optimization: theory, methods, and applications, 2nd edn. Springer, BerlinGoogle Scholar
  7. 7.
    Berenger J (1994) A perfectly matched layer for the absorption of electromagnetic waves. J Comput Phys 114:185–200. doi: 10.1006/jcph.1994.1159 CrossRefzbMATHMathSciNetGoogle Scholar
  8. 8.
    Borvall T, Petersson J (2003) Topology optimization of fluids in stokes flow. Int J Numer Meth Fl 41:77–107. doi: 10.1002/fld.426 CrossRefGoogle Scholar
  9. 9.
    Boulware JC, Jensen S (2010) Thermomagnetic siphoning on a bundle of current-carrying wires. In: Proceedings of the COMSOL conference 2010, Boston, 7–9 Oct 2010Google Scholar
  10. 10.
    Braithwaite D, Beaugnon E, Tournier R (1991) Magnetically controlled convection in paramagnetic fluid. Nature 354:134–136. doi: 10.1038/354134a0 CrossRefGoogle Scholar
  11. 11.
    Bruggi M, Cinquini C (2011) Topology optimization for thermal insulation: an application to building engineering. Eng Optimiz 43:1223–1242. doi: 10.1080/0305215X.2010.550284 CrossRefMathSciNetGoogle Scholar
  12. 12.
    Choi HS, Park IH, Lee SH (2006) Electromagnetic body force calculation based on virtual air gap. J Appl Phys 99:08H903. doi: 10.1063/1.2173207 Google Scholar
  13. 13.
    Choi HS, Park IH, Lee SH (2006) Concept of virtual air gap and its applications for force calculation. IEEE T Magn 42:663–666. doi: 10.1109/TMAG.2006.871594 CrossRefGoogle Scholar
  14. 14.
    Choi JS, Yoo J (2009) Simultaneous structural topology optimization of electromagnetic sources and ferromagnetic materials. Comput Method Appl M 198:2111–2121. doi: 10.1016/j.cma.2009.02.015 CrossRefzbMATHMathSciNetGoogle Scholar
  15. 15.
    COMSOL AB (2008) COMSOL Multiphysics, Ver. 3.5a. StockholmGoogle Scholar
  16. 16.
    COMSOL AB (2010) COMSOL Multiphysics, Ver. 4.0a. StockholmGoogle Scholar
  17. 17.
    COMSOL AB (2011) COMSOL Multiphysics, Ver. 4.2. StockholmGoogle Scholar
  18. 18.
    Cooper M, Petosa A, Wight JS, Ittipiboon A (1996) Investigation of dielectric resonator antennas for L-band communications. Paper presented at the antenna technology and applied electromagnetics symposium, ANTEM ‘96Google Scholar
  19. 19.
    Dede EM (2009) Multiphysics topology optimization of heat transfer and fluid flow systems. In: Proceedings of the COMSOL conference 2009, Boston, 8–10 Oct 2009Google Scholar
  20. 20.
    Dede EM (2010) Multiphysics optimization, synthesis, and application of jet impingement target surfaces. In: Proceedings of the 12th IEEE intersociety conference on thermal and thermomechanical phenomena in electronic systems, Las Vegas, 2–5 June 2010. doi: 10.1109/ITHERM.2010.5501408
  21. 21.
    Dede EM (2010) The influence of channel aspect ratio on performance of optimized thermal-fluid structures. In: Proceedings of the COMSOL conference 2010, Boston, 7–9 Oct 2010Google Scholar
  22. 22.
    Dede EM (2010) Simulation and optimization of heat flow via anisotropic material thermal conductivity. Comp Mater Sci 50:510–515. doi: 10.1016/j.commatsci.2010.09.012 CrossRefGoogle Scholar
  23. 23.
    Dede EM (2011) Experimental investigation of the thermal performance of a manifold hierarchical microchannel cold plate. In: Proceedings of the ASME 2011 Pacific Rim technical conference and exhibition on packaging and integration of electronic and photonic systems, MEMS and NEMS, vol 2. Portland, 6–8 July 2011. doi: 10.1115/IPACK2011-52023
  24. 24.
    Dede EM (2012) Optimization and design of a multipass branching microchannel heat sink for electronics cooling. J Electron Packaging 134:041001. doi: 10.1115/1.4007159 CrossRefGoogle Scholar
  25. 25.
    Dede EM (2012) Jet impingement heat exchanger apparatuses and power electronics modules. US Patent, 8,199,505 B2Google Scholar
  26. 26.
    Dede EM (2013) Power electronics modules and power electronics module assemblies. US Patent, 8,391,008 B2Google Scholar
  27. 27.
    Dede EM, Liu Y (2013) Experimental and numerical investigation of a multi-pass branching microchannel heat sink. Appl Therm Eng 55:51–60. doi: 10.1016/j.applthermaleng.2013.02.038 CrossRefGoogle Scholar
  28. 28.
    Dede EM, Liu Y (2013) Cold plate assemblies and power electronics modules. US Patent, 8,427,832 B2Google Scholar
  29. 29.
    Dede EM, Nomura T, Schmalenberg P, Lee JS (2013) Heat flux cloaking, focusing, and reversal in ultra-thin composites considering conduction-convection effects. Appl Phys Lett 103:063501. doi: 10.1063/1.4816775 CrossRefGoogle Scholar
  30. 30.
    Dede EM, Nomura T, Lee J (2014) Thermal-composite design optimization for heat flux shielding, focusing, and reversal. Struct Multidiscip O 49:59–68. doi: 10.1007/s00158-013-0963-0 CrossRefMathSciNetGoogle Scholar
  31. 31.
    Dent PC (2012) Rare earth elements and permanent magnets (invited). J Appl Phys 111:07A721. doi: 10.1063/1.3676616 CrossRefGoogle Scholar
  32. 32.
    Dorrell DG, Knight AM, Evans L, Popescu M (2012) Analysis and design techniques applied to hybrid vehicle drive machines—assessment of alternative ipm and induction motor topologies. IEEE T Ind Electron 59:3690–3699. doi: 10.1109/TIE.2011.2165460 CrossRefGoogle Scholar
  33. 33.
    Erentok A, Sigmund O (2008) Three-dimensional topology optimized electrically-small conformal antenna. Paper presented at the IEEE antennas and propagation society international symposium, San Diego, 5–12 July 2008. doi:10.1109/APS.2008.4619200Google Scholar
  34. 34.
    Eshelby JD (1957) The determination of the elastic field of an ellipsoidal inclusion, and related problems. P R Soc A 241:376–396. doi: 10.1098/rspa.1957.0133 CrossRefzbMATHMathSciNetGoogle Scholar
  35. 35.
    Fan Z, Antar Y, Ittipiboon A, Petosa A (1996) Parasitic coplanar three-element dielectric resonator antenna subarray. Electron Lett 32:789–790. doi: 10.1049/el:19960514 CrossRefGoogle Scholar
  36. 36.
    Finlaysan BA (1970) Convective instability of ferromagnetic fluids. J Fluid Mech 40:753–767. doi: 10.1017/S0022112070000423 CrossRefGoogle Scholar
  37. 37.
    Garimella SV, Singhal V (2004) Single-phase flow and heat transport and pumping considerations in microchannel heat sinks. Heat Transfer Eng 25:15–25. doi: 10.1080/01457630490248241 CrossRefGoogle Scholar
  38. 38.
    Gelet J-L, Gerlaud A (2013) Control of Joule heating extends performance and device life. IEEE Spectrum 5:S-24–25Google Scholar
  39. 39.
    Halbach K (1980) Design of permanent multipole magnets with oriented rare earth cobalt material. Nucl Instrum Methods 169:1–10. doi: 10.1016/0029-554X(80)90094-4 CrossRefGoogle Scholar
  40. 40.
    Harpole GM, Eninger JE (1991) Micro-channel heat exchanger optimization. In: Proceedings of the 7th IEEE SEMI-THERM symposium, Phoenix, 12–14 February 1991. doi: 10.1109/STHERM.1991.152913
  41. 41.
    Hasselman DPH, Bhatt H, Donaldson KY, Thomas JR (1992) Effect of fiber orientation and sample geometry on the effective thermal conductivity of a uniaxial carbon fiber reinforced glass matrix composite. J Compos Mater 26:2278–2288. doi: 10.1177/002199839202601506 CrossRefGoogle Scholar
  42. 42.
    Hatta H, Minoru T (1986) Equivalent inclusion method for steady state conduction in composites. Int J Eng Sci 24:1159–1172. doi: 10.1016/0020-7225(86)90011-X CrossRefzbMATHGoogle Scholar
  43. 43.
    Hull D, Clyne TW (1996) An introduction to composite materials, 2nd edn. Cambridge University Press, CambridgeCrossRefGoogle Scholar
  44. 44.
    Iga A, Nishiwaki S, Izui K, Yoshimura M (2009) Topology optimization for thermal conductors considering design-dependent effects, including heat conduction and convection. Int J Heat Mass Tran 52:2721–2732. doi: 10.1016/j.ijheatmasstransfer.2008.12.013 CrossRefzbMATHGoogle Scholar
  45. 45.
    Incropera FP (1999) Liquid cooling of electronic devices by single-phase convection. Wiley-Interscience, New YorkGoogle Scholar
  46. 46.
    Incropera FP, DeWitt DP, Bergman TL, Lavine AS (2007) Introduction to heat transfer, 5th edn. Wiley, HobokenGoogle Scholar
  47. 47.
    Jensen JS, Sigmund O (2004) Systematic design of photonic crystal structures using topology optimization: low-loss waveguide bends. Appl Phys Lett 84:2022. doi: 10.1063/1.1688450 CrossRefGoogle Scholar
  48. 48.
    Jin N, Rahmat-Samii Y (2005) Parallel particle swarm optimization and finite-difference time-domain (pso/fdtd) algorithm for multiband and wide-band patch antenna designs. IEEE T Antenn Propag 53:3459–3468. doi: 10.1109/TAP.2005.858842 CrossRefGoogle Scholar
  49. 49.
    Johnson JM, Rahmat-Samii Y (1999) Genetic algorithms and method of moments (ga/mom) for the design of integrated antennas. IEEE T Antenn Propag 47:1606–1614. doi: 10.1109/8.805906 CrossRefGoogle Scholar
  50. 50.
    Karimi-Moghaddam G, Gould R, Bhattacharya S (2012) Numerical investigation of electronic liquid cooling based on the thermomagnetic effect. In: Proceedings of the ASME 2012 international mechanical engineering Congress & Exposition, Houston, 9–15 Nov 2012. doi: 10.1115/IMECE2012-87764
  51. 51.
    Kawamoto A, Matsumori T, Yamasaki S, Nomura T, Kondoh T, Nishiwaki S (2011) Heaviside projection based topology optimization by a pde-filtered scalar function. Struct Multidiscip O 44:19–24. doi: 10.1007/s00158-010-0562-2 CrossRefzbMATHGoogle Scholar
  52. 52.
    Kishk A, Ahn B, Kajfez D (1989) Broadband stacked dielectric-resonator antenna. Electron Lett 25:1232–1233. doi: 10.1049/el:19890826 CrossRefGoogle Scholar
  53. 53.
    Kiziltas G, Psychoudakis D, Volakis JL, Kikuchi N (2003) Topology design optimization of dielectric substrates for bandwidth improvement of a patch antenna. IEEE T Antenn Propag 51:2732–2743. doi: 10.1109/TAP.2003.817539 CrossRefGoogle Scholar
  54. 54.
    Kontoleontos EA, Papoutsis-Kiachagias EM, Zymaris AS, Papadimitriou DI, Giannakoglou KC (2012) Adjoint-based constrained topology optimization for viscous flows, including heat transfer. Eng Optimiz 45:941–961. doi: 10.1080/0305215X.2012.717074 CrossRefMathSciNetGoogle Scholar
  55. 55.
    Lee J (2010) Structural design optimization of electric motors to improve torque performance. Dissertation, University of Michigan, Ann ArborGoogle Scholar
  56. 56.
    Lee J, Kikuchi N (2010) Structural topology optimization of electrical machinery to maximize stiffness with body force distribution. IEEE T Magn 46:3790–3794. doi: 10.1109/TMAG.2010.2052365 CrossRefGoogle Scholar
  57. 57.
    Lee J, Seo JH, Kikuchi N (2010) Topology optimization of switched reluctance motors for the desired torque profile. Struct Multidiscip O 42:783–796. doi: 10.1007/s00158-010-0547-1 CrossRefGoogle Scholar
  58. 58.
    Lee J, Dede EM, Nomura T (2011) Simultaneous design optimization of permanent magnet, coils, and ferromagnetic material in actuators. IEEE T Magn 47:4712–4716. doi: 10.1109/TMAG.2011.2160870 CrossRefGoogle Scholar
  59. 59.
    Lee J, Nomura T, Dede EM (2012) Heat flow control in thermo-magnetic convective systems using engineered magnetic fields. Appl Phys Lett 101:123507. doi: 10.1063/1.4754119 CrossRefGoogle Scholar
  60. 60.
    Lee J, Nomura T, Dede EM (2012) Design optimization of magnetic fluid cooling system. In: Proceedings of the ASME 2012 international mechanical engineering Congress & Exposition, Houston, 9–15 Nov 2012. doi: 10.1115/IMECE2012-85817
  61. 61.
    Leung KW, Luk KM, Yung EKN, Lai S (1995) Characteristics of a low-profile circular disk dr antenna with very high permittivity. Electron Lett 31:417–418. doi: 10.1049/el:19950291 CrossRefGoogle Scholar
  62. 62.
    Lo H, Leung K, Luk K, Yung E (1999) Low-profile equilateral-triangular dielectric resonator antenna of very high permittivity. Electron Lett 35:2164–2166. doi: 10.1049/el:19991459 CrossRefGoogle Scholar
  63. 63.
    Long SA, Conway GL, Shen L (1983) The resonant cylindrical dielectric cavity antenna. IEEE T Antenn Propag 31:406–412. doi: 10.1109/TAP.1983.1143080 CrossRefGoogle Scholar
  64. 64.
    McAllister MW, Long SA, Conway GL (1983) Rectangular dielectric resonator antenna. Electron Lett 19:218–219. doi: 10.1049/el:19830150 CrossRefGoogle Scholar
  65. 65.
    McAllister MW, Long SA (1984) Resonant hemispherical dielectric antenna. Electron Lett 20:657–659. doi: 10.1049/el:19840450 CrossRefGoogle Scholar
  66. 66.
    Mlot A, Korkosz M, Lukaniszyn M (2012) Iron loss and eddy-current loss analysis in a low-power bldc motor with magnet segmentation. Arch Electr Eng 61:33–46. doi: 10.2478/v10171-012-0003-5 Google Scholar
  67. 67.
    Mongia RK, Ittipiboon A, Bhartia P, Cuhaci M (1993) Electric monopole antenna using a dielectric ring resonator. Electron Lett 29:1530–1531. doi: 10.1049/el:19931019 CrossRefGoogle Scholar
  68. 68.
    Mongia RK, Ittipiboon A, Cuhaci M (1994) Low-profile dielectric resonator antennas using a very high permittivity material. Electron Lett 30:1362–1363. doi: 10.1049/el:19940924 CrossRefGoogle Scholar
  69. 69.
    Nakatsuka K, Hama Y, Takahashi J (1990) Heat transfer in temperature-sensitive magnetic fluids. J Magn Magn Mater 85:207–209. doi: 10.1016/0304-8853(90)90053-S CrossRefGoogle Scholar
  70. 70.
    Narayana S, Sato Y (2012) Heat flux manipulation with engineered thermal materials. Phys Rev Lett 108:214303. doi: 10.1103/PhysRevLett. 108.214303 CrossRefGoogle Scholar
  71. 71.
    Nikolova NK, Tam HW, Bakr MH (2004) Sensitivity analysis with the fdtd method on structured grids. IEEE T Microw Theory 52:1207–1216. doi: 10.1109/TMTT.2004.825710 CrossRefGoogle Scholar
  72. 72.
    Ning P, Ngo K, Wang F (2011) Thermomechanical reliability investigation of large temperature excursions in power electronics packages. In: Proceedings of the 2011 IEEE energy conversion Congress & Exposition, Phoenix, 17–22 Sept 2011. doi: 10.1109/ECCE.2011.6063786
  73. 73.
    Nomura T, Sato K, Nishiwaki S, Yoshimura M (2007) Topology optimization of multiband dielectric resonator antennas. 7th World Congress on structural and multidisciplinary optimization, Seoul, 21–25 May 2007Google Scholar
  74. 74.
    Nomura T, Sato K, Taguchi K, Kashiwa T, Nishiwaki S (2007) Structural topology optimization for the design of broadband dielectric resonator antennas using the finite difference time domain technique. Int J Numer Meth Eng 71:1261–1296. doi: 10.1002/nme.1974 CrossRefzbMATHGoogle Scholar
  75. 75.
    Nomura T, Ohkado M, Schmalenberg P, Lee J, Ahmed O, Bakr M (2013) Topology optimization method for microstrips using boundary condition representation and adjoint analysis. European microwave conference (EuMC), Nuremberg, 6–10 Oct 2013Google Scholar
  76. 76.
    Nomura T, Yoon SW, Lee J, Dede EM (2013) Level set based topology optimization of directly bonded copper substrates targeting thermal stress minimization on die-substrate bonding line. 10th World Congress on structural and multidisciplinary optimization, Orlando, 19–24 May 2013Google Scholar
  77. 77.
    Olesen LH, Okkels F, Bruus H (2006) A high-level programming-language implementation of topology optimization applied to steady-state Navier-Stokes flow. Int J Numer Meth Eng 65:975–1001. doi: 10.1002/nme.1468 CrossRefzbMATHMathSciNetGoogle Scholar
  78. 78.
    Olszewski M (2011) Evaluation of the 2010 Toyota Prius hybrid synergy drive system. ORNL/TM-2010/253, Oak Ridge National Laboratory, Oak RidgeGoogle Scholar
  79. 79.
    Özişik MN (1993) Heat conduction, 2nd edn. Wiley, New YorkGoogle Scholar
  80. 80.
    Ozoe H (2005) Magnetic convection. Imperial College Press, LondonCrossRefGoogle Scholar
  81. 81.
    Park S, Yoo J, Choi JS (2009) Simultaneous optimal design of the yoke and the coil in the perpendicular magnetic recording head. IEEE T Magn 45:3668–3671. doi: 10.1109/TMAG.2009.2023878 CrossRefMathSciNetGoogle Scholar
  82. 82.
    Petosa A, Ittipiboon A, Antar Y, Roscoe D, Cuhaci M (1998) Recent advances in dielectric-resonator antenna technology. IEEE Antenn Propag M 40:35–48. doi: 10.1109/74.706069 CrossRefGoogle Scholar
  83. 83.
    Reddy JN, Gartling DK (2000) The finite element method in heat transfer and fluid dynamics, 2nd edn. CRC Press, Boca RatonzbMATHGoogle Scholar
  84. 84.
    Rosensweig RE (1985) Ferrohydrodynamics. Cambridge University Press, New YorkGoogle Scholar
  85. 85.
    Schwab L, Hildebrandt U, Stierstadt K (1983) Magnetic Bénard convection. J Magn Magn Mater 39:113–114. doi: 10.1016/0304-8853(83)90412-2
  86. 86.
    Seo JH (2009) Optimal design of material microstructure for convective heat transfer in a solid-fluid mixture. Dissertation, University of Michigan, Ann ArborGoogle Scholar
  87. 87.
    Sigmund O (2001) A 99 line topology optimization code written in Matlab. Struct Multidiscip O 21:120–127. doi: 10.1007/s001580050176
  88. 88.
    Sobhan CB, Garimella SV (2001) A comparative analysis of studies on heat transfer and fluid flow in microchannels. Microscale Therm Eng 5:293–311. doi: 10.1080/10893950152646759 CrossRefGoogle Scholar
  89. 89.
    Sullivan PF, Ramadhyani S, Incropera FP (1992) Extended surfaces to enhance impingement cooling with single circular round jets. Joint ASME/JSME conference on electronic packaging, Milpitas, 9–12 Apr 1992Google Scholar
  90. 90.
    Svanberg K (1987) The method of moving asymptotes—a new method for structural optimization. Int J Numer Meth Eng 24:359–373. doi: 10.1002/nme.1620240207 CrossRefzbMATHMathSciNetGoogle Scholar
  91. 91.
    Tsuji Y, Hirayama K, Nomura T, Sato K, Nishiwaki S (2006) Design of optical circuit devices based on topology optimization. IEEE Photonic Tech L 18:850–852. doi: 10.1109/LPT.2006.871686 CrossRefGoogle Scholar
  92. 92.
    Tuckerman DB, Pease RFW (1981) High-performance heat sinking for VLSI. IEEE Electr Devices L 2:126–129. doi: 10.1109/EDL.1981.25367 CrossRefGoogle Scholar
  93. 93.
    Yamasaki S, Nishiwaki S, Yamada T, Izui K, Yoshimura M (2010) A structural optimization method based on the level set method using a new geometry-based re-initialization scheme. Int J Numer Meth Eng 83:1580–1624. doi: 10.1002/nme.2874 CrossRefzbMATHMathSciNetGoogle Scholar
  94. 94.
    Yee K (1996) Numerical solution of initial boundary value problems involving Maxwell’s equations in isotropic media. IEEE T Antenn Propag 14:302–307. doi: 10.1109/TAP.1966.1138693 Google Scholar
  95. 95.
    Yoon GH (2010) Topological design of heat dissipating structure with forced convective heat transfer. J Mech Sci Technol 24:1225–1233. doi: 10.1007/s12206-010-0328-1 CrossRefGoogle Scholar
  96. 96.
    Zienkiewicz OC, Campbell JS (1973) Shape optimization and sequential linear programming. In: Gallagher RH, Zienkiewicz OC (eds) Optimum structural design. Wiley, New York, pp 109–126Google Scholar

Copyright information

© Springer-Verlag London 2014

Authors and Affiliations

  1. 1.Toyota Research Inst. of North AmericaAnn ArborUSA
  2. 2.Korea Aerospace UniversityGoyang-siKorea, Republic of (South Korea)
  3. 3.Toyota Central R&D Labs.NagakuteJapan

Personalised recommendations