流体力学セミナー流体力学セミナー

数理解析研究所　流体力学セミナーのご案内です．

御来聴歓迎．

===========================================================

流体力学セミナー ２０１０

＃今回は木曜日の開催となっています．ご注意ください．

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部の
　建物になっています．ご注意ください．

日時： 2月18日（木） 15:00 から 16:30

場所： 京大 理学研究科5号館（物理学教室）413号室

講師： Prof. Sadruddin Benkadda
(International Institute for fusion Science-Universite
de Provence, Marseille France)

題目: Patterns, Intermittent Transport and Universality
in Convective Turbulence in Magnetic Fusion Plasmas

概要：Buoyancy-driven flows such as thermal convection are of great
importance for a wide range of phenomena in geophysical,
astrophysical and fusion plasmas [1,2,3]. We consider here
intermittent aspects of convective turbulence and transport in
magnetized plasma of magnetic fusion machines such as tokamaks or
stelerators. These investigations use Direct Numerical Simulation
(DNS) of Ion Temperature Gradient instability (ITG) which is
identical to the Rayleigh-Benard thermal convection problem in
neutral fluids [4,5,6]. Rayleigh-Benard convection in particular
is a fundamental paradigm for nonlinear dynamics including
instabilities and bifurcations, pattern formation, chaotic
dynamics and developed turbulence.

Using a weakly non-linear analysis, we show that the back-reaction
on the mean profile is the natural mechanism for saturation and
suggest that it will stay the main non-linear coupling mechanism
in the turbulent state. We also will review some basic aspects of
the interaction between convective cells and a mean flow [7,8]. In
particular and still along the line of the “defreezing” assumption
we study the behavior of a model for shear flow instability :
transient bursts of vorticity flux are generated in this model. We
briefly discuss the advantage of this kind of formulation compared
to the “non-normal” operator approach where the mean velocity is
also assumed frozen .

An extension of Herring model is derived. It takes into account
the self-consistent generation of a mean flow. It is shown that
our model has substantially richer dynamics than the one of
Herring. In particular the interaction between the convective
modes and the mean flow leads in the turbulent state to a
transition in the statistical properties of the transport. This
bifurcation is analogous the so-called soft to hard turbulence
transition in convection. In the strongly turbulent state,
intermittent bursts of thermal transport are observed in both
cases. For the latter regime, the reduced model as well as DNS
show that the Nusselt number Nu (normalized heat flux) scales with
the normalized ion pressure gradient Ki as Nu ‾ Ki1/3[6]. Since
the Rayleigh number for ITG turbulence is proportional to Ki, the
Nusselt number scaling for ITG turbulence is thus similar to the
classical Globe & Dropkin scaling for Rayleigh-Benard convection
in neutral fluids.

References:
[1]S. Benkadda, P. Beyer, N. Bian et al, Nuclear Fusion 41, 997
(2001)
[2] P. Beyer, S. Benkadda, X. Garbet and P.H. Diamond, Phys. Rev
Letters 85, 4892 (2000).
[3] Amita Das, Abhijit Sen, and Predhiman Kaw, S. Benkadda and
Peter Beyer, Physics of Plasmas 12, 032302 (2005)
[4] K. Takeda, S. Benkadda, S. Hamaguchi and M. Wakatani, Physics
of Plasmas 11, 3561-3571 (2004)
[5] K. Takeda, S. Benkadda, S. Hamaguchi and M. Wakatani, J.
Plasma Fusion Res 6 570 (2004)
[6] K. Takeda, S. Benkadda, S. Hamaguchi, M. Wakatani, Physics of
Plasmas 12, 052309 (2005)
[7] N. Bian, S. Benkadda, X. Garbet, O. Garcia, J. Paulsen, Physics
of Plasmas, 10, 1382, (2003)
[8] O. Garcia, N. Bian, J. Paulsen , S. Benkadda and K. Rypdal,
Plasma Physics and Controlled Fusion 45, 919-932, (2003)

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada@kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２００９

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部の
　建物になっています．ご注意ください．

日時： 11月30日（月） 15:00 から 16:30

場所： 京大 理学部６号館 ２０３号室

講師： Abraham C.-L. Chian
(National Institute for Space Research (INPE), Brazil
& RIMS, Kyoto University)

題目: Nonlinear dynamics of fluids and plasmas: On-off intermittent
turbulence

概要：The amplitude and phase dynamics of coherent structures in
intermittent turbulence in fluids and plasmas is studied using
direct simulations of Navier-Stokes equations and
magnetohydrodynamics equations, as well as in-situ observations of
atmospheric and interplanetary turbulence. Nonlinear surrogate
techniques are applied to quantify the degree of phase
synchronization in simulated and observed data of fluid and plasma
turbulence. We adopt the complex Morlet wavelet to characterize
the amplitude dynamics by computing the Local Intermittency
Measure, and to characterize the phase dynamics by computing a
phase coherence index. Our techniques are able to detect and
measure coherent structures in magnetic field turbulence in
unshocked and shocked solar wind, as well as in atmospheric
turbulence above and within the Amazon forest canopy.
Intermittent mean-field dynamo is investigated using numerical
modeling of magnetohydrodynamic turbulence driven by helical
forcing. The importance of phase synchronization and on-off
intermittent turbulence in the variability of stellar magnetic
field and its impact on the dynamics of climate and space weather
of a planet and exoplanet is discussed.

Chian ACL, Miranda RA. Cluster and ACE observations of phase
synchronization in intermittent magnetic field turbulence: a
comparative study of shocked and unshocked solar wind. Ann.
Geophys. 27, 1789, 2009.

Chian ACL, Han M, Miranda RA, Shu, C, Valdivia, JA. The planetary
-exoplanetary environment: a nonlinear perspective. Adv. Space
Res., in press, 2010.

Chian ACL, Miranda RA, Koga D, Bolzan MJA, Ramos FM, Rempel EL.
Analysis of phase coherence in fully developed atmospheric
turbulence: Amazon forest canopy. Nonlinear Proc. Geophys. 15, 567,
2008.

Koga D, Chian ACL, Miranda RM, Rempel EL. Intermittent nature of
solar wind turbulence near the Earth’s bow shock: Phase coherence
and non-Gaussianity. Phys. Rev. E 75, 046401, 2007.

Koga, D, Chian ACL, Hada T, Rempel EL. Experimental evidence of
phase coherence of magnetohydrodynamic turbulence in the solar
wind: GEOTAIL satellite data. Phil. Trans. Royal Soc. London-
Math. Phys. Sciences 366, 447, 2008.

Rempel EL, Proctor MR, Chian ACL. Intermittent nonlinear dynamo in
compressible magnetohydrodynamics. Monthly Not. Royal Astron. Soc.,
in press, 2009.

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２０１０

＃ 3 / 10 水曜日の開催となっています．ご注意ください．

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部物理教室
　になっています．ご注意ください．

日時： 3月10日（水） 15:00 から 16:30

場所： 京大 理学研究科5号館（物理学教室）525号室 (第4講義室)

講師： Paul Manneville (Ecole Polytechnique)

題目: Decay of turbulence in plane Couette flow:
turbulent bands from the lab to the computer

概要：The bifurcation diagram of plane Couette flow is characteristic
of flows without linear instability modes. After a brief
presentation of experimental findings obtained in Saclay at the
turn of the century, supporting a distinction between an upper
transitional range with oblique bands and a lower transitional
range with decaying spots, a brief review of the numerical
approaches taken up to now will be given, with special emphasis
on the ‘temporal / spatiotemporal’ issue. In order to reach
large aspect ratios, a modelling strategy having recourse to a
drastic lowering of the cross-stream resolution has been developed.
A first semianalytical approach [1] points to an interpretation
in terms of spatiotemporal intermittency [2] proposed by Pomeau
but fails to reproduce the bands, which is not the case of the
under-resolved direct numerical simulations that we have performed
using Gibson’s ChannelFlow program. These simulations faithfully
reproduce experimental findings up to a measurable shift of the
transitional range [3], which shows that the formation of bands
is a robust phenomenon involving gross features of the turbulent
flow only.

[1] M. Lagha, P. M., “Modeling transitional plane Couette flow,”
Eur. Phys. J. B, vol. 58 (2007) 433–447.
[2] P. M., “Spatiotemporal perspective on the decay of turbulence in
wall-bounded flows” Phys. Rev. E; vol. 79 (2009) 025301 [R]; 039904 [E].
[3] J. Rolland, P.M., “Numerical approach to the simulation of plane
Couette flow in extended geometry” in preparation for Theor. Comp. Fluid Dyn.

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada@kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

数理解析研究所　流体力学セミナーのご案内です．

御来聴歓迎．

===========================================================

流体力学セミナー ２０１０

＃今回は木曜日の開催となっています．ご注意ください．

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部の
　建物になっています．ご注意ください．

日時： 2月18日（木） 15:00 から 16:30

場所： 京大 理学研究科5号館（物理学教室）413号室

講師： Prof. Sadruddin Benkadda
(International Institute for fusion Science-Universite
de Provence, Marseille France)

題目: Patterns, Intermittent Transport and Universality
in Convective Turbulence in Magnetic Fusion Plasmas

概要：Buoyancy-driven flows such as thermal convection are of great
importance for a wide range of phenomena in geophysical,
astrophysical and fusion plasmas [1,2,3]. We consider here
intermittent aspects of convective turbulence and transport in
magnetized plasma of magnetic fusion machines such as tokamaks or
stelerators. These investigations use Direct Numerical Simulation
(DNS) of Ion Temperature Gradient instability (ITG) which is
identical to the Rayleigh-Benard thermal convection problem in
neutral fluids [4,5,6]. Rayleigh-Benard convection in particular
is a fundamental paradigm for nonlinear dynamics including
instabilities and bifurcations, pattern formation, chaotic
dynamics and developed turbulence.

Using a weakly non-linear analysis, we show that the back-reaction
on the mean profile is the natural mechanism for saturation and
suggest that it will stay the main non-linear coupling mechanism
in the turbulent state. We also will review some basic aspects of
the interaction between convective cells and a mean flow [7,8]. In
particular and still along the line of the “defreezing” assumption
we study the behavior of a model for shear flow instability :
transient bursts of vorticity flux are generated in this model. We
briefly discuss the advantage of this kind of formulation compared
to the “non-normal” operator approach where the mean velocity is
also assumed frozen .

An extension of Herring model is derived. It takes into account
the self-consistent generation of a mean flow. It is shown that
our model has substantially richer dynamics than the one of
Herring. In particular the interaction between the convective
modes and the mean flow leads in the turbulent state to a
transition in the statistical properties of the transport. This
bifurcation is analogous the so-called soft to hard turbulence
transition in convection. In the strongly turbulent state,
intermittent bursts of thermal transport are observed in both
cases. For the latter regime, the reduced model as well as DNS
show that the Nusselt number Nu (normalized heat flux) scales with
the normalized ion pressure gradient Ki as Nu ‾ Ki1/3[6]. Since
the Rayleigh number for ITG turbulence is proportional to Ki, the
Nusselt number scaling for ITG turbulence is thus similar to the
classical Globe & Dropkin scaling for Rayleigh-Benard convection
in neutral fluids.

References:
[1]S. Benkadda, P. Beyer, N. Bian et al, Nuclear Fusion 41, 997
(2001)
[2] P. Beyer, S. Benkadda, X. Garbet and P.H. Diamond, Phys. Rev
Letters 85, 4892 (2000).
[3] Amita Das, Abhijit Sen, and Predhiman Kaw, S. Benkadda and
Peter Beyer, Physics of Plasmas 12, 032302 (2005)
[4] K. Takeda, S. Benkadda, S. Hamaguchi and M. Wakatani, Physics
of Plasmas 11, 3561-3571 (2004)
[5] K. Takeda, S. Benkadda, S. Hamaguchi and M. Wakatani, J.
Plasma Fusion Res 6 570 (2004)
[6] K. Takeda, S. Benkadda, S. Hamaguchi, M. Wakatani, Physics of
Plasmas 12, 052309 (2005)
[7] N. Bian, S. Benkadda, X. Garbet, O. Garcia, J. Paulsen, Physics
of Plasmas, 10, 1382, (2003)
[8] O. Garcia, N. Bian, J. Paulsen , S. Benkadda and K. Rypdal,
Plasma Physics and Controlled Fusion 45, 919-932, (2003)

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada@kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２０１０

＃今回は火曜日の開催となっています．ご注意ください．

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部の
　建物になっています．ご注意ください．

日時： 1月12日（火） 15:00 から 16:30

場所： 京大 理学研究科5号館　413号室

講師： 大木谷 耕司 (Sheffield大学, UK)

題目: 非局所バーガース方程式: 最大値原理とハミルトンヤコビ方程式」

概要：ナビエストークス方程式が正則な解を持つことは、物理・工学分野
では前提とされているが、その数学的な証明はない。ここでは、こ
の問題に対して、何らかの示唆を得るべく、2つの簡単な数学的モ
デルの考察を行う。(モデルに物理的意味は無い)

通常の手法での困難の原因は、次の2点に尽きる。

(1) エンストロフィーに対する不等式が過大評価にすぎる。
(2) 圧力項があるため、最大値原理が適用できない。

3次元バーガース方程式(正則)にも (1) の困難はつきまとうが、
(2)の困難はない。非局所項がある場合、最大値原理は一般に適用できな
いが、この事は直ちにこの種の不等式が破綻することを意味しない。こ
の点を吟味するため、1次元バーガース方程式に圧力を模倣する非局所的
項を加え、解の正則性がどう変化するか数値計算を行う(with M. Dowker).

また、1次元バーガース方程式は、ハミルトンヤコビ方程式を介して可積
分となることは周知である (Forsyth-Florin-Hopf-Cole 変換)。2次元以
上の速度場のヘルムホルツ分解においては、ポテンシャル成分の他に非
圧縮成分が現れる。前者の成分については多次元バーガース方程式に対
する同様の解法として既知である。ここでは、後者のソレノイダル成分
を支配する、2ないし3次元の非圧縮性流体方程式の別の表現として、非
局所ハミルトンヤコビ方程式を導出する。さらに、対応する1次元版の非
局所ハミルトンヤコビ方程式を考え、その振舞いを数値計算で検討する。

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２００９

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部の
　建物になっています．ご注意ください．

日時： 11月30日（月） 15:00 から 16:30

場所： 京大 理学部６号館 ２０３号室

講師： Abraham C.-L. Chian
(National Institute for Space Research (INPE), Brazil
& RIMS, Kyoto University)

題目: Nonlinear dynamics of fluids and plasmas: On-off intermittent
turbulence

概要：The amplitude and phase dynamics of coherent structures in
intermittent turbulence in fluids and plasmas is studied using
direct simulations of Navier-Stokes equations and
magnetohydrodynamics equations, as well as in-situ observations of
atmospheric and interplanetary turbulence. Nonlinear surrogate
techniques are applied to quantify the degree of phase
synchronization in simulated and observed data of fluid and plasma
turbulence. We adopt the complex Morlet wavelet to characterize
the amplitude dynamics by computing the Local Intermittency
Measure, and to characterize the phase dynamics by computing a
phase coherence index. Our techniques are able to detect and
measure coherent structures in magnetic field turbulence in
unshocked and shocked solar wind, as well as in atmospheric
turbulence above and within the Amazon forest canopy.
Intermittent mean-field dynamo is investigated using numerical
modeling of magnetohydrodynamic turbulence driven by helical
forcing. The importance of phase synchronization and on-off
intermittent turbulence in the variability of stellar magnetic
field and its impact on the dynamics of climate and space weather
of a planet and exoplanet is discussed.

Chian ACL, Miranda RA. Cluster and ACE observations of phase
synchronization in intermittent magnetic field turbulence: a
comparative study of shocked and unshocked solar wind. Ann.
Geophys. 27, 1789, 2009.

Chian ACL, Han M, Miranda RA, Shu, C, Valdivia, JA. The planetary
-exoplanetary environment: a nonlinear perspective. Adv. Space
Res., in press, 2010.

Chian ACL, Miranda RA, Koga D, Bolzan MJA, Ramos FM, Rempel EL.
Analysis of phase coherence in fully developed atmospheric
turbulence: Amazon forest canopy. Nonlinear Proc. Geophys. 15, 567,
2008.

Koga D, Chian ACL, Miranda RM, Rempel EL. Intermittent nature of
solar wind turbulence near the Earth’s bow shock: Phase coherence
and non-Gaussianity. Phys. Rev. E 75, 046401, 2007.

Koga, D, Chian ACL, Hada T, Rempel EL. Experimental evidence of
phase coherence of magnetohydrodynamic turbulence in the solar
wind: GEOTAIL satellite data. Phil. Trans. Royal Soc. London-
Math. Phys. Sciences 366, 447, 2008.

Rempel EL, Proctor MR, Chian ACL. Intermittent nonlinear dynamo in
compressible magnetohydrodynamics. Monthly Not. Royal Astron. Soc.,
in press, 2009.

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２００９

＃数理解析研究所の建物耐震改修工事のため，場所が京大理学部の
　建物になっています．ご注意ください．

日時： 10月26日（月） 15:00 から 16:30

場所： 京大 理学部６号館 ２０３号室

講師：下川倫子 氏
　　　（摂南大学工学部）
　　　
題目: コーヒー滴がつくる消滅フラクタル

概要：フラクタルパターンはヴィスカスフィンガリングやバクテリア
　コロニー、電解析出といった実験で観察されてきた。これらのパター
　ンは点や線から始まり、分岐を繰り返しながら面を覆いつくし、フラ
　クタル構造を形成する。今回、発表者は牛乳の上に濃いコーヒーの滴
　を置く実験で、牛乳表面にコーヒー溶液が描くフラクタルパターンを
　発見した。このフラクタルパターンは牛乳表面に拡散したコーヒー溶液
　が次々と沈むことによってできる新しいタイプの消滅フラクタルである。
　密度相関関数法とボックスカウント法によるフラクタル解析から、パ
　ターンを特徴づけるフラクタル次元は時間、密度に依存せず、一定値
　1.88±0.06をとることが分かった。また、表面パターンの密度は時間
　と共に指数関数的に減少し、その時定数はフラクタル解析が可能とな
　る70秒と一致していたことから、表面に拡散したコーヒーが十分に沈
　み込むことが消滅フラクタルの形成にとって重要であることがわかった。

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２００９

日時： 11月 2日（月） 15:00-16:30

場所： 京大 理学部６号館 ２０３号室

講師： Prof. Abraham C.-L Chian
　　　 National Institute for Space Research (INPE), Brazil
　　　 RIMS, Kyoto Univ.
　　　
題目: Nonlinear dynamics of long waves: On-off spatiotemporal intermittency

概要：Long waves are relevant for shallow-water fluids and drift turbulence
in plasmas. We discuss the origin of on-off spatiotemporal intermittency in
high-dimensional models of nonlinear long waves governed by the
regularized long-wave equation (Benjamin-Bona-Mahony equation) and Kuramoto
-Sivashinky equation. First, we analyze the spatiotemporal dynamics and
structure of chaotic saddles before, at the onset, and after a crisis, at
the transition from temporal to sptatiotemporal chaos. The links between
chaotic saddles, crisis and spatiotemporal intermittency are elucidated.
Prior to the transition to spatiotemporal chaos, a spatiotemporally
chaotic saddle is responsible for chaotic transients that mimic the
dynamics of the post-transition attractor. At the onset of crisis, the
temporal chaotic attractor loses its stability and is converted to a
temporally chaotic saddle. After the onset of spatiotemporal chaos, we
identify temporally and spatiotemporally chaotic saddles which are
responsible for the laminar and bursty phases in the spatiotemporal
intermittency. In particular, we demonstrate that phase synchronization
due to multiscale interactions is the origin of on-off spatiotemporal
intermittency associated with laminar and bursty phases of wave energy
fluctuations in well-developed spatiotemporal chaos.

Chian ACL, Rempel EL, Macau EE, Rosa, RR, Christiansen, F.
High-dimensional interior crisis in the Kuramoto-Sivashinsky equation.
Phys. Rev. E 65 (Rapid Comm.), 035203, 2002.

He KF, Chian ACL. On-off collective imperfect phase synchronization and
bursts in wave energy in a turbulent state. Phys. Rev. Lett. 91, 034102,
2003.

He KF, Chian ACL. Critical dynamic events at the crisis of transition to
spatiotemporal chaos. Phys. Rev. E 69, 026207, 2004.

Rempel, EL, Chian ACL, Macau EEN, Rosa RR. Analysis of chaotic saddles in
high-dimensional dynamical systems: the Kuramoto-Sivashinsky equation.
CHAOS 14, 545, 2004.

Rempel EL, Chian ACL. Origin of transient and intermittent dynamics in
spatiotemporal chaotic systems. Phys. Rev. Lett. 98, 014101, 2007.

Rempel EL, Chian ACL, Miranda RA. Chaotic saddles at the onset of
intermittent spatiotemporal chaos. Phys. Rev. E 76, 056217, 2007.

Rempel EL, Miranda RA, Chian ACL. Spatiotemporal intermittency and chaotic
saddles in the regularized long-wave equation. Phys. Fluids 21, 074105,
2009.

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
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流体力学セミナー流体力学セミナー

===========================================================

流体力学セミナー ２００９

＃場所と時間にご注意ください。
＃本セミナーは京大理物理教室で １０／１６ 金曜日昼に行います。

日時： 10月 16日（金） 13:00 から 14:30

場所： 京大 理学部５号館 ４１３号室

講師：Ranga Narayanan 氏
(Director of The Center for Surface Science and Technology,
University of Florida)
　　　
題目: Instabilities due to Phase Change

概要：Phase change causes instabilities and an example is
evaporative instability. This has much in common with solidification
instability, electrodeposition and even viscous fingering instability.
It is an instability that is driven by nutrient gradients which,
in this case, are temperature gradients. In the current study we have
investigated evaporative instability in a variety of configurations.
There are several ways to view how one might conduct an evaporation
experiment and in one of these the input variables are the depths of
fluid layers, the temperature difference across the system and
the pressure at the top plate. Once these are fixed, the outputs are
the bifurcation nature and the evaporation and heat transfer rates.
We present calculations which tell us that when the instability sets
in the branching can be either a forward or backward pitchfork but
the evaporation rates are always increased. In this regard the problem
is quite unlike solidification or electrodeposition. I shall also
present results that take into account experimental complications
such as side wall effects and buoyancy. We present detailed physical
reasoning behind our observations.

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
=========================================================

流体力学セミナー流体力学セミナー

流体力学セミナー ２００９

＃数理解析研究所の建物耐震改修工事のため，場所が京大物理に
　なっています．ご注意ください．

日時： 9月7日（月） 15:00 から 16:30

場所： 京大 理 物理学教室 (理学研究科 5号館) ４１３号室

講師： Adrian Constantin 氏
(Chair of Partial Differential Equations
Univeristy of Vienna)
　　　
題目: Pressure and Particle Trajectories beneath a Stokes Wave

概要： Consider periodic two-dimensional gravity
water waves propagating in irrotational flow at
constant speed at the surface of water with a flat bed.
Then the pressure in the fluid strictly decreases horizontally
away from the crest line and strictly increases with depth.
Moreover, along each streamline the horizontal velocity
strictly decreases away from the crest line. Some particle
trajectories are closed orbits but most are looping orbits
that drift either to the right or the left, depending
on the presence of an underlying favorable or adverse current.
These results have been obtained as joint work with Walter
Strauss.

+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+–+—-+–+–+

世話人：山田 道夫(京大数理研)， 藤 定義(京大)，松本 剛(京大理)
アドバイザー：船越 満明（京大情報学）、水島 二郎(同志社大工)、
余田 成男（京大理）
連絡先：山田道夫 yamada＠kurims.kyoto-u.ac.jp
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