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2025年度 2025.4-2026.3
日時:6月13日(金)16:30-17:30
場所:お茶の水女子大学理学部1号館207室
講演者:Francesco dal Corso (Univ. Trento)
講演題目:The broad wrinkling landscape for ultra-thin parallelogram membranes
講演概要:Wrinkling is a commonly observed out-of-plane instability in membrane structures due to their extremely low bending-to-stretching stiffness ratio. It has been extensively investigated for symmetric membrane geometries and boundary conditions that induce planar non-uniform stress states by preventing the lateral contraction at the edges, and is also known to potentially display self-restabilization. This presentation outlines a recent investigation into an initially flat, parallelogram-shaped hyperelastic membrane, focusing on the influence of the inclination angle defining the membrane shape as a deviation from the rectangular geometry. It is shown that wrinkling can occur either centrally or at the two opposite obtuse-angled corners—even for small inclination angles—during stretching with unconstrained lateral contraction, a condition under which the flat configuration for the rectangular counterpart remains always stable.
Three distinct evolutions of the wrinkling pattern are numerically identified, all ultimately leading to corner localized wrinkles. This final state may arise (i) directly, without a prior bifurcation, or after the appearance of central wrinkling that either (ii) restabilizes or (iii) separates and migrates toward the corners. A closed-form expression for the critical wrinkling condition is derived by combining a perturbation approach with an energy based method in the framework of linear elasticity. This provides an accurate estimate of the onset and pattern of central wrinkling. The present findings reveal new pathways in wrinkling pattern evolution and introduce a novel approach to unconventional boundary value problems, with potential applications ranging from lightweight structural systems to flexible electronics.
日時:4月18日(金)16:30-17:30
場所:お茶の水女子大学理学部1号館207室
講演者:Katie Wu (Princeton University, Howard Stone’s Gr)
講演題目:The Motion and Deformation of Bubbles in Hele-Shaw Cells
講演概要:
We theoretically and experimentally study the propagation of a bubble in
a Hele-Shaw cell under a uniform background flow at low Reynolds
number.The bubble is flattened into a pancake-like shape, with an
approximately circular profile when viewed from above, and thin liquid
films lie between the bubble and the cell walls. Bubble motion and
deformation are determined by an interplay between the Hele-Shaw viscous
pressure, the pressure drop due to the thin films, and the capillary
pressure due to the in-plane curvature of the apparent bubble boundary.
Numerical and asymptotic results indicate that, with all other
parameters held constant, the in-plane aspect ratio of the bubble varies
non-monotonically with its size, with smaller bubbles being flattened in
the flow direction and larger bubbles being elongated. These theoretical
predictions are validated experimentally, as well as the expected loss
of fore-aft symmetry of the bubble shape due to differences between the
advancing and retreating menisci. New measurements of the bubble
velocity are also shown to agree well with theoretical predictions. The
model is also extended to describe a bubble moving in an inclined cell
due to buoyancy.
2024年度 2024.4-2025.3
日時:11月5日(火)15:30-17:30
場所:お茶の水女子大学理学部1号館201室
講演者1:横田万里亜(豊田中央研究所)
講演題目1:企業研究所と物理―ソフトマター物理を中心に―
講演概要1:
企業での物理研究について、豊田中央研究所(トヨタグループの研究所)の場合を一例としてご紹介します。企業における研究と大学での研究の違いや、研究と技術の全体像についてお話しし、今後の研究や勉学の理解を深める一助となるような内容で構成します。
講演者2:谷茉莉(京都大学)
講演題目2:手遊びから物理的な研究へ〜ひもはいつ円筒に巻き取れるのか?
講演概要2:
糸やひも、ケーブル、ロープ…細長く、小さな力でぐにゃぐにゃと変形する「ひも」状の物体は、生物・非生物問わず、また、ミクロからマクロスケールまで、我々の身近に溢れている。このような「ひも」を手元でいじった経験がある人は多いだろう。ひもを自分の指や手近なペンに巻き付けることはできるだろうか?ひもはどのように巻きつくのだろうか?手遊びから生まれたこれらの問いに対する答えを探すうち、弾性体のひもを重力下で回転円筒に巻き取るモデル系において、ぶら下がっているひもの長さによって異なる巻き付きパターンが実現されることを発見した。このようなパターンは数値シミュレーションでも再現され、さらに、パターンの境界や巻き付き間隔が弾性理論で説明できることがわかった。本講演では、ひもの巻き取りに対する研究成果[1]を紹介するとともに、私たちが日常生活で目にしている現象に潜む物理的な面白さや、それを追究する面白さについても紹介したい。
[1] M. Tani and H. Wada, Phys. Rev. Lett. 132, 058204 (2024).
日時:10月11日(金)16:40-17:40
場所:お茶の水女子大学理学部1号館201室
講演者:Joséphine Van Hulle博士(University of Liège, Belgium)
講演題目:Droplet dynamics on curved substrates
講演概要:
Understanding the dynamics of droplet motion on curved substrates is
crucial for optimizing water collection technologies, particularly in
environments where atmospheric water harvesting is essential. We
experimentally investigate the behavior of droplets on various
macroscopic structures, including vertical cylindrical fibers and
conical fibers. Through experimental observations, the research reveals
that factors such as fiber twists, gradient radii and pre-existing
wetting conditions significantly influence droplet spreading, dynamics
and shape transitions. Specifically, the descent of droplets along
vertical fibers is characterized by a self-supply mechanism, where the
liquid film left behind the droplet contributes to the formation of
subsequent droplets. On twisted fibers, droplets follow a helical path
governed by the groove geometry. Droplets on conical fibers
spontaneously move towards the base of the cone, with their dynamics
influenced by their shape. The findings of this work contribute to the
design of more efficient substrates for droplet drainage, offering
practical applications in the development of optimized fog collectors
composed of fiber meshes.
日時:9月12日(金)16:00-17:00
場所:お茶の水女子大学理学部1号館201室
講演者:Jose BICO博士(ESPCI, Paris)
講演題目:Inflating to shape: from planar sheets to 3D structures
講演概要:
Cartographers have early realized that it is impossible to draw a flat
map of the Earth without deforming continents. Gauss later generalized
this geometrical constrain in his Theorema Egregium. Can we invert the
problem and obtain a 3D shape by changing the local distances in an
initially flat plate? This strategy in widely used in Nature: leaves or
petals may develop into very complex shapes by differential growth. From
an engineering point of view, similar shape changes can be obtained when
a network of channels embedded in a flat patch of elastomer is inflated
or when extra surface gets “hidden” into wrinkles or folds in
unstretchable sheets. How can we program the final shape?
2023年度 2023.4-2024.3
日時:7月27日(木) 13:30-
場所:お茶の水女子大学理学部1号館201室
講演者:Francesco dal Corso博士(Univ. Trento)
講演題目:How to snap and to (quasi-statically and dynamically) stabilize extremely deformable structures via movable constraint
講演概要:
Nonlinear structural mechanics breaks the limits of traditional linear elastic design, to create elements working much beyond the realm of linearized kinematics, fully inside the nonlinear range, so matching the strong requirements imposed by soft robotics, flexible locomotion devices, metastructures, architected structures for vibration mitigation, and morphable structures. Within this context, the following recent results are presented:
– The number of stable equilibrium configurations for a planar strip with varying the kinematic conditions at its ends [1]. This result leads to the definition of a ‘universal snap surface’, collecting the sets of critical boundary conditions for which the system snaps;
– A catastrophe machine based on a continuous flexible element has been designed and realized [2]. In contrast to the classical Zeeman’s machine, the catastrophe locus of the elastica catastrophe machine may display a number of bifurcation points different than four and the convexity measure may significantly vary;
– The action of configurational forces on elastic structures is theoretically and experimentally proven in the presence of a specific movable constraint: a frictionless, perfectly smooth and bilateral sliding sleeve [3]. In particular, the presence of an outward configurational force at the exit of the sliding sleeve is disclosed both via variational calculus and independently through an asymptotic approach;
– The restabilization of the trivial path has been shown to appear in the presence of movable constraints and due to compressibility of a system [4];
– The stabilization of a rod against its fall in the presence of a gravitational field has been shown to be possible through a transverse oscillation of a sliding sleeve constraint. The motion results to be periodic or quasi-periodic around a finite average value of the length of the bent rod [5].
The presented structural systems are modelled as nonlinear elastic structures and solved analytically. Physical models have been designed, realized and tested, confirming the theoretical predictions. These results represent innovative concepts ready to be used for enhancing the efficiency of snapping devices, retractable/extensible soft actuators, and wave mitigation mechanisms towards advanced technological applications.
Acknowledgements
Financial support from the ERC advanced grant ERC-ADG-2021-101052956-BEYOND is gratefully acknowledged.
References
[1] Cazzolli, A., Dal Corso, F. (2019). Snapping of elastic strips with controlled ends. International Journal of Solids and Structures, 162, 285-303. [2] Cazzolli, A., Misseroni, D., Dal Corso, F. (2020). Elastica catastrophe machine: theory, design and experiments. Journal of the Mechanics and Physics of Solids, 136, 103735. [3] Bigoni, D., Dal Corso, F., Bosi, F. and Misseroni, D. (2015). Eshelby-like forces acting on elastic structures: theoretical and experimental proof. Mechanics of Materials, 80, 368-374. [4] Bigoni, D., Bosi, F., Dal Corso, F. and Misseroni, D. (2014). Instability of a penetrating blade. Journal of the Mechanics and Physics of Solids, 64, 411-425. [5] Koutsogiannakis, P., Misseroni, D., Bigoni, D., Dal Corso, F. (2023). Stabilization of an elastic rod through an oscillating sliding sleeve. Under review2021年度 2021.4-2022.3
日時:8月27日(金)16:45-18:00
場所:オンライン(Zoom)
講演者:丸岡敬和 氏(JAMSTEC 海洋機能利用部門 生命理工学センター)
講演題目:ソフトマターと第二種の自己相似性ーPDMS表面と剛体球の動的衝突における第二種の自己相似解
講演概要:
複合した混合物性とスケール依存性を特徴とするソフトマターは、その自己相似構造を解明することで、拮抗する力のダイナミクスをBarenblattによって定式化されたintermediate asymptoticsとして理解できることが期待できる。本セミナーではPDMS表面と剛体球の動的衝突の自己相似解の解明を試みる。PDMS弾性表面と剛体球の動的衝突は衝突速度、衝突半径、速度に応じて異なる冪数則を持つ。この冪数のcrossoverは弾性エネルギーより構成される無次元数とDeborah数の第二種の自己相似解として理解することができ、この無次元数の拮抗関係が冪数則を決定していることが明らかになった。本研究を通じて、ソフトマターにおけるintermediate asymptoticsの展望を論じたい。