This paper presents a formulation of unified models for beam and shell in curvilinear coordinate system, based on meta-modeling. Traditional structural mechanics is restricted to simple geometries and governing equations are available for a handful number of simple geometries. They are mainly derived based on stress resultants equilibrium of free body diagrams. This gives difficulty in analyzing structural elements with complex geometries analytically and numerically; involving tedious and error prone process. These limita- tions can be eliminated by formulating beam and shell theories for arbitrary geometry defined in curvilinear coordinate system, based on continuum mechanics. Motivated by this improvement, main objective of this work is to develop beam and shell models for arbitrary geometry, using curvilinear coordinate system based on meta-modeling. Meta-modeling guarantees the consistency of the derived beam and shell mod- els with continuum mechanics and tensorial formulation in curvilinear coordinates produces models valid for arbitrary geometries. Governing equations for any specific geometry can be easily obtained simply by substituting the metric tensor of the coordinate system for the problem. This work is mainly based on first order approximations of field variables involved and standard variation process of Hellinger-Reissner func- tional. Some verification tests are done with simple geometries found in literature and it can be clearly seen that they are well matched with literature. Some analytical advantages of derived models are: availabil- ity of governing equations for arbitrary geometries; possible rigorous treatment of material non-linearity; etc. while some numerical advantages are: reduction of per-node number of degrees of freedom; faster convergence of iterative solvers; reduction of number of elements required; increase in accuracy; etc.
We developed an equivalent continuum form for brick structures based on continuumnization proposed by Hori et al.1) This allows one to analytically study the characteristic properties of masonry brick walls, and apply numerical techniques used in continuum mechanics to simulate brick structures. Further, the continuum form opens up the possibility of developing simplified models like shells or beams, which will be convenient in designing brick structures. Based on the continuum form, we study how the wave char- acteristics, like wave speeds, etc., change according to brick arrangement and material properties. Further, we develop a PDS-FEM model2) for simulating brick structures and verify the developed model comparing numerically obtained wave speeds with that of analytical predictions.
近年，数値シミュレーションの信頼性の確保のためのアプローチであるVerifiction and Validation(V & V)に注目が集まっている．数値計算手法の基本的特性の評価および数値解析コードの検証(verifiction)においては，Roache等によって提案された創成解の方法(Method of Manufactured Solutions)が流体力学の問題を中心に広く用いられている．一方，強形式に基づく従来の創成解の方法を固体力学の問題に適用する場合には，応力の空間微分を求めることが必要となることから，これまでは使われることが少なかった．この問題点に対して，筆者等は弱形式に基づくことで応力の空間微分を回避する手法を提案している．本研究は，この手法を超弾性体の大変形問題に対する創成解の方法に適用し，従来検討されることの少なかった大変形状態における有限要素法の近似特性の評価を行うものである．
A series of cylinder drag experiments were conducted using the density-matching Poly-Styrene Beads particle-fluids mixture to study the flow characteristics of liquefied sands. PIV technique was used to visualize the velocity fields around the moving cylinder. SPH (Smoothed Particle Hydrodynamics) simulations were also conducted to compare with the experimental results. Experiments results show that the solid fraction of 0.555 is quite important in this particle fluid mixture because the drag force exerted on the cylinder increases sharply with the solid fraction if it is greater than this value. This value coincides with the random loose packing density of mono-disperse spheres. PIV analysis shows that the velocity fields are quite localized around the cylinder, and the localized zone is expanded more in the moving direction than in the perpendicular direction. On the other hand, it turned out that the SPH simulations with a simple viscous fluid model cannot reproduce the similar velocity field, which indicates this particle-fluid mixture cannot be regarded as viscous fluid.
三次元流モデルと流木モデルをカップリングした流木挙動予測モデルを作成した．流木がスタックする現象は重要であり，スタック現象では衝突および流木から水への抗力が大きく関係する．複数の流木衝突をDEM (distinct element method)により考慮し，流木から水に影響を与える抗力をTwo-wayモデルで考慮した．構造物周りにおける流木挙動予測を行うため，某ダムを対象とした模型実験の結果と同条件で計算を行い両者を比較をする．衝突効果の有無およびTwo-wayモデル効果の有無による計算結果の違いを流木の定性的挙動，流木捕捉率，平均水位，平均水面速度を比較する．
In this study, a Lagrangian formulation of the Navier-Stokes equations, based on the weakly compressible smoothed particle hydrodynamics (WC-SPH) method, was applied to simulate the seepage failure around sheet-pile. In this simulation, the advantages of SPH will be exploited to simulate the soil-water interaction. Water is considered as a viscous fluid with weak compressibility and soil is assumed to be an elastic-plastic material. The elastic-perfectly plastic model based on Mohr-Coulomb's failure criterion is implemented in SPH formulations to model the soil movement. Interaction between soil and water is taken into account by means of seepage force and pore water pressure. Numerical Simulation of the 2-D classical seepage failure problem of horizontal ground with an embedded sheet pile has been done. The numerical results were verified by comparison with model test results, the results have shown that the proposed model could be considered a powerful tool to simulate extremely large deformation and failure of soil.
Secondary flow effects are considered in two dimensional depth averaged model to simulate the open channel flow in a sharp bend channel, and the simulated flow structures are compared with different kind of secondary flow models: Nays2DH solver without considering the secondary flow effect in flow equations; Onda et al model using nonlinear secondary flow equation with additional nonlinear transport equation for secondary flow strength; a new nonlinear secondary flow model which considers the secondary flow effect on the vertical distribution of streamline velocity and the inertia effect of the secondary flow advection. These three model results are compared to experimental results. Large difference of flow structures between Nays2DH and the experimental result means that 2D (two-dimensional) depth averaged model without secondary flow effect is inapplicable for sharp bend flow prediction. Obvious weaker deviation of the mainstream from inner bank of Onda et al model than that of the experiment shows that Onda et al model is insufficient for strong nonlinear phenomenon in a sharp bend. Mainstream deviation and other unreasonable structures in linear model from the experiment are similar proofs that a refined nonlinear secondary flow modelling is necessary in simulation of sharp bend flow.