Parallel computations of incompressible flow around falling spheres in a long pipe using moving computational domain method

A 3-D Rankine type Green function boundary element method is developed to estimate the unsteady hydrodynamic interaction during ship passing piers process. To address this moving boundary problem, a free surface re-meshing algorithm based on the combination of local mesh and global mesh is proposed to update fluid boundary and the boundary value formula is solved at each time step. Two alternative numerical models for ship passing piers problem are compared with the current analysis method. Based on the three numerical models, the characteristics of the hydrodynamic loads acting on the passing ship are specified and the critical positions for the peak values have been identified. Simulation results demonstrate that the fluid disturbance induced by the piers is of importance. Therefore, the study of ship–piers hydrodynamic interaction in a river must be handled as a different forward speeds problem. Additionally, the wave elevation effect can only be neglected on condition that the forward speed is very low.

Investigation on the unsteady hydrodynamic loads of ship passing by bridge piers by a 3-D boundary element method

Six degrees of freedom coupled simulation is presented for a tilt-rotor plane represented by V-22 Osprey. The Moving Computational Domain (MCD) method is used to compute a flow field around aircraft and the movement of the body with high accuracy. This method enables to move a plane through space without restriction of computational ranges. Therefore it is different from computation of such the flows by using conventional methods that calculate a flow field around a static body placing it in a uniform flow like a wind tunnel. To calculate with high accuracy, no simplification for simulating propeller was used. Fluid flows are created only by moving boundaries of an object. A tilt-rotor plane has a hovering function like a helicopter by turning axes of rotor toward the sky during takeoff or landing. On the other hand in flight, it behaves as a reciprocating aircraft by turning axes of rotor forward. To perform such two flight modes in the simulation, multi-axis sliding mesh approach was proposed which is a computational technique to enable us to deal with multiple axes of different direction. Moreover, using in combination with the MCD method, the approach has been able to be applied to the simulation which has more complicated motions of boundaries.

Six Degrees of Freedom Numerical Simulation of Tilt-Rotor Plane

Six degrees of freedom flight simulation of tilt-rotor aircraft with nacelle conversion

Simulations of a falling sphere with concentration in an infinite long pipe using a new moving mesh system

This paper presents a new method for simulating flows driven by a body traveling with neither restriction on motion nor a limit of a region size. In the present method named 'Moving Computational Domain Method', the whole of the computational domain including bodies inside moves in the physical space without the limit of region size. Since the whole of the grid of the computational domain moves according to the movement of the body, a flow solver of the method has to be constructed on the moving grid system and it is important for the flow solver to satisfy physical and geometric conservation laws simultaneously on moving grid. For this issue, the Moving-Grid Finite-Volume Method is employed as the flow solver. The present Moving Computational Domain Method makes it possible to simulate flow driven by any kind of motion of the body in any size of the region with satisfying physical and geometric conservation laws simultaneously. In this paper, the method is applied to the flow around a high-speed car passing through a hairpin curve. The distinctive flow field driven by the car at the hairpin curve has been demonstrated in detail. The results show the promising feature of the method.

Moving Computational Domain Method and Its Application to Flow Around a High-Speed Car Passing Through a Hairpin Curve

減衰が負となる領域が発生するが,系全体の減衰を構造減衰と空力 減衰の和として表すことで,空力減衰が負となる領域についても動 的応答を求めた。ただし,構造減衰と空力減衰の和が負となる場合 はそれらの和を 0とおいて計算した。なお,今回は屋根の振動に伴 う内部容積の変化がなく,既往の研究で多く検討されている逆対称 一次モードを対象としたが,他の振動モードが動的応答に及ぼす影 響などについては今後の課題とする。一連の動的応答解析を通して 得られた結論を以下にまとめる。  気流による応答性状を比較すると,一様流の方が無次元風速の やや低い時に空力負減衰となる。しかし,空力正減衰の範囲で の動的応答を見ると接近流の乱れの影響のため,動的応答は境 界層乱流の方が大きくなる。  屋根の構造減衰が小さい場合,空力減衰が系全体の減衰に及ぼ す影響が相対的に大きくなるため,無次元風速が大きい範囲で の動的応答が大きくなるが,屋根の構造減衰が大きい場合,空 力減衰が系全体の応答に及ぼす影響が相対的に小さくなるため, 応答の急激な増加は生じにくい。  非定常空気力は屋根の動的応答に影響を及ぼすが,屋根の質量 や固有振動数,空力剛性の影響によって周波数応答関数の形状 が変化するため,無次元風速の増加に伴って必ずしも屋根の動 的応答が増加し続けるとは限らない。  無次元風速が 1 以下の範囲では,非定常空気力を考慮すると非 定常空気力を考慮しない場合と比べて動的応答が 5%程度小さ くなった。つまり,設計時に無次元風速が小さいと予想される 大スパン陸屋根については,非定常空気力を考慮せずに設計す れば応答を安全側で評価することができる。  屋根の構造減衰と空力減衰の和が 0 より小さくなる範囲につい ては,空力不安定振動が発生すると考えられるため,屋根の応 答については別途検討が必要となる。  今回対象とした大スパン屋根では,建築基準法で規定される風 速範囲では常に空力的に安定となるため,空力不安定振動をも たらすような振動が発生する可能性は低いと考えられる。しか し,想定する設計風速や建築物の立地,屋根の固有振動数やス パンによっては無次元風速が大きくなることも考えられるため, 建築物の実況に応じた検討が必要である。 謝辞 本研究は,JSPS科研費(課題番号:16J01789)および平成 28年度公益財団法 人能村膜構造技術振興財団の助成を受けたものである。ここに記して謝意を 表する。

Koji Watanabe

Papers

Moving Computational Domain Method and Its Application to Flow Around a High-Speed Car Passing Through a Hairpin Curve

Static axial reciprocal load tests for soil-cement mixing wall used as permanet piles