Numerical Simulation of Rod Jet Formed by Shaped Charge under Rigid Constraint

In order to study the forming law of rod jet formed by shaped charge under rigid boundary constraint, ANSYS/LSDYNA finite element software is used to simulate the forming process of rod jet with ALE essential boundary, and the influence of structural parameters of shaped charge on rod jet forming is studied. The results show that compared with the free boundary constraint, the head velocity of rod jet increases by 63.5 % and the tail velocity increases by 59.3 % under the rigid boundary constraint. The head velocity and length-diameter ratio of rod jet decrease with the increase of the outside curvature radius of the liner, the thickness of the liner central position and the variable ratio of wall thickness. Furthermore, the tail velocity increases with the increase of the outside curvature radius of the liner, and decreases with the increase of the thickness of the liner central position and the variable ratio of wall thickness.

Comparison Between Numerical Flow3d Software and Laboratory Data, For Sediment Incipient Motion.

In this paper, the laboratory data were compared with computational fluid dynamics (CFD) Flow3D for predicting the beginning of sediment incipient motion in rigid boundary channel for two types of sands, irrigation, and sewer types, in rectangular flume (0.5*0.5)m cross-section. Tests were made for soil samples with different diameters, specific weights. The testing was performed in slopes ranging from 0.001-0.003 for irrigation types and 0.0025-0.025 for sewer types depending on the original parameter. The Flow-3D software has simulated the laboratory work using scouring models MPM and Nielsen. the relation between sediment incipient motion velocity, particle size, and channel bed slope was predicted. The results were relatively more than laboratory data for the MPM model, while grating convergence for Nielsen model, especially for small diameter sediment. Also, the laboratory results are more close to the results of Flow3D using the Nielsen model when the value of bed slope of the channel is greater, and vice versa when the slope decreases.

Goodbye Expert-Based Policy Advice? Challenges in Advising Governmental Institutions in Times of Transformation

The global transformation towards sustainability has not only increased the demand for anticipatory and reflexive knowledge to support decision making, but also raises three challenges common to all forms of scientific policy advice: to appropriately consider societal norms and values (challenge of normativity), to integrate different forms of knowledge (challenge of integration) and to organize the participation of stakeholders (challenge of participation). While new forms of scientific policy advice in the field of sustainability research (SR) have emerged in response, the role of established actors such as the Office of Technology Assessment at the German Bundestag (TAB) is increasingly scrutinized. One of the fundamental characteristics of TAB’s model of scientific policy advice is a rigid boundary arrangement between politics and science that places a high value on the objectivity and authority of scientific knowledge. Based on a content analysis of digitalization-related TAB reports spanning three decades, we describe how a rather technocratic institution such as TAB has dealt with the challenges of normativity, integration, and participation, and we compare its approach with that of SR institutions. TAB has partly adapted its working mode to the new challenges, e.g., by trying out new methods to foster a stronger dialogue with stakeholders. However, TAB’s response to the challenges distinctly differs from the forms of transformative research conducted in the SR community. We argue that this is not only a necessary precondition to maintain its reputation as a trustworthy actor towards the Parliament but gives TAB and similar expert-based institutions a special role in the governance of societal transformation.

Effect of Computational Parameters on Output Properties of Underwater Explosion by Intelligent Numerical Simulation

The computational parameters are of great influence on underwater explosion load. A one-dimensional wedge model is established to analyze the influence of boundary condition (BC), water domain and mesh density on the numerical simulation results. The results show that flowout BC is rigid boundary and transmit BC is not suitable for simulating the collapses phase of bubble pulsation. According to propagation distance of shock wave and its reflected wave, a simple method to calculate appropriate water domain is proposed. A positive correlation between mesh density (λ) and calculated peak pressure of shock wave (P m) is found. When λ tends to infinity, simulated Pm in near field is quite reliable, but the values in relatively far field are lower than empirical results.

Love wave in porous layer under initial stress over heterogeneous elastic half-space under gravity and initial stress

In the present paper, effect of initial stresses and gravity on the propagation of Love waves has been studied in porous layer surface over a heterogeneous half-space. We have considered two types of boundary on free surfaces: (a) rigid boundary and (b) traction free boundary. The propagation of Love waves has been investigated under assumed media in both the cases of boundary and discusses a comparison study of two cases. The dispersion equations and phase velocities have been obtained in both the cases. The numerical calculations have been done and presented graphically. This study of Love waves in the assumed medium reveals that the presence of initial stress in the half-space and absence of initial stress in the layer, the displacement of phase velocity in rigid boundary is more than the traction free boundary.

Study the influence of the relative position of two vessels moving in parallel on their hydrodynamic characteristics

Эксплуатация судна сопровождается ситуациями, в которых оно испытывает дополнительные нагрузки от близости твёрдых границ, таких как плавание в ограниченном фарватере, расхождение судов на малых расстояниях, погрузочные операции. Для грамотного осуществления подобных операций необходима заблаговременная оценка возможные нагрузок и учёт гидродинамического влияния между судами или судном и твёрдой поверхностью. Целью данной работы является изучение влияния взаимного положения двух судов на гидродинамическое взаимодействие между ними, а также оценка возможного взаимодействия между судами при операциях погрузки/разгрузки на глубокой воде. Гидродинамическое взаимодействие выражается в изменении полей давления и скорости при непосредственной близости нескольких судов, изменении поперечной и продольной гидродинамических сил и моментов рыскания, действующих на оба объекта. Для определения влияния относительных расстояний между судами на их гидродинамическое взаимодействие во время разгрузочных операций проведён ряд численных экспериментов. Смоделировано обтекание потоком вязкой несжимаемой жидкости двух судов типа KVLCС2, находящихся на различных относительных расстояниях друг от друга. Математическое моделирование турбулентного потока основано на решении уравнений Рейнольдса и проведено с помощью открытого программного пакета OpenFOAM. Для моделирования турбулентности использована модель турбулентности. Результаты численного моделирования обработаны и проанализированы, они находятся в хорошем соответствии с экспериментальными данными. Вычислены максимальные силы и моменты, возникающие при взаимодействии судов при их различном взаимном положении. Hydrodynamic interaction between ships continues to be a major field of research, considering that during different stages of the investment ship’s life, ship is exposed to the presence of a close rigid boundary such as sailing in restricted areas, overtaking and encountering at small distances with other ship or during investment operation such as lightering operations. In order to perform lightering operations safely, the knowledge of the interaction effects between both ships is very important. The aim of this article is to study the changes in velocity and pressure fields resulting from the presence of the two ships in close proximity, evaluating the longitudinal and transverse forces as well as yaw momentum affecting both ships, determining their relationship to the relative longitudinal position of the two ships as well as to predict the ship-to-ship interaction during lightering operations in deep water. A series of systematic computations were performed on two KVLCC2 hulls advancing in deep water and calm weather with the same constant low speed (full scale speed 4kt) in order to investigate the influence of the relative longitudinal separations on the hydrodynamic interaction forces and moments during the lightering operation. OpenFOAM, an open-source CFD packet was used for carrying out the simulations, RANS method was used for turbulence modeling and the well-known turbulent model was used to close RANS equations. Numerical results have been post-processed, analyzed, compared and found to be of a good agreement with the experimental results. Maximum forces and moments and their relation with longitudinal position were computed.