Dynamic Test Case Research Articles

2상 격자 볼츠만 방법을 이용한 상승하는 기포 유동 2차원 수치 모사

Free energy based lattice Boltzmann method (LBM) has been used to simulate the rising bubble flows with large density ratio. LBM with compact discretization is able to reduce the spurious current of the static bubble test and be satisfied with the Laplace law. The terminal rise velocity and shape of the bubbles are dependent on Eotvos number, Morton number and Reynolds number. For single bubble flows, simulations are executed for various Eotvos number, Morton number and Reynolds number, and the results are agreed well with the experiments. For multiple bubbles, the bubble flow characteristics are related by the vortex pattern of the leading bubble. The coalescence of the bubbles are simulated successfully and the subsequent results are presented. The present method is validated for static, dynamic bubble test cases and compared to the numerical, experimental results.

Three‐dimensional test simulations of the outer radiation belt electron dynamics including electron‐chorus resonant interactions

We present results from our three‐dimensional (3‐D) simulations using the Salammbô electron radiation belt physical model. We have run steady state and dynamic storm test case simulations to study the effect of electron‐chorus resonant interactions on the radiation belt electron dynamics. When electron‐chorus interactions are introduced in the code outside the plasmasphere, results show that a seed population with a kappa distribution and a characteristic energy of 2 keV is accelerated up to a few MeV in the outer radiation belt. MeV electron fluxes increase by an order of magnitude during high magnetic activity conditions especially near L* ∼ 5 and for equatorial mirroring particles. We have also performed a parametric study of various important parameters to investigate how our results could be influenced by the uncertainty that characterizes their values. Results of this study show that if we consider higher values of the radial diffusion coefficients, different initial states, and different boundary conditions, we always observe a peak in the L* profile of the MeV electrons when electron‐chorus interactions are included.

Interface Pressure Model for Surface Tension Force for Vof-Based Methods in Interfacial Flows

In this article, the two-dimensional staggered grid interface pressure (SGIP) model is generalized and presented in three-dimensional form. The model has been used to simulate three-dimensional interfacial flows and the results have been compared with other existing models. For this purpose, various models of surface tension force for interfacial flows—CSF, CSS and PCIL models as well as the proposed model, SGIP—have been applied to simulate both static and dynamic cases. A three-dimensional motionless drop of liquid and a bubble of gas in an initially stagnant fluid with no gravity force are simulated as the static test case. The motion of small air bubbles in water is simulated as the dynamic test case. It has been demonstrated that the SGIP model produces the least maximum and norm spurious velocities in comparison with the CSF, CSS and PCIL models. Moreover, it is observed that the proposed model produces more accurate pressure jumps across the interface. Results of the dynamic case show that for both CSF and CSS models, the magnitude of spurious currents is too high to enable a successful simulation of this type of surface tension dominated flows. On the other hand, by using SGIP or PCIL models, we are able to simulate bubble rise and to obtain results which are in close agreement with the experimental data.

Dynamic Testing of Wholesale Power Market Designs: An Open-Source Agent-Based Framework

In April 2003 the U.S. Federal Energy Regulatory Commission proposed a complicated market design--the Wholesale Power Market Platform (WPMP)--for common adoption by all US wholesale power markets. Versions of the WPMP have been implemented in New England, New York, the mid-Atlantic states, the Midwest, the Southwest, and California. Strong opposition to the WPMP persists among some industry stakeholders, however, due largely to a perceived lack of adequate performance testing. This study reports on the model development and open-source implementation (in Java) of a computational wholesale power market organized in accordance with core WPMP features and operating over a realistically rendered transmission grid. The traders within this market model are strategic profit-seeking agents whose learning behaviors are based on data from human-subject experiments. Our key experimental focus is the complex interplay among structural conditions, market protocols, and learning behaviors in relation to short-term and longer-term market performance. Findings for a dynamic 5-node transmission grid test case are presented for concrete illustration.

Knowledge-based design and construction of driven piles

Specified numbers of static load tests (e.g., 1% of working piles) and dynamic tests (e.g., 10% of working piles) are often required in Hong Kong to verify the reliability of driven piles for every single project. In this research, a pile database, the Hong Kong Driven Pile Database, is developed: (a) to systematically compile historic driven pile data, which include pile data, soil investigation data, static load test results, dynamic test results and case pile wave analysis program results; (b) to provide data for reliability evaluation of design methods; (c) to assist in design of future foundation projects based on past experience; and (d) to learn from past failures. The database contains information on 1514 piles, including 308 static load test piles. In this paper, the basic information of the database such as the sources of piling data and the major components of the database is first described. Then the reliability of five termination criteria for piledriving control is evaluated against the pile test information in the database. Subsequently, a performance evaluation of three driving-stress analysis methods is conducted based on information in the database. Finally, to demonstrate possible knowledge-based pile design and construction using the database, a design example is presented illustrating how the database can be used to assist in the early stage of pile design for a future project. The information on hammers, range of final set values and resulting pile performance in case histories of similar projects can be used as a reference for the engineer to expedite design for new projects. The engineer can also learn from the past pile failures contained in the database.

Reduced-Order Design-Oriented Stress Analysis Using Combined Direct and Adjoint Solutions

A new method for extracting accurate stress information from reduced-order structural and aeroelastic models is presented. The method has second-order accuracy when approximate reduced-order direct and adjoint solutions (based on different reduced-order bases) are used simultaneously to obtain approximate stresses. The method is applicable to both static and dynamic linear analysis. A review of four common methods for structural model order reduction [two variants of the mode displacement method (standard mode displacement and the fictitious mass method), the mode acceleration method, and the Ritz vector method] identifies sources of difficulty and causes of errors in stress behavior sensitivity calculations. Considerations used for selection of the reduced-order direct and adjoint bases are discussed. A series of static and dynamic test cases is used to assess accuracy of the new method in an analysis mode. Accuracy studies of sensitivity calculations follow. We hope to contribute to the field of design-oriented structural dynamics in terms of both insight and practice.

Hydrodynamic simulations of laboratory scale bubble columns fundamental studies of the Eulerian–Eulerian modelling approach

The Eulerian–Eulerian model is used for the hydrodynamic simulation of a two-phase gas–liquid flow in a laboratory scale bubble column. The behaviour of the air–water system characterises a test case for bubbly flow with low gas void fractions. A dynamic test case with a centred gas sparger is chosen for validation of the simulation models. Long-time-averaged liquid velocity profiles and time series at specific points are compared with experimental data. The main focus lays on the influence of turbulence modelling. Laminar and turbulent simulations are carried out. A standard k– ε model is used to describe turbulence occurring in the continuous fluid. Additionally turbulent dispersion of the gas bubbles can be taken into consideration. The results show that a turbulent model has to be considered to gain correct results. The laminar model shows a chaotic behaviour and not the harmonic oscillations observed in experiments. In contrast good agreement of the results can be obtained for three-dimensional calculations including turbulence. Distinct modelling of turbulent dispersion seems not to be necessary for the chosen test case. Furthermore, it can be concluded that a three-dimensional simulation with a sufficient fine resolution is necessary for accurate results. The test column depth, which is the determining length scale, must be resolved meticulously to receive accurate turbulence intensity in the bubble column. The conclusion concerning grid refinement and independence still needs further evaluations but fails up to now due to the limited computational power. Finally, two-phase bubbly flow calculations are carried out successfully with commercial CFD software in a transient way with the two-fluid model. The computational calculations still need very high resources. Further developments and model discussions are strongly recommended.

Non-uniform and dynamic torsion of elastic beams Part 2: The double torsion test

Part 1 of this paper developed a one-dimensional fourth-order partial differential equation for dynamical torsion of rectangular beams. It was then validated against static and dynamic test cases. This concluding part applies the equation to the double torsion fracture test, in which a crack propagates along the plane joining two adjacent torsion beams as they are twisted in opposite senses. The resulting model is extensively validated against experimental and finite element results. It is then used to explain the shape of the curved crack front which is characteristic of this test.

One-dimensional finite elements based on the Daubechies family of wavelets

The development of a one-dimensional finite element is traced utilizing a Daubechies scaling function as its interpolation function. The element was developed to reduce the computational time and number of degrees of freedom needed to solve vibration and wave propagation problems. This element is used in a dynamic test case, and the results are compared with the results using a standard, constant strain, rod element. The results show a 5:1 reduction in required number of degrees of freedom and in the computational time needed for equivalent accuracy. ONVENTIONAL finite elements are formed using the Rayleigh-Ritz method wherein polynomials are used as ap- proximation functions. In most applications, constant strain or poly- nomial strain elements are used.1 To model a complex subject, addi- tional elements are combined with the first, resulting in an approx- imation of the required solution. This paper discusses a different type of finite element, the wavelet finite element, in which a wavelet approximation function is used. The wavelet finite element was developed specifically for vibra- tion problems and wave propagation analysis. The concept is that the frequency response of the wavelet's associated scaling function models displacements from 0 Hz to a certain cutoff frequency and thus models vibrations more accurately and with less CPU time than conventional elements. The finite element model of a vibrating object requires a certain density of elements to accurately simulate vibratory response. This element density is usually given in terms of the wavelength of the highest frequency. The goal of this study is to derive a finite element that will attain a high level of accuracy for a low mesh density as compared with conventional finite elements. Wavelets were used to solve the one-dimensional wave equation by Bacry et al.2 Wavelets are used in solving a two-point boundary problem by Beylkin. 3 Sarkar et al. present an investigation of the application of wavelet-like triangular functions to finite elements.4 The interpolation functions exhibit the translation and dilation prop- erties of wavelets but are not wavelets. Finite elements were derived in Kurdila et al. based on wavelets generated using affine, fractal interpolation functions and were ap- plied to two-dimension al elasticity problems.5 A wavelet-based method for solving one-dimensional displacement problems was introduced in Bertoluzza et al.6