Investigation on design flow of a millimeter-scale radial turbine for micro gas turbine

Microsystem Technologies - As compared to the conventional large scale gas turbines, the aerothermodynamics design of a micro gas turbine will be quite different not only due to the small scale...     

Viscoelastic flow past a cylinder: drag coefficient

The channel flow of a viscoelastic fluid past a circular cylinder is simulated using a parallelized unstructured Finite Volume Method (FVM) [H.-S. Dou, N. Phan-Thien, J. Non-Newtonian Fluid Mech. 77 (1998) 21–51] under a distributed computing environment through the Parallel Virtual Machine (PVM) libraries. The numerical method is based on the SIMPLER (Semi-Implicit Method for Pressure-Linked Equations Revised) algorithm, using the simplified Phan-Thien/Tanner (PTT) and the Upper Convective Maxwell (UCM) constitutive models, with the Elastic Viscous Split Stress (EVSS) formulation. The parallelization of the program is implemented by a domain decomposition strategy and the PVM software. It is found that the both shear thinning and normal stress contribute to the drag reduction. With the PTT model, the drag reduction is mainly due to shear thinning. With the UCM model, it is primarily due to the normal stress effect.     

The past recaptured: in search of lost paradigms

In the mid 1980s, a cluster of HF professionals described a new paradigm in which technology would be designed for a better fit not just with individual users but also with organizational systems and dynamics. The term 'Macroergonomics' took hold to describe this broadening of perspective. This concept was a manifestation of the holistic design philosophy and values of the user-centred design (UCD) paradigm, but tended to place more emphasis on how technology fit into organizational systems than on either design or on individual use of technology. While the benefits in the quality of work life that were expected to result from paying more attention to how organizations managed technology and technological change were many, the track record has been disappointing. The promotion of a focus on the organizational context of technology did not lead directly to practical application or make companies more humane for either their workers or for external customers. Today, however, with the maturation and broadening application of user-centred design approaches, the time is ripe to apply them to the design of information systems within companies as vigorously as they are being applied to products and systems intended for consumers.     

Steady flow past a rotating cylinder

Numerical solutions have been obtained for steady viscous flow past a rotating circular cylinder. Results are presented for Reynolds numbers of 5 and 20 and ratios of the speed of the surface of the cylinder to the fluid speed at infinity from 0 to 0.5. The effects of using different boundary conditions on the stream function at large distances from the cylinder are presented and discussed.     

Reinforcement learning in sustainable energy and electric systems: a survey

The dynamic nature of sustainable energy and electric systems can vary significantly along with the environment and load change, and they represent the features of multivariate, high complexity and uncertainty of the nonlinear system. Moreover, the integration of intermittent renewable energy sources and energy consumption behaviours of households introduce more uncertainty into sustainable energy and electric systems. The operation, control and decision-making in such an environment definitely require increasing intelligence and flexibility in the control and optimization to ensure the quality of service of sustainable energy and electric systems. Reinforcement learning is a wide class of optimal control strategies that uses estimating value functions from experience, simulation, or search to learn in highly dynamic, stochastic environment. The interactive context enables reinforcement learning to develop strong learning ability and high adaptability. Reinforcement learning does not require the use of the model of system dynamics, which makes it suitable for sustainable energy and electric systems with complex nonlinearity and uncertainty. The use of reinforcement learning in sustainable energy and electric systems will certainly change the traditional energy utilization mode and bring more intelligence into the system. In this survey, an overview of reinforcement learning, the demand for reinforcement learning in sustainable energy and electric systems, reinforcement learning applications in sustainable energy and electric systems, and future challenges and opportunities will be explicitly addressed.     

Molecular dynamics simulation of flow past a plate

Molecular dynamics simulations with a soft-sphere potential have been carried out to model two dimensional fluid flow obstructed by a plate. At fluid velocities large enough to obtain adequate signal to noise resolution, two counter-circulating vortices are observed behind the obstruction. The stationary state length scale of these vortices is found to be roughly proportional to the average velocity in the system, as predicted by the hydrodynamic theory.     

Unsteady potential flow past a group of spheres

The problem of an unsteady potential flow past a group of stationary spheres is considered using the methods of images. The problem is formulated so that the number and location of the spheres is arbitrary so long as there is no overlap between adjacent spheres. Inertial and lift coefficients are determined for several different sphere arrangements. The inertial coefficient for a sphere can vary in either direction from its isolated-sphere value of 1·5. The controlling factors on this variation are the relative geometric position of the sphere within the group and its distance from its neighbors. These same factors determine, as is expected, the lift-coefficient values. In some example configurations, there is even a drag-type force generated on an individual sphere in the potential flow.     

圆管绕流旋涡脱落诱导振动的数值模拟

利用计算流体力学软件Ansys／Flotran CFD,首先对粘性不可压缩流体的固定圆管绕流进行了数值模拟,然后结合逐步积分法完成了同时考虑纵横两向弹性支撑圆管绕流旋涡脱落诱导振动的数值模拟,并通过快速傅立叶变换,得到了弹性支撑圆管和固定圆管的升力及弹性支承圆管横向位移响应的功率谱．通过计算结果分析,得出了一些有价值的结论,可供从事具有圆管绕流构件设备设计的工程技术人员参考．     

Moving-target search: a real-time search for changing goals

Considers the case of heuristic search where the goal may change during the course of the search. For example, the goal may be a target that actively avoids the problem solver. The authors present a moving-target search algorithm (MTS) to solve this problem. The authors prove that if the average speed of the target is slower than that of the problem solver, then the problem solver is guaranteed to eventually reach the target in a connected problem space. The original MTS algorithm was constructed with the minimum operations necessary to guarantee its completeness, and hence is not very efficient. To improve its efficiency, the authors introduce ideas from the area of resource-bounded planning into MTS, including 1) commitment to goals, and 2) deliberation for selecting plans. Experimental results demonstrate that the improved MTS is 10 to 20 times more efficient than the original MTS in uncertain situations     

Variational multiscale large-eddy simulations of the flow past a circular cylinder: Reynolds number effects

Variational multiscale large-eddy simulations (VMS–LES) of the flow around a circular cylinder are carried out at different Reynolds numbers in the subcritical regime, viz. Re = 3900, 10,000 and 20,000, based on the cylinder diameter. A mixed finite-element/finite-volume discretization on unstructured grids is used. The separation between the largest and the smallest resolved scales is obtained through a variational projection operator and finite-volume cell agglomeration. The WALE subgrid scale model is used to account for the effects of the unresolved scales; in the VMS approach, it is only added to the smallest resolved ones. The capability of this methodology to accurately predict the aerodynamic forces acting on the cylinder and in capturing the flow features are evaluated for the different Reynolds numbers considered. The sensitivity of the results to different simulation parameters, viz. agglomeration level and numerical viscosity, is also investigated at Re = 20,000.     

Simulation of slow flow of a fluid past a solid sphere

The problem of slow flow past a solid sphere is considered when the outer fluid is of infinite extent. Inertial effect is included in the analysis. A numerical method is employed to obtain solutions of the equation of motion. Solutions are obtained for the spherical coordinates components of velocity. The results obtained are in complete agreement with those obtained by other workers for the flow of the Newtonian fluid past a solid sphere.     

MHD flow past a circular cylinder using the immersed boundary method

The immersed boundary method (IB hereafter) is an efficient numerical methodology for treating purely hydrodynamic flows in geometrically complicated flow-domains. Recently Grigoriadis et als. [1] proposed an extension of the IB method that accounts for electromagnetic effects near non-conducting boundaries in magnetohydrodynamic (MHD) flows. The proposed extension (hereafter called MIB method) integrates naturally within the original IB concept and is suitable for magnetohydrodynamic (MHD) simulations of liquid metal flows. It is based on the proper definition of an externally applied current density field in order to satisfy the Maxwell equations in the presence of arbitrarily-shaped, non-conducting immersed boundaries. The efficiency of the proposed method is achieved by fast direct solutions of the two poisson equations for the hydrodynamic pressure and the electrostatic potential.The purpose of the present study is to establish the performance of the new MIB method in challenging configurations for which sufficient details are available in the literature. For this purpose, we have considered the classical MHD problem of a conducting fluid that is exposed to an external magnetic field while flowing across a circular cylinder with electrically insulated boundaries. Two- and three-dimensional, steady and unsteady, flow regimes were examined for Reynolds numbers Re_d ranging up to 200 based on the cylinder’s diameter. The intensity of the external magnetic field, as characterized by the magnetic interaction parameter N, varied from N=0 for the purely hydrodynamic cases up to N=5 for the MHD cases. For each simulation, a sufficiently fine Cartesian computational mesh was selected to ensure adequate resolution of the thin boundary layers developing due to the magnetic field, the so called Hartmann and sidewall layers. Results for a wide range of flow and magnetic field strength parameters show that the MIB method is capable of accurately reproducing integral parameters, such as the lift and drag coefficients, as well as the geometrical details of the recirculation zones. The results of the present study suggest that the proposed MIB methodology provides a powerful numerical tool for accurate MHD simulations, and that it can extend the applicability of existing Cartesian flow solvers as well as the range of computable MHD flows. Moreover, the new MIB method has been used to carrry out a series of accurate simulations allowing the determination of asymptotic laws for the lift and drag coefficients and the extent of the recirculation length as a function of the amplitude of the magnetic field. These results are reported herein.     

Visualization of flashback in a premixed burner with swirling flow

In this study,the measurement object is a flame propagating in a premixed burner with swirling flow in order to investigate unsteady flame behavior in a gas turbine premixer.During flashback,the flame propagating upstream was visualized with a high-speed camera.Moreover,we established the technique to measure the instantaneous flow fields of unburned fuel-air mixture in a swirling premixed burner using particle image velocimetry(PIV).As a result,the characteristics of flame behavior propagating upstream wer...     

Parallel tabu search algorithm for the hybrid flow shop problem

The paper deals with the parallel variant of the scheduling algorithm dedicated to the hybrid flow shop problem. The problem derives from practice of automated manufacturing lines, e.g. for printed packages. The overall goal is to design a new algorithm which merges the performance of the best known sequential approach with the efficient exploitation of parallel calculation environments. In order to fulfill the above aim, there are two methods proposed in this paper: the original fast method of parallel calculation of the criterion function and the local neighborhood parallel search method embedded in the tabu search approach. The theoretical analysis, as well as the original implementation, with the use of vector processing instructions SSE2 supported by suitable data organization, are presented below. Numerical properties of the proposed algorithm are empirically verified on the multi-core processor.     

A neuro-tabu search heuristic for the flow shop scheduling problem

Flow shop scheduling deals with the sequencing of different jobs that visit a set of machines in the same order. A neural networks-based tabu search method, namely EXTS, is proposed for the flow shop scheduling. Unlike the other tabu search-based methods, the proposed approach helps diminishing the tabu effect in an exponential way rather than most commonly used way of diminishing it in a sudden manner. On the basis of the conducted tests, some rules are evolved to set the values for different parameters. The effectiveness of the proposed method is tested with 23 problems selected from literature. The computational results indicate that the proposed approach is effective in terms of reduced makespan for the attempted problems.     

Design of a simulation platform for intelligent marine search and rescue based on wireless sensors

The final line of Maritime Search and Rescue (MSR), maritime security, and marine environmental protection play important roles in the world. Ocean search and wireless sensor-based rescue involve marine objects' activity connected to various components of the ocean and rescue. Given the vastness of the ocean (components and geographical extent), such as actors, multinational corporations, conservation organizations, charities, policies are think tanks, strategies in the arrangement of frameworks, huge national actors themselves have the opportunity. Finding seized is not a surprising rescue. Wireless sensors will eventually expand and note the scale, more advanced research and maritime search and rescue assets. These advances will become a reality to close the opportunity, and many jobs will use the expectations of wireless sensors as expected. Wireless sensors monitor intelligent ocean searches and rescue sent information about it. Many proposed systems suffer from the orthogonal frequency separation performance of response and small when the previous period's length ratio impedes impulse channel. This is the degradation of the Intermediate Carrier Interference (ICI), and Inter-Symbol Interference (ISI) introduced the maximum multipath delay. The reason for this is to reduce the Intermediate Carrier Interference (ICI) itself, an intermediate code through excessive multi-way delay. Optimal Frequency Division Multiplexing (OFDM) beam formation can spatially suppress some multipath using sensing ICI / ISI and take into account the multipath characteristics of explicit channels to reduce interference. Multi-channel faucets provide significant performance improvements for maritime search and avoidance and do not exceed the delay expansion to be resolved.     

Research on group search optimizers for a reconfigurable flow shop sequencing problem

A reconfigurable manufacturing system is usually designed for quick re-adjusting of production capacity in response to market changes. In this paper, we study a flow shop sequencing problem (FSSP) with controllable processing times as a special case of reconfigurable manufacturing system. It is possible to speed up the processing times through assigning additional resources or control of machine speed. After formulating this problem mathematically, a novel evolutionary procedure, entitled group search optimizer (GSO), is devised as solution method. The adapted GSO is a population-based search tool which is devised based on the producer and scrounger behavior. GSO emphasizes on imitating searching model of real-world animals. The basic GSO with four promising improvements is elaborated and discussed for addressing the FSSP with controllable processing times. A set of computational experiments is also conducted to demonstrate the applicability of proposed FSSP and performance of improved GSOs.     

The numerical solution of the Navier-Stokes equations for laminar incompressible flow past a paraboloid of revolution

A numerical methods is presented for the solution of the Navier-Stokes equations for flow past a paraboloid of revolution. This method is based upon the ideas of van de Vooren and collaborators [1,2]. The flow field has been computed for a large range of Reynolds numbers. Results are presented for the skinfriction and the pressure together with their respective drag coefficients. The total drag has been checked by means of an application of the momentum theorem.     

Separated supersonic flow past a trailing edge at incidence

Supersonic laminar flow past a thin trailing edge at incidence is considered theoretically from the standpoint of triple-deck viscous-inviscid interactions, for large Reynolds numbers. At sufficient angles of incidence one-sided regular separation appears, leading to the possibility of a catastrophic stall. A numerical scheme based on coupling a shooting technique with windward differencing to account for flow reversals is described, along with a comparison with another method of treating reversed flow. The results obtained point to stall-free separated flow occurring, as predicted in some more recent studies. An abrupt reattachment is found to take place just prior to the trailing edge, followed by a strong downwash in the near-wake, and this forces the aavoidance of aatastrophic stall. The general features agree qualitatively with experimental observations.     

求解流水线调度问题的万有引力搜索算法

研究了以最大完工时间为目标的流水线调度问题,使用万有引力算法求解调度问题,提出了一种最大排序规则,利用物体间各个位置分量值存在的大小次序关系,并结合随机键编码的方法产生,将物体的连续位置转变成了一个可行的调度方案;提出了一种边界变异的策略使得越界的物体不再聚集在边界上,而是分布在边界附近的可行空间内,从而增加种群的多样性;结合交换算子和插入算子提出了一种新的局部搜索算法,有效地避免了算法陷入局部最优值,进一步提高了解的质量.最后证明了算法的收敛性,并且计算了算法的时间复杂度和空间复杂度,仿真实验说明了所得算法的有效性.