Virtual Force Method Research Articles

Enhancements in the Virtual Support Force Method for Tunnel Excavation Problems

Enhancements in the Virtual Support Force Method for Tunnel Excavation Problems

Effects of seismic characteristics and baffle damping on liquid sloshing

The present work concentrates on liquid sloshing in tanks under real seismic excitations with various frequency contents [the ratio of peak ground acceleration (PGA) to peak ground velocity (PGV)] by a finite-difference turbulent model. The turbulence is modeled by the large eddy simulation, and the fluid–structure interaction is resolved by the Virtual Boundary Force method. Thirteen seismic records, covering the low, intermediate and high frequency contents, are adopted to excite nonlinear sloshing waves. Both sloshing wave and hydrodynamic pressure are recorded, and their correlations with the filling level, PGA, PGV and frequency content have been identified. The findings suggest that (1) the sloshing responses are in general positively correlated with the filling level; (2) the sloshing height strongly relates to PGV and frequency content, and the seismic excitation of low frequency and meantime with a larger PGV can trigger more violent sloshing waves than others; and (3) the dynamic pressure along the tank sidewall decreases from the bottom up, which is dominated by PGA at the lower part but the stronger correlation is established with PGV and frequency content at the upper part. Finally, to damp severe sloshing waves, the horizontal, vertical and coupled horizontal and vertical baffles are introduced, and their inhibiting effects are discussed. The present work may guide the design of partially filled storage tanks under seismic excitations.

Optimal-Damage-Effectiveness Cooperative-Control Strategy for the Pursuit–Evasion Problem with Multiple Guided Missiles

In this paper, an optimal-damage-effectiveness cooperative-control strategy based on a damage-efficiency model and a virtual-force method is proposed to solve the pursuit-evasion problem with multiple guided missiles. Firstly, different from the overly ideal assumption in the traditional pursuit-evasion problem, an optimization problem that maximizes the damage efficiency is established and solved, making the optimal-damage-effectiveness strategy more meaningful for practical applications. Secondly, a modified virtual-force method is proposed to obtain this optimal-damage-effectiveness control strategy, which solves the numerical solution challenges brought by the high-complexity damage function. Thirdly, adaptive gain is designed in this strategy based on guidance-integrated fuze technology to achieve robust maximum damage efficiency in unpredictable interception conditions. Finally, the effectiveness and robustness of the proposed strategy are verified by numerical simulations.

Numerical simulation of Faraday waves in a rectangular tank and damping mechanism of internal baffles

Parametric sloshing and damping mechanism of internal baffles were systematically investigated through an in-house numerical model NEWTANK (developed by Xue and Lin, 2011). The internal baffles were modelled by the Virtual Boundary Force method. A good agreement of validation was achieved, then the numerical model was applied to investigate the mode 2 to mode 5 Faraday waves in tanks with various baffles, and the damping mechanism has been uncovered. Four kinds of baffles, including vertical, horizontal, ring and T-shape baffles, have been considered. The wave was divided into two categories: symmetric and asymmetric modes. The effectiveness of those baffles was identified by estimating the waveform, velocity and vortex fields; and the effective baffle configurations for various waveforms were proposed. The key issue was to suppress the vertical motion at the tank sidewalls for the symmetric mode; as for the asymmetric mode, the constraint of the horizontal movement at the wave nodes was proved to be more vital. The ring baffle was effective to suppress the mode 2 Faraday wave but lost efficacy for the mode 3 Faraday wave; the horizontal baffle was applicable for both mode 2 and mode 3 Faraday waves; and the vertical baffle was superior to the T-shape baffle in mitigation of the mode 2 Faraday wave, but was inferior to the latter as for the mode 3 Faraday wave. The effectiveness of the T-shape baffle in/close to the wave nodes was further identified through simulations of higher modal Faraday waves. Finally, the mitigation of the sloshing under coupled resonant surge and unstable heave excitations was presented and discussed.

A virtual force method to rectify the equation of state of the lattice Boltzmann models

In this work, to rectify the equation of state (EOS) of a recently introduced constant speed entropic kinetic model (CSKM), a virtual force method is proposed. The CSKM, as shown in Zadehgol and Ashrafizaadeh [J. Comp. Phys. 274, 803 (2014)] and Zadehgol [Phys. Rev. E 91, 063311 (2015)], is an entropic kinetic model with unconventional entropies of Burg and Tsallis. The dependence of the pressure on the velocity, in the CSKM, was addressed and it was shown that it can be rectified by inserting rest particles into the model. This work shows that this dependence can also be removed by treating the pressure gradient as a pseudo force term, expanding the source term using the Fourier series, and applying the modified method of Khazaeli et al. [Phys. Rev. E 98, 053303 (2018)]. The proposed method can potentially be used to remove other pseudo-force error terms of the CSKM, e.g. the residual error terms which become significant at high Mach numbers, ensuring thermodynamic consistency of the entropic model, at the compressible flow regimes. The accuracy of the method is verified by simulating benchmark flows.

Residual Stress and Deformation of Butt-Welded Joint of Low Carbon Steel to Stainless Steel

This paper investigates and determines residual stress and deformation of butt welded joint between two plates of low carbon steel and stainless steel. Based on the theoretical basis of the virtual force method [1-3], this study has constructed the formulas to calculate the residual stress and deformation in fusion welding of two dissimilar materials for butt joint and single-pass weld. The residual stresses and deformations in the butt-welded joint of two plates of 5 mm thickness, beveled edge, single-pass weld between low carbon steel and stainless steel are determined and compared to show the difference of residual stress and deformation in each plate. These results are also compared with the butt welded joint of two low carbon steel plates.

Focused Wave Interaction with Floating Structures by Virtual Boundary Force Method

Focused Wave Interaction with Floating Structures by Virtual Boundary Force Method

The Numerical Modeling of Coupled Motions of a Moored Floating Body in Waves

Nonlinear interactions between water waves and a moored floating body are investigated using the virtual boundary force (VBF) method. The paper first introduces an in-house three-dimensional viscous incompressible flow model (NEWTANK), which is used to simulate wave-floating structure interaction by using the VBF method. Then the coupling procedure between the mooring line model and the floater model is described. Some validation cases of the developed model, including the motions of a free-floating box in two different water waves, are presented. The present numerical results will be compared with the available experimental data and other numerical results from the published literature. After that, the validity of the mooring line in the numerical model is simulated by simulating the motions of a floating box in still water. Finally, the verified model is applied to analyze the wave-induced motions of a catenary moored floating structure, investigating the motion responses and mooring forces responses. The numerical results agree well with the experimental measurements on the whole. This indicates that the present numerical model can correctly capture the main features of the wave-moored floating structure interaction.

The artificial generation of the equilibrium marine atmospheric boundary layer for the CFD simulation of offshore wind turbines

Computational fluid dynamics (CFD) technique has been widely used in simulating dynamic responses of offshore floating wind turbines under excitations of prescribed wave and wind loads. In the simulation, the Volume of Fluid (VOF) method is generally employed to capture the free surface of the liquid, which illustratively shows the evolution of waves. The stresses at the free surface are not explicitly modeled in the VOF method, which challenge the establishment of the equilibrium marine atmospheric boundary layer (MABL) throughout the computational domain. Given the importance of the generation of the MABL in a CFD simulation of offshore wind turbines, methods for establishing sustainable wind profiles in a simulation based on the VOF method should be systematically investigated. In the present study, a virtual body force method is developed to maintain the horizontally homogeneous MABL in the VOF-based CFD simulation. The proposed method is quantitatively verified through a simulation of the equilibrium MABL with the sheared wind profile.

Application of Virtual Force Method for Deploying Mobile Sensor Networks

The virtual force method is applied for deploying a mobile sensor network in an uncertain environment. A mobile sensor network is a distributed collection of nodes, each of which has sensing, computation, communication and locomotion capabilities. Previous studies of mobile sensor deployment adopted a round by round process, that is, sensors move iteratively until the maximum coverage is reached. However, the mobile sensors probably move in a zig-zag way that waste a lot of energy in comparison with that of moving directly to a final location. We proposed a cluster-based virtual force algorithm (CVFA), which is an energy efficiency deployment strategy. CVFA can enhance the coverage after an initial random placement of sensors. By constructing virtual force, each node is attracted or repelled by other nodes, thereby forcing the network to spread itself throughout the environment. In CVFA, global information of k-hop neighbours can be acquired by the inter-cluster communications, and sensors can grasp their target locations logically. Experimental result, using ns-2 simulator, suggests that CVFA can significantly reduce the energy consumption compared to previous work, especially on maintaining similar coverage.

A Novel Self-Calibration Method and Experiment of MEMS Gyroscope Based on Virtual Coriolis Force.

This paper proposes an effective method to calibrate the microelectromechanical systems (MEMS) vibratory gyroscope based on the virtual Coriolis force. This method utilizes a series of voltage signals to simulate the Coriolis force input, and the gyroscope output is monitored to obtain the scale factor characteristics of the gyroscopes. The scale factor and bias parameters of the gyroscope can be calibrated conveniently and efficiently in the sense-mode open loop. The calibration error of the scale factor based on the turntable and the virtual Coriolis force method is only 1.515%, which proves the correction of the method proposed in this paper. Meanwhile, the non-linearity and bias value of the turntable and the virtual Coriolis force method are 742 ppm and 42.04 mV and 3389 ppm and 0.66 mV, respectively.

A novel wireless sensor network deployment scheme for environmental monitoring in longwall coal mines

Abstract Longwall mining is extensively practiced worldwide for the safe extraction of coal from underground coal mines. In this paper, we analyzed several sensor node deployment schemes and proposed a novel wireless sensor network (WSN) deployment scheme for environmental monitoring in longwall coal mines. The proposed scheme is based on the probabilistic event detection approach for complete coverage of the monitoring regions in longwall coal mines. The virtual force method is applied to minimize the redundant overlapping regions of the sensor nodes by preserving connectivity of the network. Moreover, the funneling effect that causes energy hole problem in a linear wireless sensor network is resolved. The performance of the WSN is evaluated through simulations. The simulation results showed that the proposed scheme provides best area coverage as compared to the existing node deployment strategies and is very cost effective.

GPU 기반 SIFT 방법과 가상의 힘을 이용한 이동 로봇의 위치 인식 및 자율 주행 제어

In this paper, we present localization and autonomous navigation method using GPU(Graphics Processing Unit)-based SIFT(Scale-Invariant Feature Transform) algorithm and virtual force method for mobile robots. To do this, at first, we propose the localization method to recognize the landmark using the GPU-based SIFT algorithm and to update the position using extended Kalman filter. And then, we propose the A-star algorithm for path planning and the virtual force method for autonomous navigation of the mobile robot. Finally, we demonstrate the effectiveness and applicability of the proposed method through some experiments using the mobile robot with OPRoS(Open Platform for Robotic Services).

A two-phase flow model for wave–structure interaction using a virtual boundary force method

A three-dimensional two-phase flow model is developed to study wave interaction with structures by using a virtual boundary force (VBF) method. This model solves the Navier–Stokes equations for two-phase flows. The second-order accurate volume-of-fluid (VOF) method is used to track the free surface. In order to satisfy the no-slip condition on the rigid body surface, the virtual boundary forces are applied along the surface of the body in the computation. The model is first validated for wave interaction with a structure with the curved surface. This model is then used to simulate various types of two-dimensional and three-dimensional wave–structure interaction problems, i.e., solitary wave runup and rundown on a sloping beach, nonlinear wave transformation above a submerged breakwater, and wave diffraction around a large circular cylinder. The computational results compare well with available analytical solutions and experimental data. Lastly, as a demonstration, the three-dimensional wave breaking on a floating truncated circular cylinder is simulated and discussed.

An Energy-Balanced Cluster-Based Protocol for Wireless Sensor Networks

This paper proposes a novel energy-efficient clustering protocol for wireless sensor networks. It combines the benefits of using the k-means clustering algorithm with the, recently developed, LEACH with virtual forces (LEACH-VF) protocol. In this work, the k-means algorithm is employed to determine k centroids around which the clusters will be formed. After that, the virtual field force method is applied to these clusters to determine the most suitable positions for each node. The main target of such an approach is to improve the energy balance in the network and to extend the network lifetime. Simulation results show that the proposed protocol extends the time before the first node death, minimizes the variance of the average node energy, and reduces the distance that the sensor nodes travel within their respective clusters.

Ion-6: A Positionless Self-Deploying Method for Wireless Sensor Networks

Sensor networks are deployed to monitor the interested area. Maximizing the sensing coverage depends on effectively determining the locations of sensors. In this paper, a self-deploying method named as Ion-6 is proposed. Sensors are modeled as ions, and the links between them are treated as ionic bonds. When the number of ionic bonds of a sensor is full, the sensor will expel others out of its field. Sensors organize themselves as the hexagonal format to maximize the network's coverage area, retain the network connectivity, and prevent from introducing the coverage holes. The sensors in the proposed method can compute their moving directions and distances independently without priori position information. Simulation results show that Ion-6 can organize sensors as the hexagonal format to maximize the coverage area. The deploying time of Ion-6 is less than the molecule model and efficiently eliminates the unnecessary movements of the virtual force (V-force) method.

Numerical study of ring baffle effects on reducing violent liquid sloshing

A three-dimensional (3-D) numerical model NEWTANK was developed to study viscous liquid sloshing in a tank with internal baffles of different shapes and arrangements. The numerical technique named virtual boundary force (VBF) method was used to model the internal baffles with complex geometries. Laboratory experiments were conducted for non-linear sloshing in a rectangular tank with and without vertical baffle. The numerical model was validated against the measured data together with other available theoretical solutions and numerical results for liquid sloshing under surge and pitch motions. Liquid sloshing in a 3D prismatic tank with different ring baffle arrangements (e.g., height, width, etc.) were further investigated under near-resonant excitations of surge and pitch motions. The fast Fourier transform (FFT) technique was used to identify the dominant response frequencies of the liquid system to external excitations. The effects of ring baffles on reducing violent liquid sloshing were investigated and discussed in detail. Finally, a demonstration of liquid sloshing in the tank under six degree-of-freedom (DOF) excitations was presented.

Modeling-Simulation and Analysis of MEMS Capacitive Millibar Pressure Sensor

Design and simulation of MEMS based capacitive sensor with doubly supported serpentine meander structure for millibar pressure applications proposed in this work is analyzed using INTELLISUITE™ and NISA™ softwares. In this model, microsensing membrane (MSM) is simulated using gold, silicon, and platinum materials of 1 μm and 2 μm thickness. This model has the incorporation to study the sensitivity and spring constant of the support structures for different boundary conditions. The model is validated in terms of virtual force method and finite element method. The design performance of the model is analyzed for the MSM’s support structure stability, maximum permissible displacement limit, sensitivity, pull-in, hysteresis, and dynamic behavior for different pressure loads. Design consideration is taken care to avoid deformation of MSM for the application of pressure load. The spring constant and the effect of fringing field capacitance is evaluated to optimize the design. The key factors of design information for the fabrication of millibar pressure sensor are analyzed.

Study on UAV Path Planning Approach Based on Fuzzy Virtual Force

This article proposes a novel fuzzy virtual force (FVF) method for unmanned aerial vehicle (UAV) path planning in complicated environment. An integrated mathematical model of UAV path planning based on virtual force (VF) is constructed and the corresponding optimal solving method under the given indicators is presented. Specifically, a fixed step method is developed to reduce computational cost and the reachable condition of path planning is proved. The Bayesian belief network and fuzzy logic reasoning theories are applied to setting the path planning parameters adaptively, which can reflect the battlefield situation dynamically and precisely. A new way of combining threats is proposed to solve the local minima problem completely. Simulation results prove the feasibility and usefulness of using FVF for UAV path planning. Performance comparisons between the FVF method and the A* search algorithm demonstrate that the proposed approach is fast enough to meet the real-time requirements of the online path planning problems.

Virtual-Force-Based Geometric Routing Protocol in MANETs

Routing is the foremost issue in mobile ad hoc networks (MANETs). To guarantee delivery and improve performance, most position-based routing protocols, e.g., greedy-face-greedy (GFG), forward a message in greedy routing mode until the message is forwarded to a local minimum where greedy forwarding is impossible. They then switch to a less efficient mode known as face routing. Face routing requires the underlying network to be a planar graph which makes geometric routing only theoretically feasible. To remove this constraint, this paper tackles the local minimum problem with two new methods. First, we construct a virtual small-world network by adding virtual long links to the network to reduce the number of local minima. Second, we use the virtual force method to recover from local minima without relying on face routing. Combining these two methods, we propose a purely greedy routing protocol, the small-world iterative navigation greedy (SWING+) routing protocol. Simulations are conducted to evaluate SWING+ against existing geometric routing protocols. Simulation results show that SWING+ guarantees delivery, and that its performance is comparable to that of the state-of-the-art greedy other adaptive face routing (GOAFR+) routing protocol.