Virtual Time Research Articles

Influence of human operator on stability of haptic rendering: a closed-form equation

In this paper an analytical stability criterion for linear haptic devices is determined, in the presence of the operator. The model of the haptic device and the virtual environment are assumed as mass-damper and spring-damper, respectively. Two different models for operator’s hand are assumed, and the stability boundaries are derived analytically. The main contribution of this paper is the analytical formulation of a closed-form stability equation in the presence of the operator; which can predict the stability boundary with small and even large values of virtual damping and time delay. This closed-form stability criterion can be useful in applications such as haptic rendering of deformable objects using finite element method, where the computational time delay is considerable. The influence of operator’s hand and effective mass on the stability is studied analytically and verified by simulations and experiments on a KUKA Light Weight Robot.

Haptic-enabled virtual planning and assessment of product assembly

PurposeThis study aims to present a new haptic-enabled virtual assembly system for the automatic generation and objective assessment of assembly plans. The system is intended to be used as an assembly planning tool along the product development process.Design/methodology/approachThe generation of product assembly plans is based on the analysis of the assembly movements and operations performed by the user during the virtual assembly execution, and the objective assessment of product assembly is based on the definition and computation of new proposed assembly metrics.FindingsTo evaluate the system, a case study corresponding to the assembly of a mechanical component is presented and analyzed. The results demonstrate that the proposed system is an effective tool to plan and evaluate different product assembly strategies in a more practical and objective approach than existing assembly planning methods.Research limitations/implicationsAlthough the virtual assembly execution time is larger than the real assembly execution time, the assembly planning and evaluation results provided by the system are valid. However, the development of higher performance collision detection algorithms is needed to reduce the simulation time.Originality/valueThe proposed virtual assembly system is able to not only simulate and automatically generate assembly plans but also objectively assess them from the virtual assembly task execution. The introduction and use of several assembly performance metrics to objectively evaluate assembly strategies in virtual assembly also represents a novel contribution.

411 Virtual Crossmatch and Cold Ischemic Time in Deceased Donor Kidney Transplantation

411 Virtual Crossmatch and Cold Ischemic Time in Deceased Donor Kidney Transplantation

Passive Radar Source Localization Based on Cuckoo Search NVTDOA

In order to meet the requirement of passive radar source localization in electronic warfare, the concept of the virtual time differences of arrival (VTDOA) is proposed by taking advantage of the characteristics of the same UAV in different positions at different times and the periodic rotation of radar pulse signal. The VTDOAs are the passive localization information defined as the time differences of the radar pulse transmission from the radar position to different virtual receivers. Firstly, a nonlinear VTDOA (NVTDOA) localization model is constructed. Moreover, sufficient conditions for accurately calculating the periodic integers in the model are analyzed, and the observability conditions of the localization model determined are deduced. Secondly, the convergence solution of the NVTDOA localization equation is obtained by Cuckoo search algorithm; thus, passive radar source localization is realized. Finally, the performance of the proposed method is verified by comparing with the existing methods.

Inversion of head waves in ocean acoustic ambient noise.

The virtual head wave is produced through cross-correlation processing of signals containing the real, acoustic head wave. The virtual head wave has the same phase speed as the head wave, but the travel time is offset, thus the term virtual. The virtual head wave, like the real head wave, propagates in a direction corresponding to the seabed critical angle. The virtual head wave travel time varies with array depth and water column depth. However, in a refracting environment, the travel time is also dependent on the depth-dependent sound speed profile. Previously, the virtual head wave was shown as observable from measurements of ocean ambient noise, and the arrival angle was used to estimate the seabed sound speed. By also using the virtual head wave travel times, it is possible to invert for array depth and water column depth. The previous analysis was limited to the assumption of a Pekeris waveguide, which is a special case of the more realistic refracting waveguide. In this paper, the virtual head wave and the inversion method are considered in environments having refracting sound speeds. The theoretical framework and the inversion method are presented along with illustrative simulations and application to the Boundary'03 data.

Stabilizing the virtual response time in single-server processor sharing queues with slowly time-varying arrival rates

Motivated by the work of Whitt, who studied stabilization of the mean virtual waiting time (excluding service time) in a $GI_t/GI_t/1/FCFS$ queue, this paper investigates the stabilization of the mean virtual response time in a single-server processor sharing (PS) queueing system with a time-varying arrival rate and a service rate control (a $GI_t/GI_t/1/PS$ queue). We propose and compare a modified square-root (SR) control and a difference-matching (DM) control to stabilize the mean virtual response time of a $GI_t/GI_t/1/PS$ queue. Extensive simulation studies with various settings of arrival processes and service times show that the DM control outperforms the SR control for heavy-traffic conditions, and that the SR control performs better for light-traffic conditions.

Optimal Array Steering for High Spatial Resolution Over Time Varying UAV Communication Channels

The Doppler spread in a highly dynamic environment leads to a large-scale channel variation over time for unmanned aerial vehicles (UAVs). In this letter, we adopt the high spatial resolution of massive multi-input multi-output (MIMO) technology to reduce the influence of Doppler spread. An algorithm is proposed for the asymptotically-optimal steering angle to achieve the longest virtual coherence time for large antenna arrays. We first design a matrix to detect array steering vectors of separated propagation paths. A closed-form expression of virtual coherence time over virtual channel for large antenna arrays is therefore derived for the optimal steering angle. Simulation results show that our proposed algorithm can improve the average virtual coherence time by about 13.65 to 27.35 times as compared to benchmarks.

An Optimized Sensing Arrangement in Wind Field Reconstruction Using CFD and POD

In a real wind farm, complex airflow conditions result in complexities of wind speed and direction, with possibly significant intermittency and fluctuations. This problem can be alleviated if the wind speed distribution over a wind farm is known in advance. In this article, a new method is proposed for real-time wind field reconstruction for large areas, based on the idea of a “virtual time”, i.e., a time span needed for an object to travel across a certain distance. The distribution of wind speed and direction can be acquired prior to its occurrence in the wind farm with refined spatial resolutions. A procedure is also developed to stabilize the solution process, and this stabilization leads to an optimal allocation of the wind speed sensors; this allocation is necessary for the efficient use of a limited number of sensors. The reconstruction algorithm has been substantially studied, and a mathematical quantity was correlated to the reconstruction error. This correlation enables us to obtain good reconstruction results by using the greedy algorithm we proposed in this study. Simulation and experimental results demonstrated the strong feasibility of successful reconstructions by our proposed algorithm. Moreover, the sensor optimization scheme not only reduces the error significantly but also improves the efficiency of sensor applications; this improvement should apply to a wide range of conditions.

Virtual-Vector-Based Model Predictive Current Control of Five-Phase PMSM With Stator Current and Concentrated Disturbance Observer

The finite control set model predictive current control(FCS-MPCC)can significantly improve the dynamic performance of the five-phase permanent magnet synchronous motor (5P-PMSM), but its control performance highly depends on the accuracy of the model parameters. The parameter error compensation based on the first-order sliding mode observer can improve the robustness of FCS-MPCC under Model parameter mismatch. The introduction of the sign function leads to chattering in the observation results. In order to eliminate this chattering, a first-order low-pass filter needs to be added for compensation. However, the introduction of filters will increase system design difficulty and bring system delays, which will affect the compensation effect. Therefore, a second-order sliding mode observer, based on the variable-gain Super-Twisting algorithm, is proposed to realize the parameter error estimation and one-beat delay compensation in this paper. By establishing the Lyapunov function, the stability proof of the proposed observer, and the calculation method of the observer parameters are given. Besides, the third harmonic current can be suppressed, and the computational burden of the control unit can be reduced by controlling the proportion of medium vector and large vector reasonably. According to the deadbeat control, the optimal virtual voltage vector action time in each cycle is obtained, which improves the tracking ability of the reference current. At last, Extensive experimental results validate that i) the proposed observer can significantly improve the robustness of model predictive current control even under parameters mismatch; ii) the proposed control method can effectively enhance the dynamic performance of the 5-phase PMSM.

Balanced Cloud Edge Resource Allocation Based on Conflict Conditions

Under a multiscenario environment with frequent bursts of data in the edge cloud, the resource allocation in the edge cloud will affect the stability of its nodes. To address this problem, a balanced virtual resource allocation model based on conflict conditions is proposed. Based on a thorough study of the similarity between task attributes and resources used by the host, the concept of a task backlog is implemented to achieve a preliminary balanced allocation of tasks; thus, a conflict condition based on the remaining resources of the physical and virtual machines is proposed. Further, a matrix of phased conflict coefficients is built to establish a balanced virtual machine allocation model. The results of experiments comparing the performance of the proposed model with that of other existing models indicate that the proposed model can reduce the virtual machine scheduling time by up to 8.33%, save up to 6.25% of host energy consumption, and improve the algorithm efficiency by 20.47% compared with the other algorithms. To avoid the local optimal problem caused by dynamic virtual machine migration, an improved ant colony algorithm is combined with the above model, and concepts of a pheromone volatility factor and suppression factor are implemented to optimize the pheromone measurement function and ensure that the virtual machine migration path is globally optimal. Overall, the model reduces the conflict rate of resources on the physical machine and can maintain stable operation under CPU usage fluctuation, thus realizing a balanced allocation of node resources.

Travel Time and Waveform Measurements of Global Multibounce Seismic Waves Using Virtual Station Seismogram Stacks

AbstractWe construct geographically localized bin stacks of waveforms, called virtual stations, to enhance signal‐to‐noise ratios (SNRs) for travel time and waveform measurements of multibounce S and ScS phases (S up to S6 and ScS up to ScS5), as well as direct S, ScS, and Sdiff, on tangential component data. Major arc S and ScS multibounce waves were also measured. Virtual station data are referenced to empirical wavelets constructed from direct S waves for each event. The virtual station approach is useful for low SNR data, bolstering wave path coverage in the southern hemisphere. Goodness of fit measurements between the adapted empirical wavelet and virtual station waveforms are documented, as well as SNRs, allowing for objective definition of travel time measurement quality. From a data set of 360 earthquakes and 8,407 seismographic stations, nearly 4 million records were utilized to construct 248,657 virtual station stacked seismograms, which were compared to best‐fitting empirical wavelets. After human inspection of virtual station results, 8,871 travel time measurements were retained from 19 different minor and major arc seismic wave types. Higher multibounce data improve sampling of the southern hemisphere. From 188,003 single seismograms, 3,331 multibounce wave measurements were also made. Comparisons of single seismogram and virtual station stack measurements show a consistent bias: Virtual stack onset times are systematically early due to a broadening effect from stacking records with arrival time differences, which we correct for. The travel time and waveform measurements are publicly available.

Improvements of data driven control V-Tiger evaluating virtual time response like AI

Improvements of data driven control V-Tiger evaluating virtual time response like AI

A design of V-Tiger evaluating virtual time response like AI for system with input saturation

A design of V-Tiger evaluating virtual time response like AI for system with input saturation

A design of data driven control V-Tiger evaluating virtual time response like AI for MIMO system

A design of data driven control V-Tiger evaluating virtual time response like AI for MIMO system

Virtual Time-response based Iterative Gain Evaluation and Redesign

Abstract Since Artificial Intelligence (AI) has won over human pros such as Chess, Shogi and Go, expectations for AI have been increasing dramatically. One of the reasons why AI has developed so much is the tremendous increase in the processing speed of computers, which makes it possible to virtually repeat simulated competitions such as Othello, Shogi, Go and so on in the computer very fast. Finally, AI has gained strength over human pros. Also in control engineering, if gain tuning experiments of controllers can be virtually performed in a computer, it can be expected to dramatically improve control performance with an AI-like approach. This paper proposes a new method called ‘Virtual Time-response based Iterative Gain Evaluation and Redesign’ (V-Tiger) which iterates: 1) to calculate virtual time responses of the closed-loop system when a certain controller is inserted based on one-shot experimental data, 2) to measure the overshoot and settling time from the virtual time responses, and 3) to evaluate and redesign the controller gain considering the stability margin.

A design of data driven control V-Tiger evaluating virtual time response like AI for SIMO system

A design of data driven control V-Tiger evaluating virtual time response like AI for SIMO system

Bionic Morse Coding Mimicking Humpback Whale Song for Covert Underwater Communication

A novel method of bionic Morse coding mimicking humpback whale vocal is presented for covert underwater acoustic communication. The complex humpback whale song is translated as bionic Morse codes based on information entropy. The communication signal is made akin to the natural singing of male humpback whales. The intruder can detect the signal but will not be able to recognize the communication signal due to unified resemblance with the natural sound. This novel technique gives an excellent low probability of recognition characteristics. A flawless stealthy underwater acoustic communication has been established which has negligible chances of deciphered with high imperceptibility. Standard mimicry Morse codes have been developed for the characters of the English language and compared with Morse coding. Covert information of one character per second can be watermarked with perfect stealth and clandestine communication. This novel concept has been verified at transmission distance of five km and less than 10−3 Bit Error Rate (BER) is achieved at Signal to Noise Ratio (SNR) down to negative seven dB. Zero BER is attained by estimating the channel by a matching pursuit algorithm and equalizing the errors by virtual time reversal mirror technique.

Preliminary Development of MyAras: Level 1 Mobile Virtual Lab

Process control is an essential aspect in chemical engineering, which has been emphasized in Dynamic and Control Process course (KKKR 3684) the-oretically and through a conventional laboratory experimental, A2 (Tuning and Control) for hands-on learning. The tank level is chosen as the con-trolled variable to introduce control scheme to students. This conventional lab uses an old version facility and requires constant maintenance resulting lab schedule being postponed several times. Besides that, every experiment must be carried out in a group of four to five students thus the access and learning time per student is limited. As an alternative to this conventional laboratory, a mobile-based virtual lab has been designed to cater the limita-tions using a mobile application. The proposed virtual lab is known as MyAras and is developed using Android Studio software of version 2.3.3, which also a strategy to facing the 4.0 Industrial revolution. MyAras is a mobile virtual application and time independent, cost-effective, easy access and provides unlimited self-learning period for all students. Level 1 means the mobile virtual lab is still in the development stage and has not been fully launched to students. A questionnaire has been given to students and lectur-ers regarding their awareness and the importance of mobile virtual lab prior to its development. Preliminary study has found that 81% of students have shown their interest in running the virtual lab and 38.1% of students had never used such application as their practical learning tool.

Characterizations of random walks on random lattices and their ramifications

We analyze the behavior of a particle moving along a d-dimensional lattice and representing a “doubly stochastic” random walk. Unlike the classical random walk, the lattice is randomly generated upon particle’s landing at a node. At any time, the particle is enclosed in a rectangular cylinder (i.e., with a bounded a-dimensional rectangle Ra at its base) it attempts to escape. Thus, the particle moves from one node to another at random epochs of time and, with some probability, leaves The particle may jump arbitrarily far beyond the boundary at its passage time. Furthermore, the particle’s location is not assumed to be known in real time, but only upon certain random epochs Of a key interest is the location of the particle at any time, where is the linear interpolation of particle’s positions at times τn’s. If denotes the first observed escape time (virtual first passage time), where we target the joint characteristic function of and itself, where or in tractable forms, thereby attempting to enhance as much as possible the probabilistic data lost due to the crudeness of the observations and to couple and with deterministic time intervals Among various applications, we discuss and treat antagonistic games of two active and several passive players as well as situations that occur in complex queueing systems.

Multilayer Virtual Cell-Based Resource Allocation in Low-Power Wide-Area Networks

The Internet of Things (IoT) technology has attracted widespread attention since it can connect a huge number of heterogeneous devices to construct an intelligent environment to offer various services. Driven by the decreasing expense and significant convenience, it is expected that the total number of IoT devices will reach as high as 50 billion by 2020. And, these devices will provide diversified Internet services, including smart home, elder care, and vehicle-to-everything (V2X) communications. For the IoT technology, the network performance as well as the energy efficiency are both important since most end devices are battery limited. In this article, we focus on the IoT network based on the long-range wide-area network (LoRaWAN) protocol since its chirp modulation technology can adopt different spreading factors (SFs) to realize flexible communications. We propose a novel resource allocation strategy which utilizes multilayer virtual cell-based spatial time division multiple access (STDMA) scheme. This new method can not only simplify the calculation of the interference but also enables the cell radius to be adjusted to fit the communication distance. Moreover, the relationship between the power consumption and the network data rate is also analyzed in this article. We numerically analyze the optimal power consumption to achieve the highest data rate. The final performance evaluation demonstrates the significant improvement of our proposal compared with the conventional method.