Showing papers in "Transactions of Tianjin University in 2008"

River morphology and river channel changes

Abstract: River morphology has been a subject of great challenge to scientists and engineers who recognize that any effort with regard to river engineering must be based on a proper understanding of the morphological features involved and the responses to the imposed changes. In this paper, an overview of river morphology is presented from the geomorphic viewpoint. Included in the scope are the regime concept, river channel classification, thresholds in river morphology, and geomorphic analysis of river responses. Analytical approach to river morphology based on the physical principles for the hydraulics of flow and sediment transport processes is also presented. The application of analytical river morphology is demonstrated by an example. Modeling is the modern technique to determine both short-term and long-term river channel responses to any change in the environment. The physical foundation of fluvial process-response must be applied in formatting a mathematical model. A brief introduction of the mathematical model FLUVIAL-12 is described.

Mesh size effect in numerical simulation of blast wave propagation and interaction with structures

Abstract: Numerical method is popular in analysing the blast wave propagation and interaction with structures. However, because of the extremely short duration of blast wave and energy transmission between different grids, the numerical results are sensitive to the finite element mesh size. Previous numerical simulations show that a mesh size acceptable to one blast scenario might not be proper for another case, even though the difference between the two scenarios is very small, indicating a simple numerical mesh size convergence test might not be enough to guarantee accurate numerical results. Therefore, both coarse mesh and fine mesh were used in different blast scenarios to investigate the mesh size effect on numerical results of blast wave propagation and interaction with structures. Based on the numerical results and their comparison with field test results and the design charts in TM5-1300, a numerical modification method was proposed to correct the influence of the mesh size on the simulated results. It can be easily used to improve the accuracy of the numerical results of blast wave propagation and blast loads on structures.

Failure modes for single-layer reticulated domes under impact loads

Abstract: The paper presents the theory of Hamilton variation principle which is the current method for impact problem, central difference method which is efficient solution of finite element (FE) method for impact problem and adapts to solve non-linear dynamic problem. And it introduces the ANSYS/LS-DYNA which is the popular FE software for impact problem both at home and abroad. Then it gives solutions for one simple model by analytical method and ANSYS/LS-DYNA respectively to validate function of software, and they are consistent. Afterward, it gives model of single-layer Kiewitt reticulated dome with a span of 60 m, and the cylinder impactor, and introduces the contact interface arithmetic, especially the material model of steel (piecewise linear plasticity model) which takes stain rate into account and makes steel failure stress higher under impact loads. The vertical displacement, stress in main members, and the plastic deformation for dome under impact loads were obtained. Then four failure modes (no failure, moderate failure, global failure and slight failure) were summarized according to the rules of dynamic response. And the characteristics of dynamic response for each failure mode were shown.

Spallation Mechanism of RC Slabs Under Contact Detonation

Abstract: The spallation of the concrete slabs or walls resulting from contact detonation constitutes risk to the personnel and equipment inside the structures because of the high speed concrete fragments even though the overall structures or structural members are not destroyed completely. Correctly predicting the damage caused by any potential contact detonation can lead to better fortification design to withstand the blast loadings. It is therefore of great significance to study the mechanism involved in the spallation of concrete slabs and walls. Existing studies on this topic often employ simplified material models and 1D wave analysis, which cannot reproduce the realistic response in the spallation process. Numerical simulations are therefore carried out under different contact blast loadings in the free air using LS-DYNA. Sophisticated concrete and reinforcing bar material models are adopted, taking into account the strain rate effect on both tension and compression. The erosion technique is used to model the fracture and failure of materials under tensile stress. Full processes of the deformation and dynamic damage of reinforced concrete (RC) slabs and plain concrete slabs are thus observed realistically. It is noted that with the increase of quantity of explosive, the dimensions of damage crater increase and the slabs experience four different damage patterns, namely explosive crater, spalling, perforation, and punching. Comparison between the simulation results of plain concrete slabs and those of RC slabs show that reinforcing bars can enhance the integrity and shearing resistance of the slabs to a certain extent, and meanwhile attenuate the ejection velocity and decrease the size of the concrete fragments. Therefore, optimizing reinforcement arrangement can improve the anti-spallation capability of the slabs and walls to a certain extent.

Failure process and energy transmission for single-layer reticulated domes under impact loads

Abstract: No failure, moderate failure, severe failure, and slight failure are the four failure modes generalized observed in the dynamic response of the single-layer reticulated dome under vertical impact load on apex. TE (the time that the end of impact force) and TF (the time that members are broken) are two key times in the failure process. Characteristics of dynamic responses at the two key times are shown in order to make the failure mechanism clear. Then three steps of energy transfer are summarized, i.e. energy applying, energy loss and energy transfer, energy consumption. Based on the three steps, energy transfer process for the failure reticulated dome under once impact is introduced. Energy transmissibility and local loss ratio are put forward firstly to obtain ELF (the energy left in the main reticulated dome) from the initial kinetic energy of impactor. Moreover, the distribution of failure modes is decided by ELF which leads to the maximum dynamic response of the reticulated dome, but not by the initial impact kinetic energy of impactor.

Methods for progressive collapse analysis of building structures under blast and impact loads

Abstract: Progressive collapse of building structures under blast and impact loads has attracted great attention all over the world. Progressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loads. Because of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it, it is imperative that the progressive collapse analysis methods be reliable. For engineers, their methodology to carry out progressive collapse evaluation need not only be accurate and concise, but also be easily used and works fast. Thus, many researchers have been spending lots of effort in developing reliable, efficient and straightforward progressive collapse analysis methods recently. In the present paper, current progressive collapse analysis methods available in the literature are reviewed. Their suitability, applicability and reliability are discussed. Our recent proposed new method for progressive collapse analysis of reinforced concrete frames under blast loads is also introduced.

Analysis of blast wave propagation inside tunnel

Abstract: The explosion inside tunnel would generate blast wave which transmits through the longitudinal tunnel. Because of the close-in effects of the tunnel and the reflection by the confining tunnel structure, blast wave propagation inside tunnel is distinguished from that in air. When the explosion happens inside tunnel, the overpressure peak is higher than that of explosion happening in air. The continuance time of the blast wave also becomes longer. With the help of the numerical simulation finite element software LS-DYNA, a three-dimensional nonlinear dynamic simulation analysis for an explosion experiment inside tunnel was carried out. LS-DYNA is a fully integrated analysis program specifically designed for nonlinear dynamics and large strain problems. Compared with the experimental results, the simulation results have made the material parameters of numerical simulation model available. By using the model and the same material parameters, many results were adopted by calculating the model under different TNT explosion dynamites. Then the method of dimensional analysis was used for the simulation results. As overpressures of the explosion blast wave are the governing factor in the tunnel responses, a formula for the explosion blast wave overpressure at a certain distance from the detonation center point inside the tunnel was derived by using the dimensional analysis theory. By comparing the results computed by the formula with experimental results which were obtained before, the formula was proved to be very applicable at some instance. The research may be helpful to estimate rapidly the effect of internal explosion of tunnel on the structure.

Numerical simulation of dynamic response of an existing subway station subjected to internal blast loading

Abstract: In order to design and retrofit a subway station to resist an internal blast, the distribution of blast loading and its effects on structures should be investigated firstly In this paper, the behavior of a typical subway station subjected to different internal blast loadings was analyzed It briefly introduced the geometric characteristics and material constitutive model of an existing two-layer and three-span frame subway station Then three cases of different explosive charges were considered to analyze the dynamic responses of the structure Finally, the maximum principal stress, displacement and velocity of the columns in the three cases were obtained and discussed It concluded that the responses of the columns are sensitive to the charge of explosive and the distance from the detonation It’s also found that the stairs between the two layers have significant effects on the distribution of the maximum principal stress of the columns in the upper layer The explicit dynamic nonlinear finite element software—ANSYS/LS-DYNA was used in this study

Modern Travelling Wave Based Fault Location Techniques for HVDC Transmission Lines

Abstract: The modern travelling wave based fault location principles for transmission lines are analyzed In order to apply the travelling wave principles to HVDC transmission lines, the special technical problems are studied Based on this, a fault locating system for HVDC transmission lines is developed The system can support modern double ended and single ended travelling wave principles simultaneously, and it is composed of three different parts: travelling wave data acquisition and processing system, communication network and PC based master station In the system, the fault generated transients are induced from the ground leads of the over-voltage suppression capacitors of an HVDC line through specially developed travelling wave couplers The system was applied to 500 kV Gezhouba-Nanqiao (Shanghai) HVDC transmission line in China Some field operation experiences are summarized, showing that the system has very high reliability and accuracy, and the maximum location error is about 3 km (not more than 03% of the total line length) Obviously, the application of the system is successful, and the fault location problem has finally been solved completely since the line operation

Numerical simulation of dynamic response and collapse for steel frame structures subjected to blast load

Abstract: The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A fluid-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, structural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic deformation subjected to intensive blast waves, and columns lost carrying capacity, subsequently leading to the collapse of the whole structure. The approach coupling influence between structural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.

Mitigation of blast effects on aluminum foam protected masonry walls

Abstract: Terrorist attacks using improvised explosive devices (IED) can result in unreinforced masonry (URM) wall collapse. Protecting URM wall from IED attack is very complicated. An effective solution to mitigate blast effects on URM wall is to retrofit URM walls with metallic foam sheets to absorb blast energy. However, mitigation of blast effects on metallic foam protected URM walls is currently in their infancy in the world. In this paper, numerical models are used to simulate the performance of aluminum foam protected URM walls subjected to blast loads. A distinctive model, in which mortar and brick units of masonry are discritized individually, is used to model the performance of masonry and the contact between the masonry and steel face-sheet of aluminum foam is modelled using the interface element model. The aluminum foam is modelled by a nonlinear elastoplastic material model. The material models for masonry, aluminum foam and interface are then coded into a finite element program LS-DYNA3D to perform the numerical calculations of response and damage of aluminum foam protected URM walls under airblast loads. Discussion is made on the effectiveness of the aluminum foam protected system for URM wall against blast loads.

Finite Element Analysis of Internal Gear in High-Speed Planetary Gear Units

Abstract: The stress and the elastic deflection of internal ring gear in high-speed spur planetary gear units are investigated. A rim thickness parameter is defined as the flexibility of internal ring gear. Six evenly spaced linear springs are used to describe the fitting status between internal ring gear and the gearcase. The finite element model of the whole internal ring gear is established by means of Pro/E and ANSYS. The loads on meshing teeth of internal ring gear are applied according to the contact ratio and the load-sharing coefficient. With the finite element analysis (FEA), the influences of flexibility and fitting status on the stress and elastic deflection of internal ring gear are predicted. The simulation reveals that the principal stress and deflection increase with the decrease of rim thickness of internal ring gear. Moreover, larger spring stiffness helps to reduce the stress and deflection of internal ring gear. Therefore, the flexibility of internal ring gear must be considered during the design of high-speed planetary gear transmissions.

Experimental investigation into magnetorheological damper subjected to impact loads

Abstract: A good mechanical model of magnetorheological damper (MRD) is essential to predict the shock isolation performance of MRD in numerical simulation But at present, the mechanical models of MRD were all derived from the experiment subjected to harmonic vibration loads In this paper, a commercial MRD (type RD-1005-3) manufactured by Lord Corporation was studied experimentally in order to investigate its isolation performance under the impact loads A new mechanical model of MRD was proposed according to the data obtained by impact test A good agreement between the numerical results and test data was observed, which showed that the model was good to simulate the dynamic properties of MRD under impact loads It is also demonstrated that MRD can improve the acceleration and displacement response of the structure obviously under impact loads

Decomposition of cellulose to produce 5-hydroxymethyl-furaldehyde in subcritical water

Abstract: A method for decomposition of cellulose to produce 5-hydroxymethyl-furaldehyde (5-HMF) in subcritical water-carbon dioxide binary system was proposed. A series of experiments were performed in a batch reaction vessel. Main products of the decomposition of cellulose are 5-HMF, furfural, levulinic acid and 1, 2, 4-benzenetriol. The optimum condition for the preparation of 5-HMF was found as 523.15 K, 5.0% carbon dioxide mole fraction, and 30 min reaction time. The addition of carbon dioxide to water conduced to the decomposition of cellulose to 5-HMF. As can be seen from the distribution of the prod-ucts, the decomposition mechanism of cellulose is similar to the hydrothermal reaction of D-glucose and D-fructose.

Zone 3 relay blocking scheme to prevent cascaded events

Abstract: Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events. Cascaded events can be attributed to improper operations of protective relays. The most challenging problem for the design and implementation of a defense system is the performance in accuracy and speed in a real time environment. Protective devices are normally designed to operate fast in order to isolate the fault(s). This paper proposes a new methodology to distinguish line overloads from actual faults for distance relays. In order to distinguish between line flow transfers from a line outage and an actual fault, the line outage distribution factor (LODF) and generation shift factor (GSF) based power flow estimation method, and a secure peer to peer (P2P) communication structure are adopted. Computer simulations of cascaded events for a 6-bus system and the Korean power grid have been performed to establish the feasibility of the proposed scheme.

Modeling and Defending Passive Worms over Unstructured Peer-to-Peer Networks

Abstract: Passive worms can passively propagate through embedding themselves into some sharing files, which can result in significant damage to unstructured P2P networks. To study the passive worm behaviors, this paper firstly analyzes and obtains the average delay for all peers in the whole transmitting process due to the limitation of network throughput, and then proposes a mathematical model for the propagation of passive worms over the unstructured P2P networks. The model mainly takes the effect of the network throughput into account, and applies a new healthy files dissemination-based defense strategy according to the file popularity which follows the Zipf distribution. The simulation results show that the propagation of passive worms is mainly governed by the number of hops, initially infected files and uninfected files. The larger the number of hops, the more rapidly the passive worms propagate. If the number of the initially infected files is increased by the attackers, the propagation speed of passive worms increases obviously. A larger size of the uninfected file results in a better attack performance. However, the number of files generated by passive worms is not an important factor governing the propagation of passive worms. The effectiveness of healthy files dissemination strategy is verified. This model can provide a guideline in the control of unstructured P2P networks as well as passive worm defense.

Evaluation of blast-resistant performance predicted by damaged plasticity model for concrete

Abstract: In order to evaluate the capacity of reinforced concrete (RC) structures subjected to blast loadings, the damaged plasticity model for concrete was used in the analysis of the dynamic responses of blast-loaded RC structures, and all three failure modes were numerically simulated by the finite element software ABAQUS. Simulation results agree with the experimental observations. It is demonstrated that the damaged plasticity model for concrete in the finite element software ABAQUS can predict dynamic responses and typical flexure, flexure-shear and direct shear failure modes of the blast-loaded RC structures.

Numerical simulation of shaped charge jet using multi-phase SPH method

Abstract: Since the jets and detonation gaseous products are separated by sharp interfaces, the traditional smoothed particle hydrodynamics (SPH) method is difficult to avoid the computational instability at interfaces. The multi-phase SPH (MSPH) method was applied to improving the stability, which smoothes the particle density and makes pressure continuous at interfaces. Numerical examples of jet forming process were used to test capability of the MSPH method. The results show that the method remains algorithm stability for large density gradient between the jets and gaseous products and has potential application to both the explosion and the jet problems. The effect of initiation ways of the shaped charge was discussed as well.

Modelling Impact of Dredging and Dumping in Ebb-Flood Channel Systems

Abstract: For a channel-shoal system in a funnel-shaped basin the impact of dredging and dumping is investigated using a complex process-based model. First, the residual flow and sediment transport circulations are analysed for the channel-shoal pattern, which has emerged after a long-term model simulation. Results are compared to the Western Scheldt estuary, which forms the inspiration for this study. Subsequently, different dredge and dump scenarios are modelled, according to a conceptual model, in which ebb-and flood-channels and enclosed shoals form morphodynamic units (cells) with their own sediment circulation. Model results show that dumping sediment in a channel further reduces the channel depth and induces erosion in the opposite channel, which enhances tilting of the cross-section of the cell and eventually can lead to the degeneration of a multiple channel system into a single channel. The impact of different dredging and dumping cases agrees with results from a stability analysis. This means that this type of model applied to a realistic geometry can potentially be used for better prediction of the impact of human interventions.

Effects of Temperature and Strain Rate on Dynamic Properties of Concrete

Abstract: To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB). Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed. The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature. But with temperature increasing, the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect. So, strain rate effect, strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively complex.

Effect of concrete cracks on dynamic characteristics of powerhouse for giant-scale hydrostation

Abstract: With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.

Stress uniformity process of specimens in SHPB test under different loading conditions of rectangular and half-sine input waves

Abstract: Based on the characteristics of 1D waves, the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test. The results show that the times of an elastic wave propagating from one end to the other in a specimen to attain stress equilibrium, is related to input waveforms and relative mechanical impedance between the specimen and the input/output bars. Hereinto, with the increae of the relative impedance, the times decreases under rectangular input waves loading, while it increases under half-sine input wave loading. The dimensionless stress value of specimen corresponding to the status of stress equilibrium increases with the increase of the relative mechanical impedance. However, the dimensionless stress value under half-sine input wave loading is significantly lower than the value under rectangular input wave loading for specimen with low mechanical impedance, and the relative differentia of the dimensionless stress values under two loading conditions decreases with the increase of the relative mechanical impedance. In general, the forced state of specimen with relatively low mechanical impedance under half-sine input wave loading is evidently superior to the state under rectangular input wave loading in SHPB test, and the advantages of forced state under half-sine input wave loading turns weak with the increase of the relative mechanical impedance.

Single phase-to-ground fault line identification and section location method for non-effectively grounded distribution systems based on signal injection

Abstract: A diagnostic signal current trace detecting based single phase-to-ground fault line identification and section location method for non-effectively grounded distribution systems is presented in this paper. A special diagnostic signal current is injected into the fault distribution system, and then it is detected at the outlet terminals to identify the fault line and at the sectionalizing or branching point along the fault line to locate the fault section. The method has been put into application in actual distribution network and field experience shows that it can identify the fault line and locate the fault section correctly and effectively.

Construction simulation and real-time control for high arch dam

Abstract: A method of combining dynamic simulation with real-time control was proposed to fit the randomness and uncertainty in the high arch dam construction process. The mathematical logic model of high arch dam construction process was established. By combining dynamic construction simulation with schedule analysis, the process of construction schedule forecasting and analysis based on dynamic simulation was studied. The process of real-time schedule control was constructed and some measures for dynamic adjustment and control of construction schedule were provided. A system developed with the method is utilized in a being constructed hydroelectric project located at the Yellow River in northwest China, which can make the pouring plan of the dam in the next stage (a month, quarter or year) to guide the practical construction. The application result shows that the system provides an effective technical support for the construction and management of the dam.

Reliability of substation protection system based on IEC61850

Abstract: Although the new technology of protection and automation system of substation based on IEC61850 standard has developed rapidly in China, reliability measures depending on this technology need to be further researched. By taking advantage of convenient information sharing, two kinds of new schemes, shared backup protection unit (SBPU) and signal backup (SB), have been proposed to solve the failure problem of protective devices and current/voltage transducers respectively, and the working principle of these two schemes are also described. Furthermore, the key technologies of on-line diagnosis of protective devices’ failure and on-line status diagnosis of optical or electronic current/voltage transducers to realize the two schemes are proposed.

On-line broken-bar fault diagnosis system of induction motor

Abstract: Induction motor faults including mechanical and electrical faults are reviewed. The fault diagnosis methods are summarized. To analyze the influence of stator current, torque, speed and rotor current on faulted bars, a time-stepping transient finite element (FE) model of induction motor with bars faulted is created in this paper. With wavelet package analysis method and FFT method, the simulation result of finite element is analyzed. Based on the simulation analysis, the on-line fault diagnosis system of induction motor with bars faulted is developed. With the speed of broken bars motor changed from 1 478 r/min to 1 445 r/min, the FFT power spectra and the wavelet package decoupling factors are given. The comparison result shows that the on-line diagnosis system can detect broken-bar fault efficiently.

Dynamic response of RPC-filled steel tubular columns with high load carrying capacity under axial impact loading

Abstract: Experimental investigation into impact-resistant behavior of reactive powder concrete (RPC)-filled steel tubular columns was conducted, and dynamic response of the columns under axial impact loading was studied by means of numerical simulation method. Increase coefficient of load carrying capacity and ratio of load carrying capacity between steel tube and RPC core of columns were obtained.

Damage assessment for buried structures against internal blast load

Abstract: The soil-structure interaction (SSI) decoupling is applied to simplify buried structure against internal blast load as spring effect. Shear failure, bending failure and combined failure modes are considered based on five transverse velocity profiles for the rigid-plastic structural element. The critical equations for shear and bending failure are derived respectively. Pressure-impulse diagrams are accordingly developed to assess damage of the buried structures against internal blast load. Comparison is done to show influences of soil-structure interaction and shear-to-bending strength ratio of a structural element. A case study is conducted to show the application of damage assessment to a reinforced concrete beam element of buried structure.

Application of two-order difference to gap statistic

Abstract: Gap statistic is a well-known index of clustering validity, but its realization is difficult to be comprehended and accurately determined. A direct method is presented to improve the performance of the Gap statistic, which applies the two-order difference of within-cluster dispersion to replace the constructed null reference distribution in the Gap statistic. Hence, the realization of the Gap statistic becomes easy and is reformulated, and its uncertainty in applications is reduced. Also, the limitation of the Gap statistic is analyzed by two typical examples, that is, the Gap statistic is difficult to be applied to the dataset that contains strong-overlap or uneven-density clusters. Experiments verify the usefulness of the proposed method.

Frequency-feedback based islanding detection algorithm for micro-grid

Abstract: The unintentional islanding of micro-grid may cause negative impacts on distribution loads and distributed generations, so it must be detected within the acceptable duration. In this paper a new islanding detection algorithm is proposed. This algorithm introduces the frequency feedback method by the reactive power compensation to derive the frequency continuous shift. Accordingly, the islanding can be detected by monitoring the frequency within 0.1 s. The simulation results prove that this algorithm has extremely small non-detection zone, and meanwhile it presents an excellent islanding detection speed as well.