Wave Head Research Articles

A One-Dimensional Discrete Boltzmann Model for Detonation and an Abnormal Detonation Phenomenon**Supported by National Natural Science Foundation of China under Grant Nos. 11772064, and 11502117, CAEP Foundation under Grant No. CX2019033, the opening project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology) and Science Challenge Project under Grant No. JCKY2016212A501

A one-dimensional discrete Boltzmann model for detonation simulation is presented. Instead of numerical solving Navier-Stokes equations, this model obtains the information of flow field through numerical solving specially discretized Boltzmann equation. Several classical benchmarks including Sod shock wave tube, Colella explosion problem, and one-dimensional self-sustainable stable detonation are simulated to validate the new model. Based on the new model, the influence of negative temperature coefficient of reaction rate on detonation is further investigated. It is found that an abnormal detonation with two wave heads periodically appears under negative temperature coefficient condition. The causes of the abnormal detonation are analyzed. One typical cycle of the periodic abnormal detonation and its development process are discussed.

Double‐ended travelling‐wave fault location based on residual analysis using an adaptive EKF

This paper presents the estimated residuals for detecting the traveling wave front using an adaptive extended Kalman filter based on the maximum likelihood (EKF-ML), which uses the maximum likelihood method to adaptively optimize the error covariance matrices and the initial conditions. In some situations, such as faults close to the bus or close to zero inception angle, or faults with high fault resistances, the transient waves can become weak and even become lost in the noise, which makes the discrimination of the traveling wave front become more difficult. Aiming at this, residuals between the observed values and the estimated values using the adaptive EKF exhibit remarkable singularities, and can be used for exactly determining the wave front. Thus, the exact arrival time of the initial wave head can be determined and then the fault distance can be calculated precisely. The effectiveness of exacting mutation feature using the proposed method has been demonstrated by a simulated instantaneous pulse. And it has been tested with different types of faults using ATP simulation. Simulation results verify that the estimated residuals are highly sensitive to traveling wave front and less sensitive to modeling uncertainty (such as noise disturbance).

Method of High-speed Railway Traction Nets Fault Single-ended Traveling-wave Location Based on Wavelet Transformation Adaptive Matching

In order to reduce the influence of the transmission dispersion characteristics on the wave head detection and the wave transmission velocity measurement, put forward a new algorithm. This method combined with wavelet transform singularity and similarity algorithm, extracted the reconstruction high-frequency signal of wavelet function multi-scale decomposing structure, to calculate fault traveling-wave positioning. Got characteristic value point, calculated arrival time of traveling-wave head, obtained the reference speed of traveling-wave by simulation experiment results. Analysis result of the field test data showed that the high-speed railway traction nets fault positioning method can extract the faults characteristic effectively, and eliminate the influence of traveling-wave dispersion characteristic, and the fault positioning error is no more than 100 m.

Fault location based on travelling wave identification using an adaptive extended Kalman filter

The fault location in transmission systems remains a challenging problem, primarily due to the fault location near the substation ends or the weak fault signals. In this study, an adaptive extended Kalman filter (EKF) based on the maximum likelihood (ML) is proposed to estimate the instantaneous amplitudes of the travelling waves. In this method, the EKF algorithm is used to estimate the optimal states (the clean travelling waves) with additive white noise while ML is used to adaptively optimise the error covariance matrices and the initial conditions of the EKF algorithm. Using the proposed method, the singularity points of travelling waves can be detected, and the exact arrival time of the initial wave head at the substations M and N can be easily yielded. Thus the fault distance can be calculated precisely. The effectiveness of exacting mutation feature using the proposed method has been demonstrated by a simulated instantaneous pulse. Also, the proposed method has been tested with different types of faults, such as different fault locations, different fault resistances and different fault inception angles using ATP simulation. The accuracy of fault location using the proposed method has been compared with conventional wavelet transformation scheme.

Single Phase to Ground Fault Section Location Based on Characteristics of Traveling Wave Refraction and Reflection

For single phase to ground fault in distribution networks, fault locating using traveling wave measured at one terminal only need to detect the arrival time of the initial wave head of the line mode and the zero mode. But the zero mode wave velocity is unstable. This paper proposes a fault section location method using only line mode traveling wave. It analyzes wave refraction and reflection performance at the fault point, the branch point and the end of the line. The path differences between reflected waves and the initial incident wave are estimated through Hilbert Huang Transform by indexing the arrival time of the initial wave and reflected waves, if the line mode wave velocity is assumed. Combined with the topology of distribution network, the possible propagation paths can be obtained to identify the fault section. The effectiveness of the proposed method is verified by experiments in the actual distribution network.

Novel method of locating ultrasonic wave heads based on spectrum-subtracted sub-band singular spectrum entropy

In obtaining the travel time of sound/time difference in ultrasonic measurements, locating the ultrasonic wave head is pivotal. The existing location/detection methods are poor in terms of accuracy and anti-jamming capability. Therefore, they cannot be used in certain high precision fields. Hence, this study develops a novel method based on spectrum-subtracted sub-band singular spectrum entropy (SSB-SSE), which locates the wave head by introducing both sub-band and spectrum subtraction into singular spectrum entropy (SSE). Furthermore, this study generates a reasonable sub-band selection technique. Simulation experiments demonstrate that SSB-SSE is more accurate, robust, and capable of anti-jamming than other existing spectrum entropies. Therefore it can locate ultrasonic wave heads more effectively in layered media measurements.

Hydrodynamic evolution of sperm swimming: Optimal flagella by a genetic algorithm

Swimming performance of spermatozoa is an important index for the success of fertilization. For many years, numerous studies have reported the optimal swimming of flagellar organisms. Nevertheless, there is still a question as to which is optimal among planar, circular helical and ellipsoidal helical beating. In this paper, we use a genetic algorithm to investigate the beat pattern with the best swimming efficiency based on hydrodynamic dissipation and internal torque exertion. For the parameters considered, our results show that the planar beat is optimal for small heads and the helical flagellum is optimum for a larger heads, while the ellipsoidal beat is never optimal. Also, the genetic optimization reveals that the wavenumber and shape of wave envelope are relevant parameters, whereas the wave shape and head geometry have relatively minor effects on efficiency. The optimal beat with respect to the efficiency based on the internal torque exertion of an active elastic flagellum is characterized by a small-wavenumber and large-amplitude wave in a lower-viscosity medium. The obtained results on the optimal waveform are consistent with observations for planar waveforms, but in many respects, the results suggest the necessity of a detailed flagellar structure–fluid interaction to address whether real spermatozoa exhibit hydrodynamically efficient swimming. The evolutional optimization approach used in this study has distinguished biologically important parameters, and the methodology can potentially be applicable to various swimmers.

基于支持向量机的单端行波故障测距方法

单端辐射状配电网发生单相接地故障时，单端行波法故障测距的难点在于第二个到达测量点的故障行波波头的正确辨识。针对上述难点，本文提出了一种基于支持向量机的单端行波故障测距方法。首先，利用支持向量机正确地识别出故障段，然后根据行波传播的网格图确定第二个到达测量点的故障行波波头是来自于故障点还是来自于对端母线。通过相模变换消除电磁耦合的影响，通过对小波变换相关知识的研究，选择最优小波基进行小波变换，对故障行波波头进行识别，检测故障行波波头模极大值对应的时刻，进而利用相应波头到达测量点的时间差结合波速实现故障点的精确测距。 When single-phase-to-earth fault occurred in radial distribution network supplied by single power, the key problem of the single-ended traveling wave fault location lies in the correct recognition of the second travelling wave head to reach the measuring point. In view of the above problem, this paper introduces single terminal traveling wave fault location method based on SVM. After identifying the fault section by the SVM, the second traveling wave head coming from the fault point or bus at opposite terminal is recognized based on lattice diagram of traveling waves. Elec-tromagnetic coupling effect is eliminated by phase mode transformation. Through the study of relevant knowledge of wavelet transform, the optimal wavelet base is selected for wavelet trans-form in order to identify the fault traveling wave head. The time corresponding to fault traveling wave modulus maximum is detected and time difference of arrival and velocity of the corre-sponding wave head is used to achieve fault location.

海底电缆–架空线B型混合线路行波故障测距新方法

分析了海底电缆–架空线混合线路发生故障以后行波的传播特性，并提出了一种针对海底电缆–架空线B型混合输电线路的行波测距方法。首先把原有的B型三段混合输电线路分解组合成两段A型混合输电线路，先利用每段A型混合线路两端监测装置监测到的故障初始行波浪涌到达监测点的时间差与整定时间进行比较，对故障区段初步判断，依据监测点接收行波的时间再根据单端原理得出准确的测距结果。此方法不但可以消除单端测距方法故障区段判别中对第二个波头性质的识别的难题，并且可消除双端测距方法计算故障距离时两端间不能精确同步和线路长度对测距结果的影响。PSCAD仿真实验表明，本文所提出的关于海底电缆–架空线混合输电线路故障行波测距方法是可靠的，且测距精度得到了有效提高。 After analyzing the propagation characteristics of the traveling wave after the failure of the sub-marine cable-overhead line hybrid line, a fault location method through traveling wave for the hybrid transmission line is proposed. First, the original B type hybrid transmission line is decom-posed into two hybrid transmission lines of type A. Then the time difference between the two monitoring device located in the endpoints of each A type hybrid line is used to make a preliminary judgment of the fault section. Finally an accurate fault location result is made according to the principle of single-end method. This method eliminates the difficult problem of the identification of the second wave heads in the single-end fault location method, and it also eliminates the influence of the out-sync of time and the influence of the line length which is given of the two double-end fault location method. PSCAD simulation experiments show that the presented the Fault Location Method through Traveling Wave for the Submarine Cable-Overhead Line Hybrid Line is reliable, and the accuracy of fault location has been effectively improved.

Untangling the Effect of Head Acceleration on Brain Responses to Blast Waves.

Multiple injury-causing mechanisms, such as wave propagation, skull flexure, cavitation, and head acceleration, have been proposed to explain blast-induced traumatic brain injury (bTBI). An accurate, quantitative description of the individual contribution of each of these mechanisms may be necessary to develop preventive strategies against bTBI. However, to date, despite numerous experimental and computational studies of bTBI, this question remains elusive. In this study, using a two-dimensional (2D) rat head model, we quantified the contribution of head acceleration to the biomechanical response of brain tissues when exposed to blast waves in a shock tube. We compared brain pressure at the coup, middle, and contre-coup regions between a 2D rat head model capable of simulating all mechanisms (i.e., the all-effects model) and an acceleration-only model. From our simulations, we determined that head acceleration contributed 36-45% of the maximum brain pressure at the coup region, had a negligible effect on the pressure at the middle region, and was responsible for the low pressure at the contre-coup region. Our findings also demonstrate that the current practice of measuring rat brain pressures close to the center of the brain would record only two-thirds of the maximum pressure observed at the coup region. Therefore, to accurately capture the effects of acceleration in experiments, we recommend placing a pressure sensor near the coup region, especially when investigating the acceleration mechanism using different experimental setups.

Study on Traveling Wave Signal Anti-Interference and a New Detection Method

Traveling wave in transit, wave head is easy to produce distortion and affected by environmental interference, so accurately measuring the head of traveling wave singularity occurrence time become extremely difficult. The key to improve the precision of traveling wave detection is to accurately capture the happening time of wave head of singular points. Recently, traveling wave singularity detection usually use wavelet, EMD-HHT transform technique, but both have mixing phenomenon, affecting the accuracy of detection. In this paper, we propose a new method that use Duffing chaotic oscillator to suppress traveling wave interference signal. By Matlab simulation and it is proved that this method can effectively suppress noise singular point. Meanwhile, we propose an anti-mixing EEMD-HHT wave head detection technology. Through simulation experiment and field test, it is proved that, compared with EMD, EEMD can more accurately identify the traveling wave arrival time, detection accuracy increasing by 1.52%.

Ultra-High-Speed Travelling Wave Protection of Transmission Line Using Polarity Comparison Principle Based on Empirical Mode Decomposition

The traditional polarity comparison based travelling wave protection, using the initial wave information, is affected by initial fault angle, bus structure, and external fault. And the relationship between the magnitude and polarity of travelling wave is ignored. Because of the protection tripping and malfunction, the further application of this protection principle is affected. Therefore, this paper presents an ultra-high-speed travelling wave protection using integral based polarity comparison principle. After empirical mode decomposition of the original travelling wave, the first-order intrinsic mode function is used as protection object. Based on the relationship between the magnitude and polarity of travelling wave, this paper demonstrates the feasibility of using travelling wave magnitude which contains polar information as direction criterion. And the paper integrates the direction criterion in a period after fault to avoid wave head detection failure. Through PSCAD simulation with the typical 500 kV transmission system, the reliability and sensitivity of travelling wave protection were verified under different factors’ affection.

Application of Spectrum-Subtracted Sub-band Singular Spectrum Entropy in Sediment Thickness Measurement

Obtaining the wave head location and acoustic time difference with high accuracy in measuring sediment thickness in borehole by ultrasonic is a key and hard problem. The methods available now can’t meet the precision and noise immunity requirement. This paper utilizes the good performance of Spectrum-Subtracted sub-Band Singular Spectrum Entropy (SSB-SSE) to process the echoes reflected from the sediment and get their wave head positions. Based on these obtained data, acoustic time difference can be calculated, then the sediment thickness can be achieved. The results of three typical experiments show that SSB-SSE is very suitable in locating the wave heads of thicker sediment layer’s echoes, and it also performs well even when the echo is covered by noise.

A Single-End Method for Fault Section Estimation in Distribution Network Using Wavelets

The paper presents a method for identify fault section in distribution network, which uses the traveling wave data recorded at the substation only. After modal transformation, the aerial mode component is in stable velocity and low attenuation and utilized in the method. Compared to the first wave head, subsequent wave heads of aerial mode component have some particular characteristics with time delay and wavelet transform modulus maxima (WTMM) ratio. The number of characteristic wave heads (CWHs) which are judged by characteristic time delays (CTDs) is the criteria to identify the fault section. The simulation results verify that the method has high accuracy.

A novel method to locate a fault of transmission lines by shielding failure

Lightning flashes on high voltage transmission lines are quite common and often lead to insulation breakdown which can cause outages in supply. The traditional way to locate the lightning fault on the line artificially is time-consuming. An accurate lightning location will result in faster maintenance and restoration of supply. In this paper, a novel distributed lightning fault location method for transmission line mainly for the shielding failure is proposed based on the non-contact lightning current monitoring system. First of all, according to the transient current wave polarity differences of three phases, the types of lightning are recognized, such as shielding failure, lightning striking the tower and striking the ground wire. Secondly, for the shielding failure, whether the flashover occurs or not is judged based on the time-window energy ratio of the traveling wave. Thirdly, the lightning striking range in which interval of the line is determined by comparing the signals from all the detection points. Furthermore, the sides of lightning and flashover are distinguished. At last, combing the travelling wave method and wavelet packet transform (WPT), the arrival time of wave head is extracted. The specific locations of lightning and flashover are both calculated by using the signals from the two nearest detection points. By using EMTP-ATP software, a model of lightning striking at different points on a 110 kV transmission line with five detection points is established. The simulation results indicate that the proposed scheme is very effective in locating the lightning on the transmission line with reasonable accuracy, which has important application value.

A Fault Location Method for HVDC Transmission Lines

A fault location method for HVDC (High Voltage Direct Current) transmission lines is proposed in this paper, using voltages and currents measured at two terminals of dc lines in time domain. Fault traveling waves propagate from the fault point to both terminals along the faulted line. The position that the traveling wave head arrives at some moment after the fault can be used to calculate the fault location. To determine the arrival positions of traveling wave head at each time indirectly, propagation characteristic curves of traveling wave heads at local and the remote terminals are calculated with distribution currents using the stationary wavelet transform. The accuracy of fault location will not be affected by transition resistance and fault position. Simulation results show that the presented fault location method can achieve quick and accurate fault location on the whole line under probable operation modes of a bipolar HVDC transmission system.

Travelling Wave Fault Location for Distribute Cable Network Based on Distributed Measurement

This template carries out a three-terminal accurate fault location method for distribute cable network. It is improved from type D principle fault location method. Radial distribution network is decomposed into T-type networks. A set of formulas based on three-terminal data can calculate fault distance and find fault branch. Only first transient wave heads is needed. Shorter transmission distance makes it more accurate to extract first wave heads with wavelet. The distributed measurement offers redundant transient voltage data. These data is fully used to improve location success rate and accuracy. The simulation result in ATP-EMTP shows that the location accuracy isnt influenced by wave speed, catadioptric wave, grounding resistance and initial fault phase angle.

Feasibility Study on the Fault Line Selection Method Based on Overall Trend of Zero Sequence Current

Two results were obtained by analysing electromagnetism transition condition: firstly, when the initial phase angle of fault is larger, the characteristic of travelling wave is obvious, and the polarity of the first travelling wave head is consistent with the overall trend of zero sequence current in preliminary stage; secondly, when the initial phase angle of fault is smaller, the characteristic of travelling wave is not obvious, but the fault lines and perfect lines can be recognized through the direction of decaying direct current component in zero sequence current, and the direction of decaying direct current component is consistent with the overall trend of zero sequence current in preliminary stage. Research suggests that it is feasible to make the overall trend of zero sequence current in preliminary stage as characteristic for line selection.

Numerical Simulations for the Prediction of Wave Forces on Underwater Vehicle using 3D Panel Method Code

This study describes a method useful for predicting the hydrodynamic forces on fully appended underwater vehicle when operating beneath the free surface waves. The hydrodynamic forces acting on the underwater vehicle due to waves are sum of the incident wave force, diffraction force and radiation forces. Ansys AQWA which is based on Panel Method is selected to compute wave forces both in frequency domain and time domain. Series of numerical simulations are performed considering the 2nd order Stokes wave theory and head seas conditions. The water depth is assumed infinite hence the interference effect on vertical boundaries and horizontal bottom can be neglected. The simulation procedure requires generating panels on the vehicle's surface, defining the mass properties and providing the desired the sea wave condition. In frequency domain analyses, wave forces and moments are determined at different submergence depths and wave frequencies. These analyses reveal that magnitude of surge force, heave force and pitch moment are the most dominant as compared to other forces and moments. Numerical results in the time domain are also collected in order to investigate the effect of various factors such as wave amplitude, frequency, vehicle depth, orientation, etc., on these forces and moment. The results are then used to derive analytical formulations for wave forces and moment by curve fitting approach. The accuracy of the formulations is ensured by verifying the results with real time simulations using two test conditions in which the different values of parameters are selected. The proposed method brings great convenience to assess the maneuverability characteristics of underwater vehicles operating near sea waves.

Role of helmet in the mechanics of shock wave propagation under blast loading conditions

The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurisation and impulse experienced by the head were examined. The shock wave–head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head–helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.