Initial transient process in a simple helical flux compression generator

An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current density in the stator, is developed by means of a diffusion equation. A relationship between frequency of the conducting current, root of the characteristic function of Bessel equation and decay time in the armature is given. The skin depth in the helical stator is calculated and is compared with the approximate one which is widely used in the calculation of magnetic diffusion. Our analytical results are helpful to understanding the mechanism of the loss of magnetic flux in both the armature and stator and to suggesting an optimal design for improving performance of the helical flux compression generator.

Experimental study on propagation characteristics of rotating detonation wave with kerosene fuel-rich gas

In this study, kerosene fuel-rich gas produced by the combustion in the gas generator was used as the fuel and oxygen-rich air was used as the oxidant to investigate the propagation characteristics of the rotating detonation wave (RDW). The initiation of the kerosene fuel-rich gas and propagation process of the RDW were analyzed. The influences of the oxygen content in the oxidizer, kerosene mass flow rate of the gas generator, and temperature of the kerosene fuel-rich gas on the propagation process of the RDW were studied. The experimental results revealed that the propagation velocity of the RDW could be improved by increasing the three parameters mentioned above with the kerosene mass flow rate as the strongest factor. The minimum oxygen content that could successfully initiate and maintain the stable propagation of the RDW was 32%, achieving the RDW velocity of 1141.9 m/s. The RDW mainly propagated as two-counter rotating waves and a single wave when the equivalent ratios were 0.62–0.79 and 0.85–0.87, respectively. The highest RDW velocity of 1637.2 m/s was obtained when the kerosene mass flow rate, oxygen content, and equivalent ratio were 74.6 g/s, 44%, and 0.87, respectively.

Experimental analysis for the dynamic initiation mechanism of debris flows

Debris flow is one of the major secondary mountain hazards following the earthquake. This study explores the dynamic initiation mechanism of debris flows based on the strength reduction of soils through static and dynamic triaxial tests. A series of static and dynamic triaxial tests were conducted on samples in the lab. The samples were prepared according to different grain size distribution, degree of saturation and earthquake magnitudes. The relations of dynamic shear strength, degree of saturation, and number of cycles are summarized through analyzing experimental results. The findings show that the gravelly soil with a wide and continuous gradation has a critical degree of saturation of approximately 87%, above which debris flows will be triggered by rainfall, while the debris flow will be triggered at a critical degree of saturation of about 73% under the effect of rainfall and earthquake(M>6.5). Debris flow initiation is developed in the humidification process, and the earthquake provides energy for triggering debris flows. Debris flows are more likely to be triggered at the relatively low saturation under dynamic loading than under static loading. The resistance of debris flow triggering relies more on internal frication angle than soil cohesion under the effect of rainfall and earthquake. The conclusions provide an experimental analysis method for dynamic initiation mechanism of debris flows.

Initiation and Kinematic Process of Debris Flow with the Existence of Terraced Fields at the Sources

A debris flow,with terraced fields as the source area,broke out on June 25th,2018 in the Xiaotuga area of Yunnan Province,China,and this kind of debris flow is rarely recorded.Two purposes in this study:(1)the influence of flow drag force on slope stability;(2)back-analyze the movement process of debris flow.First,the geological background and movement of this debris flow were described based on a field investigation.Then,drag force,calculated by the laminar flow theory,is added to the slope stability calculation model,which elaborates the initiation process of this disaster.Moreover,dynamic simulation software(DAN3D)was used to simulate the kinematic process of the debris flow with a variety of combination models.The study shows that the terrace area can quickly produce surface runoff and create a drag force under rainfall conditions,which is the essential reason for the initiation of debris flow.In addition,the use of the FVV(Frictional-Voellmy-Voellmy)model is found to provide the best performance in simulating this type of debris flow,which reveals that it lasts approximately 200 s and that the maximum velocity is 12 m/s.

Initial Rifting Process and Dynamics Mechanism of Huaguang Sag: Evidence from a Numerical Modeling Method

Huaguang Sag is located in the deep seawater area of Qiongdongnan Basin, and its tectonic position belongs to the intersection of NE-trending, SN-trending and NW-trending tectonic systems in the continental margin of the Northwest South China Sea. To investigate the initial rifting process and further more the dynamics mechanism of Huaguang Sag, this paper sets up the structure model of basement which mainly makes up with several depression-controlling faults, and simulates the initial rifting process of Huaguang Sag by the FLAC software. The simulation results show that only affected by the S-N trending extensional stress, the rifting center appears in northern boundary basement faults（two NEE-trending and NWW-trending faults） of Huaguang Sag while does not take place at the NNE-trending and NE-trending basement fault zone in the middle sag, and doesn’t match the current pattern that the basement fault plays a main role in controlling the sediment. In the other case, affected by the S-N trending and E-W trending extensional stress at the same time, the areas of the northern boundary faults zone and internal NNE-trending basement faults zone come to be rifting center quickly, the sedimentary is controlled by the main basement faults to different degrees, and is consistent with the tectonic-sedimentary framework of Huaguang Sag which obtained by the data of geophysical interpretation. In combination with the analysis of regional tectonic background, the paper proposes that two remote tectonic effects occurred by the collision of India-Eurasian Plate： One remote effect was the rotational extrusion of Indo China Block, which led to form a series of NE-trending and NNE-trending basement faults, as well as the E-W trending tensile stress field in Huaguang Sag. The other remote effect was that the deep mantle material of South China Block flowed southward, which resulted in the S-N trending extensional rifting of the lithosphere in northern South China Sea, and finally formed a series of EW-trending and NEE-trending basement faults and the S-N trending tensile stress field in Huaguang Sag. Affected by the above tensile stress fields and the basement faults, the initial rifting occurred in E-W and nearly S-N directions along the pre-existed basement faults（the weak structural zones） in Huaguang Sag.

Eventual Leader Election with Weak Assumptions on Initial Knowledge,Communication Reliability,and Synchrony

This paper considers the eventual leader election problem in asynchronous message-passing systems where an arbitrary number t of processes can crash（t〈n,where n is the total number of processes）.It considers weak assumptions both on the initial knowledge of the processes and on the network behavior.More precisely,initially,a process knows only its identity and the fact that the process identities are different and totally ordered（it knows neither n nor t）.Two eventual leader election protocols and a lower bound are presented.The first protocol assumes that a process also knows a lower bound α on the number of processes that do not crash.This protocol requires the following behavioral properties from the underlying network：the graph made up of the correct processes and fair lossy links is strongly connected,and there is a correct process connected to（n〈f）-α other correct processes（where f is the actual number of crashes in the considered run） through eventually timely paths（paths made up of correct processes and eventually timely links）.This protocol is not communication-efficient in the sense that each correct process has to send messages forever.The second protocol is communication-efficient：after some time,only the final common leader has to send messages forever.This protocol does not require the processes to know α,but requires stronger properties from the underlying network：each pair of correct processes has to be connected by fair lossy links（one in each direction）,and there is a correct process whose n〈f-1 output links to the rest of correct processes have to be eventually timely.A matching lower bound result shows that any eventual leader election protocol must have runs with this number of eventually timely links,even if all processes know all the processes identities.In addition to being communication-efficient,the second protocol has another noteworthy efficiency property,namely,be the run finite or infinite,all the local variables and message fields have a finite domain in the run.

Opportunities and challenges of the Sponge City construction related to urban water issues in China

Waterlogging is one of the major water issues in most cities of China and directly restricts their urbanization processes.The construction of Sponge City is an effective approach to solving the urban water issues,particularly for the waterlogging.In this study,both the urban issues emerged at the stage of rapid urbanization in China and the demands as well as problems of Sponge City construction related with the water issues were investigated,and the opportunities and challenges for the Sponge City construction in the future were also proposed.It was found that the current stormwater management focused on the construction of gray infrastructures(e.g.,drainage network and water tank) based on the fast discharge idea,which was costly and hard to catch up with the rapid expansion of city and its impervious surface,while green infrastructures(e.g.,river,lake and wetland)were ignored.Moreover,the current construction of Sponge City was still limited to low impacted development(LID) approach which was concentrated on source control measures without consideration of the critical functions of surrounding landscapes(i.e.,mountain,river,wetland,forest,farmland and lake),while application of the integrated urban water system approach and its supported technologies including municipal engineering,urban hydrology,environmental science,social science and ecoscape were relatively weak and needed to be improved.Besides,the lack of special Sponge City plan and demonstration area was also a considerable problem.In this paper,some perspectives on Good Sponge City Construction were proposed such as the point that idea of urban plan and construction should conform to the integral and systematic view of sustainable urban development.Therefore,both the basic theoretical research and the basic infrastructure construction such as monitoring system,drainage facility and demonstration area should be strengthened,meanwhile,the reformation and innovation in the urban water management system and the education system should also be urgently performed.The study was expected to provide a deeper thinking for the current Sponge City construction in China and to give some of suggestions for the future directions to urban plan and construction,as well as urban hydrology discipline.