Typical Current Profiles Research Articles

Application of the monitoring and early warning system for internal solitary waves: Take the second natural gas hydrates production test in the South China Sea as an example

Internal solitary waves (ISWs) contain great energy and have the characteristics of emergency and concealment. To avoid their damage to offshore engineering, a new generation of monitoring and early warning system for ISWs was developed using technologies of double buoys monitoring, intelligent real-time data transmission, and automatic software identification. The system was applied to the second natural gas hydrates (NGHs) production test in the Shenhu Area, South China Sea (SCS) and successfully provided the early warning of ISWs for 173 days (from October 2019 to April 2020). The abrupt changes in the thrust force of the drilling platform under the attack of ISWs were consistent with the early warning information, proving the reliability of this system. A total of 93 ISWs were detected around the drilling platform. Most of them occurred during the spring tides in October–December 2019 and April 2020, while few of them occurred in winter. As suggested by the theoretical model, the full-depth structure of ISWs was a typical current profile of mode-1, and the velocities of wave-induced currents can reach 80 cm/s and 30 cm/s, respectively, in the upper ocean and near the seabed. The ISWs may be primarily generated from the interactions between the topography and semidiurnal tides in the Luzon Strait, and then propagate westward to the drilling platform. This study could serve as an important reference for the early warning of ISWs for offshore engineering construction in the future.©2023 China Geology Editorial Office.

Modeling and experimental validation of a Hybridized Energy Storage System for automotive applications

This paper presents the development and experimental validation of a dynamic model of a Hybridized Energy Storage System (HESS) consisting of a parallel connection of a lead acid (PbA) battery and double layer capacitors (DLCs), for automotive applications. The dynamic modeling of both the PbA battery and the DLC has been tackled via the equivalent electric circuit based approach. Experimental tests are designed for identification purposes. Parameters of the PbA battery model are identified as a function of state of charge and current direction, whereas parameters of the DLC model are identified for different temperatures. A physical HESS has been assembled at the Center for Automotive Research The Ohio State University and used as a test-bench to validate the model against a typical current profile generated for Start&Stop applications. The HESS model is then integrated into a vehicle simulator to assess the effects of the battery hybridization on the vehicle fuel economy and mitigation of the battery stress.

Predicting Fusing Current for Encapsulated Wire Bonds under Transient Loads

For high power IC chips, as device size inevitably decreases, the wire diameter unfortunately must decrease due to the need of finer pitch wires. Fusing or melting of wirebonds thus increasingly becomes one of the potential failure issues for such IC's. Experiments were performed under transient loads on dummy packages having aluminum, gold, or copper wires of different dimensions. A finite element model was constructed that correlates very well with the observed maximum operating currents for such wirebonds under actual experimental test conditions. A qualitative observation of typical current profiles, as fusing conditions were approached, was that current would reach a maximum value very early in the pulse, and then fall gradually. One goal achieved through the modeling was to show that the current in the wire falls with time due to the heating of the wire material. Correspondingly, the wire reaches the melting temperature not at the peak current but rather at the end of pulse. Further, modeling shows that knowledge of external resistance and inductance of the experimental set up are highly significant in determining the details of a fusing event, but if known along with the temperature-dependent wire properties, the simulation can predict the correct voltage and current response of the part with 2% error. On the other hand, lack of external circuit characteristics may lead to completely incorrect results. For instance, the assumption that current is constant until the wire heats to fusing temperature, or that current and temperature both rise monotonically to maximum values until the wire fuses, are almost certain to be wrong. The work has been carried out for single pulse events as well as pulse trains.

Analysis of the effects of induced fields from sliding electrical contacts

Sliding electrical contact surfaces are encountered in many applications, including current-collection brushes in generators, armatures sliding between rails, and circuit breakers. The speeds of relative motion between the two contact surfaces vary according to application; in the first two, speeds on the order of 1 km/s are not uncommon. Prediction of speed and the effects of fields on speed have traditionally been made using finite element codes. Here, an alternative semianalytic method is investigated. A rectangular armature sliding between a pair of rails is studied, with a typical current profile based on published data as input for the problem. A model analytical field consistent with the total current input is used. Forces and speeds are computed, and the effects of induced fields due to motion on the speed and the current are analyzed and compared to typical experimental data.

Relaxed states for Ohmically driven tokamaks with an arbitrary aspect ratio

The relaxed state of plasma in Ohmically driven tokamaks with an arbitrary aspect ratio is explored using the principle of minimum dissipation rate subject to the helicity and the energy balance. The resulting Euler–Lagrange equations are solved analytically and numerically. The self-consistent solutions of whole Euler–Lagrange equations as well as both helicity and energy balance equations are obtained numerically for the given parameters and boundary conditions. It is found that for low and general aspect ratio tokamaks, there exist different typical minimum dissipation states, corresponding respectively to different typical current profiles observed in experiments. It is also found that there exist different types of relaxed states in the different regions of the parameter space for a selected device. Each current profile mode is achieved by adjusting controllable parameters such as plasma resistivity, boundary toroidal magnetic field or boundary electric field. The results show that there exists a key parameter E0/ηB0 in determining the final relaxed states. The typical minimum dissipation state may evolve to other forms of states abruptly by increasing E0/ηB0 to be above a critical value. Three forms of current profile are presented for the low aspect ratio National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)]. The first form peaks in the edge of the high field side similar to the typical experimental form. The second peaks in the central region on the equatorial plane. The third may have a hole or reverse in the central region. Both the second and third states could be obtained by increasing E0/ηB0 to be above the critical value.

Analysis of plasma current profile driven by coaxial helicity injection in a low aspect ratio tokamak

The plasma current profile driven by coaxial direct current helicity injection in a low aspect ratio toroidal configuration is investigated by applying the principle of minimum energy dissipation rate. It is shown that current profile modes are mainly determined by the Lagrange multiplier β. Some critical values βc are found. Different current profiles are obtained in different β ranges. Three typical current profiles are presented. The key features of the first case with β< 7.1 agree well with current experiments. Larger driven plasma current and the typical current profiles of normal tokamaks can be obtained in the region of β from 7.1 to 9.65. There exist reversals of both jφ and Bφ in the central part of the plasma when β becomes higher than βc ≈ 9.65. For a selected geometry the values of βc depend weakly on other parameters. The different β values and corresponding current profiles can be achieved by adjusting certain parameters. There exist critical values of plasma temperature, bias voltage and vacuum toroidal magnetic field that induce the transformation of the current profile mode. The profile of λ = μ0jφ/Bφ is non-uniform in the plasma and a larger deviation from force free states appears when β becomes higher.

Effect of current variation on the dynamics of railgun plasma armatures

The effect of current variations on the behavior of railgun plasma armatures is investigated with a one‐dimensional, time‐dependent model. Three typical current profiles are considered: two inductive profiles, one with a time constant of 0.5 msec and the other with a time constant of 2.0 msec, and a capacitive profile. All three calculations are for an armature in a 5 cm square‐bore railgun. It is observed that current variations create oscillations in the armature length, projectile acceleration, and projectile jerk. In addition, the current profile significantly affects the axial distribution of the plasma velocity, current density, and total pressure. The significance of these transients on the design of projectiles and the interpretation of diagnostic data is discussed, and suggestions for future calculations are outlined.