Kaipei Liu

Multiobjective Optimization of Multistage Synchronous Induction Coilgun Based on NSGA-II

The structure and trigger control strategy have become the most important factors that restrict the performance of the multistage synchronous induction coilgun (MSSICG). However, it is still a difficult task to design MSSICG under overload constraint due to coupling between the multiple parameters. In this paper, the maximization of the emission efficiency and acceleration stationarity is treated as a multiobjective optimization problem. By analyzing the relationship between the number of turns and the other structural parameters of the launch, the multiobjective optimization model of MSSICG is established by the current filament method which was verified by the experimental data and finite-element method. And then the second generation nondominated sorting genetic algorithm (NSGA-II) and multiobjective particle swarm optimization (MOPSO) were employed to optimize the model in order to maximize the energy transfer efficiency while achieving the smooth acceleration of the armature. With the formulated optimization model, a five-stage synchronous induction coilgun is optimized as a special case. A decision-making procedure based on the fuzzy membership function is used for obtaining best compromise solution from the set of Pareto-solutions obtained through NSGA-II and MOPSO. In addition, the optimization performance of the proposed multiobjective optimization model and the single-objective optimization model of the MSSICG was compared. The result of optimization shows that the proposed multiobjective optimization model of MSSICG can effectively improve the performance of the coilgun compared with the single-objective optimization model which takes of the launch velocity and overload acceleration as the combination objective function or only the launch velocity.

Multi-factor optimization of railgun using orthogonal test approach and field-circuit method

Today the energy storage systems are still encumbering, therefore it is useful to think about the optimization of a railgun system in order to achieve the best performance with the lowest energy input. In this paper, an optimal design method considering 6 parameters is proposed to improve the energy conversion efficiency of a simple railgun. In order to avoid costly trials, the field-circuit method is employed to analyze the operations of different structural railguns with different parameters respectively. And the orthogonal test approach is used to guide the simulation for choosing the better parameter combinations, as well reduce the calculation cost. The research shows that the proposed method gives a better result in the energy efficiency of the system.

Research on electromagnetic performance affected by shielding enclosure of a coil launcher

Shielding enclosure is very important to designer in a coil launcher system, which directly determines the electromagnetic performance of the coil launcher. The formulation of eddy current field involving movement is deduced, and the time step transient finite element method (FEM) calculation theory is illustrated in the paper. The simulation model of a three stage coaxial induction coil launcher is built based on ANSOFT MAWELL software. In the transient simulation model involved in moving conductor eddy current, the power pulse generator and the power electronic component are modeled as circuit simulation in MAXWELL schematic module. The circuit model is well coupled with field model in transient solver. In every time step, the current values which are obtained in circuit simulation are loaded in field model as exciting source to the coils. Three typical shielding materials, such as, iron, steel and ferrite is set in 2D field model to study the influence of shielding enclosure on the electromagnetic performance of the coil launcher. Silicon steel (laminated sheets) is taken in 3D field model. Different geometric dimensions of shielding enclosure are also taken into consideration. The speed of the armature and the magnetic field are calculated during every calculation case. The current distribution in armature and shielding enclosing are displayed as well. The laws of shielding enclosure on the electromagnetic performance are concluded. A ferrite shielding enclosure will increase the speed of armature obviously. The conductive material will induce eddy currents and decrease the leakage magnetic field outside, that shows excellent shielding performance. A silicon steel shielding enclosure has the similar impact on the speed of the armature to the ferrite, but has better shielding effectiveness than the latter. Research results shows that the silicon steel is suitable for the coil launch shielding enclosure.

Research of Varying Frequency Driving Scheme for Asynchronous Induction Coil Launcher

There are few of transient control models are adapted to asynchronous induction coil launcher (AICL) with air core coil. Thus, many papers about AICL were written with the goal of increasing muzzle velocity of projectile. This paper concentrate on how to control the projectile speed and thrust accurately by using improved current filament (CF) method and variable voltage variable frequency (VVVF) scheme. The improved CF method contains mathematical model of three-phase inverter based on switch function, including conventional two level converter and cascaded multilevel converter models. The whole launch process is programmed with MATLAB. Simulation results show that this scheme have a smoother thrust fluctuation on projectile than other driving models. The motor parameters are changing with the temperature and frequency in launching process. Hence, the constant voltage frequency ratio (V/f) in this paper is more simple and reliable than vector control. To verify the control model and simulation results, a nine stages coil launcher prototype is constructed. The measured force and muzzle velocity are basically consistent with simulation results. It is proved that the improved CF method and VVVF strategy is feasible, and it is characterized by its small calculating amount that make it a valuable tool for design of AICL. The simple and excellent control of the thrust during launch process avoids load peaks, which means that the payload is handled more carefully compared to the classical launchers.

Nonlinear scaling study of a railgun

Scaling method has been used widely in railgun technology. But nonlinear problem is seldom studied because of the complexity and uncertainty. In order to employ the scaling method better, the paper brings the nonlinear drag model to the solid armature railgun circuit. Several drag functions were compared including drag model associated with velocity (VDM), drag model associated with current (CDM), and drag force associated with integrated factors (IDM). Scaling relationships of these drag models were discussed. And then, a novel experiment was constructed to compare the drag models at low velocity. Further simulations at high velocity are also studied. At last, the nonlinear scaling method was verified by an example at high velocity. It shows that VDM is far from satisfactory at high velocity. The scaling conditions of VDM are too strict to use in practice. CDM is workable only in high velocity condition which satisfies conditions of linear scaling method (LSM) in nature. But it is worthless when the velocity is less than about 0.5 km/s. Although a bit complex, IDM is very accurate at any condition. Coefficient α in IDM should be taken considering different test conditions. Scaling relationships of IDM could not be derived at low velocity due to nonlinearity. While at high velocity, IDM could be simplified to CDM and realize LSM. Further research indicates that IDM could use the scaling method directly and realize approximate LSM at high velocity. Due to the work range of the solid armature is usually 1~2km/s, nonlinear scaling method could be used in a railgun with IDM. What should be noted is that the velocity scaling factor must be controlled above about one quarter to avoid the nonlinear field. A detailed analysis of the experiments and simulations will be presented in this paper.

Effect of geometry change on solid C shaped armature

Armature takes an important role in the electromagnetic launch process. High current densities in the armature can result in high local temperature and consequent loss of strength and even melting and erosion. Conventional C-shaped armature is widely used which experiences high current densities in three areas: the leading edge, the trailing edge, and the throat. It is argued that if the armature shape is modified to better align with the magnetic field, the current density distribution could be more uniform. This paper tries to analyze the effect of the geometry change on C-shaped armature at low velocity. The geometry of the armature was changed to improve the current density and temperature distribution and reduce the erosion. Four variants of C-shaped armatures were designed to study the specific features, including a conventional C-shaped armature (CCA), a rounded leading edge C-shaped armature (LCA), a rounded trailing edge C-shaped armature (TCA), and a rounded incorporate edge C-shaped armature (ICA). A novel low-speed experiment was constructed and tested. The armatures were eroded and recovered to compare the improved effect. Then finite element simulations according to the experiments were taken to analyze the further results. It is proved that the curved edge of the armature could reduce the nonuniformity of current density and temperature distribution greatly. LCA and ICA showed less erosion on the contact surface due to the rounded leading edge. The trailing edge could improve the uniform of the current on the interface. ICA is the best choice of the four armatures which combines the effect of LCA and TCA. Erosion and transition mechanism were analyzed at last. A detailed description of the experiments and simulations will be presented in this paper.

Driving circuit research of a coil launcher

A coaxial induction coil launcher is a hot topic in the electromagnetic launch (EML) field. Power supply is crucial equipment which determines whether induction coil launcher could be used or not. Configuration of the driving circuit influences the efficiency of the coil launcher directly. But which driving circuit is the best puzzled a lot of people. This paper gives a detailed analysis of the properties of the driving circuit construction based on the capacitor source. Three topologies of the driving circuit are compared including oscillation circuit, crowbar circuit and half-wave circuit. It is proved that which circuit has the better efficiency depends on the detailed parameters of the experiment, especially the crowbar resistance. Crowbar resistor regulates not only efficiency of the system, but also temperature rise of the coil. Electromagnetic force (EMF) applied on the armature will be another question which influence service condition of the driving circuits. Oscillation circuit and crowbar circuit should apply to the asynchronous induction coil launcher and synchronous induction coil launcher, respectively. Half-wave circuit is seldom used in the experiment. Although efficiency of the half-wave circuit is very high, speed of the armature is very low. A simple independent half-wave circuit is suggested in this paper. Generally speaking, the comprehensive properties of crowbar circuit is the most excellent in the three typical circuit. Conclusions of the paper could provide guidelines for practice. A detailed analysis will be presented in this paper.