Liquid-level control in tanks is widely used in various industrial sectors. Due to problems arising from the case that the liquid level is above or below the recommended, the process of its control is of great significance. The proportional integral differential (PID) controller is one of the most widely used controllers in applications that require accuracy and optimal automatic control. In this paper, single and coupled ship fuel tank systems are discussed. In addition, mathematical models and their linearization using two different approaches are presented. The two control approaches are used to maintain the specified liquid level in tanks. The first is based on the design of standard PID controllers, with the application of the Ziegler–Nichols, Takahashi tuning, and Auto-tuning methods. The second approach, proposed by the authors, is based on the application of the Dahlin algorithm. The simple modification of the Dahlin controller, which can avoid the “ringing” of the control signal, is suggested in the paper. Moreover, the lower limit of the decrease in the desired time constant, which ensures the desired behavior of the system, is determined. The comparisons provided for different performance indexes show the advantages of the modified Dahlin algorithm approach compared to the standard PID controllers. Furthermore, the comparison with the literature-known approaches is realized.

The chosen electrical equipment, i.e., the earthing switch has its application in marine switchgear. In this paper, the reduction of dimensions is considered with the purpose of making it more energy efficient in terms of onboard application. This test validates that the earthing switch as an electromechanical device is capable of withstanding electrodynamic forces. Two approaches are applied and compared. Both approaches are based on a simplified three-dimensional (3D) model of the earthing switch. The first approach is analytical: the electrodynamic forces are calculated with the assumption that currents flow in concentrated lines. Maximum static stress is compared to the yield point of the earthing knife material. The second approach applies the finite element method in the time domain. The results show that the rectangular cross-section can withstand the electrodynamic forces produced by the given currents. Simple cost analysis shows how much material is saved by changing the design from standard earthing knifes with C channel profile to the rectangular profile. Material savings make this study interesting for marine switchgear application. The paper shows qualitative influence of the obtained results on the Energy Efficiency Design Index of the ships.

The present paper deals with the proximity effect in a system consisting of a thin tubular conductor and a filament. The integral equation for the current density in the tubular conductor is solved by assuming a solution in the form of an infinite Fourier series. By using this solution the a.c. to d.c. resistance ratio for the tubular conductor is also found in a closed form.

Induction machines (IMs) are crucial to driving auxiliary machinery and devices of ships, such as pumps, fans, winches, and elevators, which are essential for maintaining the operational functions of a ship and are characterised by various types of loads. This is of critical importance because high surges of starting current can cause instabilities and fluctuations in a ship’s power system, directly affecting the safety and efficiency of ship operations. This paper provides a comprehensive review of analytical expressions for modelling the start-up time of directly started IMs under different ship operational conditions (no-load, linear load, fan load, and gravitational load). Validation of the analytical models was performed by comparing the speed-time characteristics obtained from the experimental measurements with the corresponding ones obtained by simulations in a MATLAB Simulink environment. The observed 1.5 kW IM reached a steady state for 0.1356 seconds when driving the load with a fan characteristic. However, when subjected to linear and gravitational loads, the IM requires longer times to reach a steady state - 0.1400 and 0.1606 seconds, respectively. The results of the simulations and experimental tests highly corresponded with the analytical predictions, confirming the reliability and practical applicability of the analytical models.

This paper presents an analysis of the proximity effect in a line consisting of two identical solid conductors of circular cross section. Integral equation for the current distribution in one of the conductors is solved approximately by...