Membrane humidifiers are often used in mobile Proton Exchange Membrane (PEM) fuel cell systems to humidify the supply air of the fuel cell. The purpose of a humidifier in a PEM fuel cell system is to prevent a dry-out of the fuel cell membrane. In this paper, a humidifier model based on the number of transfer units (NTU) approach is set-up in Modelica, calibrated and validated using measurement of a test rig. In a first step, the model is evaluated for steady state operating conditions. Second the developed membrane humidifier model is simulated with dynamically changing operating conditions that are typical for mobile applications. Those simulation results are then compared to measurements. The aim of our study is to evaluate the accuracy of the NTU humidifier model under various operating scenarios. Our results indicate that the NTU model is suitable to predict the water transfer under steady state as well as dynamically changing operating conditions with low deviations to measurements.

In power systems, subsynchronous oscillations associated with the interaction between a mechanical rotor shaft and electrical system can lead to equipment damage if improperly mitigated. This paper describes the development of a scalable, multi-mass torsional shaft model and a synchronous machine model with DC offset torque components included using Modelica. When coupled, these models can be used to perform shaft torsional studies. Two methods of coupling the shaft with the rest of the turbine-generator system are devised and analyzed. A single-machine, infinite-bus test system using the torsional shaft model and generator model developed in this paper is proposed to observe the penetration of subsynchronous oscillations throughout an electrical system. The test system is then modified to model subsynchronous resonance leading to system instability. Analysis of the models described in this paper highlights the value of the Modelica_LinearSystems2 library in determining the torsional mode shapes and frequencies associated with a turbine-generator system model.

In the development of complex, novel electrified aerial systems such as Unmanned Aerial Vehicles (UAVs) and electric vertical take-off and landing (eVTOL) systems, multi-domain modeling and simulation studies can provide indispensable insight on system design and performance. In this paper, a Modelica library used to model multi-domain drone models is introduced. This library models a drone in the electrical, mechanical, and control domains, with examples for applications such as battery-power analysis, virtual reality simulation and user interaction.