Chalmers Open Digital Repository

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Numerical Methods for mapping band-type resonance in insect flight
(2025) Zhang, Congxiao; Chalmers tekniska högskola / Institutionen för matematiska vetenskaper; Beilina, Larisa; Pons, Arion
Insect flight is a highly complex and energy-intensive process. Flapping-wing insects employ a unique muscle contraction mechanism that enables high-frequency wing beats, with metabolic rates reaching several times those at rest. Their remarkable endurance during flight highlights the importance of understanding the energy optimization involved. This thesis focuses on developing numerical methods to map band-type resonance, which serves as a benchmark for assessing whether a system achieves an energy-optimal state. We describe the mapping of band-type resonance as an optimization problem and propose two primary numerical methods: particle swarm optimization and numerical continuation. We evaluate the accuracy of the numerical solutions via the solution work loops and power waveforms and compare them with analytical approximations to the space of band-type resonant states. Our findings reveal that while the standalone particle swarm method can provide a relatively complete set of estimated solutions, the solution space lacks continuity. The numerical continuation method sacrifices some completeness in finding solution sets to ensure better continuity in the corresponding domain of the output solution set. After comparing these methods' performance in identifying potential solutions for simple cases, we improve them and propose a compound numerical method for solving more complex problems, such as higher harmonic and nonlinear oscillators. Notably, this compound algorithm performs well not only on simple linear cases with known analytical solutions but also on complex problems lacking analytical solutions, offering a valuable numerical tool for estimating the mapping zone of band-type resonance when analytical methods are not feasible. Comparing the results of mapping zones of band-type resonance with wingbeat frequency modulation behaviour observed in actual insect species suggests that such behaviour may be consistent with sustained resonant energy savings by exploiting band-type resonance. This report is written in English.
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Development and Implementation of test cells to perform DC and LI breakdown testing of materials used in HVDC cable accessories
(2025) Selvasekar , Nehru Selvan; Chalmers tekniska högskola / Institutionen för elektroteknik; Serdyuk, Yuriy; Nilsson, Susanne; Jafari, Sajad; Hussain, Rashid
Abstract The thesis work is to develop,build up and verify a test circuit for measurements of DC breakdown strength and LI testing. The work contains both practical and theoretical elements, focusing on optimizing the design of electrodes as well as the size and shape of samples and to determine the Optimal dielectric properties of the insulation test medium using COMSOL Multiphysics. The aim of the work is to develop methods and design test setups for measuring both DC breakdown strength and Lightning Impulse testing, as a function of electric fields. EPDM insulation and FGM are used in cable accessories considering EPDM rubber has low dielectric loss, making it ideal for high-voltage applications. FGM rubber can be produced by incorporating specific fillers and is designed to control and distribute electric fields within electrical insulation systems. Its main purpose is to prevent high electric field concentration, which can cause insulation breakdown and device failure.Rubber material is being tested using mechanical, chemical, and electrical methods. The dielectric test is one of the electrical testing methods used to determine the dielectric strength of rubber materials. Short-time and long-time tests are being carried out for dielectric testing. AC breakdown testing, DC breakdown testing, and LI breakdown testing on insulation EPDM and FGM samples are conducted using two different insulating liquids with variable permittivities to avoid surface flashover during a short test under international standards. Designing a test cell for a dielectric test with an applied voltage of up to 150kV. Design the test cell (CAD model) and choose the electric field simulation with COMSOL Multiphysics software. To enhance development, the molded electrode test setup has been designed to eliminate the influence of the surrounding medium and facilitate future endurance testing.
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Measurement of Complex Permittivity and Permeability Through a Cavity- Perturbation Method
(2015) Rydholm, Tomas; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Tassin, Philippe; Johansson, Joakim
Fabrication of antenna and microwave devices demands good knowledge of certain material parameters such as permittivity and permeability, including their corresponding losses. The project presented in this master’s degree thesis aims to develop an experimental setup to measure these properties at microwave frequencies. A cylindrical cavity resonator was designed for a cavity perturbation method. In this method, it is studied how the resonance frequencies shift as a sample is inserted into the cavity resonator. The permittivity and permeability can be determined from this frequency shift and the loss parameters can be obtained from the broadening of the resonance peaks in the spectrum. An alternative method is developed, in which the measurements are compared to data obtained from simulations. A set of curves or contour lines, describing the resonance frequency of a specified mode, is plotted as function of the permittivity and permeability. By performing two measurements where the sample is placed at two different positions in the cavity, the material properties can be determined from the point where the two curves cross each other. We refer to this new method as the “curve-set method”. Simulations indicate that the cavity-perturbation method can be used together with the designed cavity resonator to measure the permittivity and dielectric loss tangent accurately for nonmagnetic materials. However, it seems difficult to measure the permeability and magnetic loss tangent. On the other hand, the curve-set method appears to be a possible way to determine both the permittivity and the permeability, given that the simulations represent experiments accurately.
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Design of smart orthosis for rehabilitation of Achilles tendon ruptures
(2025) Anderson, Adam; Chalmers tekniska högskola / Institutionen för elektroteknik; Dean, Emmanuel; Brorsson, Annelie; Nilsson Helander, Katarina
Abstract This thesis presents a compact system for measuring forces under the foot, designed for rehabilitation after an Achilles tendon rupture. The aim is that this system could provide patients and care providers with critical data about the recovery process, for a more personalized and effective treatment. The core component of this system is a newly developed flexible insole that senses forces under the foot. The force is measured in three dimensions (i.e., normal and shear forces) using magnetic-based sensors, placed in a grid of 73 nodes. The large area covered by the sensor, and the flexibility, are improvements over previous magnetic-based force measurement systems. The insole and additional support electronics were mounted on a standard ankle orthosis (also known as Walker). In addition, two IMUs were used to estimate the orientation of the insole. Software was also developed to process and visualize the data. The measurements from the insole are sent to a signal processing chain to calculate relevant biomechanics parameters such as the center of pressure and joint torques. The signal processing chain was implemented within ROS2, together with micro-ros for the low-level communication with hardware. ROS2 is also used for visualization purposes. The results are promising, showing that magnetic-based sensors are feasible for measuring 3D forces under the foot. The sensors display a nearly linear response to vertical pressure, although there is considerable hysteresis that introduces errors in the measurements. Future work to improve calibration, verify reliability, and improve ease of use is needed before the system can be used in a clinical setting.
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Agrivoltaics in Sweden
(2025) Antonini, Timothe; Da Corte Vecchino, Filippo; Melkersson, Emil; Merten, Tom; Pettersson, Nathalie; Chalmers tekniska högskola; Chalmers University of Technolog; Albinsson, Bo; Albinsson, Bo
This report examines the integration of renewable energy into agriculture, focusing on agrivoltaic systems (APVs) that combine photovoltaic (PV) energy generation with farming. It compares Conventional Ground-Mounted Photovoltaics (CGMPVs) and Vertical Bifacial Photovoltaics (VBFPVs) to assess their economic viability and production potential. Additionally, it explores the implications and social acceptance of PV integration in Swedish agriculture, including land-use efficiency, food security, and market dynamics, offering insights for stakeholders seeking sustainable energy solutions in farming.