A computational iterative design method for bend-twist deformation in composite ship propeller blades for thrusters

This study investigates the feasibility of utilising common composite material layup techniques in ship propeller blade design to achieve an automatic pitch adjustment through bending-induced twist deformation. A comprehensive design approach, including various reinforcement materials and arrangements, was employed to attain the desired foil pitching, while minimising other undesirable deformation modes. The design process involved iterative computational analysis using finite element analysis and a deformation mode analysis based on foil shape parameters. The research showed that the proposed design approach effectively found options to improve the desired foil parameter pitch, while minimising undesirable deformation modes such as blade deflection and foil shape change. Furthermore, the proposed blade design was tested in thruster steering operational conditions and was found to have a pitch change well matched, potentially countering some changes in fluid flow. When compared to Kumar and Wurm’s design, which only focused on the angular orientation of glass reinforcement, the proposed design was found to outperform the twisting by achieving the same twist for a blade half the length. This study provides valuable insights into the utilisation of composite materials in ship propeller design and highlights the potential for further improvement through a composite engineering design approach.publishedVersio

Multiscale modelling of fiber composites - Investigating micromechanics of constituents' interaction

The objectives of this thesis have been to develop a script for a multiscale method based on first order homogenisation, to investigate estimation of properties and behaviour of unidirectional (UD) fiber composites. To model composites on the microscale, an algorithm that generates periodic representative volume elements (RVE) geometries from controllable parameters and a pseudo random factor was developed. The output of this algorithm (fiber populations) was used to create heuristic RVE models in the Finite Element Analysis (FEA) software, Abaqus 6.14-4. These heuristic RVE models consist of fibers, matrix and an interface. The fibers in the models were assigned linear elastic material properties and the matrix and interface were assigned elastic, plastic and damage material properties. To simulate deformations and loads, macro strains were imposed on the heuristic RVE models through constraint equations. As the properties of the RVE varied with the distribution of the fiber populations, the creation of RVE models was automated to perform multiple iterations to calculate estimations of the average properties and the statistical dispersion of these. The effect of design parameters on stiffness estimations was investigated. To get insight into the local stress field in the RVE models, the maximum principal stress and maximum shear stresses were found for normalized linear elastic load cases. The strength of the RVEs was predicted by simulating nonlinear behaviour with different assigned material models. Consistent macrostrains for the non-linear analyses were maintained by an iterative backward force balancing procedure. The results showed that the stiffness estimations generally follow micromechanical approximations based on the rule of mixture. For the strength estimations, the produced results correlate with comparable methods and results found in the literature. This suggests that the method is feasible for microscale modelling of an RVE of UD fiber composites. Further development into material models, damage models and confirmation and calibration of results with empirical data should be investigated before using such a tool for design estimates

Designing Composite Adaptive Propeller Blades with Passive Bend–Twist Deformation for Periodic-Load Variations Using Multiple Design Concepts

Four plausible design concepts are applied together to investigate composite bend–twist propeller-blade designs that show high twisting per bending deflection. The design concepts are first explained on a simplified blade structure with limited unique geometric features to determine generalized principles for applying the considered design concepts. Then, the design concepts are applied to another propeller-blade geometry to obtain a bend–twist propeller-blade design that achieves a specific pitch change under an operational loading condition with a significant periodic-load variation. The final composite propeller design shows several times more bend–twist efficiency than other published bend–twist designs and shows a desirable pitch change during the periodic-load variation when loaded with a one-way fluid–structure-interaction-derived load case. The high pitch change suggests that the design would mitigate undesirable blade effects caused by load variations on the propeller during operation

Experimental verification of the elastic response in a numeric model of a composite propeller blade with bend twist deformation

Adaptive composite propeller blades showing bend twist behaviour have received increasing interest from hydrodynamic and structural engineers. When exposed to periodic loading conditions, such propellers can be designed to have higher energy efficiency and emit less noise and vibration than conventional propellers. This work describes a method to produce an adaptive composite propeller blade and how a point load experiment can verify the predicted elastic response in the blade. A 600 mm-long hollow full-size blade was built and statically tested in the laboratory. Finite element modelling predicted a pitch angle change under operational load variable loads of 0.55°, a geometric change that notably compensates for the load cases. In the laboratory experiment, the blade was loaded at two points with increasing magnitude. The elastic response was measured with digital image correlation and strain gauges. Model predictions and experimental measurements showed the same deformation patterns, and the twist angle agreed within 0.01 degrees, demonstrating that such propellers can be successfully built and modelled by finite element analysis.publishedVersio

Experimental verification of the elastic response in a numeric model of a composite propeller blade with bend twist deformation

Adaptive composite propeller blades showing bend twist behaviour have received increasing interest from hydrodynamic and structural engineers. When exposed to periodic loading conditions, such propellers can be designed to have higher energy efficiency and emit less noise and vibration than conventional propellers. This work describes a method to produce an adaptive composite propeller blade and how a point load experiment can verify the predicted elastic response in the blade. A 600 mm-long hollow full-size blade was built and statically tested in the laboratory. Finite element modelling predicted a pitch angle change under operational load variable loads of 0.55°, a geometric change that notably compensates for the load cases. In the laboratory experiment, the blade was loaded at two points with increasing magnitude. The elastic response was measured with digital image correlation and strain gauges. Model predictions and experimental measurements showed the same deformation patterns, and the twist angle agreed within 0.01 degrees, demonstrating that such propellers can be successfully built and modelled by finite element analysis

Experimental verification of the elastic response in a numeric model of a composite propeller blade with bend twist deformation

Adaptive composite propeller blades showing bend twist behaviour have received increasing interest from hydrodynamic and structural engineers. When exposed to periodic loading conditions, such propellers can be designed to have higher energy efficiency and emit less noise and vibration than conventional propellers. This work describes a method to produce an adaptive composite propeller blade and how a point load experiment can verify the predicted elastic response in the blade. A 600 mm-long hollow full-size blade was built and statically tested in the laboratory. Finite element modelling predicted a pitch angle change under operational load variable loads of 0.55°, a geometric change that notably compensates for the load cases. In the laboratory experiment, the blade was loaded at two points with increasing magnitude. The elastic response was measured with digital image correlation and strain gauges. Model predictions and experimental measurements showed the same deformation patterns, and the twist angle agreed within 0.01 degrees, demonstrating that such propellers can be successfully built and modelled by finite element analysis