The demand for better performing structural designs gives rise to the interest in topology optimization. An accurate geometry description is fundamental in the optimization process. The Cut Finite Element Method (CutFEM) can describe the object surface on a fixed grid with an immersed boundary. To this level set method, multiple techniques from the density method can be added. In this thesis project, the performance of 3D topology optimization using CutFEM is tested. A topology optimization model using CutFEM was developed. For the elements on the boundary (Cut Elements), a cut is made to split the element in a solid and fluid part. The Gauss points that represent each part are calculated in order to find the stiffness of the Cut Elements. The performance has been tested by performing finite element analysis with CutFEM. In order to perform topology optimization, the sensitivities are calculated with the adjoint method, a filter was used with Heaviside projection and mapping, and the Method of Moving Asymptotes (MMA) is used in order to find the design of the next iteration. In order to increase the length scale, an optional robust design method was implemented which creates an eroded and dilated design. The performance of topology optimization using CutFEM was tested by optimizing a structure for minimum compliance for a set of loading conditions. This was compared to topology optimization with classical Solid Isotropic Material with Penalization (SIMP) method. Firstly, it was found that Cut Elements are an accurate method to perform a finite element analysis. Next, it was found that topology optimization using CutFEM is able to obtain a better objective function than topology optimization using the SIMP method. The computational costs of the CutFEM method are substancially higher. In 3D topology optimization using CutFEM, the design changes can happen everywhere on the boundary, so that the initial structural design is of less importance than for 2D. Next, it was found that the robust design method works well in increasing the length scale, but the objective function is decreased and the initial design is more important. It is thought that CutFEM could best be used to perform optimization with the initial design computed by the SIMP method. Finally, the CutFEM method has been used in a Navier Stokes fluid solver with Brinkman penalization implementation. It was found that this does not work, and a fluid solver with a hard boundary method is required. It is recommended to implement the CutFEM method in a fluid solver with Nitsches method.

Pioneering in the aviation is dangerous, but its rewards might be worthwhile. What if the fuselage shape is challenged to be non-circular? A better volume efficiency, easier loading and a new perception of the future aircraft are within reach, but at what costs? Carry-on luggage is expected to increase in the future. Does that result in a new fuselage shape? This report shows the design process of a 200 passenger aircraft while challenging the fuselage shape and its material. Market analysis showed a great demand for sustainable, single aisle aircraft. The current competitors are the Airbus A320neo, Boeing 737MAX-8 and the Airbus A321neo. With the use of system engineering tools, such as a functional breakdown structure, a functional flow diagram and a budget breakdown, a conceptual design was constructed: the A342 Beeblebrox. It purpose is to be able to outperform state-of-the-art aircraft and remain competitive for the next 50 years. Therefore the propulsion & performance, the electronics and the control & stability were designed to surpass the current aviation standard. To this end, off the shelf geared turbofan engines are used because it has a surpassing specific fuel consumption (SFC) and an overall good performance. The A342 is slightly more stable and controllable, because of its longer fuselage length but its overall tail size is similar to the A321neo. The A342 is an All-Electric-Aircraft to reduce subsystem and fuel weight. Its accessabillity is comparable to state-of-the-art aircraft. The maintainability is slightly worse, because of the revolutionary fuselage shape, that requires more frequent checking. The direct operating costs were calculated to be comparable with the A320neo. And because the A342 can carry more payload over longer distances, this ensures its ability to outperform other aircraft. The interior is designed such to maximise volume efficiency per passenger. This defined the inner boundaries for the fuselage cross-section, for which a lightweight structure was created. From the pressurisation requirement, it follows, both analytically and using a finite element method, that rounder shapes cope better with stresses. However, the elliptical shapes might still be an option. An elliptical shape was calculated to be roughly 1500 kg heavier than the circular of the same material. The fuselage material will consist mainly of CFRP and AFRP (Carbon/Aramid Fibre Reinforced Plastics), due to their high strength and low density. For the aerodynamics of the fuselage Computational Fluid Dynamics simulation software (CFD) was used to calculate the pressure. Subsequently, the drag was calculated analytically. It can be seen that squarish fuselages decrease the wetted area which reduces the drag. The elliptical shape has an increased L/D-ratio (Lift over Drag ratio) of 2%. The final conceptual design of the A342 Beeblebrox is a 6-abreast single aisle airliner, featuring an elliptical fuselage shape with conventional tail, better SFC and all electric systems. Each passenger has 0.107 m3 overhead luggage storage and 0.05 m3 checked-in luggage. Finally, it can be concluded that the elliptical shape is feasible to compete with state-of-the-art aircraft.