Royal Netherlands Aerospace Centre

Hydrogen-propelled aircraft can enable net-zero CO2 emissions in aviation, which is the goal of the International Civil Aviation Organization (ICAO) for 2050. One drawback of onboard hydrogen storage in aircraft is the necessity for relatively large, pressurised storage volumes. To maximise H2 volumetric efficiency, the COmposite COnformal LIquid H2 Tank (COCOLIH2T) project attempts to design, build and test a vacuum-insulated liner-less cryogenic conformal thermoplastic composite tank with conditioning subsystems for safe operation. The tank must be compatible with the design envelope in the empennage, specifically towards the aft of the pressure bulkhead of an ATR 72-like aircraft. The tank design, analysis, optimisation and demonstrator manufacturing are presented in this paper.

We study thermal transport across copper-graphene-copper interfaces using Non-Equilibrium Molecular Dynamics (NEMD), focusing on the influence of finite domain length and domain configuration, including lattice initialisation and associated graphene wrinkling, on the predicted thermal conductivity and Kapitza resistance. In the literature, NEMD simulations identified trends in the Kapitza resistance of graphene-copper interfaces. However, the simulation outcomes and reliability may depend heavily on configuration choices that are underexplored in the literature. We identify a strong sensitivity of the Kapitza resistance to domain configuration choices that affect the lattice constants and atomic density. We show that two conventional lattice initialisation strategies yield a factor of two difference in the Kapitza resistance, despite differences of only a few per cent in the lattice parameters. This behaviour is accompanied by strain-dependent shifts in the graphene and copper phonon spectra, and by increased phonon overlap at lower strain. Counter to conventional expectations, greater phonon-mode overlap coincides with higher Kapitza resistance, showing that spectral overlap alone cannot capture the interfacial heat-transfer dynamics. We suggest that in lattices initialised with lower residual strain, a damping boundary layer develops near the interface, and increases thermal resistance, as indicated by increased local structural disorder and local spectral broadening over a wider interfacial region. Beyond strain- and density-related effects associated with the lattice constants, Kapitza resistance shows no significant dependence on domain length or boundary temperature enforcement in this study. By contrast, the copper lattice conductivity exhibits clear domain-size and temperature dependence, consistent with phonon mean-free-path limitations and supported by phonon spectral analysis.

We assess the increasingly prevalent assertion that energy poverty in high-income countries disproportionately affects women and households with a migration background. Much of the existing evidence supporting this claim is non-causal and often fails to disentangle the effects of income. To address these limitations, we apply both descriptive statistical methods and a two-stage logistic regression analysis to comprehensive, high-quality administrative microdata covering nearly 90 % of Dutch households. We examine how gender, migration background, income, and housing characteristics interact to shape energy poverty outcomes. Our key finding is that what initially appears as a gender or migration bias in energy poverty statistics is, in fact, primarily a reflection of income disparities across these demographic groups. Beyond income, our results also highlight the importance of spatial, institutional, and behavioral factors in shaping vulnerability. In particular, we find that the relatively high energy quality of social housing in the Netherlands mitigates the risk that women and migrants-despite a gender and migration pay gap-end up in energy poverty. We also identify differences in energy poverty subtypes: women are more exposed to combinedenergy poverty (energy-inefficient housing and high energy costs), while men are more likely to exhibit hidden energy poverty (energy-inefficient housing but low energy costs). These findings underscore the importance of addressing structural inequalities in income and housing beyond the energy domain when designing effective policies to reduce energy poverty. A just and inclusive energy transition will therefore depend on addressing the broader socio-economic and institutional conditions that underlie energy poverty.

Multidisciplinary Design Optimization (MDO) enables the application of optimization algorithms to complex engineered systems, ranging from aerospace and automotive to robotics and microelectronics. Such multi-component systems typically consist of coupled subsystems, each characterized by its own design variables, constraints and objectives. Without adequate coordination of these couplings, subsystems may be optimal in isolation while the overall system remains suboptimal or even infeasible. Distributed design optimization coordinates coupled subsystem optimization problems while allowing them to retain control over their local design variables. Although promising coordination methods exist, their application is hindered by the lack of a comprehensive software framework which supports intuitive problem definition, provides suitable distributed coordination algorithms, is modular and extensible, enables interactive (post-)processing, and supports the distributed computation of subsystem executions. This work derives requirements for such software, assesses existing frameworks against them, and introduces DistributedDesignOptimizer, an open-source Python framework to fill this gap.

This article presents a robust and efficient methodology to compute the per-unit-length in-cell inductance and capacitance matrices required to couple unshielded multiwire bundles to a 3-D finite-difference time-domain (FDTD) solver within a multiconductor transmission line framework. The proposed approach numerically solves the 2-D electrostatic and magnetostatic Laplace problems in an inner region and represents the field in the outer region by a multipolar (MP) expansion whose coefficients are computed from the full numerical solution. This hybrid finite element method (FEM)–MP formulation decouples the in-cell parameters from the specific FDTD cell position and size, avoids repeated numerical computations when bundles cross many cells, and naturally accommodates dielectric insulation. The method is validated on three cases of increasing complexity: 1) a single insulated wire; 2) two bare wires; and 3) a realistic 31-conductor bundle. Results are compared against a pure FEM reference, a boundary element method implementation and Bérenger's center-based approximation. The proposed FEM(inner)+MP(outer) scheme matches the FEM reference with very small discrepancies. The study also shows that conductor interactions shift the effective expansion centers away from geometric centers and that electrostatic and magnetostatic centers differ in the presence of dielectrics, which are effects not captured by simplified previous analytic models.