Search

The increasing significance of energy efficiency in the building sector necessitates innovative planning to reduce energy consumption while maintaining occupant comfort. With the rise in mechanically ventilated buildings, traditional sequential planning methods, which first ensure outdoor air supply before addressing acoustics, are being reassessed due to their risk for suboptimal solutions. This study introduces a holistic algorithmic methodology for ventilation system design to minimise life-cycle costs while ensuring acoustically feasible solutions. Utilising discrete mathematics, the approach models components' impact on airflow, acoustics, power consumption, and costs, across multiple load cases, culminating in a 2-stage stochastic Mixed-Integer Nonlinear Program. A case study demonstrates the methodology's applicability and the trade-off between energy efficiency and noise levels, highlighting its potential for more complex buildings. This integrated approach marks a significant advancement in ventilation system optimisation, promoting more holistic and efficient building designs while allowing for a more transparent decision-making.

We model the Darmstadt Slip Length Tribometer (DSLT), specially designed to measure viscosity and slip length simultaneously for lubrication gaps in the range of approximately 10 micrometres at relevant temperatures and surface roughness. We investigate the inlet effect of the flow on the results by varying the inner radius of the fluid inlet pipe. The outcomes of numerical simulations suggest that variations in the diameter of this inner radius have minimal impact on the results. Specifically, any alterations in the velocity profile near the inlet, brought about by changes in the diameter, quickly revert to the profile predicted by the analytical model. The main conclusion drawn from this study is the validation of the Navier-Slip boundary condition as an effective model for technical surface roughness in CFD simulations and the negligible influence of the inlet effect on the fluid dynamics between the tribometer's plates.

Having become vital to satisfying basic human needs, water distribution systems (WDSs) are considered critical infrastructure. They are vulnerable to critical events such as extreme weather, natural and man-made disasters, armed conflicts etc. To account for critical events in the context of design and operation of WDSs, the concept of resilience is frequently mentioned. How resilience of WDSs can be assessed using resilience metrics has been the subject of research of many publications. The aim of this paper is to inspect the alignment between a general understanding of resilience in WDSs and the metrics used for resilience assessment. A novel framework for categorising resilience metrics for WDSs is presented. A literature review of resilience metrics for WDSs is performed and the results are analysed using the framework designed. The results show that resilience metrics do not really assess resilience of the systems, but rather only specific functions and properties of systems which can make them resilient.

Conventional control of fluid systems does not consider system-wide knowledge for optimising energy efficient operation. Distributed control of fluid systems combines reliable local control of components while using system-wide cooperation to ensure energy efficient operation. The presented work compares three approaches to distributed control based on multi-agent systems, distributed model predictive control (DMPC), multi-agent deep reinforcement learning (MADRL) and market mechanism design. These approaches were applied to a generic fluid system and evaluated with regard to functionality, energy efficient operation, modeling effort, reliability in the face of disruptions, and transparency of control decisions. All approaches were shown to fulfil the functionality, though a trade-off between functional quality and energy efficiency was identified. Increased modeling effort was shown to improve the performance slightly while a strong interdependence of information caused by excessive information sharing has proven to be disadvantageous. DMPC and partially observable MADRL were less sensitive to disruptions than market mechanism. In conclusion, agent-based control of fluid systems achieves greater energy efficiency than conventional methods, with values similar to centralized optimal control and thus represent a viable design approach of fluid system control., Comment: 42 pages, 10 figures updated DOI in Data Availability Statement; updated links in figure captions to files in new version of dataset; dataset changed due to correcting links to raw data files in figure.json files

The Navier slip boundary condition is interpreted as an equilibrium of shear rate and slip rate. From the argument that the slip rate shall be proportional to the molecules' collision rate, the temperature dependence of the Navier slip boundary condition is derived. The model for the temperature dependence of the slip length is validated by slip measurements of liquid hydrocarbons in a novel Couette typ tribometer being introduced. The essence of the gained experimental data for one fluid-solid-interface is the quadruple activation energy for shear and wall slip together with the viscosity and slip length at a reference temperature. This quadruple is determined for four different hydrocarbon liquids of different molecular mass, structure and polarity proving the applicability of the new measurement method. From the executed systematic measurements three conclusions regarding the slip length dependence are pointed out: (i) the slip length increases with increasing molar mass; (ii) changing the molecular structure from saturated hydrocarbon to unsaturated affects the slip length as well as the activation energy for slip; (iii) adding a small fraction of polar molecules to the hydrocarbon decreases the slip length and increases the activation energy for wall slip due to the polar end-groups of the liquid., Comment: The paper was submitted to Physical Review Letters in May 2018 as a revised version of the manuscript no. LJ15692 submitted to the same journal in September 2017

We discuss the dynamic force and torque characteristic of annular gaps resulting from an axial flow component. First, the rotordynamic influence of annular gaps with an axial flow component is recapitulated. So far there is a severe lack of understanding the dynamic force and torque characteristic of annular gaps. Second, a new simulation method is presented, using a perturbed integro-differential approach in combination with power-law ansatz functions for the velocity profiles and a Hirs' model to calculate the dynamic force and torque characteristics. Third, an extensive parameter study is carried out. To evaluate whether or not the hydraulic tilt and torque coefficients need to be taken into account, an effective stiffness is defined and the influence of the annulus length, an eccentrically operated shaft, the centre of rotation, a modified Reynolds number, the flow number and the pre-swirl is investigated., Comment: Parts of the introduction are rewritten. Layout of the pre-print was changed

We discuss the static force characteristic of annular gaps resulting from an axial flow component. So far there is a severe lack of understanding of the flow inside the annulus. First, the state-of-the-art modelling approaches to describe the flow inside the annulus are recapped and discussed. The discussion focuses in particular on the modelling of inertia effects. Second, a new calculation method, the Clearance-Averaged Pressure Model (CAPM) is presented. The CAPM uses an integro-differential approach in combination with power law ansatz functions for the velocity profiles and a Hirs' model to calculate the resulting pressure field. Third, for experimental validation, a setup is presented using magnetic bearings to inherently measure the position as well as the force on the rotor induced by the flow field inside the gap. The experiments focus on the characteristic load behaviour, attitude angle and pressure difference across the annulus. Fourth, the experimental results are compared to the calculation results., Comment: Pre-validation chapter was added. Order of magnitude analysis for the hydrodynamic entrance length was added in chapter II. Layout of the pre-print was changed

The rapid increase of population and settlement structures in the Global South during recent decades motivates the development of suitable models to describe their formation and evolution. Such settlement formation has been previously suggested to be dynamically driven by simple pattern-forming mechanisms. Here, we explore the use of a data-driven white-box approach, called SINDy, to discover differential equation models directly from available spatiotemporal demographic data for three representative regions of the Global South. We show that the current resolution and observation time of the available data is insufficient to uncover relevant pattern-forming mechanisms in settlement development. Using synthetic data generated with a generic pattern-forming model, the Allen-Cahn equation, we characterize what the requirements are on spatial and temporal resolution, as well as observation time, to successfully identify possible model system equations. Overall, the study provides a theoretical framework for the analysis of large-scale geographical/ecological systems, and it motivates further improvements in optimization approaches and data collection., Comment: 13 pages, 8 figures

Hydraulic accumulators play a central role as energy storage in nearly all fluid power systems. The accumulators serve as pulsation dampers or energy storage devices in hydro-pneumatic suspensions. The energy carrying gas is compressed and decompressed, often periodically. Heat transfer to the outside significantly determines the transfer behaviour of the accumulator since heat transfer changes the thermodynamic state of the enclosed gas. The accumulators operating mode ranges from isothermal to adiabatic. Simulating fluid power systems adequately requires knowledge of the transfer behaviour of the accumulators and therefore of the heat transfer. The Engineer's approach to model heat transfer in technical system is Newton's law. However, research shows, that in harmonically oscillating gas volumes, heat flux and bulk temperature difference change their phase. Newton's law is incapable of representing this physical phenomenon. We performed measurements on two sizes of commercial membrane accumulators. Experimental data confirm the failure of Newton's approach. Instead the heat transfer can be modelled with an additional rate dependent term and independently of the accumulator's size. Correlation equations for the heat transfer and the correct accumulator transfer behaviour are given., Comment: 23 pages, 10 figures

The two most important aneurysm types are cerebral aneurysms (CA) and abdominal aortic aneurysms (AAA), accounting together for over 80\% of all fatal aneurysm incidences. To minimise aneurysm related deaths, clinicians require various tools to accurately estimate its rupture risk. For both aneurysm types, the current state-of-the-art tools to evaluate rupture risk are identified and evaluated in terms of clinical applicability. We perform a comprehensive literature review, using the Web of Science database. Identified records (3127) are clustered by modelling approach and aneurysm location in a meta-analysis to quantify scientific relevance and to extract modelling patterns and further assessed according to PRISMA guidelines (179 full text screens). Beside general differences and similarities of CA and AAA, we identify and systematically evaluate four major modelling approaches on aneurysm rupture risk: finite element analysis and computational fluid dynamics as deterministic approaches and machine learning and assessment-tools and dimensionless parameters as stochastic approaches. The latter score highest in the evaluation for their potential as clinical applications for rupture prediction, due to readiness level and user friendliness. Deterministic approaches are less likely to be applied in a clinical environment because of their high model complexity. Because deterministic approaches consider underlying mechanism for aneurysm rupture, they have improved capability to account for unusual patient-specific characteristics, compared to stochastic approaches. We show that an increased interdisciplinary exchange between specialists can boost comprehension of this disease to design tools for a clinical environment. By combining deterministic and stochastic models, advantages of both approaches can improve accessibility for clinicians and prediction quality for rupture risk., Comment: 46 pages, 5 figures

The powertrain of battery electric vehicles can be optimized to maximize the travel distance for a given amount of stored energy in the traction battery. To achieve this, a combined control and design problem has to be solved which results in a non-convex Mixed-Integer Nonlinear Program. To solve this design task more efficiently, we present a new systematic optimization approach that leads to a convex Mixed-Integer Nonlinear Program. The solution process is based on a combination of Geometric Programming and a Benders decomposition. The benefits of this approach are a fast solution time, a global convergence, and the ability to derive local sensitivities in the optimal design point with no extra cost, as they are computed in the optimization procedure by solving a dual problem. The presented approach is suitable for the evaluation of a complete driving cycle, as this is commonly done in powertrain system design, or for usage in a stochastic approach, where multiple scenarios are sampled from a given probability density function. The latter is useful, to account for the uncertainty in the driving behavior to generate solutions that are optimal in an average sense for a high variety of vehicles and drive conditions. For the powertrain model we use a transmission model with up to two selectable transmission ratios and an electric motor model that is based on a scaled efficiency map representation. Furthermore, the shown model can also be used to model a continuously variable transmission to show beneficial energy savings based on this additional degree of freedom. The presented design approach is also applicable to a wide variety of design tasks for technical systems besides the shown use case.

Sedentism was a decisive moment in the history of humankind. In a review article Kay and Kaplan quantified land use for early human settlements and found that sedentism and the emergence of farming go hand in hand. For these settlements two primary land use categories, farming and living, can be identified, whereas for hunter gatherer societies no distinct differences can be made. It is natural to search for this in the behavior of two different groups, settlers and farmers. The development of two distinct zones and the two groups lead us to the hypothesis that the emergence of settlements is the result of diffusion-driven Turing instability. In this short communication we further specify this and show that this results in a regular settlement arrangement as can still be seen today in agricultural regions., Comment: 5 pages, short communication, 2 figures