<p>A theoretical and experimental study of mechanical properties of electrical cables with multi order helical structure has been performed. Relations between applied deformations and local strains in the first order helical structure have been developed. The model is then generalized with a hierarchical approach where the strains at any order helical structure are expressed as functions of strains in the upper order helix under the assumption that all components are sticking to each other.</p><p>The force balance between the strains and the friction forces is considered. When the cable is exposed to small bending curvature, the slippage of the component is prevented by the frictional force. At this stage, the components of the cable behave as solid beams. Slippage occurs between the components when the tensile force in the components overcomes the frictional force. This state occurs at sufficiently large bending curvatures and results in a variable bending stiffness varying with the magnitude of the applied bending curvature.</p><p>The response of the cable to pure bending is measured and the data is evaluated using the theoretical model described above. Magnitudes of un- known properties of the cable are estimated by comparing the theoretical and experimental data. To utilize the model in terms of life time estimation, a number of parameters were suggested to relate the mechanical properties of the cable to wear and fatigue. A parametric study has been done to investigate how these parameters are affected by changing cable properties or the loading condition.</p>

<p>In the sector of mobile hydraulics, valve controlled systems are predominant. In these systems the load force and speed are adjusted by control valves. In machines where multiple drives are used in parallel at extremely varying loads the energy efficiency of such systems is often compromised over large working regions. Most valve controlled systems also lack the possibility to recuperate potential energy.</p><p>A different category of hydraulic systems, called displacement controlled hydraulics are based on the manipulation of the hydraulic flow using the relative displacement of the hydraulic machines as the final control element. This type of hydrostatic power transfer, yields a resistance free velocity control, ideally leading to lossless load actuation.</p><p>This thesis concerns the introduction of a new type of displacement controlled hydraulic system, adapted for construction machinery. The system decouples the hydraulic functions using one dedicated hydraulic machine for each drive. These machines are of open circuit type, capable of over center operation which enables energy recuperation. The system also comprises four separate valves that by means of switching allow the cylinder to be controlled over all four load quadrants. Depending on the selected valve hardware, the system may also include features available in a conventional valve controlled system, such as meter-out flow control. The system supports both symmetrical and asymmetrical cylinders. However, using the asymmetrical type the load may be controlled in two distinct states of operation. This yields an increased region of operation, which is otherwise generally stated as a drawback in displacement controlled systems. It also allows the selection between different control modes, where one of the modes is always more efficient than another.</p><p>In this research both theoretical studies and a practical implementation demonstrate the energy related benefits of the new concept. The target application of this study is a medium-size wheel loader. Measurement results using the wheel loader in a short truck loading cycle show a 10% percent reduction in fuel consumption. According to the theoretical investigation, this corresponds to a 20% reduction in energy consumption for the hydraulicsystem itself.</p>

No description available.

<p>QC 20170517</p>

The cardiovascular system is an important part of the human body since it transports both energy and oxygen to all cells throughout the body. Diseases in this system are often dangerous and cardiovascular diseases are the number one killer in the western world. Common cardiovascular diseases are heart attack and stroke, which origins from obstructed blood flow. It is generally important to understand the causes for these cardiovascular diseases. The main causes for these diseases are atherosclerosis development in the arteries (hardening and abnormal growth). This transform of the arterial wall is believed to be influenced by the mechanical load from the flowing blood on the artery and especially the tangential force the wall shear stress. To retrieve wall shear stress information in arteries invivo is highly interesting due to the coupling to atherosclerosis and indeed a challenge. The goal of this thesis is to develop, describe and evaluate an in-vivo method for subject specific wall shear stress estimations in the human aorta, the largest artery in the human body. The method uses an image based computational fluid dynamics approach in order to estimate the wall shear stress. To retrieve in-vivo geometrical descriptions of the aorta magnetic resonance imaging capabilities is used which creates image material describing the subject specific geometry of the aorta. Magnetic resonance imaging is also used to retrieve subject specific blood velocity information in the aorta. Both aortic geometry and velocity is gained at the same time. Thereafter the image material is interpreted using level-set segmentation in order to get a three-dimensional description of the aorta. Computational fluid dynamics simulations is applied on the subject specific aorta in order to calculate time resolved wall shear stress distribution at the entire aortic wall included in the actual model. This work shows that it is possible to estimate subject specific wall shear stress in the human aorta. The results from a group of healthy volunteers revealed that the arterial geometry is very subject specific and the different wall shear stress distributions have general similarities but the level and local distribution are clearly different. Sensitivity (on wall shear stress) to image modality, the different segmentation methods and different inlet velocity profiles have been tested, which resulted in these general conclusions: The aortic diameter from magnetic resonance imaging became similar to the reference diameter measurement method. The fast semi-automatic level-set segmentation method gave similar geometry and wall shear stress results when compared to a reference segmentation method. Wall shear stress distribution became different when comparing a simplified uniform velocity profile inlet boundary condition with a measured velocity profile. The method proposed in this thesis has the possibility to produce subject specific wall shear stress distribution in the human aorta. The method can be used for further medical research regarding atherosclerosis development and has the possibility for usage in clinical work.

Filamentous fungi are of interest for biotechnologists particularly because of thefungi’s ability of producing commercial products after undergoing certain industrialprocess. Although because of the complicated and intricate internal mechanism ofthe fungi there are certain aspects which need to be studied to maximize the produc-tion output. A team at Chair of Measurement and Control Bioprocess Group at TUBerlin studies the internal behavior of the fungi when they are exposed to certainamount of wall shear stress (WSS) by performing small-scale experimentation. Forthis purpose a backward facing step (BFS) chamber is used.  This thesis work aims to perform Computational Fluid Dynamics (CFD) analysesto study the flow in the BFS chamber and to find appropriate locations to adherethe fungi spores on the chamber’s bottom wall. Commercially available CFD software Star CCM+ has been used for the CFD calcu-lations. The BFS chamber has been divided into two parts namely ’inflow channel’and ’step channel’ and simulations are performed separately. RANS model SST k-ωhas been used to simulate the flow in the inflow channel and Large Eddy Simulation(LES) model has been used in the step channel. The simulation result predicted that the streamwise WSS (WSS x ) is highest (≈ 8Pa) at the primary reattachment location downstream of the step. Due to reverseflow it is observed that WSS x is high (≈ 5 Pa) in the primary separation region.Standard deviation WSS x is highest (≈ 0.35 Pa) in the region around 28 x/h distancedownstream of the step on the bottom wall of the step channel and it is observedthat this is the region where the turbulence kinetic energy (TKE) is also maximumin the mean flow of the step channel. It is observed that there is small WSS x devi-ation in the primary reattachment region as well.                From the study it is concluded that the overall flow in the chamber is laminar withsome level of unsteadiness at few locations. To adhere the fungi spores on the bot-tom wall suitable location will be in the region where maximum variation in WSS xis observed. Keywords: Filamentous fungus, computational fluid dynamics, large eddy simula-tion, wall shear stress, backward facing step, turbulence kinetic energy

The focus of this work was to simulate the fluid flow within a melt pool geometry, during an additive manufacturing process, implementing the CFD software OpenFOAM version 1806. Two separate models were created and run during this work, the first using a temperature mapping from a finite element (FE) model and the second being a free-standing model with Gaussian distributed laser beam striking down on the top surface. Both models were run with the standard solver icoReactingMultiphaseInterFoam, being a multiphase solver, with phase transition possibilities. Addition of gas particles was carried out during post-processing and these were to visualise the imperfections caused by melting metal alloys in a 3D printing case. During comparison of the movement of the free-standing model, using a moving laser beam, to the mapped temperature FE model, it was revealed that the fluid flow in the molten pool was heavily influenced by the pressure introduced by the laser beam. No streamlines were found that would indicate entrapment of gas particles during solidification. / Fokuset på detta arbete var att simulera vätskeflöde i en smältpool-geometri, under en additiv-tillverkningsprocess. Detta implementerades med hjälp av CFD-mjukvaran OpenFOAM, version 1806. Två separata modeller skapades och simulerades under arbetets gång. Den första modellen kördes med hjälp av en mappning av temperaturfältet från finita-element-modellen (FE-modellen) och den andra modellen var en fristående modell tillsammans med en Gaussisk distribuerad laserstråle riktad ned på översta ytan. Båda simuleringarna använde sig av standardlösaren icoReactingMultiphaseInterFoam, vilket är en multifas-lösare, med möjlighet till fasövergångar. Tillägg av gaspartiklar utfördes under post-processing och dessa var för att visualisera porer som kan uppstå under smältning av metall-legering i en 3D-utskrivningsprocess. Vid jämförelse av den fristående modellen, som implementerade en rörlig laserstråle, till den mappade FE-modellen, uppdagades det att vätskeflödet i smältpoolen influerades starkt av trycket som orsakades av lasern. Inga strömlinjer tydde på en inkapsling av gaspartiklar under stelning.

Airflow management is crucial for the performance of cooling systems in data centers. The amount of energy consumed by data centers is huge and a large amount is related to the cooling. In attempts to develop energy efficient data centers, numerical methods are important for several reasons. Experimental procedures are more expensive and time consuming but when done carefully, experiments provide trustful results that can be used to validate simulations and give additional insights. Numerical methods in their turn have the advantage that they can be applied to proposed designs of data centers before they are built and not only to already existing data centers. In this study, Computational Fluid Dynamics (CFD) is used to study the airflow in data centers. The aim is to use an experimentally validated CFD model to investigate the effects of using different designs in data centers with respect to the performance of the cooling systems. Important parameters such as quality of the computational grid, boundary conditions and choice of turbulence model must be carefully considered in order for the results from simulations to be reliable. In Paper A, a hard floor configuration where the cold air is supplied directly into the data center is compared to a raised floor configuration where the cold air is supplied into an under-floor space instead and enters the data center through perforated tiles in the floor. In Paper B, the performance of different turbulence models are investigated and velocity measurements are used to validate the CFD model. In Paper C, the performance of different cooling systems is further investigated by using an experimentally validated CFD model. The effects of using partial aisle containment in the design of data centers are evaluated for both hard and raised floor configurations. Results show that the flow fields in data centers are very complex with large velocity gradients. The k − ε model fails to predict low velocity regions. Reynolds Stress Model (RSM) and Detached Eddy Simulation (DES) produce very similar results and based on solution times, it is recommended to use RSM to model the turbulent airflow in data centers. Based on a combination of performance metrics where both intake temperatures for the server racks and airflow patterns are considered, the airflow management is significantly improved in raised floor configurations. Using side covers to partially enclose the aisles performs better than using top covers or open aisles.

Time resolved pressure measurements in hydropower applications are of great interest. Different parts of the machine experience highly transient flows that influence the function and efficiency of the turbine. This thesis addresses different time dependent pressure phenomena. Assessment of the efficiency of a hydropower plant requires accurate flow measurements. Gibson's method is a pressure time based method to measure the flow rate. To improve the method outside its standard range an experimental investigation is performed in a laboratory setup in parallel with numerical solutions of the governing equations. The results indicate that it is possible to correct the flow measurements outside the limitations of the standard. A draft tube is an integrated part of a hydropower plant with a reaction turbine where the remaining kinetic energy of the flow after the turbine is converted into pressure. An experimental investigation is performed on a model hydropower draft tube at Älvkarleby to establish the details of the pressure recovery in the early part of the draft tube. The objective is to increase the understanding of the pressure behaviour and to contribute with data for CFD (Computational Fluid Dynamics) validations. The results show a high damping of the oscillating parts of the pressure in the axial direction. From earlier investigations done as part of the Turbine-99 workshops, it has been observed that the radial pressure distribution just under the turbine runner show a marked discrepancy between experiments and CFD. The flow in the region is highly time dependent so the behaviour of the Pitot tube used for the pressure measurements is investigated for oscillating flow in a lab setup. A method to derive more accurate data is proposed. / <p>Godkänd; 2006; 20070109 (haneit)</p>

The utilization of rivers for hydropower production leads to problems for fish migration. Migratory fish that swim upstream for reproduction need to overcome obstructions to reach their spawning grounds. On their way upstream they follow high water velocities. Since most of the water in regulated rivers flow through the power plants the fish is often attracted to the turbine outlets. To guide the fish past the power plants, fishways are often used. However the efficiency is often low due to inefficient attraction water. An attraction channel that uses a small fraction of the tailwater, or any free stream, is studied. The channel is open and U-shaped. A local acceleration of the water is created by changing the cross sectional area in the downstream end of the channel. The flow in the channel is measured with LDV in a lab setup to examine the acceleration of the water, and in full-scale to investigate the fish tendency to use the channel. The results show that the velocity out of the channel can be as much as 38 % higher than the approaching flow. The acceleration is detectable downstream the channel up to 18 times the exit water depth of the channel. The results from the field work shows that fish do use the channel and it is important that it is painted dark. / <p>Godkänd; 2006; 20070109 (haneit)</p>