Showing posts with label Mechanical Projects. Show all posts
Showing posts with label Mechanical Projects. Show all posts

Investigation of Film Cooling Strategies CFD versus Experiments-Potential for Using Reduced Models (Mechanical Project)

 ,


The ability and efficiency of today’s gas turbine engines are highly dependent on development of cooling technologies, among which film cooling is one of the most important. Investigations have been conducted towards discovering different aspects of film cooling, utilizing both experiments and performing CFD simulations.


Although, investigation by using CFD analysis is less expensive in general, the results obtained from CFD calculations should be validated by means of experimental results. In addition to validation, in cases like simulating a turbine vane, performing CFD simulations can be time consuming. Therefore, it is essential to find approaches that can reduce the computational cost while results are validated by experiments.


This study has shown the potential for reduced models to be utilized for investigation of different aspects of film cooling by means of CFD at low turn-around time. This has been accomplished by first carrying out CFD simulations and experiments for an engine-like setting for a full vane. Then the computational domain is reduced in two steps where all results are compared with experiments including aerodynamic validation, heat transfer coefficient and film effectiveness. While the aerodynamic results are in close agreement with experiments, the heat transfer coefficient and film effectiveness results have also shown similarities within the expected range.


Thus this study has shown that this approach can be very useful for e.g. early vane and film cooling design.
Source: Linköping University
Authors: Nadalina Jafabadi, Hossein


Download Project







A New Method for Robust Route Optimization in Ensemble Weather Forecasts (Mechanical Project)

 ,


This paper presents a new dynamic programming method for multi-objective route optimization of ships. The method, which is an extension of the known Dijkstra’s algorithm, uses the concept of Pareto efficiency to handle multi-objective optimization and can be used with both deterministic and ensemble weather forecasts.


The advantage of the presented method in combination with deterministic weather forecasts is demonstrated in comparison to Dijkstra’s algorithm. The comparison between the methods (non surprisingly) shows that both find the same minimum time route, but only the method suggested in this paper was able to find the true minimum fuel route, with about 15% saving.


Evaluation of the presented method in combination with ensemble weather forecasts show that there is an advantage when the objective of the optimization is to minimize fuel consumption.
Source: KTH
Author: Skoglund, Lukas


Download Project







Combustion and Heat Transfer in Meso-Scale Heat Recirculating Combustors (Mechanical Project)

 ,


Combustion in small-scale systems faces problems related to time available for chemical reaction to go to completion and the possible quenching of the reaction by the increased effects of interfacial phenomena (thermal quenching and radical quenching) that occur at the combustor walls due to higher surface to volume ratio.


Heat recirculation, where in a portion of the energy from the products is fed back to the reactants through structural conduction is one of the strategies employed in meso-scale combustors to overcome the problems of thermal quenching of the flame. When liquid fuels are employed, structural conduction can help pre-vaporize the fuel and thereby removes the necessity for a fuel atomizer.


This dissertation focuses on the design, development and operational characteristics of meso-scale combustors employing heat recirculation principle. Self-sustained combustion of propane-air and methanol-air flames were achieved in sub centimeter dimensions (32.6 mm3). The effects of design and operational parameters like wall thermal conductivity, heat exchanger size/channel length, combustion chamber geometry, equivalence ratio, Reynolds number, and external heat transfer (loss) coefficient on the combustor performance were investigated experimentally and numerically.


The experimental procedure involved fabrication of combustors with different geometric features employing materials of different thermal conductivities and then obtaining their operating limits. Thermal performance with respect to various flow conditions was obtained by measuring the reactant preheating and exhaust gas temperatures using thermocouples. Numerical simulations were performed for both reacting and non-reacting flow cases to understand the heat transfer characteristics with respect to various design and operational conditions. Both experiments and numerical simulations revealed that wall thermal conductivity is one of the most important parameters for meso-scale combustor design.


For typical meso-scale dimensions wall materials with minimal thermal conductivity (< 1W/m-K), especially ceramics would yield the best performance. Results showed that the most thermally efficient operating condition occurs for fuel lean cases at higher Reynolds numbers. Flame dynamics inside the combustor were investigated through high-speed imaging and flame acoustic spectrum mapping. Due to the small length scales involved, hydrodynamic instabilities have negligible effect on meso-scale combustion. Flame was observed to be extremely stable with negligible fluctuations. However, a significant amount of thermoacoustic phenomena is present within the combustion regime. Chemiluminescence imaging was employed to correctly map the flame zone inside the combustor.
Source: University of Maryland
Author: Gupta, Ashwani K


Download Project







Optimization of Calculation Models of Maintenance Offers for new Civil Engines (Mechanical Project)

 ,


The sales support department performs calculations concerning maintenance offerings for civil engines based on the use of complex tools. This report describes the missions conducted during my Master’s thesis: firstly, the establishment of a monitoring and security tool in the process of calculating maintenance costs.


The second achievement is the creation of a tool for decision support in order to estimate and compare some of the maintenance costs associated with the use of the new commercial engine and those associated with its competitor. The goal is to estimate offers configurations giving advantages for Snecma.
Source: KTH
Author: Pechoutre, Jean-Baptiste


Download Project







Suspension Design for Off-road Construction Machines (Mechanical Project)

 ,


Construction machines, also referred to as engineering vehicles or earth movers, are used in a variety of tasks related to infrastructure development and material handling. While modern construction machines represent a high level of sophistication in several areas, their suspension systems are generally rudimentary or even nonexistent.


This leads to unacceptably high vibration levels for the operator, particularly when considering front loaders and dump trucks, which regularly traverse longer distances at reasonably high velocities. To meet future demands on operator comfort and high speed capacity, more refined wheel suspensions will have to be developed. The aim of this thesis is therefore to investigate which factors need to be considered in the fundamental design of suspension systems for wheeled construction machines.


The ride dynamics of wheeled construction machines are affected by a number of particular properties specific to this type of vehicle. The pitch inertia is typically high in relation to the mass and wheelbase, which leads to pronounced pitching. The axle loads differ considerably between the loaded and the unloaded condition, necessitating ride height control, and hence the suspension properties may be altered as the vehicle is loaded.


Furthermore, the low vertical stiffness of off-road tyres means that changes in the tyre properties will have a large impact on the dynamics of the suspended mass. The impact of these factors has been investigated using analytical models and parameters for a typical wheel loader. Multibody dynamic simulations have also been used to study the effects of suspended axles on the vehicle ride vibrations in more detail. The simulation  model has also been compared to measurements performed on a prototype wheel loader with suspended  axles.


For reasons of manoeuvrability and robustness, many construction machines use articulated frame steering. The dynamic behaviour of articulated vehicles has therefore been examined here, focusing on lateral instabilities in the form of “snaking” and “folding”. A multibody dynamics model has been used to investigate how suspended axles influence the snaking stability of an articulated wheel loader.


A remote-controlled, articulated test vehicle in model-scale has also been developed to enable safe and inexpensive practical experiments. The test vehicle is used to study the influence of several vehicle parameters on snaking stability, including suspension, drive configuration and mass distribution. Comparisons are also made with predictions using a simplified linear model.


Off-road tyres represent a further complication of construction machine dynamics, since the tyres’ behaviour is typically highly nonlinear and difficult to evaluate in testing due to the size of the tyres. A rolling test rig for large tyres has here been evaluated, showing that the test rig is capable of producing useful data for validating tyre simulation models of varying complexity.


The theoretical and experimental studies presented in this thesis contribute to the deeper understanding of a number of aspects of the dynamic behaviour of construction machines. This work therefore provides a basis for the continued development of wheel
suspensions for such vehicles.
Source: KTH
Authors: Adam Rehnberg


Download Project


>> More Thesis Downloads on Hydro Pneumatic Suspension





Microfabrication and Analysis of Manifold Microchannel Coolers for Power Electronics (Mechanical Project)

 ,


This research presents the analysis and realization of a single phase high performance manifold microchannel cooler for improving the thermal and hydrodynamic performance of multi-chip power electronic modules. This heat exchanger, microfabricated directly into the substrate, enables higher power density electronic products by more efficiently removing the high levels of heat generated.


The improved thermal performance and efficiency of the heat exchanger is demonstrated using both numerical and experimental techniques. The improved heat removal is due to the reduction in the number of packaging layers between the device and the heat exchanger and by improvement in convective heat transfer. In addition, the efficiency of the device is enhanced by minimizing fluid pressure drop through the use of large manifold channels to transport fluid to the cooling area and smaller crossover microchannels in the active cooling area. This combination of channels also improves the uniformity of the temperature distribution across the device.


The manifold microchannel coolers were fabricated and tested both with and without electrical isolation between the chip and the coolant. Experimentally, the coolers without electrical isolation demonstrated thermal resistivity values as low as 0.06 K/(W/cm2), which is up to a 50X improvement over a standard power package with significant size and weight reduction. The coolers with an incorporated aluminum nitride electrical isolation layer experimentally demonstrated up to a 15X improvement.


In addition to experimental results, the interaction between the manifold channels and multiple microchannels was numerically modeled and compared to simpler, one-dimensional approximations based on the Hagen-Poiseuille equation. The comparison shows that the one-dimensional model, while under-predicting total pressure drops, can provide insight into the effect of varying dimensions on system performance. The numerical models were used to identify the impact of varying dimensions across the entire length of the cooler, and a sensitivity analysis was performed with respect to system pressure drop, thermal resistance and uniformity. Additionally, large microchannel velocity gradients, some larger than 10X, were observed along the length of the device which impacts the chip non-uniformity. The simulations showed that when comparing the manifolded design to a comparable straight microchannel cooler, there is a 38X reduction in system pressure drop for similar thermal performance.
Source: University of Maryland
Author: Lauren Marie Boteler


Download Project







Underwater Movement of Obstacles Due to Explosive Detonation (Mechanical Project)

 ,


The U.S. Navy has an interest in researching the movement of obstacles in shallow water due to an explosive detonation. Obstacles that are placed in shallow water on a shoreline can damage vehicles that are attempting to land on shore.


The U.S. Navy believes that explosives can be used to clear the obstacles out of the way and create a safe path for vehicles. Conducting tests on small scale is a cheap and relatively safe, but it would normally require reducing atmospheric pressure by the scale factor which cannot be easily achieved.


The Naval Surface Warfare Center, Indian Head Division, is investigating a “Low Pressure” scaling method that should work for small scales in normal atmospheric pressure. The method alters the depth and size of charge in order to create the same gas bubble growth as measured in full scale conditions.


This study examines the validity of the Low Pressure scaling method by comparing the results to other similar studies. This study also makes some independent analysis of factors such as depth of water, size of charge, obstacle orientation and obstacle stand off distance from the charge.
Source: University of Maryland
Author: Alexander Sergeevich Tsarev


Download Project







A Hybrid Nonlinear Vibration Energy Harvester (Mechanical Project)

 ,


Vibration energy harvesting converts mechanical energy from ambient sources to electricity to power remote sensors. Compared to linear resonators that have poor performance away from their natural frequency, nonlinear vibration energy harvesters perform better because they use vibration energy over a broader spectrum.


We present a hybrid nonlinear energy harvester that combines bi-stability with internal resonance to increase the frequency bandwidth. A two-fold increase in the frequency bandwidth can be obtained compared to a bi-stable system with fixed magnets. The harvester consists of a piezoelectric cantilever beam carrying a movable magnet facing a fixed magnet.


A spring allows the magnet to move along the beam and it provides an extra stored energy to further increase the amplitude of vibration acting as a mechanical amplifier. An electro-mechanically coupled mathematical model of the system is presented to obtain the dynamic response of the cantilever beam, the movable magnet and the output voltage. The perturbation method of multiple scales is applied to solve these equations and obtain approximate analytical solutions.


The effects of various system parameters on the frequency responses are investigated. The numerical approaches of the long time integration (Runge-Kutta method) and the shooting technique are used to verify the analytical results. The results of this study can be used to improve efficiency in converting wasted mechanical vibration to useful electrical energy by broadening the frequency bandwidth.
Source: Binghamton University
Authors: Wei Yang | Shahrzad Towfighian


Download Project







Low Temperature Waste Heat Solutions (Mechanical Project)

 ,


The report comprises two separate parts:


Part 1: Temperature needs for district heating in the paint shop for axles in building 210


Part 2: Energy and low temperature waste heat solutions in heating and cooling systems for building 64 with surroundings


The paint shop for axles in part 1 has air quality requirements in places for coating of axles. To achieve desired air properties there are different process ventilation systems, which consist of ventilation coils for heating and cooling, plus air humidifier. The ventilations coils for heating use district heating. Today the ventilation coils use water of 100°C to achieve necessary air demands in the coating boxes.


This part of the report investigates whether the existing system would achieve the air requirements with a water temperature of 75°C instead of 100°C in the ventilation coils during the coldest parts of the year. The conclusion is that it is not possible; the existing system is adjusted for a water temperature of 100°C to achieve the air requirements. To use a water temperature of 75°C, more or major ventilation coils are needed.


The focus of the report is at part 2. In this part, possibilities for low temperature waste heat solutions are investigated. Those partly aim at specific local solutions for building 64 with surroundings and on the other part of general waste heat solutions for new buildings and reconstructions in the future. To make these parts possible, the systems for heating and cooling in building 64 have been identified. During this identification, potential savings that are not of waste heat character have also been observed.
Source: Linköping University
Author: Svensson, Klas | Wallenskog, Jonas


Download Project







Dynamics Study of an Automobile Exhaust System (Mechanical Project)

 ,


Low vibration levels are a critical objective in automobile exhaust system design. It is therefore important for design engineers to be able to predict, describe and assess the dynamics of various system design proposals during product development.


This thesis aims at providing a deeper understanding of the dynamics of automobile exhaust systems to form a basis for improved design and the development of a computationally inexpensive theoretical system model. Modelling, simulation and experimental investigation of a typical exhaust system are performed to gain such an understanding and to evaluate modelling ideas. Special attention is given to the influence of the bellows-type flexible joint on the dynamics of the exhaust system.


The investigations show that the exhaust system is essentially linear downstream of the flexible joint. Highly simplified finite element models of the major components within this part are suggested. These models incorporate adjustable flexibility in their connection to the exhaust pipes and a procedure is developed for automatic updating of these parameters to obtain better correlation with experimental results. The agreement between the simulation results of the updated models and the experimental results is very good, which confirms the usability of these models.


Furthermore, the investigations show the great reduction of vibration transmission to the exhaust system that the bellows-type joint, either with or without an inside liner, gives in comparison with a stiff joint. For the combined bellows and liner joint, vibration transmission is, however, higher than for the bellows alone. Inclusion of the liner also makes the exhaust system behavior significantly non-linear and complex, whereas the system behavior proves to be essentially linear when the joint has no liner. This shows the importance of including a model of the liner in the theoretical system model when the liner is present in the real system. The choice of whether or not to include a liner in the real system is obviously a complex issue. The advantages of reduced bellows temperature and improved flow conditions should be weighed against the disadvantages found in this work.


By combining the above findings it is concluded that in coming studies of how engine vibrations affect the exhaust system, the latter may be considered as a linear system if the flexible joint consists of a bellows. If the joint also includes a liner, the system may be considered as a linear subsystem that is excited via a non-linear joint.
Author: Johan Wall
Source: Blekinge Institute of Technology


Download Mechanical Project







Anti Roll Tanks in Pure Car and Truck Carriers (Mechanical Project)

 ,


Rolling motions is something that is undesired in all kinds of seafaring. In terms of propulsion resistance, comfort and route planning it would be desirable to reduce these motions.


This study is an investigation on how different roll stabilising systems affect the performance of an 8000 unit PCTC vessel, special emphasis is put on investigating the performance of anti roll tanks. The ship in question has a recorded incidence of parametric rolling and the ability of the tanks to countervail this phenomenon is also investigated.


The tank and fin stabilising systems are relatively equal when it comes to roll damping performance related to changes in the required forward propulsion power. The tanks however, have a higher potential for improvements, addition of features such as heeling systems and parametric roll prevention systems.


The tank performance is also independent of the speed of the ship. The tanks are easier to retrofit and do not require the ship to be put in dry dock during installation. The conclusion of this thesis is that a combined anti roll and heeling system should be installed but that a further study has to be made on the performance of active rudder stabilisation.


It is shown that passive tanks are efficient at preventing parametric rolling in some sea states. A proposal is made for a further study on a control system that could achieve the same performance for all sea states.
Source: KTH
Author: Windén, Björn


Download Project







A Temperature Control System for the Alfvén Laboratory Balloon Experiment (Mechanical Project)

 ,


The polarized Gamma-ray Observer (PoGOLite) is a balloon-borne experiment that will measure the polarization of soft gamma rays in the energy range 25 keV-80 keV. PoGOLite will carry an auroral diagnostics package, ALBERT, to measure the auroral emissions that will enhance the background level.


The spectrophotometers of the Alfven Laboratory Balloon ExpeRimenT consists of a photo multiplying tube (PMT), lenses and a Fabry-Perot etalon, to measure auroral emissions as well as surrounding background emissions. The etalon requires a temperature stabilized environment. In this thesis a thermal analysis of ALBERT has been performed and a control system has been designed.


ALBERT has a power budget of 28 W and to meet the thermal requirements the pressure vessel will be insulated with 15 mm of Aerogel Spaceloft on the inside and 5 mm on the outside. A Peltier element is used to heat or cool the vessel.


At times when heating with a Peltier element is not efficient, due to too high temperature difference, a 12 W air heater will be used in instead. The air heater and the Peltier element will be upported by a 12 W bench heater, which by heating the optical setup ensures a correct temperature of the Fabry-Perot etalons.


The control system will consist of one PID for the air heater and one for the Peltier element. The bench heater will be controlled by a PD regulator with feed forward. The PMT has a built in Peltier element and this will be controlled by a PID regulator with feed forward.
Source: KTH
Author: Magnus Söderquist


Download Project







Vehicle Handling, Stability and Bifurcaiton Analysis for Nonlinear Vehicle Models (Mechanical Project)

 ,


Vehicle handling, stability, and bifurcation of equilibrium conditions were studied using a state vector approach. The research provided a framework for an improved method of vehicle handling assessment that included non-linear regions of performance and transient behavior.


Vehicle models under pure lateral slip, constant velocity, and constant front steer were developed. Four-wheel, two-axle vehicle models were evolved from simpler models and were extended to include vehicle roll dynamics and lateral load transfer effects. Nonlinearities stem from tire force characteristics that include for tire force saturation. Bifurcations were studied by quasi-static variations of vehicle speed and front steer angle.


System models were expanded, assessing overall stability, including vehicle behavior outside normal operating ranges. Nonlinear models of under steering, over steering, and neutral steering vehicles were created and analyzed. Domains of attraction for stable equilibrium were discussed along with physical interpretations of results from the system analysis.
Source: University of Maryland
Author: Nguyen, Vincent


Download Project







Injector design and test for a high power electrodeless plasma thruster (Mechanical Project)

 ,


The HPEP (High Performance Electric Propulsion) thruster is expected to be the outcome of an innovative project initiated by the Swedish Space Corporation. It combines the concept of a 10 kW electrodeless plasma thruster designed by the Elwing Company and the ADN based monopropellant LMP-103S developed by ECAPS and used in the HPGP thrusters of the Prisma Satellites.


Using a chemically energetic propellant in an EP thruster will allow mass and cost reduction by providing two propulsion systems sharing the same tank. This thruster will be suitable for the apogee raising manoeuvre of geostationary satellites; it will allow to carry more transponders and to obtain a better return on investment than with a classical apogee kick motor.


This project focuses on the design and test of the injector that will thermally decompose the liquid LMP-103S so it can enter in the plasma chamber in a gaseous state. The heating power required by the injector is calculated, which leads to a final design composed by a cartridge heater of 400 W inserted in a stainless steel cylinder. The liquid flows through seven other holes drilled around the heater. This injector is tested at both atmospheric and low pressure with deionized water.


Results regarding the power required to vaporize water confirm the theoretical estimation. Steam flow without any liquid droplets is achieved in steady state at low pressure with a maximum temperature on the surface of the injector between 230°C and 260°C.
Source: KTH
Author: Delanoë, Romain


Download Project







Symbol-Based Control of a Ball-on-Plate Mechanical System (Mechanical Project)

 ,


Modern control systems often consist of networks of components that must share a common communication channel. Not all components of the networked control system can communicate with one another simultaneously at any given time. The “attention” that each component receives is an important factor that affects the system’s overall performance.


An effective controller should ensure that sensors and actuators receive sufficient attention. This project describes a “ball-on-plate” dynamical system that includes a digital controller, which communicates with a pair of language-driven actuators, and an overhead camera.


A control algorithm was developed to restrict the ball to a small region on the plate using a quantized set of language-based commands. The size of this containment region was analytically determined as a function of the communication constraints and other control system parameters. The effectiveness of the proposed control law was evaluated in experiments and mathematical simulations.
Source: University of Maryland
Author: Yip, Phillip Thomas


Download Project







Life Consumption Monitoring for Electronics (Mechanical Project)

 ,


Life consumption monitoring is a method to assess product’s reliability based on its remaining life in a given life cycle environment. The life consumption monitoring process involves continuous or periodic measurement, sensing, recording, and interpretation of physical parameters associated with a system’s life cycle environment to quantify the amount of degradation.


This project explains a life consumption monitoring methodology for electronic products, which includes failure modes, mechanisms and effects analysis (FMMEA), virtual reliability assessment, monitoring product parameters, data simplification, stress and damage accumulation analysis and remaining life estimation. It presents two case studies to estimate the remaining life of identical circuit card assemblies in an automobile underhood environment using the life consumption monitoring methodology.


Failure modes, mechanisms, and effects analysis along with virtual reliability assessment is used to determine the dominant failure mechanism in the given life cycle environment. Temperature and vibration are found to be the environmental factors, which could potentially cause malfunction of the circuit card assembly through solder joint fatigue. Temperature sensor and accelerometers are used along with a data logger to monitor and record the environmental loads during the experiment.


A data simplification scheme is used to make the raw sensor data suitable for further processing. Stress and damage models are used to estimate the remaining life of the circuit card assembly based on the simplified data. Performances of the test board assemblies are monitored through resistance monitoring. The life cycle environment and results for the case studies are compared with each other. The estimated results are also compared with experimental life results.
Source: University of Maryland
Author: Mishra, Satchidananda


Download Project







Assessment of Pollution Levels Resulting from Biomass Gasification (Mechanical Project)

 ,


Today the large scale introduction of biomass gasification is hampered by health, safety and environmental issues which present a major barrier in the deployment of this technology. The condensate in particular resulting from producer gas cooling before use in gas engines is highly toxic and carcinogenic which, if not adequately controlled, can lead to detrimental impacts on human health and the environment.


The study was therefore aimed at assessment of pollution levels resulting from biomass gasification organic condensates. The study involved assessing the concentration of polycyclic aromatic hydrocarbons (PAHs) and BTEX (i.e. benzene, toluene, ethylbenzene and xylene) in the condensate deemed toxic and carcinogenic, mention their impact on human health and the environment as well as recommend measures aimed at minimizing pollution levels resulting from biomass gasification.


The gasifier installation at Makerere University was run in downdraft mode using maize cobs as biomass fuel. The producer gas was cooled using a water cooled condenser connected to the exhaust pipe of the gasifier. The condensate was then transferred into sampling bottles made of opaque glass to minimize photochemical reactions in water samples and preserved in a cooler at 2oC to 6oC until the time for analysis to minimize volatilization and bacterial degradation of the hydrocarbons. The capillary gas chromatography with mass spectrometric detector (CGCMSD) was used to analyze the condensate for the selected hydrocarbons.
Source: KTH
Author: Menya, Emmanuel


Download Project







Test Turbine Measurements and Comparison with Meanline and Throughflow Calculations (Mechanical Project)

 ,


This study is a collaboration between Siemens Industrial Turbomachinery(SIT) and Royal Institute of Technology(KTH). It is aimed to study and compare the outputs of two different computational approaches in axial gas turbine design procedure with the data obtained from experimental work on a test turbine.


The main focus during this research is to extend the available test databank and to further understand and investigate the turbine stage efficiency, mass flow parameters and reaction degree under different working conditions. Meanwhile the concept and effect of different loss mechanisms and models will be briefly studied.


The experimental part was performed at Heat and Power  Technology department on a single stage test turbine in its full admission mode. Three different pressure ratios were tested.


For the medium pressure ratio a constant temperature anemometry (CTA) method was deployed in two cases, with and without turbulence grid, to determine the effect of free-stream turbulence intensity on the investigated parameters. During the test campaign the raw gathered data was processed with online tools and also they served as boundary condition for the computational codes later.


The computational scope includes a one-dimensional design approach known as mean-line calculation and also a two-dimensional method known as throughflow calculation. An in-house SIT software, CATO, generated the stage geometry (vane, blade and the channel) and then two other internal computational codes, MAC1 and BETA2, were employed for the one-dimensional and two-dimensional computations respectively.


It was observed that to obtain more accurate mass flow predictions a certain level of channel blockage should be implemented to represent the boundary layer development and secondary flow which is typically around 2%.


The codes are also equipped with two options to predict the friction loss: One is a more empirical correlation named as the Old approach in SIT manuals and the other works based on allocation of boundary layer transition point, named as BL in the present thesis. Simulations were done by use of both approaches and it turned out that the latter works more accurately if it is provided with appropriate transition point and blockage estimation.


The measured data also suggests the idea that the transition point of the vane and blade is not affected by a change in turbulence intensity at least up to 6% in the tested Reynolds numbers, . Amongst different solutions the one which used BL approach and constant transition point (while the turbulence intensity changed) managed to predict this behavior.


Also it was investigated and revealed that the codes inherently predict poor results in off-design loadings which is mainly due to positive incidence angle in addition to high spanwise gradient of the flow parameters.
Source: KTH
Author: Mikaillian, Navid


Download Project





Developing Highly Accurate And Stable Open-region Electromagnetic Simulations (Mechanical Project)

 ,


In open-region electromagnetic simulations, the computational domain has to be truncated by an absorbing boundary condition (ABC) to model the infinite space. The performance of ABC strongly affects the accuracy of overall numerical simulation.


For a class of advanced problems demanding high accuracy, such as in the modeling of medical detection devices, indoor wireless communication systems and remote sensing equipments, the received signal can be several orders of magnitude less than the transmitted signal. Furthermore, wide-band simulations require long running times for transients-based simulations, which increase the potential for instability. Therefore, accuracy and stability of absorbing boundary conditions are identified as critical in the design of numerical algorithms compatible with advanced applications.


In this work, theory of Concurrent Complementary Operators Method (C-COM) in both transient and frequency-domain numerical simulations is investigated. The C-COM is based on the basic premise of primary reflection cancellation. The C-COM applications to numerically derived ABCs in finite difference time-domain (FDTD) method, and to frequency domain ABCs in both finite difference frequency domain (FDFD) method and finite element method (FEM) method are developed.


Extensive numerical experiments are conducted showing dramatic increase in accuracy when the C-COM is applied in comparison to previous published techniques. Previous works that addressed the boundary instability arising from the application of the absorbing boundary condition used either the von Neumann analysis or the Gustafsson-Kreiss-Sundström (GKS) analysis. These earlier works, however, did not explain the inconsistencies that have been observed between the theoretical predictions and numerical experiments.


This study presents a new stability analysis applicable to boundary conditions. This new analysis, referred to as Coupled Stability Analysis (CSA), is based on the fundamental assumption that absorbing boundary conditions are not perfect, and therefore, generate waves that reflect back into the computational domain. It is found that this analysis yields results that are fully consistent with those obtained from numerical experiments. As an important consequence of this analysis, and contrary to earlier conjectures, we show that Higdon’s absorbing boundary condition of order 3 (and possibly, higher orders) to be unconditionally unstable.
Source: University of Maryland
Author: Wu, Xin


Download Project





Sizing and Balance Module Development for Aircraft Conceptual Design (Mechanical Project)

 ,


This work was done in order to improve the capabilities in a preliminary aircraft analysis program, DIBA, at Saab Aerosystems. The areas that this was done are in the sizing and balance. One sizing tool was developed in order to make a performance analysis with the DIBA generated geometry and customer and/or regulation based criteria. A balance diagram, a neutral point estimation function, a landing gear plot and a trim program was created in order to extend the weight and balance analysis.


Results show that various aircraft both military and civil can be analyzed with good comparison to other analysis and reality. For example EXCEL implemented analysis and graphs over real aircrafts shown in the report.
Source: Linköping University
Author: Peterson, Gustav


Download Project