The great challenge of the 21st century to mitigate climate change requires generation of green electricity to be an achievable goal. One way of producing green electricity is through usage of wave energy converters which are devices that use the energy of the ocean waves to produce electricity.   W4P Waves4Power AB is a company from Sweden, devoted to commercializing their wave energy converter called the WaveEl buoy. The WaveEl buoy is a point absorber that produces electricity by using the energy of the waves to run a hydraulic motor connected to a generator. The working principle of the buoy is to let a water piston oscillate in a tube with a water column. The water column exerts flow resistance forces on the piston as it oscillates, and these forces create a frame of reference upon which the hydraulic motor system may operate. There are leakage clearances at the sides of the water piston that allow for flow of water past the piston and associated with this flow are parts of the flow resistance forces. The flow resistance forces that are present due to water flow in the leakage clearances are calculated with the use of a flow resistance parameter and, in the literature, there is little investigation conducted as to the importance of this parameter.  The goal of present thesis work was to investigate the effect on 4 parameters of the WaveEl buoy system (power captured from the waves, flow resistance force acting on the piston, mean piston position, and number of bumper hits) due to adoption of 3 different values of the flow resistance parameter. One of these values was the currently assigned value by Waves4Power at the time when this study was conducted. The value was the constant 0.75 and was a guess by Waves4Power. The other two values were received from a parallel thesis work done at Karlstad University by Linnéa Tebelius where, with the use of CFD, Tebelius calculated the flow resistance parameter with different levels of accuracy.  The results of present thesis work were generated from simulations in a MATLAB Simulink model describing the dynamics of the WaveEl buoy system. Simulated time varied from 5.5 to 8.5 minutes per simulation. Generated results were compared to the results from using 0.75 as the value for the flow resistance parameter and showed that the energy captured from the waves was, at most, overestimated by approximately 13 % and underestimated by 6 %, depending on applied level of accuracy for description of the dynamic flow resistance parameter and simulated wave state. Furthermore, it was found that number of bumper hits varied extensively, in some cases from 0 to 47, between simulations where the only difference was applied value of the flow resistance parameter – further indicating that assigning a more accurate value on the dynamic flow resistance parameter may be of great importance when modelling the dynamics of the WaveEl buoy system.

Published Article / Although research has been conducted in the field of Acoustic Doppler Borehole Flowmeters (ADBF), it has been focused on point source of flow and three dimensional borehole flow techniques. However as of yet, no studies have been conducted on the possible use of Acoustic Doppler Borehole Profiling (ADBP). This technique of borehole flow measurement is possibly a revolutionary concept in how vertical flow in a borehole is measured. It makes use of a single inexpensive transducer that can float on the surface of the water in a borehole and use Acoustic Doppler techniques to profile the flow in a borehole. No complicated and expensive flow probe winching systems will be required. Another added benefit of the ADBP will be the non-evasive technologies that comprise its design. Current borehole flow probes are required to be present at the point of flow measurement in the borehole. The presence of the probe inadvertently alters the flow in the borehole by adding resistance to the flow in the borehole. Under stressed or pumped flow tests these flow resistance effects cause sufficient pressure gradients at the flow sensors to divert part of the flow away from the sensor. This causes erroneous readings of flow as a part of the flow in the borehole is not accounted for. In ADBP the sensor is not physically present at the point of flow being read. This makes the ADBP technique of borehole flow measurement far more representative of the natural flow conditions in the borehole under ambient and stressed conditions.

A spur dike is a hydraulic structure built on the bank of a river at some angle to the main flow direction. A series of spur dikes in a row may also be placed on one side or both sides of a river to form a spur dike field. Spur dikes are used for two main purposes, namely river training and bank protection. For river training, spur dikes may be used to provide a desirable path for navigation purposes or to direct the flow to a desirable point such as a water intake. For bank protection, spur dikes may be used to deflect flow away from a riverbank and thus protect it from erosion. It has also been observed that spur dikes provide a desirable environment for aquatic habitat. Despite the fact that spur dikes are useful hydraulic structures, they have been found to increase the flow resistance in rivers and hence increase the flow stage. The present study focuses on the quantification of the flow resistance and associated flow stage increase due to a single spur dike and also that of a spur dike field. Increased flow stage is referred to herein as a backwater effect.<p> In the first stage of the study, the flow resistance due to a single spur dike, expressed as a drag force exerted on the flow in an open channel, was studied and quantified. The work was carried out in a rigid bed flume, with the model spur dike being simulated using various sizes of a two-dimensional (2-D) rectangular plate. Several discharge conditions were studied. The drag force exerted by the spur dike for both submerged and unsubmerged flow conditions was determined directly from measurements made using a specially designed apparatus and also by application of the momentum equation to a control volume that included the spur dike. It was found that the unit drag force (i.e., drag force per unit area of dike) of an unsubmerged spur dike increases more rapidly with an increase in the discharge when compared with that of a submerged spur dike. The results also showed that an increase in the blockage of the open channel cross-section due to the spur dike is the main parameter responsible for an increase in the spur dike drag coefficient, hence the associated flow resistance and backwater effect. Based on these findings, relationships were developed for estimating the backwater effect due to a single spur dike in an open channel.<p> In the second stage of the study, the flow resistance due to a spur dike field expressed as a drag force exerted on the flow was quantified and subsequently related to the backwater effect. The work was carried out in a rigid bed flume, with the model spur dikes simulated using 2-D, rectangular plates placed along one side of the flume. For various discharges, the drag force of each individual spur dike in the spur dike field was measured directly using a specially-designed apparatus. For these tests, both submerged and unsubmerged conditions were evaluated along with various numbers of spur dikes and various relative spacings between the spur dikes throughout the field. It was concluded that the configuration of a spur dike field in terms of the number of spur dikes and relative spacing between the spur dikes has a substantial impact on the drag force and hence the flow resistance and backwater effect of a spur dike field. The most upstream spur dike had the highest drag force amongst the spur dikes in the field, and it acted as a shield to decrease the drag force exerted by the downstream spur dikes. From the experiments on the submerged spur dikes, it was observed that the jet flow over the spur dikes has an important effect on the flow structure and hence the flow resistance.<p> In the third stage of the study, the flow field within the vicinity of a single submerged spur dike was modeled using the three-dimensional (3-D) computational fluid dynamic (CFD) software FLUENT. Application of the software required solution of the 3-D Reynolds-averaged Navier-Stokes equations wherein the Reynolds stresses were resolved using the RNG ê-å turbulence model. One discharge condition was evaluated in a smooth, rectangular channel for two conditions, including uniform flow conditions without the spur dike in place and one with the spur dike in place. The CFD model was evaluated based on some experimental data acquired from the physical model. It was found that the CFD model could satisfactorily predict the flow resistance and water surface profile adjacent to the spur dike, including the resulting backwater effect. Furthermore, the CFD model gave a good prediction of the velocity field except for the area behind the spur dike where the effects of diving jet flow over the spur dike was not properly modeled.

No description available.

No description available.

A spur dike is a hydraulic structure built on the bank of a river at some angle to the main flow direction. A series of spur dikes in a row may also be placed on one side or both sides of a river to form a spur dike field. Spur dikes are used for two main purposes, namely river training and bank protection. For river training, spur dikes may be used to provide a desirable path for navigation purposes or to direct the flow to a desirable point such as a water intake. For bank protection, spur dikes may be used to deflect flow away from a riverbank and thus protect it from erosion. It has also been observed that spur dikes provide a desirable environment for aquatic habitat. Despite the fact that spur dikes are useful hydraulic structures, they have been found to increase the flow resistance in rivers and hence increase the flow stage. The present study focuses on the quantification of the flow resistance and associated flow stage increase due to a single spur dike and also that of a spur dike field. Increased flow stage is referred to herein as a backwater effect.<p> In the first stage of the study, the flow resistance due to a single spur dike, expressed as a drag force exerted on the flow in an open channel, was studied and quantified. The work was carried out in a rigid bed flume, with the model spur dike being simulated using various sizes of a two-dimensional (2-D) rectangular plate. Several discharge conditions were studied. The drag force exerted by the spur dike for both submerged and unsubmerged flow conditions was determined directly from measurements made using a specially designed apparatus and also by application of the momentum equation to a control volume that included the spur dike. It was found that the unit drag force (i.e., drag force per unit area of dike) of an unsubmerged spur dike increases more rapidly with an increase in the discharge when compared with that of a submerged spur dike. The results also showed that an increase in the blockage of the open channel cross-section due to the spur dike is the main parameter responsible for an increase in the spur dike drag coefficient, hence the associated flow resistance and backwater effect. Based on these findings, relationships were developed for estimating the backwater effect due to a single spur dike in an open channel.<p> In the second stage of the study, the flow resistance due to a spur dike field expressed as a drag force exerted on the flow was quantified and subsequently related to the backwater effect. The work was carried out in a rigid bed flume, with the model spur dikes simulated using 2-D, rectangular plates placed along one side of the flume. For various discharges, the drag force of each individual spur dike in the spur dike field was measured directly using a specially-designed apparatus. For these tests, both submerged and unsubmerged conditions were evaluated along with various numbers of spur dikes and various relative spacings between the spur dikes throughout the field. It was concluded that the configuration of a spur dike field in terms of the number of spur dikes and relative spacing between the spur dikes has a substantial impact on the drag force and hence the flow resistance and backwater effect of a spur dike field. The most upstream spur dike had the highest drag force amongst the spur dikes in the field, and it acted as a shield to decrease the drag force exerted by the downstream spur dikes. From the experiments on the submerged spur dikes, it was observed that the jet flow over the spur dikes has an important effect on the flow structure and hence the flow resistance.<p> In the third stage of the study, the flow field within the vicinity of a single submerged spur dike was modeled using the three-dimensional (3-D) computational fluid dynamic (CFD) software FLUENT. Application of the software required solution of the 3-D Reynolds-averaged Navier-Stokes equations wherein the Reynolds stresses were resolved using the RNG ê-å turbulence model. One discharge condition was evaluated in a smooth, rectangular channel for two conditions, including uniform flow conditions without the spur dike in place and one with the spur dike in place. The CFD model was evaluated based on some experimental data acquired from the physical model. It was found that the CFD model could satisfactorily predict the flow resistance and water surface profile adjacent to the spur dike, including the resulting backwater effect. Furthermore, the CFD model gave a good prediction of the velocity field except for the area behind the spur dike where the effects of diving jet flow over the spur dike was not properly modeled.

Mikrosiebe stellen auf Grund ihrer Geometrie einen geringeren Strömungswiderstand im System dar und ermöglichen somit eine höhere Filtrationsgeschwindigkeit. Der Einsatz solcher Mikrosiebe anstelle herkömmlicher Membranen in Filtrationsprozessen kann deren Effizienz enorm steigern. Im Rahmen der Diplomarbeit wurden mittels partikelassistierter Benetzung hergestellte Mikrosiebe charakterisiert. Hierfür wurde zunächst ein Filtermodul für Kreuzstromfiltrationen entwickelt, welches anschließend in einen Versuchsaufbau integriert und charakterisiert wurde. Neben den Strömungswiderständen der rechteckigen Kanäle des Moduls wurde außerdem der Strömungswiderstand für Mikrosiebe einer Porengröße bestimmt und mit der Theorie verglichen. Es zeigt sich, dass Theorie und Praxis gut übereinstimmen und es sich bei dem entwickelten Versuchsaufbau um eine gute Methode handelt Strömungswiderstände von Mikrosieben zu bestimmen.

No description available.

O problema da previsão da resistência ao escoamento em canais tem atraído a atenção dos engenheiros há longo tempo. Durante os últimos decênios a resistência ao escoamento em canais abertos de fundo fixo tem sido amplamente investigada, usando rugosidade artificial nas superfícies de canais experimentais. A adoção do coeficiente de rugosidade para um canal natural significa estimar a resistência de este ao escoamento. A utilização de um valor incorreto deste coeficiente pode ter grandes impactos na estimação da vazão e em conseqüência no dimensionamento dos projetos de obras hidráulicas. Apresenta-se, mediante pesquisa bibliográfica, os métodos de cálculo para avaliação do coeficiente de rugosidade ou coeficiente de resistência, dando ênfase a aqueles desenvolvidos para canais naturais com rugosidade de grande escala, sem os efeitos do transporte de sedimentos. Em modelo físico avaliam-se os efeitos da distribuição, tamanho e forma dos elementos geométricos na resistência ao escoamento. Espera-se que os resultados da pesquisa proporcionem ao engenheiro os critérios necessários para a avaliação do coeficiente de rugosidade. Os métodos diretos de medição de vazões nos rios nem sempre podem ser levados a cabo em rios de montanha , especialmente na época de cheia, devido às grandes declividades (i>1%), material de grandes dimensões no leito (pedras, seixos, matacões), submersão relativa menor do que 1, condições estas de escoamento que podem ser perigosas para os equipamentos de medição. Em tais circunstâncias é necessário o uso de métodos indiretos. A aplicação das relações de resistência ao escoamento em rios de montanha torna-se difícil pelos escassos conhecimentos na avaliação do coeficiente de resistência. Faz-se uma comparação das diferentes formulações existentes da resistência ao escoamento com dados de um rio dos Andes peruanos, determinando-se uma equação de ajuste. / The flow resistance estimation problem in channels has attracted the engineer's attention for a long time. During the last decades the flow resistance in open channels with rigid bed has been research with the use of artificial roughness in bed flumes. Adapting a natural channel roughness coefficient means the estimation of the corresponding resistance to flow. The use of an incorrect value in this coefficient might produce a big impact in the discharge estimation, as well as in the hydraulic work project. The calculation methods to estimate the roughness coefficient or resistance coefficient are showed through this bibliographic research, attaching importance to those developed for channels with large scale roughness; this without the sediment transport effects into account. The distribution, size and shape effects of the geometric elements in the flow resistance are evaluated in a physical model. It is expected that the research results provide the engineer with the required criteria to estimate the roughness coefficient. The direct methods of the discharge measurement in rivers can not always take place in mountain rivers, owing to the following reasons: high gradients (i>1%), big dimension material (cobbles and boulders), relative submergence lower than unit; flow conditions that might be dangerous for the measuring equipment. Under these circumstances it is necessary the use of indirect methods. The application of flow resistance relations in mountain rivers turns very difficult, due to the limited knowledge in resistance coefficient evaluation. In the following research has been made a comparison of the different existing flow resistance equations in mountain rivers, for a river in the Peruvian Andes by establishing a fitting curve.

O problema da previsão da resistência ao escoamento em canais tem atraído a atenção dos engenheiros há longo tempo. Durante os últimos decênios a resistência ao escoamento em canais abertos de fundo fixo tem sido amplamente investigada, usando rugosidade artificial nas superfícies de canais experimentais. A adoção do coeficiente de rugosidade para um canal natural significa estimar a resistência de este ao escoamento. A utilização de um valor incorreto deste coeficiente pode ter grandes impactos na estimação da vazão e em conseqüência no dimensionamento dos projetos de obras hidráulicas. Apresenta-se, mediante pesquisa bibliográfica, os métodos de cálculo para avaliação do coeficiente de rugosidade ou coeficiente de resistência, dando ênfase a aqueles desenvolvidos para canais naturais com rugosidade de grande escala, sem os efeitos do transporte de sedimentos. Em modelo físico avaliam-se os efeitos da distribuição, tamanho e forma dos elementos geométricos na resistência ao escoamento. Espera-se que os resultados da pesquisa proporcionem ao engenheiro os critérios necessários para a avaliação do coeficiente de rugosidade. Os métodos diretos de medição de vazões nos rios nem sempre podem ser levados a cabo em rios de montanha , especialmente na época de cheia, devido às grandes declividades (i>1%), material de grandes dimensões no leito (pedras, seixos, matacões), submersão relativa menor do que 1, condições estas de escoamento que podem ser perigosas para os equipamentos de medição. Em tais circunstâncias é necessário o uso de métodos indiretos. A aplicação das relações de resistência ao escoamento em rios de montanha torna-se difícil pelos escassos conhecimentos na avaliação do coeficiente de resistência. Faz-se uma comparação das diferentes formulações existentes da resistência ao escoamento com dados de um rio dos Andes peruanos, determinando-se uma equação de ajuste. / The flow resistance estimation problem in channels has attracted the engineer's attention for a long time. During the last decades the flow resistance in open channels with rigid bed has been research with the use of artificial roughness in bed flumes. Adapting a natural channel roughness coefficient means the estimation of the corresponding resistance to flow. The use of an incorrect value in this coefficient might produce a big impact in the discharge estimation, as well as in the hydraulic work project. The calculation methods to estimate the roughness coefficient or resistance coefficient are showed through this bibliographic research, attaching importance to those developed for channels with large scale roughness; this without the sediment transport effects into account. The distribution, size and shape effects of the geometric elements in the flow resistance are evaluated in a physical model. It is expected that the research results provide the engineer with the required criteria to estimate the roughness coefficient. The direct methods of the discharge measurement in rivers can not always take place in mountain rivers, owing to the following reasons: high gradients (i>1%), big dimension material (cobbles and boulders), relative submergence lower than unit; flow conditions that might be dangerous for the measuring equipment. Under these circumstances it is necessary the use of indirect methods. The application of flow resistance relations in mountain rivers turns very difficult, due to the limited knowledge in resistance coefficient evaluation. In the following research has been made a comparison of the different existing flow resistance equations in mountain rivers, for a river in the Peruvian Andes by establishing a fitting curve.