Design and evaluation of a sustainable blended study programme in higher education

IntroductionBlended learning, i.e., a mix of online and in-class education, can be deployed for enhancing the educational quality and resilience in higher education (HE). It may also contribute to HE’s sustainability objectives by lowering the carbon emissions of students commuting to campus. In this study, pedagogical design principles for sustainable blended learning and teaching are developed and evaluated taking into account these opportunities.MethodsA prototype for a sustainable blended study program at a University of Applied Sciences was developed and evaluated using a form of Educational Design Research.ResultsThe design stage, carried out by a team of eight lecturers, resulted in a design based on six pedagogical design principles. This design also included an effort to reduce student travel by limiting on-campus education to two days a week. The results show the effects of students’ increased online learning skills and diminished travel movements on their satisfaction with the blended learning design, and their travel behaviour, which can lead towards an attitude change regarding commute and online learning. The lecturers’ observations and experiences, depending on their personal preferences, contradicted (self-regulation skills) as well as confirmed (online learning experiences) the students’ evaluations.DiscussionThe developed design principles are important to support a new balance between virtual and physical spaces, learning activities, moments in time and sustainability

Structural reduction of carbon emissions through online education in Dutch Higher Education

Dutch institutions of Higher Education have to meet stringent requirements for energy efficiency andreducing carbon emissions imposed by the national government. The commute of students and staffgreatly contributes to the carbon footprint of a Higher Education Institution. International students inDutch Higher Education also have a substantial impact on the environment due to air travel. Theirnumber increases every year. The deployment and use of ICT can contribute substantially to thereduction of energy use and carbon emissions through decreasing mobility of students and staff byincreasing virtualization and digitalization of educational processes.This exploratory study examines the opportunities of online learning as a means to reduce the impactof students’ traveling on the carbon footprint. The research methodology consists of a systematicreview of literature and a series of interviews with experts of online learning and managers of energy,ICT and/or sustainability.An obstacle for decreasing the carbon footprint of a Higher Education Institution using online learningare differences in opinion as expressed by professionals, regarding the quality of this form ofeducation. Our research shows that those in favour of face-to-face education believe, that the socialprocesses are essential for high quality education. Proponents of online learning emphasize theopportunities by focusing on the advantages for individual students – i.e. giving students more controlover their own learning process. So far, only a minority have recognized that online learning can leadto decreased mobility and a reduction of carbon emissions

Probabilistic examination of the change in eigenfrequencies of an offshore wind turbine under progressive scour incorporating soil spatial variability

The trend for development in the offshore wind sector is towards larger turbines in deeper water. This results in higher wind and wave loads on these dynamically sensitive structures. Monopiles are the preferred foundation solution for offshore wind structures and have a typical expected design life of 20 years. These foundations have strict serviceability tolerances (e.g. mudline rotation of less than 0.25° during operation). Accurate determination of the system frequency is critical in order to ensure satisfactory performance over the design life, yet determination of the system stiffness and in particular the operational soil stiffness remains a significant challenge. Offshore site investigations typically focus on the determination of the soil conditions using Cone Penetration Test (CPT) data. This test gives large volumes of high quality data on the soil conditions at the test location, which can be correlated to soil strength and stiffness parameters and used directly in pile capacity models. However, a combination of factors including; parameter transformation, natural variability, the relatively small volume of the overall sea bed tested and operational effects such as the potential for scour development during turbine operation lead to large uncertainties in the soil stiffness values used in design. In this paper, the effects of scour erosion around unprotected foundations on the design system frequencies of an offshore wind turbine is investigated numerically. To account for the uncertainty in soil-structure interaction stiffness for a given offshore site, a stochastic ground model is developed using the data resulting from CPTs as inputs. Results indicate that the greater the depth of scour, the less certain a frequency-based SHM technique would be in accurately assessing scour magnitude based solely on first natural frequency measurements. However, using Receiver Operating Characteristic (ROC) curve analysis, the chance of detecting the presence of scour from the output frequencies is improved significantly and even modest scour depths of 0.25 pile diameters can be detected

Estimation of the Vibration Decrement of an Offshore Wind Turbine Support Structure Caused by its Interaction with Soil

In today’s cutting costs environment in the offshore wind industry, significant achievements can be made with a better assessment of dynamic soil-pile interaction. More knowledge regarding the contribution of the dynamic soil-pile interaction to damping of an offshore wind turbine structure (OWT) could perceptibly reduce the fabrication costs of an OWT. Currently, not much is known about the contribution of soil to the total damping of the vibration of an OWT which consists of five main damping mechanisms: aerodynamic-, hydrodynamic-, structural-, soil- and a passive sloshing damper in the nacelle. The values for this contribution applied in the industry today - mostly calculated analogously to a study performed in 1980 by M.F. Cook - can be expected to be on the low side (conservative), and it is acknowledged that it might be higher. More research on the topic is recommended. Increased damping of the vibrations of an OWT decreases the occurring stresses in the structure which in turn results in lower (often design driving) fatigue damage accumulation. Presence of more damping than currently assumed would justify either designing more light-weight structures using less construction steel, or allowing for longer (insured) OWT lifetimes than the currently applied 20 years. Both measures significantly reduce costs of offshore generated wind power. This research evaluates measured signals of twelve ’rotor stop’ - tests on an offshore wind turbine at the Dong Energy owned - Burbo Bank wind farm in the Irish Sea. The recorded data comprises the vibration decay of the structure, measured with an accelerometer and strain gauges along the tower. An analytical model has been developed enabling analyses of the origin of the measured signals. Two main frequencies were identified in the measurements and, using the different measurement locations and the model, the corresponding modal shapes were identified. A crucial distinction between the two modal shapes is the difference in motion of the lower part of the structure. The amplitudes of displacement and velocity at this location are much smaller for the second observed modal shape than for the first. A large difference in damping ratio between the two frequencies was identified. The difference in damping is attributed to the different effect the soil can have on the damping of these two frequencies. This can be explained by the varying amplitudes of their modes in the soil embedded part of the structure. The measured total damping (19 % logarithmic decrement which is 3 % ratio of critical) for the first natural bending frequency of the tower, and the possible order of magnitude of the found contribution of soil on this damping (~ 9.5 % log. decr. or 1.5 % ratio) of this particular OWT is significantly larger than the order of magnitude used in the industry today (respectively ~ 2.5 % log. decr. and ~0.44 %).Offshore Engineering/Offshore WindHydraulic EngineeringCivil Engineering and Geoscience

Identification of effective 1D soil models for large-diameter offshore wind turbine foundations based on in-situ seismic measurements and 3D modelling

Offshore wind generated electricity is currently one of the most promising sources of energy to contribute in creating a sustainable global energy mix. The latter is essential for minimising the detrimental impact of human-induced accelerated climate change. The cost of offshore wind power has strongly decreased over the past years due to (amongst others) progressive R&amp;D, the increased capacity of the plants and due to a lower perceived risk (i.e., interest rates). The current thesis contributes to further lowering the cost of this energy source; it justifies the application of less steel in the design of the most often applied monopile (MP) foundation, by providing a more accurate and less conservative design method for the soil-structure interaction (SSI) of rigidly behaving MP foundations. More specifically, this thesis addresses the lateral \emph{small-strain} soil response towards rigidly behaving piles that typically have a relatively low ratio of embedded length L to diameter D: L/D&lt;7. It is the small-strain regime that governs the overall dynamic properties of the offshore wind turbine (OWT), which in turn define the accumulation of steel fatigue damage - most often the main design driver in dimensioning the support structure (foundation and tower). The work aims to improve both the currently applied in-situ characterisation of the soil properties and the design model used for simulating the complex SSI of MP foundations. For capturing the in-situ small-strain soil properties, it is suggested to add seismic measurements to the standard site characterisation scope. The currently applied geotechnical Cone Penetration Test measures the very local, large-strain strength parameters, whereas the output of a geophysical method like the Seismic Cone Penetration Test reflects the more global, small-strain stiffness properties of the soil. Regarding the design model, it is suggested to benefit from the accuracy of a 3D model, as it automatically captures the various soil reaction mechanisms that dominate the SSI of rigidly behaving piles. The soil in interaction with the small pile displacements of the fatigue-limit-state load case can be idealised to behave as a linear elastic material. The basic soil stiffness parameters captured by the seismic measurements can be directly used to fully characterize a linear elastic continuum of a 3D model. This physics-based approach, which first identifies the stiffness of the soil and subsequently that of the soil-pile system, is a more versatile and accurate method than the most often applied semi-empirical p-y curve method. The latter method employs the depth-dependent modulus of horizontal subgrade reaction k(z) to quantify a particular soil-pile initial lateral stiffness, to be used in a 1D Winkler foundation model. The Winkler model is the all-time favourite engineering model due to its simplicity and intuitive representation of the main involved physics in the SSI, and the subgrade modulus is a very useful SSI parameter. However, k(z) is an empirical tuning parameter, depending not only on the properties of the (stratified) soil, but also on those of the pile. As the currently used p-y curves were calibrated on small-diameter, flexible piles, they are not representative for the soil reactions to short, rigidly behaving MP foundations. In only assuming a lateral, uncoupled soil reaction - being the dominant restoring force for flexible piles, and hence the assumption in the p-y curve method - one underestimates the complete restoring reaction of the soil, which is induced by additional, more complex soil mechanisms. To become truly useful for design, the 3D model should not only serve as a design check, but its accuracy should be directly integrated into the design models. Similar to various other engineering design procedures, the thousands of load simulations required in the design of offshore wind support structures, make the 3D model computationally too expensive to replace the simple, 1D design model. To employ the speed and simplicity of the 1D model with the accuracy of the 3D model, the current thesis presents - as its main contribution - 2 methods to obtain a 1D effective model that mimics the 3D modelled response. The first, `local' method establishes an effective 1D stiffness keff(z), by optimising the profile of the uncoupled (local) lateral springs that renders the response of the 1D Winkler model of a rigid pile in stratified soil the same as that of the static response of the 3D model in terms of displacement, slope, rotation and curvature along the full embedded length of the pile. Accurate matches can be obtained for quite a broad range of pile geometries and soil (stiffness) profiles, however, this local method seems to perform worse for piles with L/D<4.5, softer and/or very irregular soil stiffness profiles. The same methodology was found to be able to also generate an effective damping profile ceff(z) to additionally mimic the energy dissipation in the SSI - provided that a previously found static stiffness profile keff(z) accurately captures the static response.In the second, `non-local' method, effective 1D global stiffness kernels are computed which fully capture the coupled 3D reactions of the stratified soil to the pile, for both the static and the low-frequency dynamic SSI. With the use of the stiffness kernels for the lateral and rotational degrees of freedom, the need of searching for various separate 1D stiffness elements, like distributed lateral and rotational springs along the pile or similar discrete springs at the pile tip, has become obsolete; such mechanisms are all automatically incorporated in the non-local stiffness kernels. The non-local method was shown to be very versatile, irrespective of pile geometry and soil stiffness profile, providing accurate matches of the 3D simulated response of the embedded pile.Finally, for increased confidence, methods and models should be validated - preferably by measuring the response of a realistic and representative version of the structure of interest. As no measurements of the dynamic response of a large scale MP foundation were reported in literature, an extensive measurement campaign was designed and executed on a `real' MP foundation of a near-shore wind farm. The setup involved a large amount of sensors on the pile and in the adjacent soil distributed over the full length of the pile, applying a steady-state excitation with a custom-made hydraulic shaker. The structure being a stand-alone pile, excluding dynamic disturbance of the to-be-installed super structure of tower and turbine, and the test comprising a controlled (known) loading, this campaign was shown to yield a much lower uncertainty regarding the soil response than for the commonly applied monitoring of the operational full OWT structure. Together with the inclusion of realistic saturated, nonhomogeneous sandy soil conditions and installation effects, a `first-off' opportunity was created to validate a model for the lateral, dynamic response of rigidly behaving monopiles. In the presented analyses of the measured response, the predicted effective stiffness was employed as an initial guess in a model-based identification of the stiffness, damping and fundamental frequency of the soil-pile system. It was shown that the proposed design procedure yields a 7 times higher accuracy in predicting the in-situ initial stiffness than the best-estimate p-y curve model. Furthermore, 2 adaptations of the 1D model were employed to investigate the presence of soil-added mass effects in the higher-frequency response of the system. Finally, the stiffness and damping of the pile-only system were related to those observed for the full OWT system, and the assumption of linear elastic soil response was validated using the observed pile response. An initial estimation of the possible benefit of the developed stiffness method, showed a 8% saving potential for the primary steel (shell) mass of the complete support structure (MP, transition piece and tower). This exercise was performed for a contemporary soil-pile case, for which (only) the fatigue-driven wall thickness was optimized and compared to the thickness needed when applying the conventional (softer) p-y curve profile. As the cost for MP support structures typically constitute more than 20% of the total capital cost of an offshore wind farm, the presented and validated work is foreseen to have a significant beneficial impact on the feasibility of future offshore wind projects.Offshore Engineerin