Calibrating on the space utilization data of this study, such models could become more realistic in terms of transmission dynamics. They could provide more accurate and precise estimations to tackle infectious diseases cost-effectively. The study has several limitations. It was a pilot study and had a limited sample size. Most participants were adult males. Potential female participants said they rarely go beyond village boundaries and thus were not eligible to be included in the study. It may have introduced a selection bias, but it points to the fact that the mobility preferences between the two genders were too different that they were essentially two different populations requiring separate analyses. The most commonly reported occupation was farming and most people in this study area, indeed, farm for at least part of the year. However, people in the study area usually perform different types of work according to the season and assigning a single occupation to a person may not be appropriate. Employment in this region is almost entirely informal, and most working-age men will work in agriculture for part of the year and in other types of labor during other parts of the year. Responses to surveys about employment will therefore vary by the time of year, even within a single research participant. While we believe that this cohort is representative of adult males in this setting, more studies that are demographically representative of rural villages in this setting could be useful for understanding differences in travel patterns by age and gender. Mobile GPS devices have their own limitations. As explored in the Extended data: Figure S2, flood tray their readings could be inaccurate. Because of their small size, their battery capacity was limited. During the study period, participants may have failed to carry the GPS device . Mechanical failures may also cause problems in data collection.

Even though the utmost care was taken to preserve data integrity, there could be errors and bias from data collection or data manipulation. While the categories do match our authors’ understanding of the area, no validation was done on the ground after categorization for this analysis. Our estimation of home location as the median center of all the GPS points where the participant spent the night, each of which in turn is derived from the last GPS point of the day between 6pm to 12 midnight, may not be robust enough to capture the actual home location. This could be overcome by having the field supervisors record each participant’s home location with a GPS device in the future studies. Categorization of home area may be too wide to discern land use that is very close to home. Finally, the estimation of land utilization regardless of the method used is imperfect. Having two consecutive GPS points to constitute usage of the land area provide too crude a result . While the BRB method provide more accurate and precise estimates , it is not without its caveats. The BRB approach assumes that consecutive points that were more than three hours apart were uncorrelated. Since the GPS logger went into sleep mode while stationary, the current land utilization estimation under-estimates the time spent motionless and hence resulting in lower usage of home in Extended data: Figure S6 compared to that in Figure 2.Starting as the technologies of the rural electrification program, the electricity generating wind turbines has been developed to one of the biggest renewable energy power production facilities on the planet. Latest estimates from the International Renewable Energy Agency shows that onshore wind is already at grid parity with fossil fuel electricity .

According to latest reports of the Energy Information Administration of the U.S. Department of Energy and annual energy report of the European Commission, the levelized cost of energy for the onshore wind falls within a range of $0.04 – $0.10 per kWh, making them extremely cost-competitive with conventional power sources as coal, integrated gasification combined cycle and nuclear energy . Moreover, the wind energy is the fastest growing power production sector. To provide a comparison: during the period of 2000 to 2012, the installed capacity from nuclear power plants only increased by 9 GW, while the increase for wind power was 266 GW and around 100 GW for solar power plants. Further, the wind turbines technologies have the largest remaining cost reduction potential which can be achieved through advanced research and developments. During the last several decades engineers and scientists put significant effort into developing reliable and efficient wind turbines. Since the 1970’s most of the work focused on the development of horizontal-axis wind turbines . Vertical-axis wind turbines were generally considered as a promising alternative to HAWTs. Before the mid-90’s VAWTs were economically competitive with HAWTs for the same rated power. However, as the market demands for electric power grew, VAWTs were found to be less efficient than HAWTs for large-scale power production. In recent years the offshore wind energy are getting increased attention. The total global installed capacity of offshore wind reached 4.1GW at the end of 2011. Far from the shore energy can be harvested from stronger and more sustained winds. Also, the noise generation and visual impact is no more a limitations in turbine designs. In the offshore environments large-size HAWTs are at the leading edge. They are equipped with complicated pitch and yaw control mechanisms to keep the turbine in operation for wind velocities of variable magnitude and direction, such as wind gusts.

One of the most challenging offshore wind turbine designs is a floating wind turbine. Starting 2009, the practical feasibility and per-unit economics of deep-water, floating-turbine offshore wind was seen. The world’s first floating full-scale offshore wind turbine has been lunched in the North Sea off the coast of Norway by Norwegian energy giant StatoilHydro in 2009. The turbine, known as Hywind, rests upon a floating stand that is anchored to the seabed by three cables. Water and rocks are placed inside the stand to provide ballast. The world’s second full-scale floating wind turbine, named WindFloat, was designed by Principle Power and lunched in 2011 by the coast of Portugal. In 2013, as a part of US Department of Energy’s Wind Program, the VolturnUS, first offshore wind turbine in Americas was powered up to provide electricity. Later, the same year, Japan switched on the first floating turbine at a wind farm 20 kilometeres off the coast of Fukushima. Up-to-date there are many projects on building the floating wind turbine farms in Asia, Europe and Americas. Moreover, wind-energy technologies are maturing, and several studies were recently initiated that involve placing VAWTs off shore, such as DeepWind project by Riso DTU National Laboratory for Sustainable Energy and other. As the problem remains for large-scale wind turbines, especially offshore, with grid connection and energy storage, the urban areas, closer to direct consumer become very attractive. Recently VAWTs resurfaced as a good source of small-scale electric power for urban areas. There are two main configurations of VAWTs, employing the Savonius or Darrieus rotor types. The Darrieus configuration is a lift-driven turbine: The power is produced from the aerodynamic torque acting on the rotor. It is more efficient than the Savonius configuration, which is a drag-type design, 4×8 grow tray where the power is generated using momentum transfer. The main advantage of VAWTs over the HAWTsis their compact design. The generator and drive train components are located close to the ground, which allows for easier installation, maintenance and repair. Another advantage of VAWTs is that they are omidirectional , which obviates the need to include expensive yaw control mechanisms in their design. However, this brings up issues related to self-starting. The ability of VAWTs to self-start depends on the wind conditions as well as on airfoil designs employed. Studies in reported that a three-bladed H-type Darrieus rotor using a symmetric airfoil is able to self-start. In the author showed that significant atmospheric wind transients are required to complete the self-starting process for a fixed-blade Darieus turbine when it is initially positioned in a dead-band region defined as the region with the tip-speed-ratio values that result in negative net energy produced per cycle. Self-starting remains an open issue for VAWTs, and an additional starting system is often required for successful operation. As a wind power production demands grow, the wind energy research and development need to be enhanced with high-precision methods and tools. These include time-dependent, full-scale, complex-geometry advanced computational simulations at large-scale. Those, computational analysis of wind turbines, including fluid-structure interaction simulations at full scale is important for accurate and reliable modeling, as well as blade failure prediction and design optimization. Due to increased recent emphasis on renewable energy, and, in particular, wind energy, aerodynamics modeling and simulation of HAWTs in 3D has become a popular research activity. FSI modeling of HAWTs is less developed. Accurate and robust full-machine wind-turbine FSI simulations engender several significant challenges when it comes to modeling of the aerodynamics. In the near-tip region of the offshore wind turbine blades the flow Reynolds number is O, which results in fully-turbulent, wall-bounded flow. In order to accurately predict the blade aerodynamic loads in this regime, the numerical formulation must be stable and sufficiently accurate in the presence of thin, transitional turbulent boundary layers.

Recently, several studies were reported showing validation at full-scale against field-test data for medium size turbines, and demonstrating feasibility for application to larger-size offshore wind-turbine designs. However, 3D aerodynamics and FSI modeling ofVAWTs is lagging behind. The majority of the computations for VAWTs are reported in 2D, while a recent 3D simulation in employed a quasi-static representation of the air flow instead of solving the time-dependent problem. The aerodynamics and FSI computational challenges in VAWTs are different than in HAWTs due to the differences in their aerodynamic and structural design. Because the rotation axis is orthogonal to the wind direction, the wind-turbine blades experience rapid and large variations in the angle of attack resulting in an air flow that is constantly switching from being fully attached to being fully separated, even under steady wind and rotor speeds. This, in turn, leads to high-frequency and high-amplitude variations in the aerodynamic torque acting on the rotor, requiring finer mesh resolution and smaller time-step size for accurate simulation. VAWT blades are typically long and slender by design. The ratio of cord length to blade height is very low, requiring finer mesh resolution also in the blade height direction in order to avoid using high-aspect-ratio surface elements, and to better capture turbulent fluctuations in the boundary layer. High-fidelity modeling of the underlying aerodynamics requires a numerical formulation that properly accounts for this flow unsteadiness, and is valid for all flow regimes present. It is precisely this unsteady nature of the flow that creates significant challenges for the application of low-fidelity methods and tools to VAWTs. Another challenge is to represent how the turbulent flow features generated by the upstream blades affect the aerodynamics of the downstream blades. The VAWT simulation complexity is further increased when several VAWTs are operating in close proximity to one another. Due to their compact design, VAWTs are often placed in arrays with spacing that is a little over one diameter between the turbine towers. In [1], this type placement was found beneficial for increased energy production. When the FSI analysis of VAWTs is performed the simulation complexity is further increased. As can be seen in the flexibility in VAWTs does not come from the blades, which are practically rigid , but rather from the tower itself, and its connection to the rotor and ground. As a result, the main FSI challenge is to be able to simulate a spinning rotor that is mounted on a flexible tower.In order to account for addressed challenges, the FSI formulation should be robust, accurate and efficient for the targeted class of problems. The FSI framework used in current work was originally developed in [37, 38]. The aerodynamics formulation makes use of FEM-based moving-mesh ALE-VMS technique combined with weakly-enforced essential boundary conditions. The former acts as a turbulence model, while the latter relaxes the mesh size requirements in the boundary layer without sacrificing the solution accuracy.