Riblets and Tripwires and their role in reducing drag over underwater Essay

Riblets and Tripwires and their role in reducing drag over underwater aerofoils - Essay Example Their optimal specifications, mechanism of functioning and potential applications for drag reduction over underwater aerofoils have also been dealt with. Riblets and tripwires In case of underwater vehicles, fluid mechanical drag (hydrodynamic drag) reduces the speed with which they travel through water. For a specific limit of engine power, the maximum speed that can be attained by the vehicle is drastically reduced due to the formation of eddies very close to the surface of the vehicle. Apart from this, another source of hydrodynamic drag is the development of pressure drag due to laminar flow at the boundary layers. Riblets can be used to reduce the formation of eddies near the surface of the vehicle, while tripwires can be used to reduce the pressure drag and induce turbulence at the boundary layers. Riblets: These are minute grooves, longitudinally placed on the surface of a vehicle or airfoil, and are in alignment with the direction of flow. They â€Å"have been shown by Walsh and Lindemann [1984] at the National Aeronautics and Space Administration (NASA) and Reidy and Anderson [1988] at the Naval Ocean Systems Center (NOSC) to produce as much as 8 percent turbulent flow drag reduction on flat plates†.1 Studies on â€Å"fully submerged axisymmetric bodies†1 conducted by Beauchamp and Philips [1986 and 1987], have shown that the use of riblets reduces skin friction by seven percent.1 Tripwires: Tripwires, also known as turbulators, are thin wires that are attached at the hull of a vehicle or at the nose of a submarine or aircraft. These are used to â€Å"trip† or disturb the boundary layer and introduce turbulence, thereby reducing pressure drag. These are â€Å"one of the oldest and most used methods of turbulence stimulation†.2 1. Mechanism To comprehend the mechanism of functioning of riblets and tripwires, it is essential to understand the types of drag imposed on a vehicle and the process of their induction. The total drag experienced by a body, includes a combination of pressure and friction. The frictional drag can be reduced by using smooth surfaces. However, studies have shown that this form of drag is further reduced with the help of riblets. The boundary layer of flow around a vehicle can be distinguished into three parts, â€Å"a relatively small viscous sublayer, the middle buffer layer and the logarithmic layer†.3 The riblets that are used to reduce drag â€Å"extend into the buffer layer. With this kind of riblets a drag reduction of about 8-10%† has been achieved. This is because the riblets restrain the movement of eddies, which are prevented from coming very close, within 50 microns, to the surface of the aircraft or vehicle. â€Å"By keeping the eddies this tiny distance away, the riblets prevent the eddies from transporting high-speed fluid close to the surface, where it decelerates and saps the aircraft's momentum†.4 To reduce the pressure drag over a vehicle, tri pwires are used. Pressure drag occurs when there is a â€Å"lack of pressure recovery on the back of the body, due to separation of the flow around the body†.5 This results from laminar flow in the boundary layer around the vehicle. By using tripwires, it is possible to induce turbulence in this laminar layer, thereby reducing pressure drag. 2. Optimal Specifications The extent of drag reduction is found to increase with the size of riblets. However, for very

Paperless office database - Topic title Coursework

Paperless office database - Topic title - Coursework Example There is also need to reach out to the global market (Digital IEEE Software House Advertisement, 2013).Previously, it was easier due to the geographical region had to cover as compared to currently when there are no boundaries globally, and you want to reach out to them. The way to collect information about the advertisement company is to do document review of journals, books, and articles. The step is very vital because there are many people out there who have carried out research on the topic, and it is necessary to consider their opinions. Further, there would be an interview with experts in the field to get first-hand information on their experiences and trending ways of advertisements (Reeves, 2014). In addition, questionnaires will also be used to reach out to experts who are willing to help but are far thus it is not possible to interview them. There are a lot of data challenges in advertisement companies. First, there is a lot of incoming data from consumers. These data needs to be analyzed, and patterns drawn from it to make projections. The results are important in making decisions in the company. The company also needs to get real-time retrieval of information concerning their customers. It is a significant challenge with traditional means to achieve this. Thus, a relational database management system is required. Handling of varied formats of data is also inevitable (Digital Magazines House Advertisement, 2014). A database system offers a lot of flexibility in storing a lot of data with different formats. They can also handle a lot of data at the same time as compared to any traditional means. Databases further encourage validation of data, segmentation of consumers and proper organization of data in the media industry. The system wishes to achieve a number of milestones. First, is to omit manual handling of data using files and cabins by digitizing content.