Design and test of a friction damper to reduce engine vibrations on a space launcher
Space launchers are submitted to complex vibration environments and this can impact the payload it is carrying. Ensuring the protection of the payload therefore requires the addition of a secondary system. In this paper, a rapid design method for the dimensioning of a friction damper is developed, based on the equivalent energy dissipation with that of a viscous damper. A friction damper is designed and a prototype is built. The friction damper is first characterised alone and it is then mounted inside a scale model of a launcher last stage. The friction damper is adequately modelled by a spring in series with a friction element. The damper prototype proves to efficiently damp the rocket engine vibrations, and the design method used for dimensioning the friction damper gives a good approximation for the optimal sliding force of the damper.
A study of friction vibration absorber: impact of friction modeling on the efficacy of the absorber and friction coefficient optimization
In this paper, a one degree of freedom system connected to a friction vibration absorber is considered. Friction vibration absorber reduces mechanical vibrations using the dissipation of the energy through friction between both bodies. However, the contact between both bodies and the optimal parameters design deserve to be examined closely. In this paper, the effect of friction modeling is first investigated. Two friction modelings are considered: macroscopic (Coulomb) and microscopic (Dahl and LuGre), according to physical and tribological behaviors. For each model, the responses are determined in sticking and sliding regimes of motion and a comparison is made to conclude on the efficacy of the friction absorber. Second, the optimization of friction coefficient is established using two approaches: Den Hartog optimal parameters and the minimization of the frequency displacement of the main mass.
Ocean thermal energy conversion: The promise of a clean future
Due to the world's heavy dependence on fossil fuels for electricity, pollution and global warming is on the rise. However, numerous countries are still relying on diesel generators as their main source of energy. There is a lack of practical alternative energy source that can meet the global energy demand without posing any threat to the natural environment. Ocean Thermal Energy Conversion (OTEC) is a concept that has the potential to address this growing issue. It is basically a mechanism that exploits the temperature difference between warm surface seawater and cold deep ocean water, to produce electricity. Although OTEC has a low energy density, the thermal energy in the ocean is vastly abundant. OTEC development has been dormant for a long time since it was first proposed in 1881. However, it has now regained recognition worldwide as a realistic solution to our world energy issue. Instead of having a great potential for power generation, it also carries the ability to produce high value products from the large volume of Deep Sea Water (DSW) that can be released as byproducts of OTEC plant operation. These products can hold a very profitable place in industries such as pharmaceutical, food, cosmetics and mineral water production. Further research on ocean current and DSW properties can someday lead to the commercial used of OTEC. This paper is a review of the basic concept, present status and future prospects of OTEC around the world.