Radu D. Rugescu

Dynamic modelling of a 3-DOF parallel manipulator using recursive matrix relations

In this paper, a simple and convenient method – Recursive Matrix method – is proposed for kinematic and dynamic analysis of all types of complex manipulators. After addressing the principle of the method, an example – a 3-DOF parallel manipulator with prismatic actuators – is demonstrated for the efficiency of the method in solving kinematic and dynamic problems of complex manipulators. With the inverse kinematic solutions, the inverse dynamic problem is solved with the virtual powers method. Matrix relations and graphs of the acting forces and powers for all actuators are analysis and determined. It is shown that the proposed method is an effective mean for kinematic and dynamic modelling of parallel mechanisms.

Potential of the Solar Energy on Mars

The problem of energy accessibility and production on Mars is one of the three main challenges for the upcoming colonisation of the red planet. The energetic potential on its turn is mainly dependent on the astrophysical characteristics of the planet. A short insight into the Mars environment is thus the compulsory introduction to the problem of energy on Mars. The present knowledge of the Martian environment is the result of more than two centuries of attentive observation on its astronomical appearance and, more recently, on its on-site astrophysical features. Recent surface measurements of Martian geology, meteorology and climate had fixed the sometime-unexpected image of a completely desert planet. Mars is one of the most visible of the seven planets within the solar system and thusfor its discovery cannot be dated, still the interest for Mars is old. It was easily observed from the ancient times by necked eye and the peculiar reddish glance of the planet had induced the common connection of the poor planet with the concept of war. The god of war and the planet that inherited his name had provoked, still from antiquity, curiosity and disputes on the most diverse themes. These disputes are at a maximum right now regarding the habitability of Mars. The red planet owes his color to still unexplained causes, where a yet undisclosed chemistry of iron oxides seems to be the main actor. The visit card of Mars is fast increasing in the quantity of data and is now quite well known (Bizony, 1998), as we observe from the description that follows.

Inverse dynamics of star parallel manipulator

Recursive matrix relations for kinematics and dynamics of a Herves star parallel manipulator are established in this paper. The prototype of this robot is a three-degree of freedom spatial mechanism, which consists of a system of parallel kinematical chains. Supposing that the position and the translation motion of the platform are known, an inverse dynamic problem is solved using a new matrix approach. Finally, some iterative matrix relations and some graphs for the torques and the powers of the three active couples are determined.

Front Wave Prediction in Water Hammer Phenomena Involving Two-Phase Flows

A genuine mathematical model for one dimensional, unsteady, two phase (liquid-gas) flows is presented that intends to solve the complex problem of two phase behavior of fluids. The mechanism of the model describes the fluid flow characteristics of the mixture, supposing that the conditions for homogeneous vaporization are fulfilled and the condensate fraction of the composite fluid keeps constant. In particular, the equation of momentum conservation for the gas phase is derived from the Voinov equation. For its domain of validity (bubbly flows), the model is of hyperbolic type and can be written in the conservative form. The numerical results obtained for the water hammer phenomena show that the present work is able to supply accurate results, at least of the same degree of confidence as the results provided by an ordinary, commercial CFD code, still with a considerable reduction in computational time.Copyright

Fuzzy Thrust Staging Kinematics for the NERVA Strap-On Boosters

NERVA small space launcher under development in Romania by Politehnica University is based on the solution of hard take-off with three strep-on SRM boosters. Due to the very high thrust enhancement a lift-off loading of more than 40 g-s appears, which is quite challenging. The main challenge is connected with the possible uneven thrust and burn duration of the three SRE-s of the first stage, which we call fuzzy thrust. Experimental data show variations of up to 0.5 seconds in the duration of the powered phase of SRE-s, from a total of 3.0 seconds of a mean burn. Yet undetermined variations in the total ignition delay between individual motors are a stronger concern. While for the unique booster of the standard SA-2 vehicle the ignition delay has no impact, when those engines are forced to work in parallel the individual differences become catastrophic. Severe imbalance between the two lateral engines may occur, ending in a potentially severe damage of the launching rail, possible loss of flight stability along the boost phase and damage of the second stage structure. The problems regarding the efficiency of the propulsion system that accompany this project are considered and solutions are proposed for the high thrust augmentation of the booster stage. Cryogenic vs storable propellants are studied for thrust augmentation of the boosters.

Collision Induced Loads in Pro-Injectors of ADDA Rocket Motors

The major improvement introduced by ADDA in space propulsion is the new Compound Rocket Motor concept (CRM), where, in contrast to the inefficient hybrid motors, the completion of combustion is very high. This new motor construction is also remarkable through its new injector type called pro-injector, currently under examination for patenting, with the capability of cutting out the dangerous reversed flow of the liquid component in a definitely short amount of time. The pro-injector device, quite critical when instable, high energy compounds like nitrous oxide are sprayed into the CRM combustion chamber, was designed, tested and successfully applied within the NERVA-ORVEAL project coordinated by the ADDA research team in cooperation with the AEROFINA partner. The results of the research regarding the pro-injector behavior are described. It was observed that unexpectedly high dynamic loads appear upon the seat of the pro-injector due to the collision-type motion when a shock wave in the combustion chamber develops. It is shown that such occurrence impedes application of fragile materials in the construction of the injector seat which otherwise would better serve the construction. Numerical simulations are presented as performed under rational assumptions regarding the mechanical behavior of mobile parts, in order to secure a smooth work of the device at the fast response required to downwind gas pressure shocks. The pro-injector proved being an innovative device currently submitted for patenting

Inviscid Nozzle for Aerospike Rocket Engine Application

A computational method for the steady 2-D flow in axially symmetrical rocket nozzles with a given profile is developed, in order to determine the Maximum thrust contour of rocket engine nozzles with large expansion ratio. The optimized nozzles proved a more than 10% increase in the integral specific impulse recorded during the variable altitude atmospheric flight of rocket vehicles. The method is well suited for application in the design of the optimum contour for axially-symmetric nozzles for atmospheric rocket ascent, specifically for aerospike type nozzles, as for other similar industrial applications in gas and steam turbine technology.

Orbital Launcher NERVA as the First Proof of the Discontinuous Variational Solution for the Atmospheric Ascent

Since the earliest days of astronautics, more than a century ago, low cost space launchers persevered to be a long desire for the space flight thinkers. Once space flight became a daily business along the late `50-s, first by consuming large financial resources, the interest for cheap space launchers became even more laud. Today’s growing interest in small satellites have bolstered a large series of space technology companies including Virgin Galactic Corp., Garvey Spacecraft Corp., Quantum Research International, Ventions LLC, Sierra Nevada Corp., Generation Orbit Launch Services and even the giant Boeing to work on the development of various types of such vehicles, some of them of actually small size. They have announced recent progresses in their efforts to develop and test small-satellite launchers and rocket engines. Romanian space launcher effort includes the NERVA project, with the ORVEAL compound engine for the upper stage, securing the orbital injection, project developed by the team of professors and researchers from ADDA Ltd, Bucharest. This project is based on a series of innovative concepts, including the optimal ascent program first proposed by the ADDA team by means of the new discontinuous variational optimization, which is here described in detail.

Starting Transient Experiments in the MEC-80 Rocket Engine Scaled Ignition Device

One of the main sources of concern within the design and manufacturing of rocket engines is the starting device, due to the relatively low reliability of the ignition of the main combustion process in these engines. Not only is necessary for the igniter to produce a sound ignition, but the starting pressure transient should manifest a tightly controlled build-up, in a very definite time interval. A specific research and development work was done by the authors in order to reliably assess the requirements for the ignition device of the newly developed compound, solid-liquid experimental rocket engine MEC-80 of the ADDA team. Computer predictions and scaled experiments on the constant volume combustion into a modified calorimeter were performed with notable results that led to the optimal design of the ignition device of the motor. The test results are presented with emphasize on the predictability of the ignition delay.

Cavitation Avoidance in Nitrous Oxide Rocket Engines Using the Efficient Transient 1D Downwind Prediction

Nitrous oxide has recently entered violently the arena of space propulsion and gained interest, due to its high energy and gasification potential and despite its low oxygen content as an oxidizing chemical and its instability over some 600 C. However, its physical and chemical instability soon proved to be a potential hazard and led to a renewed interest in the study of its behavior as a fluid. In the present contribution computer simulation of the liquid phase flow of the nitrous oxide under high pressure is used to predict and avoid the cavitation into the feeding line tract of rocket engines, specifically of the compound rocket engines feeding line. The method involves a substantially simplified 1-D description of the fluid motion with sufficiently accurate determination of cavitation risk where the feeding duct suffers blunt variations of the cross area or steep turns and corners involving sensible static pressure variations of the fluid. A means of avoiding dangerous behaviors of the nitrous oxide is thus developed that could increase safety margins during the handling of this quite unpredictable oxidizer for the compound, combined or hybrid rocket engines.