| dc.description.abstract | Although rotary steerable systems have been evolving rapidly and delivering
unprecedented rates of drilling penetration, drillers nevertheless seek technologies that
further accelerate the drilling process. Currently, most down-hole motors with rotating
drill bits are driven by positive displacement motors and down-hole turbine motors. These
motors are classified depending on the type of power sections that are used to convert the
hydraulic energy of high pressure fluids to mechanical energy in the form of torque
output. In these designs, the power is transmitted from the power section to the drill bit
through different mechanical arrangements, such as drive shafts, coupling assemblies,
bearings, etc. During the transmission process, part of the developed torque is wasted,
which reduces the efficiency. In addition, bearing stresses limit the transfer of possible
forces to the drill bit. We proposed a novel concept to overcome these difficulties.
The proposed concept is unique because of the combination of a linear electrical machine
and gas springs. These gas springs allow the piston of the linear electrical machine to
oscillate at different frequencies depending on the required load conditions. The
characteristics of the high energy gas springs provide the opportunity to oscillate heavier
piston with longer stroke lengths. A large electromagnetic force from permanent magnets
and coils, in combination with gas springs, creates a high power linear electric actuator.
The oscillating heavy piston causes a considerable vibration in the housing, which is
utilized in the drilling application. The load can then be attached directly to the housing
and the machine can be made hermitically sealed, which eliminates leakage problems.
These features make the actuator suitable as a hammer in oil drilling applications.
A linear permanent magnet actuator (oscillomotor) is an energy conversion device that
integrates a linear permanent magnet (PM) machine and gas springs into a single unit.
My research work mainly addresses the design criteria, analytical and finite element
method (FEM) design calculations and dynamic analysis of the linear permanent magnet
actuator with gas springs. The selection of a suitable linear PM machine configuration is
very important to achieve the required demands, such as a compact diameter size, easy integration of gas springs, reduced losses to reduce heat generation, robustness, less
maintenance and higher force from the starting position. Different linear PM machine
configurations, such as flat, double flat, tubular longitudinal and transverse flux, are
discussed for drilling applications. The tubular longitudinal flux configuration is selected
as the most promising for drilling applications. This study analyses the selection of
different mover configurations and different magnet patterns. Design parameters such as
pole pitch, magnet width, stator inner diameter and air gap size are optimized based on
the analytical analysis of force characteristics. The complete design process of the linear
machine is discussed. Dynamic models of the linear actuator are developed.
Three prototypes of the linear actuator are built to verify the novel concept and validate
the force characteristics and dynamic modelling. The Force characteristics of the
prototype I is verified with the FEM simulated results. Impact tests are carried out using
prototype III. The test results shows the power input required at resonance is very low
compared to the other frequencies. The impact force per amp at resonance is 9.26kN. The
possibility of producing these higher power impacts at resonance, suitable for hard rock
drilling. Drill test is carried out using prototype II. The Effect of feed force on the dynamic
behaviour is discussed. The rate of penetration with different resonant frequencies and
different weight on bits are discussed.
This study also focuses on the suitability of this novel concept in other offshore
applications, such as wireline jar applications and ocean wave power generation.
Henceforth, this thesis describes the concept of the conversion of the movement of a float
in a wave power plant, which is characterized by high force and low speed energy, to a
high speed and low force energy in a linear generator by using gas springs. The simulation
model shows that an oscillating piston that is supported by gas springs and is compressed
and decompressed by a wave can convert more kinetic energy per volume from the float
to a secondary piston compared to a secondary piston that is simply attached to the float.
This model has not yet been validated with experimental work. According to the
simulation results, the size of the generator can be reduced by a factor of 12 for the same
power output compared to a buoy-connected piston. | nb_NO |
