3498 research outputs found
Sort by
The influence of the static and dynamic characteristics of power sources on the behaviour of short circuiting CO2 shielded welding arcs
No full textThe work discussed in this report has examined, oscillographically,
the influence of variable slope and variable inductance on the characteristics
of short circuiting CO2 shielded metal arcs, and the variables affecting the
optimum welding conditions have been determined. It has been established
th9.t this optimum is usually below the maximum of the frequency voltage curve.
Both the slope of the power source characteristic and the value of the
inductance in the circuit have similar qualitative effects on the stability
of the short circuiting arc. Nevertheless, control of the dynamic response
by varying inductance has been found to be more flexible and effective. For
this reason, it is suggested that separate control of the static characteristic
and dynamic response is not necessary to obtain optimum conditions. Thus the
correctly designed power source for short circuiting CO2 shielded arc welding
should have constant slope of the static characteristic and continuous control
of the dynamic response
Welding embrittlement of the parent plate outside the visible heat affected zone region
No full textEnbrittlement of steels outside the visible heat affected zone region
due to plastic straining from the weldment and subsequent ageing has been
reported by several authors. The problem is reviewed in this Note and an
attempt made to detect this region in a semi-killed mild steel by means of
a micro hardness testing survey taken at regular intervals in a direction
away from the veld fusion boundary. Recommendations for future work in
understanding the magnitude of this Problem particularly in multi stressed
welded joints are given
Incremental control
No full textThis Note describes the control of a centre lathe using stepping motors
and a small computer. The mechanical conversion is low cost and the system
described is readily adaptable to the simultaneous control of a group of
machine tools
GENENG : A generic turboprop engine model
No full textThis report describes GENENG, a code developed t o model the performance of a generic turboprop engine. Using published data from various
sources, a database of 7 turboprop engines suitable for General Aviation, Commuter & Regional transport aircraft was developed. This database consists of the values of the SHP available, Fuelflow, and Jet Thrust produced by the engines at
specific altitudes between sea-level and 35000 ft and
forward speeds between 0 and 350 knots (TAS), at
max. take-off, max. Climb & max. Cruise ratings. GENENG can then be used to obtain realistic estimates of any of these three parameters for a
generic engine that lies within this database at any
operating condition, i.e. altitude, forward speed,
and engine rating. The user has to specify the
ball-parking criterion, i.e. the desired value of any
one of the three parameters at a specific operating
condition. The generic engine is then positioned
in the database, by identifying the nearest two engines at the ball-parking criterion. The fractional
ratio of the location of the generic engine from
these two engines is then calculated. Assuming
that the same fractional ratio would also apply at
all the other data points, the values of all the parameters at all engine ratings are then generated
at specific combinations of forward speed and altitude. Using Bicubic Spline interpolation routines, the value of any of the three parameters at any
forward velocity and altitude can then be obtained.The Universit
A simulation of the Boeing B-747 aircraft
No full textThis report describes a computer simulation model of the Boeing B-747 aircraft which is intended for use as a general purpose tool for research into advanced flight control systems for civil aircraft. The previously published model reference [1], has been adapted with little change and implemented in the Advanced Continuous Simulation Language (ACSL), for use on an appropriate personal computer. Three distinct computer models of the aircraft have been produced, a decoupled linear longitudinal model, a decoupled linear lateral-directional model and a fully coupled non-linear model. All of the aerodynamic data used in the models was obtained from reference [1] since this was considered to be the most convenient starting point. It should be noted that standard imperial units are used throughout.This report describes a computer simulation model of the Boeing B-747 aircraft which is intended for use as a general purpose tool for research into advanced flight control systems for civil aircraft. The previously published model reference [1], has been adapted with little change and implemented in the Advanced Continuous Simulation Language (ACSL), for use on an appropriate personal computer. Three distinct computer models of the aircraft have been produced, a decoupled linear longitudinal model, a decoupled linear lateral-directional model and a fully coupled non-linear model. All of the aerodynamic data used in the models was obtained from reference [1] since this was considered to be the most convenient starting point. It should be noted that standard imperial units are used throughout.CI
Viscous flux limiters
No full textWe present Numerical Viscosity Functions, or NVFs, for use with Riemann-problem based shock-capturing methods as applied to viscous flows. In particular, viscous flux limiters are derived. The analysis pertain to a linear convection-diffusion model equation. Our NVFs combine the physical viscosity, the role of which is maximised, with numerical viscosity, whose role is minimised, to capture TVD solutions to viscous flowsCranfield Institute of Technolog
Hazards due to helicopter wakes
No full textThe local velocities induced in the wake of a helicopter can be a serious hazard to light aircraft operating nearby. A theoretical model is developed which makes it possible to estimate the rolling moment induced on a light aircraft entering the wake of a helicopter. The model shows good agreement with the limited amount of flight test data available. An annotated bibliography of the literature available on helicopter wakes is presented in order to identify specific areas in which further research is required.The Universit
A numerical investigation of the artificial compressibility method for the solution of the Navier-Stokes equations
No full textThe Artificial Compressibility approach is an important numerical method for solving the incompressible Navier-Stokes Equations. The application of high resolution numerical methods to the equations of the artificial compressibility approach is a relatively new phenomenon and deserves further investigation. In this paper we examine the performance of five Riemann solvers: an exact Riemann solver, and four approximate solvers. The application of reflective boundary conditions is investigated, as well as the way in which the artificial compressibility coefficient is chosen.CI
Formulation and System Identification of the Equations of Motion for a Dynamic Wind Tunnel Facility.
No full textThis document describes the equations of motion of an aircraft model tested in Cranfield’s 4 degreeof-
freedom (DoF) wind tunnel facility. In previous research, the equations have been derived assuming
that the model’s centre of gravity (cg) is coincident with the gimbal mechanism about which the model
rotates on the rig. However, in this report a general approach is taken with the cg assumed to be located
away from the gimbal. The equations are developed from first principles and reduced to a linearised
form where motion can be represented as small perturbations about trim. The equations are also decoupled
into longitudinal and lateral/direction expressions and converted into state space form. It had
been found in practice that models tested in the facility are very responsive in heave and can only be
operated open-loop if movement is restricted to purely rotational motion. Therefore, the equations for
this 3DoF case are also developed. Having obtained theoretical expressions, a series of wind tunnel
tests were conducted on a 1/12 scale BAe Hawk model in order to establish if the theoretical relations
were valid in practice. The particular technique used in testing the model was dynamic simulation and
the analysis of the experimental data was performed using system identification. An established model
structure determination procedure is used to determine which stability and control derivatives should be
included in the equations of motion. Frequency domain, equation error parameter estimation is then
employed to obtain numerical values for the stability and control derivatives. For both the longitudinal
and lateral/directional examples described, the final model structure obtained from experiment matches
that derived from theory. Derivatives values obtained from parameter estimation and empirical analysis
are also in good agreement
Mars Xpress. Summary of the Group Design Project, MSc in Astronautics and Space Engineering, 1997/98, Cranfield University
No full textThis is a summary of the Group Design Project of the MSc course in Astronautics
and Space Engineering in the College of Aeronautics at Cranfield University for
the academic year 1997/98. Executive summaries from all the individual reports
are contained in an Appendix to this report. The project represents about 8000
hours’ e®ort by the students of the course directed by sta®, and takes the form
of a preliminary mission feasibility study. The project was based on ESA’s Mars
Express mission.
The proposed mission is for a Martian lander composed principally of a rover
equipped to search for signs of past or present life on Mars. A controlled
descent is required to ensure landing close to sites of particular interest. The
surface exploration is planned to last 250 Martian days. A Mars orbiter (also
part of the Mars Express mission) is used as a relay for the rover to
communicate with Earth.
The mission appears feasible as far as the study goes. Topics requiring further
study were identified and include thermal design, communications with Earth,
achieving the required landing precision, and mobility on the Martian s