6 research outputs found
Measurement of constant radius swept features in cultural heritage
none3The dimensional characterization of archaeological fragment is a very complex
operation and could prove to be useful for identifying the presence of standard attributes in the
ceramics found from a specific archaeological site, or for making comparisons and analysis of
similarities or for studying ancient technologies used for manufacture of objects. The
dimensional analysis of the fragments is now carried out manually with traditional measuring
devices. Typically, the results obtained are inaccurate and non-repeatable measurements.
This paper focuses on the dimensional characterization of a specific geometric class of features:
the constant radius swept features (called here CRS features). Several archaeological features,
such as rims, bases, decorative motifs, processing marks and grooves are referable from a
geometric point of view to the class of CRS features. These are detail features, which may be
very interesting for the investigation of some aspects related to the historical-archaeological
classification of the find. CRS features are often found on worn, damaged (e.g. chipped) or
fragmented objects; they are frequently characterized, from a geometric point of view, by free
form surfaces and by a limited cross sectional extension. In some cases, CRS features can be of
axially symmetrical geometry: this occurs quite frequently in the case of archaeological pottery.
For all these reasons, it is often difficult to apply traditional manual methods for the quantitative
dimensional characterization of CRS features.
This paper describes an original methodology for the measurement of CRS features acquired by
scanning technologies. The algorithmic implementation of this methodology, consisting of a
suitable processing of the feature nodes, allows to carry out automatically the dimensional
characterization of the feature.Di Angelo L., Di Stefano P., Morabito A.E.Di Angelo, L.; Di Stefano, P.; Morabito, A. E
An investigation on methods for axis detection of high-density generic axially symmetric mechanical surfaces for automatic geometric inspection
none2noThe detection of the symmetry axis from discrete axially symmetric surfaces is an interesting topic, which is transversal to various fields: from geometric inspection to reverse engineering, archeology, etc. In the literature, several approaches have been proposed for estimating the axis from high-density triangular models of surfaces acquired by three-dimensional (3D) scanning. The axis evaluation from discrete models is, in fact, a very complex task to accomplish, due to several factors that inevitably influence the quality of the estimation and the accuracy of the measurements and evaluations depending on it. The underlying principle of each one of these approaches takes advantage of a specific property of axially symmetric surfaces. No investigations, however, have been carried out so far in order to support in the selection of the most suitable algorithms for applications aimed at automatic geometric inspection. In this regard, ISO standards currently do not provide indications on how to perform the axis detection in the case of generic axially symmetric surfaces, limiting themselves to addressing the issue only in the case of cylindrical or conical surfaces. This paper first provides an overview of the approaches that can be used for geometric inspection purposes; then, it applies them to various case studies involving one or more generic axially symmetric surfaces, functionally important and for which the axis must be detected since necessary for geometric inspection. The aim is to compare, therefore, the performances of the various methodologies by trying to highlight the circumstances in which these ones may fail. Since this investigation requires a reference (i.e. the knowledge of the true axis), the methodologies have been applied to discrete models suitably extracted from CAD surfaces.openE Guardiani; A MorabitoGuardiani, E; Morabito,
An investigation into heat dissipation from a stationary commercial vehicle disc brake in parked conditions.
Detailed understanding of heat dissipation from a stationary disc brake is of considerable
importance for vehicle safety. This is essential for both park braking on inclines and for
preventing brake fluid boiling in hydraulic brakes. Despite the experience proving the
significance of such conditions, there is very little published data dealing with this phenomenon,
and even ECE Regulation 13 does not specify hot parking braking performance. The problem of
heat dissipation from stationary brake may appear simplistic but it is actually more complex
than from a rotating disc, due to the lack of symmetry through or a dominant mode of heat
transfer as natural convection is the only driving force behind the airflow. All three heat transfer
modes exist in a transient process, with complex heat transfer paths within and between brake
components.
This Thesis investigates the cooling performance of a Commercial Vehicle (CV) brake whilst in
stationary conditions. The research is predominantly orientated towards the thermal aspects of
Electric Parking Brake (EPB) application in CVs. Contraction of large brake components after
hot parking may lead to vehicle rollaway on inclines, with tragic consequences. An extensive
theoretical and experimental study was conducted. An analytical model of a disc brake in free
air was developed, enabling good prediction of disc temperatures and average surface
convective heat transfer coefficients (hcâ‚’nv) over the entire cooling range. A comprehensive
CFD modelling of the 3-dimensional flowfield around the disc brake was also conducted, as
well as predicting the surface convection coefficient distribution. Shear Stress Turbulence
model was found to be most suitable for such studies. FE models were created to predict
temperatures in all components of the brake assembly. A special Thermal Rig was developed
for experimental validations, which uses an induction heater for heating the disc brake, and
numerous surface mounted and embedded thermocouples for measuring component
temperatures, as well as ‘free standing’ for determining air temperatures in specific points. IR
cameras provided further temperature field information.
The results clearly show little influence of the conductive heat dissipation mode. The study also
showed, for the experimental arrangement used, a constant value of surface emissivity (É› = 0.92). With well-defined conductive and radiative heat dissipation modes, the emphasis was
placed on investigating convective heat dissipation from a stationary disc brake. It has been
demonstrated that the anti-coning straight vane design of brake disc does not cool effectively in
stationary conditions. Expected ‘chimney effects’ in disc vent channels do not materialise due to
large scale recirculation regions preventing airflow from entering the channels, which
drastically reduces the convective cooling. Complex thermal interactions between the large
assembly components are explained, with typical cooling time being just over an hour for disc
brake cooling from 400°C to 100°C.
Extracted heat transfer coefficients were used for establishing a complex FE assembly model,
which enables accurate prediction of temperatures of individual components over the entire
cooling period. The developed approach is used for predicting temperature of the existing brake
assembly but is equally suited for generating new designs with more favourable characteristics.
In addition to being a powerful design tool for assisting in EPB design and validation process,
the methodology developed offers wide applications, such as thermal optimisation of the caliper
housing for the installation of continuous wear monitoring sensors, smart slack adjusters (for
low friction drag brakes), etc.
EPBs in passenger cars have been successfully used for over 10 years now. They use a
relatively simple approach for ensuring safe parking from hot by over-clamping (applying
approximately twice the required actuating force) and re-clamping (repeated application after
the vehicle has been parked). Large CV actuating forces prevent the use of over-clamping as
this could damage the disc, whilst re-clamping would need to be repeated several times over a
much longer period of time, requiring the vehicle battery to power the electronic systems for a
longer period of time without recharging. Neither approach is acceptable, requiring a more in-
depth thermal study of the CV brake in stationary conditions, as investigated in this Thesis. In
addition to technical, there are marketing and financial aspects which make EPB introduction
and acceptance in commercial vehicles very different to passenger car applications.
Such an investigation was conducted, exploring the market the CV EPB will be sold in and
whether it would accept the new technology. Two questionnaire analyses were carried out, with
the second giving the respondent detailed information about the EPB. It was found that using an
informed, knowledge based approach yielded more positive feedback to the proposed product.
The outcome may be even considered more contrary than expected, rather than instigating
mistrust, the new CV EPB technology created interest. Furthermore, reports of pneumatic
malfunction indicated that independence from the pneumatic system should be used as the key
selling point for the EPB, for all beneficiary segments.Engineering and Physical Sciences (EPSRC)Eng