Browsing by Author "Tirovic, Marko"

Now showing 1 - 14 of 14
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    Analysis and optimisation of disc brake calipers
    (Cranfield University, 2010) Sergent, Nicolas; Tirovic, Marko
    Disc brake calipers are subjected to complex mechanical loading and interaction of individual components in a typical brake assembly makes design improvement very challenging. To analyse caliper behaviour, complex Finite Element models were created and successfully validated using a variety of experimental techniques, including exceptionally suitable Digital Image Correlation. A novel methodology to optimise caliper design was developed, using non-linear contact Finite Element Analysis and topology optimisation, to generate lightweight, high performance brake calipers. The method was used on a Formula 1 brake assembly and significant improvement in structural design was achieved, with the new caliper being lighter and stiffer than the original. The same approach was used on more conventional 4 pistons calipers using various boundary conditions with particular focus on mass reduction and considerably lighter designs were achieved. The influence of specific features of the optimised calipers on the structural performance was also successfully investigated.
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    CFD and experimental study of heat dissipation from an anti-coning, pin vented, inboard mounted brake disc
    (Sage, 2022-09-29) Mingozzi, Filippo; Verdin, Patrick G.; Gucci, Lorenzo; Tirovic, Marko
    Anti-coning brake discs are known for their superior NVH characteristics when compared to other disc designs, but also for poorer heat dissipation. Cooling characteristics of such a disc design are studied numerically and experimentally on a specially developed Thermal Spin Rig. The disc is installed inboard on a high-performance off-road vehicle, with portal axles and wheel drives, resulting in nearly fourfold higher disc rotational speeds in comparison to the wheel speeds. Being exposed to the free-flowing air and rotating much faster makes this application well worth the attention and deeper study in terms of disc cooling. Computational Fluid Dynamics (CFD) analyses show a detailed distribution of air velocities and pathlines, temperatures, pressures, and convective heat transfer coefficients. The results are all very coherent, conveying very useful information, both qualitatively and quantitatively. Their cumulative effect has been successfully validated by comparing the CFD predicted average convective heat transfer coefficients (hconv) with the experimental results obtained on the Thermal Spin Rig, in a controlled environment. CFD results show to be very close to average hconv values calculated from measured cooling curves. The agreement is very good for the wide temperature and speed range. The overall relative differences are under 5%, and in most cases under 3%, except for the low disc rotation speeds, which show a maximum relative difference of 12.5% calculated at 200 rpm, for the disc heated to 300◦ C. Such outcomes give confidence in the CFD results for future work in both disc design and vehicle installations.
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    Design synthesis and structural optimisation of a lightweight, monobloc cast iron brake disc with fingered hub
    (Taylor and Francis, 2018-11-23) Topouris, Stergios; Tirovic, Marko
    This article focuses on generating a monobloc fingered hub (top-hat) disc design, aiming at reducing disc mass but maintaining rotor thermal capacity, while also improving heat dissipation characteristics. The analyses and tests demonstrated that such a design is possible to achieve, with mass reduction of just over 9%. The activities included research into cast iron modelling, which gave very important insights into the limits of mechanical performance under bending. Initial finite element analyses enabled considerable progress to be made towards establishing a baseline design, but only through shape optimization and topology optimization procedures was the full potential of the design accomplished. Shape optimization facilitated the reduction of maximum principal stress by 32%, considerably improving disc torsional strength with practically no increase in mass. The safety factor in torsion achieved a value of 3.57. Topology optimization provided further, although small, mass reduction (1.5%) while maintaining low stress levels.
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    Experimental investigation of the cooling characteristics of a monobloc cast iron brake disc with fingered hub
    (SAGE, 2019-05-02) Tirovic, Marko; Topouris, Stergios; Sherwood, Glenn
    The paper compares heat dissipation characteristics of two interchangeable ventilated brake discs, a standard solid hub and a newly developed fingered hub version, both single piece cast designs. The tests were conducted on a specially developed Thermal Flow Rig, which enables disc induction heating to 450°C and cooling for a range of rotational and air speeds, in parallel and angular cross flow. The Rig facilitated very accurate and repeatable experiments to be conducted for numerous combinations of operating conditions. From the recorded cooling curves, average heat transfer coefficients for convection and radiation were extracted and the results also presented in a generic form, using Nusselt numbers. The fingered design demonstrated superior convective heat dissipation, with the improvements varying depending on the rotational speed, air cross flow velocity and angle, as well as disc temperature. The gains were ranging from 3.5% to over 20%. The fingered design is 8.5% lighter and being a single piece cast disc, it remains inexpensive to mass produce.
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    Fibre Bragg grating sensors for the analysis of pressure distribution at a disc brake/pad interface
    (SPIE, 2017-04-24) Major, B. T.; Tiwari, Divya; Correia, Ricardo; James, Stephen W.; Tirovic, Marko; Tatam, James P.
    The use of optical fibre Bragg gratings (FBGs) to monitor the Interface Pressure Distribution (IPD) on an automotive disc brake pad under a variety of loading conditions is studied. The results demonstrate successful strain transfer from the brake pads to the attached FBG sensors under static loading, with a linear response to increasing pressure, and with the measured IPD showing good agreement with that recorded using pressure sensitive paper. Results are also presented demonstrating that changes in the IPD as a result of torque acting on the brake pads can be monitored by the FBG sensors.
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    Heat dissipation from a stationary brake disc, Part 1: Analytical modelling and experimental investigations
    (SAGE, 2017-05-18) Stevens, Kevin; Tirovic, Marko
    The main aim of the research is to support the development of the commercial vehicle electric parking brake. Though nowadays widely used on passenger cars, electric parking brake applications on commercial vehicles present completely different challenges. With the brake mass, thermal capacity and required clamp forces an order of magnitude higher, safe parking demands much more attention. In the first instance, the priority is placed upon predicting heat dissipation from the brake disc only. The research is presented in two parts; part one (presented here) focuses on analytical modelling and experimental verification of predicted disc temperatures over long cooling periods, with part two investigating the air flow, velocities and convective heat transfer coefficients using computational fluid dynamics modelling, also followed by experimental validations. To begin the analytical analysis, a study was conducted into the variance in mean local convective heat transfer coefficients over a simplified brake disc friction surface, by investigating typical dimensionless air properties. A nonlinear equation was derived for the average surface convective heat transfer coefficient (h conv hconv ) variability with temperature drop for the entire cooling phase. Starting from fundamental principles, first-order differential equations were developed to predict the bulk disc temperature. By including variation of the convective and radiative heat dissipation throughout the cooling period, a good correlation was achieved with measured values, to within 10%. Experiments were conducted on a specifically designed thermal rig which uses 15 kW induction heater to heat the disc. Numerous experiments proved the results are very repeatable, throughout the cooling period. It was established, for the grey cast iron brake disc with a fully oxidised surface, the emissivity value are practically constant at ɛ = 0.92. Although the research is being conducted on a brake disc, the results have generic application to any disc geometry, whatever the application.
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    Heat dissipation from a stationary brake disc, Part 2: CFD modelling and experimental validations
    (SAGE, 2017-05-18) Tirovic, Marko; Stevens, Kevin
    Following from the analytical modelling presented in Part 1, this paper details a comprehensive computational fluid dynamics modelling of the three-dimensional flow field around, and heat dissipation from, a stationary brake disc. Four commonly used turbulence models were compared and the shear stress turbulence model was found to be most suitable for these studies. Inferior cooling of the anti-coning disc type is well known but the core cause in static conditions was only now established. The air flow exiting the lower vane channels at the inner rotor diameter changes direction and flows axially over the hat region. This axial flow acts as a blocker to the higher vane inlets, drastically reducing convective cooling from the upper half of the disc. The complexity of disc stationary cooling is further caused by the change of flow patterns during disc cooling. The above axial flow effects slowly vanish as the disc temperatures reduce. Consequently, convective heat transfer coefficients are affected by both, the change in the flow pattern and decrease in air velocities due to reduced air buoyancy as the disc cools down. As in Part 1, the special thermal rig was used to validate the computational fluid dynamics results quantitatively and qualitatively. The former used numerous thermocouples positioned strategically around the brake disc, with the latter introducing the concept of laser generated light plane combined with a smoke generator to enable flow visualisation. Predicted average heat transfer coefficients using computational fluid dynamics correlate well with the experimental values, and even two-dimensional analytical values (as presented in Part 1) reasonably closely follow the trends. The results present an important step in establishing cooling characteristics related to the electric parking brake application in commercial vehicles, with future publications detailing heat transfer from the entire brake assembly.
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    Heat dissipation from stationary passenger car brake discs
    (University of Ljubljana - Faculty of Mechanical Engineering, 2020-01-31) Topouris, Stergios; Stamenković, Dragan; Olphe-Galliard, Michel; Popović, Vladimir; Tirovic, Marko
    This paper presents an experimental investigation of the heat dissipation from stationary brake discs concentrated on four disc designs: a ventilated disc with radial vanes, two types of ventilated discs with curved vanes (a non-drilled and cross-drilled disc), and a solid disc. The experiments were conducted on a purpose-built thermal spin rig and provided repeatable and accurate temperature measurement and reliable prediction of the total, convective and radiative heat dissipation coefficients. The values obtained compare favourably with computational fluid dynamics results for the ventilated disc with radial vanes and solid disc, though the differences were somewhat pronounced for the ventilated disc. The speeds of the hot air rising above the disc are under 1 m/s, hence too low to experimentally validate. However, the use of a smoke generator and suitable probe was beneficial in qualitatively validating the flow patterns for all four disc designs. Convective heat transfer coefficients increase with temperature, but the values are very low, typically between 3 W/(m2K) and 5 W/(m2K) for the disc designs and temperature range analysed. As expected, from the four designs studied, the disc with radial vanes has the highest convective heat dissipation coefficient and the solid disc the lowest, being about 30 % inferior. Convective heat dissipation coefficient for the discs with curved vanes was about 20 % lower than for the disc with radial vanes, with the cross-drilled design showing marginal improvement at higher temperatures.
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    An investigation into heat dissipation from a stationary commercial vehicle disc brake in parked conditions.
    (Cranfield University, 2013-11) Stevens, Kevin; Tirovic, Marko; Skipworth, Heather
    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 (hcₒnv) 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 (ɛ = 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.
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    Methodology for predicting brake squeal propensity using complex eigenvalue analysis, including thermo-mechanical effects
    (Sage, 2018-04-12) Tirovic, Marko; Vianello, Michele; Bannister, Paul
    With brake squeal being the most prevalent noise vibration and harshness issue in modern vehicles, this paper presents an improved methodology for brake squeal propensity prediction at the design stage. The research established four clearly defined ‘Stages’ in conducting finite element squeal analyses, describing crucial input data, modelling procedures, output and validation results. Stage 1 deals with free-free modal characteristics of individual brake components and their material characteristics. Stage 2 combines individual parts, conducting brake assembly mechanical finite element analyses. Stage 3 concentrates on fully coupled thermo-mechanical finite element analyses, and the concluding stage, Stage 4, focuses on brake assembly stability analyses. Validations proved that very accurate predictions are possible, but the geometries, material characteristics and established modelling procedures must be strictly followed. Material characteristics were most prone to introduce discrepancies with measured values. ‘Generic’ values are found to be unacceptable and conducting own measurements was necessary, in particular for the friction material, whose anisotropic properties have been measured in detail, leading to high accuracy in predicting pad natural modes and frequencies. In Stage 4, the stability analyses of the full brake assembly were based on the complex eigenvalue analysis (which included thermal aspects), with the sign of the real part giving an indication of stability and the imaginary part defining the frequency of the unstable mode. Instabilities and frequencies predicted match well with the values measured in dynamometer tests, clearly demonstrating the influence of thermal effects. The final output of the procedures described in this paper is a validated three dimensional thermo-mechanical finite element noise vibration and harshness brake assembly model in which natural frequencies and modes, instabilities and contributing factors can be predicted at any time during a brake application.
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    Multi-scale, electro-thermal model of NMC battery cell
    (IEEE, 2019-09-23) Morganti, M. V.; Longo, Stefano; Tirovic, Marko; Blaise, C. Y.; Forostovsky, G.
    Battery models often either fail to deliver a complete picture of the physical phenomena occurring in the cell or fail to minimize computational effort. So far, the demand for a detailed internal thermal model of battery cells with a reasonable computation time has remained unanswered. This paper addresses such question introducing a multi-domain model whose accuracy makes it suitable for thermal management system development, at a lower computational cost than competing models. The approach features an equivalent circuit parameter model with chemistry-based parameters coupled with an internal heat transfer model. The internal heat transfer model includes different sections of the cell, addressing the anisotropy and the temperature-dependence of physical properties. Material properties are partly based on manufacturer's data sheet, partly taken from literature. The development software platform enables a sensible reduction of computational effort with respect to traditional modeling techniques. Results were validated against an aggressive current at different temperatures and against current profiles obtained from two different drive cycles at different ambient temperature. The model proves to be very good in terms of accuracy.
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    Optimisation of convective heat dissipation from ventilated brake discs
    (Cranfield University, 2009-05) Galindo-Lopez, Carlos Hannover; Tirovic, Marko
    Fast heat dissipation from brake discs is sought in current vehicles, where high power braking duties demand harmonic combination of strength, (undamped) disc mass and cooling abilities for a wide speed range. This work analyses the convective heat dissipation from ventilated brake discs and proposes means for its optimisation. The focus of research is the ventilation geometry of a standard brake disc with an outer diameter of 434mm and radial channels of 101mm in length. After analysing in detail data calculated with CFD simulations and from experimental work for various ventilation patterns, a parameter relating the local channel-averaged convective heat transfer coefficient to channel circumferential width, and radial location was derived. This new numerical parameter termed Flow Index, depicts graphically the link between channel geometry (width and position) to the heat transfer coefficient level attained. The FI was not only used as a tool to analyse the convective performance of conventional and new ventilation geometries, but it also allowed clear identification of changes necessary in the channel width in order to improve its convective heat transfer coefficients. New, optimised for convective heat transfer, ventilation geometries designed with the FI were achieved in this Thesis. Industrial (patenting) and academic applications are foreseen from the results of this Thesis and its future activities. Also, the work developed in this Thesis gives path and supporting frame for future research in the field of brake disc convective heat dissipation.
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    Thermal-managed oriented, multi-domain battery modelling and experimental validation.
    (Cranfield University, 2019-12) Morganti, Manlio Valerio; Longo, Stefano; Tirovic, Marko
    A cross-domain battery simulation methodology, that could allow, a more streamlined design process, was needed. Acausal, object-oriented, multi-domain modelling strategies are becoming more and more common, beside traditional co-simulation methods, since they avoid the development of several different models for each causality type and leaving therefore flexibility to the user. A multi-domain, re-scalable, battery model and a reconfigurable battery-module test-rig are introduced in this thesis. The chosen approach allows the final user to generate different module and pack layouts from a single cell model. Materials were fully characterised, then initial conditions were defined, boundary conditions outlined and ultimately the strategy was tested against different scenarios. It is therefore possible to generate arrays of more cell models connected with each other, resulting in a module model. Such an approach achieved higher accuracy than a lumped element model with computational cost being lower than finite element models. The error in simulated voltage estimation was low and the model could handle the transient with a reduced error in temperature. In order to validate such models a test-rig, capable of hosting different battery layouts was implemented. Extensive hardware characterisation, including sensor uncertainty analysis was carried out on the experimental layout. The model of a battery module was successfully implemented. When comparing with experimental data, the discrepancies in the case of the module were larger than in the case of single cell, but the outcome was still laying in the interval of confidence. The temperature profile has been predicted well for cell and module at reduced computational costs. The case studies proved the effectiveness of cooling which was accurately captured by the models developed. Moreover, it was demonstrated that indirect liquid cooling based on removable heat cold plates can be very effective in keeping the battery module within safety operational temperatures during fast charging.
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    Video re-sampling and content re-targeting for realistic driving incident simulation
    (2011-11-17T00:00:00Z) Heras, Alejo M.; Breckon, Toby P.; Tirovic, Marko
    We present a video generation and visualization system for integration into a driving incident simulator. We combine the use of video re-sampling, target tracking and object segmentation for content re-targeting to generate realistic video content that can be adapted on demand, based upon simulator inputs to generate a range of driver incident test scenarios