Fraunhofer Chalmers Research Centre for Industrial Mathematics
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Managing Stakeholder Communication in Construction Projects: A case study of a consultancy company
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Railway wheel tread damage: Detection and consequences of wheel-rail impact loading
No full textSwedish transport authorities are investing large amounts of capital in technologies aimed at detecting railway wheel tread damage to reduce the costs for maintenance and repair of wheelsets and railway infrastructure. Wheel impact load detectors (WILDs) based on load cells and accelerometers is one such type of technology currently in use by Trafikverket (the Swedish Transport Administration).
This thesis consists of two related parts. The first part is a statistical analysis of data collected by WILDs to assess accuracy and increase confidence in their performance. The statistical tool used to fit the measured data is a multiple linear regression model. For a few selected wheels with evolving rolling contact fatigue damage, data collected over a one-year period have been analysed. At the early stages of wheel tread degradation, it is shown that the measured dynamic loads are considerably influenced by the train speed. For wheels with severe tread damage, the loads are also significantly influenced by the time since the previous wheel maintenance or replacement (probably related to the increasing wheel tread degradation rate over time). It is observed that the accuracy of the detectors cannot be firmly checked since the data are shown to be influenced by train speed and the time of measurement, and because of lack of measured data within a short time window where the tread damage is close to constant. However, a few observations indicating a need for detector calibration are given by comparing the results from different detectors when based on data registered for the same set of wheels.
In the second part of the thesis, a Python script for the Abaqus software has been written to automatically generate a parameterized wheelset model. The Python script allows to easily alter the geometrical features of the wheel design, such as the rim thickness. A non-powered wheelset model is used to evaluate the fatigue resistance of the hollow wheelset axle. A case of warning alarm values registered by a WILD is used to define the periodic loads acting on the rolling contact circle of the wheels. It is shown that the Sines’ criterion is the most suitable to calculate the equivalent stress of the most stressed section. For the given set of applied loads, the calculated stress state in the hollow axle does not induce a fatigue damage to the axle.
Key words: wheel impact load detectors, multiple linear regression model, parameterized wheelset model, dynamic analysis
Fatigue analysis of aluminum components in powertrain mounts
No full textComponents in the powertrain mounts systems withstand a large number of load
cycles with varying amplitude during their operational life. Despite this, no fatigue
analysis has previously been carried out of the studied components. The main aim of
this study was therefore to create a method for analyzing fatigue in aluminum components
in powertrain mounts. A bracket in the powertrain mounts system made
of high pressure die cast aluminum EN– 46000 was in focus. The study partially
aimed to account for and determine the effect of pretension on the bracket fatigue
resistance. A widespread problem with fatigue analysis is the access to material
fatigue parameters, and approximated material data are often employed. To investigate
the consequences the influence of using various material fatigue parameters
for EN– 46000 was investigated.
Based on a literature study, a strain-based approach to fatigue was selected. This
allows to account for plasticity. The construction of strain – life curve combined with
the establishment of a Ramberg – Osgood equation for cyclic stress – strain relationship
was the basis of the fatigue analysis. Due to the mean stress that arose from
the pretension, a mean stress correction following Smith –Watson –Topper was utilized.
To decrease computational time, a linear elastic stress FE-analysis was carried
out, Neuber correction was employed to account for local plasticity in the fatigue
analyses.
Fatigue analyses of the bracket were performed with approximated material fatigue
parameters using the Bäumel – Seeger method. The bracket was predicted to sustain
an infinite number of load cycles. An investigation of how much larger the loads
could be to sustain 4 standard operational lives was conducted. The result was
2.4 times the applied load. It was also found that small areas were affected by
fatigue. Fatigue analyses were carried out with and without the pretension. A
slight decrease in fatigue life was obtained without pretension due to compressive
mean stresses. From a sensitivity analysis, it was concluded that employed material
fatigue parameters have a significant impact on fatigue life, and that approximated
material should not be used for the final fatigue analysis.
Keywords:fatigue, aluminum alloys, nCode DesignLife, pretension, strain-based,
stress-based, powertrain mounts, material fatigue parameter
Lösning av polynomekvationer
No full textPolynomekvationen är ett grundläggande matematiskt begrepp men det är inte möjligt att hitta en exakt representation av nollställena för gradtal större än fyra. Trots att det inte går att hitta exakta lösningar till dessa polynomekvationer kan man med olika metoder ofta uppnå en god approximation till nollställena. Det finns mer eller mindre enkla sätt att approximera rötterna till ett polynom av hög grad och i denna rapport utforskar vi tre av dessa metoder där respektive metod är baserad på: Sturmkedjor, argumentprincipen eller kompanjonmatrisen
Genom litteraturstudier bekantade vi oss med ämnesområdet som i grunden är teoretiskt. Befintliga numeriska metoder för approximativa lösningar av polynom analyserades och bevisades matematiskt. Vi testade sedan olika lösningsmetoder inklusive Sturmkedjemetoden, argumentprincipmetoden samt kompanjonmatrismetoden. Vi testade sedan beräkningsprogrammet roots i Matlab som använder kompanjonmatrismetoden för att hitta rötter till polynomekvationer.
De tre metoder som vi testade har alla sina fördelar och nackdelar. Vi kunde inte utse en bästa metod för att hitta nollställen till alla former av polynomekvationer. Ska man beräkna många polynom och det inte spelar någon roll att reella lösningar kan få en liten imaginärdel kan kompajonmatrismetoden vara intressant. Om endast reella lösningar efterfrågas och polynomen har heltalskoefficienter är Sturmkedjemetoden mycket användbar. Argumentprincipenmetoden fungerar bra för de flesta rötter men när polynomets gradtal stiger så behöver den betydligt längre beräkningstid än de andra metoderna. Vilken metod som passar bäst beror således på vilket problem som ska lösas
Factors that drive efficiency of construction logistics
No full textTitle Factors that drive efficiency of construction logistics
Introduction
ÅF is a design and engineering company that has developed a construction logistics solution (CLS) for large construction projects that include a construction consolidation center, an IT-system for coordination and planning, and a third-party logistics provider that handles all operational logistics activities at the logistics center and at the construction site. To be able to reach the full potential of the construction logistics solution, an evaluation of the logistical setup and the material flow hava to be performed. To be able to implement the construction logistics solution in other construction projects, it is necessary to gain knowledge about what factors that make it successful.
Purpose
Identify potential improvements in the construction logistics solution and increase knowledge about factors that drive efficiency of this solution.
Research questions
RQ1: What are the materials handling activities that exist in the material flow of the construction logistics solution?
RQ2: What are value-adding, non-value-adding and necessary activities in the material flow in the construction logistics solution and how can non-value-adding activities be eliminated?
RQ3: What different factors affect the materials handling activities in the construction logistics solution?
Methodology
A Value Stream Mapping (VSM) process has been performed to be able to map the material and information flow in the current state of the case study. Lean production principles have been used to categorize activities according to value-adding, non-value-adding and necessary work and to find areas of improvement to increase efficiency of the current construction logistics solution. This master thesis is a qualitative study and the methodological path that has been followed is a triangular approach with a literature review, an interview-series and a case study to increase knowledge about factors that drive efficiency of this solution.
Result and Conclusion
Three different delivery planning approaches have been analyzed and all activities in the material flow and the information flow have been categorized according to a HATS analysis (Handling, Administration, Transportation and Storage analysis) and divided into value-adding, non-value-adding and necessary work. It is the administrative activities that vary the most depending on which delivery planning approach that is being used. Most of the activities in the construction logistics solution have been categorized as non-value-adding and necessary work. Areas of improvement include elimination of non-value-adding activities, ergonomics, storage policies, planning and coordination, development of work process standards and communication between actors. Most of the factors presented in this thesis were identified both in literature and for the studied case. Factors identified in the case study are mostly connected to administrative activities.
It is not enough to just look at one factor to decide if the CLS is efficient to use in a construction project or not. It is not the impact from one single factor that is critical, it is the combination and correlation between different factors. The CLS needs to be adapted to the specific case and maintain some flexibility during the production phase to be able to tackle impact from uncontrollable factors
Deformations in body openings: Correlation between vehicle testing and simulation data
No full textA comprehensive complete vehicle test was performed within a thesis work by
Alexander Jörud and Carl Jacobsson in order to measure the diagonal deformation
in major body openings. Their main focus was on preparing and performing
the physical test. They also updated the FE model to emulate the actual physical
test. The aim with this thesis work is continue their study and to enable comparison
between the simulation and test data. The correlation is performed in both time
and frequency domains. The final aim is to identify the capability of the complete
vehicle simulation procedure to predict body deformations.
A procedure to perform a correlation between simulation and physical test has been
developed. This study is performed for three different road conditions: Belgian
Pavé (PAV), Washboard in phase (WIP) and Washboard out of phase (WOP). The
relative displacement is analysed for the car when driven at 30 km/h and 50 km/h
on each road condition. The data is processed in order to perform the actual correlation
study. This includes converting the data from acceleration to displacement
and applying coordinate transformations. The E-line and Diagonal methods have
been implemented in order to evaluate the distortion in all closure openings. This
study consider time domain using the statistical evaluation (SEP) approach and
also frequency domain analysis. For that reason three comparison filters have been
developed.
An initial validation study resulted in a cutoff frequency at 5 Hz, as the accelerometers
gave impercise data below these frequencies. Secondly, both rigid body and
structural modes were identified between 5 and 20 Hz. Three different rigid body
motions were clearly identified when analysing the local components of the E-line
method. A modal analysis in the simulation code Adams was performed in order to
analyse the different rigid body motions of the body, engine and wheel suspension
further.
To prepare for correlation analysis the load level was compared between the physical
test data measured using a wheel force transducer (WFT) and simulation data obtained
with a Ftire model. Furthermore, the correlation study included a number of
different criteria like influence from velocity, modal damping and road profile. The
local and global component correlation pattern were analysed.
A clear pattern was identified for all load cases during the correlation investigation.
For instance, the rear door was subjected to larger deformations than the front door.
This pattern was present for all load cases. A likely explanation is that the structure
of the car is stiffer close to the A-pillar, which is a closed section, compared to the
open sections at the B and C pillars. Furthermore, the PAV road condition contributed
to the highest displacement at all closure openings. Both PAV and WOP
give torsional loads, causing a higher distortion at the sunroof and the tailgate compared
to the side doors. A clear symmetry between left and right side of the vehicle
was observed when evaluating the distortion in the side door openings. This was
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also observed for the left and right side of the tailgate opening.
The absolute distortion value was compared between physical test and two simulations:
one with 2% and one with 15% modal damping. The correlation between
physical test and simulation varies clearly for the different openings. It was not
possible to find one modal damping value to give a good correlation for all closure
openings. Therefore, a deeper analysis is required to understand why certain
modes give strong or weak contribution. However, when assessing all openings for all
load cases it could be concluded that simulation with 2% modal damping is clearly
over-predicting the relative motion, whereas simulation with 15% modal damping is
slightly under-predicting as compared to the physical test. Finally the local component
pattern was studied. For PAV only the front doors and the tailgate presented a
clear pattern for physical test and simulation. The results for WOP solely presented
a pattern for the tailgate opening. For WIP no clear no clear pattern was identified
for any of the openings.
Keywords:Body opening distortion, correlation, modal analysis, E-line method,
Adams, Diagonal method, modal dampin