Railway Engineering

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Analysis and Prediction of Track Geometry Degradation: Case study of Addis Ababa Light Rail Transit
(Addis Ababa University, 2021-06) Aisha, Kabange; Daniel, Haile (PhD)
Development of good maintenance policy requires better understanding of the long-term behavior of railway track systems. Addis Ababa Light Rail Transit is new system which has been in operation for the last five years. Understanding the degradation pattern of such system will help in scheduling and controlling maintenance activities, which is a problem to many railway operating entities. Track safety and maintenance effectiveness are improved by clearly understanding future condition of the track. This paper analyses and predicts the track geometry degradation of Addis Ababa Light Rail Transit. Track geometry degradation models developed by different researchers were critically reviewed to determine suitable model for AALRT. Factors which contribute to track geometry degradation were analyzed to determine the relationship between the factors and track degradation. Factors such as Number of Trips, Curve Radius, Speed, Grade, Tonnage and Track Surface were analyzed. All analyzed factors except Track Surface were found to have influence on rate of degradation for curved and straight sections of AALRT. The selected influencing variables and longitudinal leveling changes were used to develop track degradation model. Multiple regression model was developed in SPSS while Artificial Neural Network model (ANN) was developed on MATLAB software. The performances of two models were evaluated for straight and curved sections of North South line. North South line is a double line, model development was performed per each direction (Uplink line and Downlink line) and whole line regardless of direction. Six multiple regression models were developed. For straight sections three models were developed in which Downlink line displayed tremendous performance (R2=98%) compared to Uplink line (R2=85%) and North South line (R2=88%). For curved sections performance of 91% was observed on Uplink line and Downlink line while North South line had performance of 88%. Six ANN models were also developed as a complex model to predict future condition of track. Performance of 97% R-squared was obtained for both curved and straight sections of Uplink line while performance of 96% was observed in straight section and 93% performance was observed in curved sections of Downlink line. North South line display performance of more than 90% for both straight and curved sections of line. Comparison of two models showed that both can predict the longitudinal levelling changes with very low error. Although the ANN model has better performance than Regression model.
Analysis of Fatigue Failure on Motor Powered Train Axle of AALRT
(Addis Ababa University, 2017-06) Beza, Takele; Habtamu, Tkubet (Mr.)
Fatigue is one kind of phenomena that results breakdown of such material that are under a cyclic load or repeated stress. Fatigue is a main process resulting in a structural degradation and failure during axles’ service life. Railway axles are commonly operated over a service life of 30 years or more which refers to a very high number of loading cycles in the order of 10 iii 9. This project is all about AALRT train axle failures due to fatigue and discus about how to analyze the fatigue and stress. The reason why the project idea directed to around this area is that nowadays AALRT is operating beyond its design limit. The train designed to load 8 persons in one meter square space in the condition of overload. But practically the train is operating by loading more than 8 passengers in one meter square space. When the train load and operates beyond its design load limit many parts of the train life span will be shorten. One of the sensitive parts of the train that could easily damage and may cause derailment accident is axle. Because the whole train load directs toward to the axle. So the train axle will subject to fatigue and finally failure. The objective of this project is analyzing the axle of AALRT to clearly specify its fatigue life and stress concentration and distribution. This is done by collecting the data from ERC and Internet and analyzing the data that collected using formulas and software. The result will be discussed by comparing the axle fatigue life with the standard axle fatigue life.. And it tried to show that stress analysis by using software like Abacus. According to the data collected and by using approaches and software At Leghar station which is on the worst loading condition the result of the Maximum Principal Stress and the von misses stress are N/m 2 2017 and N/m 2 respectively. The result of the pressure is N/m 2 . The reaction force is N. The fatigue life is calculated as cycles. . When comparing with the standard axle life it’s found that the life of the AALRT axle life has less fatigue life. According to the standard axle life the cycle of the fatigue life reaches more than Giga cycles. The result validates and it is proven. Therefore AALRT should load passengers according to its design load limit and adding additional trailer will make less and disperse the concentrated axle load. Another solution is that using better fatigue resistant material for the axle would make longer the life of the axle.
Analysis of Passenger Demand Forecasting Models in The Context Of AALRT
(AAU, 2016-10) Babey, Bezabih; Birhanu, Beshah (Assoc. Prof.); Biniyam, Ayalew (Mr.) Co-Advisor
High rate growth of population and economic activity of Addis Ababa increases the traffic flow of the city and results in high congestion of traffic and unbalance between the demand and mode of transport. To minimize this congestion of traffic and unbalance appropriate passenger demand forecasting model is needed. So, this study tries to fill this gap. To select a suitable rail passenger demand forecasting model the two most common rail passenger demand forecasting models are compared based on their limitation and delimitation in the context of AALRT. According to this comparison the four stage passenger demand forecasting is found better than the elasticity passenger demand forecasting model for new rail service. Then, the analysis of estimating of passenger demand forecasting has been done by using the four stage passenger demand forecasting model. The four stage model has trip generation, trip distribution, mode choice or modal split and trip assignment stages. The study analysed through the first three stages because AALRT has only one line to travel from origin to destination of the trip maker. So, in this study the data analysis has been based on the data collected from different sources (like central statistics agency, city government of Addis Ababa education bureau, etc.). The data analysis result shows 11,666,568 trips are generated in Addis Ababa and 876072 total trips are generated in Kirkos sub city in the generation step; the generated trips in Kirkos has distributed into neighbor sub cities of Kirkos and in itself (Kirkos, Arada, Lideta, Bole Nifas Silk Lafto and Yeka is 662986.8, 6694, 66086, 33324, 24023 and 57766 respectively); choose the best transport mode to travel from origin zone to the destination zone. As the finding of this thesis shows that the four stage rail passenger demand forecasting model is a better model in the context of AALRT. Finally the study recommended for ERC and other organizations to use four stage passenger demand forecasting model to estimate their demands.
Analysis of The Performance of Disc Brake System of Addis Ababa Light Rail Transit Using Temperature and Coefficient of Friction as A Parameter
(Addis Ababa University, 2014-09) Andinet, Kumella; Demiss, Alemu (PhD); segaye, Feleke (Mr.)
Most of railroad passenger vehicles in the world use disc brake system which is mounted on the axle but some uses brake shoe directly applied onto the wheels treads. This system causes wheel heating, which in turn gives rise to thermal stresses and loss of mechanical strength. On the contrary, brake disc and pads, do not heat the wheels as shoe brakes do. Braking performance of trains is mainly affected by temperature and µ. This Research work presents the development of a modular tool for the prediction of passengers train braking performance. Particular attention is devoted to the accurate prediction of stopping distance, determination of nodal temperature and friction coefficient, considering different loading and operating conditions, necessary to verifying safety requirements for the movement of trains as a whole. Analysis was done on thermal transient of a brake disc for railway vehicles using finite element analysis method (FEM) simulation software called ANSYS. Performed analysis deals with two cases of braking; the first case considers service braking to a standstill; the second case considers emergency braking to a standstill and maintaining a constant speed. Once the model of the disc brake is done on solid works for simulation purpose, then simulation was followed using Multiphysics Ansys workbench. In general analysis results shows that, the performance of the disc brake is highly affected during emergency brake due to minimum stopping distance and delay time, results the increment value of coefficient of friction; although the nodal temperature is also high compared to service braking condition but it is less than the maximum temperature achieved by the disc in the literature review. However for the case of service brake its performance is good for all stations. Therefore validation results were encouraging using experiments, dynamometer test, and allowed a more accurate identification of the friction factor and temperature influence on braking performance of passenger trains as a whole.
Analysis the Effect of Unequal Force Application on A.A LRT Disc Brake During Emergency Brake
(Addis Ababa University, 2016-09) Biniyam, Belayneh; Tsegaye, Feleke (Mr.)
A train disc brake system is used to perform three basic functions, i.e. to reduce speed of a vehicle, to maintain its speed when travelling downhill and to completely stop the vehicle. During these braking events, the disc brake may suffer of temperature, deformation and stress issues. It is quite sometimes that the disc brake components fail structurally and/or having severe deformation on the pad. Thus, this paper aims to examine stress concentration, structural deformation and contact pressure of brake disc and pads during braking event by employing commercial finite element software, ANSYS and CATIA for modeling purpose with considering the effect of unequal pressure application on the two opposite side of the disc which are developed due to brake line corrosion, caliper sticking, failure of piston seal, variation of rotor thickness and also failure of caliper bolts. The main results of this analysis is consider factors which are relate about disc brake structure and contact behavior such as deformation, Von Misses stress and temperature which rise when breaking action with considering the unequal heat flux which generate on opposite side of disc when unequal pressure applied on two opposite side of the disc and define from the analysis result there is a high deformation, stress and temperature difference between equal pressure and unequal pressure applied on two opposite side. I.e. when unequal pressure applied on two opposite side, there are greater temperature, heat flux, deformation and stress as compare with equal pressure applied on two opposite disc side
Assessment and Evaluation of Addis Ababa Light Railway Transit Track Structures
(Addis Ababa University, 2016-11) Biniam, Shawul; Abebe, Dinku (Prof.)
To effectively solve the problem of urban transportation, especially that of the downtown area, the government of Ethiopia has planned and constructed light railway transit in the city of Addis Ababa. The AALRT railway tracks basically consists a flat framework made up of rails and sleepers which is supported on ballast. The ballast rest on a sub ballast layer which form the transition layer to the formation. The significance of this research is to construct Phase-II AALRT project plan more reliable, efficient and esthetically attractive then the first phase AALRT project. This research would assess and evaluate lesson learned from first phase AALRT project. It focuses on external interactions that occur between the various components of a track structures and its supporting systems, integration with landscape, highway transportations and infra-structures. Besides, safety, future expansion, aesthetics and drainage system, wastage of materials and human power, the technology, knowledge and skill gained during construction and operation track structures. The research were held through site investigations, desk studies and questionnaires response. The primary data for research gained from desk study through review detail design documents and literature from the Ethiopian railway corporation. The questionnaires are on the findings of the research analyzed using simple statistical approaches, Likert‟s scale and standard error deviation. Within this study it is possible to conclude assessment and evaluation the constructed AALRT project track structures. The research identifying that providing light railway transit for resident of city has the effective solution for the immediate transportation problem. Besides, there is also lack of integration between the constructed railroad with existing buildings, pipes, wires and transportation situation. The commercial activities decrease due to cause of the laid railroad separate the city in two sides. The constructed AALRT project would not consider safety, future expansion and urban aesthetics. It also shows that there was wastage of properties, materials,
Barcode Based Fare Ticketing System for AA LRT
(Addis Ababa University, 2017-06-16) Teklay, Gebreslassie; Birhanu, Re’esom (Mr.)
Technological development has resulted in a boundary free digital world. This development has resulted in transaction through virtual money instead of real ones, e-ticketing is mostly used system for such transactions. But AA LRT uses weak and unreliable ticketing system which is called paper ticketing. The thesis system makes use of barcode for verification and identification of the user. A unique barcode will be generated for each customer that is registered to the system. Using this barcode, the customer will be able to make transactions, which is an automated fare collection. This system solves all the drawback of the manual ticketing system which currently happened in AA LRT. Two dimensional bar codes could provide for more complex ticket types. The barcode based card number of the user is used which provides the information of the user. This system provides an efficient way of travelling while maintaining the security. This system is implemented using Visual studio 2013 development environment, C# programing language and database (SQL server). In the implementation of this system it requires barcode scanner with gate controller which scans the profile from the ID card, then sends to the database to check the validation and desktop application to register new customers profile and amount paid, generate the barcode based ID card, update customer balances and configured the stations. Finally, the system software is successfully developed.
Design of Hybrid Solar Energy System for The Application of Train Locomotive Power Source for The AALRT And Ethio-Djibouti Routs
(Addis Ababa University, 2015-03) Shimels, Kebede; Habtamu, Tkubet (Mr.)
Revolutionary changes have been taken place in the life of the mankind since human beings acquired the capability of walking fast. Now a days rail transport become a cheap means of transportation system to any class of people and goods. The train uses a diesel or electrical energy for its propulsion based on its design but due to the raise of fuel price and environmental pollution factor, the modern train uses an electrical energy which is finally converted in to mechanical support for the propulsion. The electrical energy is generated from different form of energy sources among the various forms of energy, solar energy is the best form to use in the present situation due to its, abundablity, environmental friendly and sustainability. In this study, the applications of solar energy to railway locomotive power propulsion system, using photovoltaic solar panels is analyzed and develop a grid connected system with a storage battery to store excess energy for emergency and night time, the rest excess generated energy is send back to the grid through the return line which is already build up by Ethiopian Rail way corporation power system directly through the line and as a form of regenerative energy during brake. The research mainly focuses on the conversion, the amount of electrical energy produced from the sun with the pre defined solar panel and its application for the railway propulsion system as a supplemental energy source for the electrical and diesel traction system for the selected newly build up Ethiopian rail way car and routs by maximize the solar source and minimizing the others. Therefore the different literatures was asses, important data was collected from different rail way companies and national meteorology agency and other sources, the amount of energy produced is mathematically calculated, the data which is collected was computed by using a Microsoft excel and Mathlab, the hybrid energy system layout and a physical model of a train car could be developed using a Microsoft Visio and CATIA software respectively. In this research, the well known Angstrom correlation, which used sunshine hour duration for the selected station through the Ethio-Djibouti railway rout, was used to compute the daily radiation and energy computation from a 3 to 5 years collected data. The result shows the minimum and maximum radiation distribution through the rout is 4.37kw/m2 /day during August at Addis Ababa and 7.2kw/m2 /day at Diredawa during May respectively. In general, Ethiopia has an average radiation of 5.87ke/m2/day, which indicates a great potential to generate electric power from the sun. Based on the technical proposal of the ERC, Box type, YZ25G and DFN7G and AALRT of train car had been selected for the installation of solar panels at the top roof surface area which is varying based on the number and size of the train car. For all selected trains a total number of 2011 panels with a total 30 years life cost of 56,764,325birr. The generated energy may cover 4.455 to 356.9% of required energy based on the sunshine hour duration, types of car and configuration, therefore the excess energy shall be sent to the main grid for other purposes to reduce the wastage of it. Based on the minimum energy production and maximum configuration the cost return time may be 12 years. The research generally shows the possibility of application of solar energy through the selected route and the best solution for sustainable energy supply and for the overall economy development in the country
Design of Passenger Information System and Smart Passenger Crowdedness Avoidance: Case of AALRT
(Addis Ababa University, 2017-06) Yetages, Rorissa; Abebe, Teklu (Mr.)
Addis Ababa Light Rail Transit is playing a prominent role in alleviating the city’s transportation problem. Currently, it only has an onboard passenger information system, and there is no wayside passenger information system. Consequently, passengers waiting at the station are unable to know if a train is coming, the estimated arrival time of the train, the crowdedness level on the train and whether the train is single or coupled. The other challenge is that on pick hours there exist a high passenger crowdedness on the trains which makes the service unintentionally unfair as only who can survive the high congestion on the train use the service. The primary objective of this thesis is to avoid the existing passenger information system problems of Addis Ababa Light Rail Transit by devising a reliable passenger information system and come up with a cost-effective solution for the current passenger over crowdedness problem. Hence, a passenger information system was designed by developing a website, an Android application and station displays which will all show the available space on the next train, the number of passengers expected to get off on that station, and its estimated remaining time of arrival. The simulation result showed that we achieved the stated objective as it can give detail information about the train for each passengers waiting at the stations. In addition to this, we introduced a passenger overcrowding solution. It is a passenger counting system that will put a limit on passengers getting on a train when the train load exceeds its carrying capacity. Android based point of sale (POS) ticketing device is proposed to be used as a passenger counter and ticketing at the same time. It is expected that the current manual ticketing problems encountered by Addis Ababa Light Rail Transit can be solved by this device.
Evaluation of Different Seepage Treatment Methods in Railway Tunnels Case Study: Addis Ababa Light Rail Transit System (LRT)
(Addis Ababa University, 2016-03) Dereje, Tesfu; Dereje, Hailu (PhD)
This research investigated and evaluated water blocking techniques in tunnel sections present at the St. Georgis tunnel using 2D modelling by numerical simulation software namely GeoStudio. With the help of GeoStudio extension, GeoStudio SEEP/W, the tunnel geometry along with material property of the concrete and backfill material using readily available hydraulic property as an assumption was modelled. This together with simplifying assumptions such as material homogeneity and isotropy, maximum water flux or infiltration pressure was seen at tunnel bottom of the side wall and clearly seen much like the actual condition. With this assumptions, the model showed that, the tunnel section exhibits maximum flux or infiltration in the bottom corner each side. The inner lining of the tunnel in particular have been studied and results show that the nodes exhibit water infiltration occurs in each node point with the maximum 9.75E /s. Proper application of water proofing helps in preventing water infiltration throughout the tunnel lining. Even if exterior waterproofing is part of the solution, it is also necessary to implement a drain pipe at the bottom of the tunnel to remove the water that will accumulate near the tunnel bottom. One additional finding here would be that the protection of the waterproofing on the tunnel side linings will be greatly increased if a rock-fill can be implemented on the as a backfill material for a limited width so that the gravitational drainage of the rock-fill avoids any saturation to develop at the tunnel side lining. In both cases though, the implementation of a drain pipe is mandatory. Furthermore the research has managed to deduce the applied water proofing material has malfunctioned or otherwise since it has been claimed that water proofing material has been implemented on all section of the tunnel, where there should have been less threat of leakage according to the research, the top slab of the tunnel, on actual ground it was seen to have had high leakage.
Fatigue Analysis of the Railcar Wheelset Under Different Loading and Traction Condition: The Case of AALRTS
(Addis Ababa University, 2019-08) Sileamlak, Ayenew; Celestin, Nkundineza (PhD)
Railcar wheelset is a type of wheelset specially designed for use on rail tracks to transmit the sprung and unsprung weight of the train to the rail and to give traction. However, since they are subjected to cyclic axial, lateral and horizontal loads fatigue failures are common. In addition, a railway companies like Addis Ababa light rail train (AALRT) Transport passengers and goods in most cases face overloading beyond the loading capacity. On the other hand, the speed has a direct effect on the fatigue of wheelset. By fundamental mechanics for a train moving at constant power, increase in speed causes the decrease in axle twisting moment leading to a decrease in torsional stresses; but, this effect is only significant at relatively low and medium speeds. Also, according to Hirakawa & Kubota (2001), increase in speed causes an increase in axle bending stresses; but, this effect is only significant at very high speeds and the effect is nonexistent for speeds less than 60 km/hr. Therefore, the main objective of this paper is to perform stress and fatigue analysis of a wheelset under different loading and traction conditions on a straight railroad in case of AALRT. This research uses both primary and secondary data sources for analysis. The researcher employs different analytical and numerical approaches, to determine induced stresses and loads that act on the wheelset. We use different mechanics theories (static and dynamic) and FEA analysis was carried out by ANSYS 15.0 for different loading (39158.25 N, 51571.36 N & 57307.88 N) and traction condition ( . On the bases of this analysis the results show that the fatigue life improves by 57 % if the trains carry passengers only by seat and by 16% if AALRT limits the passenger number to 317 passengers/train instead of 420 passengers per train. Also, the results show that the increased average speed up to 40 km/hr. contributes to the increase of fatigue life and factor of safety of the axle caused by a combination of twisting and bending moments by 3.1 % and 4%, respectively. The results in this analysis provide a good start to be taken by an urban rail transit such as AALRT to determine optimum train loadings and travel speed range in combination of other detrimental factors that were out of scope of this research.
Fatigue Durability Analysis for Welded Bogie Frame of AALRT
(Addis Ababa University, 2016-06) Ruhama, Minwuyelet; Daniel, Tilahun (PhD)
This research paper presents the fatigue durability analysis for the welded bogie frame of AALRT. The purpose of this research is to observe the fatigue life of the welded bogie frame and to protect it from failure. In the analysis of the research a three-dimensional finite element model of the bogie frame has been used to investigate the effect of the applied loading force at the frame surface area and observing the effects on the welded joints. The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of the applied loads and welding seams. On the bases of the model analysis the following results have been achieved. Output results without Sensitivity Factor: – maximum and minimum log10 damage values are 30 and -7.09 respectively, maximum and minimum log10 endurance safety factors are 1 and -5.11 respectively, maximum and minimum fatigue limits are 282 N/mm2 and 255 N/mm2 respectively, and fatigue life is 2e^6. Output results with small weld seam sensitivity Factor: – maximum and minimum log10 damage values are 30 and -20 respectively, maximum and minimum log10 endurance safety factors are 1 and -5.11 respectively, maximum and minimum fatigue limits are 282 N/mm2 and 0 N/mm2 respectively, and fatigue life is 2e^6. Hence it is possible to conclude that the maximum damage result, which is 30 in number is much exaggerated result, it is because the weld quality that I have taken is poor. Whereas the fatigue limit at each analytical outputs has been proved to be the recommended value. The endurance safety factor is below the anticipated value. There for a special attention should be given to the welded joints. Based on sensitivity seam thickness results, it is possible to conclude that welded connections are almost nearer to failure because they are highly exposed to residual stress. The study is significant and applicable because it introduces new knowledge on fatigue life analysis of welded bogie frame in the minds of the beneficiaries of the study particularly to those who are working in Railway Corporation.
Feasibility Study of At-grade Versus Highway Overpass Rail-Road Crossing. Case Study of Addis Ababa Light Rail Transit: East-west line
(Addis Ababa University, 2019-06) Josepine, Aguti; Bikila, Teklu (PhD)
The Addis Ababa Light Rail Transit, East-West line in particular, has a number of at-grade rail-road crossings with an increasing road traffic volumes and train frequencies which affect the smooth operation of the Light Rail Vehicles. Therefore, a study on feasibility of at-grade versus highway overpass rail-road crossings was sought of, by considering the economic aspects involved with each; with the objective of determining which of the two crossings would be feasible for investment. Different techniques used to achieve the objectives included: manual traffic counts technique, document review, field observations, queuing model, and NPV, IRR, BCR analysis methods, sensitivity analysis technique, etc. Based on the methodology, different economic and transport impact cost and benefit values were obtained, with the highway overpass crossing generating a net benefit of $6,758,782.17, unlike the at-grade rail-road crossing that gave a net loss of -$7,753,428.07. The aggregated at-grade and highway overpass rail-road crossing cost values of $2,613,280 and $1,880,786, respectively; and benefit values of $307,866 and $763,011.38, respectively, were obtained. The feasibility of highway overpass crossing over the at-grade rail-road crossing was determined based on the NPV, BCR, IRR analysis results. Where, $119,875.45 NPV, 15.87% IRR and 3.3704 BCR value for highway overpass crossing; and -$3,427,488.39 NPV, 0.2576 BCR and a negative IRR for at-grade rail-road crossing. These results show that the highway overpass crossing is feasible than the at-grade crossing. Therefore, this thesis is relevant in identification and quantification of the transport and economic impacts; supports decision-making when choosing a rail-road crossing alternative.
Investigation of Common Section Interlocking System for Addis Ababa Light Rail Transit
(Addis Ababa University, 2019-10) Genet, Belay; Yalemzewd, Negash (PhD)
An interlocking is "an arrangement of signals and signal appliances so interconnected that their movements must succeed each other in proper sequence". Railway interlocking is a safety, monetary and environmentally critical system because its failure may cause serious consequences such as loss of human life, severe injuries, and large scale of environmental damages or considerable economic penalties. The safety and complexity of this system requires formal modeling and step by step refinement for its construction and development. Computer-based interlocking (CBI) is a device controlling the signaling equipment by computerizing both the electrical and mechanical systems of the existing interlocking device. CBI is preferred in Addis Ababa Light Rail Transit (AALRT) because of its simple lightweight structure, failsafe configuration, high-speed processing of data and simplicity in changing hardware and software. This paper dealt with an investigation of common sections interlocking system which ensured system a synchronization and concurrency by modeling suitable interlocking systems with the help of Petri net. Petri nets are a graphical and mathematical modeling tool applicable to many systems. Petri net is also used in railway application like scheduling rail operation, in supervisory control approach for railway network, modeling train control system for level crossing, and in developing interlocking and signaling system with safety verifications. At first, the physical layout of five stations of AALRT are being drawn using AutoCAD with its full components, such as signals, switches, and track circuits. After that, a proper model of interlocking system is being modeled with the help of Petri net software and the model alleviates the problem which has been encountered in the interlocking system by allowing the interlocking to check the trains asynchronously without any collision.
Optimisation of Internal Shape of Disc Brake to Increase Ventilation
(Addis Ababa University, 2017-02) Abrham, Tibeb; Demiss, Alemu (PhD)
Brake system has always been one of the most critical active safety systems. Brake cooling is further an important aspect to consider for brake disc durability and performance. In railway transport, braking the train without overheating the discs and losing the braking capacity is a matter of safety. In urban railway transport, like AALRT, the speed of trains is confined to the lower limit because it is difficult to decelerate and stop the train within the short distance of the closely spaced stations. During braking, all the kinetic energy of the train is changed into frictional and finally to heat energy which causes the brake to overheat and lose its braking capacity. To prevent the occurrence of brake heating, brake rotor must be designed such that it ensures sufficient heat dissipation. The special structure for ventilation not only increases the surface area of the disc rotor but also enhances airflow around the surface of the disc to achieve a higher convectional heat transfer. In this research a fluid flow CFX, Thermal and Stress analysis is done on three types of disc brakes; a curved vane and two types of pin vented rotors using finite element method. The fluid flow CFX is used to calculate the cooling effect of the moving air relative to the brake rotor. The pin vented rotors have elliptic cross section with different geometric parameters. Pin vented rotor creates turbulence and gives higher heat transfer coefficient. It has been observed that the pin vented disk brake with elliptic cross section pins which has higher eccentricity has good heat dissipation characteristics. Changing the geometry of the pins increasing the eccentricity of the elliptic cross section creates larger surface area to volume ratio and less obstruction to the air flow which enables to have higher convection heat transfer coefficient. After emergency braking of AALRT with maximum track gradient of 3.15 0 and overload condition, a maximum temperature gradient of 334.95 0 C is achieved with one of the pin vented brake which has higher eccentricity while it is 340.93 o C and 346.89 o C for the second type of pin vented brake and the curved vane rotors respectively.
Overload Effect on The Life Cycle of Car Body Structures for AALRT Trains
(Addis Ababa University, 2017-08-31) Ehetaferahu, Berhanu; Tollossa, Deberie (Mr.)
Ethiopian railways corporation invest a lot of money and construct AALRT and it's warmly welcomed by the people. Since it is been 1 and half year the trains start working, And even if the design life cycle of AALRT train car body structure should not be less than 30 years, train's body start to degrade from day to day. This will be a problem for AALRT in terms of quality of service, in terms of maintenance cost and damage of train body before design life cycle. This paper aims to discuss the effect of un acceptable passenger over load effect on life cycle of AALRT train car body steel structure and show the effect of different loading conditions by modeling car body steel structure and making analysis using Catia and Ansys software . The methodology of this paper starts by collected real overload condition data's, studied car body frame structure and materials used for AALRT trains, designed frame steel structure of AALRT train using Catia V5R19 software and analyzed by Ansys workbench 15.0 software using seven different loading conditions. The total fatigue life analyzed by using PalmgrenMiner Linear Damage Rule and the final fatigue life cycle result found. The calculated life cycle result converted to time. The output of the analysis shows that some parts of under frame steel structures on Exit/Entrance area have fewer life cycles. The connection of the high floor and low floor area and near to turning table have less life cycle than design life, when the loading condition reach at maximum level . But the total life cycle is above from the design life. Finally the total fatigue life cycle of four parts on Motor car had below the design life cycle. By adding additional reinforcement to those four parts, it is possible to increase the fatigue life. Even it can resist the over load at standing and seat area beyond designed load limit.
Performance Investigation of Addis Ababa Light Rail Transit Communication Systems
(Addis Ababa University, 2017-07) Samuel, Tamire; Yalemzewd, Negash (PhD)
Railway communication system is an essential part of the railway system. It is the back bone for the railway operation and management, to control and monitor the different subsystems of the railway system. Thus, the data communication services required for the signaling and interlocking system, for passenger information at station terminals, for Supervisory Control and Data Acquisition (SCADA) and telemetry data which are used for monitoring and management of other subsystems such as power should be safe, reliable, effective and efficient. Thus, there is no doubt taking performance investigation of the railway communication system. Because, capabilities and performance of the railway communication systems (subsystems) degrade the safety, reliability, effectiveness and efficiency, and also can affect the railway operation. Assessing performance investigation in Addis Ababa Light Rail Transit (AALRT) communication system is necessary to determine whether or not there is a performance problem requiring action. There are performance problems occurred currently as observed in the AALRT communication system. Most of the performance problems occurred in the transmission system, such as communication failure alarm type 56%, service failure alarm type 8% and equipment failure alarm type 36%. These performance problems could affected the day to day activities of the AALRT such as unable to transmit quickly, accurately and reliably the information and/or data, unable to make emergency calls and fail to transport data for signal system; it makes the dispatcher of the control center unable to real-time monitor important areas like station platforms, important level crossing of line, substation and switch section of depot. This thesis found out all the details or facts and accomplishment about the communication system of the Addis Ababa Light Rail Transit. It also identified, analyzed and studied the root causes for the performance problems; discussed their impact and effect on the system. It also proposed a frame work of KPI parameters for the performance investigation and effective maintenance of the AALRT communication system.
Stability of trains under aerodynamic excitation for Addis Ababa Light railway transit (A.A.L.R.T)
(AAU, 2015-05) Abel, Demissie; Habtamu, Tkubet
Railway train aerodynamic problems are closely associated with the flows occurring around train. This work is based on numerical model using Computational Fluid Dynamics (CFD) approach to obtain the impact of air flow around a train operating in selected scenarios. These scenarios are train passing each other and train passing through the tunnel. The model of generic passenger train was developed using CatiaV5 and generated the wind tunnel and applied the boundary conditions in ANSYS workbench 13.0. The simulation work of the test vehicle and grid system is constructed by ANSYS-13.0. FLUENT which is the CFD solver and employed in the present work. In this study, numerical iterations are completed, then after aerodynamic data and detailed complicated flow structure are visualized The paper aimed at investigating the aerodynamic impact on a lightweight railway vehicle used in A.A.LRT. The performed simulation allows measuring the aerodynamic forces on the vehicles. Numerical prediction of incompressible flow has been performed in AALRT train moving at a speed of 22.2m/s (80k/hr). Fluent, the CFD code which incorporates - turbulence model and segregated implicit solver was used for the computation. The aerodynamic analysis was performed to study the flow behavior of the air over the train body. The analysis includes the study of contours of pressure and velocity. The peak pressure difference along the train is 1615KPa which is exhibited for trains passing each other. The two scenarios conducted for a train exiting and entering the tunnel shows that the pressure deviation is very low with a magnitude of 1411Kpa and 1355Kp respectively
Structural Analysis of Addis Ababa City Light Railway Transit Tram Car Body Using Steel and Aluminum Honeycomb Sandwich Material
(Addis Ababa University, 2014-09) Benyam, Adane; zewdu, Abdi (PhD); Tollosa, Debrie (Mr.) Co-Advisor
The structural design of railway vehicle bodies depends on the loads they are subject to and the Characteristics of the materials they are manufactured from. In this study structure analysis of Addis Ababa city tram passenger car made of the exact steel material and aluminum honeycomb material are analyzed. Finite element method is used to assess the static structure behavior of the tram car by ANSYS 14.5 software. For 3D modeling used solidwork11 and to simplify the core material selection process and to design the layers for aluminum honeycomb material by ANSYS Composite Prep Post (ACP). The result of the finite element analysis (FEA) shows that the structural analysis of the tram car using Aluminum Honeycomb reduce the gross weight by 12.14% with almost the same maximum principal stress and also its stress and deformation result of tensile, compression, lateral and vertical loading condition result validated against Structural requirements of railway vehicle bodies stated under EN 12663 and EN 15227 standard. The finite element result value of aluminum honeycomb and steel maximum principal stress of minimum variation but due to compression load applied on tram car using Aluminum Honeycomb higher compare to steel material to reduce the variation multi- material approach used to further reduce the stress and the deflection.
Thermal Analysis of Vented Disc and Optimization of the Shape of The Vented Curves In AALRT
(Addis Ababa University, 2015-05) Berhane, Tafere; TSegaye, Feleke (Mr.)
The disc brake is a device for slowing or stopping the rotation of a wheel. Braking of the vehicle leads to heat generation during each braking event. Transient thermal analysis of the Rotor Disc of Disk Brake is aimed at evaluating the performance of ventilated disc brake rotor of a rail vehicle under emergency braking conditions and there by assist in optimization the curves of the shape of ventilated disc to identified the thermal analysis effect during braking. Here Disc brake modeled with CATIA software and its analysis is done using ANSYS workbench 12 with considering CFD-cfx package software. The main purpose of this study is to analyzing the thermal behavior of the ventilated disc brake during the braking phase by optimization the shapes of the curves of the vented disc and compare results. The coupled thermal-structural analysis is used to determine the Von Mises stress established in the disc for ventilated disc with the same materials and other data from ERC to enhance performance of the rotor disc. The results from the simulation with changing shapes of the vane like vane number, vane angle and vane curve radius; as vane number 50 ,60, 70 and 80 , then temperature generated reduced from 311.76-302.67[°C] until vane number 70. But at vane number 80 it is 308.94 [°C].And with changing the straight vane number 50 to 5, 10 and 20 angles its values of temperature generating at a time of 5.2488 [s] is 302.9, 239.86 and 302.24 respectively and at vane numbers 60 and 70 at angle 5 and 20 their values are 310.44, 310.19[°C] at time 5.2488 [s] and 309.86, 309.72 [°C] at time 5.0868 [s]respectively. At changes of vane curve radius from straight to 120 to 60mm its generating temperature is reduced 312.03 to 309.83 [°C] at time 5.2488[s]. Generally from simulation of emergency brake at braking time 9.72[s], reduced generating temperature at vane number 70 and at vane angle 5 with vane number 50 are 302.67 and 302.9[°C] respectively which preferable at emergency brake-1, when simulated at tentative with applying initial temperature induced at emergency brake-1, induced temperature at emergency brake-2 increase to 361.99 and 362.55[°C], these are preferable to compare from the current AALRT uses which is induced 383.26[°C] at emergency brake-2.

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