Display:

Results

Viewing 1 to 30 of 21620
2017-03-28
Technical Paper
2017-01-1025
Qinghe Luo, Baigang Sun, Xi Wang
Hydrogen is the most promising way for energy carrier because it has fast combustion velocity, the wide range of sources and the cleaning of combustion products. The hydrogen internal combustion engine (HICE) with turbocharger has been used to solve the contradiction of the power density and controlling NOx. However, the selection of the compressor for HICE with turbocharger is very different from the traditional engines because of the gas fuel. Hydrogen as the gas fuel takes the cylinder volume, which will increase the pressure and reduce the mass flow rate of air in the cylinder. Thus, this paper put forward a new method for the HICE with turbocharger taking into account of the effect of hydrogen in the cylinder. This method can calculate the turbocharging pressure ratio and the mass flow rate of air through the target power and the general parameters such as the displacement of cylinder, the intake temperature of hydrogen and the equivalence ratio of the mixture.
2017-03-28
Technical Paper
2017-01-0693
Seungwoo Kang, Wonkyu Cho, Choongsik Bae, Youngho Kim
This paper investigated the influence of injector nozzle hole number on fuel consumption and exhaust emission characteristics of diesel engine. The engine used for the experiment was the 0.4L single-cylinder compression ignition engine which is modified from an 1.6L four-cylinder automotive diesel engine. The fuel injection equipment were operated under 250MPa injection pressure. Three injectors with identical hydraulic flow rate with various combinations of the nozzle hole number(8, 9, and 10) and diameter(105 μm, 100 μm, 95 μm) were compared. The indicated specific fuel consumption and NOx emission of three injectors were on same level because of the identical fuel flow rates and similar in-cylinder pressure traces. Without EGR, the particulate matter(PM) emission were lower with larger nozzle hole number. However, the NOx-PM trade-off were similar at low oxygen concentration with high EGR rate.
2017-03-28
Technical Paper
2017-01-1075
Wen Chen, Reda Adimi, Xingfu Chen, Todd Brewer, Ling Shi
In CAE analysis of cylinder bore distortion, valve seat distortion, valve guide-to-seat misalignment and cam bore misalignment, nodal displacements on the cylinder bore inner surface and on the gage lines of valve seats, valve guides and cam bores are typically output. Best fit cylinders, best fit circles and best fit lines are computed by utilizing the output displacements of the deformed configuration. Based on the information of the best fit geometry, distortions and misalignments are assessed. Some commercial and in-house software is available to compute the best fit cylinders, best fit circles and best fit lines. However, they suffer from the drawback that only one best-fit geometry can be computed at a time. For example, in the valve seat distortion analysis of a typical 4-cylinder, 4-valve engine, 16 best fit circles are needed.
2017-03-28
Technical Paper
2017-01-0323
Rosa Radovanovic, Samuel J. Tomlinson
Press-in-place gasket stability is required to maintain consistent and predictive sealing compression in a sealing joint utilizing a housing groove and a mating component sealing surface. Without proper balance between height of the groove and height of the gasket, the sealing joint can be compromised. It is industry standard to balance design variables with the desire to achieve long term sealability and gasket stability. The percent of gasket out of groove was varied to study the interactions of the design control and the resultant deviation of gasket centerline to the groove centerline. Finally, an optimal percentage of gasket out of groove is recommended.
2017-03-28
Technical Paper
2017-01-0250
Jizhou Zhang, Jianhua Zhou, Mian LI, Min Xu
To improve the system performance, precision manufacturing is required for production of the internal combustion engines (ICEs), a typical complex nonlinear system. Previous studies show that tolerances of critical dimensions have significant impacts on the engine performance. Among many critical factors, friction loss is one of the most important ones that affect the output performance of ICEs. It is necessary to recognize and control the tolerances which affect the friction loss. Of all the friction pairs for the engine, it is observed that the piston-cylinder friction pair and the bearing system take up nearly 70% of the total friction loss. In this work a novel multi-objective tolerance design optimization problem considering two friction systems mentioned above is proposed and solved. First two separated simulation models, the piston-cylinder and the bearing are built using AVL Excite Piston & Ring® and AVL Excite Power Unit®, respectively.
2017-03-28
Technical Paper
2017-01-0543
Oliver Hofmann, Shijin Han, Daniel Rixen
This study discusses model-based injection rate estimation in common rail diesel injectors exhibiting aging phenomena. Since they result in unexpected injection behavior, aging effects like coking or cavitation may impair combustion performance, which justifies the need for new modeling and estimation approaches. To predict injection characteristics, a simulation model for the bottom section of the injector is introduced, with a main focus on modeling the hydraulic components. Using rail pressure and control piston lift as inputs, a reduced model is then derived in state-space representation, which may be used for the application of an observer in hardware-in-the-loop (HIL) environments. Both models are compared and validated with experimental data, with which they show good agreement. Aging efects and nozzle wear, which result in model uncertainties, are considered using a fault model in combination with an extended Kalman filter (EKF) observer scheme.
2017-03-28
Technical Paper
2017-01-0244
Joshua Lyon, Junheung Park, Yakov Fradkin, Jeff Tornabene
This paper describes a tool developed by Ford Motor Company to help business analysts revise sourcing plans when business conditions change. A common scenario is demand increasing beyond installed capacity – how should the business respond? Likewise, how should production change when demand is lower than expected? Sometimes the company can move production to different locations or outsource parts in order to reduce costs. This paper focuses on making such decisions for stamped sheet-metal parts. We describe an optimization tool used to periodically reassess where to stamp parts. The tool uses mathematical optimization to balance logistic and outsourcing costs. An important component is the user interface, which allows stamping experts to adjust the model in real time to reflect different constraints and competing objectives. This allows the algorithm to efficiently seek alternative solutions while the business expert guides for nuances that may be hard to represent mathematically.
2017-03-28
Technical Paper
2017-01-0366
Xingyu Liang, Yuesen Wang, Shuhe Huang, Guichun Yang, Lin Tang, Guoqi Cui
Due to the mechanical forces under high temperature and pressure conditions, the engine cylinders cross section will not be a round circle any more once they are installed. Therefore, both static and dynamic conditions can change the geometry of the cylinders. On the other hand, deformation of engine cylinder causes increasing lubricating oil consumption and abnormal wear, resulting of worse fuel economy and emissions. However, prediction of deformation on a liner has not been made because of the complication of conditions and structure. In this study, a V6 engine body model was built and meshed with Hypermesh suit software. Also, cylinder deformation under static condition has been simulated and analyzed. Basically, few parameters like pre-tightened force, structure and distribution of bolts have been investigated to figure out how the cylinder bore deformation behaves via finite element analysis. Also, a simple Matlab program had been developed to process the data.
2017-03-28
Technical Paper
2017-01-0387
Deepak Anand Subramanian, Shanmugam Mathaiya, V Srinivasa Chandra
In today's commercial vehicle scenario, designing and developing a component which will never fail throughout its lifespan is next to impossible. For a long time especially in the field of automotive, any crack initiation shall deem the component as failed and the design requires further modification. This paper deals with studying the failure of one such component and understanding the effect the crack has on the overall life of the component i.e. understanding the remnant life of the component. The component under study was gear shift lever bracket and is mounted on the engine exhaust manifold. It experiences two types of loads: inertial load due to the engine vibration and gear shift load. Frequent failures were observed in the field and in order to simulate it at lab, an accelerated test approach was adopted. The engine operating speed was used to identify the possible excitation frequency which the component might experience.
2017-03-28
Technical Paper
2017-01-1709
Zhigang Wei, Sarat Das, Ryan Barr, Greg Rohrs, Robert Rebandt, Xiao Wu, HongTae Kang
Recent stringent government regulations on emission control and fuel economy drive the vehicles and their associated components and systems to the direction of lighter weight. However, the achieved lightweight must not be obtained by sacrificing other important performance requirements such as manufacturability, strength, durability, reliability, safety, noise, vibration and harshness (NVH). Additionally, cost is always a dominating factor in the lightweight design of automotive products. Therefore, a successful lightweight design can only be accomplished by better understanding the performance requirements, the potentials and limitations of the designed products, and by balancing many conflicting design parameters. The combined knowledge-based design optimization procedures and, inevitably, some trial-and-error design iterations are the practical approaches that should be adopted in the lightweight design for the automotive applications.
2017-03-28
Technical Paper
2017-01-0860
PengBo Dong, Jun Yamauchi, Keiya Nishida, Youichi Ogata
With the aim of improving engine performance, recent trend of fuel injection nozzle design followed by engineers and researchers is focusing on more efficient fuel break up, atomization, and fuel evaporation. Therefore, it is crucial to characterize the effect of nozzle geometric design on fuel internal flow dynamics and the consequent fuel-air mixture properties. In this study, the internal flow and spray characteristics generated by the practical multi-hole (10 holes) nozzles with different nozzle hole length and hole diameter were investigated in conjunction with a series of computational and experimental methods. Specifically, the CFD commercial code was used to predict the internal flow variation inside different nozzle configurations, and the high-speed video observation method was applied to visualize the spray evolution processes under non-evaporating conditions. Moreover, the Laser Absorption Scattering method was implemented to explore the spray evaporation characteristics.
2017-03-28
Technical Paper
2017-01-1229
Ken Yamamoto, Nobuyasu Sadakata, Hidetoshi Okada, Yusuke Fujita
Electric oil pumps (EOP) for automobiles are used to lubricate and cool moving mechanisms and supply oil pressure to components. Conventional EOPs consist of two separate units including a driver and a pump system comprised of a motor and a pump, which, as a result, impedes layout flexibility for vehicles. To overcome this shortcoming, we have developed an ECU-integrated oil pump in which a driver, a motor and a pump are incorporated as a single unit. In the course of the project, we focused on improving vibration resistance and developing a compact design. The first challenge was to improve vibration resistance because of the driver located in close proximity of the powertrain. Since the driver is installed on the motor unit via bus bars that are electrically welded, the joints of the driver and the bus bar become susceptible to vibration.
2017-03-28
Technical Paper
2017-01-1240
Koki Matsushita
Demands for improving fuel economy and reducing carbon dioxide emmision in automobiles have been increasing rapidly. Since the ratio of alternator loss to entire loss of automobile is high, reducing the alternator loss is effective for fuel economy improvement. The alternator loss consists of three main losses; copper loss, iron loss and rectification loss. Above all, the ratio of rectification loss to the alternator loss, which is approximately 30%, is relatively high. DENSO has developed “MOS rectifier” to reduce the rectification loss. The MOS rectifier is a commutating device which has MOSFETs as rectifying devices instead of diodes. The MOS rectifier contributes to fuel economy improvement of automobiles by reducing rectification loss with low On-Resistance(Ron) MOSFET. Since the MOS rectifier is exposed to severe temperature environment from -40 °C to 120 °C, temperature stress on solder and Aluminium wire is large.
2017-03-28
Technical Paper
2017-01-0188
Yoichiro Higuchi, Hiroyuki Kobayashi, Zhiwei Shan, Mikiharu Kuwahara, Yoshiharu Endo, Yuha Nakajima
As vehicle emission regulations become increasingly rigorous, the automotive industry is accelerating the development of electrified vehicle platforms such as Battery Electric Vehicles (BEV) and Plug-in Hybrid Electric Vehicles (PHEV). Since the available waste heat from these vehicles is limited, additional heat sources such as electric heaters are needed for cabin heating operation. However, using electric heaters for winter heating may consume more than 50% of vehicle’s total energy usage which results in less available energy for driving and significant reduction of the driving range of electric vehicles. Use of a heat pump is a solution to improve EV driving range at cold ambient. However prior-art heat pump systems still need the assistance of electric heaters at very cold ambient conditions and for dehumidification operations, which increases system cost and reduces the benefits of heat pump systems.
2017-03-28
Technical Paper
2017-01-0480
Mingde Ding
For structural application, composite parts structure is much more affected by load cases than steel part structure. Engine room bracket of EV, which is structural part and is used to bear Motor Controller, Charger and so on, has different load cases for different EV. Three commonest load cases that are Case 1: bearing 65kg (without suspension part), Case 2: bearing 68kg(including 3.5kg suspension part) and Case 3: bearing 70.1kg (including 5.6kg suspension part). According to topology optimization, structurel 1 was obtained, and then CAE analysis including (strength, stiffness and model) was carried out for abovement three load cases. For Case 1 and Case 2, the analysis result can meet the requirement. However, for Case 3, the stiffness and model analysis result can not satisfy the requirement. To meet the analysis result of Case 3, Structure 1 was optimized and structure 2 was obtained. The CAE analysis was conducted and the results can satisfy the requirements.
2017-03-28
Journal Article
2017-01-0484
Harchetan Singh Aneja, Harmeet Singh, Aashish Parmar, Rohan Sharma
The automotive industry, known for its competitiveness & innovations globally, researches for continuous improvement of part performances along with reduction of cost & weight. These are amongst the top priority goals across all OEMs. In the long list of automobile parts, pipe clamps have paved their way of design through generations from being of metal to plastic that has expanded its scope of application & performance. In an automobile, plastic clamps are widely used to hold single or multiple water, fuel or brake pipes of various diameters to vehicle body at various locations such as underbody (prone to stone chipping) or engine room (prone to high temperatures), etc. Plastic clamps are preferred over metallic clamps for their cost, weight, performance & productivity. Primarily, in all application areas, a clamp must be able to hold the pipes with consistent & sufficient performance that is quantified through parameters such as thrust force and pipe removal force.
2017-03-28
Technical Paper
2017-01-0416
Vishal Barde, Baskar Anthonysamy, Ganeshan Reddy, Senthil S, Visweswara lenka, Gurdeep Singh Pahwa
Abstract New trend in steering system such as EPS is coming up, but still hydraulic power steering system is more prevalent in today’s vehicles. Power steering pump is a vital component of hydraulic power steering system. Failure of steering pump can lead to loss of power assistance. Prediction of hub load on pump shaft is an important design input for pump manufacturer. Higher hub loads than the actual designed load of pump bearing may lead to seizure of pump. Pump manufacturer has safe limits for hub load. Simulations can assist for optimization of belt layout and placement of accessories to reduce the hub load. Lower hub load can have direct effect on improvement of pump durability. This paper deals with dynamic simulation of belt drive system in MSC.ADAMS as well as vehicle level measurement of hub load on power steering pump.
2017-03-28
Technical Paper
2017-01-0893
Marek Tatur, Kiran Govindswamy, Dean Tomazic
Abstract Demanding CO2 and fuel economy regulations are continuing to pressure the automotive industry into considering innovative powertrain and vehicle-level solutions. Powertrain engineers continue to minimize engine internal friction and transmission parasitic losses with the aim of reducing overall vehicle fuel consumption. Strip friction methods are used to determine and isolate components in engines and transmissions with the highest contribution to friction losses. However, there is relatively little focus on friction optimization of Front-End-Accessory-Drive (FEAD) components such as alternators and Air Conditioning (AC) compressors. This paper expands on the work performed by other researchers’ specifically targeting in-depth understanding of system design and operating strategy.
2017-03-28
Technical Paper
2017-01-1080
Yanan Wei, Shuai Yang, Xiuyong Shi, Jiaqi Li, Xuewen Lu
Abstract This paper aimed at a gasoline engine "cylinder head- cylinder gasket-cylinder body-bolt" sealing system, built the 3D solid model and the finite element model of the assembly, and calculated the stress and strain of the cylinder gasket under the cylinder pressure and the deformation of the engine block. In addition, based on the calculation results, this paper put forward the optimization scheme of the cylinder gasket structure, re-established the simulation model, and get the calculation results. The calculation results showed that the cylinder pressure had influence on the sealing performance of the cylinder gasket, and the influence of cylinder pressure should be taken into consideration when designing the cylinder gasket. When the cylinder pressure was applied, the overall contact stress of the cylinder gasket had decreased, and the whole remaining height of the gasket had increased.
2017-03-28
Technical Paper
2017-01-0445
Muthukumar Arunachalam, Arunkumar S, PraveenKumar Sampath, Abdul Haiyum, Yash Khakhar
In recent years, there is increasing demand for every CAE engineer on their confidence level of the virtual simulation results due to the upfront robust design requirement during early stage of an automotive product development. Apart from vehicle feel factor NVH characteristics, there are certain vibration target requirements at system or component level which need to be addressed during design stage itself in order to achieve the desired functioning during vehicle operating conditions. Vehicle passive safety system is one of which primarily consists of acceleration sensors, control module and air-bag deployment system. As the sensors act as the front-end of passive safety system and control module’s decision is based on these sensors signals, its mounting locations should meet the sufficient inertance or dynamic stiffness performance in order to avoid distortion in signals due to its structural resonances.
2017-03-28
Technical Paper
2017-01-0446
Xiao Chuan Xu, Xiuyong Shi, Jimin Ni, Jiaqi Li, Xiaochuan Xu Sr.
Abstract Oil pump is a critical part of engine lubrication system. The performance and efficiency of oil pump are greatly affected by vibration and noise, which would lead to the pump service life decreasing and pump body easily wearing. Hence the vibration and noise of oil pump is of great importance to study. In this paper, a FEA model of the variable displacement oil pump(VDOP) was established to carry on the modal and noise analysis, while the geometric structure was optimized with test verification. The modal analysis of VDOP was carried out by ABAQUS software, the 3-D unsteady flow field in VDOP was simulated by Pumplinx software, and the sound field was analyzed by ACTRAN acoustic module. Using a special oil pump test bench combined with B&K PULSE vibration and noise test equipment, the NVH and comprehensive performance experiment of the VDOP were carried out here.
2017-03-28
Technical Paper
2017-01-0460
Erina Yasuda, Hiroki Kobayakawa, Seiji Amano, Yuto Otsuki, Tomohiro Ukai
Abstract The number of vehicles with engines using idling stop systems and hybrid systems to improve fuel consumption has recently been increasing. However, with such systems the frequent starts and stops of the engine, where the oil film between the bearings and shaft is squeezed out and direct contact between the components is more likely, can result in increased wear of the engine bearings, particularly in the main bearing. Bearings with resin overlays have been shown to display superior resistance to wear from such start-stop cycles. Moreover, cast iron shafts without quenching treatment have also been used in engines for cost reduction. Because the cast shaft has low hardness and unstable surface graphite after abrasive finishing, increase in the wear amount cannot be suppressed by conventional resin overlay in comparison with steel shaft. Therefore, the resin overlay with improved wear resistance achieved by adding hard particles was developed.
2017-03-28
Technical Paper
2017-01-1066
Christoph Beerens, Alexander Mueller, Kimm Karrip
Abstract As emissions regulations and carbon footprint are more and more demandingly controlled, thermal efficiency of engine components must be optimized. Valve group components have to allow for ever increasing temperatures, endure aggressive condensates or even contribute directly to rising efficiency and emissions demands. Even with integrated and cooled exhaust manifolds, the exhaust valves are meeting full combustion temperatures, especially for stoichiometric combustion. MAHLE has developed a new technology in order to measure valve temperatures in real time, i.e. Transient Valve Temperature Measurement (TVTM). This is a complex methodology using thermocouples installed inside of the valves, offering the possibility to run the engine at different conditions, without any functional changes in the valve train system at all. Specifically valve rotation is not affected and thus temperatures all around the valve seat can be captured during rotation.
2017-03-28
Technical Paper
2017-01-1333
Sasikumar P, C. Sujatha, Chinnaraj K.
Abstract In commercial vehicles, exhaust system is normally mounted on frame side members (FSM) using hanger brackets. These exhaust system hanger brackets are tested either as part of full vehicle durability testing or as a subsystem in a rig testing. During initial phases of product development cycle, the hanger brackets are validated for their durability in rig level testing using time domain signals acquired from mule vehicle. These signals are then used in uni-axial, bi-axial or tri-axial rig facilities based on their severity and the availability of test rigs. This paper depicts the simulation method employed to replicate the bi-directional rig testing through modal transient analysis. Finite Element Method (FEM) is applied for numerical analysis of exhaust system assembly using MSC/Nastran software with the inclusion of rubber isolator modeling, meshing guidelines etc. Finite Element Analysis (FEA) results are in good agreement with rig level test results.
2017-03-28
Technical Paper
2017-01-1331
Marko Basic, Thomas Resch
Abstract This paper describes a numerical study of the effect of hollow crankshafts on crankshaft local strength and durability as well as slider bearing contact behavior. Crankshaft dynamic simulation for durability is still a challenging task, although numerical methods are already worldwide established and integrated part of nearly every standard engine development process. Such standard methods are based on flexible multi-body dynamic simulation, combined with Finite Element analysis and multi-axial fatigue evaluation. They use different levels of simplification and consider the most influencing phenomena relevant for durability. Lightweight design and downsizing require more and more detailed methods due to higher deformation of the crankshaft. This is especially true for hollow shafts, as present in motorsport design or aerospace applications, but also for standard engine having high potential for significant weight savings.
2017-03-28
Journal Article
2017-01-1124
Enrico Galvagno, Pablo Gutierrez, Mauro Velardocchia, Alessandro Vigliani
Abstract This paper investigates the effect of the powertrain mounting system on the linear and nonlinear torsional dynamical behaviour of a transmission system. To this aim, two dynamic models, one with rigid mounts and the other with flexible mounts, are presented and compared: the first model considers only the torsional dynamics of transmission and driveline, while the second model includes also a 3 degrees-of-freedom powertrain block. The mechanical coupling and interaction between the powertrain block and transmission system is discussed and formulated. These models are then analyzed in terms of vibrational mode shapes, natural frequencies and Frequency Response Functions (FRFs); a sensitivity analysis of the main transmission parameters, e.g. the gear ratio, is also presented.
2017-03-28
Technical Paper
2017-01-1122
Yashodhan V. Joshi
Vehicle noise has reduced over the years due to the customer demand for quieter vehicles. As engines have become quieter by efforts to reduce the combustion noise, as well as, by moving away from mechanical fuel pumps to common rail fuel pumps, the geartrain noise has come under increased scrutiny. Gear whine could be a result of multiple factors, and gear profile distortion is one of those factors. ISO 10064 provides guidance on the distortion due to temperature effects, but does not describe other influences in detail. There is not much published literature about gear whine due to profile distortion. The work attempts to fill that gap by describing a gear whine problem due to profile distortion and load change and it’s resolution by changing the gear design.
2017-03-28
Technical Paper
2017-01-1147
Hyunjun Kim, Jingeon Kang, Dongsuk Kum
Abstract Input- and output-split hybrids using a single planetary gear (PG) can provide high fuel economy, but they tend to suffer from low acceleration performance. In order to improve their acceleration performance, speed reduction (multiplication) gears (SRG/SMG) have often been employed in various mass-produced split hybrids. In fact, adding one SRG (SMG) to input- or output-split hybrids can improve not only the acceleration performance, but also the fuel economy. Nevertheless, the full potentials of using SRGs (SMGs) have not yet been thoroughly investigated because the design space of input- and output-split configurations using one SRG (SMG) is huge; 432 configurations can be generated using two PGs where one PG is used as an SRG/SMG. Thus, in order to investigate the impacts of SRG (SMG) within a reasonable time, an efficient analysis procedure is required.
2017-03-28
Technical Paper
2017-01-0684
Vickey B. Kalaskar, Raphael Gukelberger, Bradley Denton, Thomas Briggs
Dedicated Exhaust Gas Recirculation (D-EGR) has shown a lot of promise in multi-cylinder engines . In this study a 4-cylinder turbocharged GDI engine was modified to a D-EGR configuration. The aim of the study was to understand the effects of valve phasing and different injection strategies on the reformate production in the dedicated cylinder, and the engine performance. This engine with positive valve overlap capability gave the best platform to study reformate from the dedicated cylinder at various valve phasing and fuel injection strategies with provisions for individual cylinder control for both PFI and DI injection systems. Three speed-load combinations were studied, 2000 rpm 4 bar IMEPg, 2000 rpm 12 bar IMEPg, and 4000 rpm 12 bar IMEPg. This paper can be divided into 2 parts.
2017-03-28
Technical Paper
2017-01-0840
Carlo Beatrice, Marianna Migliaccio, Alessandro Montanaro, Valentina Fraioli, Pierpaolo Napolitano, Luigi Allocca
In the aim of reducing CO2 emissions and fuel consumption, the improvement of the diesel engine performance is based on the optimization of the whole combustion system efficiency. The focus of new technological solutions is devoted to the optimization of thermodynamic efficiency specially in terms of reduction of losses of heat exchange. Swirl supported combustion system employed in diesel engines configurations does not help reducing heat transfer and in principle a quiescent combustion system could reduce the wall heat transfer through the piston, bowl and liner walls. However, the hypothesis of reducing heat transfer losses via the reduction of swirl motion could be theoretically considered only leaving the well assessed multi-hole injector configuration that needs swirl motion for an appropriate spray atomization level. Only appropriate solutions for nozzle configurations, intrinsically capable of high spray atomization level, could be coupled with quiescent combustion systems.
Viewing 1 to 30 of 21620

Filter

Subtopics