Monthly Archives: May 2017

Flight Dynamics

Flight dynamics is the study of the performance, stability, and control of vehicles flying through the air or in outer space. It is concerned with how forces acting on the vehicle influence its speed and attitude with respect to time. In fixed-wing aircraft, the changing orientation of the vehicle with respect to the local air flow is represented by two critical parameters, angle of attack (“alpha”) and angle of sideslip (“beta”). These angles describe the vector direction of airspeed, important because they are the principal source of modulations in the aerodynamic forces and moments applied to the aircraft.

Spacecraft flight dynamics involve three forces: propulsive (rocket engine), gravitational, and lift and drag (when traveling through the earth’s or any other atmosphere). Because aerodynamic forces involved with spacecraft flight are very small, this leaves gravity as the dominant force. Aircraft and spacecraft share a critical interest in their orientation with respect to the earth horizon and heading, and this is represented by another set of angles, “yaw”, “pitch”, and “roll”, which angles match their colloquial meaning, but also have formal definition as an Euler sequence. These angles are the product of the rotational equations of motion, where orientation responds to torque, just as the velocity of a vehicle responds to forces. For all flight vehicles, these two sets of dynamics, rotational and translational, operate simultaneously and in a coupled fashion to evolve the vehicle’s state (orientation and velocity) trajectory.

Three right-handed, Cartesian coordinate systems see frequent use in flight dynamics. The first coordinate system has an origin fixed in the reference frame of the Earth:

  • Earth frame
    • Origin – arbitrary, fixed relative to the surface of the Earth
    • xE axis – positive in the direction of north
    • yE axis – positive in the direction of east
    • zE axis – positive towards the center of the Earth

In many flight dynamics applications, the Earth frame is assumed to be inertial with a flat xE,yE-plane, though the Earth frame can also be considered a spherical coordinate systemwith origin at the center of the Earth.

The other two reference frames are body-fixed, with origins moving along with the aircraft, typically at the center of gravity. For an aircraft that is symmetric from right-to-left, the frames can be defined as:

  • Body frame
    • Origin – airplane center of gravity
    • xb axis – positive out the nose of the aircraft in the plane of symmetry of the aircraft
    • zb axis – perpendicular to the xb axis, in the plane of symmetry of the aircraft, positive below the aircraft
    • yb axis – perpendicular to the xb,zb-plane, positive determined by the right-hand rule (generally, positive out the right wing)
  • Wind frame
    • Origin – airplane center of gravity
    • xw axis – positive in the direction of the velocity vector of the aircraft relative to the air
    • zw axis – perpendicular to the xw axis, in the plane of symmetry of the aircraft, positive below the aircraft
    • yw axis – perpendicular to the xw,zw-plane, positive determined by the right hand rule (generally, positive to the right)

Asymmetric aircraft have analogous body-fixed frames, but different conventions must be used to choose the precise directions of the x and z axes.

The Earth frame is a convenient frame to express aircraft translational and rotational kinematics. The Earth frame is also useful in that, under certain assumptions, it can be approximated as inertial. Additionally, one force acting on the aircraft, weight, is fixed in the +zE direction.

The body frame is often of interest because the origin and the axes remain fixed relative to the aircraft. This means that the relative orientation of the Earth and body frames describes the aircraft attitude. Also, the direction of the force of thrust is generally fixed in the body frame, though some aircraft can vary this direction, for example by thrust vectoring.

Analysis of Disc Brake Rotors

disc brake is a type of brake that uses calipers to squeeze pairs of pads against a rotor in order to create friction that retards the rotation of a shaft, such as a vehicle axle, either to reduce its rotational speed or to hold it stationary. The energy of motion is converted into waste heat which must be dispersed. Hydraulic disc brakes are the most commonly used form of brake for motor vehicles but the principles of a disc brake are applicable to almost any rotating shaft. Compared to drum brakes, disc brakes offer better stopping performance because the disc is more readily cooled. As a consequence discs are less prone to the brake fade caused when brake components overheat. Disc brakes also recover more quickly from immersion. Most drum brake designs have at least one leading shoe, which gives a servo-effect. By contrast, a disc brake has no self-servo effect and its braking force is always proportional to the pressure placed on the brake pad by the braking system via any brake servo, braking pedal, or lever. This tends to give the driver better “feel” and helps to avoid impending lockup. Drums are also prone to “bell mouthing” and trap worn lining material within the assembly, both causes of various braking problems.

The rotor is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon–carbon or ceramic matrix composites. Brakes are mechanical or sometimes electrical devices or components that help to decelerate the vehicle and eventually stop the vehicle in a certain time and certain distance called the stopping distance or the braking distance. The automotive brake is basically a mechanical device which inhibits motion, slowing or stopping a moving object, here, the automobile, and thereby preventing its motion. Brakes are one of the most significant safety systems in any automobile. Functioning of brakes is based on the conservation of energy. Most commonly used brakes are frictional brakes, where the friction produced between two objects convert the kinetic energy of the moving vehicle into heat energy.

Theory of brakes

Frictional brakes: Friction brakes are the most commonly employed braking system in commercial or special purpose vehicles. They generally are rotating devices with a rotating wear surface like Disc or drum and a stationary pad or a shoe. Here, the kinetic energy of the moving vehicle is utilized to stop the vehicle by conversion of this kinetic energy into heat energy/frictional energy. A few common configurations of this type of braking are disc brakes, drum brakes and hydrodynamic brakes.

Disc brakes: Shoes or pads contract and provide compressive frictional force on the outer surface of a rotating Disc. It is a circular metal Disc on which the pads are mounted. Usually it is made up of cast iron material. The design of Disc brakes is varied depending on the application, amount of exposure, thermal properties of the material and the amount of heat dissipation required when brakes are applied and the total mass to be stopped.

This project report will contain the design of a Disc brake rotor, and analyze results of Structural and Thermal Analysis at a later stage.

Drum brakes: Shoes or lining expand and rub against the inside surface of a rotating drum. Drum is again made up of cast iron material and mounted in the wheel hub in such a manner that the liner pads attach themselves to the inner surface of the drum and during the braking process, the shoe or brake lining expand or move outwards, due to the cam and spring action, to attach themselves to the brake drum which provides friction and causes the drum to retard or stop its rotating motion. Drums are usually heavier than Disc brakes and occupy significantly more space due the lining and drum it and hence its application in commercial vehicles is somewhat restricted.

The purpose of this research is to analyze different types of disc brake rotors, which are commonly used in automobile industry and to propose a new design of brake rotor. Analysis of brake rotor includes Structural analysis and Steady state Thermal analysis for each design. A comparison between the existing brake rotors and proposed new design is carried out and based on the results the best design is found out by ANSYS software.

Manufacturing System

A flexible manufacturing system (FMS) is a manufacturing system in which there is some amount of flexibility that allows the system to react in case of changes, whether predicted or unpredicted. This flexibility is generally considered to fall into two categories, which both contain numerous subcategories. The first category, machine flexibility, covers the system’s ability to be changed to produce new product types, and ability to change the order of operations executed on a part. The second category is called routing flexibility, which consists of the ability to use multiple machines to perform the same operation on a part, as well as the system’s ability to absorb large-scale changes, such as in volume, capacity, or capability.

Most FMS consist of three main systems. The work machines which are often automated CNC machines are connected by a material handling system to optimize parts flow and the central control computer which controls material movements and machine flow. The main advantages of an FMS is its high flexibility in managing manufacturing resources like time and effort in order to manufacture a new product. The best application of an FMS is found in the production of small sets of products like those from a mass production.

An Industrial Flexible Manufacturing System (FMS) consists of robots, Computer-controlled Machines, Numerical controlled machines (CNC), instrumentation devices, computers, sensors, and other stand alone systems such as inspection machines. The use of robots in the production segment of manufacturing industries promises a variety of benefits ranging from high utilization to high volume of productivity. Each Robotic cell or node will be located along a material handling system such as a conveyor or automatic guided vehicle. The production of each part or work-piece will require a different combination of manufacturing nodes. The movement of parts from one node to another is done through the material handling system. At the end of part processing, the finished parts will be routed to an automatic inspection node, and subsequently unloaded from the Flexible Manufacturing System.

The FMS data traffic consists of large files and short messages, and mostly come from nodes, devices and instruments. The message size ranges between a few bytes to several hundreds of bytes. Executive software and other data, for example, are files with a large size, while messages for machining data, instrument to instrument communications, status monitoring, and data reporting are transmitted in small size. There is also some variation on response time. Large program files from a main computer usually take about 60 seconds to be down loaded into each instrument or node at the beginning of FMS operation. Messages for instrument data need to be sent in a periodic time with deterministic time delay. Other types of messages used for emergency reporting are quite short in size and must be transmitted and received with an almost instantaneous response. The demands for reliable FMS protocol that support all the FMS data characteristics are now urgent. The existing IEEE standard protocols do not fully satisfy the real time communication requirements in this environment. The delay of CSMA/CD is unbounded as the number of nodes increases due to the message collisions. Token Bus has a deterministic message delay, but it does not support prioritized access scheme which is needed in FMS communications. Token Ring provides prioritized access and has a low message delay, however, its data transmission is unreliable. A single node failure which may occur quite often in FMS causes transmission errors of passing message in that node. In addition, the topology of Token Ring results in high wiring installation and cost.

A design of FMS communication that supports a real time communication with bounded message delay and reacts promptly to any emergency signal is needed. Because of machine failure and malfunction due to heat, dust, and electromagnetic interference is common, a prioritized mechanism and immediate transmission of emergency messages are needed so that a suitable recovery procedure can be applied. A modification of standard Token Bus to implement a prioritized access scheme was proposed to allow transmission of short and periodic messages with a low delay compared to the one for long messages.

Manufacturing System can be defined as the process involved in the production of merchandise using machines, tools, labour which may be intended for use or sale. It is the method of organizing production.
Manufacturing takes turns under all types of economic systems. In a free market economy, manufacturing is usually directed toward the mass production of products for sale to consumers at a profit. In a collectivist economy, manufacturing is more frequently directed by the state to supply a centrally planned economy. In mixed market economies, manufacturing occurs under some degree of government regulation.

Related Journals of Manufacturing System:
Journal of Material Sciences & Engineering, Advances in Automobile Engineering, Journal of Aeronautics & Aerospace Engineering, Journal of Applied Mechanical Engineering, Journal of Manufacturing Processes, Manufacturing Letters, Journal of Manufacturing Systems, Journal of Advanced Manufacturing Systems, International Journal of Mechatronics and Manufacturing Systems

High Performance EMC

C P Wong is the Charles Smithgall Institute Endowed Chair and Regents’ Professor at Georgia Institute of Technology, and Dean of Engineering at the Chinese University of Hong Kong. He received his primary and secondary education in Hong Kong and furthered his education in the US. He received his BS degree from Purdue University, and PhD degree from the Pennsylvania State University. He received many awards, among those, the AT&T Bell Labs Fellow Award in 1992, the IEEE CPMT Society Outstanding Sustained Technical Contributions Award in 1995, the Georgia Tech Sigma Xi Faculty Best Research Paper Award in 1999, Best MS, PhD and Undergraduate Thesis Awards in 2002 and 2004, respectively, the University Press (London) Award of Excellence, the IEEE Third Millennium Medal in 2000. His research interests lie in the fields of polymeric materials, electronic packaging and interconnect, interfacial adhesions, nano-functional material syntheses, Si etching and energy storage. His work includes nano-composites such as well-aligned carbon nanotubes, graphenes, lead-free alloys, flip chip underfill, ultra high k capacitor composites superhydrophobic coatings and supercapacitors. He holds over 65 US patents, numerous international patents, has published over 1000 technical papers, 12 books. He is a Member of the National Academy of Engineering of the USA since 2000, and a Foreign Academician of the Chinese Academy of Engineering 2013.

As the number of electronic components in automobiles increases, the electronic industry has seen an increasing need for organic packaging materials that meet property requirements for long cycling operations under harsh environments. Of the many materials involved in a package, epoxy-based molding compound (EMC) is the outermost encapsulation, and it is essential for the molding material to offer high temperature durability. Research has shown that the adverse effects of thermal aging on EMC can be attributed to temperature-induced shrinkage and oxidation. EMCs currently on the market use multiaromatic structure in the resin to add thermal stability to the cured composite, but still show undesirable changes in material properties at temperatures above ~175°C, where resin decompositions and loss of volatile species are observed. For improved thermal stability, it is desirable for EMCs to have high glass transition temperature. We enhance the resin crosslinking and thermal resistance by utilizing the superior heat resistance of the epoxy-triazine copolymer in the curing system. In this case, the highly aromatic epoxy matrix increases the EMC’s Tg, and the s-triazine moiety further enhances high temperature stability the EMC. In this talk, we will show preliminary results on the incorporation of s-triazine into EMC and the thermal stability improvements that results.

Automotive electronics are electronic systems used in road vehicles, such as: engine management, ignition, radio, carputers, telematics, in-car entertainment systems and others. Electronic systems have become an increasingly large component of the cost of an automobile, from only around 1% of its value in 1950 to around 30% in 2010. The earliest electronics systems available as factory installations were vacuum tube car radios, starting in the early 1930’s. The development of semiconductors after WWII greatly expanded the use of electronics in automobiles, with solid-state diodes making the automotive alternator the standard after about 1960, and the first transistorized ignition systems appearing about 1955.

The availability of microprocessors after about 1974 made another range of automotive applications economically feasible. In 1978 the Cadillac Seville introduced a “trip computer” based on a 6802 microprocessor. Electronically-controlled ignition and fuel injection systems allowed automotive designers to achieve vehicles meeting requirements for fuel economy and lower emissions, while still maintaining high levels of performance and convenience for drivers. Today’s automobiles contain a dozen or more processors, in functions such as engine management, transmission control, climate control,antilock braking, passive safety systems, navigation, and other functions. Modern electric cars rely on power electronics for the main propulsion motor control, as well as managing the battery system. Future autonomous cars will rely on powerful computer systems, an array of sensors, networking, and satellite navigation, all of which will require electronics.