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Assignment on Vehicle Vibration Analysis

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Added on  2020-04-21

Assignment on Vehicle Vibration Analysis

   Added on 2020-04-21

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SOLUTIONS TO THE QUESTIONS QN 1) Vehicle Vibration Vehicle vibration is normally caused by the ground interaction with road roughness, force dynamics, unbalanced wheels, and/or engine problems. Vehicle vibration has become a critical design issue that Mechanical Engineers in the Auto-industry are increasingly undertaking research to succinctly uncover the phenomenon. However, firstly, we define the following terms: Modes- or simply stated as mode of vibration refers to the finite ways in which vibration in a body can occur. Each way of vibration will have a distinct frequency range and amplitude. Complex objects can pose great difficulty in accurately determining the characteristics of the vibration modes. However, in vibration analysis, there are techniques that can be used to infinitesimally link the theory to the actual performance (in terms of vibration). Eigen values-These are special sets of scalars that are normally linked with a system of linear equations. To demonstrate this, Wolfram (2017) gives the following mathematical definition: Firstly, let A be a linear transformation represented by a matrix A’ such that: Ax’= λx’...(i) Where λ is the eigen value and x’ is the eigen vectorEigen vectors and values are significant in the analysis of mechanical vibrations where the solutions obtained are used to represent the state space of the system, a process known as matrix diagonalization (Wolfram, 2017)Eigen vectors- This is a paired correspondence of the eigen values hence the eigen vectors are often accompanied by the eigen values as shown in equation (i)Now, we get back to Vehicle vibration. Notably, vehicle vibration can never be covered without an in-depth look at the major causes of this phenomenon hence the following are the major causes of vehicle vibration (as mentioned earlier): (i)Engine Problems The engine normally has reciprocating and rotating components. Due to unbalanced forces, motion of these components can sometimes be a major cause of engine vibrations. Although designers have integrated some mechanical means to restrict the degrees of freedom, failures in engine firing and reciprocating parts unbalances are often combined to produce a complex source of vibration which varies with engine operating conditions. Additionally, the transmission shaft and crank shaft normally have mountings on them such as couplings. The centre of gravity of these shafts lies
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somewhere in the middle such that during rotational movements, the shafts would experience centrifugal force. If these forces are not balanced, then the shafts would begin wobbling and further increasing the engine vibration. (ii)Road surface roughnessThe roughness of road surface is another contributor to vehicle vibrations. As the car moves along, the tires interact with the surface such that up and downward motion occur in a repetitive fashion. Although the suspension springs are designed to absorb these vibration shocks, a poorly designed suspension would allow transmission to the passenger couches hence causing greater discomfort. To overcome this, the predisposing surface conditions are normally taken into account so that we end up with vehicles that can actually surmount the rugged terrain with just a little amount ofdiscomfort at play. (iii)Force dynamicsA balanced state of force systems in the car is one way of ensuring that car vibration is brought under control. The car suspension system and the chassis design would come in handy in this case. However, should this not be done properly then force balance in the car could be far-fetched. As a result of this, the test engineers must always perform rigorous tests to check on the car mechanics both in motion and stationary state. (iv)Unbalanced wheelsUnbalanced wheels normally cause uneven rotation of the wheels so that a rotation of all the wheels is not synchronized. This may result into serious problems such as loosening of bolts and nuts. Therefore, if this is unchecked then it can lead to fatal injuries especially when car is moving at high speed. In conclusion, vehicle vibration need not be trivialized as it has proven detrimental to the health of the passengers. It can lead to driver fatigue as prolonged exposure causes the muscles to be less responsive hence characteristically drowsiness would often set in. It can also make the occupant safety to be at stake as vibration is likely tocause accidental disassembly of bolted components such as the wheel and axle. Unfortunately, during high speed drives, the probability of fatal injuries due to prolonged vibration would be higher. However, as mentioned earlier, engineers have come up with sophisticated tools and methodologies to detect and measure the levels of vibration in the car body. According to Popović & Matijević (2016) one of these critical whole-body vibration tests is the bump test. This test can be envisaged as one in which a hummer hits an object and the whole object vibrates. The resulting frequency is measured and cross checked to ascertain that it is within the
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safe range. A series of bump tests are done and in the process the resonance frequency can be measured. However, engine vibrations can be minimized incorporating viscoelastic materials with a higher damping factor. Notably, mechanical system models have been designed to aid in understanding how engine vibrations occur so that reduction techniques can be integrated in the design. For instance, as argued by Deulgaonkar, Kallurkar & Mattani (2016), constrained layer damping has successfully been applied in the engine design to limit the excessive vibrations. Additionally, tuned viscoelastic damping seems to register more positive results than the constrained layer damping. Furthermore, there has been advancement in analytical tools; which are normally applied to derive an ideal vibratory system. The resulting models are then used to uncover the performance characteristics of the said system. Admittedly, Design Engineers would often rely on these scientific findings and sometimes even form part of the teams to explore these phenomena so that in the next design phase, a more superior product would result. Transfer Path Analysis is among the analytical techniques that are often applied in these vibration scenarios (Popović & Matijević , 2016) . The method would enable identification of the paths relative to the total vibration produced by the whole body. In fact, its functionality can be extended to include analysis of engine noise, vibration and harshness (NVH). It enables tracing of the vibrations rightfrom its source (perhaps the engine) down to the transmission (the gears and gearbox) and finallyto the passenger seat. These are then summed up by picking on the individual forces and vibrations. Therefore, this would allow complex vibratory systems to be modeled and analyzed easily. However, there are limitations with the method as it cannot exhaustively identify all the vibration hotspots and singularize them; it is practically impossible to do this with the technique. In conclusion, therefore, vehicle vibration still presents an interesting arena for research engineers and scientists do explore further. But what is encouraging is that their efforts are causing further advancement in the vehicle vibration control technologies. QN 2) Passenger comfort and ride quality Passenger comfort and ride quality are often two critical parameters that enhances acceptance from customers and ultimately lead to repeat purchases on the side of the buyers (Shirahatt, A,Prasad, P & Panzade, P. (2 008). The entire design of the vehicle greatly determines the performance levels of these two factors. Many a research engineers have attempted to study different vehicle models with the aim of establishing the degree of comfort and ride quality in those automobiles. This section will focus on such design factors that can affect the comfort and ride quality of the vehicle. Notably, central to this is the engine design. In the engine, where masses spin, rotate and reciprocate at menacingly higher speeds, coupled with out-of-balance mechanisms, it is inevitable for the car to remain smooth in motion. However, inasmuch as engineers do attempt to deaden the engine vibration, passengers are still likely to be affected by discomfort arising from the engine motion. However, there are
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