It is evident that technology is soaring and changing and adapting to new ways. This brings out a need to ponder over and re-evaluate standards and methodology of engineering education in India.
Tackling multidisciplinary situations for engineers have become prevalent in every product line. Owing to remote diagnostics, to observability and controllability in real time, to control theory, sensors and actuators must all be well acquainted by a mechanical engineer. However, the inception point for any mechanical design is the holistic appreciation of physics and technological aspects of the components being designed that go to make a sub- assembly or a machine.
In this blog series on engineering-learning, we will discuss physics gaps between industry and academia and subsequently we will discuss the pedagogical ideas to bridge the gap.
In order to provide perfect clarity on what is being discussed, we pick up a specific discussion on vibration margin for a typical shaft. Now let us map learning in machine design to expectations:
The first question is what are the expectations for a design course?
The course must achieve the following capabilities:
- To Identify and idealise boundary conditions.
- To conceive loads and interaction with neighbouring components.
- To conceive unobvious strength and surface failures.
- To conceive failure of functionality and performance.
- To conceive scope for optimisation
What typical academia achieves?
Our detailed survey of various undergraduate design courses offered across the country; the following procedure is adopted to establish the vibration margin, making it too simplistic.
- Estimate the stiffness of the shaft assuming fixed-fixed or simple supports
- Assume the operating speed and keep the first flexural natural frequency above the operating speed by a certain percentage
- Assume the shaft to be massless
Breaking down the challenges in detail:
In real time design, the challenges are many-fold. Now considering only component design aspects, as system design aspects makes the discussion very complex, let us see the gaps between academic approach against practical design approach.
Let us break down the various aspects of design and appreciate each one of them in detail:
- Estimate the effective stiffness (a few factors)
- Stiffness is affected by temperature.
- Shear stress and rotary inertia effect.
- Stiffness of bearing support structure must be included.
- Bearing support structure may be symmetric or asymmetric.
- If the shaft system is maneuvered and kept in a machine (say a moving machine) then Coriolis and Gyro-effect either stiffens or softens the system
- Effect of pre-stress in the shaft
- Effective stiffness method for stepped shaft
- Disc effect (when the disc is significantly heavy)
- Stiffness asymmetry owing to design features (key slot etc)
- Estimate the effective inertia (a few factors)
- Accounting mass of the shaft
- Inertia of the system is different for different modes.
- Effect of principal inertia difference becomes important in case of shaft tilt.
- Physical damping if present must be accounted.
- Hysteretic damping from bearing support structure must be accounted.
- Bearing and type of support
- What bearing means what boundary condition?
- If two bearing are mounted in tandem, then what BC to be assumed?
- Other aspects
- Should we look at torsional vibrations-margin.
- What factors during operation could reduce resonance margin?
- How to evaluate HCF, if there is a dwelling resonance?
- If there is bearing wear, does it significantly reduce the natural frequency, how do you condition monitor it.
- Do we need a Campbell plot to look at margins for many possible modes?
- May the shaft rub while vibrating in bell mode? Is the running clearance, ok?
- Where could I remove mass to minimise weight keeping the vibration margin?
- How do you define balancing standards?
And the list goes on….
To appreciate all the above aspects, no advanced physics is required. It is just the ability to generalise and think critically from a typical aero/auto product perspective. Hence classroom design is characterised by too many assumptions, but real-time design eliminates all assumptions and physical conditions are accounted for.
A young engineer need not appreciate every facet of design in detail, but he or she needs to be sensitised and must have basic physics-awareness so that the right question is asked to the right industry expert to exploit their engineering data and literature.
At INNOVENT engineering solutions, we sensitise the young engineers and learners about these facets and quantify most of them without a mathematical burdening, using various pedagogical approaches and rigorous real-life like animations. Let us discuss the same in detail in our next blog episode of the same series.
Preparing thinkers for tomorrow!