Mechanical Engineering Report: Bearing Design and Monitoring System

This report provides a comprehensive analysis of bearing design and a monitoring system for a sustainable wave energy converter. The report begins with an introduction to sustainable energy generation and the application of wave energy converters. It then delves into the specifics of bearing design, including the calculation of forces, torques, and bearing pressure, and selection of appropriate materials such as stainless steel for its corrosion resistance and structural integrity. The report also details the design of a monitoring system that utilizes temperature and flow sensors to regulate bearing conditions, ensuring optimal performance and longevity. The monitoring system incorporates a feedback loop with components such as thermistors and potentiometers to control temperature and oil levels, respectively, and includes an alarm system to alert of any potential issues. The report concludes with references to relevant literature and resources.

Design and Operation of Sustainable Systems
Prepared By:
Dated:
1. INTRODUCTION
Increased research in sustainable energy generation has led companies to
adopt more innovative strategies to harness various forms of power. Figure 1
shows wave energy converter with floaters as shown. This device is being
developed across the United Kingdom as one of the ways to boost power
availability in the country. In this report, design and selection of its bearing is
undertaken and a suitable monitoring system suggested. Notably, break water
selected is expected to produce a total of 100kW of power. Furthermore, it is
assumed that the average height of the waves is 0.4m pounding at intervals of
5 seconds. Therefore, the aim is to: design bearing that provides minimum
wear and easy maintenance. Additionally, an active monitoring system to
monitor bearing condition and prevent the bearing failure is to be suggested.
Figure 1: Floaters with wave energy converter

2. BEARING DESIGN AND SELECTION
2.1 The data given is as shown in the table 1:
Table 1: Design data
PARAMETER VALUE (Given ) Calculated Value
Area around floater 4m2 -
Arm length 3m -
Lever length 1.5m -
Wave height 0.4m -
Intervals between waves 5sec -
Force on piston 4000N -
Force applied by float 2000N -
Mass of system 250kg -
Wear on bearing Not more than 1mm 2.724x10-5mm
Electrical Power 1000kW 247.23kW
2.2 Bearing Design
Referring to the Gibrattar Project, the electrical power to be generated is 100kW
The system is composed of 8 floats, with uniform energy conversion capacity hence:
Each is to generate= 1000/8= 125kW
Assuming hydraulic and mechanical efficiencies of 79% and 64% respectively
Hence overall efficiency= ή0= ήmxήh = 0.79 x 0.64= 0.5056
Hydraulic power = Rated Electrical power/ ή0 = 125/0.5056= 247.23kW
Now, Weight on bearing is equivalent to sum of resultant force and weight of
components
Weight of components= Mg= 250x9.81= 2452.5N
The resultant force Fr= (F2h +F2v)0.5 = {(4000+2452.5)2 + 20002}0.5= 6 755.35N
Torque on bearing= Fv x L2= 6 755.35 x 1.5 = 10.133kN
Rocking speed= Wave height/time = 0.4/5= 0.08m/s
Since the float is assumed circular, the bearing diameter can be estimated:
Diameter of float D= {(4x 4)/π}0.5= 2.257m or 2257mm

Now, by size approximation, we can assume that the bearing is 20 times smaller
than the float diametrically
Hence Diameter of bearing is fixed at d = 2257/20 = 112.85mm
From table 26.3 (Khurmi and Gupta, 2005), the ratio l/d is selected, since it is
ranging from 0.2 to 2, I can use 1.47
L=1.47d
Hence length of journal bearing, l = 112.85x 1.47= 165.89mm
The bearing pressure is given by P= W/ld= 6 755.35/(165.89x 112.85)=
0.3609N/mm2
Referring to table 26.3 (Khurmi and Gupta, 2005), Maximum allowable bearing
pressure is 1.75N/mm2 hence this is a safe design
The angular speed, w= P/T= 247.23/10.133= 24.4rad/s
Or w= 2xπxN/60
hence N= 60x24.4/2x3.142= 233rpm
The maximum allowable specific wear rate can be determined:
Coefficient of friction for journal bearing is given as:
u = 33x10-8(ZN/P)(d/c)+k
The following can be deduced from table 26.3:
Z= 0.03, c/d= 0.001
And k= 0.002 since l/d is between 0.75 and 2.8
Hence substituting:
U = 33x10-8(0.03x233/0.3609)(0.001)-1+0.002= 0.00839144
Now, the wear volume V= 2/3πr3L/2r= 2/3 x3.142x(112.85/2)3x (165.89/2x 112.85)
= 0.000276m3
Specific wear rate= V/T= 0.000276/10.133x1000= 2.724x10-8m or 2.724x10-5mm
This much lower than the 1mm limit hence it is designed for easy maintenance
The frictional force Fu= uN
= 6 755.35x 0.00839144
= 56.687N

Linear velocity v= wr= 24.4 x 0.11285/2= 1.376m/s
Power loss Pl= Fux v= 1.376x 56.687= 78.045W
Now, the mechanical power Pm= 125/0.64= 195.3kW
Percent Loss in Power (assumed purely mechanical) = 78.045/195.3x1000= 0.04%
This is a negligible power loss hence the selected bearing will work efficiently
Notably, for the bearing material, stainless steel material is to be selected since it is
resistant to corrosion and have got great structural integrity. Besides, it is relatively
tough on the surface hence cracking is less likely over a span of 25 years. With
proper lubrication, the bearing would last a lifetime hence minimizing maintenance
and repair costs. The bearing caps must be properly selected to match with the
journal bearing characteristic.
3. BREAKWATER MONITORING SYSTEM
The block diagram in figure 2 illustrates how the system will work:
Power Source
LCD display
Comparator
Controller Element
-Temperature control
-Oil level control
Feedback loop
Filter
Noise
elimination
LED temp and oil
indicator
Alarm system for oil
level
Sensor signal
Thermistor
/Potentiometer

The system is configured such that there are two sensors: temperature and flow
sensors. The former regulates temperature by controlling the thermistor (actuating
mechanism) linked to the artificial cooling unit. In high temperatures above the
maximum design limit, the temperature sensor detects this change and sends a
signal to the thermistor for activation of the cooling unit hence bearing is cooled.
However, once low temperatures are stabilised, the sensor detects this change
again and the cooling unit is isolated automatically. Notably, this works in unison with
the flow sensor. Due to leakage, amount of lubricating oil is lost in the bearing with
time hence when oil level falls below minimum such that metal to metal contact is
just beginning, the flow sensor detects this change and cause the flow valve to open
and hydrodynamic condition is restored. As mentioned, these two sensor-actuating
mechanisms must work interdependently to ensure the system is regulated and the
bearing life is extended. Notably, for the temperature regulation, actuation is via
thermistor and for the oil level/thickness actuating mechanism is via potentiometer.
REFERENCE
Khurmi, R.S and Gupta, J.K. (2005). Machine Design. Eurasia, New Delhi. pp 996-
1020
Machinerylubrication.com. (2018). Journal Bearings and Their Lubrication. [online]
Available at: http://www.machinerylubrication.com/Read/779/journal-bearing-
lubrication [Accessed 19 Mar. 2018].
Patriot Technologies, Inc. (2018). Critical Infrastructure/Industrial Controls Security |
Patriot. [online] Available at: http://patriot-tech.com/solutions/industrial-control-
systems-security-monitoring/ [Accessed 19 Mar. 2018].