Structural Analysis of Laterally Aerated Moving Bed (LAMB) Dryer by using Robot Structural Analysis (RSA) Professional 2018

The structural design of Laterally Aerated Moving Bed (LAMB) dryer is subjected to buckling effects due to the loads of the paddy bed, self-weight and static pressures by the air blower to overcome the air resistance in the paddy bed, perforated tube and the bed chamber perforated wall. The dryer structural type is a spatial complex structure where the boundary conditions are not very clear, thus the Robot Structural Analysis (RSA) Professional 2018 is used to determine the critical values of loads when the overall structural elements instability occurred to form buckling. The RSA analysed the global buckling of a structure to find the critical coefficient value to be multiply with the case load for the critical buckling load determination. Three different model of dryer structural designs were prepared and analysed by RSA to find the buckling critical coefficient values (αcr), displacements (mm), reactions (N) and moments (Nm). All structural design model was designed with similar type of materials, different sizes and geometrical arrangements. The RSA results within the three structural design models were compared. The structural design model with the best buckling coefficient values with minimum displacement had been selected for the actual LAMB dryer structural construction.


Introduction
The Laterally Aerated Moving Bed (LAMB) dryer is a new design for paddy rice drying based on the bioreactor concept which have a vertical perforated tube to provide uniform air flow distribution. The principle of the system is to achieve drying uniformity by aerating the paddy bed laterally. The short air flow distance across the paddy bed produces lower aeration energy contributes to the smaller air flow pressure drops. It has many advantages against the existing industrial paddy rice dryers such as good drying uniformity, low labour intensive, less dust pollution, good heat and mass transfer ability which shorten the drying period (Nor Hidayah Kamin and Jidon Janaun 2017).
The structural analysis of the LAMB dryer structure is vital to ensure it has adequate strength to withstand the loads of paddy bed and pressure inside the dryer vessel. The bed chamber perforated wall and tube are the most crucial areas as there have direct contact with the paddy and pressure from the air blower. The structures are prone to instability due to the loads compression where it starts to ICME-EAM 2018 IOP Conf. Series: Materials Science and Engineering 606 (2019) 012016 IOP Publishing doi: 10.1088/1757-899X/606/1/012016 2 change shapes or deflection. Sudden deflection of the structures caused by the compressive load generates the critical stress commonly known as buckling phenomenon (Helbig D., et al. 2016). The structural analysis software such as the RSA is useful to determine the critical values of loads on complicated spatial structures where the boundary conditions are not clear. The structural analysis result obtained by the RSA software is less than 5% difference compared to the result obtained from the analytical way which is acceptable. The critical force, Ncr determined by the RSA is always on the safe way (Chen and Wierzbicki 2000).
The selection of materials for LAMB paddy dryer must considers the abrasiveness of the paddy rice husk. The paddy husk contains high silica that causes excessive wear to parts of processing machine (IRRI n.d.). The fabrication of column paddy dryer, galvanised steel was been used for the dryer construction (Olaniyan and Alabi 2014). The fixed bed dryer (Flatbed & Inclined bed dryers) perforated floor and frames were made of mild steel (Wimberly 1983). The plug-flow fluidised-bed paddy dryer was made of stainless steel and mild steel (Khanali et al. 2012). Thus, the materials selected for the LAMB paddy dryer are stainless steel 304 sheet ASTM A240 for the dryer vessel walls, square hollow steel (SHS) and rectangular hollow steel (RHS) ASTM A500 for the dryer structural frames to reduce the excessive wear problems.
The LAMB paddy dryer's capacity of 1000kg was selected for this study. Paddy rice drying analysis by the LAMB dryer was performed to determine the parameters needed for the loads analysis such as the heater power, air flow rate, static pressure and the mass of paddy. These load parameters were used in the RSA to determine the buckling critical coefficient values (αcr), displacements (mm), reactions (N) and moments (Nm).
The RSA is capable to identify any errors on the structural joints due to the nodes instability which is very helpful to detect any design faults of the particular structures. It could analyses the global buckling of a structure to find the critical coefficient values to be multiply with the case load for the critical buckling load determination. In EN1991 The LAMB dryer is consisted of two main structures namely the dryer vessel and support chute. In this research, the dryer structural designs were prepared in three different models and analysed by the RSA for comparison. All model was designed with similar type of materials with different sizes and geometrical arrangement to suit the fabrication and installation processes. The vessel structure design models are shown in the Figures 1, 2 and 3 while the support chute is shown in Figure 4. The RSA final results on buckling coefficient values were compared where the design model with the best buckling critical coefficient values was selected for the dryer structures construction. On the support chute structural design, it is confirmed the RSA results obtained in compliance with the Eurocode-3 buckling critical coefficient value, αcr ≥ 10 (elastic analysis) and αcr ≥ 15 (plastic analysis).
In conclusion, the Robot Structure Analysis (RSA) professional 2018 package is capable to analyse the buckling effects on LAMB dryer structural analysis.

Paddy drying analysis
This analysis is to determine paddy mass and internal pressure needed for the loads analysis. Given, the Inner pipe diameter, D1 = 0.64m, Paddy Bed diameter, D2 = 1.17m, Outer wall diameter, D0 = 1.97m, Dryer height, H = 3.00m, Dryer designed weight capacity, Wp = 1000kg, Bulk density of paddy = 495 kg.m 3 , Specification for the perforated sheer / wall: Perforate (Aperture), Diameter of one exit hole = 0.003m, Number of holes (Aperture) = 43.1 holes per inch 2 or 66805 holes per m 2 , Area of holes = 0.4722 m 2 holes per m 2 of sheet.

Paddy mass
The designed capacity of the LAMB dryer is 1000kg, thus the maximum mass of paddy for the load analysis is 1000kg. where, Mw = Mass of water (kg), Cp = Specific heat capacity of water (kJkgK -1 ) and ΔT = Temperature dried grain -Initial temperature of dryer ( o C).

Loads analysis
The loads on the dryer vessel frame were contributed by the vertical force due to the mass of paddy and the horizontal forces caused by the internal pressure of the vessel.

Vertical loads
The forces are determined by Newton's second law (F = mg), where m = mass (kg) and g = gravity acceleration (9.8 m/s 2 ). The vertical forces were caused by the load of the paddy mass from (1.1.).

Horizontal loads
Horizontal forces are determined by F = PA, where F = horizontal force (N), P = pressure (Pa or N/m 2 ) and A = surface area (m 2 ).

Horizontal load on the outer wall
The pressure at the outer wall is merely the residual pressure through the bed perforated wall.

Structural analysis
Three structural models were prepared for the LAMB dryer vessel and analysed by the RSA. The RSA results were then compared to select the best structural strength for the LAMB dryer structures construction. Given; the vertical load, Fz = 10kN and the horizontal loads; Fx0 = Fy0 = 0.01kN, Fx1 Fy1 = 4.40kN and Fx2 = Fy2 = 8.01kN (In the RSA, the horizontal loads shall be in x and y axis, the vertical loads shall be in z axis.).

Model Structure No. 1
The selected materials for model no.1 are RHS 50x25x2.5 and SHS 50x50x3 as shown in Figure 1.
The buckling analysis results on critical coefficient values for the Support Chute as shown in Table 4 are also found to be in compliance with the EN1991-1-8 (2005): Eurocode-3: Design of Steel  (Part 1-8) standard, the buckling critical coefficient values should be, αcr ≥ 10 (elastic analysis) and αcr ≥ 15 (plastic analysis).

Conclusion
The Robot Structural Analysis (RSA) Professional 2018 package is capable to perform structural analysis for the Laterally Aerated Moving Bed (LAMB) dryer.
The best structural model design for the LAMB dryer vessel is Model Structure No.3 as shown in Figure 3 and Table 3 to be used for the actual construction of the dryer vessel structure.
Further studies and experiments will be carried out upon completion of the LAMB dryer construction for processes validation, cost and performance optimisation, serviceability and sustainability.