A Numerical Study for Rice Using Distinct Element Method
Tomoyuki Miyamoto 1, So Noguchi 1, Shinya Matsutomo 2121

Graduate School of Information Science and Technology, Hokkaido University, Japan

Department of Electronic Control Engineering, Niihama National College of Technology, Japan

Introduction

In this paper, we discuss the fundamental simulation data ofa rice processing machine for optimum planning, effective
designing and cost-reduction. Rice variously and complicatedly
behaves in the processing machine because the amount of water,
the degree of adhesion, and the grain size are various anddepending on a breed in the rice, even if the rice grains have asame shape. The above affects the performance of the riceprocessing equipment. In this study, a numerical simulation iscarried out using three-dimensional Distinct Element Method(DEM) based on the measured angle of repose in each rice breedin order to highly accurately reproduce the behaviour of rice inthe processing equipment as an Optical Sorter.
2Distinct Element Method

The DEM is a numerical method used for computing
stresses and displacements in a volume containing a large
number of particles such as grains of sand [1]. Granular material
is modelled as an assembly of rigid particles and interaction
between each particle is explicitly considered (shown in Fig. 1).
Here, in the effects of normal and shear directions, Kn and Ks are
the elastic stiffness, ηn and ηs are the viscous damping and μ is
the friction slider. The particle shapes and geometries arespecified by a user. Sphere shape is commonly employed.

Ks
ηnKn

μηs

Table 1. Angle of Repose in Rice.
VarietyAngle of Repose

Long Grain Raw Rice

40-42 degree

Long Grain Parboiled Rice45-47 degree

3.2Subject Outline in Optical Sorter
Commonly, a rice processing equipment has an OpticalSorter. The Optical Sorter is the machine that sorts discoloredrice and foreign material like a stone and a glass by recognizingthem with a high-performance camera, and blows away theforeign particle with an ejector like an air-gun. Fig. 2 shows theschematic view of the optical sorter. There are three processes inthe equipment. First, the material is supplied with a chute.
Second, good particles or bad particles are recognized with thehigh-performance camera. Third, the bad particles are sortedwith the ejector. As technical advantages of the optical sorter it
is necessary to supply the material to sensing station withconstant speed and suitable density. Thereby, the influence ofskin friction for the chute surface is reduced. However, the chutestructure is very simple, therefore it is impossible to regulate theflow of material.
Especially, the flow of the Parboiled Rice is uneven andagglomerated on the chute. These behaviour causes todeteriorate the sorting performance (quality, amount ofthroughput, yield rate). The Raw Rice and the Parboiled Riceflowing on the chute are shown in Fig. 3, which were capturedby the camera of the Optical Sorter.

Effects of Normal Direction
Effects of Shear Direction
Fig. 1. Contact Model for DEM.

3

Material Hopper

Agenda Details

Characteristics of Rice
There are Long Grain, Middle Grain, and Short Grain in thekinds of rice. Moreover, they are classified into Non-glutinous
Rice and Glutinous Rice according to starchiness. What has thebest rice harvest in the world is the Long Grain Non-glutinous
Rice. The Long Grain is the rice that the length is more than 6.6mm and the aspect ratio (length/width) is less than 3.0. Raw
Rice and Parboiled Rice belongs to the Long Grain. The Raw
Rice is what has simply milled Paddy, and the Parboiled Rice iswhat has milled just as Paddy after steaming and drying the rice.
The character of the Raw Rice is much different from theParboiled Rice (shown in Table 1). Irrespective of same-shaped
rice, the Parboiled Rice has a higher angle of repose than theRaw Rice’s because the rice surface adhesion is high bysteaming process.

Chute3.1

FeederLamps

CamerasSignal Processor

Ejectors
Compressed AirRejects Accepts
Fig. 2. Schematic View of Optical Sorter.

Acknowledgements
We appreciate that SATAKE Corporation has suggested thesubject of this research and provided the valuable information ofthe rice.
Raw Rice

References
[1]

[2]

Parboiled RiceFig. 3. Captured Images by Optical Sorter.

4

Tej B. S. Pradhan, S. Sawada, Distinct element analysis of sandunder cyclic loading using oval elements, Proc. of 10th WCEE,
pp.1163-1168, 1992
Oleg D. Neikov, Stanislav S. Naboychenko, Gordon Dowson,
Handbook of Non-Ferrous Metal Powders: Technologies andApplications, Elsevier Science, USA, pp.39, 2009Verification Approach by Numerical Simulation

Simulation Models
Firstly, we carried out a virtual simulation of the angle ofrepose for the Raw Rice and the Parboiled Rice. The difference
between them is produced by the elastic stiffness, the viscousdamping, and the friction slider of the parameter in the DEM.
The simulation model is the Ledge Method in a measurement
method of the angle of repose (shown in Fig. 4). The material isinitially charged into a rectangular box. A slot at the base of one
vertical wall is closed by a board. The closure board is thenremoved to allow the material to flow slowly through a narrowslot. The angle of the horizontal plane of the surface of thematerial equilibrium is measured when the flow stops [2].
Secondly, we carried out a virtual simulation of the material
flowing on the chute of the Optical Sorter with these parameters.
These are compared with the actual behaviour of rice.

41°

4.1

Experimental

41°

Simulated
Raw Rice45°θθ : Angle of Repose
Fig. 4. Simulation Model for Angle of Repose.

Simulation Results
The angle of repose for the Raw Rice and the Parboiled Rice
was virtually simulated (shown in Fig. 5). We figured out thatthe angle of repose was particularly affected by the viscousdamping of the parameters in the DEM. In addition, the rice
flowing on the chute of the Optical Sorter was also virtuallysimulated by the DEM with the particles of spheres (shown inFig. 6).

Experimental

45°

4.2

5

Simulated
Parboiled RiceFig. 5. Simulation Results for Angle of Repose.

Conclusion

In this study, the numerical simulation was carried out using
the three-dimensional Distinct Element Method based on themeasured angle of repose in each rice breed in order to highly
accurately reproduce the behaviour of rice in the Optical Sorter.
We figured out that the DEM is effective in the development of
the Optical Sorter. In future prospects, the particle shape of theDEM will be extended from sphere to particle consisting ofsome sphere or ellipsoid in order to model the real shape of therice. Moreover, we will discuss the effective designing toimprove the behaviour of the Parboiled Rice in the OpticalSorter.

Raw RiceParboiled RiceFig. 6. Simulation Results for Optical Sorter.