Design and Optimization for Straw Treatment Device Using Discrete Element Method (DEM)

Abstract

Due to the dense crop residue in the Huang-Huai-Hai region, challenges such as large resistance, increased power consumption, and straw backfilling arise in the process of no-till seeding under the high-speed operations. This paper presents the design of a straw treatment device to address these issues. The cutting edge of a straw-cutting disc is optimized using an involute curve, and the key structural parameters of the device are designed by analyzing the process of stubble cutting and clearing. In this study, the Discrete Element Method (DEM) was employed to construct models of compacted soil and hollow, flexible wheat straw, forming the foundation for a comprehensive interaction model between the tool, soil, and straw. Key experimental variables, including working speed, rotation speed, and installation centre distance, were selected. The power consumption of the straw-cutting disc (PCD) and the straw-clearing rate (SCR) were used as evaluation metrics. Response surface methodology was applied to develop regression models linking the experimental factors with the evaluation indexes using Design-Expert 12 software. Statistical significance was assessed through ANOVA (p < 0.05), and factor interactions were analyzed via response surface analysis. The optimal operational parameters were found to be a working speed of 14 km/h, a rotation speed of 339.2 rpm, and an installation centre distance of 100 cm. Simulation results closely matched the predicted values, with errors of 1.59% for SCR and 9.68% for PCD. Field validation showed an SCR of 86.12%, improved machine passability, and favourable seedling emergence. This research provides valuable insights for further parameter optimization and component development.

1. Introduction

No-till seeding technology plays a crucial role in improving soil quality and enhancing crop yields [1,2,3,4,5]. In the Huang-Huai-Hai region, the dense straw cover in the fields, combined with the short sowing window for subsequent crops, leads to blockages in the seeding device if the straw is not properly managed in time. This blockage can negatively impact both the sowing accuracy and machinery passability [6,7]. In the process of high-speed seeding, the interaction between implement, straw, and soil is more complicated, increasing the difficulty of straw treatment and work resistance. Therefore, it is a focal point in high-speed anti-block tasks to reduce resistance and power consumption, meeting the orderly management of straw.

To mitigate blockage issues during no-till seeding, numerous researchers have explored and implemented advanced technologies. One proposed solution involves combining active and passive components to achieve effective cutting based on the supported cutting principle. This approach enhances machine passability, reduces operational power consumption, and improves operational quality, as evidenced by increased cutting frequency [8,9,10]. Additionally, notched disc cutters designed using biomimetic principles have demonstrated excellent performance in cutting straw and soil [11,12]. However, a larger width of soil-contacting parts can increase resistance and power consumption across various operating speeds, leading to significant soil disturbance. Furthermore, the operation in higher speeds intensify the movement of straw and soil, resulting in the backfilling of straw to seed beds and reducing straw clearing rates [13,14,15]. Therefore, employing a smaller tillage width is more favourable for high-speed operations. Simultaneously, when straw cover is abundant, this approach ensures effective straw cutting and guarantees that the clean seeding belt achieves optimal seeding performance.

The Discrete Element Method (DEM), initially introduced by Cundall, is a numerical approach used to simulate the behaviour of granular materials. With advancements in computational technology, DEM has demonstrated significant efficacy in agricultural engineering applications [16,17]. Comparative analyses between soil-bin experiments and simulations have validated the applicability of DEM in agricultural settings [18]. Li et al. [19] employed DEM to model the dynamic interactions between straw and machine components, elucidating the working width influence on resistance force. By simulating interactions among straw, soil, and machinery, DEM has provided substantial data support for optimizing key components and deepening the understanding of operational mechanisms, thereby greatly enhancing research precision and efficiency [20,21,22,23,24]. During field operations, these components engage directly with soil and straw, lifting and processing them to achieve effective clearing. The power consumption and performance of these components can vary significantly under different operating parameters, which can be efficiently evaluated using DEM. Zhang et al. [25] utilized DEM to construct an interaction model, improving simulation accuracy. Analyzing the effects of various parameters that minimized soil disturbance and enhanced cutting efficiency. However, the problem of power consumption was not mentioned. Wu et al. [26] studies the influence of working parameters on effects and captures the movement of particles, but the compatibility of model with reality needs further development.

To achieve better operational results and reduce resistance and power consumption during high-speed no-tillage seeding, this paper proposes a cut-and-pull combined straw treatment device. By optimizing the blade profile of the straw-cutting disc and rationalizing the device’s structure, the optimal parameter combination was determined through discrete element simulation tests. These simulations were used to develop an interaction model of straw and soil, and the optimal parameters were subsequently installed on the seeding machine for field verification. During high-speed operation, the device effectively enhances straw clearing capability and improves sowing performance.

2. Materials and Methods

2.1. Overall Structure of the Device

In the Huang-Huai-Hai region, the cultivation pattern involves two crops per year with short intervals between post-harvest and planting operations. To maximize growth time and improve efficiency, straw treatment devices are employed to remove straw covering the ground surface prior to sowing. However, these devices often result in higher power consumption, reduced working performance, and inadequate adaptation to high-speed conditions [6,27,28,29]. Related studies have demonstrated that soil-contacting components with larger widths generate greater resistance, which impedes high-speed operation [30]. Additionally, the soil and straw are thrown into a complex motion state, leading to poor straw clearing rates (SCR) and failure to meet sowing requirements due to straw accumulation on the clearing belt.

To address these issues, a smaller-width cutter is utilized to reduce the risk of clogging when straw is scattered irregularly across the field. It is crucial to design efficient straw treatment devices. To ensure a high-quality seedbed environment for subsequent crops and to avoid cutting stubble, it is necessary to thoroughly clean the residues of previous crops from the seeding belt. Based on these requirements, a cut-and-pull combined straw treatment device has been designed. This device primarily consists of a straw cutting component, a straw-clearing component, a power mechanism, a transmission system, a depth-limiting mechanism, and a frame. The straw-cutting component and straw-clearing component are positioned at the front and rear, respectively, with their overall structure illustrated in Figure 1. The design aims to enhance straw clearing efficiency, reduce power consumption, and ensure optimal seeding conditions under high-speed operations.

2.2. Key Component Design

The straw-cutting disc directly impacts operational efficiency. To ensure effective straw cutting during high-speed sowing, it is essential to optimize the cutting-edge curve of the straw-cutting disc to maintain stable operation. An involute curve, defined as a straight line that rolls purely along a circle, is utilized to minimize relative sliding during the cutting process. This design facilitates better interaction between the disc and both the straw and the soil. The slip-cutting angle must exceed the friction angle between the soil and straw, or the cutter material. Typically, the friction angle between crop straw and metal ranges from 20° to 40° [31]. Therefore, the optimal cutting range for the slip-cutting angle at the starting and ending points of the designed cutting-edge curves (Q₁, Q₂) is between 50° and 70° [32,33]. By ensuring that the slip-cutting angle at every point on the cutting edge falls within this optimal range and by dynamically adjusting the slip-cutting angle of the curve, the length of the cutting edge can be reduced. This reduction in cutting edge length, in turn, helps lower power consumption [34].

As illustrated in Figure 2a, Q₁ and Q₂ represent the starting and ending points of the edge line, respectively. O and O₁ denote the rotational centre and the centre of the base circle. R₀ is the radius of the base circle. Consider a point Q on the edge curve, where the normal to the curve intersects the base circle at point K. This intersection defines the slip angle at this point as τ. The relationship between the radius vector R_k and R₀ is given by R₀ = R_k cosα, where l_oQ = ρ, and the eccentricity distance is e. This relationship leads to the following expression for the slip angle:

$$\left\{\begin{array}{l}\rho =e\cos \theta +e\sqrt{{\left({\displaystyle \frac{R_0}{e\cos \alpha }}\right)}^2-{\sin }^2\theta }\\ \tau =\arctan {\displaystyle \frac{\rho }{\raisebox{1ex}{$d\rho $}\!\left/ \!\raisebox{-1ex}{$d\theta $}\right.}}=\arctan {\displaystyle \frac{\sqrt{{\left(\frac{R_0}{e\cos \alpha }\right)}^2-\sin \theta }}{\sin \theta }}\end{array}\right.$$

(1)

As shown in Equation (1), the slip-cut angle τ continuously varies with the position of the cutting edge during the cutting process, thereby enhancing the ability to cut straw and break soil. The selected cutting-edge curve is rotated counterclockwise around the rotary centre, resulting in the formation of multiple notches (1st notch, 2nd notch, 3rd notch, …, 9th notch). To ensure the disc’s hardness and safety, 65Mn steel was chosen as the material, and an eccentric curve was utilized for easier fabrication. The root positions of the teeth are susceptible to significant resistance stress, which can lead to tooth fracture [35]. Additionally, when the clearance between the disc teeth is minimal, straw may become trapped in the gaps, causing serious congestion. Therefore, it is necessary to increase the clearance between the teeth while maintaining the optimal slip angle range. To prevent straw blockage at the tooth roots, the design incorporates a rounded curve at the base of each tooth, enhancing clearance at the bottom. The design of the cutting straw disc is illustrated in Figure 2b.

The sowing depth of summer maize is typically 3–5 cm, and the tilling depth H is set to 5.5 cm to minimize soil disturbance. If the teeth are too long, they may break, reducing performance smoothness. Therefore, the height of the disc teeth l_h is set to 6 cm to ensure operational stability. During the straw cutting process, straw may become congested due to the winding of the disc axis when the disc shaft is positioned too low. Conversely, a high disc shaft results in an excessively large rotational radius, leading to rotational blockage and increased rotational imbalance [10,33,36]. To meet high-speed operation requirements and based on operational experience, the thickness of the straw-cutting disc is set to 6 mm, with the blade thickness at 1.2 mm. The rotary radius is designed to be R_c = 245 mm.

Straw is a hollow, flexible material, and its movement results in increased collisions, rebounds, and other dynamic states. To mitigate the impact of these unpredictable movements and achieve an optimal clearing zone, oppositely mounted finger-type straw clearing discs are used, which help clear backfilled and irregularly moving straw. Additionally, the tilted fingertips of the discs crush large clods of soil, reducing the resistance encountered during operation. The toggling action of the straw-clearing disc moves the straw out of the sowing area, effectively preventing straw interference and accumulation. Reducing the distance at the top of the clearing teeth minimizes the leakage clearing area (W_b), ensuring the cleanliness of the sowing belt. A schematic diagram of the clearing area is shown in Figure 3. In the Huang-Huai-Hai region, both strip sowing and wide seedling belt sowing are commonly used. Strip sowing arranges the seeds in evenly spaced rows with a row spacing of 15 cm, reserving a 30 cm corn seeding belt, while wide seedling belt sowing uses a row spacing of 20 cm without reserving a corn seeding belt. Wide seedling belt planting has been shown to improve wheat yields [37]. To achieve optimal sowing performance and reduce working resistance, the working area between the rows was designed to avoid cutting stubble. Accordingly, the maximum width of the working area was set to 20 cm, with the installation angle of the straw removal disc set at 28° and the working depth at 2 cm. The rotary radius of the straw removal disc was calculated to be 170 mm. To prevent straw from being picked up and sliding down to the roots during the dumping process, the tops of the grass-raking teeth were designed with a slanted profile to direct the straw outward, ensuring the efficiency of the sowing belt. This design helps maintain the clearing effect of the sowing belt and reduces blockage rates. Based on operational experience and comprehensive analysis, the values for δ₁ and δ₂ were set to 58° and 3.5°, respectively, to achieve uniform straw cleaning and an optimal working area width W:

$$W=2L\sin \alpha +W_b$$

(2)

where α is the angle between the straw-clearing disc and the forward direction (°), L is the distance between the intersection of the straw-clearing disc and the ground surface (cm), and W_b is the leakage clearing area of the straw (cm).

2.3. Working Process Analysis

During operation, the tool not only performs a circular motion around the knife axis but also moves at a constant speed under the traction of the tractor. The working speed is denoted as V_i. Optimal straw cutting performance is achieved when the trajectory of the disc apex Q intersects with a trochoid, as shown in Figure 4.

Its equation of motion is showed in Equation (3):

$$\left\{\begin{array}{l}{X}_M=V_{i}t+R_c\cos \omega t\\ Z_M=-R_c\sin \omega t\end{array}\right.$$

(3)

where X_M and Z_M are the displacement of point M along the x and z axes (m), respectively. R_c is the rotational radius of the straw-cutting disc (m), w is the rotational angular speed of the straw-cutting disc (rad/s), and t is the operation time (s). From Figure 4, it can be observed that the point Q is at Q₀ when t = 0. By differentiating Equation (3), the absolute motion speed of point Q is given by Equation (4):

$$V_Q=\sqrt{{V_i}^2-2V_i\omega \sin \left(\omega t\right)+{\left(R\omega \right)}^2}$$

(4)

As indicated by Equation (4), both working speed and rotational speed are crucial factors affecting operational performance when the radius R_c is determined. During high-speed operation, the difference between the instantaneous linear velocity at the disc’s contact point with the soil and the working speed is minimal when the straw-cutting disc rotates forward at a low rotational speed, which reduces the effectiveness of continuous straw cutting and increases the likelihood of operational inefficiency. Conversely, increasing the rotational speed leads to higher power consumption. To optimize performance, a reverse rotation scheme is adopted for the straw-cutting disc. This approach enhances the relative speed between the disc and the ground, facilitating a more efficient cutting action where the straw is driven forward and split to either side of the clearing belt.

It is assumed that the disc consistently cuts a specific area of straw. The cutting process is analyzed by studying the forces acting on the straw, as shown in Figure 5. The disc edge at the critical point makes the initial contact with the straw when reaching the critical cutting state. From this moment, the straw-cutting disc slides relative to the straw, causing the straw to move from the proximal to the distal end of the blade and cut.

By neglecting air resistance and the effects of mutual collisions between straw segments and assuming a balanced cutting condition, the following differential equation of motion is derived by examining the forces acting on the straw:

$$\left\{\begin{array}{l}{G}_1\sin \varphi +F_{n1}-F_{N1}\sin \varphi -f_1\cos \varphi =m_1{\displaystyle \frac{d^2{x}_n}{d{t}^2}}\\ F_{N1}\cos \varphi +F_{t1}-F_{f1}-G_1\cos \varphi -f_1\sin \varphi =m_1{\displaystyle \frac{d^2{x}_t}{d{t}^2}}\end{array}\right.$$

(5)

where F_f1 is the frictional force between the straw-cutting disc and the straw (N), F_t1 is the tangential force between the straw-cutting disc and the straw (N), F_n1 is the normal pressure exerted by the straw-cutting disc on the straw (N), F_N1 is the force exerted by the ground on the straw (N), G₁ is the gravitational force of straw (N), f₁ is the frictional force between the straw and the soil (N), ϕ is the angle between the forward direction and the normal to the blade edge of teeth (°), x_n and x_t represent the displacement of the straw in the normal and tangential directions of the blade line (m), respectively. The analysis revealed that the straw accumulation area opens when straw contacts the blade edge and slides toward the distal end, resulting in the expulsion of straw from both sides and the severing of the central portion. Equation (5) demonstrates that the straw is lifted out of the ground constraints, causing its acceleration to increase in the normal direction while decreasing in the tangential direction as the angle ϕ increases. Consequently, the straw is propelled forward in the normal direction of the blade edge, preventing it from falling back onto the clearing belt. This action reduces the risk of secondary cutting and minimizes power consumption. Additionally, it shortens the cutting path and improves cutting efficiency due to the rolling motion, thereby enhancing operational performance and reducing the risk of clogging. However, higher rotational speeds cause the straw to be thrown closer to the blade edge, prolonging contact time and increasing power consumption. Conversely, lower rotational speeds result in the straw being thrown farther from the blade edge, reducing contact time and leading to insufficient cutting. Thus, the effectiveness of the blade edge is constrained by the rotational speed.

During the straw-clearing process, the teeth of the straw-clearing disc penetrate the straw layer, generating rotary motion upon contact. The linear velocity of the tooth tips matches the working speed. In the continuous movement of the straw, it is necessary to overcome ground friction and the friction between the cutter teeth and the straw, resulting in the expulsion of the straw. Figure 6 illustrates the force on the straw, and the relationship is expressed in Equation (6):

$$\left\{\begin{array}{l}{F}_{n2}+F_{N2}\sin \phi -G_1\sin \phi -f_1\cos \phi =m_2{a}_n\\ f_2\sin \phi +F_{N2}\cos \phi -F_{f2}-G_2\cos \phi =m_2{a}_t\end{array}\right.$$

(6)

where f₂ represents the friction between the straw and the soil (N), F_f2 is the friction between the straw and the clearing disc (N), G₂ is the gravitational force (N), F_n2 is the thrust of the clearing teeth on the straw (N), F_N2 is the force exerted by the ground on the straw (N), φ is the angle between the normal direction of the contact surface of the clearing teeth and the horizontal direction (°).

The angle φ gradually increases from the point where the teeth contact the straw to where they move away from it. The tangential acceleration increases more rapidly than the normal acceleration, causing the trajectory of the straw to shift toward the clearing teeth. When the speed of the straw is lower than the linear velocity of the clearing teeth at the contact point, the straw moves with the clearing teeth. Due to the characteristics of the clearing teeth, the straw slides outward, reducing the risk of clogging. As the straw reaches the top of the clearing teeth, it detaches from the teeth, exhibiting an oblique downward trajectory when its speed exceeds the linear velocity at the departure point. Conversely, when the speed of straw is less than the linear velocity at the departure point, it remains close to the clearing teeth and is pushed outward by the ramp at the top to prevent rotation. It is evident that the working speed has a significant impact on the effectiveness of straw treatment as mentioned above.

After the straw is processed by the straw-cutting disc, it gradually detaches from the disc, becoming an independent moving body and returning to a static state, while the straw-clearing disc continues to operate. Setting a smaller distance between the two components increases the complexity of soil and straw movement in the processing area, thereby reducing the success rate of straw treatment. Conversely, setting a larger distance extends the overall longitudinal length of the machine, directly impacting its stability. Therefore, the installation distance between the two components plays a critical role in overall operational effectiveness.

2.4. Construction of Discrete Element Simulation Model

In no-till seeding conditions, the soil experiences compaction, leading to changes in its mechanical properties compared to its original state. To accurately model these characteristics, the Edinburgh Elasto-Plastic Adhesion (EEPA) model, which incorporates viscous, elastic, and plastic behaviours, was chosen [38,39]. The relationship between normal contact force and displacement for this contact model is shown in Figure 7.

The total normal contact force f_n primarily comprises the hysteretic resilience force f_hys and the normal damping force f_nd. The overlap relation between the normal contact force and inter-particle for this particle contact model is detailed in Equations (7)–(9):

$$f_n=\left(f_{\mathit{hys}}+f_{nd}\right)\cdot u$$

(7)

$$f_{\mathit{hys}}=\left\{\begin{array}{l}{f}_0+k_1{\delta }^n\begin{array}{cc}& \begin{array}{c}\begin{array}{c}\begin{array}{cc}& \end{array}\end{array}\end{array}\end{array} k_2({\delta }^n-{{\delta }^n}_p)\ge k_1{\delta }^n\\ f_0+k_2\left({\delta }^n-{{\delta }^n}_p\right)\begin{array}{cc}\begin{array}{cc}& \end{array}& k_1{\delta }^n\end{array}\ge k_2({\delta }^n-{{\delta }^n}_p)\ge -k_{\mathit{adh}}{\delta }^n\\ f_0-k_{\mathit{adh}}{\delta }^n\begin{array}{cc}& \begin{array}{cc}& \end{array}\end{array} -k_{adh}{\delta }^n\ge k_2({\delta }^n-{{\delta }^n}_p)\end{array}\right.$$

(8)

$$\left\{\begin{array}{l}{f}_{\mathit{nd}}={\beta }_n{v}_n\\ \\ {\beta }_n=\sqrt{{\displaystyle \frac{4m^{*}{k}_1}{1+{\left(\frac{\pi }{\mathit{Ine}}\right)}^2}}}\\ m^{*}={\displaystyle \frac{m_i\cdot m_j}{m_i+m_j}}\end{array}\right.$$

(9)

where u represents the unit normal vector directed from the contact point toward centre of mass, f₀ denotes the initial bond strength between particles (Pa). k₁ and k₂ correspond to the loading and unloading stiffness coefficients, respectively, while δ_p indicates the overlap distance at the contact point between particles (mm), k_adh reflects the viscous adhesion strength coefficient. v_n is the normal contact velocity (m/s). β_n represents the damping coefficient. m* denotes the effective mass of the contacting particles, and e is the restitution coefficient of the soil particles.

The tangential contact force between particles (f_t) in the soil model is composed of tangential stiffness (f_ts) and tangential damping (f_td). Their relation is expressed in Equation (10):

$$f_t=\left(f_{\mathit{ts}}+f_{td}\right)$$

(10)

The tangential stiffness between particles is determined iteratively, as presented in Equation (11):

$$\left\{\begin{array}{l}{f}_{\mathit{ts}}=f_{\mathit{ts}}\left(n-1\right)+\Delta f_{\mathit{ts}}\\ \Delta f_{\mathit{ts}}=-{\gamma }_t{k}_1{\delta }_t\end{array}\right.$$

(11)

where f_ts(n−1) represent the tangential force at a moment (N), and Δ is the time step (s). Δf_ts denotes the tangential force increment (N), while γ_t is the tangential stiffness coefficient of the particles. δ_t represents the tangential overlap between particles (mm). The tangential damping primarily depends on the interparticle tangential damping coefficient β_t and the interparticle tangential velocity v_t, as described by the following Equation (12):

$$\left\{\begin{array}{l}{f}_{\mathit{td}}=-{\beta }_t{v}_t\\ {\beta }_t=\sqrt{{\displaystyle \frac{4m^{*}{k}_t}{1+{\left(\frac{\pi }{\mathit{Ine}}\right)}^2}}}\end{array}\right.$$

(12)

Soil particles experience interactions of slide, with tangential friction governed by the Coulomb friction criterion. Accordingly, the particle shear strength under normal stress is limited as follows:

$$f_{\mathit{ct}}\le \mu \left(\left|f_{\mathit{hys}}+k_{\mathit{adh}}{\delta }^n-f_0\right|\right)$$

(13)

where f_ct denotes the maximum tangential friction between particles (N), and μ is the coefficient of static friction between particles.

In EDEM, soil particle sizes were determined based on sieve test results. To reduce computational load, particles larger than 4 mm were set to 5 mm, representing 35.46% of the total, while particles smaller than 4 mm were set to 3 mm, accounting for 64.54% [39,40]. The EEPA contact model consisted of nine parameters: collision recovery coefficient, static friction coefficient, dynamic friction coefficient, constant pull-off force, surface energy, contact plastic deformation, loading branch index, adhesion branch index, and tangential stiffness factor. Since the constant pull-off force remains between particles, it was excluded from this study. The loading branch index in EDEM 2022 software was constrained to values between 1 and 1.5, with a value of 1.5 selected based on existing literature [41].

Following preliminary calibration and validation tests to ensure suitability for high-speed operation according to the literature [40], the parameters for the soil contact model were determined, as shown in

Table 1. Soil contact modelling parameters.

Parameters	Values
Crash Recovery Factor e	0.4
Coefficient of Static Friction us	0.55
Coefficient of Kinetic Friction ur	0.35
Surface Energy Δγ(J/m2)	7.32
Contact Plastic Deformation Ratio λp	0.543
Bonding Branching Index X	1.75
Tangential Stiffness Factor Ktm	0.575

, and the generated soil model is presented in Figure 8.

Wheat straw is randomly distributed in the field and exhibits flexibility, generating a complex movement process during equipment operation. To accurately represent the original straw, a hollow flexible straw model was developed using the Hertz–Mindlin Bonding V2 model in EDEM, where bonding was established between particles to simulate the effects of tension, compression, shear, and torsion [42,43]. Custom properties, including force (F_n,t) and moment (M_n,t), are defined as follows:

$$\begin{array}{l}d{F}_n=K_{n}d{\delta }_n={\displaystyle \frac{E_{b}A}{l_b}}{v}_{n}dt\\ d{F}_t=K_{t}d{\delta }_t={\displaystyle \frac{G_{b}A}{l_b}}{v}_{t}dt\\ d{M}_n=K_{\mathit{mn}}d{\theta }_n={\displaystyle \frac{G_b{I}_p}{l_b}}{\omega }_{n}dt\\ d{M}_t=K_{\mathit{mt}}d{\theta }_t={\displaystyle \frac{E_{b}I}{l_b}}{\omega }_{t}dt\end{array}$$

(14)

where dF_n, dF_t, dM_n, and dM_t represent the increments of normal force (F_n), shear force (F_t), torsional moment (M_n), and bending moment (M_t), respectively. dδ_n, dδ_t, dθ_n, and dθ_t are the increments of normal deformation (δ_n), shear deformation (δ_t), torsional angular deformation (θ_n), and bending angular deformation (θ_t). K_n, K_t, K_mn, and K_mt represent normal, shear, torsional, and bending stiffness, respectively. The bond is modelled as a cylinder with radius R_B, length l_b, cross-sectional area A = πr_b², area moment of inertia I = πR_B⁴/4, and polar area moment of inertia I_p = πR_B⁴/2. The E_b and G_b represent Young’s modulus and shear modulus, respectively. Bond deformation is calculated based on corresponding velocities (v_n, v_t, w_n, w_t) and the product of the time step (d_t).

The motion of spherical particles and all particle components is governed by Newton’s second law:

$$\begin{array}{l}m{\displaystyle \frac{d^{2}x}{d{t}^2}}={\displaystyle \sum F}\\ J{\displaystyle \frac{d^2\theta }{d{t}^2}}={\displaystyle \sum M}\end{array}$$

(15)

where x and θ represent the translational displacement and angular displacement of spherical particles with mass (m) and rotational moment of inertia (J), respectively, F denotes the combined forces driving the translational motion of straw components (N), and M represents the combined forces driving their rotational motion (N·m).

Bond fracture occurs when the normal and tangential shear stresses exceed the threshold values defined for straw cracking, as shown in Equation (16):

$$\begin{array}{l}{\sigma }_{\max }\le {\displaystyle \frac{-F_n}{A}}+{\displaystyle \frac{2M_t}{J}}{R}_B\\ {\tau }_{\max }\le {\displaystyle \frac{-F_t}{A}}+{\displaystyle \frac{2M_n}{J}}{R}_B\end{array}$$

(16)

where σ_max is the maximum positive stress and τ is the maximum shear stress.

According to the no-tillage sowing requirements for the Huang-Huai-Hai region, wheat straw is chopped to lengths of less than 10 cm and evenly distributed across the soil surface. Field-collected samples revealed that the straw lengths varied between 3 cm and 9 cm. To simplify model construction and reduce computational demands, an average length of 6 cm was selected as the standard length for the straw model. The Hertz–Mindlin Bonding V2 model was employed to develop the discrete element model in EDEM 2022 software. The parameters for this straw model—including normal stiffness per unit area, shear stiffness per unit area, normal strength, shear strength, and bond disc scale (set to 1)—were calibrated through experimental testing, as listed in

Table 2. Parameters of straw contact model.

Parameters	Values
Normal Stiffness per Unit Area	5 × 1010 N/m
Shear Stiffness per Unit Area	9 × 1010 N/m
Normal Strength	60 MPa
Shear Strength	60 MPa

.

Following the methodology outlined in [32], the discrete element model of the straw—based on the aforementioned parameters—is illustrated in Figure 9.

2.5. Test Methods

To optimize simulation time and reduce complexity, the device model was simplified while retaining the essential functions of the straw-cutting disc and straw-clearing disc. An interaction model involving the device components, straw, and soil was developed using EDEM 2022 software. The straw-cutting disc was modelled using 65Mn material, characterized by a Poisson’s ratio of 0.30, a density of 7800 kg/m³, and an elastic modulus of 2.054 × 10¹¹ Pa. Wheat straw parameters were set with a Poisson’s ratio of 0.40, a density of 241 kg/m³, and an elastic modulus of 5.141 × 10⁸ Pa, while soil parameters were defined with a Poisson’s ratio of 0.38, a density of 1251 kg/m³, and an elastic modulus of 1.3 × 10⁶ Pa [25,40,41,42]. Additionally, a soil bin with dimensions of 1000 × 300 × 150 mm was created as a particle bed.

The hollow flexible straw closely mimics the actual straw shape. However, generating large number of straws to accurately represent field conditions can dramatically increase computational demands. To address this, straws were randomly generated within a confined area and distributed above the soil layer to match the straw coverage observed in the field. This approach simulates the natural scattering of straw in a seeding field through free-fall dynamics, thereby streamlining calculations. The width of zone matches the width of wheat planting row, which is less than the length of zone selected.

Table 3. Contact model parameters.

Contact Model	Coefficient of Static Friction	Coefficient of Rolling Friction	Coefficient of Restitution
Straw–Straw	0.27	0.35	0.25
Straw–Soil	0.489	0.49	0.323
Straw–Steel	0.38	0.24	0.12
Steel–Soil	0.55	0.34	0.243
Soil–Soil	0.4	0.55	0.35

provides the parameters for the contact models, and the model is illustrated in Figure 10.

DEM provides a method for adjusting working parameters and minimizes the need for extensive field testing, thereby enhancing both efficiency and accuracy. To accommodate high-speed sowing requirements, three levels of operational speed (12, 13, and 14 km/h) were selected. Additionally, three rotational speeds for the straw-cutting disc—specifically 200, 300, and 400 rpm (20.94, 31.42, and 41.89 rad/s)—were chosen to suit high-speed conditions. Installation centre distances of 60, 80, and 100 cm were set based on practical agricultural experience. The coded levels of these test factors are presented in

Table 4. Test code table.

Level	Test Factor
	Working Speed (A)	Rotation Speed (B)	The Installation Centre Distance (C)
−1	12 km/h	200 rpm	60 cm
0	13 km/h	300 rpm	80 cm
1	14 km/h	400 rpm	100 cm

.

Response surface tests were conducted on the working parameters using Design-Expert 12 software, comprising a total of 17 test groups. The device model, in “igs” format, was imported into EDEM 2022 software, where the working parameters for the straw treatment components were configured as outlined in

Table 5. Response surface experiment scheme.

Number	Test Factor			Index
	A	B	C	SCR (%)	PCD (kW)
1	−1	−1	0	80.8	0.985
2	1	−1	0	76.5	0.748
3	−1	1	0	73.5	1.346
4	1	1	0	85.36	1.7051
5	−1	0	−1	78.08	1.0653
6	1	0	−1	81.06	0.951
7	−1	0	1	77.45	1.454
8	1	0	1	83.72	0.8775
9	0	−1	−1	79.93	1.0569
10	0	1	−1	79.16	1.302
11	0	−1	1	78.09	0.7774
12	0	1	1	86.91	1.741
13	0	0	0	77.80	1.2315
14	0	0	0	79.03	1.1265
15	0	0	0	78.32	1.318
16	0	0	0	77.12	1.218
17	0	0	0	78.35	1.29

. Additionally, the rotation of the straw-clearing disc was set to active rotation, replacing passive rotation to ensure compatibility with the operational speed. Based on an analysis of the operation process, response surface tests were performed using the straw-clearing rate (SCR) and power consumption of the straw-cutting disc as evaluation metrics. The SCR was calculated using Equation (17):

$$e\left(\%\right)=1-{\displaystyle \frac{m_1}{m_0}}\times 100\%$$

(17)

where m₁ represents the weight of the remaining straw (kg), and m₀ denotes the initial weight of the straw (kg).

The torque exerted on the straw-cutting disc by contacting particles during the simulation process was measured, and the power consumption of the straw-cutting disc (PCD), was calculated using Equation (18):

$$P={\displaystyle \frac{T\cdot n}{9550}}$$

(18)

where T is the torque of the straw-cutting disc (N·m), and n is the rotational speed of the straw-cutting disc (r/min).

3. Results and Discussion

3.1. Analysis of Results

3.1.1. Variance Analysis

The experimental design and results are presented in Table 5, where factors A, B, and C correspond to working speed, rotational speed, and installation centre distance, respectively. An analysis of variance (ANOVA) was conducted on the simulation results to assess statistical significance (p < 0.05).

The ANOVA results for SCR are presented in

Table 6. ANOVA.

Project	Source	Sum of Squares	Freedom	Mean Square	F Value	p Value
SCR	Model	0.0167	9	0.0019	13.6	0.0012
	A	0.0035	1	0.0035	25.95	0.0014
	B	0.0012	1	0.0012	8.48	0.0226
	C	0.0008	1	0.0008	5.79	0.047
	AB	0.0065	1	0.0065	47.97	0.0002
	AC	3.00 × 10−4	1	3.00 × 10−4	1.99	0.2014
	BC	0.0023	1	0.0023	16.89	0.0045
	A2	8.85 × 10−8	1	8.85 × 10−8	0.0007	0.9804
	B2	0.0004	1	0.0004	2.68	0.1457
	C2	0.0016	1	0.0016	11.98	0.0105
	Residual	0.001	7	0.0001
	Lack of Fit	0.0008	3	0.0003	4.94	0.0783
	Pure Error	0.0002	4	0.0001
	Cor Total	0.0176	16
PCD	Model	1.19	9	0.1328	8.52	0.005
	A	0.0404	1	0.0404	2.59	0.1513
	B	0.7981	1	0.7981	51.21	0.0002
	C	0.0282	1	0.0282	1.81	0.2208
	AB	0.0888	1	0.0888	5.7	0.0484
	AC	0.0534	1	0.0534	3.43	0.1066
	BC	0.1291	1	0.1291	8.28	0.0237
	A2	0.0316	1	0.0316	2.02	0.1977
	B2	0.0088	1	0.0088	0.5667	0.4761
	C2	0.0169	1	0.0169	1.08	0.3329
	Residual	0.1091	7	0.0156
	Lack of Fit	0.0871	3	0.029	5.29	0.0707
	Pure Error	0.022	4	0.0055
	Cor Total	1.3	16

, demonstrating an overall significant effect (p < 0.01). Working speed, rotational speed, and installation centre distance each have significant impacts on SCR. Additionally, the interaction effects of AB and BC, as well as the quadratic term C², are significant. Other interaction and quadratic terms do not significantly affect the response values. The factors influencing SCR are ranked in order of importance as follows: A > B > C. After removing non-significant factors, the regression equation describing the effect of each factor on the straw removal rate is shown in Equation (19):

$$\begin{array}{l}{Y}_1=0.7853+0.021A+0.012B+0.0099C\\ +0.0404AB+0.0240BC+0.0202C^2\end{array}$$

(19)

A lack-of-fit test was conducted on the variance, revealing no significance (p > 0.05). This indicates that the test results are reliable and that the regression equation provides an excellent fit. The coefficient of determination (R²) is 0.9459, which decreases to 0.9098 after removing non-significant factors. This suggests that the model accounts for over 90% of the variance in the results, making it suitable for predictive purposes.

The ANOVA for PCD is presented in Table 6, with the overall experimental results being significant (p < 0.01). The effect of rotational speed on PCD was highly significant. Additionally, the interaction effects of factors AB and BC on power consumption were significant, while the remaining terms were not. The order of influence on the response value is as follows: B > A > C. After eliminating non-significant factors, the regression equation describing the effect of each factor level on PCD is provided in Equation (20):

$$\begin{array}{l}{Y}_2=1.19-0.0711A+0.3159B+0.0593C\\ +0.149AB+0.1796BC\end{array}$$

(20)

A lack-of-fit test was conducted on the variance and found to be non-significant (p > 0.05), indicating that the test results are reliable and that the regression equation provides an excellent fit. The coefficient of determination (R²) is 0.9163. After removing insignificant factors, R² decreases to 0.8317, suggesting that the model explains over 83% of the variance in the results, making it suitable for predictive purposes.

3.1.2. Response Surface Analysis

To investigate the effects of factor interactions on the experimental indicators, the results were analyzed using response surface methodology in Design-Expert 12 software, as illustrated in Figure 11 and Figure 12.

As illustrated in Figure 11a, when the installation centre distance is fixed and the working speed is at its initial stage, SCR decreases with increasing rotational speed. However, as the working speed rises, SCR initially decreases and then increases, ultimately exhibiting an overall upward trend and significantly improving straw-clearing efficiency. When the rotational speed is at its initial stage, SCR decreases as the working speed increases. As the rotational speed continues to rise, SCR shows a clear increasing trend due to the enhanced cutting capacity for straw. Additionally, as shown in Figure 11b, when the working speed is held constant and the installation centre distance is at its initial state, SCR increases significantly with rising rotational speed. However, as the installation centre distance increases, SCR first increases and then decreases with further increases in rotational speed. At low rotational speeds, SCR initially decreases and then increases as the installation centre distance grows. As rotational speed continues to rise, SCR exhibits a trend of first decreasing and then increasing with increasing installation centre distance, ultimately showing an overall decreasing trend.

As shown in Figure 12a, when the installation centre distance is fixed and the working speed is at its initial state, PCD increases with rotational speed. However, as the working speed rises, PCD continues to increase with rotational speed, eventually experiencing a significant surge. At lower rotational speeds as shown in Figure 12b, PCD decreases as the working speed increases. As rotational speed further increases, PCD initially decreases with rising working speed before subsequently increasing. When the working speed is held constant and the installation centre distance is at its initial state, PCD increases with rotational speed. As the installation centre distance grows, PCD shows a substantial increase with higher rotational speeds. At lower rotational speeds, PCD decreases as the installation centre distance increases. However, as rotational speed continues to rise, PCD first decreases and then increases with further increases in installation centre distance, ultimately resulting in an overall increase.

3.1.3. Parameter Optimization and Simulation Verification

To obtain the optimal parameter combination for the device, the parameters for SCR and PCD were optimized using the optimization function in the Design-Expert 12 software. The constraints are outlined in Equation (21).

$$\left\{\begin{array}{l}\max Y_1(A,B,C)\ge 85\%\\ \min Y_2(A,B,C)\\ \\ s.t\left\{\begin{array}{l}-1\le A\le 1\\ -1\le A\le 1\\ -1\le A\le 1\end{array}\right.\end{array}\right.$$

(21)

The objective function was optimized, yielding the final parameter combination: a working speed of 14 km/h, a rotational speed of 339.2 r/min, and a centre distance of 100 cm. Under these conditions, the predicted SCR was 87.1%, and the PCD was 1.219 kW. A simulation was conducted to verify these results, achieving an SCR of 85.71% and a PCD of 1.337 kW. The errors relative to the predicted values were 1.59% for SCR and 9.68% for PCD, indicating good agreement between experimental and predicted values.

3.2. Simulation Process Analysis

To further elucidate the interactions among the straw treatment components—straw and soil—simulations were conducted using EDEM software, as illustrated in Figure 13. As shown in Figure 13a, the straw-cutting disc effectively cuts and disperses the straw to both sides. During cutting, when straw contacts the blade, it is either cut or directly ejected by rotation, gaining speed. After leaving the blade, the straw continues its outward trajectory, forming a narrow clearing belt away from the blade position, with minimal straw remaining near the blade. In Figure 13b, the rotating straw-clearing discs direct stalks obliquely outward from both sides, further widening the cleared strip. The opposing action of the straw-clearing discs creates a clearance zone, with the narrowed strip produced by the discs enhancing the efficiency of straw removal within this area. This outcome aligns with the analysis in Section 2.3, illustrating that the discrete element method effectively supports the optimization of the device.

3.3. Field Trial

3.3.1. The Trial Process

Field trials were conducted to assess straw-clearing efficiency and machine passability under optimal operating conditions, as illustrated in Figure 14a. Five tests were performed within the operational area, with each measurement zone spanning 100 cm in length and a single sowing row in width. Straw samples were collected from each zone both before and after operation, and their weights were recorded, as shown in Figure 14b. The machine passability of the implements was evaluated in accordance with Operation specification for no-tillage maize drilling machinery and Technical specification forno-tillage seeding machinery operation to determine continuous and normal equipment operation and to assess blockage levels during use. The tests consisted of three operational passes over a designated 50 m measurement area. Machine passability was considered satisfactory if no blockage or only minor blockage occurred.

3.3.2. Results and Analyses of Field Trials

The experimental results obtained after the operation are presented in

Table 7. The effect of straw clearing.

Number	m1/kg	m0/kg	e/%
1	0.0109	0.084	87.02
2	0.0125	0.09	86.06
3	0.0129	0.0921	85.99
4	0.0126	0.0853	85.23
5	0.0113	0.0829	86.31

.

The analysis indicates an average straw clearing rate (SCR) of 86.12%. As illustrated in Figure 15, the straw between rows was effectively cleared, validating the predictive accuracy of the straw–soil–tool interaction model. The planter demonstrated continuous and reliable operation across all three operational processes. During these processes, straw was efficiently lifted and scattered beyond the sowing rows, ensuring unobstructed operation. No significant blockages were observed upon completion, and the machine successfully passed the passability test.

In addition, the straw-cutting disc was designed based on involute curve, setting eccentricity to manufacture simply, which can promote the release of straw after cutting. The straw-clearing disc can help straw, backfilling after complex movement, to leave the clearing area. They can be optimized by using the methods of DEM and experimental design. The straw treatment device integrated into the planter met the requirements of seedbed for high-speed sowing operations, demonstrating its suitability for efficient and reliable field performance. When the amount of straw cover is not uniform, the higher tool shaft can reduce the entanglement and blockage of the straw, and the rotation of the disc helps to cut the straw layer and divide it into two side. Therefore, it can adapt to anti-blocking processes in many conditions, but rotation speed needs to be further studied.

3.3.3. Discussion

The device can be used in the high-speed condition, the function of cutting and pulling weaken the impact of complex movement and decrease the soil disturbance than other active stubble cutting device. Traditional passive discs do not have enough power to cut off straw in the region of large amounts of residue, leading to a weak working effect. The cut-and-pull combined straw treatment device is designed by adopting the scheme of dynamic drive straw cutting, enhancing straw handling capacity under the state of low power consumption.

However, the DEM simulation was implemented under a given condition of soil environments and straw residues. Future work should consider the verification of sowing quality and seeding emergence effect after integrating the device into the seeding system. This will move the device closer to industrialization and adoption by farmers.

4. Conclusions

To complete the overall structure of cut-and-pull combine straw treatment device, design the cutting-edge curve of the straw-cutting disc based on the involute curve. Optimize the structure parameters of the straw-clearing disc. The feasibility was verified through theoretical calculations and an analysis of the process of cutting and clearing straw. In this process, the factors affecting working effect were obtained, which was instrumental to further improving the device.

A compact soil simulation model and a flexible straw model were developed using the Edinburgh Elasto-Plastic Adhesion (EEPA) contact model and the Hertz–Mindlin Bonding V2 contact model. A discrete element model incorporating interactions among the device, straw, and soil was subsequently established. Response surface tests were conducted on key factors impacting performance, including forward speed, rotational speed, and centre distance. Variance analysis (p < 0.05) confirmed the significance of these factors. Regression models for SCR and PCD were developed. Response surface analysis of factor interactions identified optimal machine operating parameters: a forward speed of 14 km/h, rotational speed of 339.2 rpm, and an installation centre distance of 100 cm.

Simulations indicated a predicted SCR of 87.1% and a PCD of 1.219 kW. A verification simulation achieved an SCR of 85.71% and a PCD of 1.337 kW, resulting in prediction errors of 1.59% for SCR and 9.68% for PCD, thereby demonstrating the accuracy of the regression model. Field tests conducted using the optimized parameters achieved an SCR of 86.12%, indicating effective operational performance. These results confirm the efficacy of the DEM and the response surface optimization approach.