In the context of the intelligent transformation of energy storage and transportation, oil tank cleaning technology urgently needs to break through the dual constraints of efficiency and safety. We have developed a new intelligent cleaning system based on special robot technology. The core innovation of our intelligent robot lies in the cleaning execution mechanism, whose performance directly determines the system’s operational effectiveness. Facing the complex internal conditions of oil tanks, an ideal working head must meet key technical indicators such as zero damage to the substrate, corrosion resistance, and easy controllability. Traditional methods, whether manual or using mainstream devices like scraping or shovel-type heads, suffer from long cycles, significant safety risks, functional limitations, low cleaning efficiency, and the potential to damage the tank body. Our research focuses on a fluidic-structural innovation: the development of a self-excited oscillation pulsed jet working head, which effectively enhances the quality of storage tank cleaning operations.
The generation of self-excited pulses is mainly influenced by two aspects: the structural parameters of the self-excited nozzle (the main internal dimensions and shape) and the operating conditions (primarily the pressure and flow velocity at the inlet of the upper nozzle). According to measured data, when the jet terminal pressure drops to 0.007 MPa, it is considered the critical point for possessing effective impact force. For our designed nozzle, the corresponding effective range can reach up to 13.34 m. The core of our intelligent robot is this advanced working head.
1. Jet Mode Optimization and Theoretical Foundation
Based on a comparative analysis of jet modalities, self-excited oscillation jet technology utilizing the Helmholtz resonance principle demonstrates superior technical feasibility. This technology achieves spontaneous modulation of a continuous jet through cavity structure design, generating high-frequency pulsed jets without external excitation.
The core of the mechanism is the Helmholtz resonator model applied to fluid dynamics. When a continuous water jet passes through a specially designed chamber, pressure fluctuations are amplified at a specific natural frequency. This frequency \( f \) is given by:
$$ f = \frac{c}{2\pi} \sqrt{\frac{A}{V L_{eq}}} $$
where \( c \) is the speed of sound in the fluid, \( A \) is the cross-sectional area of the nozzle neck, \( V \) is the volume of the oscillation chamber, and \( L_{eq} \) is the effective length of the neck. By carefully designing these parameters, we can tune the system to produce powerful, periodic pressure pulses that enhance cleaning.
The key technological innovations in our design are as follows:
1.1 Dual-Stage Nozzle Energy Gradient Enhancement System
Constructed based on the principle of hydrodynamic staged acceleration, this system features a dual-stage nozzle structure. The first stage employs a contracting nozzle with a 30° angle, increasing the initial jet velocity to 20 m/s. The second stage innovatively introduces a conical impact wall structure. Utilizing fluid impingement effects, an energy focal zone is formed. When the jet reaches the wall, the concentration of its velocity vector increases by 40%. The momentum transfer during this impact stage is crucial and can be described by analyzing the change in momentum flux.
1.2 Coupled Optimization of Helmholtz Resonance Cavity Parameters
Based on the vortex mode-acoustic mode coupling mechanism, we established a dynamic matching model for the cavity aspect ratio. Experimental data indicate that when the ratio of resonance cavity diameter to outlet diameter is 1.8:1, and the axial length of the cavity is 2.3 times the outlet section length, a characteristic frequency of 1.2 kHz is excited. This parameter combination causes the jet to produce a periodic vortex ring structure, achieving a cleaning coverage density of 98.7%. The Strouhal number \( St \), a dimensionless number describing oscillating flow mechanisms, is relevant here:
$$ St = \frac{f D}{v} $$
where \( f \) is the frequency, \( D \) is a characteristic diameter (e.g., of the nozzle), and \( v \) is the flow velocity. Optimizing for a high \( St \) within effective ranges promotes strong, discrete vortex formation.
2. Design of the Self-Excited Oscillation Pulsed Nozzle and Supporting Systems
The performance of the intelligent robot cleaning system is critically dependent on the structural and operational parameters of its core component: the self-excited oscillation nozzle.
2.1 Determination of Optimal Operational Parameters
Through numerical simulation and experimental verification, we determined the optimal working pressure threshold to be 1.5 MPa. At this pressure, a stable vortex ring structure can form in the jet core region. The effective working radius is defined by the pressure decay along the jet axis. When the target distance exceeds 13.34 m, the jet terminal pressure decays below 0.007 MPa, which is the critical point for effective impact. The pressure decay for a free turbulent jet can be approximated by:
$$ \frac{P_x}{P_0} = k \left( \frac{d}{x} \right)^n $$
where \( P_x \) is the pressure at distance \( x \) from the nozzle, \( P_0 \) is the exit pressure, \( d \) is the nozzle diameter, and \( k, n \) are empirical constants. Our design aims to extend \( x \) for a given \( P_x \).
2.2 Structural Parameter Design of the Nozzle
Based on fluid dynamics calculations and empirical formulas, the core structural parameters were determined as summarized in the table below. These parameters are the result of an optimization process balancing jet coherence, oscillation strength, and cavitation inception.
| Structural Parameter | Design Value | Design Basis & Optimization Range |
|---|---|---|
| Upper Nozzle Diameter (du) | 12 mm | Derived from optimal inlet velocity (45 m/s) and flow rate (20 m³/h). The area is given by \( A = Q/v \), leading to \( d_u = 2\sqrt{A/\pi} \). |
| Lower Nozzle Diameter (dl) | 25 mm | The diameter ratio \( d_l / d_u \approx 2.1 \) falls within the optimal range of 2.2–2.6 to enhance impact while minimizing energy dissipation. |
| Lower Nozzle Length (Ll) | 120 mm | Chosen with a length-to-diameter ratio of 4.8:1 to ensure flow stabilization and passage of coherent structures. |
| Oscillation Chamber Diameter (Dc) | 150 mm | The ratio \( D_c / d_l = 6 \), within the effective range of 5.0–6.5 for strong self-excitation. |
| Oscillation Chamber Length (Lc) | 135 mm | The ratio \( L_c / D_c = 0.9 \), within the optimal range of 0.36–1.0, extending cavitation bubble collapse time. |
| Impact Wall Cone Angle (θ) | 120° | Literature-recommended optimal value for effective flow guidance and concentrated bubble collapse. |
2.3 Power System Configuration
A five-stage centrifugal pump group is selected as the power source for the intelligent robot. The design parameters are as follows:
- Head: 200 m (including pipeline loss compensation)
- Flow Rate: 24 m³/h (including system margin)
This configuration ensures that the pressure at the oscillation chamber inlet remains stable above 1.5 MPa, satisfying the conditions for triggering self-excited oscillation. The required pump power \( P_{hyd} \) can be estimated by:
$$ P_{hyd} = \frac{\rho g Q H}{\eta} $$
where \( \rho \) is fluid density, \( g \) is gravity, \( Q \) is flow rate, \( H \) is head, and \( \eta \) is pump efficiency. The selected pump meets this hydraulic power demand.
2.4 Spatial Positioning System: The Multi-DOF Robotic Arm
To achieve full three-dimensional spatial coverage cleaning, a multi-degree-of-freedom robotic arm system was designed. This arm is a critical component of the intelligent robot, providing the dexterity needed to direct the high-performance nozzle to all interior surfaces of the tank.
| Component | Specification |
|---|---|
| Structural Composition | Three-stage hinged arm (Φ45 mm stainless steel tube). |
| Motion Range | ±120° pitch and ±120° yaw rotation. |
| Drive Method | Servo motor + harmonic reducer for precise positioning. |
| Pipeline Routing | Internal high-pressure water pipeline (Φ32 mm outer diameter). |
| Positioning Accuracy | ±1° for the nozzle head, enabling 360° dead-angle cleaning. |
The first rotation arm’s base is fixed to a turntable, enabling full circumferential traversal. The entire assembly is powered electrically, allowing the self-excited oscillation pulsed nozzle to perform axial scanning and喷射.
3. Performance Advantages and System Integration of the Intelligent Robot
The integration of the self-excited oscillation working head with the robotic positioning system and control units creates a superior intelligent robot for tank cleaning. The advantages are multidimensional.
3.1 Revolutionary Improvement in System Energy Efficiency
By utilizing fluid self-excitation to convert energy, traditional electro-hydraulic drive modules are eliminated. Field tests show that for the same cleaning intensity, the system’s operating energy consumption is reduced by approximately 35%, and the equipment volume is reduced to 1/3 of that of traditional mechanical cleaning devices.
3.2 Multidimensional Breakthrough in Cleaning Efficacy
- High-Frequency Pulsation (>1 kHz): Induces cavitation cloud collapse effects, generating localized instantaneous impacts up to 800 MPa.
- Enhanced Removal: Coupled with a vacuum suction system, the decomposition efficiency of crude oil tank bottom sludge is increased to 82.5%, with oil-water separation accuracy reaching 96.3%.
- Complete Coverage: The three-dimensional rotating head achieves 360° cleaning with residue thickness < 0.5 mm.
The cleaning effectiveness \( E \) can be conceptually modeled as a function of key parameters:
$$ E \propto f_{pulse} \cdot \Delta P_{amp} \cdot C_{cov} \cdot t_{exp} $$
where \( f_{pulse} \) is the pulse frequency, \( \Delta P_{amp} \) is the amplitude of pressure fluctuation, \( C_{cov} \) is the coverage factor from the robotic arm, and \( t_{exp} \) is the exposure time. Our design maximizes these factors.
3.3 Significant Enhancement in Engineering Adaptability
The modular design supports rapid configuration of nozzle parameters, adapting to cleaning needs for tanks ranging from 5 to 50 m³ in capacity. For areas with 4 m thick sludge at the tank bottom, using a directed enhancement mode reduces the cleaning cycle to 1/4 of that of traditional methods. The intelligent robot system can adapt its operational parameters based on tank size and contamination level.
3.4 System Performance Validation
Based on multi-scenario verification, the high-pressure water jet technology of our intelligent robot, through dynamic pressure regulation (0–50 MPa) and intelligent parameter matching, solves the problems of substrate corrosion and residue associated with traditional mechanical cleaning. Post-cleaning, the system can directly connect to an oil-water separation module, achieving a water resource recycling rate of 85%.
| Performance Metric | Traditional Method | Our Intelligent Robot System | Improvement |
|---|---|---|---|
| Single-Tank Cleaning Cycle | 5–7 days | 32 hours | Reduced to ~1/4 |
| Energy Consumption (Relative) | Baseline (100%) | 65% | 35% reduction |
| Peak Pulse Pressure (Relative) | Baseline (100%) | 137% | 37% increase |
| Effective Jet Range | ~11 m | 15.2 m | ~38% extension |
| Substrate Damage | High Risk | Zero Damage | Fundamental Solution |
| Cleaning Coverage | < 85% | 98.6% | Comprehensive Coverage |
4. Conclusion
Through this analysis and design process, we have established a comprehensive solution for the intelligent robot working head. The key outcomes are:
- Technical Economic Analysis: High-pressure water jet technology with self-excited oscillation has been confirmed as the optimal operational scheme for oil tank cleaning robots, solving the problem of substrate damage inherent to traditional mechanical cleaning.
- Nozzle Design Innovation: The improved nozzle design based on Helmholtz resonance theory, through cavity structure optimization (cavity diameter ratio, impact wall angle), significantly enhances the cavitation effect. The peak pulsating pressure reaches 12 MPa, a 37% increase over traditional structures. The design improves jet coverage width and effective range by 22% and 18%, respectively. When integrated with modern communication technology, it enables remote real-time adjustment of nozzle parameters, greatly enhancing operational flexibility for the intelligent robot.
- Robotic Integration: The developed three-stage robotic arm system achieves precise control of the cleaning trajectory, with an operational coverage rate of 98.6%, increasing comprehensive cleaning efficiency by 4.2 times compared to non-robotic methods.
The integrated intelligent robot system, featuring the self-excited oscillation pulsed jet working head and the multi-DOF robotic manipulator, provides an innovative, efficient, and safe solution for cleaning high-risk confined spaces like oil tanks, marking a significant step forward in the automation and intelligence of industrial maintenance.