UUV Hydraulic Circulation Control for Cold-Water Viscosity Stability
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Solution Overview
Problem
Hydraulic systems in unmanned underwater vehicles face challenges in deep water conditions due to thickening of hydraulic fluid at low temperatures, leading to operational issues such as current spikes and reduced flow efficiency, for which existing solutions like low viscosity fluids or electrical heating are inefficient or impractical.
Innovation Solution
A temperature-controlled hydraulic system that uses a controller to manage the flow of hydraulic fluid through a hydraulic circuit, activating circulation below a minimum temperature to prevent cooling and deactivating above a maximum temperature to prevent overheating, utilizing a flow restrictor for friction-based heating and maintaining fluid circulation without actuating tools, thus maintaining fluid viscosity and preventing stagnation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hydraulic fluid is used in cold deep water conditions, then power transmission is convenient without electrical connections, but the fluid becomes thick and difficult to move through the hydraulic circuit
Solution Approach 1:
The system performs preliminary action by activating the pump to circulate hydraulic fluid before tools are actuated or during periods of inactivity. This prevents the fluid from becoming stagnant and thickening due to cold temperatures, ensuring reliable operation when tools are needed. The controller monitors temperature and activates circulation in advance to maintain fluid readiness.
Solution Approach 2:
The hydraulic pump operates continuously or periodically to maintain fluid circulation through the hydraulic circuit, preventing stagnation and temperature-related thickening. This continuous useful action ensures the fluid remains mobile and ready for tool operation, resolving the contradiction between operational convenience and flow reliability in cold conditions.
2Reliability
If low viscosity hydraulic fluid is used to alleviate thickening in cold surroundings, then fluid flow improves, but operation at relatively high temperature conditions is affected
Solution Approach 1:
The system changes the parameter of fluid viscosity dynamically by controlling fluid temperature through circulation. Rather than selecting a fixed low-viscosity fluid that compromises high-temperature performance, the system maintains the fluid in its optimal viscosity range by active circulation and temperature management, allowing the use of higher-quality fluids designed for broader temperature ranges.
Solution Approach 2:
The controller monitors hydraulic fluid temperature and uses feedback to regulate pump operation. When temperature drops and viscosity increases, the controller activates circulation to warm the fluid. This feedback mechanism ensures the fluid maintains appropriate viscosity for reliable operation across varying temperatures without requiring low-viscosity fluid that would compromise high-temperature performance.
3Reliability
If electrical heating is used to warm hydraulic fluid in cold conditions, then fluid viscosity is reduced, but power consumption increases and failure risk increases
Solution Approach 1:
The system replaces the electrical heating mechanism with a mechanical circulation system. The hydraulic pump circulates fluid through the circuit, using mechanical energy from the vehicle's existing hydraulic power source rather than electrical heating elements. This substitution reduces power consumption and eliminates the risk of electrical failures while maintaining fluid temperature through continuous movement and friction-based heating.
Solution Approach 2:
The hydraulic system serves itself by using its own pump and circulation infrastructure to warm and maintain fluid temperature. Rather than adding a separate electrical heating system that consumes additional power, the existing hydraulic pump performs the dual function of tool actuation and fluid temperature maintenance, reducing overall power requirements and leveraging the system's own resources.
4Reliability
If hydraulic valves are controlled to maintain fluid circulation in cold conditions, then fluid temperature is maintained, but power consumption increases
Solution Approach 1:
Instead of continuous pump operation, the system uses periodic action by activating the pump at intervals or in response to temperature thresholds. The controller monitors fluid temperature and activates circulation only when needed to prevent thickening, allowing the system to maintain reliability while minimizing energy consumption during periods when the fluid is already at appropriate temperature.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively maintains hydraulic fluid temperature and flow efficiency in deep water conditions, preventing thickening and current spikes, and reducing power consumption by using friction heating and controlled circulation, allowing normal viscosity fluids to be used without the need for low viscosity oils or electrical heating.
Implementation Method 1
A hydraulic system uses a pressurized hydraulic fluid, e.g. oil, to power hydraulic tools. The hydraulic system typically comprises a hydraulic pump driven by a motor to pressurize the hydraulic fluid.
Implementation Method 2
utilizing a flow restrictor for friction-based heating
Data Source
Figure 1
Figure 2
AI summary
An unmanned underwater vehicle (UUV) with a hydraulic system (100) for use in cold surroundings and method of controlling such hydraulic system. The hydraulic system (100) comprises a hydraulic circuit (10). One or more tools (21,22) may be hydraulically operable via the hydraulic circuit (10). A pump (32) is configured to pressurize a flow of hydraulic fluid (F) via the hydraulic circuit (10) e.g. for actuating the tools (21,22). A valve system (40) comprises control valves (41,42,43) disposed in the hydraulic circuit (10) for controlling the flow of hydraulic fluid (F) through the hydraulic circuit (10). A controller (50) is configured to control one or more of the control valves (43) as a function of a temperature (T) of the hydraulic fluid (F).