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Submarine rescue

The history of submarine operation is mixed with tragedy and success but modern navies are going for high quality deep sea rescue technologies to save their fellow sailors who dedicatedly maintain undersea strike capability for their country.

Fourteen years after 118 submariners met a grisly death at the bottom of the ocean in the Kursk, a British team has developed the most advanced underwater rescue system in the world. It is time that runs out quickly if there is an undersea accident.

Thus, timely signal and communication can save many lives. That is why modern navies are investing on rescue missions more than the submarine project.  

During a war exercise recently, a British co-pilot of the rescue vehicle speaks slowly and deliberately into his microphone: ‘Lima, Lima, Lima.’

The signal is broadcast directly into the Mediterranean Sea via underwater telephone using low frequency sound waves.

The message is picked up in the control room of the Alrosa, a Russian submarine from the Black Sea fleet. The code words mean that the NATO rescue vehicle, known as Nemo, has successfully mated, or docked, with the Russian sub.

At the same time a diver clambers through a hatch in the floor of Nemo with a spanner. He follows up the message with two loud taps on the hatch of the submarine casing beneath him, then after a short pause taps a third time.

This is the signal that it is now safe for the Russian crew to open the outer hatch. The two vessels have established a hydrostatic water-tight seal, and suction is now the only thing holding them together 300ft underwater.

All this is happening on the bottom of the Mediterranean Sea just off the coast of Cartagena in south-east Spain. Shortly afterwards the submarine hatch of the diesel submarine opens and a smiling Russian face appears. History has been made.

When it was built during the Cold War, the Kilo-class Alrosa was designed for anti-submarine and anti- ship warfare. Its mission was to snoop, avoid detection, and try to track and, if required, attack NATO forces.

Difficult conditions

Inside the rescue vehicle it is cramped and humid. In the forward compartment, with its bulbous clear acrylic nose on the front, the pilot and co-pilot sit surrounded by joysticks and a myriad of dials and switches.

Behind them, a Navy diver acts as the operator for the rescue chamber, which in an emergency can deliver up to 15 people at a time to the surface, or two injured submariners on stretchers. Yet, any action under sea is a great challenge.

Submarine crew rescue would be difficult when the broken DISSUB (distressed submarine) cabin is in hyperbaric status.

The common submarine rescue systems are the Deep Submergence Rescue Vehicle (DSRV) and the Rescue Bell. But most rescue system cabin internal pressure-bearing is less than 0.6MPa atmosphere absolute (0.6ATA), the hyperbaric rescue depth is limited to 50 meters.

For broken DISSUB rescue, it is a key point to carry out rapid decompression and holding crew habitat in a safe range. At present, the naval ventilation system is only making ventilation and air exchange, allowing considerable margin of error by reason of manual operation mode.

Experts are using hybrid control system to achieve precise control for the whole ventilation and rapid decompression based on a developing Distressed Submarine Ventilation Decompression System (DSVDS).

The decompression course control is more complex, it includes a discrete event dynamic system (DEDS) and a continuous variable dynamic system (CVDS), and related factors of mutual interaction and influence.

The layering model which is based on hybrid control theory divides the whole course into three parts: discrete events, interface and continuous dynamic system.

It was noted that the developing of submarine rescue always has three hard cores: submarine crew survival, escape and rescue.

It depends on two ways: the first is to build a rescue system (DSRV, ROV, and so on) which is supported by the RSV (rescue surface vessel) and air force (transporter, and helicopter) in order to bring forth the systems to the DISSUB.

The second is to research dive physiology, design a new submarine crew survival system and escape apparatus to promote the living capability.

When the disabled submarine crashes to the bottom, the false hull would be broken and flooded in most cases.

To assure crew survival in the damaged cabin, it needs to blow down water using hyperbaric gas in order to prevent flooding even more. Even if crew entered into the intact cabin or finished damage control, it is also kept in a hyperbaric environment in the DISSUB.

Hyperbaric condition

After long stop under hyperbaric condition, crews would meet a hard nut to crack in the course of returning to the surface. The first is the survival problem in the hyperbaric cabin. The second is safety decompression technology which can let crews leave the DISSUB to return to the surface normally.

There are two common hyperbaric rescue methods which are used in the world.The system must keep the same internal pressure with DISSUB and rescue crews.

Only if it returns to the mother-ship, the crew enters into the deck decompression chamber and accomplishes decompression.

This method is safer to crews, and can supply adequate medical care. But it is so strictly that rescue systems have to suffer heavy pressure, need more gas source and energy power.

Since most rescue system cabin internal pressure-bearing is less than 0.6MPa atmosphere absolute (0.6ATA); the hyperbaric rescue depth is limited in 50 meters.

Building a hyperbaric-bearing rescue system, is not achievable overnight. It requires a lot of money, a long building period, complicated supporting equipment, and a large rescue vessel.

After decompression is finished, crews can return to the surface which use single escape equipment themselves or aboard the rescue system.

The rescue systems in most countries do not own the deeper depth hyperbaric rescue ability at the present stage.

So, it is important to develop hyperbaric rapid decompression technology, make crew survival and decompression sickness treatment research, and build new type DSVDS (disable submarine ventilation decompression system).

In recent years, there has been exploration of new ideas and technologies in the hyperbaric rescue field. Through all kinds of experiments, experts are trying to establish safe DISSUB rapid decompression tables.

At the same time, experts put forward a new way to improve the old submarine ventilation system in order to promote rapid decompression ability. They would enlarge ventilation and exhaust pipe size, redesign interface location and piping layout.

The key point is to use a hybrid control system to achieve precise control of the whole DSVDS, making precise, fast and secure implementation of ventilation, decompression, oxygenating, exhaust and gas monitoring.

Therefore, in modeling the system, one must also take into account the discrete and continuous part of the section. Current hybrid control system has more sophisticated and effective methods to solve the common modeling for discrete and continuous part.

One can divide the whole hyperbaric rescue course into seven stages. They can take place separately, and also together.

Using all kinds of sensors and gas analyzers to gather DISSUB cabin environment data, it would be sent to the control decision system to make data fusion, perform analysis and processing.

This stage is on all the way, gathering the environment data real time, and starting or stopping the event.

If CO2 and other toxicity gases are out of the safe range, it is important to firstly make ventilation and oxygenating inside of cabin.

Using all kinds of sensors and gas analyzers to gather DISSUB cabin environment data, it would be sent to the control decision system to make data fusion, perform analysis and processing.

This stage is on all the way, gathering the environment data real time, and starting or stopping the event.

If CO2 and other toxicity gases are out of the safe range, it is important to firstly make ventilation and oxygenating inside of cabin.

Each person’s ventilation rate can not be lower than 60 L/min, and one must always pay attention to the oxygen to do not surpass the maximum pressure limitation.

One should use the special saturation decompression tables to deal with hyperbaric decompression in cabin.

Firstly, cabin pressure decreases rapidly to about 0.1MPa 10 meter to set up the maximum pressure differential. Next, the decompression controller starts to reduce the inner pressure according to the given rate.

During the decompression period, it only can work 16 hours and leave 8 hours to rest every day.

Actual arrangement is 8 hours decompression, 6 hours rest, 8 hours decompression, and 2 hours rest. Besides normal decompression control, the system also monitors the DISSUB environment-any-time.

When pressure decreases to the atmospheric or terminative range, crews can choose proper methods (DSRV, rescue bell, single escape equipment) to leave.

Interfere and coupling can exist in the control course, it can lead to control action default. So, DSVDS must have abilities which can handle these fault events: can do, repeated action; when the repeated action reach preplanned time, turn into emergency phase; when interfere value or some environment variables go beyond anticipation, turn into lost events handling phase.

Failure events handling and emergency phase must switch to manual work in emergency measures, which are aborted lost events, personnel casualty, or awful broken submarine.

However, DISSUB hyperbaric decompression control is troublesome, because of more complicated DISSUB environment.

Different gases not only have own content and pressure but also alter continuously, they would affect crew survival. Environment and pressure variety course are complicated, dynamic, and nonlinear.

Existing interferences which are due to depth, temperature, broken status, and other influence factors, it is difficult to make accurate prediction and precise modeling.

A series of discrete dynamic events exist: ventilation, decompression and oxygen supply. These discrete events are involved with a large number of continuous variables: gases, pressure, temperature, etc.

It is essential that the system must make accurate responses in the correct time. So, the systemic criterion not only has logical time, but also physics.

DSRV technology

NATO’s submarine rescue system is the most advanced in the world and is based in Faslane just north of the Firth of Clyde. Nemo was built in North Yorkshire and Britain is a world leader in this technology.

The system is jointly owned by Britain, France and Norway, and is now managed by Rolls-Royce. The £75 million cost for development,construction and the first ten years of its life is shared three ways.

Nemo can operate in heavy seas, in waves up to 16ft high, and can rescue from depths of 2,000ft beneath the surface. Beyond that, submariners recognise that there is no hope-their boat will simply implode and be blasted into pieces.

This latest ‘free-swimming’ vehicle replaced an earlier LR5 rescue vehicle, the idea for which came to former Royal Navy submariner Roger Chapman after he almost died when he was trapped 1,575ft down in a civilian mini-submarine in 1973.

He and a colleague had been laying a telephone cable in a two-man sub on the bed of the Atlantic, 150 miles off the cost of south-west Ireland. After three and a half days they were found and pulled to safety.

If a submarine is in danger it will release UHF/VHF indicator buoys, which broadcast using reserved maritime frequencies. They can also release buoys linked to satellites which send signals with an ID for the submarine which can only be recognised by its own country’s authorities.

Rescuers can then log on to a password-protected website, which holds details of all the potential rescue systems around the world, and their availability, and they can plan via instant messaging and in secure chat rooms.

But it is once they are alerted that the problems begin: how deep is the stricken submarine, how bad is the damage, what is the state of the sea, how is the submarine positioned, is there debris around it, and how many injuries are there? The Submarine Rescue Diving and Recompression System’s (SRDRS) Rescue Capable System (RCS) replaced the Deep Submergence Rescue Vehicle Mystic (DSRV-1) as the US Navy’s deep-submergence submarine rescue asset.

RSRDS is a rapidly deployable rescue asset that can be delivered by air or ground, installed on pre-screened military or commercial vessels of opportunity (VOO) via a ship interface template, and mated to a distressed submarine within a 72-hour time to first rescue period.

Mystic, a US Navy program, is a small rescue submarine capable of deploying via air or ground to a port where it is mated to a specially-configured submarine which serves as the host platform for the voyage to the disabled submarine.

SRDRS is a three-phased acquisition program that delivers advanced submarine rescue and treatment assets to the fleet. The first phase of the program was the Atmospheric Dive System 2000 (ADS2000) which was delivered to the Navy in 2006.

ADS2000 is a manned, one-atmosphere dive suit capable of inspecting disabled submarines and clearing debris from escape hatches. The RCS constitutes SRDRS’ second phase.

The final phase of the SRDRS program is the Submarine Decompression System (SDS), which was delivered in late 2012. SDS allows rescued submariners to remain under pressure during the transfer from the PRM to hyperbaric treatment chambers aboard the VOO.

Unlike Mystic, which could only be transported to the disabled submarine via modified submarines, SRDRS is a fly-away system that can quickly and easily be mobilized via large military or civilian transport aircraft and installed aboard a variety of VOOs within hours of notification of a submarine in distress.

In recent years, the demand for unmanned vehicles is rapidly increasing not only in the field of military use but also in disaster relief, industry and agriculture field.

Going unmanned

Factors behind this include the fact that unmanned vehicles can conduct missions that are not suitable for human beings called 3D (Dangerous, Dirty, Dull), such as dangerous missions conducted in the airspace of the area occupied by the enemy, missions in the area contaminated by chemical substances and radiation, and dull missions such as long hours monitoring and surveillance.

In addition, they are more cost-effective than manned vehicles for the following reasons: space and equipment for crew such as cockpit is not required; there is no need to secure the safety of the pilot; and it is possible to reduce the size.

One of the unmanned vehicles for military use is an unmanned aerial vehicle (UAV), which was initially used for aerial targets in training and reconnaissance purposes, and has been developed to a multi-purpose vehicle to conduct various missions and a vehicle for attack.

Recently developed UAV include stealth type, carrier-based type, and ones equipped with supersonic flight capability.

Other unmanned vehicles include Unmanned Ground Vehicle (UGV), Unmanned Maritime Vehicle (UMV), Unmanned Surface Vehicle (USV), and Unmanned Undersea Vehicle (UUV), whose usage has been expanding in land and maritime missions. These vehicles are developed and used for the same purpose as UAV.

On the other hand, due to their characteristics, the utility of unmanned vehicles are widely recognized in many countries and it is expected that development and introduction of unmanned vehicles will be further promoted, instead of manned vehicles.

Therefore, use of ROVs and AUVs have also gained significance for submarine and underwater rescue operations.

In fact, Falcon, another DSRV program, can conduct rescue operations to a depth of 2,000 feet, can mate to a disabled submarine at a list and trim of up to 45 degrees, and can transfer up to 16 personnel at a time.

Mystic required its own power source-necessitating a two-hour battery charge between cycles. Because SRDRS-RCS receives its power from a VOO via an umbilical, it can operate around the clock without pause.

Oceanic space-docking plays an important role in underwater vehicle technology for applications of deep submarine rescue and sub-sea space station. Reliable dynamic positioning (DP) is essential for operation of underwater vehicle docking in badly situation.

In order to realize automatic docking process, the hybrid control system based on 6-DOF DP is designed. The bottom of the hybrid control system is different control functions to control 6-DOF motions of the vehicle.

The middle is conversion interface to generate events according to system states and produce control rules. The upper is operation machinery of discrete event to analyze events and guide the docking process.

Taking notice of oceanic space-docking plays an important role in underwater vehicle technology, more and more research are being developed in the worldwide.

A new DSRV (Deep Submergence Rescue Vehicle) for automatic mating simulated tester that has been developed mainly solves the automatic mating problem of wreck submarine with a large incline in a poor sea state.

It is being described an automatic dynamic positioning system for ROVs (DPSROV) that is based on a mechanical passive arm (PA) measurement system.

This addresses the problem of dynamic positioning of under actuated autonomous underwater vehicles (AUVs) in the presence of constant unknown ocean currents and parametric modeling uncertainty.

The automatic docking system of underwater vehicle is equipped with some measure instruments, control system and actuating system, to sample the required information in real-time accurately, so that the controller can calculate the required thrust force to approach the disable submarine and realize the dynamical positioning and mating mission.

The measurement system is composed of an orientation sensor, depth sensors, guiding sonar out skirt, positioning sonar in skirt, altimetry sensor, displacement measuring device and water leakage detector for the electronic cabin.

Two depth sensors are used and it is redundant to the altimetry sonar, which not only increases the accuracy of the measurement system but also guaranteed the experimental security in the limited depth of the tank.

The control system includes the 6-DOF dynamic positioning control system, the submarine communication subsystem, the displacement measuring device and localization altimetry sonar measurement system.

Propellers and actuators consist of five electrical propellers, frequency converter gear, and longitudinal and transverse adjusting mechanism.

The skirt and shock mitigation system allows the vehicle to mate with the docking seat on the submarine rescue/escape trunk. The skirt allows a watertight seal to be made between the DSRV and the submarine. After a seal is made, the submarine upper access hatch can be opened and swung up into the skirt cavity.

The skirt looks like a frustum of a cone which is reduced to the scale of 1:2 compared to the actual docking skirt. There are three inner positioning sonars on the wall of the lower cavity room, which are well distributed over the skirt as 120 degrees array.

Four pairs of depth sonar are well distributed and stagger the inner positioning sonar shifts. There are brackets in the outer side of the skirt wall, which used for the installment of the outer positioning sonar. In the hemline of the mating skirt, eight touched sensors are installed, which used to measure the contract situation between the skirt department and docking seat in real-time.

Hybrid control

Hybrid control system (HS) is a uniform dynamic system combined with Continuous Variable Dynamic System (CVDS) and Discrete Event System (DES).

While continuous variable dynamic system control is designed to get the control ratio to make the performance specification minimize under given control region. There are three layers in the hybrid control system.

The bottom is composed of two parts: real vehicle and controller. For automatic docking of the vehicle, controller includes roll adjustor, pitch adjustor, vertical controller, horizontal controller and heading controller.

In the vehicle, it is equipped with extractors and measurement system introduced above.

The middle is conversion interface; it is composed of event generator and extractor.

Event generator is mainly used to judge the system state based on signal which measured from bottom. Extractor produces control rule to decide which controller should work and how to work.

The upper is the operation machinery of discrete event; it is composed of event analysis and control decision.

Event analysis is used to judge whether the vehicle can meet with the mating conditions or not, namely whether every state error exceed usual data or not. If exceeding, control decision will decide correlative mode and send control signal.

The vehicle movement in sea is continuous which state space is divided into limited regions, every region is the relative position and posture between mating skirt and docking seat.

When coordinating with skirt and seat, the region may be entered easily for vehicle. The movement of vehicle is driven by thrusters and longitudinal and transverse adjusting mechanism, while their control actions become events, as well as failure actions coursed by disturber.

Vehicle hangs over the disable submarine, if it enters a region which planning in advance, a signal will generate. DES controller receives this signal and sends the control instruction.

Every control module will translate the continuous action and adjust its movement. After successful mating, DES controller generates signal to seal between the vehicle and the docking plane.