The Challenges of Engineering Design for the Marine Space
A tremendous amount of design effort goes into buildings, bridges, roads, airports, and other terrestrial structures. But what about the marine space? Oceans account for over 70% of the Earth's surface but water-based designs are often overlooked when people are discussing the most impressive engineering projects. This could be because projects in the marine space require unique expertise to ensure successful designs.
Marine engineers must understand how structures will be configured both at the surface and underwater, as well as what they'll encounter once they're submerged - whether it's waves, currents,, or corrosion-inducing saltwater. But every project poses different problems, so there is no single solution for building anything in any body of water.
Designing for marine space covers six major disciplines:
1.) Seawater engineering
2.) Structural design (foundations)
3.) Mechanical systems (thermal & hydro-engineering)
4.) Marine construction (marine-based and onsite construction control)
5.) Construction materials (marine corrosion)
6.) Environmental impacts (law enforcement and regulations)
The challenges of dealing with these areas in a single project can result in costly delays. So it's crucial to understand how each one affects the others and plan for them accordingly.
When engineers design structures that will exist in or cross over any body of water, they need to know what to expect from the environment where their structures will be placed. They also need to know the best way to build in this environment: whether it's out at sea in an open yard or barge; in a freshwater lake; or in a marine environment from an inland river, to the open sea or coastal waters.
The Main Challenges of Working on Marine Engineering Projects
Some of the environmental factors that engineers should consider when designing marine projects include:
Water Temperature and Thermal Expansion
Seawater temperature varies around the world but is usually colder than freshwater because saltwater has a higher density. The temperature differential between seawater at depth and the surface creates convective currents which are directional, so they must be accounted for in engineering design.
Saltwater's high ionic content also conducts electricity, so engineers designing power transmission grids or other electrical systems need to be aware of this.
Salinity and Corrosion
Salt in seawater is corrosive, especially for metals. Differences in salinity also cause different water densities which can affect currents and vessel stability.
Wave Action & Sediment Transport
Winds generate waves, whose shape and direction depend on the depth of the water and its temperature, as well as how it interacts with the ground underneath it.
Winds blowing over a surface can also create currents. Since 95% of the Earth is covered in water, winds and atmospheric pressure constantly interact with it to cause changes in current and wave patterns around the world.
Pressure increases with depth (1 atmosphere every 10 meters). This causes compression in objects submerged below the sea level and tension in those above it. Seawater density changes with temperature, salinity and pressure; these factors will affect how much stress the structure will have to endure.
Hydrostatic pressure increases with depth, so it's essential that engineers account for this when building structures. This is why oil rigs are built on legs that can extend thousands of feet below sea level - to ensure they stay grounded even under high water pressure.
Though technically not currents, tides are constantly changing ocean water levels. They can be diurnal (daily) or semidiurnal (twice daily). Tides always affect the region where engineering projects are built, so they must be taken into account when designing for marine environments.
Tidal forces act on every shoreline in the world; this affects both aquatic and coastal projects.
Density and Weight
Marine structures must be lightweight or they won't float well. But unlike aircraft, marine structures also have to be tough enough to withstand harsh waves and water pressure. They must also be resistant to the corrosive effects of seawater and resist damage from ship anchors or collisions with other vessels.
The weight and volume of a structure affects its buoyancy: an object displaces (or takes up) as much water as its own volume. If it's too light, it floats; if it's too heavy for its size, it will sink.
Typically, it's easier to design a structure that floats than one that's designed not to sink - but the opposite may be preferable for some projects if they need to withstand high water pressure or resist additional downward force from currents and waves.
Large bodies of water on or near the surface have 2 forces acting on them: gravity and buoyancy. But the buoyancy is actually pushing in the opposite direction of gravity, so these forces are constantly trying to tip or flip large bodies of water over.
This causes "hyperbolic instability" because large bodies of water naturally form an oblong shape when they tip over, like a football.
This affects the engineering design of large ships, as well as oil and gas extractions.
Many coastal engineering projects have environmental restrictions that must be taken into account. These can include fishing grounds, wildlife habitats, and protecting endangered species. Engineers also need to consider petroleum storage facilities, which require special consideration in the event of a leak or spill.
Prior to building in the marine environment, engineers must understand these factors in order to plan, design and build projects that are not only functional but also safe.
Ice Forces & Brine Flotation (Ice Shedding)
Marine construction also follows a unique structure progression. Planning begins with a navigation plan, which includes site selection, anchoring, mooring plans for barge/ship-based work, cofferdams, and scuttling techniques for dropping below the waterline. The size of floating vessels must be carefully considered when choosing a site.
Because the water is much deeper than it looks, objects fall much faster due to buoyancy when submerged. This results in much more force on structures and equipment from sinking debris. Debris also may have sharp edges that can damage propellers and other underwater components.
Once objects are assembled above the waterline, they still need to be stabilized with tension wire struts or heavy rigging before being submerged into their final positions - especially for larger vessels that will take longer to sink completely below the surface.
The workspace also needs to take marine conditions into account: navigation plans must allow room for large freighters and tankers, currents should be taken into consideration during construction, and vessels cannot leave until all debris from the installation has been cleared.
Navigation plans must also include safe work zones or "hot work" where welding or other activity can take place without the risk of igniting gas tanks, oil spills or other environmental hazards.
Tidal changes force seabed materials to move and change position. When drilling, these forces can pull casing out of place or damage components on the seabed.
Also, offshore structures must be designed with ice forces in mind so they won't be tipped or damaged by large moving sheets of ice.
The weight of anchor cables is important for preventing large ships from being pulled out to sea during high winds. These are all factors that affect the engineering design of marine structures.
Even small vessels used on river work sites need to be prepared for weather conditions caused by hydrostatic pressure on waterways under higher atmospheric pressure. Working on large marine projects requires extensive planning and preparation so workers can safely build and install structures in a way that reduces risk while meeting project goals.
Advantages of Working on Marine Projects
However, there are advantages to working on marine projects. These include deep space, long-term jobs with less fieldwork required during installation, and the opportunity to work in multiple locations for oil or gas companies.
Many engineering firms specialize in marine projects because they offer more money than typical civil engineering jobs - which is helpful to young engineers trying to pay off their student loans.
Engineers also enjoy extra hours at sea because it is far less crowded than an office environment and the views are spectacular. The challenges of marine projects may outweigh these advantages, but it's still good to have some things to look forward to if you decide to take on a marine-based job.
In conclusion, working on marine projects requires extensive planning and consideration of forces such as buoyancy, ice shedding, torque from brine/ice floes, and environmental impact. These factors can affect cutting and welding processes, damage underwater components, and cause equipment to be unstable both while it is being transported and while it is in place.
Engineers who work on marine projects must plan carefully for the powerful forces at work in this challenging space - if they don't, there could be consequences such as injury or loss of project goals.