First, on that note, National Geographic made an interesting CGI on how the Titanic sank:

At the time of her construction, the Titanic was the largest ship ever built. It was 230m long, 25 stories high, and weighed 46,000,000 kg. The ship’s turn-of-the-century design and technology included sixteen major watertight compartments in her lower section that could easily be sealed off in the event of a punctured hull and hence deemed her unsinkable.

On the night of April 14th, although the wireless operators had received several ice warnings from other ships in the area, the Titanic continued to rush through the darkness at nearly full steam. Unfortunately, by the time the lookouts spotted the massive iceberg, it was only less than a quarter of a mile off the bow (or front) of the ship, making the crash into the iceberg unavoidable.

Imagine trying to suddenly avoid a head-on collision in a car; that sounds hard, right? The Titanic was about 20,000 times heavier and had the full momentum of all that weight driving it forward. Though the engines were immediately thrown into reverse and the rudder turned hard left, slowing and turning took an incredible distance because of the tremendous weight (or mass) of the ship. Without enough distance to alter her course, the Titanic sideswiped the iceberg, damaging nearly 100 meters of the right side of the hull above and below the waterline [1].

The massive side impact caused enough damage to allow water to flood into six of the sixteen major watertight compartments. As water rushed into the starboard side of the ship’s bow, the ship began to tilt down in front and slightly to the right. However, the back (or stern) of the ship had three large and heavy propellers. Just like a lever, as shown in Figure 2, if the board is not strong enough when one side becomes extremely heavy, and the other end is pushed down—the board breaks.

This is almost exactly what happened on the Titanic, too. The front of the ship started to go into the water, leading to the lifting of the stern of the ship out of it. When the ship was almost at 45 degrees, the stresses in the ship’s midsection increased beyond the material limits of steel (210 MPa). The Titanic almost split wide open in the middle! This is how the Titanic sank. [1]

Discover the benefits of cloud-based CFD simulation with SimScale, in this features overview download.

Exploring the Titanic Why Did the Titanic Sink?

While we have had a glimpse as to what caused the ship to start sinking, was that the only reason? What are the scientific theories that have emerged on why the Titanic sank?

One of the first major scientific insights into the sinking of the Titanic was obtained after a 1991 expedition, called the Imax, to the Titanic wreck. This expedition and the research that followed opened numerous discussions that led to the uncovering of clues on why the Titanic sank. Surprisingly, one of the major discoveries of this expedition included chunks of metal that were once a part of the Titanic’s hull. These Frisbee-sized pieces of steel were about one inch thick with three rivet holes, each one 1.25 inches in diameter [1].

So why did the Titanic sink? As shown in Figure 3, the ship is believed to have sunk due to multiple contributing factors.

Titanic Analysis Evidence and Analysis of Why the Titanic Sank

Failure Due to Impact on Hull

One of the key pieces in reconstructing the theory of why the Titanic sank included the pieces of steel that were recovered. Let’s see how some pieces of steel helped answer the question “Why did the Titanic sink?”

Most engineers would have done uniaxial tests during their laboratory sessions. Here a specimen, shaped like a dog bone, is pulled to understand how the material changes shape (or deforms) for the applied load. This is continued until the specimen breaks into two pieces. While materials like aluminum undergo ductile fracture, others like cast iron show no yielding and are brittle. For more information on the brittle-ductile–yield criterion, please read the article “What is the meaning of von Mises stress and yield condition?”

In spite of the captain of the ship trying his best to slow down, the huge mass and momentum meant that the Titanic was still moving at a powerful speed when it impacted the iceberg. This high-speed impact was the start of the disaster. When the Titanic collided with the iceberg, the hull steel and wrought iron rivets failed, due to “brittle fracture”.

Most often, for many commonly used structural materials, impact at extremely high speeds results in brittle fracture without any yielding (or plastic deformation). This is a type of catastrophic failure in structural materials, the causes of which include low temperature, high-impact loading, and high sulfur content.

You guessed it right! On the night of the Titanic disaster, all three factors were present. The water temperature was below freezing, the Titanic was traveling at a high speed on impact with the iceberg, and the hull steel contained high levels of sulfur. It is here where the chunk of iron discovered during the expedition played a major role in providing the hint that the brittle fracture of the hull steel contributed to the disaster. The condition of the edges of the recovered piece of steel was noted to be jagged, almost shattered (like broken china), and sharp upon cleaning it. This brittle fracture of hull steel is probably what the survivors of the disaster then described as a loud noise that sounded like breaking china. Today, typical high-quality ship steel is more ductile and deforms rather than breaks [1]. Astonishingly, scientists discovered that the metal pieces showed no evidence of bending or deformation, they simply shattered! This is one of the main answers to the question “Why did the Titanic sink?”

Laboratory Testing of Hull Materials

In order to confirm this hypothesis on why the Titanic sank, scientists subjected a cigarette-sized specimen/coupon from the pieces to the Charpy test. This is a highly popular test to measure the brittleness of a material. It is run by holding the specimen against a steel backing and striking it with a 30-kg pendulum with a 0.75-meter-long arm. The pendulum’s point of contact is instrumented, with a readout of forces electronically recorded in millisecond detail.

A piece of modern, high-quality steel was tested along with the coupon from the hull steel. Both coupons were placed in a bath of alcohol at -1°C to simulate the conditions on the night of the Titanic disaster. When the coupon of the modern steel was tested, the pendulum swung down and halted with a thud; the test piece had bent into a “V”. However, when the coupon of the Titanic steel was tested, the pendulum struck the coupon with a sharp “ping”, barely slowed, and continued upon its swing; the sample, broken into two pieces, sailed across the room [1].

The pictures above show the two coupons following the Charpy test confirming the brittleness of the Titanic’s hull steel. When the Titanic struck the iceberg, the hull plates did not deform, as they should have. Instead, they fractured! This leaves us wondering if the designers anticipated this fracture, and it contributes to the reasons why the Titanic sank.

Did Chemistry Have an Effect?

In the search for answers to the question “Why did the Titanic sink?”, the steel from the Titanic was further analyzed for chemical components and was found to contain high levels of both oxygen and sulfur, which implied that the steel was semi-kilned, low-carbon steel, made using the open-hearth process. If one had a powerful microscope to zoom in on the dimensions of order or micrometers, you would see that steel shows a grain structure, as shown in Figure 5.

High sulfur content disrupts the grain structure of steel, leading to an increase in its brittleness. When sulfur combines with magnesium in the steel, it forms stringers of magnesium sulfide which act as “highways” for crack propagation. Although most of the steel used for shipbuilding in the early 1900s had a relatively high sulfur content, the Titanic’s steel was particularly high, even for those times [3].

While the material is normally quite ductile, the addition of oxygen causes the material to transition from ductile to brittle in nature. This proved the plausibility of brittle fracture of the hull steel. It is a known fact that high oxygen content in steel leads to an increased ductile-to-brittle transition temperature, which was determined as 25°C to 35°C for the Titanic steel. Most modern steels would need to be chilled below -60°C before they exhibited similar behavior.

Further Design Flaws

Material flaws were not the only factors that led to the sinking of the Titanic and hence are not the complete answer to the question “Why did the Titanic sink?” The design of the ship was not nearly good enough to deem it an unsinkable ship. The watertight compartments in the ship’s lower section were not exactly watertight, in any sense. The lower section of the Titanic was divided into sixteen major watertight compartments that could easily be sealed off if part of the hull was punctured and leaking water. These watertight compartments, which made the ship designers claim that the ship was unsinkable, were only watertight horizontally.

The tops of these compartments were open, and the walls extended only a few feet above the waterline [3]. In order to contain water within the damaged compartments, it was imperative that the walls of the watertight compartments positioned across the width of the ship be a few feet taller. Although this is not the reason why the Titanic sank, without this design flaw it would have slowed down the sinking process, possibly allowing enough time for nearby ships to help.

The collision with the iceberg damaged the hull portion of six of these sixteen compartments, and the compartments were immediately sealed. But as the water filled these compartments, the ship began to pitch forward from the weight of the water in this area of the ship, and the compartments began to spill over into adjacent compartments due to the horizontal watertight nature. The bow compartments were extensively flooded, and subsequently, the entire ship was flooded, causing the Titanic to be rapidly pulled below the waterline.

The watertight compartments, rather than countering the damage done by the collision with the iceberg, contributed towards accelerating the disaster by keeping the flood waters in the bow of the ship. Without the compartments, the Titanic would have remained horizontal as the incoming water would have spread out. Eventually, even in this case, the ship would have sunk, but she would have remained afloat for a few more hours before capsizing [1]. Scientists maintain that this amount of time would have been sufficient for nearby ships to reach the Titanic’s location and all of her passengers and crew could have been saved.

What Could Have Been Done Better?

The Titanic disaster serves as a perfect example of how engineering flaws can have catastrophic effects. Analyzing the answers to the question “Why did the Titanic sink” takes us to the conclusion that had the design of the ship and the materials chosen been better, the disaster could have been easily warded off.

If the ship had double bottoms, constructed by taking two layers of steel that span the length of the ship and separating them by five feet of space, extending up the sides of the hull, the bottom plate of the hull would have been punctured without damage incurred to the top plate. With a double bottom, the chance that a punctured hull would allow water into the watertight compartments is minimized.

By extending the double bottoms up the sides of the hull, the watertight compartments could remain undamaged. The addition of a layer of steel to the sides of the ship ensures that in the event of an iceberg or a collision with another ship, only the space between the inner and outer sidewalls would flood with water, barely puncturing the hull. Also, if the transverse bulkheads of the watertight compartments were raised, the spilling of water over the tops of the bulkheads into adjacent, undamaged compartments could have been avoided, as the ship pitched forward under the weight of the water in the bow compartments.

Here it is, an engineer’s analysis of why the Titanic sank. Although it is important to understand the errors of the past, it is crucial to make sure they are not repeated in the future. A proper design process can prevent such catastrophes.

If you’d like to read more on this topic, here are other articles that also talk about why the Titanic sank:

• Why did the Titanic sink? by Science Illustrated
• The secret of how the Titanic sank by US News

There are many more out there that answer the question “Why did the Titanic sink?”

Using Modern Tools of FEA and CFD for Ship Design

Today, with advanced tools at hand, you can use CFD and FEA simulations to virtually test a ship’s design to make sure such catastrophes don’t happen in the future.

If you want to explore further the reasons why the Titanic sank, you can use the SimScale cloud-based simulation platform to analyze the stresses on the ship’s hull due to the water, for example. This CAD model of the Titanic is already uploaded to the platform and you can just copy the project and set up a simulation. To discover all the features provided by the SimScale cloud-based simulation platform, download this overview.

To learn how to run simulations with SimScale, you can watch the recording of the first session of the CFD Master Class. Just fill out this short form, and it will play automatically.

The post Why Did the Titanic Sink? An Engineer’s Analysis appeared first on SimScale.

What happened on that fateful day of August 10th? Was it expected? Why did the Vasa ship sink? Let’s dive deeper into the heart of the mystery. Several videos analyzing the Vasa ship can be found on YouTube. Here is a particularly brief yet interesting one:

As we go ahead, we will need to understand the terminologies related to shipbuilding. Hence, defining some terms visually could be the best solution.

1. Mainsail
2. Staysail
3. Spinnaker
4. Hull
5. Keel
6. Rudder
7. Skeg
8. Spar
9. Spreader
10. Shroud (sailing)
11. Sheet
12. Boom
13. Mast
14. Spinnaker pole
15. Backstay
16. Forestay
17. Boom vang

The Vasa Ship The Building of the Vasa Warship

We can never get the full story without first understanding the events that unfolded relating to the building of the ship and the historical time in which it was built. It was on the 16th of January, 1625, that King Gustav II Adolph of Sweden directed Admiral Fleming to sign a contract with the shipbuilders of Stockholm (Hendrik and Arend Hybertsson) to build four ships. Two smaller ships (108-ft keel length) and two bigger ships (135-ft keel length) were to be built over the course of four years. In the months that followed, King Gustav changed his orders several times, leading to total chaos and confusion for the builders.

The Swedish Navy lost ten ships on the 10th of September 1625, which led the king to order that the two smaller ships be built on an accelerated schedule to compensate for those they had lost. One can’t blame him, as those were the days when various parts of the world were colonized, and naval forces meant strength. These were meant to be two small ships (111-ft and 135-ft ships). Please note that the dimensions stated relate to the keel length unless explicitly specified otherwise.

On one front, the construction of the 111-ft ship with a single gun deck began. Simultaneously, on the other, the king received news that the Danish were building a ship with two gun decks. How did the king react to this one-upmanship? If you know anything about the egos of kings and dictators, you will have guessed it right. He immediately ordered Admiral Fleming to build a 135-ft ship with two gun decks. Until then, no one in Sweden had ever built a ship with two decks. This development from one- to two-deck warships marked a significant change in Naval architecture between 1600–1700.

While the original Vasa was a traditional architecture that was commonly used in shipbuilding, it is believed that it is likely that no specifications, crude designs, or plans were made. Hybertsson was an experienced shipbuilder and would likely have taken it on as another standard, traditional job. However, once the circumstances changed, no modified plans were found for the larger, more complex version of the Vasa. Under time pressure, it is believed that Henrik Hybertsson just “scaled up” the dimensions of the original 108-ft ship to meet the length and breadth of the new 135-ft Vasa. Since this was totally unplanned, the width of the upper parts of the ship was wider than originally planned by one foot and five inches. At this point, the Vasa ship was becoming much wider at the top than the bottom. The ship’s center of gravity was much higher than designed.

At this point, you must already be sensing the impending disaster and wondering how everyone else failed to notice. Time can be a funny thing! The Vasa ship was a disaster waiting to happen. Additionally, it did not help that the primary designer, Henrik Hybertsson, fell ill and died in 1627, almost one year before the Vasa was completed.

The plans were undocumented, there were no detailed specifications, and five different teams were working on the hull without any intercommunication! This was one of the biggest projects in Sweden at that time, and it was a total disaster just waiting to happen.

Vasa Ship Was the Vasa Ship Tested?

While the Vasa ship already seemed unstable at the harbor, at this point in history, there were no known methods to measure the stability, center of gravity, or heeling (or toppling) characteristics. Most captains simply used trial and error to understand the best operational characteristics.

Admiral Fleming and Captain Hannson (Vasa’s captain) ran a test with 30 men running side-to-side (a “lurch” test). After three rounds by the men, the test was stopped at the ship rocked so violently that it was feared that it would heel. However, no one had any ideas to help stabilize the ship. While additional weight below the floorboard would have been one option, there was barely any floor space. In addition, the Vasa had 120 tons—almost twice what was needed to stabilize, and if any more were to be added, this would have sent the lower deck gun portals to the waterline of the ship.

Even knowing that the ship had stability issues, it was given the go-ahead, which was the result of three factors:

1. Pressure from King Gustav,
2. The king of Poland had started a war campaign, and;
3. No one knew what else to do.

The Vasa Ship Disaster The Dreadful Day for Vasa

The Vasa ship was one of the costliest projects of the time, with hundreds of ornate, gilded, and painted carvings depicting biblical, mythical, and historical themes. It was meant to be the most impressive ship, and no cost was spared. However, all these extra features only further raised the ship’s center of gravity!

On the 11th of August 1628, the Vasa left Stockholm harbor. It barely made it two nautical miles when it was faced with a wind gust of eight knots. The wind was so light that the sails were extended by hand and just one person was sufficient to hold the sheets out. Even with such a light wind, the ship heeled (toppled) on its side, water filled the ship through its gun portals, and it eventually sank in the harbor, taking 53 lives with it. The captain of the ship survived the incident and was immediately jailed for incompetence. However, a formal hearing was conducted in September of the same year, and the captain and crew were set free, and the charges of incompetence were dropped. However, no exact reason was determined.

Vasa Ship Learning Restoration and Lessons from Vasa

The ship had sunk in the shallow waters of the Baltic sea, and due to the salinity of the water, the wooden vessel survived infestation and degradation. Exactly 333 years later, it was pulled up to the surface of the harbor. After the water and mud were pumped out, and the gun portals sealed, the Vasa ship floated. Today, it stands in a separate museum of its own—Vasa Museum.

The factors that contributed to the failure of the Vasa ship were plentiful but can be summarized in 4 main reasons:

1. Unreasonable time pressure
2. Changing specifications and lack of documentation or project plan
3. Over-engineering and innovation
4. Lack of scientific methods and reasoning

As evident, one of the primary scientific reasons can be attributed to a lack of stability due to the ship’s raised center of gravity. Without the existence of proper tools for the design and testing phase, building Europe’s mightiest warship and preventing foundering was even harder.

Three centuries later, we have access to all of these tools, but design mistakes are still being made. Engineering simulation software is not always integrated into the design process, mostly due to high costs and lack of specialized training. With the SimScale cloud-based platform, however, engineers working in shipbuilding and boat design can use CFD and FEA simulation via a standard web browser and from any computer. As for the training, there are hundreds of free learning materials available online. An on-demand webinar about multiphase flow is a good start. Just fill out this form and watch it for free.

The post Why The Swedish Vasa Ship Sank appeared first on SimScale.

A fender can be defined as a bumper that absorbs kinetic energy during contact between a berthing vessel and the harbor jetty. Fenders are used to protect vessels and jetties from destruction during parking in the harbor and are produced from rubber or other elastomers. The main function of the rubber fender is to effectively absorb the kinetic energy and lower reaction force.

The main goal of the project presented in this article was to perform a structural analysis with SimScale to check the contact between the rubber fender and a yacht hull. The vessel has a speed of 1,5m/s and pushes against the fender connected to the jetty.

Simulation Steps

The geometry of the model was created with CAD software and imported into the SimScale CAE platform, where the meshing and definition of the model and material properties were done. This was performed easily as SimScale supports several geometry formats: STEP, IGES, BREP, STL.

Besides the user-friendly interface which makes the simulation process faster, the documentation and public projects library definitely help with answering questions and learning. Experience with other commercial software enables a very smooth adaptation to SimScale.

SimScale divides the analysis into three parts: mesh generator, simulation designer, and post-processor:

1. Mesh generator – the user uploads the CAD design ready to be meshed
2. Simulation designer – the user chooses the solver and analysis type, defines the domain and contact type, and chooses contact areas. This step allows the definition of the material and assigns it to the geometry. The basic information used in the simulation such as boundary conditions and initial conditions are defined in this part. After this, the user runs the analysis.
3. Post-processor – in the last step, the user is able to review the completed analysis and plot the required results. It is possible to plot the solver information such as the number of iterations and residuals. SimScale allows plotting simulation fields such as displacement and stress fields.

SimScale’s CEO David Heiny tests the capabilities of the platform to solve a real-life engineering problem. Fill in the form and watch this free webinar to learn more!

Watch Webinar

Structural Analysis of the Fender

The model was built from three parts: part of the vessel(1), fender(2), and jetty(3).

For this situation, some analytical calculations should be performed in order to select the type of fender. Below are the analytical calculations of the fender with a picture of the vessel used for calculations.

The first step in the structural analysis is to find the stiffness of the fender and its energy absorption. For this, it is necessary to analyze it with a load of 1N. Thereafter the fender’s deflection needs to be checked, which is shown in the picture below.

The stiffness of the fender can be calculated as follows:

A contact analysis between the fender and vessel was done as well:

For numerical calculations, it is necessary to make some assumptions. Because only a part of the vessel is modeled, the density of the material needs to be changed to keep a correct mass of the structure.

The next step is meshing the structure. For model discretization, 3D elements were used. The meshed model can be seen below:

The model was built from three elements and in this case, it is necessary to use contact definition for the connected parts. Contact between fender and jetty is defined as a bonded contact. The connection between vessel and fender is defined as a physical connection with no friction.

The model was created with three types of material: fender – rubber, jetty – concrete, and vessel – steel (density 7,81 t/m³).

The vessel’s velocity is defined as an initial condition with a value of 1,5m/s. The model is constrained on the sides of the jetty as fixed.

The next step of the analysis is to plot the stress fields, displacements, and deformation fields.

To check the calculations, analytical calculations were prepared.

For verification of the results, the kinetic energy between results of the numerical calculations and the kinetic energy received from analytical formulas was compared.

Numerical calculations:

Analytical calculations can be found below:

The difference between the two results was 16%.

Conclusion

During this structural analysis, a self-modeled shape of the fender was used. There was no specific information about energy absorption. Normally, fender producers will use specialized laboratories to find out more about the product’s properties, but most of the time, this type of solution is quite expensive.

In this analysis, SimScale was used as a lab to find out more about the shape and its parameters. Deformation results of the fender gave possibilities to check energy absorption of the structure. By using numerical analysis (CAE), engineers can analyze and optimize many shapes before the final one will be chosen and tested with a physical prototype.

This simulation was performed by Pawel Dereszewski from FEM NEWS.

The post Boat Fender Design Testing and Optimization with FEM appeared first on SimScale.