2018 Nature's top 10 scientific news

2018 is about to end and we are flooded with summaries: 2018 sports summary, 2018 news summary etc. Nature magazine has published an online audio-visual its top 10 scientific news of 2018 with short explanatory videos and podcasts (link to article). This post presents a summary of the Nature’s top 10, and a respective link to the article.

2018 Nature Top 10 science news

  • The maser goes mainstream. Diamond microwave lasers. A MASER (Microwave Amplification by Stimulated Emission of Radiation) are concentrated beams of energy, similar to lasers (Actually maser was invented before laser), with the difference that masers are based on energy rather than light. This difference provides maser with the unique ability to penetrate cloud cover, living tissue, and other solid materials undisturbed.
  • The mysterious death of the Baobab trees. Baobab trees are the iconic millennial trees of Africa. These trees have been around for thousands of years. However, it was discovered that baobab trees are dying.
  • The tale of the Edith's checkerspot: Butterflies caught in an evolutionary trap. The Edith's checkerspot butterflies from Nevada are experiencing a rapid local extinction due to an evolutionary trap very sensitive to human activities. 
  • Rats versus reefs. Rats have decimated bird populations on certain islands in the Chagos Archipelago. This lack of birds means a lack of fertilising guano, which has not only affected plant life, but the health of surrounding coral reefs as well.
  • Blood, rats and anticoagulants. The story of warfarin. All the anticoagulants are based on warfarin. Few people know that warfarin was developed as rat poison. It may be important to review the history of warfarin.
  • Meet the computer chemist. Computer science has developed an AI-based chemistry robot that is able to perform experiments and search for new reactions.
  • The secret physics of dandelion seeds. Scientists have studied the fluid dynamics of air flow around the seed and discovered a completely new type of flight based on a previously unknown kind of vortex.
  • Nobel laureate Donna Strickland talks lasers and gender. A summary of the laser research that led to the first woman to win the Nobel Prize in physics in 55 years. 
  • Ion drive: The first flight. A plane powered by an ‘ion drive’ flew for the first time. The drive uses high powered electrodes to ionise and accelerate air particles, creating an ‘ionic wind’. This may be the first step for silent drones and silent planes.
  • The American opioid crisis. Mathematical modelling is being applied to the current opiod crisis in America.
Article:


Indonesia earthquake and soil liquefaction

On 28 September 2018, a 7.5 maginute earthquake struck in the neck of the Minahasa Peninsula, Indonesia. The quake was located 77 km (48 mi) away from the provincial capital Palu and was felt as far away as Samarinda on East Kalimantan and also in Tawau, Malaysia (590 km away, equivalent to the distance from Washington DC to Toronto).


Unlike previous earthquakes/tsunamis events, most of the building collapse were due to liquefaction. Hundreds of buildings collapsed due to liquefaction. In many cases, objects and structures above ground sink into the earth - with some swallowed completely.

What is liquefaction?

Liquefaction occurs when loose sand and silt that is saturated with water behaves like a liquid when shaken by an earthquake. There are 4 condition for the occurrence of liquefaction:
  1. Earthquake waves cause water pressures to increase in the sediment and the sand grains to lose contact with each other, leading the sediment to lose strength and behave like a liquid. The soil can loose its ability to support structures, flow down even very gentle slopes, and erupt to the ground surface to form sand boils. Many of these phenomena are accompanied by settlement of the ground surface — usually in uneven patterns that damage buildings, roads and pipelines. Three factors are required for liquefaction to occur:
  2. Loose, granular sediment — typically "made" land and beach and stream deposits that are young enough (late Holocene) to be loose.
  3. Saturation of the sediment by ground water (water fills the spaces between sand and silt grains). This is an interesting requirement because it defines a seasonality risk of liquefaction. For instance, in much of the San Francisco Bay region the ground water is closest to the surface (saturating the younger sediment) in the Winter/Spring, during and following the "wet season". In 1906, the Bay region was fortunate that the previous wet season had been relatively dry. In 1989, the Loma Prieta earthquake occurred at the end of the dry season in October, when ground water levels are relatively deep beneath the ground surface — still, there was considerable liquefaction-related damage!
  4. Strong shaking — all parts of the San Francisco Bay region have the potential to be shaken hard enough for susceptible sediment to liquefy.


When all four conditions are present, the loose material begins to compress under the force of gravity, closing the spaces between the grains. However, the water already occupying the spaces resists the change, and pressure begins to build in the material. Eventually, the pressure rises enough that the grains become buoyant and float in the water. At this point, the soil has completely lost its strength. Soil that was solid begins to act like a liquid.

With lower bearing strength, liquefied soil can no longer support the same amount of weight as it did when it was solid. Objects on the surface, such as buildings, may partially settle or sink into the liquefied soil, causing damage to building foundations and the structure that they support. Soil can remain liquefied for several hours after the earthquake shaking has stopped, although it will gradually solidify and regain bearing strength as the pressure within the material disperses.

Levee and Super Levee


A levee is defined as a “man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to reduce risk from temporary flooding”.

Maruyama river Japan


Levees are designed to manage a certain amount of floodwater and can be overtopped or fail during flood events exceeding the level for which they were designed. Levee failures can also be caused by structural failures resulting from improper maintenance, inadequate foundations, seismic activity, erosion, seepage, or burrowing animals. 
Levees and floodwalls are typically built parallel to a waterway, most often a river, to reduce the risk of flooding on the landward side. Flood walls, which are typically made of concrete or steel, are often constructed on a levee crown to increase the height of the levee, without increasing the base of the embankment. Figure shows the components of a typical levee.
levee protection

Super Levee
When a levee fails, the result can be more catastrophic than if the levee had never been constructed. For that reason, some urban areas in Japan (especially in Tokyo and Osaka) developed a new flood protection known as Super levee. Super levees are thicker levees that will not fail even in the most extreme events. Super levees are failure proof embankments that ensure safety even during a flood larger than the design one. The three main examples describing the safety advantages of Super Levees are:
  • Overtopping. During unexpectedly extreme events, water may overtop and break ordinary levees. On the other hand, super levee will not break and water will flow slowly on the levee.
  • Seepage. Water seeps may break the levee. On the other hand, super levee will not break because it is wide.
  • Earthquake. During earthquakes ordinary levees may experience liquefaction and fail. On the other hand, super levees will are strong against liquefaction because the ground is improved and the slope is gentle.

flood protection Japan



Google Imagery in QGIS 3

QGIS is the second most popular GIS software and the most popular free GIS. Few month ago, the latest version QGIS 3 Girona was released. It has important improvements and new features, but it also has some limitataion compared with previous versions. One important limitation is that some plugins were not updated yet. For instance the plugin for imagery services such as Google Maps is not available. In this post we present a solution for this issue.

Google Maps Layer is hosting somewhere on the Google server and sends the tab to the user who requests it. Technically it is called Tile Map Service (TMS). Therefore, we just need to find the TMS that Google uses to use the Google Maps layers. The Google Maps Layer TMS are:

  • Google Maps: https://mt1.google.com/vt/lyrs=r&x={x}&y={y}&z={z}
  • Google Satellite: http://www.google.cn/maps/vt?lyrs=s@189&gl=cn&x={x}&y={y}&z={z}
  • Google Satellite Hybrid: https://mt1.google.com/vt/lyrs=y&x={x}&y={y}&z={z}
  • Google Terrain: https://mt1.google.com/vt/lyrs=t&x={x}&y={y}&z={z}
  • Google Roads: https://mt1.google.com/vt/lyrs=h&x={x}&y={y}&z={z}

Add Google imagery to QGIS 3
To add the Google Maps map service in QGIS 3:

Go to XYZ Tiles in the Browser panel. Right-click on XYZ Tiles and create a new connection.

Enter the name, for example: Google Satellite. Copy and paste one of the Google Maps TMS listed above into the URL. Adjust the maximum zoom level (suggested to 19).

Strongest Typhoon to hit Japan: 5 numbers to understant it

Typhoon Jebi is the most powerful typhoon to hit Japan in 25 years. Last Tuesday (September 04, 2018) it slammed into the western part of the country on Tuesday, killing at least seven and injuring more than 200, disrupting transportation, heavily damaging the bridge that leads to Kansai International Airport and leading authorities to call for evacuations of areas in its path.  

As of 10 p.m. Tuesday, Jebi was traveling north-northeast over the Sea of Japan north of Niigata Prefecture at a speed of 70 kilometers per hour. Near Kansai International Airport, strong winds swept away a tanker berthed in Osaka Bay, slamming it into the sole bridge that connects the airport to the mainland and taking a large chunk out of the bridge.

There are already several posts and news about Jebi. The video from NHK shows some footages to understand the damage. In this post we summarize 5 important numbers:
  • 590. More than 590 flights cancelled
  • 57 000. More than 57000 air passengers affected
  • 2 Million. More than 2 million houses suffered power outage
  • 500. Up to 500 mm rain in one day
  • 175. Sustained winds up to 175 mph


Differences the Internet vs the Web

There are several confusions about internet terms. Unfortunately, the easiness of pressing share button created several confusions and regarding the internet.

It is very easy to find terror histories and conspiracy theories about the deep web and the dark web only because of the name "deep" or "dark". The deep web is nothing illegal nor secret; moreover, we all use the deep web quite often (as will be explained by future posts).

Before explaining the deep web or the dark web, it is important to provide some basic information about the internet and the web. There are important differences between the internet and the web, and this post will summarize them.
What's the difference between internet and web?

Dam collapse in Laos devastates several villages (July 2018)

Last Monday (July 23, 2018), one hydropower dam in Laos collapsed, causing a massive flood that destroyed several towns and several deaths (the number is still unknown). The flood destroyed town located as far as more than 70 km downstream. 

The dam was still under construction when it collapsed. The dam was part of the Xe-Pian Xe-Namnoy hydropower project being constructed by Laotian and Thai and South Korean firms. The collapsed dam was not a main dam; it was a dam designed to help divert water around a local reservoir. The dam was 8 m wide, 770 m long and 16 m high.
Image. Flood due to dam collapse in Laos (Source: scmp)

Laos dam collapse time frame (July 22 - July 24, 2018)

  • Sunday 21:00 local time (14:00 GMT) - The dam is found to be partially damaged. The authorities are alerted and villagers near the dam start to be evacuated. A team is sent to repair the dam - but is hampered by heavy rain, which has also damaged many roads.
  • Monday 03:00 - Water is discharged from one of the main dams (Xe-Namnoy dam) to try to lower water levels in the subsidiary dam.
  • Monday 12:00 - The state government orders villagers downstream to evacuate after learning that there could be further damage to the dam.
  • Monday 18:00 - More damage is confirmed at the dam.
  • By Tuesday 01:30, a village near the subsidiary dam is flooded, and by 09:30 seven villages are flooded.

Image. Dam collapse and areas affected (Source: bbc)

The difference Windows vs Mac. Should I buy windows or Mac?

 A Windows Microsoft PC or Mac? This is a common question among computer users. The best answer is: It depends on your needs. In order to understand this question and its answer, it is important to understand how a computer works. To make it easy, we can describe a computer as 4 components:
What is the difference between widows and PC?

  • The interface is where the user interacts, is what the users sees and where the user works. In other words, is the screen with the windows and commands.
  • The software or apps. This component process the user's instructions and tells the computer what to do. 
  • The operating system receives the instruction from the software and re-sends it to the specific hardware. Actually, it translates the instruction to the language of the hardware and delivers the translated instruction so that the hardware will understand the instruction. We can say that it contains the drivers for each component (the word drivers is not the right one, but I will use it in this post because it is easier to understand).
  • The hardware performs all the tasks. It performs the computations, it prints, it scans, it does everything.

difference between windows and mac

Image 1. Components of a computer

Usually the question PC Microsoft vs Mac refers to the operating system.

The difference between Windows and Mac

A Mac computer is only compatible with Mac components (only Mac hardware). If you have a Mac you can only install Mac hardware. When Mac makes a given hardware it also makes the specific drivers for that hardware. 
On the other hand, Microsoft goes for compatibility. That means that you can add any hardware (from any brand) to a Windows Microsoft PC, but you also have to install the drivers that come with the hardware.
One simple example is the use of a printer. If the user has a Mac a want to buy a printer, he must buy a printer Mac. On the other hand, if the user has a Microsoft PC, he can buy any printer he wants. 

Advantages and disadvantages

Both Operating Systems have their own advantages and disadvantages depending on your needs.
Price. One clear difference is that Mac is much more expensive because Mac hardware is designed specifically for Mac. On the other hand, Microsoft PC accepts any brand; thus, brands that focus on one given hardware can produce hardware at lower cost. Besides, the user can choose between different options (Point for Windows).
Availability. This is another disadvantage for Mac and one of the main reasons why I do not use Mac. When a given software or hardware is released, it is immediately available for Windows Microsoft PC. On the other hand, Mac requires a specific version, then they (Mac) test it, and after some months they release it. Actually this lack of compatibility is an important limitation for Mac because Microsoft PC is the most used operating system. Therefore, sometime data processed in a Mac cannot be shared or delivered (Point for Windows).
Open source compatibility. This is a result of the previous point. This is another reason why I do not use Mac, because this may become a serious limitation especially when you work with open source or when you make your own code (Point for Windows).
Security. Since Mac produces and controls the software and hardware allowed to be used with a Mac, there is low probability to be attacked by a computer virus or to have malfunction due to bugs. Applications that may contain hidden doors to viruses usually are not allowed to be installed on a Mac and Mac drivers usually contain less bugs because they are tested before being released. I believe this one is the only advantage of a Mac (Point for Mac).

Drone battle: Parrot ANAFI vs DJI Mavic

Last month (June 2018), Parrot announced the release of its new drone ANAFI. ANAFI is a small and foldable drone in the same concept as the DJI Mavic and is planned to be a direct competitor for the DJI Mavic. ANAFI is already on sale (since July 2018), and some drone enthusiasts are curious about its capabilities and the comparison ANAFI vs Mavic. 5 points were considered.
  • Camera
  • Portability
  • Flight ttime
  • Price
  • Additional features

Which drone should I buy

Camera
After commenting in several photography forums, we can conclude that ANAFI is better than Mavic for the following reasons:
Although both drones sport a Sony CMOS camera sensor for photo and video, while Anafi employs a superior 1/2.4” sensor that shoots 21MP (5,344 x 4,016) (Mavic Air uses a 1/2.3” sensor capable of 12MP 4,056 x 3,040). 
Comparing lenses, the ANAFI has a superior aperture (F2.4 vs F2.8) and can hit faster shutter speeds (1/10000s vs 1/8000s). This may be an important advantage for surveying applications because it would allow for higher resolution images and higher elevation flights; thus, higher elevation flight means more area covered in less flying time. 
Besides, Parrot implemented a dynamic new lossless digital zoom. This allows you magnify up to 2.8x without a reduction in image or video quality, making it easier to get details without having to get so close.
Yet another camera advantage is that ANAFI's camera is not embedded in the frame. ANAFI's camera sits by itself allowing 180 degrees of vertical movement.
ANAFI also has an advantage in video because it allows filming in 4K Cinema mode (4,096 x 2,160), which would be a great advantage in filming. Nevertheless, there is one video filming capability in favor of Mavic. Mavic films 120 FPS compared to the 24 FPS of ANAFI.
gimbal camera
Image. ANAFI 360 degree camera

Portability
In this point I would call it a draw. Although Mavic is shorter, it is a little wider. This led to some confusion arguing that ANAFI is smaller. However, comparing the total size of ANAFI (244mm * 66mm * 63.5mm) with the total size of Mavic (168mm * 83mm *49mm), we see that Mavic is much smaller (Mavic = 683256 mm3; ANAFI = 1022604 mm3). This appears to be point for Mavic. However, ANAFI's 320 g are much lighter than Mavic's 430 g. Therefore, we call this point a 1-1 draw.
small foldable drones
Image. Folding ANAFI
Flight time
This may also be considered a draw. ANAFI allows for 25 min flight. Although this is longer time than the Mavi Air, it is quite shorter that the Mavic Pro 27 min (point for Mavic). However, the tests showed that ANAFI has better stability. ANAFI resists winds up to 68 km/h, while Mavic (and any DJI drone) is limited to winds up to 55 km/h (point for ANAFI). Thus, this point is also a draw.
Price
This one is a point for ANAFI. ANAFI costs only 699 $ in Amazon, which is almost half the price of Mavic Pro (1300 $). Moreover, ANAFI is even cheaper than Mavic Air's 800 $.  
Additional features
Several blogs argue that obstacle avoidance would be an advantage of Mavic. However, I do not believe so because of 2 reasons:
  • Flight planning. As a drone user, you should always plan your flight (actually I would change the should for MUST plan the flight). Flying without flight plan is like traveling without a destination. Thus, potential obstacles can be avoided prior the flight.
  • Flight regulations. Flight regulations forbid to flight drones over crowded areas. Thus, you should not be worried about crashing into a home or a person because you are not supposed to fly over houses or persons.

As we are talking about regulations, I would like to mention that several NATO countries (North Atlantic Treaty Organization) issued concerns (and in some cases bans) over DJI products. This would be a point for ANAFI (French industry). Thus, let's call it a draw.
An additional feature that may result in a point for Mavic, is that third party applications have not included updates to control ANAFI yet. Nevertheless, they already answered that upgrades including ANAFI compatibility will be issued soon.
Final result
As we can see in the following table, ANAFI wins 2-0. We can make an analogy with the current world cup, and we can consider each feature as a game. Thus, after 5 games we have 3 draws and 2 ANAFI victories
ANAFI overcomes Mavic in the features that made Mavic so popular. ANAFI is lighter, has longer flying time, better camera and is cheaper.
comparing DJI vs Parrot drones
Image. Comparisson ANAFI vs Mavic


Physics of bicycle kick (scissors kick) in football soccer

In soccer, the bicycle kick has provided viewers moments of breathtaking spectacle that seem virtuosic in scope. The novelty of such moments is underscored by the rarity with which players have performed this complex skill during national or international tournaments. 

The rarity of these occurrences is both a product of perceptions that it is a high-risk, low return skill and by the fact that there is a dearth of scientific research on the biomechanics of the technique. Pelé, Cristiano Ronaldo (CR7), Ronaldinho, Messi, all the best players have performed at least once a bicycle kick.
Cristiano Ronaldo best goal

This magic skill has captivated fans and also the scientific community. Some studies such as Shan et al., (2015) applied 3D motion capture and numerical simulations to better analyze and understand this movement. 

In this post we will summarize the physics processes involved in bicycle kick (or scissor kick) taking as example the famous kick from Pele, the greatest player of all times. This movement of less than 1 second will always amaze soccer fans and physics fans.

Bicycle kick movements

The movements of the bicycle kick  can be described in three phases:

1. The jumping: The player (Pelé) places himself back to the intended direction of the kicked ball and to jump, his center of gravity (CG), defined as a point where the resultant of all the weight forces can be considered acting upon, projects a little behind of his impulse foot. This allows him to gain rotational momentum when he applies force on the ground that passes within a certain distance from the CG to jump like in a back somersault. 
Barcelona Real Madrid

2. The scissors: Once completely in the air, Pelé, in astonishing synchrony with the ball trajectory, elevates the leg which is going to hit the ball and moves the other leg in the opposite direction; like the movement of a scissors, as can be seen by the angles between the thigh and the trunk for each leg shown in Figure1c. 

While the movement is performed, the head is kept in a very stable posture because he must gaze at the ball. To facilitate the rotational movement of the kicking leg at the beginning, he bends the knee of this leg, approximating his limbs to the hip, and fully extends this leg just before the kick to hit the ball as high as possible, like the divers do to rotate faster during a dive. 

The physical property being altered is called the rotational inertia, the property of a body to resist change in its state of angular movement. The rotational inertia is calculated as the product between the body mass and the squared distance from the body to the center of rotation. 

Decreasing the distances of each segment to the hip joint decreases the total rotational inertia of the lower limb. In the air, the arms stabilize the body position: the arms are kept away from the trunk in the frontal plane to intentionally increase the body’s rotational inertia in the longitudinal direction to diminish any rotational perturbation in this direction, like a circus acrobat walking on a rope with a balancing beam in the hands.

3. The ball striking: The leg, at high speed, intercepts the ball above the height of a standing person, and changes its movement. Then, for a moment (see the video), it seems as if his body stops in the air and only the legs rotate around the hip. 

This phenomenon is due to the movement of other segments of the body that move faster than the trunk: although the entire body CG is in a parabolic trajectory, as predicted by the classical laws of motion, the trunk vertical trajectory (trunk CG) actually slows down in its apex.
Pele best goal
Figure 1. Analysis of Pele's bicycle kick (Source: Demotu)

How dos GPS work? How many satelittes are required for GPS?

Several times I encountered people misunderstanding how GPS works and believes that GPS requires just 3 satellites. Other misunderstood concept regards how GPS works. Some people believe its triangulation. The real methodology is "rilateration".

In this post, we will summarize how GPS works and we will show that it requires at least 4 satellites.

How many GPS satellites are orbiting the Earth?

How GPS works?

GPS are based on trilateration, which is a method of determining the relative positions of objects using the geometry of triangles.

GPS does not use triangulation because it does not measure angles. We can visualize this concept in the following way:
  • When a GPS connects with a satellite, the GPS device estimates the distance between the device and a satellite. This distance define the radius of one sphere. Thus, the GPS device can be located on any point of the sphere’s surface.
  • When the GPS connects to a second satellite, it defines another sphere. The intersection of those 2 spheres define a circle. The GPS can be located anywhere on the surface of that circle.
  • When the GPS connects to a third satellite, it defines another sphere. The intersection of this third sphere defines 2 potential points (in a worst case scenario it may define a line segment). Thus, 3 satellites are not enough to define one single location. The GPS requires a fourth satellite to define one single location.

GPS trilateration triangulation
Image 1. GPS trilateration (Source: Trimble)

Time is the 4th variable

Some people argue that 3 satellites are enough to define one position, because one of the mentioned 2 potential locations is a not reasonable one, or non real one. This idea could be better understood by looking at the math.

When GPS connects with three  satellites, it is possible to define three distance equation with three unknown variables  (the x, y and z coordinates of the point).

The equations are quadratic ones. Therefore, sometimes one solution may involve imaginary numbers or very far location. Thus, some people  believe that 3 satellites may be enough. However, in GPS we have a fourth variable.  This 4th variable is time.

Summarizing, GPS estimates the distance to a satellite based on the travel time of a  signal emitted from the satellite.

Satellites are emitting signals at given times, and when  the GPS receives the signal it records the time when signal was received. However, the  satellite’s clocks are more accurate than the clock of the GPS device. Thus, there is a  time discrepancy that will affect the measurements and the solution. GPS solves this  problem by applying a correction factor (a 4th variable). Therefore, GPS has to solve  4 variables
  • X coordinate
  • Y coordinate
  • Z coordinate
  • C time correction factor
4 equations (4 satellite connections) are needed to solve the 4 variable.
mathematics of the GPS point distances
Image 2. Set of equation solved by GPS

Note. for simplicity I used the term GPS. However, currently the new term is GNSS (Global Navigation Satellite System)

Simulating World Cup Russia 2018

Soccer World Cup has arrived and maths are being used to analyze potential results. Spanish newspaper El Pais combined current statistics with a parametric model based on a Poisson regression and uncertainty analysis to simulate potential results and to estimate the probability of each team to win games and to become the new world champion. At the end of the post you can find the results. Much more important than the results however, is the methodology applied in the model. In this post we are interested in the maths and we present a short summary about this model. Further statistical-mathematical questions about the model may be discussed later.

The model can be described in three parts: strength of the team, simulating individual games and simulating the whole tournament.

Strength of team
Some teams (Brazil, Argentina or Germany) are stronger than others (Panama, Egypt or Saudi Arabia). This difference is quite important in this case, because national teams do not play many games together. Thus, some individual players like Neymar may be vital to win some games. The strength was calculated based on the well known Elo Rating System. This system calculates the relative skills of each participant based on its performance ratings. Although originally developed for chess players, the Elo Rating System has been successfully applied to several sports. The model from El Pais used 3 different Elo ratings. One for the players, one for the teams, and one based on the goals marked by each team.

Simulating individual games
Individual games simulate the probability of goals marked by each team. This  technique is based on a Poisson regression model proposed by Dixon and Coles (1995). Thus, the model calculates the probability of victory. The model was calibrated considering more than 17000 games. The model calibration considered difference performances for home games, away games and games in neutral field.
The calibrated model was evaluated based on the Rank Probability Score proposed by Constantinou and Fenton (2012)

Image. Calibration of the model (Source: El Pais)

Simulating the whole tournament
The previous step not only simulates the victory, but also simulates the goals. This is an important point to simulate the whole tournament. By simulating the number of goals the model can predict the first place and second place of each group; hence, defining the matches for the following stages. The last two steps were repeated 10 000 times (10 000 iterations) in order to consider different uncertainties. Although there are no details about the probability rules to define the next iteration, this was an important step because the model estimated the probability of each team to win a specific game, to pass to the next stage and to become the new Champion.

The following image shows the result of the beast teams. You can visit the whole table.
Image. Simulation result of the best teams

Satellite images from Hidroituango hydropower dam crisis Colombia 2018

Last days we have been following the Hidroituango Hydropower dam crisis in Colombia. We published posts about the crisis time frame (link to post) and the analysis from the technical committee (link to post). In this post we will not discuss about the event. Instead, we present satellite images to visualize the problem, like we did with the Oroville dam (Link to post).

Image 1 shows a comparison of the site in March 26 (before the event) and in May 17 (during the crisis). We want to point to 3 details:

  • The first noticeable detail is the water behind the dam (on the reservoir). On XXX the reservoir is empty. On the other hand, by May 17th the water level has risen so much that the reservoir is almost full. It is possible to see that the water level is very close to the spillways and the top of the dam.
  • Other important detail is the visualization of the landslides. As mentioned in a previous post, this crisis began because of landslides that blocked the tunnels. The image from May 17th clearly shows 2 landslides on the right margin of the river.
  • The third important detail is the water flow downstream the dam. The image from May 17th shows water flowing downstream the dam. This is an important detail, because the spillways were not working yet. Thus, the water flow downstream is a sign of the seepage described by the technical committee. 

Ituango Hydropower Colombia
Image 1. Hidroituango dam satellite image March 26 (Source: Planet Labs)


Flood Colombia due to hydropower dam fail
Image 2. Hidroituango dam satellite image May 17 (Source: Planet Labs)

The other image (Image 3) pair shows 2 images in an animated GIF (images from May the 02nd and May the 07th). This pair of images has less detail, but it covers a much bigger area. This second comparison shows the backwater effect of the dam. Several tributaries were flooded by the backwater effects.

flood Satellite images
Image 3. Animated GIF of images from Hidroituango (Source: GIPHY)

5 facts about the Fuego volcano eruption in Guatemala (June 2018)

Last week, Fuego volcano (Guatemala) erupted. It was the strongest eruption in several decades. We already posted some basic concepts about volcanoes. This post presents 5 facts about this eruption.

  1. The erupted ashes were about 650 degrees Celsius
  2. The erupted ashes elevated almost 10 000 m high
  3. The Fuego volcano eruption did not throw much lava. The eruption threw tons of ashes
  4. The eruption was the strongest eruption in 4 decades
  5. Currently, the main problem are the so called lahares. That is, the mixture of the volcanic ash with rain.


Check the video

Basic concepts about volcanoes and volcanic eruptions

Last week we were flooded with about volcanic eruptions in Hawaii and Guatemala. This post present some basic concepts regarding volcanoes and how volcanoes erupt?
Why do volcans erupt?

What are volcanoes?

Volcanoes are openings, or vents where lava, tephra (small rocks), and steam erupt on to the Earth's surface.

Many mountains form by folding, faulting, uplift, and erosion of the Earth's crust. Volcanic terrain, however, is built by the slow accumulation of erupted lava. The vent may be visible as a small bowl shaped depression at the summit of a cone or shield-shaped mountain.

Through a series of cracks within and beneath the volcano, the vent connects to one or more linked storage areas of molten or partially molten rock (magma). This connection to fresh magma allows the volcano to erupt over and over again in the same location. In this way, the volcano grows ever larger, until it is no longer stable. Pieces of the volcano collapse as rock falls or as landslides.

How do volcanoes erupt?

Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually, some of the magma pushes through vents and fissures in the Earth's surface. Magma that has erupted is called lava.

Magma can be erupted in a variety of ways. Sometimes molten rock simply pours from the vent as fluid lava flows. It can also shoot violently into the air as dense clouds of rock shards (tephra) and gas. Larger fragments fall back around the vent, and clouds of tephra may move down the slope of the volcano under the force of gravity.

Ash, tiny pieces of tephra the thickness of a strand of hair, may be carried by the wind only to fall to the ground many miles away. The smallest ash particles may be erupted miles into the sky and carried many times around the world by winds high in the atmosphere before they fall to the ground.

Robotic total station (demonstration videos)


A total station is an electronic surveying instrument that measures distances and angles. It can be described as an electronic theodolite with an electronic distance meter integrated with a microprocessor and a data collector storage system. Modern total stations can be divided into manual and automatic total stations.
  • Manual total stations. In manual total stations the user manually has to sight the target to the telescope, manually adjusts the horizontal and vertical screws in order to align the cross-head to the target and operates the equipment to store the data.
  • Robotic total stations. Robotic total stations perform all those steps automatically. The telescope turns automatically. Besides, automatic aiming algorithms allows the robotic total station to automatically search the target (the prism), aim at the target and follow the target.
The main benefits of robotic total stations are:
  • Faster surveying (more productivity)
  • Remote operation (less persons)
  • Avoid potential miscommunication between operator and target
There are 4 operation types of robotic total stations:
  • Automatic target aiming. By pressing a button the equipment automatically searches and aims the prism, and collects the data
  • Automatic target lock. Once the equipment defines a prism target, it locks and follows the target and collects the desired point
  • Power search. It is a combination of the previous 2. The equipment searches the target and locks to it. Then, if it loses sight of the target due an obstruction, it again searches the target and locks to it. This type is very convenient for surveying areas with interruptions due to infrastructure.
  • Imaging. The image observed by the equipment is displayed in an external screen.
The video shows a visual explanation of thefour types of operation options (link to video)

Hidroituango hydropower dam Colombia. Opinion from Dr Ordoñez

Last week we presented time frame of the Hidroituango dam fail emergency (link) in Colombia. Engineers reported that the dam reached the target level. This post in a translation of the communication from Dr. Jaime Ordoñez from the technical commission from Sociedad Colombiana de Ingenieros. The original publication in Spanish is in this link.
Colapso en represa Hidroituango Colombia

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May 25, 2018.

Yes, we should regret that a greater number of members of the Commission had not attended the meeting and helped us in the drafting of this document. Unfortunately, despite the seriousness of the subject we have before us, very few people came. Only those who know the thing well know that the Ituango project is dead and there is no control over it, so the most natural thing is to expect it to fail; we are sure that it is easier for him to fail to fail, and we are truly in a panic, seeing ourselves that nobody seems to understand what is coming, nobody wants to believe that there is going to be a huge tragedy.

We have considered, who we call this meeting, that it is totally absurd that the project managers insist on not letting the Project Engineers speak directly, thereby misinforming rather than informing. That's why you and many other engineers have not heard the seriousness of the situation and still believe there is something to be done, that there is something we can and should help, although it is much clearer that there is nothing to do!

We must know that all the "decisions" taken so far to mitigate the emergency have not really been technical decisions, but solutions forced by the failure of EPM criteria and its engineers to plug the diversion tunnels instead of installing the gates provided for make them work as a background download of the Project. They decided, to gain time and be able to start the project this year, to do more of an "intermediate" tunnel between the detour and the loading, which is the one that failed to start the emergency! From then on being this a strong winter, everything has been to look desperate as the level of the water rises without control, to allow the flooding of the cavern as the only solution so that it does not spill the water on the dam, which would cause its destruction, and now, race, raise the dam 15 to 20 meters, (now they plan to take it to level 415), to see if they can pass the water through the dump of excesses, which is not even finished, and will be a new source of failures when start working, if the floodgates, which have not had time to rehearse, work!

And what to say about the fact that the tunnels below are already filtering water, and there is nothing to do to avoid it! The massif of the right margin, the one that had the failures before the rise of the water, that is to say when it was dry, is now saturated and under pressure, and the pressure continues to rise as the level of the reservoir rises! If water is already filtering through the tunnels, it is because of internal cavities, cavities and dents, caves, because there are several cargo tunnels, two original detours and the "intermediate" all in the same pitiful been and without possibility of arrangement, those cavities as I said, has been enlarged and at any time one or more of them will explode, as happened last Saturday, and through that gap all the water comes and fails the dam the right abutment !.

The approximate calculations we have made reveal a breakthrough rate of more than 100,000 mcs; more than 3 times the flow that destroyed Armero! and that there will be no avalanche is ridiculous! they believe that there will only be an avalanche if the water passes over the dam, but the dam will still go if the breach is by the right-hand abutment; In addition, the avalanche of solids is not due to the volume of material from the dam, it is due to the volume of sediments in the bed and the multiple landslides that would generate an avenue of similar size, on the slopes of a very steep canyon. extraordinarily unstable You must remember that the Farallones project could not be done because the failure of the slopes by itself was enough to fill the glass, together with the 45 million tons a year the river carries. What difference can there be between "Avenue" and "Avalanche"? any avenue of such a flow is in itself an avalanche generator even if most of the dam remains standing !.

And the worst thing is to think that even if there is no fault in these few days until the level of the reservoir reaches the flow through the landfill, there will be no way to make arrangements in the project without emptying the reservoir, which does not it can be done without removing the prey; you can not even know if the tunnel cavities are still working or if they no longer serve as is hardly expected!

And you tell us that our statement can generate panic! Sorry to tell you that the panic is already with those poor people !, that you do not know anymore, if you stay or if you leave their homes, they say that many leave and a few days return, because they simply have nowhere to go, and as every time they tell them that danger is almost over, well, no way, they come back! And if the dam fails tonight, only God knows how many will die while we decide if we speak or we do not speak because the owners of this great project are poor. I remind you that the communities have been pleading for more than 10 years not to do this project, and that no one has ever given them the least care; Now they say that it is what matters most to the owners of the project, and they have even made a truly laughable offer of money, so that they leave the area!

One of the worst problems that is faced to save people is that there is no Contingency Plan or Evacuation Plan !. The one that is being executed is that of the NGRD, that is, the government, which is generic and was not made to evacuate cities. Plan of Cotingencia is not to blow a whistle when there is danger, but to establish the materials and means to transfer the population to a safe area: buses, trucks, helicopters, etc. and provide room and food for that population in that safe area. It is not to harass the families in tents, as they are showing us in the news, in a public place in the same town, like the stadium, or a school, or a church, that will be rolled to the bottom of the canyon when the city collapses. hillside to the passage of the "Avenue" or "Avalanche" !!

Our communiqué is a call, (done quite late!), So that those who truly know what the tragedy is going to be pinched, inform the government in a clear way what is going to happen, and stop saying stupid things, that maybe not generate the panic that scares you so much, but that will surely produce the dead that we are all going to regret!

That is the meaning of what we said, to see if our President and Board of the SCI are pinched equally, (something that neither the Space building nor the Chirajara Bridge nor the Lizama spill have done. nor with this problem that some are already saying that it will be the second biggest catastrophe in the world after Chernobyl !!), I have always thought that you 'think like us, Gilberto, that you have to talk about things as they are and not as they sound beautiful! Otherwise, why are we here?

It's my humble point of view, you do not have to accept it!

Regards,

Jaime Iván
Jaime Iván Ordóñez Dr. Eng.


Note. This is a translation from the original post by W radio (Link)
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Importance of fire flows to calibrate water distribution models

Over the years, I have found several engineering projects and journal articles in the topic of modeling water distribution networks. One common mistake that I found in most of them is that they "calibrate" the model (pipe roughness) considering only normal flow conditions instead of high demand conditions such as fire flow tests. Actually, it is not possible to calibrate a model without considering high demand conditions. 
fire hydrant and water distribution network

Water distribution modelling

There are several water distribution models (water distribution software) such as EPANET, InfoWater, WaterGEMS, Mike Urban and others. It is important to remember that water distribution models are based on physical processes and they simulate the network by solving a matrix system based on:
  • Conservation of mass in every node
  • Conservation of energy in every pipe
In the conservation of mass we have 3 variables:
  • Flow. This is a known value. Is a boundary condition.
  • Area. This value is calculated based on pipe size (known value)
  • Velocity. This is a function of flow (known value) and pipe size (known value)
In the conservation of energy we have 4 variables:
  • Pressure. This is the value to be calculated
  • Velocity. This is a function of flow (known value) and pipe size (known value)
  • Elevation. This is a known value
  • Head losses. This is a calculated based on the Hazen-WIlliams equation, which is a function of flow (known value), pipe size (known value) and pipe roughness (to be calibrated)
Thus, we have 2 unknown values: pressure and pipe roughness. By assuming a proper pipe roughness we can calculate the pressure. This process of assuming the proper roughness is the calibration of the model. 

Fire flow and pipe head loss

Head losses are calculated based on the Hazen Williams equation. Hazen Williams equation relates the friction head loss as power function of the flow. Thus, it becomes more sensitive to higher flows (you can solve the Hazen-Williams equation online). Let’s show one simple example.

head loss water pipe
Let’s assume a 1 km pipe reach of a 250 mm pipe, and considering different roughness values from 130 (new pipe) to 70 (pipe in a very bad condition). The head loss can be calculated online with this tool. Let’s find the pressure drop for different flows between 1500 cmd and 5450 cmd. 1500 cdm and 5450 cdm were the considered flows because:
  • Assuming a 300 l/hab day, 1 500 cmd would be enough to supply water to a 5 000 habitants zone
  • 5 450 cmd is equivalent to a standard fire demand (1 000 gpm)
pressure drop
As we can see, considering a 1 500 cmd water flow would led to accept a wide range of roughness values. We could assume any roughness value between 70 to 130, and pressure differences would be 1.3 m (about 1.9 psi). On the other hand, those roughness values (between 70 to 130) with fire flow demand produces a 14.5 m pressure difference (about 20.5 psi). Thus, high flows such as fire flow really show the sensitivity of the pipe to roughness. 

Suggestions to calibrate water distribution models

My suggestions for calibrating water distribution models are:
  • Use normal conditions data to verify connectivity issues only. Do not use it to verify roughness. 
  • If you want to calibrate the model, then perform fire flow tests or collect data during high demand equivalent or greater than 1 000 gpm.
  • If is not possible to collect high flow data, do not say that your model is calibrated (because it is not). In this case perform a sensitivity analysis.