Solving something at the end of the pipe is usually a less desired approach. However, in dredging, it is the place where the valuable stuff is delivered, it might be a good place to start monitoring your process. Let me explain this to you by going back to latest discussed exhibit at the Damen Dredging Experience1.
You might have observed in the pictures of the pump power exhibit, that the velocity of the water flow is indicated by the parabolas of the trajectory. The arc of water is bound by gravity and obeys this trajectory always; independent of the density of the mixture. The two equations of motion can be combined, where the time parameter falls away and the height for a certain distance is only depending on the initial horizontal velocity2. As such, it is fairly accurate indication of the pipe flow. The calculation is universally applicable on earth and the results can be presented in a very simple graph to take with you. Every parabola is labelled with the corresponding horizontal velocity.
The above example is a straightforward method to measure the mixture velocity. The US Geological Survey even extended this approach as a standard method to measure the production of wells3. The resulting nomogram has a slightly different layout, as it is intended for finding the production instead of the velocity. For production planning, this will be useful. For monitoring your dredging process, the velocity might be more important. Both approaches of this elegant method do have the benefit, that there is no obstruction needed as in the case of an orifice measurement4.
There is an unconfirmed anecdote that my old professor de Koning started his career as a velocity measurer. In the old days, when he was working as a twelve year old boy with the dredging company of his father. He was assigned to keep watch at the end of the pipe and monitor the mixture pouring out. He had a simple beam with a plumb bob. The beam was moved along the top of the pipe, until the plumb bob was touching the arc of mixture. On the beam were two markings. When the beam was moved in and passed the first mark, the mixture velocity was too low and a red warning flag had to be displayed. If the beam had to move out and the mixture velocity was too high at the second mark, a green flag had to be flown. There was also another white flag, in case only water came on the reclamation area. With this very simple setup, the dredge master could check through his binoculars what the state of the dredging process was.
They were clever in those days. But the physics still apply. So, even today, one might have a situation, where there is no electronic velocity measurement available (broken, not supplied, not (yet) purchased) and you have to push the limits of the operating envelope of the dredging process. Then, there is probably always somebody around that might be appointed volunteer to be head of the velocity measurement crew. Who knows, he might have a bright future in the dredging academia.
Egypt is a great nation when it comes to ancient engineering. No other country has such a concentration of impressive monuments and such an interesting history as over there. If you are not convinced that modern Egyptians are not capable of great engineering feats you are wrong. Last Monday, Omar Karam graduated at our R&D department of Damen Dredging Equipment1 on his thesis about ‘CSD Rock Cutting.’
Cutting processes have been extensively described by Sape Miedema in ‘The Delft Sand, Clay & Rock Cutting Model’2. Omar has been using the frame work of Miedema to make some useful tools for the estimation of the production of our dredging equipment in rock. In due time, you will find the results of his thesis in the online dredge selection tool ‘Sandy’. Omar’s curiosity and ingenuity does not end here. He will continue studying at a university, but I do hope to meet him again, as he would be a valuable asset for our dredging community. Keep an eye out for him.
His graduation brings me back to my first lessons in dredging technology at the Delft University of Technology by the illustrious professor de Koning. In a sense he was an old school engineer, who hammered it in to us that thinking is done by doing it with your hands3. Back than the Polytechnic School was just rebranded to University and he was mocking that as a university, we had to set the topics in a broader perspective. So, he started his introduction on cutting technology with some slides of the unfinished obelisk at Aswan4 as every aspect of the cutting process could be illustrated.
The story according to de Koning is: ‘Around the quarry of the obelisk, they have found diorites5. These are some sort of volcanic balls of rock. In combination with the marks and scratches all around the obelisk, archaeologists believe these stones have been used to pound the granite. The impact compresses the bedrock and the resulting stresses fracture the contact surface(1). For every hit a whiff of dust is created. Eventually the dust is collected and scooped away for the next layer. Next, trees would be planted in the trench on one side of the obelisk. The growing root system displaces volume and create shear stress underneath the obelisk that would sever the obelisk from the bed rock(2). At last the trees are removed and dry wooden dowels would have been inserted in the shear cracks. Saturating the wooden dowels will make them grow. The last strands of rock will now be broken due to tensile stresses(3). Repeated insertion of new dry dowels and saturating them will lift the whole obelisk enough to pull some ropes under and carry the obelisk away to the building site.’
Although the diorites and the scratch marks are a smoking gun, current archaeologists argue about the feasibility of this process as experiments yield a very low production and it is doubted that the obelisk could be finished in the lifetime of the client6. Even if disputed, de Koning told a story that conveys the message; I vividly remember it and makes me understand the rock cutting process.
These mysterious monolithic ornamental spires have been an inspiration for many legends and stories. When we have solved the riddle of the rock cutting with diorite balls, it may inspire the development of new rock cutting technology for the dredging community and we can put the story of the obelisks to an end.7
Sorry folks. It has been several weeks since my last post and I hope you haven’t forgotten my dredging details. This website is just a personal side line that I have to maintain and expand in my own time. Lately my time was rather limited and all my creative capabilities were engaged on an urgent case for my employer. But I do have some thoughts that I wanted to share with you, they just have to wait for better times. Part of my job is, to take care of a ‘Dredging Experience Centre’. A touch and feel museum area, where we can take customers and sales- and service people to explain and discuss about their particular dredging project. I have tons of material for presentations and handouts on this topic, so it will be useful next time, when I am otherwise occupied. I just needed an opening to offer you some perspective on the scattered articles that will pop up sometimes.
And what a better opening can be than the opening of the Dredging Experience itself. On Wednesday November 16th, 2016, Mr. Kommer Damen himself opened our new office building and received the honour to show him our exhibits1.
The starting point of a tour through the dredging experience is the overview poster with all the different processes that are explained with the available exhibits. Each process is indicated at the corresponding dredging vessels, that feature the relevant equipment. Processes and phenomena range from basic soil mechanics to fluid dynamics and the influence of the various processes on the total dredge production. There are also exhibits specifically on explaining our design choices, e.g. our mechanical seal. Other exhibits show recent research and development like ‘spud pole holding forces’ and the DynaCover2.
The Dredging Experience is exactly what it says: you will be able to ‘experience’ the various processes. Most of them require some manual effort and this will show you the differences in soil properties or hydraulic configuration. This provides an excellent opportunity to have an in depth discussion with clients about their particular dredging project and the best possible solution for their specific requirements. Regularly, I see happy faces of enlightenment coming out of the exhibition. Commercial colleagues when they understand the customer across language barriers. And especially customers as they feel at ease, because they can explain on a practical level about their problem and see how much we go into the details of the dredging process to optimize for their purpose. And even when they walk out without buying, they do so with an everlasting positive impression. They will easily apply the new insights into their daily operation at home.
The approach in designing and selecting the exhibits was in line with what I learned from my old professor de Koning. He insisted that even as academic students, we still had to examine the dredging processes by hand to truly understand what we were learning3. His favourite quote was from Denis the Rougemont4: ‘But the true condition of man is to think with his hands.’