Venice is one of the most prosperous cities in all of Europe. Its wetland setting and breath-taking water infrastructure are perfectly extraordinary. The city stands on 118 small islands, even though its buildings are believed floating on water or anchored to the seafloor by unknown mechanism. A couple of centuries ago, evident consequences happened due to subsidence and sea level increased substantially. At the rate of 2 millimeter per year, the city sinks gradually. However, not until 1966 when a major flood occurred, the water rises above 1.9 meters. Due to this sudden calamity, the Italian government made a contingency plan to fix damages by the help of expert engineers.
The Venice Water Authority (VWA) considered the plan to solve the existing problems that cover both in conventional and in a groundbreaking remedy. The priorities among the plans are the enhancement of building and bridge structures, more sophisticated yet strong in foundation and with first class materials being utilized. For the past century, the city of Venice implemented an immediate tactic; increasing the height of the accessible pedestrian walkways. However, upon increasing the concrete level conflict occurred in terms of some functionality issues of the current doorways in the city (Scearce 8).
The series of buoyant steel gates that are installed during that time in the three inlets that precedes the portion of land occupied by Venice is the most workable remedy. The Modulo Sperimentale Elettromeccanico (MOSE) or Experimental Electromechanical Module is the proposed system. The Lido inlet with two rows of gates, 41 gates, the Chioggia holds a row of 18 inlets, and the Malamocco contains a row of 18 gates as Water Authority 1. The original estimates in the area are about 4.5 billion dollars despite the constantly changing of budgets of the project. In 2008, the cost reaches to about 7 billion dollars as estimated (Poggioli 1).
On the ocean floor lays the 80 steel modules rest atop of concrete bases or containers. The modules are filled with enough amount of water to sustain its weight to keep the modules stable at the bottom of the ocean (Lorenzet 3). As forecasted with the event of high tide conditions, air compression is pumped into the respective gates to achieve floatation state. The function of the air is to move directly toward the module; the higher the air increases its pressure the stronger it will block higher sea level. On the edge of each steel module, hinges are attached to anchor steadily at the corner to create the effect of a wall that is vertically concreted.
Figure 1: The process of pumping air into each module.Source: http://www.cspo.org/igscdocs/Andrea%20Lorenzet.pdf
The system has its main concept, to allow freely the exchange of water between the Laguna di Venezia and the Adriatic Sea (Scearce 8). It means that the gates are left at rest on the bottom of the concreted beds. The rows of each three inlets are solely independent; the power will rise on each individual row while the other rows are at rest and inactive, an advantage in the part of the recipients in the city for energy consumption wise. The standard procedure is regulated at 110-centimeter high sea level to activate the MOSE system; the air pump is triggered at a maximum of 3 meters additional clearance of sea level. The three – meter clearance is criticized for its insufficiency in terms of service to the needs of the city in 100 years as estimated; the sea level is expected to increase a substantial amount for more than 110 centimeters (Lorenzet 8).
Topics Involved in the MOSE Project: Fluid Mechanics
There are several fundamental principles of fluid mechanics in the operation of the project. The major principle is hydrostatics, the hydrostatic force on a plane surface in particular. The authors in A Brief Introduction to Fluid Mechanics book, Young and Munson, stated that the force of the pressure vary linearly with its depth the moment the fluid is not compressible. In the case of Laguna di Venezia and Adriatic Sea, project engineers have calculated methodically the hydrostatic pressure in two ways. First, when the modules are laid inactive on the concreted bases, the water pressure is exerted above, as illustrated in first frame, figure 1. Given the equation,
Where γ represents the specific weight of water and h represents the height to the water surface. Similarly, the resultant force on the steel plate, given the equation,
Where A represents the surface area of the steel module
Second, the gates are raised to block the incoming high sea level or tides. The plates are mainly the inclined surface and complexity happened due to the two specific weight constants occurred and necessary for thorough consideration; the specific water weight in Laguna di Venezia and Adriatic Sea. A pressure force exerted by the Laguna di Venezia water, perpendicular to the surface pushes the gates in upward direction, and the pressure from the Adriatic Sea pushes the gates in downward direction as shown in second and third frame, figure 1. Bothe pressures are calculated using the equation, FR= γhcA
Where hc represents the vertical distance from the surface of the fluid to the centroid of the area below the surface (Young 49). The mechanism has a certain function and it can be done through an analysis, the Archimedes’ principle. The buoyant force as acted on the modules is produced through the difference of the pressure. If the center of gravity is above the center of its buoyancy then the structure is stable enough. However, there are two different levels in the surface of the fluid and a hydrostatic pressure approach is highly recommended and preferred.
Shown below, the simplified free body diagram of an elevated MOSE gate.
A simplified free body diagram of a raised MOSE gate is shown below. Previously, the air is pumped and the water is displaced inside the thin steel layers that achieve the vertical position as desired.
Suggested Computational Application
It is necessary to use an algorithm to automate the process of the entire row of the MOSE modules. The algorithm is simple and applicable to any object oriented programming language. The main objective is to activate all the rows when the considerable tide sea level is seen as excessive by the program. In addition, this is to obtain the value of the variety of forces acting on every gate installed. C++ programming language simplifies the following descriptions.
The program is primarily concerned on the receiving input from the VWA as its function. The “Adriatic h” is a variable that stores the value of the current tide sea level for the Adriatic Sea in meters. The “air fraction” and “water fraction” are the two circumstantial variables that store the current contents of the modules in a format proportionally with its values that range from zero to one. For example, the following are the stored values of the variables: Adriatic h = 50, air fraction = 0.3, water fraction = 0.7 respectively. Spontaneously, the sum of air fraction and water fraction is one. Thus, the tide sea level variable of water and air proportions are the inputted data that obtained from its sensor installed within the steel modules. Technically, the value of the water fraction variable is closely to one, gate lying on the floor, the value of the air fraction is closely to zero.
A constant volume is assigned for the module. According to the MOSE system specification, the gate standard dimensions are 20 meters wide, 18.5 meters high, and 3.6 meters thick (Salve 1). As a result, “module vol” constant is introduces with a value of 1332 cubic meters. The initial height of the Laguna di Venezia is equal to the surface height of the Adriatic Sea. Thus, Laguna h is equal to Adriatic h, respectively.
(Table 1: Summary of the proposed input variables)
Processing functions and computations
If the value falls above a set of point for floods, Boolean variable is helpful and “pump air” is set as “true.” The sensors in the module read the “air fraction” variable that is close to 1. A recommended mechanism is used to verify the correct behavior of the system that air fraction is greater than or equal to 0.9.
With the used of the hydrostatic principles as provided in section2, the program proceeds to calculate the resultant forces due to its resulting pressures. The program utilized the equal value of adriatric h and laguna h to calculate the height of the centroid of the module plate as the gates are raised prior the tide will rise. The distance from the surface to the centroid of an assumed gate with a vertical coordinate centroid is the difference between the Laguna height and the vertical centroid, as shown below,
Cent dist = laguna h – cent vert.
The resulting value of the “cent dist” variable is used in the formula FR= γhcAas hc. Then, substitute it to the component area and divide the volume by its thickness that is equal to 3.6 meters. Repeat the procedure by using the updated value of adriatric h to determine the value resultant pressure force due to the Adriatric Sea. According to the determined densities of the two bodies of water, the specific weights are provided.
(Table 2: Additional processing variables)
Water vol = water fraction x module vol
Air vol = air fracation x module vol
Assumed that the specific weights of water and air in the tank are given, simply multiply both by the volumes and obtaining the values of water weight and air weight, respectively.
The Analysis of Results
The computed module with forces acted on it, hydrostatic analysis is performed to make sure that the plates are stable enough. There are codes integrated in the program to automate the analysis effectively. The gates can withstand with its 3 – meter tide sea level clearance; to include such functionality in the program is significant to have a warning signal the moment “tide rise” is greater than 3 meters or 2.9 meters as a reliable clearance. The fact that the program calculates the resultant forces on each gates individually, there is a display panel showing the different value on each gate. This program is highly suggested to enhance information access.
A Note on Societal and Environmental Implications
As estimated and well – planned, that the project will lessen flood damages in the next one hundred years, still there are criticisms and debates about the hazards that may cause the environment as the project undergo since 1998 (Lorenzet 4). The primary concern is the possibility that the sea bottom will be destroyed upon the installation of the concreted bases for the modules. The morphology of the lagoon will be severely affected by the project according to some environmentalists and scientists. The Italian government is already aware regarding the concerns of some private sectors in the country. They plan to implement the best measures on how to build ecological procedures for the prevention of massive damages; sad to say that such damages caused by the progress of the project is permanent. Another concern is that how will the project affect other aspects such as trade and business, transportations, and the access of the lagoon in general. Partially, the concern on these aspects is addressed accordingly. In fact, the ability of the MOSE system has an exemplary technique in the operation; it operates module rows individually, in this manner, there are some functional inlets allowed in any access. However, the issue regarding the large vessel materials and equipments to be utilized in the project is still under a thorough discussion and hopefully have a proper resolution or be resolved accordingly in due time.
Lorenzet, Andrea. “Technology and the City: The Case of the MoSE Project in Venice”
Università degli Studi di Trento, Italy. March 31, 2007. Web, November 23, 2012. http://www.cspo.org/igscdocs/Andrea%20Lorenzet.pdf
Anonymous. “Moses Project keeps Venice dry”. Manila Bulleting Publishing Corporation.
September 19. 2011. Web, November 23, 2012 http://www.mb.com.ph/node/334869/mo#.UK-vPIdfCSo
Poggioli, Sylvia. “MOSE Project aims to Part Venice Floods” NPR. January 7, 2008. Web,
November 23, 2012. http://www.npr.org/templates/story/story.php?storyId=17855145
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& Sons, 5th Edition. Print, 2011.