Transformation of wavy way in Salerno gulf

TRANSFORMATION OF WAVY WAY IN SALERNO GULF

Antonio Manzo

Politecnico di Torino. Italy

We must start to explain few but important information about maritime engineering. This is a part of hydraulics that studies the features of the wavy way and the interaction between waves and structures near the coasts.Tire waves have an energy formed by two components, one potential and another kinetics; the first depend on altitude of the liquid

~ Antonio Manzo. 2016

surface respect to the state of quiet, the second depend on the movement of the liquid particles. In this case, the study is focused on wind-generated waves, they are waves of gravity and they contain waves of very different dimensions between them. Tire wind gives energy to the sea with tangential actions to the wave profile and, for this reason, there is the making of the waves; however the wind can have different directions and time of propagation so, if waves have already generated the same direction of the wind they will grow in size but, if the wind have opposite direction there will be new waves that flatten preexisting waves. Finally, another important information about the wavy way is that waves are generated far from the coast, with small dimension and with different directions but, when they are closer to the coast the size increase and the direction becomes the same.

The purpose of the study is to control that the software Largo Coste is fully functional; in tliis software (designed by Medus: Maritime engineering university of Salerno) we can put all the parameters for the study of wavy way on a coast.

However tliis software does not do calculations, but it set up all the files that we use to another software SWAN (Simulating Waves Nearshore) developed by Delft university. Tliis last software will estimate the value of the waves.

Largo Costa is a software very simple to use and with it we can use SWAN even more easily.

When we open the software Largo Coste tliis is the screen that we can see:

CREA CAR TELIA LA'ATRO

Path                                | BROWSER

Folder Wo* .                           ] [ CREA

PARAMETRI SWAN

Angoto Rotazione Domrao d Cakolo CN)

BATIME TRIA

Fie BATlMETRIAda Surfer

Fie OUTPUT. SWAN ......

Numero NODI r> X

Nirnero NODI n Y

Omensone Domreo d Cakolo X Y:

LUNG

CARAT ТЕ RIST CHE MOTO ONDOSO

Penodo d Pkxo Spettrate Is) - vakxe nwwno20

Penodo d Pkxo Spettrate (s) - vafore maearnoKO

Penodo d Pxxo Spettrate - data Tp.................   05

Aiezza S«gnrf>cativa Spettro Moto Ondoeo П)

Frequenza mrvna Spettro Moto Ondoeo (Hz) .....

Frequenza maeema Spettro Moto Ondoeo (Hz) ..... Nixnero Herve* Frequenza Spettro Moto Ondoeo

Numero Herva* Daeoonai Spettro Moto Ondoeo

Nome PUNTO hdagne Sottocosta____

Coordnata X PUNTO indagne

Coordnata Y PUNTO ndaqne

Fie SWANRUN bat

Drezrone Pro vereenza Moto Ondoeo • imte H (*N) Ore воле Provereenza Moto Ondoeo ■ tmte sup CN) Deeoone Provenenza Moto Ondoeo ■ delta DIR .

FILE ONOE LARGO

Fie ONDE LARGO ao

/ Ш ли пм А fdenategy^Mt

COPYRIGHT MEDUS (MARITIME ENGINEERING DIVISION UNIVERSITY OF SALERNO)

The various commands are:

• •    PATH, is the command that will create the folder where you will place the spreadsheet and the results obtained;

• •    FOLDER WORK, this command insert in the previous folder other folders where Largo Coste inserts bathymetry and the study results about the values of the wavy way and the values of the transport coefficient;

• •    FILE BATIMETRIA DA SURFER, here we must put the file that represents the bathymetry, that you can create with the software Dxf2xyz 2.0;

• •    FILE OUTPOUT x SWAN, with this command we can assign the name of the output fde of swan;

• •    NUMERO NODI, when we create the bathymetry with the software Dxfxyz 2.0 we have an area made by a number of points, in this part of the software we must put the number of point along the axis x and y;

• •    CARATTERISTICHE DEL MOTO ONDOSO, here we must decide the energy range of the waves and the direction range that the waves have offshore;

• •    PARAMETRI SWAN, in this part of the software we must insert the inclination to the north of the bathymetry and other features of the wave spectram, after this part, we can insert the coordinates of the points that we want study, in this case the study was made for a single point very near to the coast;

• •    FILE SWANRUN BATIMETRIA, here we must insert the software swan to star the calculations;

• •    FILE ONDE LARGO, when swan end calculations we must put in this part of software measurements obtained with buoy, in this way we can have the values that we want.

The most important thing about the study is the phenomenon of refraction.

The waves are formed far from the coast and when they have their lines of crest parallel to each other. When the waves arrive near to the coast the lines of crest have sections with different depth. In this situation the different traits wave will have different speed, so the wave will wrap parallel to the bottom level. The phenomenon of refraction acts in areas with low depth so; we can know the height of the waves near to the coast.

The first step is based on the study of an ideal bathymetry, with constant slope and level curves parallel to each other. To know if the results are acceptable we study the bathymetry varying the study area than in the north of the reference system comparing the results between them.

We obtain two graphics, the first correlates the direction of the waves far from the coast and near the cost, the second correlates the direction of the waves far from the coast and a coefficient of shoaling refraction which is the height of the waves in the high waters divide the height of the waves in the low waters.

The coefficient of shoaling-refraction says us how the waves grow near the coast. After this study we can control if the results are acceptable because for orthogonal directions to the coast we must have the greatest values of the coefficient of shoaling-refraction, besides if the direction of the wind that generate the waves is orthogonal to the coast, in an ideal bathymetry, there isn’t the refraction phenomenon, whatever the intensity of the wind. Below we show a case study.

Wave direction offshore (degrees)

----Тр=2 ----Тр=2,5

Тр=3 ----Тр=3,5

----Тр=4

Тр=4,5 ----Тр=5 ----Тр=5,5 ----Тр=6 ----Тр=6,5 ----Тр=7 ----Тр=7,5 ----Тр=8 ----Тр=8,5

Тр=9 ----Тр=9,5 —Тр=10 ----Тр=10,5 —Тр=11

Тр=11,5

----Тр=12 ----Тр=12,5

—Тр=13

Picture 6: Graphic that shows how change the waves direction near to the coast with different energy range (Tp in seconds).

---Tp=2 ----Tp=2,5

Tp=3 ----Tp=3,5 ----Tp-4 —Tp=4,5 ----Tp=5 ----Tp=5,5 —Tp=6 —Tp=6,5 ----Tp=7 ----Tp=7,5 ----Tp=8 ----Tp=8,5

Tp=9 ----Tp=9,5 ----Tp=10

Tp=10,5 ----Tp=ll ----Tp=ll,5 ----Tp=12 ----Tp=12,5 —Tp=13 —Tp=13,5 ----Tp=14

Picture 7: Graphic that shoes how change the coefficient of shoaling-refraction with different energy range (Tp in seconds).

The second step is the study of a real bathymetry, in our case the gulf of Salerno; it is possible to observe the gulf and the direction of the waves of this study case.

The methodology is the same of first step but. in tliis case, to liave accuracy of results, we liave studied fist a less accurate representation of the bathymetry and. after, we have represented a bathymetry more accurate, with a best representation of level curves. The results are similar with not relevant differences and they gave back a good description of refraction phenomenon and good values of the coefficient of shoaling-refraction. In the next graphics we can see that we aren’t differences between the first bathymetry (Tp3) and the bathymetry more accurate (Tp2); in fact, the calculated values are very similar in tins two cases for both the graphics.

Tp3=4s

^^—Tp3=5s

—Tp3=11s

^—Tp3=12s

----Tp2=4s

—Tp2=5s

----Tp2=11s

—Tp2-12s

Wave direction offshore (degrees)

Tliis study allows knowing the influence of the waves on the coasts, so. for example, we can do works of protection to defend the coasts from erosion.

With this study we can say that the software Largo Coste, designed by Medus: Maritime engineering university of Salerno) works perfectly and it can help to use more easy and fast the software SWAN with the creation of a big number of input file simply inserting the maximum and minimum values of study and the steps that the technician wants.