Modelling the ocean enables advances in maritime tech

A digi­tal twin is the digi­ti­sa­tion of a given envi­ron­ment : this very gene­ral defi­ni­tion encom­passes many very varied appli­ca­tions. Inter­ac­tive digi­tal twins allow a human to inter­act with the vir­tual envi­ron­ment, thanks to tra­cking sen­sors, control organs (joys­tick, joys­ticks, etc.) or force feed­back inter­faces (hap­tic inter­faces). These tools are inter­dis­ci­pli­na­ry in seve­ral res­pects : in terms of their fields of appli­ca­tion (medi­cine, mari­time indus­try, etc.) and the sciences they mobi­lise (mecha­ni­cal, ther­mal, bio­lo­gi­cal, etc.). 

Anders Tho­rin, a research engi­neer at the CEA List’s Inter­ac­tive Simu­la­tion Labo­ra­to­ry, has been wor­king in the team deve­lo­ping the XDE Phy­sics soft­ware for the past twen­ty years. This soft­ware, which allows the crea­tion of digi­tal twins in the field of robo­tics, has attrac­ted the inter­est of Tech­nip Ener­gies for pro­jects in the mari­time sec­tor. The resear­chers then deve­lo­ped new func­tio­na­li­ties to meet the needs of the com­pa­ny. Today, it has been repa­cka­ged in a soft­ware package cal­led “CETO”, dedi­ca­ted to inter­ac­tive mari­time simu­la­tion. It allows immer­sion in vir­tual rea­li­ty (VR) within a crane on board a floa­ting struc­ture, which can be used for fore­cas­ting and risk assess­ment for com­plex lif­ting ope­ra­tions, or for staff training.

CETO makes it pos­sible to repro­duce the phy­si­cal cha­rac­te­ris­tics of the sea, its envi­ron­ment, and nume­rous objects from the mari­time world – contai­ner ships, port cranes, cables, pipes – in an inter­ac­tive simulation. 

The first step was the phy­si­ca­li­sa­tion of the envi­ron­ment to be stu­died – a step in which the resear­chers will model the consti­tuent ele­ments of the sce­na­rio, star­ting with the sea. “To model the sea, we typi­cal­ly use 600 spec­tral com­po­nents,” says the resear­cher. Each spec­tral com­ponent cor­res­ponds to a sinu­soi­dal wave, which has seve­ral para­me­ters : ampli­tude (from the peak to the trough of the wave), direc­tion, phase, and fre­quen­cy. Other envi­ron­men­tal condi­tions must be consi­de­red during the inter­ac­tive simu­la­tion : wind and cur­rent, for example.”

After an ini­tial simu­la­tion pro­to­type, the resear­chers were able to improve the pre­ci­sion and the­re­fore the rea­lism of the simu­la­tion by increa­sing the level of detail of the models : taking into account pro­pel­lers, cables, cranes, etc., with a view to kno­wing, or rather veri­fying, how it will react to the move­ment of the sea, the wind, the swell and so on. “Phy­si­ca­li­sa­tion is not always neces­sa­ry depen­ding on the pur­pose,” he says, “but when it is, the inter­ac­tive nature means that the phy­si­cal equa­tions have to be sol­ved in real time, which often involves a sim­pli­fi­ca­tion phase of the phy­si­cal models.”

For example, a slen­der rigid struc­ture is model­led by a ‘beam’ of a cer­tain size, which is a sim­pli­fi­ca­tion to allow real-time simu­la­tion in XDE Phy­sics. With this step, the ques­tion may arise : can a digi­tal twin be so accu­rate that it repro­duces rea­li­ty, des­pite being a sim­pli­fi­ca­tion ? The resear­cher no lon­ger asks this ques­tion : “in science, eve­ry­thing is a model. Even a concept as simple as a right angle does not exist in nature. The chal­lenge for a digi­tal twin in inter­ac­tive simu­la­tion is to adopt a model that is suf­fi­cient­ly pre­cise to be of prac­ti­cal use in a given context. In addi­tion, the model equa­tions cho­sen must be able to be sol­ved qui­ck­ly enough with the hard­ware pro­vi­ded. Per­fect accu­ra­cy is not requi­red to obtain use­ful results, and so much the bet­ter, as this is not attainable.”

A good example of this is put­ting a defor­mable pipe in the water. Once the pipe has been model­led as a beam, the labo­ra­to­ry team will be able to assess its strength during lif­ting and lowe­ring ope­ra­tions, depen­ding on the wea­ther condi­tions and the actions of the crane ope­ra­tor in the vir­tual world. This mul­ti­tude of digi­tal­ly com­bi­ned ele­ments allows for an inter­ac­tive simu­la­tion of any desi­red sce­na­rio. This allows the user to assess whe­ther the pipe will withs­tand hand­ling without having to achieve per­fect accu­ra­cy in the simu­la­tion. All this is much safer and more eco­no­mi­cal than real-life testing. 

A digi­tal twin can the­re­fore allow sce­na­rios to be vali­da­ted before being applied in the phy­si­cal world. The uses are the­re­fore count­less, and the advan­tages consi­de­rable. “There is a real bene­fit to this type of simu­la­tion,” says Anders Tho­rin. “First­ly, in terms of cost, because it requires less time to car­ry out a pro­ject, limits the need to move equip­ment, avoids the use of models, etc. And in terms of repro­du­ci­bi­li­ty, because each sce­na­rio can be vali­da­ted on the same simu­la­tion, the para­me­ters being able to be modi­fied as required.”

The uses of the digi­tal twin are count­less, and the bene­fits considerable.

In fact, if we want to esti­mate the dif­fe­rence in move­ment that a ship can have in calm water, com­pa­red to rough water, only the para­me­ters that influence the dyna­mics of the water and the wind need to be chan­ged, name­ly : the direc­tion of the wind, its speed, and its constan­cy, etc. “It is a form of fore­cas­ting an event under cer­tain pre­de­fi­ned condi­tions – wind, swell, cur­rent, and many others,” adds the researcher.

Howe­ver, the use­ful­ness of this type of digi­tal twin does not stop at sce­na­rio ‘fore­cas­ting’. Having a real vir­tual world, acces­sible through a VR head­set, all as true as pos­sible to the phy­si­cal rea­li­ties of the ele­ments around us, would allow for effec­tive use in trai­ning. “Tech­nip Ener­gies adjus­ted a chair to repli­cate (this time in the real world) the cabin of a crane with its joys­ticks,” he explains. “This allo­wed a crane ope­ra­tor to come on site for trai­ning, in addi­tion to hands-on practice.”

Cou­pled with its two main bene­fits (cost and repro­du­ci­bi­li­ty), such soft­ware would have an unde­niable added value to crane ope­ra­tor trai­ning, espe­cial­ly for dea­ling with extreme situa­tions, such as high winds.

Pablo Andres