272
I. Gankevich and A. Degtyarev
x
y
z
Ramp-up interval
Fig. 6 Ramp-up interval at the beginning of the OX axis of the realisation
on the border (too far away from the studied marine object). If ship stability with
manoeuvring is studied, then the interval may be simply discarded from the realisation (the size of the interval approximately equals the number of AR coefficients in
each dimension). However, this may lead to a loss of a very large number of points,
because discarding is done for each dimension. Alternative approach is to generate
ocean wavy surface on ramp-up interval with LH model and generate the rest of the
realisation with ARMA model.
Algorithm of wavy surface generation is data-parallel: the realisation is divided
into equal parts along the time axis each of which is generated independently, however, in the beginning of each realisation there is ramp-up interval. To eliminate it
for MA process, overlap-add method [24–26] (a popular method in signal processing) is used. The essence of the method is to add another interval, size of which
is equal to the ramp-up interval size, to the end of each part. Then wavy surface is
generated in each point of each part (including points from the added interval), the
interval at the end of part N is superimposed on the ramp-up interval at the beginning of the part N + 1, and values in corresponding points are added. To eliminate
the ramp-up interval for AR process, the realisation is divided into part along each
dimension, and each part is computed only when all dependent parts are ready. For
that purpose, an array of current part states is maintained in the programme, and all
the parts are put into a queue. A parallel thread acquires a shared lock, finds the first
part in the queue, for which all dependent parts have “completed” state, removes this
part for the queue, frees the lock and generates the part. After that a thread updates
the state of the part, and repeats the same steps until the queue becomes empty. This
algorithm eliminates all ramp-up intervals except the one at the beginning of the
realisation, and the size of the parts should be sufficiently small to balance the load
on all processor cores.
I. Gankevich and A. Degtyarev
x
y
z
Ramp-up interval
Fig. 6 Ramp-up interval at the beginning of the OX axis of the realisation
on the border (too far away from the studied marine object). If ship stability with
manoeuvring is studied, then the interval may be simply discarded from the realisation (the size of the interval approximately equals the number of AR coefficients in
each dimension). However, this may lead to a loss of a very large number of points,
because discarding is done for each dimension. Alternative approach is to generate
ocean wavy surface on ramp-up interval with LH model and generate the rest of the
realisation with ARMA model.
Algorithm of wavy surface generation is data-parallel: the realisation is divided
into equal parts along the time axis each of which is generated independently, however, in the beginning of each realisation there is ramp-up interval. To eliminate it
for MA process, overlap-add method [24–26] (a popular method in signal processing) is used. The essence of the method is to add another interval, size of which
is equal to the ramp-up interval size, to the end of each part. Then wavy surface is
generated in each point of each part (including points from the added interval), the
interval at the end of part N is superimposed on the ramp-up interval at the beginning of the part N + 1, and values in corresponding points are added. To eliminate
the ramp-up interval for AR process, the realisation is divided into part along each
dimension, and each part is computed only when all dependent parts are ready. For
that purpose, an array of current part states is maintained in the programme, and all
the parts are put into a queue. A parallel thread acquires a shared lock, finds the first
part in the queue, for which all dependent parts have “completed” state, removes this
part for the queue, frees the lock and generates the part. After that a thread updates
the state of the part, and repeats the same steps until the queue becomes empty. This
algorithm eliminates all ramp-up intervals except the one at the beginning of the
realisation, and the size of the parts should be sufficiently small to balance the load
on all processor cores.