Fix BCAST issue

Author: haochey

src/simulation/m_acoustic_src.fpp

@@ -192,9 +192,11 @@ contains
             ! Allocate buffers for random phase shift
             allocate (phi_rn(1:bb_num_freq(ai)))
 
-            call random_number(phi_rn(1:bb_num_freq(ai)))
-            ! Ensure all the ranks have the same random phase shift
-            call s_mpi_send_random_number(phi_rn, bb_num_freq(ai))
+            if (pulse(ai) == 4) then
+                call random_number(phi_rn(1:bb_num_freq(ai)))
+                ! Ensure all the ranks have the same random phase shift
+                call s_mpi_send_random_number(phi_rn, bb_num_freq(ai))
+            end if
 
             !$acc loop reduction(+:sum_BB)
             do k = 1, bb_num_freq(ai)