a = Simulation.where(user_id: 1, visibility: 0).where_values.reduce(:and)
a.to_sql
=> "\"simulations\".\"user_id\" = $1 AND \"simulations\".\"visibility\" = $2"
b = Simulation.where(visibility: 1).where_values.reduce(:and)
b.to_sql
=> "\"simulations\".\"visibility\" = $1"

Simulation.where(a.or(b)).to_sql
=> "SELECT \"simulations\".* FROM \"simulations\" WHERE (\"simulations\".\"user_id\" =  AND \"simulations\".\"visibility\" =  OR \"simulations\".\"visibility\" = )"

Simulation.where(a.or(b), 1,2,3).first
  Simulation Load (2.8ms)  SELECT  "simulations".* FROM "simulations" WHERE ("simulations"."user_id" = $1 AND "simulations"."visibility" = $2 OR "simulations"."visibility" = $3)  ORDER BY "simulations"."id" ASC LIMIT 1
PG::ProtocolViolation: ERROR:  bind message supplies 0 parameters, but prepared statement "" requires 3
: SELECT  "simulations".* FROM "simulations" WHERE ("simulations"."user_id" = $1 AND "simulations"."visibility" = $2 OR "simulations"."visibility" = $3)  ORDER BY "simulations"."id" ASC LIMIT 1
ActiveRecord::StatementInvalid: PG::ProtocolViolation: ERROR:  bind message supplies 0 parameters, but prepared statement "" requires 3
: SELECT  "simulations".* FROM "simulations" WHERE ("simulations"."user_id" = $1 AND "simulations"."visibility" = $2 OR "simulations"."visibility" = $3)  ORDER BY "simulations"."id" ASC LIMIT 1
from /home/jhedtrich/.rvm/gems/ruby-2.1.5/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:592:in `async_exec'