Server Administration :: Cannot Audit Entry In Dump

I am trying to enable auditing as

SQL> alter system set audit_trail=OS SCOPE=SPFILE;

System altered.

SQL> STARTUP FORCE
ORACLE instance started.

Total System Global Area 171966464 bytes
Fixed Size 2019320 bytes
Variable Size 113246216 bytes
Database Buffers 50331648 bytes
Redo Buffers 6369280 bytes
Database mounted.
Database opened.

SQL> show parameter audit

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
audit_file_dest string /u01/app/oracle/admin/orcl/adu
mp
audit_sys_operations boolean FALSE
audit_syslog_level string
audit_trail string OS
SQL>

SQL> create user apexos identified by abc1;

User created.

SQL> grant connect, resource to apexos;

Grant succeeded.

SQL> audit select table, insert table by apexos by access;

Audit succeeded.

SQL> audit table by apexos by access;

SQL> SELECT audit_option, failure, success, user_name
FROM dba_stmt_audit_opts;

AUDIT_OPTION FAILURE SUCCESS USER_NAME
---------------------------------------- ---------- ---------- ------------------------------
TABLE BY ACCESS BY ACCESS APEXOS
SELECT TABLE BY ACCESS BY ACCESS APEXOS
INSERT TABLE BY ACCESS BY ACCESS APEXOS

cONN APPOS/ABC1

SQL> CREATE TABLE TAB1 (ID NUMBER, NAME VARCHAR2(20));

Table created.

SQL> insert into tab1 values (10, 'Michel');

1 row created.

SQL> insert into tab1 values (30, 'Andrew');

1 row created.

SQL> select * from tab1;

ID NAME
---------- --------------------
10 Michel
30 Andrew

SQL> /

ID NAME
---------- --------------------
10 Michel
30 Andrew

SQL>

SQL> select username, timestamp, action_name, action, SES_ACTIONs, sql_text
2 from USER_audit_trail where username='APEXOS';

no rows selected

SQL>

I also did not find any file contiaing the above statement as audit record in
/u01/app/oracle/admin/orcl/adump.

There are numerous old file in the /u01/app/oracle/admin/orcl/adump locaton. But When I executed the sql statement then that time no audit file was not generated in the location.

how to find audit record.