[ERROR] [1608996333.891904672, 187.321000000]: Updating ModelState: for model[MyrobotName], specified reference frame entity [world_ned] does not exist ?

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 <?xml version="1.0"?>

<robot name="  MyrobotName">
    <gazebo>
        <static>true</static>
    </gazebo>
    <material name="white">
        <color rgba="1 1 0.8 1"/>
    </material>
    <link name="  MyrobotName/base_link">
        <visual>
            <geometry>
                <mesh filename="package://gb_description/meshes/base_link.STL"/> 
                <!--box size="1 0.5 0.2"/-->
            </geometry>
            <material name="white"/>
            <origin rpy="3.14 0 0" xyz="0 -3.81548 0.85"/>
        </visual>
    </link>



    <link name="  MyrobotName/dvl">
        <visual>
            <origin rpy="0 0 0" xyz="1.153 0 0.129"/>
        </visual>

        <inertial>
            <origin xyz="0 0 1" rpy="0 0 0"/>
            <mass value="1"/>
            <inertia
                ixx="1.0" ixy="0.0" ixz="0.0"
                iyy="1.0" iyz="0.0"
                izz="1.0"/>
        </inertial>
    </link>

    <joint name="base_link_to_dvl_joint" type="fixed">
        <parent link="  MyrobotName/base_link"/>
        <child link="  MyrobotName/dvl"/>
        <origin rpy="0 0 0" xyz="1.153 0 0.129"/>
    </joint>

    <link name="  MyrobotName/altimeter">
        <visual>
            <origin rpy="0 0 0" xyz="1.45 0 -0.085"/>
        </visual>

        <inertial>
            <origin xyz="0 0 1" rpy="0 0 0"/>
            <mass value="1"/>
            <inertia
                ixx="1.0" ixy="0.0" ixz="0.0"
                iyy="1.0" iyz="0.0"
                izz="1.0"/>
        </inertial>
    </link>

    <joint name="base_link_to_altimeter_joint" type="fixed">
        <parent link="  MyrobotName/base_link"/>
        <child link="  MyrobotName/altimeter"/>
        <origin rpy="0 0 0" xyz="1.45 0 -0.085"/>
    </joint>

    <link name="  MyrobotName/gps">
        <visual>
            <origin rpy="0 0 0" xyz="-0.62 0 -0.28"/>
        </visual>

        <inertial>
            <origin xyz="0 0 1" rpy="0 0 0"/>
            <mass value="1"/>
            <inertia
                ixx="1.0" ixy="0.0" ixz="0.0"
                iyy="1.0" iyz="0.0"
                izz="1.0"/>
        </inertial>
    </link>

    <joint name="base_link_to_gps_joint" type="fixed">
        <parent link="  MyrobotName/base_link"/>
        <child link="  MyrobotName/gps"/>
        <origin rpy="0 0 0" xyz="-0.62 0 -0.28"/>
    </joint>

    <link name="  MyrobotName/imu">
        <visual>
            <origin rpy="0 0 0" xyz="0 0 0"/>
        </visual>

        <inertial>
            <origin xyz="0 0 1" rpy="0 0 0"/>
            <mass value="1"/>
            <inertia
                ixx="1.0" ixy="0.0" ixz="0.0"
                iyy="1.0" iyz="0.0"
                izz="1.0"/>
        </inertial>
    </link>

    <joint name="base_link_to_imu_joint" type="fixed">
        <parent link="  MyrobotName/base_link"/>
        <child link="  MyrobotName/imu"/>
        <origin rpy="0 0 0" xyz="0 0 0"/>
    </joint>

</robot>

The above file is my file.urdf. I want to simulate my robot (load the urdf file to gazebo), but i got some errors :

1. [ERROR] [1608996333.891904672, 187.321000000]: Updating ModelState: for model[MyrobotName], specified reference frame entity [world_ned] does not exist.

2. My model in gazebo was behaving weird / unexpected, then I add <static>true</static>. It solved it, but when I simulated it, my model in Gazebo did not move even though my model in rvis can move. Could anyone tell me what causes it ? and does anyone know how to sole it ?